This work was supported by grants from the National Key Research and Development Program of China [2017YFD0500102]; the National Natural Science Foundation of China [31572544]; the State Key Laboratory of Veterinary Etiological Biology [SKLVEB2016KFKT005]; the Shanghai Agriculture Applied Technology Development Program, China [G2016060201].

The mouse infection experiments were approved by the Laboratory Animal Monitoring Committee of Jiangsu Province, China and performed in the Laboratory Animal Center of Nanjing Agricultural University (Permit number: SYXK (Su) 2017-0007).
1. Preparation of Bacteria
Note: S. suis serotype 2 virulent strain P1/7 was isolated from a diseased pig with meningitis19. Strain P1/7 was grown in Todd-Hewitt broth (THB, formula per liter of THB: Heart Infusion, 3.1 g; neopeptone, 20.0 g; dextrose, 2.0 g; sodium chloride, 2.0 g; disodium phosphate, 0.4 g; sodium carbonate, 2.5 g) and plated on Todd-Hewitt agar (THA, formula per liter of THA: Heart Infusion, 3.1 g; neopeptone, 20.0 g; dextrose, 2.0 g; sodium chloride, 2.0 g; disodium phosphate, 0.4 g; sodium carbonate, 2.5 g; agar, 15.0 g) at 37 &#176;C and 5% CO2.
<ol>
	<li>Collection of strain P1/7 planktonic cells
	<ol>
		<li>Collect 5 mL of planktonic cells from mid-log phase culture (OD600=0.6), centrifuge for 3 min at 8000 &#215; g, and then wash 3 times with PBS.</li>
		<li>Resuspend the cells with 5 mL of 25% glycerol in THB, aliquot into 5 tubes, and then store at -80 &#176;C.</li>
	</ol>
	</li>
	<li>Collection of strain P1/7 biofilm state cells
	<ol>
		<li>Take 20 mL of an overnight culture and add to 180 mL of fresh THB; divide the diluted culture into 10 round culture plates equally, and then put the plates in an incubator at 37 &#176;C in 5% CO2 for 24 h.</li>
		<li>After incubation,&#160;shake the plate gently to resuspend the bacteria that have not adhered to the plate, and then discard the supernatant by aspiration. 
		NOTE: Shake the plate gently and avoid resuspending the sediment.</li>
		<li>Add 5 mL of PBS to harvest biofilm state cells, resuspend the sediment completely, and then transfer the sample to a new tube.</li>
		<li>Sonicate the biofilm state cells from the last step with the following parameters: 60 W, 4 cycles, 5 s on and 10 s off.</li>
		<li>Centrifuge for 3 min at 8000 &#215; g and store the supernatant at -80 &#176;C. 
		NOTE: The supernatant may contain biofilm components and it can be used to resuspend the biofilm bacteria before infection as described in the animal experiments (Step 3).</li>
		<li>Resuspend the sediment with 10 mL 25% glycerol in THB and then store the biofilm state cells at -80 &#176;C.</li>
	</ol>
	</li>
</ol>
2. Scanning Electron Microscopy (SEM) Analysis
<ol>
	<li>Fix the collected biofilm state cells and planktonic cells using 4% paraformaldehyde for 12 - 24 h at 4 &#176;C.</li>
	<li>Rinse the samples quickly with distilled water and dehydrate the samples sequentially with an increasing concentration of ethanol (25%, 50%, 70%, 90%, and 100%) for 30 min in each solution.</li>
	<li>Adhere the dried samples to metal holders with double-sided tape and finally coat them in an evaporator with gold and palladium.</li>
	<li>Observe the samples by a scanning electron microscope using the following parameters: EHT (Extra High Tension) = 10 kV; WD (Working Distance) = 7.0 or 8.0 mm; Magnification = 5000 &#215;; Signal A= SE1.</li>
</ol>
3. Animal Experiments
<ol>
	<li>Use SPF 6-week-old female BALB/c mice in this study. Infect all mice through the intracranial subarachnoidal route of infection whose injection site is located 3.5 mm rostral from the bregma. The stereotaxic coordinates of the injection site were clearly described by Chiavolini et al17.
	<ol>
		<li>For histopathological analysis, infect two groups of mice (5 mice per group) using planktonic cells or biofilm state cells at a dose of 3 &#215; 107 colony-forming units (CFU), and another 5 mice were injected with PBS as a control.</li>
		<li>For detection of mRNA expression of TLR2 and cytokines in brain, infect two additional groups of mice (6 mice per group) using planktonic cells or biofilm state cells at a dose of 3 &#215; 107 CFU.</li>
		<li>Determine the number of viable bacteria by plating serial dilutions on to THA.</li>
		<li>Euthanize all mice at 12 h post-infection for further research. 
		&#8203;NOTE: Glycerol in the stock medium must be removed before infection. Both planktonic cells and biofilm state cells recovered from -80 &#176;C are washed 3 times with PBS. Then, planktonic cells are resuspended with PBS and diluted to the appropriate dose for infection; biofilm state cells are resuspended with the stored supernatant (from step 1.2.5) and diluted to the appropriate dose for infection. The volume for infection should not be more than 50 &#181;L.</li>
	</ol>
	</li>
	<li>Detecting the mRNA expression of TLR2 and cytokines in brain tissue
	<ol>
		<li>Extract the total RNA from brain tissue using a RNA extraction kit.
		<ol>
			<li>For each mouse, use whole brain tissue for extracting RNA. Divide whole brain tissue into 5 tubes. Take up to 100 mg brain tissue and add 1 mL of lysis solution to each tube containing the lysing matrix provided by the kit.</li>
			<li>Process the tube in a homogenizer for 40 s at a setting of 6.0, and then centrifuge the tube at 12000 &#215; g and 4 &#176;C for 5 min.</li>
			<li>After centrifugation, transfer the upper phase to a new microcentrifuge tube.</li>
			<li>Incubate the transferred sample for 5 min at room temperature; add 300 &#181;L of chloroform, vortex for 10 s, and then incubate for 5 min at room temperature.</li>
			<li>Centrifuge the tube at 12000 &#215; g and 4 &#176;C for 5 min. Transfer the upper phase to a new tube.</li>
			<li>Add 500 &#181;L of cold absolute ethanol to the tube, before inverting it for 5 times, and then store the sample at -20 &#176;C for at least 1 h.</li>
			<li>Centrifuge the tube at 12000 &#215; g and 4 &#176;C for 15 min and remove the supernatant. Wash the pellet with 500 &#181;L of cold 75% ethanol in RNase-free H2O.</li>
			<li>Remove the ethanol, air dry the pellet for 5 min at room temperature, and resuspend the RNA in 100 &#181;L of RNase-free H2O.</li>
			<li>Incubate the RNA for 5 min at room temperature and determine the RNA concentration using a RNA bioanalyzer.</li>
		</ol>
		</li>
		<li>Perform cDNA synthesis, including elimination of genomic DNA (gDNA), using a thermocycler with a reverse transcription (RT) reagent kit.
		<ol>
			<li>Add 1 &#181;g of RNA to a tube containing 2 &#181;L of 5x gDNA elimination buffer, 1 &#181;L of gDNA elimination enzyme and RNase-free H2O until the volume reaches 10 &#181;L. Incubate for 2 min at 42 &#176;C.</li>
			<li>Add 10 &#181;L of master mix (1 &#181;L of RT enzyme Mix I, 1 &#181;L of RT Primer Mix, 4 &#181;L of 5x Buffer 2, and 4 &#181;L of RNase-free H2O) to the reaction solution from the last step and then mix gently. Proceed immediately with the RT reaction: 37 &#176;C for 15 min and then 85 &#176;C for 5 s.</li>
			<li>Perform the quantitative real-time PCR (RT-qPCR) analysis using a Real-Time PCR machine with a SYBR RT-qPCR kit. Add 10 &#181;L of 2x enzyme, 0.8 &#181;L of forward primer, 0.8 &#181;L of reverse primer, 0.4 &#181;L of 50x ROX Reference Dye II, 2 &#181;L of cDNA template, and RNase-free H2O until a total volume of 20 &#181;L.</li>
			<li>Run each sample in triplicate using the following thermal parameters: 30 s at 94 &#176;C, followed by 40 cycles of 5 s at 95 &#176;C, and 34 s at 60 &#176;C, with a final stage of 15 s at 95 &#176;C, 1 min at 60 &#176;C, and 15 s at 95 &#176;C. Primers for RT-qPCR are listed in Table 1. Housekeeping genes B2m and 18s rRNA were used as the internal controls.</li>
		</ol>
		</li>
		<li>Calculate the relative fold change based on the 2-&#916;&#916;Ct method.</li>
	</ol>
	</li>
	<li>Observation of histological sections
	<ol>
		<li>After 24 h fixation with 10% formalin, reconstruct the fixed brain tissue into appropriate sizes of tissue pieces at 2 - 3 mm.</li>
		<li>Put the tissue pieces in an embedding cassette and immerse in a new fixative solution for dehydration with an automatic vacuum dehydrator.</li>
		<li>Take out the fixed tissue and dehydrate it sequentially in increasing concentrations of ethanol (70%, 80%, 95%, 95%, and 100%) for 30 min in each solution.</li>
		<li>Transparentize the sample with xylene for 15 min, dip it in liquid paraffin at 60 &#176;C for 90 min, and then embed using an embedding machine.</li>
		<li>Cut the paraffin block embedded tissue into 3 &#181;m slices, tile the slice on water at 45 &#176;C, and then dry it in the air.</li>
		<li>Incubate the section for 3 h at 60 &#176;C, stain it using the haematoxylin and eosin (HE) method, and seal it with the neutral gum.</li>
		<li>Observe the histopathological changes of the brain with an optical microscope. A four-point grading system was used to evaluate histological changes. Use an unpaired t test for statistical analysis. 
		Congestion/haemorrhage: absent, score 0; small area of focal congestion/haemorrhage, score 1; large area of focal congestion/haemorrhage, or multiple sites of small area of focal congestion/haemorrhage, score 2; up to three large focal congestion/haemorrhage sites, score 3; diffuse congestion/haemorrhage, score 4. 
		Necrosis: absent, score 0; focal necrosis, score 1; diffuse occurrence of 1 - 10 necrotic cells, score 2; foci of confluent necrosis, score 3; extensive confluent necrosis, score 4. 
		Inflammatory cell infiltration: absent, score 0; few and focal infiltrations, score 1; multifocal infiltration or infiltrations with formation of aggregates, score 2; up to three aggregates, score 3; and more than four aggregates, score 4.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

The intracranial subarachnoidal route of infection described here has obvious advantages over other routes of infection. It allows investigators to study the host-bacterium interaction and the effect of bacterial components on host immune responses directly in the brain, which mimic bacterial entrance into the central nervous system. Thus, this route of infection can be extended for investigating the mechanisms of meningitis caused by other bacteria. In addition, it can also be used to test the efficacy of drugs against ...

Streptococcus suis (S. suis) is a major bacterial pathogen of pigs worldwide, causing severe diseases including meningitis, pneumonia, septicaemia, endocarditis, and arthritis1. It is also an emerging zoonotic agent. So far, it has been reported that nine serotypes can cause infection in humans, including serotypes 2, 4, 5, 9, 14, 16, 21, 24, and 312,3,4. In humans and pigs, meningitis is one of the major clinical signs of S. suis infections. In Vietnam and Thailand, S. suis is the major cause of meningitis in adults5. Microbial biofilms are microorganisms that adhere to each other and are concentrated at an interface; they are essential for bacterial virulence, survival in diverse environments, and antibiotic resistance5. Biofilms are typically surrounded by an extracellular matrix that generally contains polysaccharides, proteins, and DNA6. The latter is able to elicit host inflammatory responses and cytokine production7. Biofilm formation has been reported to be involved in streptococcal meningitis in previous studies. Biofilms contribute to Streptococcus agalactiae meningitis in a tilapia fish model and biofilm formation has been revealed within brain tissues and around meningeal surfaces in vivo through intra-abdominal inoculation8. During meningitis, Streptococcus pneumoniae is in a biofilm-like state and bacteria in such a biofilm state were more effective in inducing meningitis in a mouse infection model9. In addition, in our previous study, the biofilm state associated with S. suis in mouse brain contributes to bacterial virulence by survival analysis10. However, direct evidence for biofilm involvement in S. suis meningitis requires further investigation.
Animal models of S. suis infection have been developed in mice using the intraperitoneal (i.p.)11, intranasal (i.n.)12, intravenous (i.v.)13, and the intracisternal (i.c.) routes of infection14,15,16. However, the i.p., i.n., and i.v. routes of infection are not suitable for studying the roles of S. suis surface components in meningitis directly in the brain. These include extracellular matrix from biofilms. Although the i.c. inoculation was used for S. suis infection, the precise injection site has not been described in those papers. In contrast, the stereotaxic coordinates of the injection site for intracranial subarachnoidal inoculation has clearly been described in a previous study17. This allowed easy recognition of the inoculation point and more simplistic experimental protocol. In addition, the intracranial subarachnoidal route of infection mimics bacterial entrance into the central nervous system from the sinuses or the middle ear17, and the relationship between the middle ear and meningitis caused by S. suis has been demonstrated by Madsen et al18. Moreover, by applying the intracranial subarachnoidal route of infection in mice, we have demonstrated that S. suis small RNA rss04 contributes to meningitis in our previous study10.
In the present study, the intracranial subarachnoidal route of infection was used in mice to investigate the roles of biofilms in S. suis meningitis. Mice were infected with planktonic cells or biofilm state cells of S. suis by this route of infection. Histopathological analysis and increased mRNA expression of TLR2 and cytokines from brain tissue of mice injected with biofilm state cells clearly indicated that S. suis biofilm contributes to meningitis.

<table border="0" cellpadding="0" cellspacing="0" style="width:828px;" width="827">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr>
			<td height="46">Todd Hewitt Broth(THB)</td>
			<td style="width:225px;">Becton, Dickinson and Company</td>
			<td style="width:115px;">DF0492078</td>
			<td style="width:304px;">Dissolve 30 g of the powder in 1 L of purified water. Autoclave at 121&#176; for 15 min.</td>
		</tr>
		<tr>
			<td>Agar</td>
			<td style="width:225px;">DSBIO</td>
			<td style="width:115px;">16C0050</td>
			<td style="width:304px;">Dissolve 15 g of the powder in 1 L of THB. Autoclave at 121&#176; for 15 min.</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:184px;">Milli-Q Reference Water Purification System</td>
			<td style="width:225px;">Merck KGaA</td>
			<td style="width:115px;">Z00QSVCUS</td>
			<td style="width:304px;">Without Dnase/ Rnase</td>
		</tr>
		<tr height="21">
			<td>NaCl</td>
			<td style="width:225px;">Tianjin Kemiou Chemical Reagent Co., Ltd</td>
			<td style="width:115px;">10019318</td>
			<td style="width:304px;">Dissolve 8 g NaCl, 0.2 g KCl, 1.42 g Na2HPO3 , 0.27 g KH2PO4 in 1 L of purified water. Autoclave at 121&#176; for 15 min. Use KOH to adjust pH to 7.4.</td>
		</tr>
		<tr height="21">
			<td>Na2HPO3</td>
			<td style="width:225px;">Xilong Scientific Co., Ltd</td>
			<td style="width:115px;">9009012-01-09</td>
			<td style="width:304px;">Dissolve 8 g NaCl, 0.2 g KCl, 1.42 g Na2HPO3 , 0.27 g KH2PO4 in 1 L of purified water. Autoclave at 121&#176; for 15 min. Use KOH to adjust pH to 7.4.</td>
		</tr>
		<tr height="21">
			<td>KCl</td>
			<td style="width:225px;">Xilong Scientific Co., Ltd</td>
			<td style="width:115px;">9009017-01-09</td>
			<td style="width:304px;">Dissolve 8 g NaCl, 0.2 g KCl, 1.42 g Na2HPO3 , 0.27 g KH2PO4 in 1 L of purified water. Autoclave at 121&#176; for 15 min. Use KOH to adjust pH to 7.4.</td>
		</tr>
		<tr height="20">
			<td>KH2PO4</td>
			<td style="width:225px;">Xilong Scientific Co., Ltd</td>
			<td style="width:115px;">9009019-01-09</td>
			<td style="width:304px;">Dissolve 8 g NaCl, 0.2 g KCl, 1.42 g Na2HPO3 , 0.27 g KH2PO4 in 1 L of purified water. Autoclave at 121&#176; for 15 min. Use KOH to adjust pH to 7.4.</td>
		</tr>
		<tr height="24">
			<td>KOH</td>
			<td style="width:225px;">Xilong Scientific Co., Ltd</td>
			<td style="width:115px;">9009014-01-09</td>
			<td style="width:304px;">Dissolve 8 g NaCl, 0.2 g KCl, 1.42 g Na2HPO3 , 0.27 g KH2PO4 in 1 L of purified water. Autoclave at 121&#176; for 15 min. Use KOH to adjust pH to 7.4.</td>
		</tr>
		<tr height="42">
			<td>Glycerol</td>
			<td style="width:225px;">Sionpharm Chemical Reagent Co., Ltd</td>
			<td style="width:115px;">10010618</td>
			<td style="width:304px;">Diluted with equal volumu of purified water, autoclave at 121&#176; for 15 min</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:184px;">4% paraformaldehyde</td>
			<td style="width:225px;">Sionpharm Chemical Reagent Co., Ltd</td>
			<td style="width:115px;">80096675</td>
			<td style="width:304px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:184px;">25% Glutaraldehyde</td>
			<td style="width:225px;">Sionpharm Chemical Reagent Co., Ltd</td>
			<td style="width:115px;">30092436</td>
			<td style="width:304px;">10-fold diluted with purified water for fixation.</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:184px;">Ethanol</td>
			<td style="width:225px;">Sionpharm Chemical Reagent Co., Ltd</td>
			<td style="width:115px;">10009218</td>
			<td style="width:304px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Chloroform</td>
			<td style="width:225px;">Sionpharm Chemical Reagent Co., Ltd</td>
			<td style="width:115px;">10006818</td>
			<td style="width:304px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Spctrophotometre</td>
			<td style="width:225px;">DeNovix Inc.</td>
			<td style="width:115px;">DS-11+</td>
			<td style="width:304px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:184px;">Ultrasound cell crusher</td>
			<td style="width:225px;">NingBo Scientz Biotechnology Co.,Ltd</td>
			<td style="width:115px;">JY96-IIN</td>
			<td style="width:304px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:184px;">Centrifuge</td>
			<td style="width:225px;">Hitachi Koki Co., Ltd</td>
			<td style="width:115px;">CT15RE</td>
			<td style="width:304px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:184px;">Refrigerator</td>
			<td style="width:225px;">Aucma Co., Ltd</td>
			<td style="width:115px;">DW-86L500</td>
			<td style="width:304px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:184px;">Scanning electron microscope</td>
			<td>Zeiss</td>
			<td style="width:115px;">EVO-LS10</td>
			<td style="width:304px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">FastRNA Pro Green Kit</td>
			<td>MP Biomedicals</td>
			<td style="width:115px;">#6045-050</td>
			<td style="width:304px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">FastPrep-24 Instrument</td>
			<td>MP Biomedicals</td>
			<td style="width:115px;">116005500</td>
			<td style="width:304px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:184px;">Instrument for PCR</td>
			<td style="width:225px;">SensoQuest GmbH</td>
			<td style="width:115px;">1124310110</td>
			<td style="width:304px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">QuantStudio 6 Flex</td>
			<td style="width:225px;">Thermo Fisher Scientific</td>
			<td style="width:115px;">4485689</td>
			<td style="width:304px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:184px;">SYBR Premix Ex Taq II</td>
			<td style="width:225px;">Takara Biomedical Technology (Beijing) Co., Ltd</td>
			<td style="width:115px;">RR820A</td>
			<td style="width:304px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:184px;">PrimeScript RT reagent kit with gDNA Eraser</td>
			<td style="width:225px;">Takara Biomedical Technology (Beijing) Co., Ltd</td>
			<td style="width:115px;">RR047A</td>
			<td style="width:304px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:184px;">Fully Enclosed Tissue Processor</td>
			<td style="width:225px;">Leica Biosystems Nussloch GmbH</td>
			<td style="width:115px;">ASP200S</td>
			<td style="width:304px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:184px;">Heated Paraffin Embedding Module</td>
			<td style="width:225px;">Leica Biosystems Nussloch GmbH</td>
			<td style="width:115px;">EG1150H</td>
			<td style="width:304px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:184px;">Semi-Automated Rotary Microtome</td>
			<td style="width:225px;">Leica Biosystems Nussloch GmbH</td>
			<td style="width:115px;">RM2245</td>
			<td style="width:304px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:184px;">Water bath for paraffin sections</td>
			<td style="width:225px;">Leica Biosystems Nussloch GmbH</td>
			<td style="width:115px;">HI1210</td>
			<td style="width:304px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:184px;">Autostainer XL</td>
			<td style="width:225px;">Leica Biosystems Nussloch GmbH</td>
			<td style="width:115px;">ST5010</td>
			<td style="width:304px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:184px;">Agilent 2100</td>
			<td style="width:225px;">Agilent Technologies</td>
			<td style="width:115px;">G2939A</td>
			<td style="width:304px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:184px;">Optical microscope</td>
			<td style="width:225px;">Olympus</td>
			<td style="width:115px;">BX51</td>
			<td style="width:304px;"></td>
		</tr>
	</tbody>
</table>

intracranial subarachnoidal route of infection for investigating roles of streptococcus suis biofilms in meningitis in a mouse infection model

Streptococcus suis is not only a major bacterial pathogen of pigs worldwide but also an emerging zoonotic agent. In humans and pigs, meningitis is a major manifestation of S. suis infections. A suitable infection model is an essential tool to understand the mechanisms of diseases caused by pathogens. Several routes of infection in mice have been developed to study the pathogenesis of S. suis infection. However, the intraperitoneal, intranasal, and intravenous routes of infection are not suitable for studying the roles of S. suis surface components in meningitis directly in the brain, such as the extracellular matrix from biofilms. Although intracisternal inoculation has been used for S. suis infection, the precise injection site has not been described. Here, the intracranial subarachnoidal route of infection was described in a mouse model to investigate the roles of biofilms in S. suis meningitis. S. suis planktonic cells or biofilm state cells were directly injected into the subarachnoid space of mice through the injection site located 3.5 mm rostral from the bregma. Histopathological analysis and increased mRNA expression of TLR2 and cytokines of the brain tissue from mice injected with biofilm state cells clearly indicated that S. suis biofilm plays definitive roles in S. suis meningitis. This route of infection has obvious advantages over other routes of infection, allowing the study of the host-bacterium interaction. Furthermore, it permits the effect of bacterial components on host immune responses directly in the brain to be assessed, and mimics bacterial entrance into the central nervous system. This route of infection can be extended for investigating the mechanisms of meningitis caused by other bacteria. In addition, it can also be used to test the efficacy of drugs against bacterial meningitis.

SEM analysis was performed to examine biofilm formation under the experimental conditions. As shown in Figure 1, there is a significant difference in biofilm formation between planktonic cells (Figure 1A) and biofilm state cells (Figure 1B). SEM analysis showed that biofilm bacteria were in clumps and multiple layers and they were encased in the extracellular matrix,...

Watch this Scientific Journal Video about Intracranial Subarachnoidal Route of Infection for Investigating Roles of Streptococcus suis Biofilms in Meningitis in a Mouse Infection Model at JoVE.com

Intracranial Subarachnoidal Route of Infection for Investigating Roles of Streptococcus suis Biofilms in Meningitis in a Mouse Infection Model

Here, we describe the intracranial subarachnoidal route of infection in mice to study roles of biofilms in Streptococcus suis meningitis. This infection model is also suitable for studying the pathogenesis of other bacterial meningitis and the efficacy of new drugs against bacterial meningitis.

Intracranial Subarachnoidal Route of Infection for Investigating Roles of Streptococcus suis Biofilms in Meningitis in a Mouse Infection Model

Streptococcus suis is not only a major bacterial pathogen of pigs worldwide but also an emerging zoonotic agent. In humans and pigs, meningitis is a major ...

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Research

JoVE Journal

Immunology and Infection

7.2K Views.  Nanjing Agricultural University. Here, we describe the intracranial subarachnoidal route of infection in mice to study roles of biofilms in Streptococcus suis meningitis. This infection model is also suitable for studying the pathogenesis of other bacterial meningitis and the efficacy of new drugs against bacterial meningitis.

Video: Intracranial Subarachnoidal Route of Infection for Investigating Roles of Streptococcus suis Biofilms in Meningitis in a Mouse Infection Model

Genotypic Inference of HIV-1 Tropism Using Population-based Sequencing of V3

Background: Prior to receiving a drug from CCR5-antagonist class in HIV therapy, a patient must undergo an HIV tropism test to confirm that his or her viral population uses the CCR5 coreceptor for cellular entry, and not an alternative coreceptor. One approach to tropism testing is to examine the sequence of the V3 region of the HIV envelope, which interacts with the coreceptor.
Methods: Viral RNA is extracted from blood plasma. The V3 region is amplified in triplicate with nested reverse transcriptase-PCR. The amplifications are then sequenced and analyzed using the software, RE_Call. Sequences are then submitted to a bioinformatic algorithm such as geno2pheno to infer viral tropism from the V3 region. Sequences are inferred to be non-R5 if their geno2pheno false positive rate falls below 5.75%. If any one of the three sequences from a sample is inferred to be non-R5, the patient is unlikely to respond to a CCR5-antagonist.

HIV tropism can be inferred from the V3 region of the viral envelope. V3 is PCR amplified in triplicate using nested RT-PCR, sequenced, and interpreted using bioinformatic software. Samples with with 1 or more sequence(s) with low g2P scores are classified as non-R5 virus.

Background: Prior to receiving a drug from CCR5-antagonist class in HIV therapy, a patient must undergo an HIV tropism test to confirm that his or her ...

Introducing Shear Stress in the Study of Bacterial Adhesion

During bacterial infections a sequence of interactions occur between the pathogen and its host. Bacterial adhesion to the host cell surface is often the initial and determining step of the pathogenesis. Although experimentally adhesion is mostly studied in static conditions adhesion actually takes place in the presence of flowing liquid. First encounters between bacteria and their host often occur at the mucosal level, mouth, lung, gut, eye, etc. where mucus flows along the surface of epithelial cells. Later in infection, pathogens occasionally access the blood circulation causing life-threatening illnesses such as septicemia, sepsis and meningitis. A defining feature of these infections is the ability of these pathogens to interact with endothelial cells in presence of circulating blood. The presence of flowing liquid, mucus or blood for instance, determines adhesion because it generates a mechanical force on the pathogen. To characterize the effect of flowing liquid one usually refers to the notion of shear stress, which is the tangential force exerted per unit area by a fluid moving near a stationary wall, expressed in dynes/cm2. Intensities of shear stress vary widely according to the different vessels type, size, organ, location etc. (0-100 dynes/cm2). Circulation in capillaries can reach very low shear stress values and even temporarily stop during periods ranging between a few seconds to several minutes 1. On the other end of the spectrum shear stress in arterioles can reach 100 dynes/cm2 2. The impact of shear stress on different biological processes has been clearly demonstrated as for instance during the interaction of leukocytes with the endothelium 3. To take into account this mechanical parameter in the process of bacterial adhesion we took advantage of an experimental procedure based on the use of a disposable flow chamber 4. Host cells are grown in the flow chamber and fluorescent bacteria are introduced in the flow controlled by a syringe pump. We initially focused our investigations on the bacterial pathogen Neisseria meningitidis, a Gram-negative bacterium responsible for septicemia and meningitis. The procedure described here allowed us to study the impact of shear stress on the ability of the bacteria to: adhere to cells 1, to proliferate on the cell surface 5and to detach to colonize new sites 6 (Figure 1). Complementary technical information can be found in reference 7. Shear stress values presented here were chosen based on our previous experience1 and to represent values found in the literature. The protocol should be applicable to a wide range of pathogens with specific adjustments depending on the objectives of the study.

During the infection process, a key step is the adhesion of pathogens with host cells. In most instances this adhesion step occurs in the presence of mechanical stress generated by flowing liquid. We describe a technique that introduces shear stress as an important parameter in the study of bacterial adhesion.

During bacterial infections a sequence of interactions occur between the pathogen and its host. Bacterial adhesion to the host cell surface is often the ...

Single-cell Analysis of Bacillus subtilis Biofilms Using Fluorescence Microscopy and Flow Cytometry

Biofilm formation is a general attribute to almost all bacteria 1-6. When bacteria form biofilms, cells are encased in extracellular matrix that is mostly constituted by proteins and exopolysaccharides, among other factors 7-10. The microbial community encased within the biofilm often shows the differentiation of distinct subpopulation of specialized cells 11-17. These subpopulations coexist and often show spatial and temporal organization within the biofilm 18-21.
Biofilm formation in the model organism Bacillus subtilis requires the differentiation of distinct subpopulations of specialized cells. Among them, the subpopulation of matrix producers, responsible to produce and secrete the extracellular matrix of the biofilm is essential for biofilm formation 11,19. Hence, differentiation of matrix producers is a hallmark of biofilm formation in B. subtilis.
We have used fluorescent reporters to visualize and quantify the subpopulation of matrix producers in biofilms of B. subtilis 15,19,22-24. Concretely, we have observed that the subpopulation of matrix producers differentiates in response to the presence of self-produced extracellular signal surfactin 25. Interestingly, surfactin is produced by a subpopulation of specialized cells different from the subpopulation of matrix producers 15.
We have detailed in this report the technical approach necessary to visualize and quantify the subpopulation of matrix producers and surfactin producers within the biofilms of B. subtilis. To do this, fluorescent reporters of genes required for matrix production and surfactin production are inserted into the chromosome of B. subtilis. Reporters are expressed only in a subpopulation of specialized cells. Then, the subpopulations can be monitored using fluorescence microscopy and flow cytometry (See Fig 1).
The fact that different subpopulations of specialized cells coexist within multicellular communities of bacteria gives us a different perspective about the regulation of gene expression in prokaryotes. This protocol addresses this phenomenon experimentally and it can be easily adapted to any other working model, to elucidate the molecular mechanisms underlying phenotypic heterogeneity within a microbial community.

Single-cell Analysis of Bacillus subtilis Biofilms Using Fluorescence Microscopy and Flow Cytometry

Microbial biofilms are generally constituted by distinct subpopulations of specialized cells. Single-cell analysis of these subpopulations requires the use of fluorescent reporters. Here we describe a protocol to visualize and monitor several subpopulationswithin B. subtilis biofilms using fluorescence microscopy and flow cytometry.

Biofilm formation is a general attribute to almost all bacteria 1-6. When bacteria form biofilms, cells are encased in extracellular matrix that is mostly ...

Total Protein Extraction and 2-D Gel Electrophoresis Methods for Burkholderia Species

The investigation of the intracellular protein levels of bacterial species is of importance to understanding the pathogenic mechanisms of diseases caused by these organisms. Here we describe a procedure for protein extraction from Burkholderia species based on mechanical lysis using glass beads in the presence of ethylenediamine tetraacetic acid and phenylmethylsulfonyl fluoride in phosphate buffered saline. This method can be used for different Burkholderia species, for different growth conditions, and it is likely suitable for the use in proteomic studies of other bacteria. Following protein extraction, a two-dimensional (2-D) gel electrophoresis proteomic technique is described to study global changes in the proteomes of these organisms. This method consists of the separation of proteins according to their isoelectric point by isoelectric focusing in the first dimension, followed by separation on the basis of molecular weight by acrylamide gel electrophoresis in the second dimension. Visualization of separated proteins is carried out by silver staining.

Total Protein Extraction and 2-D Gel Electrophoresis Methods for Burkholderia Species

Members of the Burkholderia genus are pathogens of clinical importance. We describe a method for total bacterial protein extraction, using mechanical disruption, and 2-D gel electrophoresis for subsequent proteomic analysis.

The investigation of  the intracellular protein levels of bacterial species is of importance to  understanding the pathogenic mechanisms of diseases ...

Monitoring Changes in Membrane Polarity, Membrane Integrity, and Intracellular Ion Concentrations in Streptococcus pneumoniae Using Fluorescent Dyes

Membrane depolarization and ion fluxes are events that have been studied extensively in biological systems due to their ability to profoundly impact cellular functions, including energetics and signal transductions. While both fluorescent and electrophysiological methods, including electrode usage and patch-clamping, have been well developed for measuring these events in eukaryotic cells, methodology for measuring similar events in microorganisms have proven more challenging to develop given their small size in combination with the more complex outer surface of bacteria shielding the membrane. During our studies of death-initiation in Streptococcus pneumoniae (pneumococcus), we wanted to elucidate the role of membrane events, including changes in polarity, integrity, and intracellular ion concentrations. Searching the literature, we found that very few studies exist. Other investigators had monitored radioisotope uptake or equilibrium to measure ion fluxes and membrane potential and a limited number of studies, mostly in Gram-negative organisms, had seen some success using carbocyanine or oxonol fluorescent dyes to measure membrane potential, or loading bacteria with cell-permeant acetoxymethyl (AM) ester versions of ion-sensitive fluorescent indicator dyes. We therefore established and optimized protocols for measuring membrane potential, rupture, and ion-transport in the Gram-positive organism S. pneumoniae. We developed protocols using the bis-oxonol dye DiBAC4(3) and the cell-impermeant dye propidium iodide to measure membrane depolarization and rupture, respectively, as well as methods to optimally load the pneumococci with the AM esters of the ratiometric dyes Fura-2, PBFI, and BCECF to detect changes in intracellular concentrations of Ca2+, K+, and H+, respectively, using a fluorescence-detection plate reader. These protocols are the first of their kind for the pneumococcus and the majority of these dyes have not been used in any other bacterial species. Though our protocols have been optimized for S. pneumoniae, we believe these approaches should form an excellent starting-point for similar studies in other bacterial species.

Monitoring Changes in Membrane Polarity, Membrane Integrity, and Intracellular Ion Concentrations in Streptococcus pneumoniae Using Fluorescent Dyes

Unlike that seen for eukaryotes, there is a paucity of studies that detail membrane depolarization and ion concentration changes in bacteria, primarily as their small size makes conventional methods of measurement difficult. Here, we detail protocols for monitoring such events in the significant Gram-positive pathogen Streptococcus pneumoniae utilizing fluorescence techniques.

Membrane depolarization and ion fluxes are events that have been studied extensively in biological systems due to their ability to profoundly impact ...

Capsular Serotyping of Streptococcus pneumoniae by Latex Agglutination

Latex agglutination reagents are widely used in microbial diagnosis, identification and serotyping. Streptococcus pneumoniae (the pneumococcus) is a major cause of morbidity and mortality world-wide. Current vaccines target the pneumococcal capsule, and there are over 90 capsular serotypes. Serotyping pneumococcal isolates is therefore important for assessing the impact of vaccination programs and for epidemiological purposes. The World Health Organization has recommended latex agglutination as an alternative method to the &#8216;gold standard&#8217; Quellung test for serotyping pneumococci. Latex agglutination is a relatively simple, quick and inexpensive method; and is therefore suitable for resource-poor settings as well as laboratories with high-volume workloads. Latex agglutination reagents can be prepared in-house utilizing commercially-sourced antibodies that are passively attached to latex particles. This manuscript describes a method of production and quality control of latex agglutination reagents, and details a sequential testing approach which is time- and cost-effective. 
This method of production and quality control may also be suitable for other testing purposes.

Capsular Serotyping of Streptococcus pneumoniae by Latex Agglutination

Latex agglutination testing is a simple, rapid and inexpensive method for serotyping Streptococcus pneumoniae, and has also been widely applied in diagnostic microbiology. This manuscript describes the in-house production of latex agglutination reagents, quality control procedures and the application of this technique to pneumococcal serotyping.

Latex agglutination reagents are widely used in microbial diagnosis, identification and serotyping. Streptococcus pneumoniae (the pneumococcus) is a major ...

Non-invasive Imaging of the Innate Immune Response in a Zebrafish Larval Model of Streptococcus iniae Infection

The aquatic pathogen, Streptococcus iniae, is responsible for over 100 million dollars in annual losses for the aquaculture industry and is capable of causing systemic disease in both fish and humans. A better understanding of S. iniae disease pathogenesis requires an appropriate model system. The genetic tractability and the optical transparency of the early developmental stages of zebrafish allow for the generation and non-invasive imaging of transgenic lines with fluorescently tagged immune cells. The adaptive immune system is not fully functional until several weeks post fertilization, but zebrafish larvae have a conserved vertebrate innate immune system with both neutrophils and macrophages. Thus, the generation of a larval infection model allows the study of the specific contribution of innate immunity in controlling S. iniae infection.
The site of microinjection will determine whether an infection is systemic or initially localized. Here, we present our protocols for otic vesicle injection of zebrafish aged 2-3 days post fertilization as well as our techniques for fluorescent confocal imaging of infection. A localized infection site allows observation of initial microbe invasion, recruitment of host cells and dissemination of infection. Our findings using the zebrafish larval model of S. iniae infection indicate that zebrafish can be used to examine the differing contributions of host neutrophils and macrophages in localized bacterial infections. In addition, we describe how photolabeling of immune cells can be used to track individual host cell fate during the course of infection.

Non-invasive Imaging of the Innate Immune Response in a Zebrafish Larval Model of Streptococcus iniae Infection

Here, we present a protocol for the generation and imaging of a localized bacterial infection in the zebrafish otic vesicle.

The aquatic pathogen, Streptococcus iniae, is responsible for over 100 million dollars in annual losses for the aquaculture industry and is capable of ...

A Murine Model of Group B Streptococcus Vaginal Colonization

Streptococcus agalactiae (group B Streptococcus, GBS), is a Gram-positive, asymptomatic colonizer of the human gastrointestinal tract and vaginal tract of 10 - 30% of adults. In immune-compromised individuals, including neonates, pregnant women, and the elderly, GBS may switch to an invasive pathogen causing sepsis, arthritis, pneumonia, and meningitis. Because GBS is a leading bacterial pathogen of neonates, current prophylaxis is comprised of late gestation screening for GBS vaginal colonization and subsequent peripartum antibiotic treatment of GBS-positive mothers. Heavy GBS vaginal burden is a risk factor for both neonatal disease and colonization. Unfortunately, little is known about the host and bacterial factors that promote or permit GBS vaginal colonization. This protocol describes a technique for establishing persistent GBS vaginal colonization using a single &#946;-estradiol pre-treatment and daily sampling to determine bacterial load. It further details methods to administer additional therapies or reagents of interest and to collect vaginal lavage fluid and reproductive tract tissues. This mouse model will further the understanding of the GBS-host interaction within the vaginal environment, which will lead to potential therapeutic targets to control maternal vaginal colonization during pregnancy and to prevent transmission to the vulnerable newborn. It will also be of interest to increase our understanding of general bacterial-host interactions in the female vaginal tract.

A Murine Model of Group B Streptococcus Vaginal Colonization

The purpose of this protocol is to imitate human group B Streptococcus (GBS) vaginal colonization in a murine model. This method may be used to investigate host immune responses and bacterial factors contributing to GBS vaginal persistence, as well as to test therapeutic strategies.

Streptococcus agalactiae (group B Streptococcus, GBS), is a Gram-positive, asymptomatic colonizer of the human gastrointestinal tract and vaginal tract of ...

Influenza A Virus Studies in a Mouse Model of Infection

Influenza viruses cause over 500,000 deaths worldwide1 and are associated with an annual cost of 12 - 14 billion USD in the United States alone considering direct medical and hospitalization expenses and work absenteeism2. Animal models are crucial in Influenza A virus (IAV) studies to evaluate viral pathogenesis, host-pathogen interactions, immune responses, and the efficacy of current and/or novel vaccine approaches as well as antivirals. Mice are an advantageous small animal model because their immune system is evolutionarily similar to that found in humans, they are available from commercial vendors as genetically identical subjects, there are multiple strains that can be exploited to evaluate the genetic basis of infections, and they are relatively inexpensive and easy to manipulate. To recapitulate IAV infection in humans via the airways, mice are first anesthetized prior to intranasal inoculation with infectious IAVs under proper biosafety containment. After infection, the pathogenesis of IAVs is determined by monitoring daily the morbidity (body weight loss) and mortality (survival) rate. In addition, viral pathogenesis can also be evaluated by assessing virus replication in the upper (nasal mucosa) or lower (lungs) respiratory tract of infected mice. Humoral responses upon IAV infection can be rapidly evaluated by non-invasive bleeding and secondary antibody detection assays aimed at detecting the presence of total or neutralizing antibodies. Here, we describe the common methods used to infect mice intranasally (i.n) with IAV and evaluate pathogenesis, humoral immune responses and protection efficacy.

Influenza A viruses (IAVs) are important human respiratory pathogens. To understand the pathogenicity of IAVs and to perform preclinical testing of novel vaccine approaches, animal models mimicking human physiology are required. Here, we describe techniques to evaluate IAV pathogenesis, humoral responses and vaccine efficacy using a mouse model of infection.

Influenza viruses cause over 500,000 deaths worldwide1 and are associated with an annual cost of 12 - 14 billion USD in the United States alone ...

Constructing Mutants in Serotype 1 Streptococcus pneumoniae strain 519/43

Streptococcus pneumoniae serotype 1 remains a huge problem in low-and-middle income countries, particularly in sub-Saharan Africa. Despite its importance, studies in this serotype have been hindered by the lack of genetic tools to modify it. In this study, we describe a method to genetically modify a serotype 1 clinical isolate (strain 519/43). Interestingly, this was achieved by exploiting the Pneumococcus&#8217; ability to naturally acquire DNA. However, unlike most pneumococci, the use of linear DNA was not successful; to mutate this important strain, a suicide plasmid had to be used. This methodology has provided the means for a deeper understanding of this elusive serotype, both in terms of its biology and pathogenicity. To validate the method, the major known pneumococcal toxin, pneumolysin, was mutated because it has a well-known and easy to follow phenotype. We showed that the mutant, as expected, lost its ability to lyse red blood cells. By being able to mutate an important gene in the serotype of interest, we were able to observe different phenotypes for loss of function mutants upon intraperitoneal and intranasal infections from the ones observed for other serotypes. In summary, this study proves that strain 519/43 (serotype 1) can be genetically modified.

Constructing Mutants in Serotype 1 Streptococcus pneumoniae strain 519/43

Here, we describe a S. pneumoniae serotype 1 strain 519/43 that can be genetically modified by using its ability to naturally acquire DNA and a suicide-plasmid. As proof of principle, an isogenic mutant in the pneumolysin (ply) gene was made.

Streptococcus pneumoniae serotype 1 remains a huge problem in low-and-middle income countries, particularly in sub-Saharan Africa. Despite its importance, ...