Name: fluorescence microscopy methods for determining the viability of bacteria in association with mammalian cells
Uploaded: 2013-09-05T12:00:00
Description: Watch this Scientific Journal Video about Fluorescence Microscopy Methods for Determining the Viability of Bacteria in Association with Mammalian Cells at JoVE.com

We thank Asya Smirnov and Laura Gonyar for critical reading of the manuscript. This work was supported by grants NIH R00 TW008042 and R01 AI097312 to A.K.C. M.B.J. was supported in part by NIH T32 AI007046.

1. Assessing Bacterial Viability with Propidium Iodide and SYTO9
<ol>
	<li>Infect cells that are adherent to 12 mm diameter circular glass coverslips in 24-well plates with bacteria of interest. Do NOT fix the cells with aldehydes or organic solvents.</li>
	<li>Rinse cells once gently in 0.1 M 3-(N-morpholino)propanesulfonic acid (MOPS), pH 7.2, containing 1 mM MgCl2 (MOPS/MgCl2).</li>
	<li>Incubate cells for 10 min in the dark at room temperature with Alexa Fluor 647-coupled anti...

<ol>
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P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enumeration+of+water-borne+bacteria+using+viability+assays+and+flow+cytometry:+a+comparison+to+culture-based+techniques.">Enumeration of water-borne bacteria using viability assays and flow cytometry: a comparison to culture-based techniques.</a> J Microbiol Methods. 55, 585-597 (2003).</li><li>Oh, H., Siano, B., Diamond, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neutrophil+isolation+protocol.">Neutrophil isolation protocol.</a> J. Vis. Exp.. (17), e745 (2008).</li><li>Allen, L. 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A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Statins+enhance+formation+of+phagocyte+extracellular+traps.">Statins enhance formation of phagocyte extracellular traps.</a> Cell Host Microbe. 8, 445-454 (2010).</li><li>Thulin, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Viable+group+A+streptococci+in+macrophages+during+acute+soft+tissue+infection.">Viable group A streptococci in macrophages during acute soft tissue infection.</a> PLoS Med. 3, e53 (2006).</li><li>Kubica, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+potential+new+pathway+for+Staphylococcus+aureus+dissemination:+the+silent+survival+of+S.+aureus+phagocytosed+by+human+monocyte-derived+macrophages.">A potential new pathway for Staphylococcus aureus dissemination: the silent survival of S. aureus phagocytosed by human monocyte-derived macrophages.</a> PLoS One. 3, (2008).</li><li>Swords, W. 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N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+determination+of+Mycobacterium+leprae+viability+by+use+of+real-time+PCR.">Molecular determination of Mycobacterium leprae viability by use of real-time PCR.</a> J. Clin. Microbiol. 47, 2124-2130 (2009).</li><li>Botha, M., Botes, M., Loos, B., Smith, C., Dicks, L. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lactobacillus+equigenerosi+strain+Le1+invades+equine+epithelial+cells.">Lactobacillus equigenerosi strain Le1 invades equine epithelial cells.</a> Appl. Environ. Microbiol. 78, 4248-4255 (2012).</li><li>Allen, L. A., Schlesinger, L. 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Presented here are two protocols that use DNA binding and viability dyes in conjunction with a fluorescent lectin to identify live and dead bacteria attached to and inside human cells. Since both protocols effectively discriminate live from dead bacteria, the choice of which protocol to use depends upon the goal of the experiment. The first protocol uses propidium iodide to detect nonviable bacteria and SYTO9 to detect intact bacteria. Shown in Figure 4A is a representative image of protocol 1 applied to...

There is a dynamic interaction and co-evolution between bacteria and the hosts in which they reside. Bacteria have evolved adherence organelles, secretion systems, and/or the ability to produce toxins that enable their productive infection of host phagocytic and non-phagocytic cells. The bacteria must also contend with recognition and antimicrobial activities of the host immune system. The host immune system is comprised of innate and adaptive components including physical and chemical barriers, immune cells, the complement system, and other components of humoral immunity. While many bacteria are susceptible to killing and clearance by the multilayered host immune response, some pathogenic and opportunistic bacteria have evolved mechanisms to infect a variety of host cells and subvert clearance by the host immune response 1. Neisseria gonorrhoeae is one example of a bacterial pathogen that is highly adapted to persist in its human host. N. gonorrhoeae readily colonizes the luminal surfaces of mucosal epithelial cells of the urogenital tract, pharynx, conjunctiva, and rectum. Colonization triggers the abundant recruitment of neutrophils at mucosal sites. Neutrophils are professional phagocytes that possess a variety of antimicrobial processes to kill microorganisms; however, N. gonorrhoeae is capable of surviving in the presence of neutrophils 2-5. Understanding how bacterial pathogens such as N. gonorrhoeae subvert, suppress, and hijack the immune response to ultimately survive in normally hostile host environments is crucial to the development of new therapies for combating infectious diseases.
Experimental protocols often used to investigate bacterial survival in host cells include colony count assays, gentamicin protection assays, and electron microscopy. In colony count assays, a population of infected cells is lysed (for instance, with a detergent to which the bacteria are resistant) to liberate the bacteria. The lysates are diluted and plated on agar-based media, and colony-forming units in the lysates are enumerated for each time point and/or experimental condition. This approach reports the viability of the entire bacterial population but is not capable of differentiating between intracellular and extracellular survival. A variation on the colony count assay, the gentamicin protection assay, specifically measures intracellular bacterial survival, based on the inability of the antibiotic gentamicin to cross the eukaryotic plasma membrane 6. However, this assay is dependent on the bacteria being susceptible to killing by gentamicin (or another antibiotic that is similarly eukaryotic membrane-impermeant) and the inability of the antibiotic to have access to internal bacteria. Therefore, a gentamicin protection assay may not be effective for examination of all bacterial species or when examining bacterial survival in highly pinocytic cells such as neutrophils. Neither of these approaches reveals the subcellular localization or other behavior of individual bacteria (e.g. if the bacteria form aggregates or microcolonies that behave differently from individual bacterial cells). Another frequently used approach to examine the viability of individual external and internal bacteria is thin-section transmission electron microscopy (TEM). This approach is advantageous in that it can provide information regarding the location of the bacteria in host cells (e.g. phagosome, cytoplasm, autophagosome), which can be further investigated by immunoelectron microscopy with gold-coupled antibodies against subcellular markers. However, electron microscopy is not especially sensitive at assessing bacterial viability. When embedded sections are stained with uranyl acetate, lead citrate, or other electron-dense reagents and imaged by electron microscopy, electron-dense bacteria are considered viable and electron-lucent nonviable 7,8. However, this assumption overestimates bacterial viability, since only those dead bacteria with severely disrupted membranes and devoid of cytoplasm appear electron-lucent. In addition, some bacterial species may display a range of electron densities depending on their stage of growth, making it difficult to determine viability.
As an alternative or in addition to these widely used methods, here we provide protocols and rationale for the use of fluorescent dyes that indicate bacterial viability to assess the survival of bacteria attached to and internalized by host cells. To identify extracellular bacteria, infected cells are first exposed to a fluorescent reagent, such as a lectin or bacteria-specific antibody. The infected cells are then permeabilized and exposed to DNA-specific dyes that are differentially accessible to bacteria with intact vs. degraded membranes, as a surrogate for bacterial viability. In the first protocol, the membrane permeable dye SYTO9 identifies the total bacterial population, while propidium iodide is only accessible to those bacteria that have compromised membranes and are thus considered nonviable. Propidium iodide and SYTO9 have been used to evaluate bacterial viability in biofilms, discriminate pathogenic from nonpathogenic bacteria, and enumerate viable water-borne bacteria 9-12. In the second protocol, 4&#39;,6&#39;-diamidino-2-phenylindole (DAPI) identifies total bacteria, while SYTOX Green is only accessible to the nonviable population. These viability dye pairs can be combined with immunofluorescence to determine each bacterium&#39;s location in relation to a protein of interest, for instance to define bacterial subcellular localization. The use of these assays provides key insight into the interactions that result in bacterial killing or survival during infection of host cells. The protocols outlined in this article were used to assess the viability of N. gonorrhoeae that is attached to and inside primary human neutrophils, including in different populations of neutrophil phagosomes 5,13,14. However, these protocols can be applied to assess viability of gram-positive and gram-negative bacteria in professional phagocytes, non-professional phagocytes, and protozoa 15-24.

<table border="1">
	<tbody>
		<tr>
			<td>Name of Reagent/Material</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>21 G 3/4 butterfly needles for blood collection</td>
			<td>Becton Dickinson</td>
			<td>367251</td>
			<td></td>
		</tr>
		<tr>
			<td>Blood collection tubes with Sodium Heparin 10 ml</td>
			<td>Becton Dickinson</td>
			<td>366480</td>
			<td></td>
		</tr>
		<tr>
			<td>Sterile water for irrigation</td>
			<td>Baxter</td>
			<td>07-09-64-070</td>
			<td></td>
		</tr>
		<tr>
			<td>Dextran 500</td>
			<td>Sigma</td>
			<td>31392</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Chloride</td>
			<td>Fisher Scientific</td>
			<td>S641</td>
			<td></td>
		</tr>
		<tr>
			<td>Dextrose</td>
			<td>Ricca Chemical Company</td>
			<td>RDCD0200</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s PBS no Ca2+ or Mg2+</td>
			<td>Thermo Scientific</td>
			<td>SH3002802</td>
			<td></td>
		</tr>
		<tr>
			<td>Ficoll solution</td>
			<td>GE Healthcare</td>
			<td>17-1440-03</td>
			<td></td>
		</tr>
		<tr>
			<td>Acetic Acid</td>
			<td>Fisher Scientific</td>
			<td>BP2401</td>
			<td></td>
		</tr>
		<tr>
			<td>12 mm circular glass coverslips</td>
			<td>Fisher Scientific</td>
			<td>12-545-80 12CIR-1</td>
			<td></td>
		</tr>
		<tr>
			<td>24-well plates</td>
			<td>Corning Incorporated</td>
			<td>3524</td>
			<td></td>
		</tr>
		<tr>
			<td>Pooled Human Serum</td>
			<td>Sigma</td>
			<td>S7023</td>
			<td></td>
		</tr>
		<tr>
			<td>RPMI</td>
			<td>Mediatech</td>
			<td>15-040-CV</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum</td>
			<td>Thermo Scientific</td>
			<td>SH3007103</td>
			<td></td>
		</tr>
		<tr>
			<td>Human interleukin-8</td>
			<td>R&#38;D Systems</td>
			<td>208-IL/CF</td>
			<td></td>
		</tr>
		<tr>
			<td>MOPS</td>
			<td>Sigma</td>
			<td>M3183</td>
			<td></td>
		</tr>
		<tr>
			<td>MgCl2</td>
			<td>Fisher Scientific</td>
			<td>BP214</td>
			<td></td>
		</tr>
		<tr>
			<td>Propidium Iodide</td>
			<td>Life Technologies</td>
			<td>L7007 or L7012</td>
			<td></td>
		</tr>
		<tr>
			<td>SYTO9</td>
			<td>Life Technologies</td>
			<td>L7007 or L7012</td>
			<td></td>
		</tr>
		<tr>
			<td>Saponin</td>
			<td>Fluka Analytical</td>
			<td>47036</td>
			<td></td>
		</tr>
		<tr>
			<td>Alexa Fluor 647-coupled soybean lectin</td>
			<td>Life Technologies</td>
			<td>L-32463</td>
			<td></td>
		</tr>
		<tr>
			<td>DAPI</td>
			<td>Sigma</td>
			<td>D8417</td>
			<td></td>
		</tr>
		<tr>
			<td>SYTOX Green</td>
			<td>Life Technologies</td>
			<td>S7020</td>
			<td></td>
		</tr>
		<tr>
			<td>Mouse anti-CD63</td>
			<td>Developmental Studies Hybridoma Bank</td>
			<td>H5C6</td>
			<td></td>
		</tr>
		<tr>
			<td>Alexa Fluor 555 Antibody Labeling Kit</td>
			<td>Life Technologies</td>
			<td>A20187</td>
			<td></td>
		</tr>
		<tr>
			<td>Hemacytometer Bright Line</td>
			<td>Hausser Scientific</td>
			<td>1492</td>
			<td></td>
		</tr>
		<tr>
			<td>Forceps</td>
			<td>EMS</td>
			<td>78320</td>
			<td></td>
		</tr>
		<tr>
			<td>Sorvall Legend RT + Centrifuge</td>
			<td>Thermo Scientific</td>
			<td>75004377</td>
			<td></td>
		</tr>
	</tbody>
</table>

fluorescence microscopy methods for determining the viability of bacteria in association with mammalian cells

Central to the field of bacterial pathogenesis is the ability to define if and how microbes survive after exposure to eukaryotic cells. Current protocols to address these questions include colony count assays, gentamicin protection assays, and electron microscopy. Colony count and gentamicin protection assays only assess the viability of the entire bacterial population and are unable to determine individual bacterial viability. Electron microscopy can be used to determine the viability of individual bacteria and provide information regarding their localization in host cells. However, bacteria often display a range of electron densities, making assessment of viability difficult. This article outlines protocols for the use of fluorescent dyes that reveal the viability of individual bacteria inside and associated with host cells. These assays were developed originally to assess survival of Neisseria gonorrhoeae in primary human neutrophils, but should be applicable to any bacterium-host cell interaction. These protocols combine membrane-permeable fluorescent dyes (SYTO9 and 4&#39;,6-diamidino-2-phenylindole [DAPI]), which stain all bacteria, with membrane-impermeable fluorescent dyes (propidium iodide and SYTOX Green), which are only accessible to nonviable bacteria. Prior to eukaryotic cell permeabilization, an antibody or fluorescent reagent is added to identify extracellular bacteria. Thus these assays discriminate the viability of bacteria adherent to and inside eukaryotic cells. A protocol is also provided for using the viability dyes in combination with fluorescent antibodies to eukaryotic cell markers, in order to determine the subcellular localization of individual bacteria. The bacterial viability dyes discussed in this article are a sensitive complement and/or alternative to traditional microbiology techniques to evaluate the viability of individual bacteria and provide information regarding where bacteria survive in host cells.

The protocols outlined were used to examine survival of N. gonorrhoeae after exposure to primary human neutrophils 5,26. Neutrophils were infected with N. gonorrhoeae and processed with protocol 1, using the green-fluorescent viability dye SYTO9 and the red-fluorescent propidium iodide (Figure 4A). The dyes were added in the presence of saponin, which sequesters cholesterol to preferentially permeabilize host cell plasma membranes, not N. gonorrhoeae membranes. Other...

Watch this Scientific Journal Video about Fluorescence Microscopy Methods for Determining the Viability of Bacteria in Association with Mammalian Cells at JoVE.com

Fluorescence Microscopy Methods for Determining the Viability of Bacteria in Association with Mammalian Cells

Central to the field of bacterial pathogenesis is the ability to define if and how microbes survive after exposure to eukaryotic cells. This article outlines protocols for the use of fluorescent dyes that reveal the viability of individual bacteria inside and associated with host cells.

Central to the field of bacterial pathogenesis is the ability to define if and how microbes survive after exposure to eukaryotic cells. Current protocols ...

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

Fluorescence in situ Hybridizations (FISH) for the Localization of Viruses and Endosymbiotic Bacteria in Plant and Insect Tissues

Fluorescence in situ Hybridizations FISH for the Localization of Viruses and Endosymbiotic Bacteria in Plant and Insect Tissues

Fluorescence in situ hybridization (FISH) is a name given to a variety of techniques commonly used for visualizing gene transcripts in eukaryotic cells ...

Electroporation of Functional Bacterial Effectors into Mammalian Cells

The study of protein interactions in the context of living cells can generate critical information about localization, dynamics, and interacting partners. ...

Porphyromonas gingivalis as a Model Organism for Assessing Interaction of Anaerobic Bacteria with Host Cells

Porphyromonas gingivalis as a Model Organism for Assessing Interaction of Anaerobic Bacteria with Host Cells

Anaerobic bacteria far outnumber aerobes in many human niches such as the gut, mouth, and vagina. Furthermore, anaerobic infections are common and ...

Analysis of Lymphocyte Extravasation Using an In Vitro Model of the Human Blood-brain Barrier

Analysis of Lymphocyte Extravasation Using an In Vitro Model of the Human Blood-brain Barrier

Lymphocyte extravasation into the central nervous system (CNS) is critical for immune surveillance. Disease-related alterations of lymphocyte ...

Quantification of Efferocytosis by Single-cell Fluorescence Microscopy

Studying the regulation of efferocytosis requires methods that are able to accurately quantify the uptake of apoptotic cells and to probe the signaling ...

High-throughput Measurement of Plasma Membrane Resealing Efficiency in Mammalian Cells

In their physiological environment, mammalian cells are often subjected to mechanical and biochemical stresses that result in plasma membrane damage. In ...