The authors would like to thank Prof. Enno Jacobs for his continuing support.

1. Extraction of Bacterial DNA
<ol>
	<li>Preparation of PBS Solution
	<ol>
		<li>Weigh 1.65 g Na2HPO4 x 2H2O, 0.22 g NaH2PO4 x 2H2O and 8.80 g NaCl in a flask and fill with distilled water to a final volume of 1,000 ml. Adjust the pH to 7.4. For final use filter the solution through a bacteria-proof (0.22 &#181;m) filter.</li>
	</ol>
	</li>
	<li>DNA Extraction of Gram-negative Bacteria
	<ol>
		<li>Streak the patient material on appropriate culture media ...

The authors declare that they have no competing financial interests.

Both MALDI-TOF MS and 16S rRNA gene sequencing offer the possibility to identify large numbers of different bacteria. MALDI-TOF MS is a fast and inexpensive method, which is easy to handle and large databases of bacterial mass spectra are available. For this reason, MALDI-TOF MS is a rapid, cost effective and reliable method to conduct screening studies focused on rare bacterial pathogens 17,20,39,51. In a prospective study comparing MALDI-TOF MS with other phenotypic identification methods, Seng et al.</e...

Secure identification of rare pathogens in routine diagnostics is hampered by the fact that classical cultural and biochemical methods are cumbersome and sometimes questionable. Furthermore, a diagnostic microbiology laboratory has to process a large number of pathogens, ranging from a few hundred to several thousands, daily, which requires the use of automated systems. In addition to the management of a high daily throughput, the precise identification of bacterial species is needed. This is warranted since they differ in their antimicrobial susceptibility pattern and therefore correct identification provides the clinician with essential information to choose appropriate antibiotics (e.g., Enterococcus spp., Acinetobacter spp.) 12,43.
Automated microbial identification systems (aMIS) apply standardized sets of enzymatic reactions to characterize the metabolic properties of bacterial isolates 13,15,16,26,27. Although the cartridges used in these systems utilize a large number of different biochemical reactions, e.g., 47 in the GN card of the aMIS used in this study 52, this strategy permits secure identification only for a limited set of bacteria. Furthermore, the database, an advanced expert system, is clearly focused on detection of relevant and highly relevant bacteria of medical importance 13,15,16,36. Two further systems, widely used in laboratories, also apply this biochemical approach for bacterial identification. Recent studies demonstrate a comparable identification accuracy between the aMIS used in this study and one of the competitors (93.7% and 93.0% respectively), while the 3rd aMIS has an identification accuracy of only 82.4% on species level 35. Such discrepancies may be explained by the quality of the underlying identification data references, the versions of kits and software, differences in metabolism and proficiency of technical personnel 35,36.
Two automated MALDI-TOF MS systems (MALDI-TOF microbial identification system, mMIS) are mainly used. These systems allow for detection of a large number of bacterial species based on their protein fingerprint mass spectra. For instance, the database of the mMIS used contains 6,000 reference spectra. Identification systems based on mass spectrometry offer fast and reliable detection of a great variety of microorganisms including rare pathogens 11,48,51. To date only a few direct comparisons are available between the mMIS used in this study and its competitor 19,33. According to Daek et al. both systems provide a similar high rate of identification accuracy, but the mMIS used in this study seems to be more reliable in species identification 19.
Similarly, molecular techniques addressing well conserved but also distinct genes (e.g., 16S rDNA or rpoB) permit a clear species identification 3,22,61. Among these, the 16S rDNA is the most widely used housekeeping gene because of its presence in all bacteria 34. Its function remains unchanged and finally, with roughly 1,500 bp, it is long enough to be suitable for bio-informatics 14,34. Many researchers regard 16S rRNA gene analysis as the &#34;gold-standard&#34; for bacterial identification 21. This is due to the fact that few laboratories use DNA-DNA hybridization techniques to date for identification of rare or new bacteria 14,34. Additionally, more and more databases are available which can be used for 16S rRNA gene analysis 50. However, it has to be taken into account that 16S rDNA based detection systems have a limited sensitivity compared to standard PCR protocols. Moreover, the molecular approach is sophisticated, time consuming and requires highly trained personnel as well as dedicated laboratory facilities and is, therefore, not easily implemented into routine diagnostics 55. Furthermore, it has been shown that the combination of at least two different methods of bacterial identification leads to highly accurate strain identification. The combination of MALDI-TOF MS and 16S rDNA sequencing permits the identification of large numbers of different bacterial species with high accuracy. Recently the combination of MALDI-TOF MS and 16S rRNA gene analysis was presented for bacterial identification studying epidemiological questions and rare pathogens 56.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>CHROMASOLV, HPLC grade water, 1 L</td>
			<td>Sigma-Aldrich Chemie, M&#252;nchen, Germany</td>
			<td>270733</td>
			<td></td>
		</tr>
		<tr>
			<td>Tissue Lyser LT</td>
			<td>Qiagen, Hilden, Germany</td>
			<td>85600</td>
			<td>Oscillating Homogenizer</td>
		</tr>
		<tr>
			<td>Glass-beads 1,0mm</td>
			<td>VWR International, Darmstadt, Germany</td>
			<td>412-2917</td>
			<td></td>
		</tr>
		<tr>
			<td>Thermomixer 5436</td>
			<td>Eppendorf, Hamburg, Germany</td>
			<td>2050-100-05</td>
			<td></td>
		</tr>
		<tr>
			<td>QIAamp DNA Mini Kit (250)</td>
			<td>Qiagen, Hilden, Germany</td>
			<td>51306</td>
			<td></td>
		</tr>
		<tr>
			<td>Taq PCR Core Kit (1000 U)</td>
			<td>Qiagen, Hilden, Germany</td>
			<td>201225</td>
			<td></td>
		</tr>
		<tr>
			<td rowspan="2">Forward Primer TPU1 (5&#180;-AGA GTT TGA TCM TGG CTC AG-3&#8217;)</td>
			<td rowspan="2">biomers.net GmbH, Ulm, Germany&#160;</td>
			<td rowspan="2">-</td>
			<td></td>
		</tr>
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			<td></td>
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		<tr>
			<td rowspan="2">Reverse Primer RTU4 (5&#180;-TAC CAG GGT ATC TAA TCC TGT T-3&#180;)</td>
			<td rowspan="2">biomers.net GmbH, Ulm, Germany&#160;</td>
			<td rowspan="2">-</td>
			<td></td>
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			<td></td>
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			<td>Mastercycler&#160;</td>
			<td>Eppendorf, Hamburg, Germany</td>
			<td>-&#160;</td>
			<td>Thermocylcer</td>
		</tr>
		<tr>
			<td>Reaction tube 1.5 mL</td>
			<td>SARSTEDT, N&#252;mbrecht, Germany</td>
			<td>72,692</td>
			<td></td>
		</tr>
		<tr>
			<td>Reaction tube 2 mL</td>
			<td>SARSTEDT, N&#252;mbrecht, Germany</td>
			<td>72,693,005</td>
			<td></td>
		</tr>
		<tr>
			<td>PCR 8er-CapStrips</td>
			<td>Biozym Scientific, Hessisch Oldendorf, Germany</td>
			<td>711040X</td>
			<td></td>
		</tr>
		<tr>
			<td>PCR 8er-SoftStrips</td>
			<td>Biozym Scientific, Hessisch Oldendorf, Germany</td>
			<td>711030X</td>
			<td></td>
		</tr>
		<tr>
			<td>Sharp R-ZV11&#160;</td>
			<td>Sharp Electronics, Hamburg, Germany</td>
			<td>-</td>
			<td>Microwave</td>
		</tr>
		<tr>
			<td>Titriplex III (EDTA Na2-salt dehydrate; 1 kg)</td>
			<td>Merck, Darmstadt, Germany</td>
			<td>1084211000</td>
			<td></td>
		</tr>
		<tr>
			<td>SeaKem LE Agarose</td>
			<td rowspan="2">Biozym Scientific, Hessisch Oldendorf, Germany</td>
			<td rowspan="2">849006</td>
			<td></td>
		</tr>
		<tr>
			<td>(2 x 500 g)</td>
			<td></td>
		</tr>
		<tr>
			<td>SmartLadder SF - 100 to 1000 bp</td>
			<td>Eurogentec, L&#252;ttich, Belgium</td>
			<td>MW-1800-04</td>
			<td></td>
		</tr>
		<tr>
			<td>Bromphenol blue (25 g)</td>
			<td>Sigma-Aldrich Chemie, M&#252;nchen, Germany</td>
			<td>B0126</td>
			<td></td>
		</tr>
		<tr>
			<td>Xylene cyanol FF (10 g)</td>
			<td>Sigma-Aldrich Chemie, M&#252;nchen, Germany</td>
			<td>X4126</td>
			<td></td>
		</tr>
		<tr>
			<td>ComPhor L Maxi&#160;</td>
			<td>Biozym, Hessisch Oldendorf, Germany</td>
			<td>-</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethidium bromide solution 1&#160;%(10 mL)</td>
			<td>Carl Roth, Karlsruhe, Germany</td>
			<td>2218.1</td>
			<td></td>
		</tr>
		<tr>
			<td>Gel Doc 2000</td>
			<td>Bio-Rad Laboratories, M&#252;nchen, Germany</td>
			<td>-</td>
			<td>Gel-documentation system&#160;</td>
		</tr>
		<tr>
			<td>ExoSAP-IT (500 reactions)</td>
			<td>Affymetrix UK, Wooburn Green, High Wycombe, United Kingdom</td>
			<td>78201</td>
			<td></td>
		</tr>
		<tr>
			<td>Buffer (10 x) with EDTA&#160;</td>
			<td>Life Technologies, Darmstadt, Germany</td>
			<td>402824</td>
			<td></td>
		</tr>
		<tr>
			<td>BigDye Terminator Kit v1.1</td>
			<td>Life Technologies, Darmstadt, Germany</td>
			<td>4337450</td>
			<td></td>
		</tr>
		<tr>
			<td>Hi-Di formamide (25 mL)</td>
			<td>Life Technologies, Darmstadt, Germany</td>
			<td>4311320</td>
			<td></td>
		</tr>
		<tr>
			<td>DyeEx 2.0 Spin Kit (250)</td>
			<td>Qiagen, Hilden, Germany</td>
			<td>63206</td>
			<td></td>
		</tr>
		<tr>
			<td>3130 Genetic Analyzer</td>
			<td>Life Technologies, Darmstadt, Germany</td>
			<td>-</td>
			<td>Sequenzer</td>
		</tr>
		<tr>
			<td>MicroAmp optical 96-well reaction plate with barcode</td>
			<td>Life Technologies, Darmstadt, Germany</td>
			<td>4306737</td>
			<td></td>
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		<tr>
			<td>3130 Genetic Analyzer, plate base 96-well</td>
			<td>Life Technologies, Darmstadt, Germany</td>
			<td>4317237</td>
			<td></td>
		</tr>
		<tr>
			<td>3130 Genetic Analyzer, plate retainer 96-well</td>
			<td>Life Technologies, Darmstadt, Germany</td>
			<td>4317241</td>
			<td></td>
		</tr>
		<tr>
			<td>3130 Genetic Analyzer, well plate septa</td>
			<td>Life Technologies, Darmstadt, Germany</td>
			<td>4315933</td>
			<td></td>
		</tr>
		<tr>
			<td>3130 Genetic Analyzer, POP-7 Polymer, 7 mL</td>
			<td>Life Technologies, Darmstadt, Germany</td>
			<td>4352759</td>
			<td></td>
		</tr>
		<tr>
			<td>3130 Genetic Analyzer, 4-Capillary Array, 50 cm</td>
			<td>Life Technologies, Darmstadt, Germany</td>
			<td>4333466</td>
			<td></td>
		</tr>
		<tr>
			<td>Sequencing Analysis Software 5.4</td>
			<td>Life Technologies, Darmstadt, Germany</td>
			<td>-</td>
			<td></td>
		</tr>
		<tr>
			<td>microflex (the MALDI TOF MS maschine)</td>
			<td>Bruker Daltonik, Bremen, Germany</td>
			<td>-</td>
			<td></td>
		</tr>
		<tr>
			<td>MALDI Biotyper (the MALDI TOF MS system)</td>
			<td>Bruker Daltonik, Bremen, Germany</td>
			<td>-</td>
			<td>our mMIS</td>
		</tr>
		<tr>
			<td>VITEK MS&#160;</td>
			<td>bioM&#233;rieux, N&#252;rtingen, Germany&#160;</td>
			<td></td>
			<td>2nd mMis&#160;</td>
		</tr>
		<tr>
			<td>flexControl 3.4 (control software)</td>
			<td>Bruker Daltonik, Bremen, Germany</td>
			<td>-</td>
			<td></td>
		</tr>
		<tr>
			<td>Biotyper Realtime Classification 3.1 (RTC), (analysis software)</td>
			<td>Bruker Daltonik, Bremen, Germany</td>
			<td>-</td>
			<td></td>
		</tr>
		<tr>
			<td>&#945;-cyano-4-hydroxycinnamic acid, HCCA, 1&#160;g</td>
			<td>Bruker Daltonik, Bremen, Germany</td>
			<td>201344</td>
			<td></td>
		</tr>
		<tr>
			<td>Peptide Calibration Standard II</td>
			<td>Bruker Daltonik, Bremen, Germany</td>
			<td>222570</td>
			<td></td>
		</tr>
		<tr>
			<td>MSP 96 target polished steel</td>
			<td>Bruker Daltonik, Bremen, Germany</td>
			<td>8224989</td>
			<td></td>
		</tr>
		<tr>
			<td>peqgreen&#160;</td>
			<td>peqlab&#160;</td>
			<td>37-5010</td>
			<td></td>
		</tr>
		<tr>
			<td>MALDI Biotyper Galaxy&#160;</td>
			<td>Bruker Daltonik, Bremen, Germany</td>
			<td>Part No. 1836007&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Vitek 2&#160;</td>
			<td>bioM&#233;rieux, N&#252;rtingen, Germany&#160;</td>
			<td></td>
			<td>our aMis&#160;</td>
		</tr>
		<tr>
			<td>MicroScan&#160;</td>
			<td>Beckman Coulter&#160;</td>
			<td></td>
			<td>2nd aMis&#160;</td>
		</tr>
		<tr>
			<td>BD Phoenix&#8482; Automated Microbiology System</td>
			<td>BD</td>
			<td></td>
			<td>3rd aMis&#160;</td>
		</tr>
		<tr>
			<td>Staphylococcus aureus&#160;subsp.&#160;aureus&#160;Rosenbach (ATCC&#174;&#160;25923&#8482;)</td>
			<td>ATCC&#160;</td>
			<td></td>
			<td>postive control for PCR&#160;</td>
		</tr>
	</tbody>
</table>

identification of rare bacterial pathogens by 16s rrna gene sequencing and maldi-tof ms

There are a number of rare and, therefore, insufficiently described bacterial pathogens which are reported to cause severe infections especially in immunocompromised patients. In most cases only few data, mostly published as case reports, are available which investigate the role of such pathogens as an infectious agent. Therefore, in order to clarify the pathogenic character of such microorganisms, it is necessary to conduct epidemiologic studies which include large numbers of these bacteria. The methods used in such a surveillance study have to meet the following criteria: the identification of the strains has to be accurate according to the valid nomenclature, they should be easy to handle (robustness), economical in routine diagnostics and they have to generate comparable results among different laboratories. Generally, there are three strategies for identifying bacterial strains in a routine setting: 1) phenotypic identification characterizing the biochemical and metabolic properties of the bacteria, 2) molecular techniques such as 16S rRNA gene sequencing and 3) mass spectrometry as a novel proteome based approach. Since mass spectrometry and molecular approaches are the most promising tools for identifying a large variety of bacterial species, these two methods are described. Advances, limitations and potential problems when using these techniques are discussed.

MALDI-TOF MS is a novel, fast and inexpensive method for microbiological routine diagnostics. Bacterial species identification by MALDI-TOF MS produces spectra mainly composed of ribosomal proteins but also other &#34;very conserved proteins with house-keeping functions affected to a minimal extent by environmental conditions&#34; 17.The database of this mMIS contains a large set of reference spectra and even bacteria which are rarely found in clinical isolates can be securely ...

Watch this Scientific Journal Video about Identification of Rare Bacterial Pathogens by 16S rRNA Gene Sequencing and MALDI-TOF MS at JoVE.com

Identification of Rare Bacterial Pathogens by 16S rRNA Gene Sequencing and MALDI-TOF MS

Matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) and molecular techniques (16S rRNA gene sequencing) permit the identification of rare bacterial pathogens in routine diagnostics. The goal of this protocol lies in the combination of both techniques which leads to more accurate and reliable data.

There are a number of rare and, therefore, insufficiently described bacterial pathogens which are reported to cause severe infections especially in ...

The overall goal of this MALDI-TOF Mass Spectrometry protocol is to improve typing of rare pathogens through a rapid and cost-effective procedure. This method can help to answer key questions in the field of diagnostic microbiology, it allows rapid edification of rare bacterial pathogens. Today, we want to talk about odoratimimus and bacteria of the genus Myroides.To demonstrate the method and to talk about the interpretation of the results. Generally, individuals new to this method might find it difficult since transfer of bacteria, overlay with metrics, and interpretation of results require technical skills and microbiological expertise. We first had the idea to use MALD-TOF MS to screen for rare bacteria when we had a patient in our hospital suffering from a diabetic food infection caused by myroides odoratimus.Begin this protocol with the extraction of bacterial DNA, 16S ribosomal DNA PCR and Sanger sequencing as described in the text protocol. Use a wooden toothpick to transfer a single bacterial colony to a well of a 96 well steel target. Spot one microliter of 70%formic acid on top of the air-dried organism on the steel target, and leave to dry for approximately two to three minutes.Overlay the spot with one microliter of matrix solution containing 50 mg/ml of CHCA in an organic solvent composed of 50%acetonitrile, 2.5 trifluoroacetic acid, and 47.5%water. Let the smear and overlaid matrix air dry for about five minutes in a hood. To introduce the samples, aerate the sample loading port of the mass spectrometer by pressing the in/out button of the instrument.Open the loading port and insert the MALDI-TOF MS target plate with the dried bacterial smear plus matrix. Close the port and evacuate again. Observe the vacuum and when it reaches 4.5 million millibar start the measurement.Open the MMIS analysis software and click the file menu. Select New Classification"and a new window called MALDI Biotyper Real Time Classification Wizard"should open. Type the project name in the field Project Name"and click New, under the new dialogue box named New Project, check the project name and proceed by clicking the Okay"button.In the MALDI Biotyper Real Time Classification Wizard, observe the Analyte placement window. Select target positions, right click any selected position, and select Add samples. In the automatically opened table view, type in the sample name, sample ID, and optionally, a comment.Click the Next"button to proceed. Next, observe the selection of MALDI Biotyper methods window. Select Bruker Taxonomy"from the MSPs from Taxonomy Trees and click Next"to continue.Then, observe the project summary window. Check the inserted entries given above for the actual classification project. Start the classification run by clicking the Finish"button.Measurements start automatically when the appropriate vacuum is reached. Follow the classification run until the measurement is successfully completed. Once the measurement is complete, open the menu View"and click Results"to view the results table in the MALDI Biotyper Real Time Classification Project One.View the Bruker-Daltonik MALDI Biotyper classification results as an html file in the default web browser. Print and save the results. Shown here are spectra obtained by MALDI-TOF MS that are measured and classified in real time.The spectra are assigned a species name and a score value reflecting the quality of the measurement. Scores above 2.300 represent a highly-probable species identification. A score between 2.000 and 2.300 indicates a secure species identification.A score below 1.700 and 2.000 designates a probable species identification. And a score below 1.700 is non-reliable. The identification of bacterial pathogens grown on a pure culture on a solid medium takes two to three minutes.It is important to remember that rare bacteria pathogens can only be found with MALDI-TOF MS when the instruments reliably contains the appropriate spectra. Otherwise, it has to be expunged by integrating MaSDA spectra from typed strains of their characterized isolates. In the case where score results do not lead to an unequivocal strain identification, further methods, such as biochemical profiling or 16S rDNA sequencing can be applied.Though this method can provide insight into bacterial detection, it can also be applied to other microorganisms such as fungi or anaerobes. Furthermore, bacteria-resistance can be measured. Don't forget working with a matrix which is a hazardous substance, wear gloves, protective goggles, and work under a hood.Furthermore, it is absolutely necessary to dry the matrix and smear thoroughly to avoid splash overs in the analyzation chamber.

identification-rare-bacterial-pathogens-16s-rrna-gene-sequencing

Research

JoVE Journal

Immunology and Infection

16.9K vues.  TU Dresden. The overall goal of this MALDI-TOF Mass Spectrometry protocol is to improve typing of rare pathogens through a rapid and cost-effective procedure. This method can help to answer key questions in the field of diagnostic microbiology, it allows rapid edification of rare bacterial pathogens. Today, we want to talk about odoratimimus and bacteria of the genus Myroides.To demonstrate the method and to talk about the interpretation of the results. Generally, individuals new to this method mi...