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Development of a DNA microarray method for detection and identification of all 15 distinct O-antigen forms of Legionella pneumophila.

ABSTRACT: Legionella is ubiquitous in many environments. At least 50 species and 70 serogroups of the Gram-negative bacterium have been identified. Of the 50 species, 20 are pathogenic, and Legionella pneumophila is responsible for the great majority (approximately 90%) of the Legionnaires' disease cases that occur. Furthermore, of the 15 L. pneumophila serogroups identified, O1 alone causes more than 84% of the Legionnaires' disease cases that occur worldwide. Rapid and reliable assays for the detection and identification of L. pneumophila in water, environmental, and clinical samples are in great demand. L. pneumophila bacteria are traditionally identified by their O antigens by immunological methods. We have recently developed an O serogroup-specific DNA microarray for the detection of all 15 distinct O-antigen forms of L. pneumophila, including serogroups O1 to O15. A total of 35 strains were used to verify the specificity of the microarray, including 15 L. pneumophila O-antigen standard reference strains and seven L. pneumophila clinical isolates as target strains, seven reference strains of other non-pneumophila Legionella species as closely related strains, and six non-Legionella bacterial species as nonrelated strains. The detection sensitivity was 1 ng of genomic DNA or 0.4 CFU/ml in water samples with filter enrichment and plate culturing. This study demonstrated that the microarray allows specific, sensitive, and reproducible detection of L. pneumophila serogroups. To the best of our knowledge, this is the first report of a microarray serotyping method for all 15 distinct O-antigen forms of L. pneumophila.

SUBMITTER: Cao B

PROVIDER: S-EPMC3811488 | biostudies-literature | 2013 Nov

REPOSITORIES: biostudies-literature

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Development of a DNA microarray method for detection and identification of all 15 distinct O-antigen forms of Legionella pneumophila.

Cao Boyang B Yao Fangfang F Liu Xiangqian X Feng Lu L Wang Lei L

Applied and environmental microbiology 20130823 21

Legionella is ubiquitous in many environments. At least 50 species and 70 serogroups of the Gram-negative bacterium have been identified. Of the 50 species, 20 are pathogenic, and Legionella pneumophila is responsible for the great majority (approximately 90%) of the Legionnaires' disease cases that occur. Furthermore, of the 15 L. pneumophila serogroups identified, O1 alone causes more than 84% of the Legionnaires' disease cases that occur worldwide. Rapid and reliable assays for the detection ...[more]

PMID: 23974134

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Project description:Legionella pneumophila is a gram-negative opportunistic human pathogen that infects and multiplies in a broad range of phagocytic protozoan and mammalian phagocytes. Based on the observation that small regulatory RNAs (sRNAs) play an important role in controlling virulence-related genes in several pathogenic bacteria, we attempted to test the hypothesis that sRNAs play a similar role in L. pneumophila. We used computational prediction followed by experimental verification to identify and characterize sRNAs encoded in the L. pneumophila genome. A 50-mer probe microarray was constructed to test the expression of predicted sRNAs in bacteria grown under a variety of conditions. This strategy successfully identified 22 expressed RNAs, out of which six were confirmed by northern blot and RACE. One of the identified sRNAs is highly expressed when the bacteria enter post exponential phase and computational prediction of its secondary structure reveals a striking similarity to the structure of 6S RNA, a widely distributed prokaryotic sRNA, known to regulate the activity of Ï70-containing RNAP. A 70-mer probe microarray was used to identify genes affected by L. pneumophila 6S RNA in stationary phase. The 6S RNA encoded by the ssrS gene positively regulates expression of genes encoding type IVB secretion system effectors, stress response genes such as groES and recA as well as many genes with unknown or hypothetical functions. Deletion of 6S RNA significantly reduced L. pneumophila intracellular multiplication in both protist and mammalian host cells, but had no detectable effect on growth in rich media. A microarray was designed for the detection of 101 predicted sRNAs by using OligiWiz version 2.1.3 (Nielsen et al., 2003, Wernersson & Nielsen, 2005). The prokaryotic setting was used to design 50-mers probes located, when possible, at the 3â end of the predicted genes. Probes for 10 negative controls, representing 10 genes of the L. pneumophila Paris plasmid, were also designed. Probes (Illumina) were dissolved in 50% DMSO to a final concentration of 30 uM and printed in triplicate on UltraGAPS coated glass slides (Corning) using a PerkinElmer SpotArray microarray printer. Fifteen micrograms of total RNA was labelled during cDNA synthesis using Superscript II reverse transcriptase (Invitrogen) and amino-allyl dUTP (Sigma). Bacterial genomic DNA was used as the reference channel on each slide to allow comparison of each time point and different samples (Talaat et al., 2002). Five micrograms of genomic DNA (gDNA) was labelled with amino-allyl dUTP by using Klenow fragment and random primers (Invitrogen) at 37 Â°C for 18 h. DNA was subsequently coupled to the succinimidyl ester fluorescent dye AlexaFluor 546 (for cDNA) or Alexa Fluor 647 (for gDNA) (Invitrogen) following manufacturerâs protocols. Hybridization and data acquisition were performed as previously described (Hovel-Miner et al., 2009).Very low density array, like the sRNA microarray used here, cannot be normalised with common procedure like total intensity or lowess. Local background was removed from spot signal intensity and the noise signal was estimated by recording the average signal intensity of 10 negative controls printed on the chip. Normalisation of signal intensity was carried out by calculating the fold increase over the noise signal value. Correlation of replicates using this normalisation procedure was â¥ 0.95.

Dataset Information

Development of a DNA microarray method for detection and identification of all 15 distinct O-antigen forms of Legionella pneumophila.

Publications

Development of a DNA microarray method for detection and identification of all 15 distinct O-antigen forms of Legionella pneumophila.

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