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A Vibrio cholerae pathogenicity island associated with epidemic and pandemic strains
D K Karaolis1, J A Johnson, C C Bailey
1Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, MD 21201, USA. karaolis@umaryland.edu
Abstract:
The bacterial species Vibrio cholerae includes harmless aquatic strains as well as strains capable of causing epidemics and global pandemics of cholera. While investigating the relationship between pathogenic and nonpathogenic strains, we identified a chromosomal pathogenicity island (PAI) that is present in epidemic and pandemic strains but absent from nonpathogenic strains. Initially, two ToxR-regulated genes (aldA and tagA) were studied and were found to be associated with epidemic and pandemic strains but absent in nontoxigenic strains. The region containing aldA and tagA comprises 13 kb of previously unidentified DNA and is part of a PAI that contains a regulator of virulence genes (ToxT) and a gene cluster encoding an essential colonization factor and the cholera toxin phage receptor (toxin-coregulated pilus; TCP). The PAI is 39.5 kb in size, has low %G+C (35%), contains putative integrase and transposase genes, is flanked by att sites, and inserts near a 10Sa RNA gene (ssrA), suggesting it may be of bacteriophage origin. We found this PAI in two clinical non-O1/non-O139 cholera toxin-positive strains, suggesting that it can be transferred within V. cholerae. The sequence within this PAI includes an ORF with homology to a gene associated with the type IV pilus gene cluster of enteropathogenic Escherichia coli, a transposase from Vibrio anguillarum, and several ORFs with no known homology. As the PAI contains the CTXPhi receptor, it may represent the initial genetic factor required for the emergence of epidemic and pandemic cholera. We propose to call this island VPI (V. cholerae pathogenicity island).
Insights
A novel Vibrio cholerae pathogenicity island (VPI) was identified, containing virulence genes and the cholera toxin phage receptor. This island is present in epidemic strains, suggesting its role in cholera pandemics.
Area of Science:
- Microbiology
- Genetics
- Epidemiology
Background:
- Vibrio cholerae causes cholera, ranging from harmless to pandemic strains.
- Understanding genetic differences between pathogenic and nonpathogenic strains is crucial.
Purpose of the Study:
- To identify genetic elements differentiating epidemic/pandemic Vibrio cholerae strains from nonpathogenic ones.
- To characterize a novel pathogenicity island (PAI) associated with cholera virulence.
Main Methods:
- Comparative genomic analysis of Vibrio cholerae strains.
- Identification and characterization of a 39.5 kb chromosomal pathogenicity island (VPI).
- Sequence analysis of VPI, including identification of virulence genes and mobile genetic elements.
Main Results:
- A 39.5 kb Vibrio cholerae pathogenicity island (VPI) was identified in epidemic and pandemic strains, absent in nonpathogenic strains.
- VPI contains virulence regulators (ToxT), the toxin-coregulated pilus (TCP) gene cluster, and the cholera toxin phage receptor.
- VPI exhibits characteristics of bacteriophage origin (low %G+C, integrase/transposase genes, att sites) and was found in clinical strains, indicating potential for horizontal transfer.
Conclusions:
- The VPI is a key genetic factor potentially responsible for the emergence of epidemic and pandemic cholera.
- The VPI's presence and transferability highlight its significance in Vibrio cholerae evolution and virulence.
- This discovery provides insights into the genetic basis of cholera outbreaks.