Comparison of distribution of virulence determinants in clinical and environmental isolates of Vibrio cholera.
The virulence of a pathogenic Vibrio cholerae is dependent on a discrete set of genetic determinants. In this study, we determined the distribution of virulence determinants among the clinical and environmental isolates of V. cholerae.



The antibiotic resistance profiles of the isolates were determined using standard disk diffusion assay. PCR assay was performed to analyze the presence of toxin genes of ctx, zot and ace. The composition of cholera toxin encoding element (CTX) region flanking of the V. cholerae isolates was also analyzed.



All of the clinical isolates (100%) showed a complete set of virulence genes and also the attachment site of the filamentous bacteriophage CTXphi. None of the environmental isolates contained the virulence genes and the attachment site of the CTXphi. Analysis of the flanking regions including the toxin-linked cryptic element and repeat in toxin genes revealed their integrity in the clinical isolates while in the environmental isolates they were absent or contained incomplete sequences. Comparison of the antibiotic resistance assay of the environmental and clinical isolates showed a significant difference in the resistance profiles of the isolates obtained from the two sites. High rates of resistance to co-trimoxosol, streptomycin and chloramphenicol were found with clinical isolates.



The absence of all virulence determinants in the environmental strains may suggest that certain ecological features must be present for V. cholerae to acquire a complete set of virulence determinants and to turn them into pathogenic strains.
Bakhshi
Bita
B
Department of Bacteriology, Pasteur Institute of Iran, Pasteur Ave., Tehran, Iran.|Faculty of Medicine, Isfahan University of Medical Sciences, Hezarjerib Ave., Isfahan, Iran.
Pourshafie
Mohammad Reza
MR
Department of Bacteriology, Pasteur Institute of Iran, Pasteur Ave., Tehran, Iran.
Navabakbar
Farahtaj
F
Faculty of Medicine, Isfahan University of Medical Sciences, Hezarjerib Ave., Isfahan, Iran.
Tavakoli
Akbar
A
Faculty of Medicine, Isfahan University of Medical Sciences, Hezarjerib Ave., Isfahan, Iran.
Shahcheraghi
Fereshteh
F
Department of Bacteriology, Pasteur Institute of Iran, Pasteur Ave., Tehran, Iran.
Salehi
Mansoor
M
Faculty of Medicine, Isfahan University of Medical Sciences, Hezarjerib Ave., Isfahan, Iran.
Faradjzadegan
Ziba
Z
Faculty of Medicine, Isfahan University of Medical Sciences, Hezarjerib Ave., Isfahan, Iran.
Zahraei
Seyed Mohsen
SM
Dept. of Enteric Bacteria,Center for Disease Control, Tehran, Iran.