Virulence genes in environmental strains of Vibrio cholerae.
The virulence of a pathogen is dependent on a discrete set of genetic determinants and their well-regulated expression. The ctxAB and tcpA genes are known to play a cardinal role in maintaining virulence in Vibrio cholerae, and these genes are believed to be exclusively associated with clinical strains of O1 and O139 serogroups. In this study, we examined the presence of five virulence genes, including ctxAB and tcpA, as well as toxR and toxT, which are involved in the regulation of virulence, in environmental strains of V. cholerae cultured from three different freshwater lakes and ponds in the eastern part of Calcutta, India. PCR analysis revealed the presence of these virulence genes or their homologues among diverse serotypes and ribotypes of environmental V. cholerae strains. Sequencing of a part of the tcpA gene carried by an environmental strain showed 97.7% homology to the tcpA gene of the classical biotype of V. cholerae O1. Strains carrying the tcpA gene expressed the toxin-coregulated pilus (TCP), demonstrated by both autoagglutination analysis and electron microscopy of the TCP pili. Strains carrying ctxAB genes also produced cholera toxin, determined by monosialoganglioside enzyme-linked immunosorbent assay and by passage in the ileal loops of rabbits. Thus, this study demonstrates the presence and expression of critical virulence genes or their homologues in diverse environmental strains of V. cholerae, which appear to constitute an environmental reservoir of virulence genes, thereby providing new insights into the ecology of V. cholerae.
Chakraborty
S
S
National Institute of Cholera and Enteric Diseases, Beliaghata, Calcutta 700 010, India.
Mukhopadhyay
A K
AK
Bhadra
R K
RK
Ghosh
A N
AN
Mitra
R
R
Shimada
T
T
Yamasaki
S
S
Faruque
S M
SM
Takeda
Y
Y
Colwell
R R
RR
Nair
G B
GB
D000595:Amino Acid Sequence; D000818:Animals; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002771:Cholera / Q000382:microbiology; D002772:Cholera Toxin / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004783:Environmental Microbiology; D036781:Fimbriae Proteins; D005618:Fresh Water / Q000382:microbiology; D015964:Gene Expression Regulation, Bacterial; D020459:Genes, rRNA; D006801:Humans; D008969:Molecular Sequence Data; D011817:Rabbits; D015183:Restriction Mapping; D021521:Ribotyping; D017422:Sequence Analysis, DNA; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014734:Vibrio cholerae / Q000145:classification / Q000235:genetics* / Q000472:pathogenicity*; D014774:Virulence / Q000235:genetics
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C085807:TcpA protein, Vibrio cholerae; D014157:Transcription Factors; C499324:toxR protein, Vibrio cholerae; C066719:toxR protein, bacteria; D036781:Fimbriae Proteins; D002772:Cholera Toxin