Reassessment of the prevalence of heat-stable enterotoxin (NAG-ST) among environmental Vibrio cholerae non-O1 strains isolated from Calcutta, India, by using a NAG-ST DNA probe.
A collection of 521 environmental isolates of Vibrio cholerae which were previously examined by the suckling mouse assay and found to be negative for the heat-stable enterotoxin NAG-ST were reassessed by a recently developed DNA probe for NAG-ST. A total of 12 (2.3%) of the isolates hybridized with the NAG-ST probe. By using a cholera toxin (CT) DNA probe, the CT gene was detected in six of the strains in the collection, although none of the isolates of V. cholerae non-O1 hybridized with both of the toxin probes. All of the NAG-ST and CT probe-positive strains were hemolysin positive. Thirty-fold-concentrated supernatants of the three representative NAG-ST DNA probe-positive V. cholerae non-O1 strains gave positive fluid accumulation ratios in the suckling mouse assay even after heating (100 degrees C for 5 min) and also inhibited the binding of a NAG-ST monoclonal antibody to the bound NAG-ST in a competitive enzyme-linked immunosorbent assay (ELISA). Likewise, all six CT probe-positive V. cholerae non-O1 strains produced in vitro CT when examined by the CT bead ELISA. HindIII digest patterns of chromosomal DNA from the representative NAG-ST gene-positive strains were visually indistinguishable. Between the groups of NAG-ST probe-positive strains examined, there was a variation in the hybridizable fragments, with one group of strains exhibiting a hybridizable fragment similar to that of the NRT 36 reference strain; a smaller HindIII fragment hybridized with the NAG-ST probe in the other group of strains.(ABSTRACT TRUNCATED AT 250 WORDS)
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National Institute of Cholera and Enteric Diseases, Beliaghata, Calcutta, India.
Ramamurthy
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Bhadra
R K
RK
Takeda
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Shimada
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Takeda
Y
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Nair
G B
GB
Pal
S C
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Chakrabarti
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D000818:Animals; D000833:Animals, Suckling; D001681:Biological Assay; D015342:DNA Probes; D004768:Enterotoxins / Q000032:analysis / Q000235:genetics*; D004797:Enzyme-Linked Immunosorbent Assay; D005798:Genes, Bacterial; D007194:India; D051379:Mice; D012703:Serotyping; D014734:Vibrio cholerae / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification; D014871:Water Microbiology
D015342:DNA Probes; D004768:Enterotoxins; C037420:stN protein, Vibrio cholerae