Use of polymerase chain reaction for detection of toxigenic Vibrio cholerae O1 strains from the Latin American cholera epidemic

In January 1991, an outbreak of cholera started in Peru and spread throughout most of Latin America within 8 months. As of March 1992, over 450,000 cases and approximately 4,000 deaths have been reported to the Pan American Health Organization. The causative organism is toxigenic Vibrio cholerae O1 of the El Tor biotype and is distinct from the U.S. Gulf Coast strains. A polymerase chain reaction (PCR) that amplifies a 564-bp fragment of the cholera toxin A subunit gene (ctxA) was used to identify toxigenic V. cholerae O1 strains. A total of 150 V. cholerae O1 isolates were tested. They were of unknown toxin status, were associated with recent outbreaks, and were isolated from patients, food, and water. One hundred forty isolates were found to be toxigenic both by PCR and the routine diagnostic enzyme-linked immunosorbent assay. Thirty-eight known toxigenic strains isolated worldwide from 1921 to 1991 were also positive in the PCR. A collection of 18 nontoxigenic V. cholerae O1 strains, 35 Escherichia coli heat-labile-enterotoxin-I-producing strains, 26 Campylobacter strains, and 8 strains of Aeromonas hydrophila, previously reported to produce cholera toxin-like toxin, were all negative in the ctxA PCR. We conclude that this PCR is a diagnostic method that specifically detects toxin genes in V. cholerae O1 strains in a reference laboratory. It is more rapid and less cumbersome than other diagnostic methods for detection of toxicity in these strains.