Plasmid-borne multiple drug resistance in Vibrio cholerae serogroup O1, biotype El Tor: evidence for a point-source outbreak in Bangladesh

In 1979, an outbreak of plasmid-borne, multiply drug-resistant Vibrio cholerae serogroup O1 biotype El Tor (V. cholerae O1) occurred in the Matlab area of Bangladesh. The outbreak could have resulted from the introduction into the area of a single resistant strain or from multiple conjugations of drug-sensitive V. cholerae O1 with C plasmids in other environmental flora. Resistant strains were phage typed to determine their relatedness, and plasmid studies were conducted to determine the frequency of C plasmids in nonvibrio flora of family contacts of cholera patients. Forty-one (85%) of 48 resistant strains of V. cholerae O1 examined belonged to two closely related phage types new to the area, whereas 59 drug-sensitive strains from the same period were primarily of two different phage types. Group C plasmids were in nonvibrio strains from five of 36 family contacts of patients with drug-resistant cholera but none of 82 family contacts of patients with sensitive cholera. This outbreak most likely began from the introduction into the area of a single, multiply drug-resistant strain of V. cholerae O1. C plasmids detected in the nonvibrio flora of family contacts probably came from the resistant strain of V. cholerae O1.