Isolation of drug-resistant Aeromonas hydrophila from aquatic environments.

Antibiotic-resistant strains of Aeromonas hydrophila have been isolated from the natural environment in the Chesapeake Bay and areas surrounding Dacca and the Matlab region of Bangladesh. The Bangladesh strains carried resistance to chloramphenicol, streptomycin, and tetracycline, and 57% of them had a multiple streptomycin-tetracycline resistance phenotype correlated with the presence of a large plasmid. The Chesapeake Bay strains were resistant to polymyxin B ane tetracycline, but showed neither multiple resistance nor R-factor carriage. Twenty-five percent of the environmental strains were toxigenic in a Y-1 adrenal cell assay. Toxigenicity showed no positive correlation with drug resistance or with plasmid carriage. Environmental areas of heavy human impact appear to be associated with a higher incidence of antibiotic-resistant strains of aeromonads.