Drug resistance in Detroit River gram-negative bacilli

Detroit River Gram-negative bacilli were examined for resistance to agents of interest to public health. The total recoverable population and the lactose-fermenting organisms existed at approximately 10(5) and 10(2) colony forming units per litre, respectively. Lactose-nonfermenting and lactose-fermenting isolates demonstrated resistance to six and four of nine antimicrobial agents, respectively, when tested by a paper disc procedure. Multiple resistance in lactose-nonfermenting organisms included up to five agents. Lactose-fermenting isolates produced multiple resistance to two antibiotics. Only 7% of antibiotic resistance strains were proven to contain plasmids. Biochemical testing indicated that the most common group of resistant bacteria was Pseudomonas fluorescens. Comparison of protein profiles produced by polyacrylamide gel electrophoresis indicated that there was variation between P. fluorescens strains demonstrating the same multiple resistance.