Mechanism of nitrofuran resistance in Salmonella enteritidis phage type 4 and interpretation of nitrofuran susceptibility tests.
The mechanism of nitrofuran resistance in Salmonella enteritidis phage type 4 was studied. Nitrofuran reductase activity was inversely related to the furazolidone MIC for the organism. Strains with low-level nitrofuran resistance, typically found in almost all isolates of S. enteritidis PT4, had intermediate nitrofuran reductase activity. Disc diffusion tests with furazolidone, 15 or 50 micrograms discs, and nitrofurantoin, 50 or 300 micrograms discs, failed to distinguish reliably between susceptible populations and those with low-level resistance. In order to detect low-level resistance to nitrofurans a dilution method should be used with a furazolidone breakpoint of 1 mg/l or a nitrofurantoin breakpoint of 16 mg/l.
Drug Resistance, Microbial↗