Incidence and in vitro acquisition of transferable drug resistance in Salmonella arizonae.

Fifty-eight cultures of Salmonella arizonae isolated in 1983 from poultry sources and 21 cultures isolated in 1972 to 1974 were screened for resistance to nalidixic acid, chloramphenicol, triple sulfa, ampicillin, tetracycline, streptomycin, and kanamycin by the standardized disc susceptibility method. Sensitivity to all seven drugs was observed in 51% of the cultures tested (76% of the older cultures and 41% of the recent isolates). Resistance to two or more drugs was observed in 36% of the cultures tested (14% of the older cultures and 43% of the newer ones). The highest incidence of resistance was to streptomycin. Salmonella arizonae cultures sensitive to all seven drugs were tested for the ability conjugatively to acquire kanamycin, streptomycin, tetracycline, and ampicillin resistance determinants from a multiply resistant strain of Escherichia coli K12NA. Complete or intermediate resistance to all antibiotics was transferred to 93% of the sensitive cultures at 41 C and 85% at 28 C. Kanamycin resistance was transferred most frequently, and ampicillin resistance least frequently.