Frequency of antimicrobial resistance and plasmid profiles of Bacillus cereus strains isolated from milk

Abstract

Plasmid profile analysis and susceptibility to eight commonly used antimicrobial agents was done on sixty Bacillus cereus (B. cereus) strains isolated from milk. About seventy two percent (71.7%) of the isolates contained plasmids. The number of plasmids per isolate ranged between 1 and 5, while plasmid sizes ranged between 60 and 0.1 megadaltons (Mda). All isolates were resistant to ampicillin with a relatively high rate of resistance to cotrimoxazole and sulphamethoxazole. The isolates showed a low frequency of resistance to the other antimicrobial agents, with all of them being susceptible to streptomycin. Approximately ninety one (90.7%) percent of the isolates showed multiple resistance. There was no apparent relationship between carriage of plasmids and drug resistance.