Antimicrobial resistance patterns and plasmid profiles of Staphylococcus aureus isolated from milk and meat.

OBJECTIVES: To determine the frequency of resistance of Staphylococcus aureus to various antimicrobial agents, and the relationship between antimicrobial resistance of the isolates and carriage of plasmids. DESIGN: A random sampling of milk and meat samples was carried out. SETTING: Milk was collected from various dairy co-operative societies in Nairobi and Kiambu districts. Minced meat samples were purchased from various outlets in the city of Nairobi. SUBJECTS: Ninety six Staphylococcus aureus isolates from milk (seventy five isolates) and minced meat (twenty one isolates) samples. MAIN OUTCOME MEASURES: Plasmid profiles and antimicrobial susceptibility tests to ampicillin, lincomycin, penicillin, erythromycin, methicillin, minocycline, cotrimoxazole and chloramphenicol. RESULTS: Seventy one per cent of the isolates carried between one and six plasmids of molecular sizes ranging from 0.1 to 14.5 kilobases. High frequency of resistance was observed with lincomycin (67.7%), penicillin (66.7%) and cotrimoxazole (51%). A high percentage (76%) of isolates were susceptible to minocycline followed by erythromycin (57.3%). Most (80.2%) of isolates were multiply resistant to between two and six antibiotics. CONCLUSION: Most Staphylococcus aureus isolates were multiply resistant to various antimicrobial agents, but there was no apparent relationship between carriage of plasmids and antimicrobial resistance. Milk and meat may contain resistant Staphylococcus aureus posing a potential risk to consumers.

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

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.