One hundred and twenty faecal sample of commensal Escherichia coli strains were collected from different healthy persons and tested for their susceptibility to 12 β-lactam antibiotics by disc diffusion and minimum inhibitory concentration methods. Colonization with strains resistant to ampicillin (Amp), amoxicillin, carbenicillin and peperacillin was detected in 36.7% of the tested isolates. Resistance patterns to 3-6 β-lactams was observed in 91.7% of the tested E. coli isolates. Transfer of Amp resistance marker by conjugation was usually associated with Strepomycin (Stm) and sulfonamise (Sul) in 100% of tested isolates and with chloramphenicol (Clm) and tetracycline (Tet) in 63.3 and 45.6% of the isolates, respectively. This suggests that resistance markers to Amp, Stm, Sul, Tet and Clm existed as cossets on cojugative plasmids. Therefore, resistance to these antibiotics could rapidly disseminate and persist in the Saudi Society. All Amp resistant isolates produced one or two types of β-lactamases with molecular weights of 28.9 and 28.8 KDa, which indicated TEM-1 and SHV-1. Both types of β-lactamases are known to be plasmid-mediated in enteric bacterial species and are common in E. colicommensal faecal flora. Extended-spectrum β-lactamases (ESBLs) were not detected in any of the tested strains and therefore, these types of β-lactamases are uncommon in commensal E. coli in citizens of Taif. Measures should be taken to prevent the misuse of β-lactams and the spread of antibiotic resistance in Saudi Society.
Key words: Antibiotic resistance, β-lactams, β-lactamases, commensal Escherichia coli.
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