Study of Resistance to 82 Clinical Cases Enterobacteriaceae to Beta-lactam Antibiotics

  •  Mahnaz Milani    


Knowledge of antimicrobial resistance patterns in E. coli, the predominant pathogen associated with urinary tract infections (UTI) is important as a guide in selecting empirical antimicrobial therapy. To describe the antimicrobial susceptibility of E. coli associated with UTI in a major university hospital in Tehran (Iran), seventy-six clinical isolates of E. coli were studied for susceptibility to Beta-lactam antibiotics by the disc diffusion method and Minimal Inhibitory Concentrations determination. All isolates were resistant to ampicillin, amoxicillin and oxacillin. Resistance to the other tested antibiotics was shown to be 93.4% to cefradine, 76.3% to carbenicillin, 47.3% to cefazoline, 50% to cefalexin and 32.8% to cephalothin while 1.3% expressed resistance to cefoxitime, and 2.6% were resistant to ceftizoxime and ceftriaxone. Substrate hydrolysis by ultra violet spectroscopy showed that 87.4% harbored penicillinases, 9% produced cephlosporinases and 3.6% degraded both substrates. Clavulanic acid inhibited enzyme activity in 82.9%, of which 78.95% was penicillinases (group IIa) and 3.95% was cephalosporinases (group IIb) of the Bush classification system. These results indicate that E. coli can posses a variety of Beta-lactamases that are responsible for Beta-lactam resistance. Members of the family Enterobacteriaceae, particularly Escherichia coli is the most common causes of urinary tract infections in hospitals and societies. Beta-lactam antibiotics, particularly the third and fourth generation of cephalosporins are effective in treating these infections.

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