PCR detection of plasmid mediated TEM, SHV and AmpC β-lactamases in community and nosocomial urinary isolates of Escherichia coli

Fifty clinical isolates of Escherichia coli from two groups of subjects (hospitalized and outpatients) were studied for their susceptibility to twelve β-lactam antibiotics. All isolates were resistant to ampicillin, amoxicillin, oxacillin and cefradine. Carbenicillin resistance was found in all but one outpatient isolate. Resistance to cephalothin, cephalexin and cefazoline ranged from 76% to 96% among the test bacteria. On the other hand, the majority of the isolates were sensitive to cefoxitime, ceftizoxime and ceftriaxone (84-100%). β- lactamases from all bacteria were inhibited by clavulanic acid and none harbored extended spectrum β- lactamases as shown by the double disc diffusion method. Gene amplification by polymerase chain reaction (PCR) using specific primers for AmpC, TEM and SHV enzymes showed that 92% of all organisms carried blaTEM alone, or along with SHV or ampC genes. Presence of all three genes was shown in 8% of the hospitalized patients and 20% of the outpatients. Conjugative transfer of β-lactam resistance markers into susceptible host recipients occurred for 72% of the isolates in each group. Overall, the antibiotic susceptibility profile, the distribution of the β-lactamase gene type and the rate of conjugative transfer of the resistance markers were similar in both subject groups.