Prevalence of the genes encoding extended-spectrum beta-lactamases, in Escherichia coli resistant to beta-lactam and non-beta-lactam antibiotics.

The prevalences of extended-spectrum beta-lactamases (ESBL) and their encoding bla genes, TEM, SHV and CTX_M, were investigated in isolates of Escherichia coli that were resistant to beta-lactam and/or non-beta-lactam antibiotics. Of the 250 E. coli isolates investigated, all of which came from patients in a major hospital in southern Lebanon, 61 (13.3%) were found to have ESBL, their production of beta-lactamase being confirmed by the ceftazidime and ceftazidime/clavulanic-acid disc methods. All 61 ESBL isolates were resistant to beta-lactams and sensitive to imipenem, piperacillin/tazobactam and cefoxitime. Only 40% were resistant to fluoroquinolones, 33% were resistant to aminoglycosides, and 18% were considered to have multi-drug resistance. The results of the PCR-based amplification of the bla gene in DNA samples from the 61 ESBL isolates indicated that 11 (18%) of the isolates carried both the TEM and SHV genes, 37 (61%) carried the TEM gene but not the SHV, and 13 (21%) had the SHV gene but not the TEM. None of the isolates carried the CTX_M gene. Of the 37 TEM-positive/SHV-negative isolates, 43% were resistant to fluoroquinolones and 37% to aminoglycosides. Increased resistance to non-beta-lactam antibiotics was observed in the isolates harbouring both the TEM and SHV genes, of which 54% were resistant to all of the tested antibiotics except imipenem, 36% were only resistant to fluoroquinolones, and 9.1% only resistant to aminoglycosides. The possibility that the concomitant presence of TEM- and SHV-type beta-lactamases is associated with resistance to non-beta-lactam antibiotics requires further research. The prevalences of ESBL and their encoding genes in Gram-negative bacteria collected from various regions in Lebanon will now be investigated.