[Detection of CTX-M-15 type extended spectrum beta-lactamase in an Escherichia coli strain isolated from the urine sample of a hospitalized patient]

Zerrin Aktaş, Nevriye Gönüllü, Ines Schneider, Ciğdem Bal, Adolf Bauernfeind
Mikrobiyoloji Bülteni 2005, 39 (4): 421-9
In this study, a CTX-M type extended spectrum beta-lactamase (ESBL) enzyme has been detected in a multiresistant Escherichia coli strain which was isolated from the urine sample of a hospitalized patient. Minimum inhibitor concentrations (MIC) of the tested antibiotics were determined by the agar dilution technique according to the Clinical and Laboratory Standards Institute (CLSI, formerly NCCLS) guidelines. The isolate was found to be sensitive to imipinem, moderately susceptible to chloramphenicol and resistant to ceftazidime, cefotaxime, aztreonam, ciprofloxacin, tobramycin, tetracycline and trimethoprim/sulphamethoxazole. Ceftazidime/ceftazidime-clavulanic acid and cefotaxime/cefotaxime-clavulanic acid rates were found as >8 and the results were accepted as positive for an ESBL. The MIC of cefotaxime (256 microg/ml) was found four fold higher than that of ceftazidime (64 microg/ml) and the production of a CTX-M- type ESBL was investigated in the strain. Cefotaxime resistance, together with tobramycin and tetracycline resistance, was transferred to the recipient strain by conjugation. The pl's of the culture extracts of the isolate were found as 5.4, 7.5 and 9.1 by isoelectric focusing (IEF) method, but cefotaxime was hydrolysed only by the beta-lactamase focusing at a pl of 9.1 in the following bioassay. The bla-gene was amplified with the CTX-M group specific primers and sequencing of the polymerase chain reaction (PCR) product proved the enzyme to be CTX-M-15. This isolate was also found to harbor TEM- and SHV-type and OXA-10-like ESBLs, by IEF and PCR.

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