Detection of extended-spectrum b-lactamases in members of the family enterobacteriaceae at a teaching hospital, Riyadh, Kingdom of Saudi Arabia

OBJECTIVE: To determine the prevalence of extended spectrum b-lactamase at King Khalid University Hospital, Riyadh, Kingdom of Saudi Arabia and to compare the ability of the disc diffusion, double disc potentiation methods and the extended-spectrum b-lactamase E test to detect exended-spectrum b-lactamase among enterobacteriaceae.

METHODS: This study was undertaken during the time period period January 1 through to September 30 1999, at King Khalid University Hospital, Riyadh, Kingdom of Saudi Arabia. A total of 187 multiresistant isolates of enterobacteriacae from different clinical specimens were tested for the extended-spectrum b-lactamases. The performance of disc diffusion, double disc potentiation methods using cefotaxime, ceftazidime, ceftriaxone and aztreonamand the extended-spectrum b-lactamase E based on the reduction of the minimum inhibitory concentration of ceftazidime in the presence of clavulanic acid were compared for the detection of extended-spectrum b-lactamase production.

RESULTS: Thirty six percent of our isolates produced extended-spectrum b-lactamases. Among these 42% were Klebsiella pneumoniae and 20% were Escherichia coli. Other species of Enterobacteriaceae produced extended-spectrum b-lactamase in low numbers. Disc diffusion method was not suitable for detecting extended-spectrum b-lactamases among the isolates. Double disc potentiation performed comparably well with the extended-spectrum b-lactamases E test.

CONCLUSION: Extended-spectrum b-lactamases occurs in Klebsiella pneumoniae and Escherichia coli at a significant number. The use of double disc potentiation method for screening is practical and the extended-spectrum b-lactamase E test with ceftazidime is a useful confirmatory test for extended-spectrum b-lactamase production.