Prevalence of extended-spectrum beta-lactamases (ESBLs) produced in blood isolates of gram-negative bacteria in a teaching hospital in southern Thailand.

One hundred and eighty-three strains of gram-negative bacteria were isolated from 177 bacteremic patients during a 6-month period in 2004 at a teaching hospital in southern Thailand. Extended-spectrum beta-lactamases (ESBL) production was detected in K. pneumoniae, E. coli, and E. cloacae, at rates of 16/36 (44.4%), 3/59 (5.1%), and 2/13 (15.4%), respectively. All but one of the screened positive strains were also positive by both the combination disk method and the E-test. All of the K. pneumoniae strains that were resistant to ceftazidime by disk diffusion were demonstrated to be positive for ESBL production by both the combination disk and E-test methods. Most of the ESBL positive strains had a high MIC (more than 32 microg/ml) to ceftazidime. However, all the ESBL positive strains were sensitive to imipenem.