Phenotypic confirmation of extended-spectrum B-lactamases (ESBL) in clinical isolates of Escherichia coli and Klebsiella pneumoniae at the San Juan Veterans Affairs Medical Center.

Extended-spectrum Beta (beta)-lactamases (ESBLs) have emerged as an important mechanism of resistance to B-lactam antibiotics in gram-negative bacteria (GNB). They are enzymes that hydrolyze older B-lactam antibiotics as well as broad-spectrum cephalosporins and monobactams. ESBL producers have been reported in many bacteria but special attention has been paid to the ones in E.coli and Klebsiella spp. Detection of the ESBLs by the clinical laboratory is a special challenge. Surveillance to monitor resistance is important to decide when detection of ESBLs must be started. This study determined the prevalence of ESBL producers in the strains E.coli and K.pneumoniae at the San Juan VA Medical Center, and characterized their phenotypes to evaluate the importance to identify these bacteria as a standard routine procedure in the institution. All E.coli and K.pneumoniae isolated from Jan 1 to Mar 31, 2003 were evaluated according to National Committee for Clinical Laboratory Standards (NCCLS) screening criteria for suspected ESBL producers. Phenotypic confirmation of the ESBL production was performed using the Etest method. A total of 112/253 (44%) E.coli and 72/137 (53%) K.pneumoniae were identified as suspected ESBL producers. Etest was performed in 60% of the E.coli and 57% of the K.pneumoniae suspected to be ESBL producers. The overall ESBL prevalence for E.coli was 25% and in K.pneumoniae was 26%. Most E.coli ESBL-producers were from urine while the K.pneumoniae were from sputum. ESBL-producers were isolated from different sources including pleural and synovial fluids, blood, and skin besides urine and sputum. According to susceptibility results, the most reliable antibiotic in predicting a negative ESBL was cefpodoxime (CPD), and in the strains studied, the ESBL producers were consistently resistant to aztreonam (ATM). A large proportion (95%) of ESBL producing K.pneumoniae were susceptible to cefepime (CEP). Of the ESBL producing E.coli, 24% were susceptible. In the case of E.coli ESBLproducers, Cefepime can be considered as a therapeutic option if susceptibilities are available. Automated identification and sensitivity systems are valid alternatives for routine evaluation of B-lactam resistance but when increased resistance is documented in GNB and/or ESBL prevalence is high, ESBL detection should be performed. All confirmed ESBL producers should be reported resistant to all penicillins, cephalosporins, and aztreonam in spite of having susceptible ranges with routine susceptibility tests. Inappropriate antibiotic selection in infections caused by these organisms is associated with treatment failures, poor clinical outcomes, increased mortality and longer hospital stays.