Predominance of CTX-M genotype among extended spectrum beta lactamase isolates in a tertiary hospital in Saudi Arabia

To determine the molecular characterization of extended-spectrum beta-lactamases [ESBL] isolates from a tertiary center in Saudi Arabia using multiplex polymerase chain reaction [PCR] technique and assess their antibiotic susceptibility pattern. Prospective study conducted at the Saudi Aramco Dhahran Health Center, Dhahran, Saudi Arabia between April-December 2006. Extended-spectrum beta-lactamases phenotype of isolates identified by automated methods was confirmed using E-test. Multiplex PCR for the detection of blaTEM, blaSHV and blaCTX-M was performed. Susceptibility to a panel of antibiotics was determined. One hundred isolates [Escherichia coli [E.coli] n=84; Klebsiella pneumoniae [K. pneumoniae] n=16] were studied and 71% harbored the blaCTX-M gene. For E.coli isolates 43 [51%] harbored CTX-M+TEM combination and 21 [25%] had CTX-M alone. In contrast, only one K. pneumoniae isolate [6.2%] harbored the CTX-M+TEM combination and 3 [18.8%] isolates had CTX-M only. One E.coli and 7 K. pneumoniae isolates were blaSHV positive. The blaCTX-M gene was found predominantly in urinary isolates [n=63/71; 88.7%]. The presence of blaCTX-M was significantly higher in isolates from outpatients compared to inpatient [p<0.05]. Sensitivity to imipenem was 100% and 78% to nitrofurantoin. Resistance to amoxicillin-sulbactam was significantly higher in blaCTX-M positive isolates [p<0.05]. The findings indicate a high-level of blaCTX-M positive ESBL isolates circulating in our setting with the dissemination of these in the community. The trend of multidrug resistance profile associated with carriage of blaCTX-M gene is cause for concern