Molecular Detection of Extended Spectrum Beta-Lactamases in Clinical Isolates of Pseudomonas aeruginosa

Pseudomonas aeruginosa producing extended spectrum beta lactamases (ESBL) is a major concern in the hospital settings. It is usually reported in Enterobacteriaceae and is less frequently observed in P. aeruginosa. There is no recommended test for ESBL detection in P.aeruginosa. Therefore, we determined the occurrence of ESBL in clinical isolates of P.aeruginosa by both phenotypic and genotypic methods. Antimicrobial susceptibility tests were done on two hundred and thirteen isolates of P. aeruginosa. Phenotypic detection of ESBL was performed using combined disk method and ESBL encoding genes such as blaVEB, blaPER, blaPSE, blaGES, blaTEM, blaSHV, blaCTX-M, blaBEL, blaOXA1, blaOXA10, blaOXA2 were studied by simplex PCR. Of the 213 isolates, 85 were identified as resistant to ceftazidime and 27/85 isolates were confirmed to be ESBL producers by phenotypic method. The presence of genes encoding ESBLs comprising of blaTEM (n=44), blaOXA-10 (n=19) isolates, blaOXA-1 (n=5), blaOXA-2 (n=3) were found. All OXA gene positive isolates exhibited the ESBL phenotype. The blaGES gene were identified in 4/85 (5%) isolates. This study shows the prevalence of ESBL among clinical isolates of P.aeruginosa and in particular, the presence of GES beta lactamases.