Detection of Extended Spectrum Beta Lactamases Among Clinical Isolates of Pseudomonas aeruginosa

Infections caused by Pseudomonas aeruginosa are tough to treat as the majority of these isolates exhibit varying degrees of beta-lactamase mediated resistance. These enzymes are capable of hydrolyzing broad spectrum cephalosporins and monobactams but inactive against cephamycins and imipenem. Resistance to broad-spectrum beta lactams, mediated by extended-spectrum beta lactamases (ESBLs), is an increasing problem worldwide. In addition, ESBL producing organism’s exhibit coresistance to several other classes of antibiotics resulting in limitation of therapeutic option. This resistance poses problems for testing and reporting. Increased prevalence of ESBLs among clinical isolates creates a great need for laboratory testing methods that will accurately identify their presence. Thus the present study was designed to investigate the prevalence of extended-spectrum beta lactamases (ESBLs) in clinical isolates of P. aeruginosa. A total of 150 clinical isolates of P. aeruginosa were isolated from various clinical samples were tested for antimicrobial susceptibility by Kirby-Baeur disk diffusion method. 75 isolates showing a zone diameter less than 18 mm to Cefoxitin (screen positive) were tested for the presence of extended spectrum beta-lactamase (ESBL) by disk approximation method using cefoxitin inducer and cefotaxime indicator method as per Clinical and Laboratory Standards Institute (CLSI) guidelines. Antibiogram of P. aeruginosa isolates revealed that, highest resistance was observed to gentamycin (73.67%), followed by ceftazidime (70.67%), amikacin (63.33%), ciprofloxacin (52.67%) in that order of frequencies. Maximum susceptibility was observed to carbenicillin (72%). Multiple drug resistance was common phenomenon observed, in more than 50% of strains. 78 (52%) isolates showed resistance to six or more antibiotics. 65.33% of P. aeruginosa strains showed extended spectrum beta-lactamase production in (70.73%) isolates from pus followed by urine (62.5%). The study emphasizes the high prevalence of multidrug resistant P. aeruginosa producing extended spectrum beta-lactamase using a simple disk approximation method. Thus proper antibiotic policy and measures to restrict the indiscriminative use of cephalosporins and carbapenems should be taken to minimize the emergence of this multiple beta-lactamase producing pathogens.