Detection of Antibiotic Resistance and Metallobetalactamase among Pseudomonas Aeruginosa Clinical Isolates

BACKGROUND AND OBJECTIVE: Pseudomonas aeruginosa infections are becoming an important cause of morbidity in hospitalized patients. The increasing resistance of P.aeruginosa to various antibiotics mainly carbapenems is becoming an important concern. Emergence of Metallobetalactamase producing organisms is alarming and reflects the excessive use of carbapenems. The present study was conducted at our hospital with an aim to know the prevalence of Carbapenem resistance and production of metallo-betalactamases by four different phenotypic methods. METHODOLOGY: A total of 211 P. aeruginosa isolates from various clinical samples were tested. Antibiotic sensitivity testing was carried out by Kirby- Bauer method according to CLSI guidelines and detection of Metallobetalactamase production was carried out by Meropenem - EDTA combined disc method, Double Disc Synergy Test, Modified Hodge test and E test. RESULTS: Among the isolates males were more commonly affected in the above 40 years age group and the isolates were obtained from inpatients frequently. Pus swab is the predominant specimen obtained mostly from surgery ward. Cellulitis is the most observed infection. The resistance pattern to various antibiotics were- Amikacin (32.23%), Gentamycin (36.02%), Tobramycin (35.07%), Ceftazidime (71.09%), Ciprofloxacin (46.45%), Cefaperazone+sulbactum(35.07%), Cefipime (29.86%), Piperacillin+tazobactum (18.96%), Aztreonam (23.22%), Meropenem (7.58%); in urine isolates, Ofloxacin (23.8%), Norfloxacin (71.43%), Nitrofurantoin (80.95%). Among Meropenem resistant isolates, 93.75% were positive for Metallobetalactamase production detected by E test. Only 81.25% of MBL were detected by Combined Disc Test (CDT) and Double Disc Synergy Test (DDST), 75% were detected by Modified Hodge Test (MHT). E test method for MBL detection was found to have a sensitivity, specificity, positive predictive value, negative predictive value and accuracy of 100 %, 100%, 100%, 100% and 100%. CONCLUSION: E test method is a simple and reliable method for metallobetalactamase detection which can be used routinely in any laboratory. DDST and CDT are almost equally effective and more sensitive than MHT for detection of MBL production in small laboratories which can’t afford E test. Thus routine screening for MBL mediated carbapenem resistance coupled with strict infection control practices is critical to prevent the consequences of this worrying resistance mechanisms and to ensure appropriate treatment of infections caused by them in clinical settings