Frequency of extended spectrum beta lactamase producer P. aeruginosa strains isolated from burned patients of Motahari hospital, Teharan, Iran

Pseudomonas aeruginosa is an opportunistic pathogen which is naturally resistant to a large range of antibiotics like lots of Beta–Lactams (penicillins, cephalosporins and carbapenems) and may cause additional resistance after unsuccessful treatment. The understanding of beta-lactamase identification and detection in these bacteria is very valuable. In recent years a number of variety of new beta-lactamases were detected, apparently as a consequence of the clinical use of novel classes of beta-lactam antibiotics. Thus a reliable test to detect extended spectrum beta-lactamases (ESBLs) in clinical isolates of P.aeruginosa is needed. In this study, a total of 100 clinical isolates of P. aeruginosa were studied to assess sensitivity of P.aeruginosa isolated from burned patients of Motahari Hospital in Tehran and determine ESBL production in them. Antibiogram test was done by disk diffusion method. Beta-lactamases producers were screened by Starch-paper strip method. Further confirmation was done for ESBL producers by double disc test (DDT) and double disc synergy test (DDST). Among the total of 100 isolates that were considered beta-lactamase producer by starch paper strip method, 17% were ESBL positive by DDST, a figure that increased to 70% after imipenem was included. In addition, 20% of isolated P.aeruginosa strains were ESBL positive by other confirmatory test. This study is the first that uses a combination of paper strip method with DDT and DDST.