Abstract
Extended spectrum beta lactamase (ESBL) producing members of the family Enterobacteriaceae are a major health problem in the hospitals and community. These enzymes confer bacterial resistance to penicillins, first, second and third generation cephalosporins and aztreonam. The prevalence of ESBLs varies from organism to organism and is increasing day by day. The study was designed to test typhoidal salmonellae for production of ESBL. One hundred and fifty eight (158) isolates of typhoidal salmonellae; Salmonella Typhi (n=126), Salmonella Paratyphi A (n=26) and Salmonella Paratyphi B (n=6) were collected from different hospitals of Lahore and Gujranwala. The isolates were identified morphologically, biochemically (API-20E) and serologically (BD Difco, USA). ESBL production has been tested by three methods; CLSI screening method, double disk diffusion synergistic method and CLSI phenotypic confirmatory method. CLSI screening method detected twenty two (22) strains as ESBL producers. However, when tested by the CLSI confirmatory method and by disk diffusion synergistic method, none proved to be ESBL producer. Based on our study, we concluded that the extended spectrum beta lactamase enzyme does not exist in tested clinical isolates of typhoidal salmonellae, however the isolates suspected to be ESBL by phenotypic methods must be subjected further for molecular analysis. Key words: ESBL, typhoidal salmonellae, isolate.
Highlights
Salmonella enterica subspecies enterica is an important genus of the family Enterobacteriaceae
These isolates were confirmed to be non-Extended spectrum beta lactamase (ESBL) producers when tested with the disk diffusion phenotypic confirmatory method and by double disk diffusion synergistic method
Among our 158 isolates of typhoidal salmonellae, no ESBL was detected. In another comparative study of screening methods for ESBL detection was done on 38 isolates comprising of 30 reference strains, that is, E. coli and K. pneumoniae already defined ESBL producers by Isoelectric focusing and DNA sequencing, and eight laboratory isolates not confirmed to be ESBL producer, no reduced susceptibility pattern to extended spectrum cephalosporins and aztreonam was seen, according to this study, only 52% ESBL producing isolates were detected by disk diffusion screening method (Vercauteren et al, 1997)
Summary
Salmonella enterica subspecies enterica is an important genus of the family Enterobacteriaceae. Extended spectrum beta lactamases (ESBL) are enzymes that mediate resistance to the extendedspectrum cephalosporins; ceftazidime, cefotaxime, and ceftriaxone and monobactams like aztreonam but do not affect cephamycins. Plasmids responsible for ESBL production tend to be large (80 Kb or more in size) and carry resistance against several antimicrobials that are aminoglycosides, fluoroquinolones, tetracyclines, chloramphenicol and trimethoprim-sulfamethoxazole (Coque et al, 2008; Nathisuwan et al, 2001). This fact imparts an important limitation in the design of treatment alternatives (Jacoby and Medeiros, 1991)
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