Surveillance on Extended Spectrum β-lactamase and AmpC β-lactamase producing gram negative isolates from nosocomial infections

Background: Extended spectrum beta lactamases (ESBLs) and AmpC beta-lactamases conferring resistance to expanded-spectrum cephalosporins, continue to be a major problem in health care settings. Knowledge of their occurrence is essential to guide the clinicians towards the appropriate anti-microbial treatment. The purpose of this study is to evaluate the incidence of ESBL and AmpC β-lactamases, and to analyse their antibiotic susceptibility in nosocomial gram-negative clinical isolates from a tertiary care hospital.

Material and Methods: A total number of 180 consecutive non repetitive clinical isolates of Escherichia coli (n=67), Klebsiella pneumoniae (n=9),P.aeruginosa (n=23), Proteus spp.(n=5),citrobacter spp. (n=3), Enterobacter spp.( n=2) and Acinetobacter spp.(n=13) obtained over a period of four months (January to April, 2011) , were screened for ESBLs and AmpC production by Kirby Bauer disk diffusion method and suspected isolates were subjected to double disk synergy, combined disk, MIC reduction and AmpC disk tests for confirmation.

Results: 49(27.2%) and 32(17.7%) were found to be ESBL and AmpC producers from 80(44.4%) and 59 (32.7%) screened out isolates respectively. Organism wise distribution of ESBL and AmpC isolates showed E.coli (27.5% & 15.9%), Klebsiella spp (33.8% & 18.4%),Proteus spp (40% & 0), P.aeruginosa (26% & 13%) and Acinetobacter spp ( 0 & 46.15%) respectively and they were significantly multidrug resistance too.

Conclusion: The incidence of ESBLs and AmpC was found to be lower in our hospital. Both the double disk synergy and combined disk tests showed equal efficacy in detection of ESBLs. Given the need for a test for AmpC ß-lactamases, the AmpC disk test could fill a current gap in diagnostic microbiology as it is reliable, simple and rapid.

Author(s): R.K.Manojkumar Singh*, Nishith Kumar Pal, Mandira Banerjee, Soma Sarkar, Manideepa SenGupta

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