AmpC beta-lactamase producing bacterial isolates from Kolkata hospital.

Background and Objective: The widespread use of beta-lactam antibiotics has lead to the development of resistance to this group of antibiotics in bacterial pathogens due to beta-lactamase production. Information on such pathogens is not available from eastern region of India. This study was undertaken to determine the AmpC beta-lactamase production in pathogens isolated from hospitalized patients in Kolkata.

Methods: Non-repeat clinical isolates (284) from pus, urine, sputum and other clinical specimens of hospitalized patients were taken. Disk agar diffusion (DAD) and minimum inhibitory concentration (MIC) with different beta-lactam antibiotics, and double disc synergy test (DDST) with clavulanic acid and sulbactam were done. Disk antagonism test (DAT) and three-dimensional extract test (TDET) were conducted for phenotypic confirmation of AmpC and inducible AmpC beta-lactamase production. Nitrocefin spot test and microiodometric assay of beta-lactamase were also performed.

Results: Twenty seven isolates were found to be resistant to cefoxitin, a alpha-methoxy-beta-lactam. Of these, 19 were observed to be AmpC beta-lactamase producers and 4 were inducible AmpC beta- lactamase producers by DDST, DAT and TDET. Remaining 4 were non AmpC beta-lactamase producers. Of the 23 AmpC beta-lactamase producers, the distribution of different species was as follows: Escherichia coli 11 (47.8%), Pseudomonas aeruginosa 4 (17.3%) Klebsiella pneumoniae 3 (13%), and Klebsiella aeruginosa 1 (4.3%).

Interpretation and Conclusion: Our finding showed 6.7 per cent AmpC beta-lactamase and 1.4 per cent inducible AmpC beta-lactamase producing clinical isolates from Kolkata. AmpC beta-lactamase producing bacterial pathogens may cause a major therapeutic failure if not detected and reported in time.