Detection of Amp C beta lactamases production in Escherichia coli & Klebsiella by an inhibitor based method.

BACKGROUND & OBJECTIVE: Detection of AmpC-mediated resistance in Gram-negative organisms poses a problem due to misleading results in phenotypic tests. There are no recommended guidelines for detection of this resistance mechanism and there is a need to address this issue as much as the detection of extended spectrum beta lactamases (ESBLs) since both may co-exist and mask each other. Though resistance to cefoxitin is used as a screening test, it does not reliably indicate Amp C production. This study was undertaken to detect Amp C beta lactamases in certain Gram-negative bacteria employing an inhibitor base test using boronic acid. METHODS: A total number of 76 consecutive non repetitive clinical isolates of Escherichia coli (n=67) and 9 Klebsiella pneumoniae (n=9) obtained over a period of two months, were screened for amp C production by disc diffusion method using cefoxitin (30 microg) dics and confirmed by inhibitor based test using boronic acid as inhibitor. RESULTS: A total of 36 of 76 isolates (47.3%) screened harboured amp C enzymes, of which a majority 31 (86.1%) co-produced ESBL enzymes. Pure ampC production was seen in 7 (9.2%) of isolates only. INTERPRETATION & CONCLUSION: Most of the amp C producers also produced ESBL enzymes. The inhibitor based test was useful in identifying cefoxitin susceptible amp C producers and could also effectively differenciate ESBL from amp C producing isolates.

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.