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


CONCLUSIONS
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.
Hemalatha
V
V
Department of Microbiology, Sri Ramachandra Medical College & Research Institute [Deemed University], Chennai, India.
Padma
M
M
Sekar
Uma
U
Vinodh
T M
TM
Arunkumar
A S
AS
D001426:Bacterial Proteins / Q000096:biosynthesis*; D001897:Boronic Acids / Q000633:toxicity; D002440:Cefoxitin / Q000633:toxicity; D052978:Disk Diffusion Antimicrobial Tests; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D007709:Klebsiella / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D013045:Species Specificity; D001618:beta-Lactamases / Q000096:biosynthesis*
D001426:Bacterial Proteins; D001897:Boronic Acids; D002440:Cefoxitin; C048795:AmpC beta-lactamases; D001618:beta-Lactamases