Abstract :
Introduction: ESBLs (Extended spectrum beta lactamases) are detected routinely in most laboratories but
Amp c Beta lactamases are neglected to large extent. Pseudosusceptibility seen in Amp C producers leads
to resistance to extended-spectrum cephalosporins resulting in inappropriate antimicrobial regimens and
therapeutic failure. Thus, there is a need to know an appropriate phenotypic method for easy detection of
Amp C b -lactamases as they have clinical relevance.
Aim: To detect and compare different phenotypic methods for Amp C b -lactamases in Gram-negative
clinical isolates of Enterobacteriaceae family
Materials and Methods: A prospective study was done at Mamata Medical college, Khammam for period
of three months. Phenyl boronic acid method, Cefoxitin Cloxacillin-Double disc synergy test, TRIS EDTA
method, Disc approximation test were done on isolates after screening by Cefoxitin disc.
Results: Out of 140 isolates tested, 80(57%) were positive (resistant) for screening test by cefoxitin. Out
of them 61(76.2%) were Escherichia coli, 16 (20.1%) isolates were Klebsiella pneumoniae and 3 (3.75%)
were Enterobacter sp. Phenotypic confirmatory methods by Cefoxitin Cloxacillin Double disc Synergy
(CC-DDS) test showed zone difference of >4mm in 38(47.5%) isolates , by Phenylboronic acid method
(PBA) > 5mm zone difference was observed in 34(42.5%) isolates, by TRIS EDTA method 32 (40%)
showed indentation near EDTA disc and by Disc approximation test 32(40%) were positive for Amp C
production. E coli was the commonest isolate showing Amp c production by all four methods.
Conclusion: CC-DDS method has better detection rate compared to other phenotypic confirmatory
methods. We suggest CC-DDS method as it is easy to perform.
Keyword :
Amp C, Cefoxitin cloxacillin double disc synergy (CC-DDS) test, Phenylboronic acid method,
TRIS EDTA method, Disc approximation test.