Plasmid mediated AmpC b-lactamase producing Klebsiella (K.) pneumoniae and Escherichia (E.) coli have been responsible for nosocomial outbreaks of infections and colonisation.7 AmpC b-lactamases are associated with erroneous antimicrobial susceptibility in routine testing.8 AmpC b-lactamases are not inhibited by b-lactamase inhibitors such as clavulanic acid.3 Strains with AmpC genes are often resistant to multiple antibiotic.
AmpC b-lactamases, in contrast to extended-spectrum beta-lactamases (ESBLs), not only hydrolyse broad and extended-spectrum cephalosporins but are resistant to inhibition by b-lactamase inhibitors such as clavulanic acid.14 In our study 21.53% K.
Moreover, the
b-lactamase inhibitors such as clavulanic acid or tazobactam can reduce the minimal inhibitory concentration (MIC) of drugs.
AmpC b-lactamases are not inhibited by
b-lactamase inhibitors like clavulanic acid and are clinically significant because they resist to a wide variety of
b-lactamase inhibitors including a-methoxy-b-lactam such as cefoxitin.2,3 These enzymes are mostly produced by Escherichia coli, Klebsiella species and other Gram-negative bacteria.4
Two different b-lactamase inhibitors (ethylenediaminetetraacetic acid [EDTA] and boronic acid) were used for the evaluation of class A and B production.
In combination with b-lactamase inhibitors phenotypic double disc diffusion method, temocillin 30mg disc was also used for the OXA carbapenemase detection.
Other phenotypic methods like the "Kirby-Bauer disk potentiation method with some
b-lactamase inhibitors, or the cefoxitin-Hodge test, AmpC disc test, combined disc diffusion test and AmpC E test methods" are labour- intensive, technically complex, expensive and unsuitable for routine screening in clinical microbiology laboratories and may not detect all AmpC beta-lactamases.
