AmpC Disk Test for Detection of Plasmid-Mediated AmpC β-Lactamases in Enterobacteriaceae Lacking Chromosomal AmpC β-Lactamases

Abstract

Although plasmid-mediated AmpC ␤-lactamases were first reported in the late 1980s, many infectious disease personnel remain unaware of their clinical importance. These enzymes are typically produced by isolates of Escherichia coli, Klebsiella spp., Proteus mirabilis, and Salmonella spp. and are associated with multiple antibiotic resistance that leaves few therapeutic options. Plasmid-mediated AmpC ␤-lactamases have been associated with false in vitro susceptibility to cephalosporins. Many laboratories do not test for this resistance mechanism because current tests are inconvenient, subjective, lack sensitivity and/or specificity, or require reagents that are not readily available. In this study a new test, the AmpC disk test, based on filter paper disks impregnated with EDTA, was found to be a highly sensitive, specific, and convenient means of detection of plasmid-mediated AmpC ␤-lactamases in organisms lacking a chromosomally mediated AmpC ␤-lactamase. Using cefoxitin insusceptibility as a screen, the test accurately distinguished AmpC and extendedspectrum ␤-lactamase production and differentiated AmpCs from non-␤-lactamase mechanisms of cefoxitin insusceptibility, such as reduced outer membrane permeability. The test is a potentially useful diagnostic tool. It can provide important infection control information and help to ensure that infected patients receive appropriate antibiotic therapy.

Detection of Methicillin Resistant, ESBL and Amp C Producing Uropathogens from a Tertiary Care Hospital in North India

“…After incubation the plates were examined for indentation or flattening of the zone of inhibition beside Amp C discs (positive result). The absence of a distortion or no flattening is considered as negative for Amp C production (Black et al, 2005;Kolhapure et al, 2015).…”

Prevalence of AmpC β-lactamase in Clinical Isolates of Escherichia coli, Klebsiella spp., and Proteus mirabilis in a Tertiary Hospital in Tehran, Iran

“…The production of β-lactamases, including AmpC β-lactamase and extended-spectrum β-lactamase (ESBL), is an important mechanism of drug resistance in Gramnegative bacteria (1,2).…”

Extended-spectrum β-lactamase/AmpC-producing uropathogenic Escherichia coli from HIV patients: do they have a low virulence score?

“…PCR-based detection of ESBL gene families, bla CTX-M , bla TEM and bla SHV , was carried out using previously described primers (Chang et al, 2001;Pagani et al, 2003;Yagi et al, 2000). Phenotypic detection of AmpC b-lactamase production was performed by an inhibitor (boronic acid)-based method (Coudron, 2005) and further confirmed by AmpC disc test (Black et al, 2005). E. coli ATCC 25922 was used as the negative control.…”