ABSTRACT
AmpC β-lactamases are clinically important cephalosporinases encoded on the chromosomes
of many Enterobacteriaceae and a few other organisms, where they mediate resistance to cephalothin, cefazolin,
cefoxitin, most penicillins, and β-lactamase inhibitor/β-lactam combinations. The
increase in antibiotic resistance among Gram-negative bacteria is a notable example
of how bacteria can procure, maintain and express new genetic information that can
confer resistance to one or several antibiotics. Detection of organisms producing
these enzymes can be difficult, because their presence does not always produce a resistant
phenotype on conventional disc diffusion or automated susceptibility testing methods.
These enzymes are often associated with potentially fatal laboratory reports of false
susceptibility to β-lactams phenotypically. With the world-wide increase in the occurrence,
types and rate of dissemination of these enzymes, their early detection is critical.
AmpC β-lactamases show tremendous variation in geographic distribution. Thus, their accurate
detection and characterization are important from epidemiological, clinical, laboratory,
and infection control point of view. This document describes the methods for detection
for AmpC β-lactamases, which can be adopted by routine diagnostic laboratories.
Key words:
AmpC β-lactamases - disk approximation test - gram-negative bacteria - three-dimensional
extract test
