AmpCtype

AmpC-type refers to a family of AmpC beta-lactamases, enzymes that hydrolyze beta-lactam antibiotics and belong to Ambler class C. They are commonly produced by Gram-negative bacteria and can be encoded chromosomally or carried on plasmids (pAmpC). Chromosomal ampC genes are typically inducible and increased expression can occur under antibiotic exposure, leading to resistance. Plasmid-mediated ampC genes can spread between species and often confer broader and higher-level resistance.

Biochemical properties: AmpC enzymes hydrolyze most penicillins and cephalosporins, including cephamycins like cefoxitin and cefotetan, and are generally not inhibited by clavulanic acid. Some AmpC producers are susceptible to newer inhibitors; avibactam-containing combinations are active against many AmpC enzymes.

Genetic diversity: Many AmpC genes exist, with CMY-, DHA-, FOX-, ACT-, ACC-, MOX- and others. CMY-2 is among the most common plasmid-encoded variants worldwide.

Clinical impact: AmpC production can mask ESBL detection and complicate therapy. Laboratory detection relies on phenotypic screening for AmpC activity and molecular methods to identify ampC genes; inducible expression may require special testing.

Treatment considerations: Infections caused by AmpC producers are often managed with carbapenems, as many remain resistant to third-generation cephalosporins. Susceptibilities vary; some isolates retain activity to newer cephalosporins or cephalosporin–inhibitor combinations, but careful susceptibility testing is essential.