pAmpC

pAmpC refers to plasmid-mediated AmpC beta-lactamases, enzymes that confer resistance to a wide range of beta-lactam antibiotics by hydrolyzing the beta-lactam ring. Encoded on transferable plasmids, these enzymes can spread between different Gram-negative species, contributing to the emergence of multidrug-resistant infections.

Origins and diversity: While AmpC enzymes are chromosomal in several genera, plasmid-borne variants have emerged globally. The major pAmpC families reported in clinical isolates include CMY (notably CMY-2), DHA, FOX, MOX, ACT, and ACC. These genes are carried on diverse plasmids and can be inducible or constitutively expressed.

Enzymatic activity and phenotype: pAmpCs hydrolyze cephalosporins, including many third-generation agents, and cephamycins such as cefoxitin. They generally are not inhibited by clavulanic acid, which complicates detection; newer inhibitors such as avibactam can inhibit many pAmpCs, depending on the particular enzyme. Phenotypic detection is challenging; routine susceptibility testing may underestimate resistance, and confirmatory tests or molecular methods are recommended.

Clinical significance and treatment: pAmpC–producing organisms are primarily Enterobacterales, including Escherichia coli and Klebsiella pneumoniae, but can be found in other genera. Infections can limit therapeutic options and are often associated with additional resistance determinants. Carbapenems remain effective for many pAmpC-producing infections; several non-carbapenem options, including ceftazidime-avibactam or aztreonam-avibactam, may be active depending on coexisting resistance. Susceptibility testing is essential for guiding therapy.

Diagnosis and surveillance: Detection relies on molecular methods to identify bla_CMY, bla_DHA, bla_MOX, bla_ACT, bla_FOX families, or comprehensive sequencing; phenotypic tests include AmpC disk tests or boronic acid inhibition tests. Surveillance programs monitor the spread of plasmid-mediated AmpCs to inform infection-control and antimicrobial stewardship measures.