Gram negative organisms, usually "SPICEM" (Serratia, Pseudomonas, Providencia, Citrobacter, Enterobacter, Morganella), that have a chromosomal beta-lactamase.
Most AmpC organisms are nosocomially encountered, are GI flora and are part of the Enterobacteriaceae family.
Syndromes caused by the organism that possesses AmpC (see individual organism).
AmpC organisms are difficult to identify using susceptibility reports alone. A pathogen may harbor AmpC and/or ESBL enzymes if it appears resistant to multiple beta lactams.
In the lab, AmpCs test resistant to cefoxitin and cefotetan, whereas ESBLs remain susceptible to these.
ESBLs vs. AmpC: Most ESBLs are plasmid-encoded, whereas AmpCs are usually inducible and chromosomal.