- Hafnia alvei
- Enterobacter cloacae
- Citrobacter freundii, youngae
- Klebsiella (Enterobacter) aerogenes
- Yersenia enterocolitica
Organisms historically presumed to be at risk for the development of clinically significant ampC expression, such as Serratia marcescens, Morganella morganii, and Providencia species, are unlikely to overexpress ampC. When S. marcescens, M. morganii, or Providencia spp. are recovered from clinical cultures, the panel suggests selecting antibiotic treatment according to susceptibility testing results (e.g., administer ceftriaxone if susceptible to ceftriaxone).