- Carbapenem until susceptibility known, then step down to aminoglycoside or fluoroquinolone if susceptible.
- These organisms usually produce inducible beta-lactamase which cause failure of 3rd generation beta-lactam therapy, despite in vitro susceptibility
- SPICE organisms (Serratia spp, Providencia spp, "indole positive" Proteus spp (does not include mirabilis), Citrobacter, Enterobacter spp, Acinetobacter, Morganella) have inducible, chromosomal beta-lactamase genes known as AmpC.
- Resistance may not be detectable initially, but appears after a period of exposure to beta-lactam antibiotics including extended spectrum penicillins, B-lactam/B-lactamse inhibitor combinations.
- Resistance to third generation cephalosporins may develop in 3-4 days.
