Carbapenemase should be suspected if:
Ertapenem zone is ≤ 22mm (Enterobacteriaceae) or
Meropenem zone is ≤ 25mm (Enterobacteriaceae / P. aeruginosa).
MBL suggested if:
- Resistance to Ceftazidime
- No synergy between Cephlasporin & Clavulanate
- Reduced susceptibility to Carbapenems
KPC will show:
- Negative metallo-β-lactamase test
- Synergy between Boronic acid and Carbapenems
- No synergy between Cloxacillin and Carbapenems
OXA-48 like suspected if:
- Negative results on all synergy tests
- No zone of inhibition with Temocillin 30μg disc
Combined disc test
Apply one tablet of:
Meropenem (MRP10)
Meropenem + Phenylboronic acid (MRPBO) - KPC & AmpC inhibitor
Meropenem + Cloxacillin (MRPCX) - AmpC inhibitor
Meropenem + Dipicolinic acid (MRPDP) - metallo-β-lactamase inhibitor
Temocillin (TEMOC)
On an inoculated Mueller-Hinton agar plate (McFarland 0.5).
Interpretation