Temocillin and meropenem to discriminate resistance mechanisms leading to decreased carbapenem susceptibility with focus on OXA-48 in Enterobacteriaceae.

A temocillin minimal inhibitory concentration ≥ 128 mg/L combined with the results of meropenem double disc synergy testing was used to (i) discriminate carbapenemase production from other resistance mechanisms leading to decreased carbapenem susceptibility; and (ii) differentiate Ambler classes in carbapenemase-producing enterobacteriaceae (CPE). The suggested test algorithm discriminated all extended spectrum ß-lactamase/AmpC from CPE isolates, which could further be divided correctly into Ambler classes A and B enzymes as well as OXA-48 in all cases. The algorithm is simple to implement as part of the daily routine in a standard microbiology laboratory with limited access to or resources for molecular biological tools.