Abstract

Objective: Identifying the presence and type of carbapenemases is essential to determine the treatment choices for carbapenem-resistant Gram-negative bacilli (CRB). Genotypic characterization of CRB needs technical support and experienced staff and is not an option for most laboratories due to its high cost. For this reason, especially in countries with limited resources, cheap, reliable phenotypic methods are an alternative, do not require experience, and can be easily applied in daily practice. The goal of the study was to evaluate the performance of phenotypic methods for carbapenemase production in CRB and to form a simple algorithm to differentiate carbapenemase types such as bla_OXA-48 or bla_NDM, which are common in our country.

Methods: The study included 16 consecutive carbapenem-resistant, Gram-negative bacteria. Simplified carbapenem inactivation methods (sCIM) and modified Hodge test (MHT) were performed. Genes responsible for carbapenemase production (bla_OXA-48, bla_NDM, and bla_KPC) were detected by real-time polymerase chain reaction. Temocillin resistance and ceftazidime-avibactam disc diffusion test were also applied to define carbapenemase types.

Results: The carbapenemase gene was detected in 12 of the 16 strains; sCIM positivity was found in 11, and MHT was positive in 10. Sensitivity for sCIM and MHT were 91.9% and 83.3%, respectively. All Enterobacterales strains were positive for sCIM, and bla_OXA-48 was the most common carbapenemase. sCIM false negativity was detected for only one strain. High-level temocillin resistance (MIC >128 μg/mL) was present in all strains with bla_OXA-48; it wasn’t detected in the strain carrying isolated bla_NDM.

Conclusion: sCIM positivity was present for all Enterobacterales, which were shown to carry the carbapenemase gene by RT-PCR. Our findings support the usage of sCIM in daily practice to screen for carbapenemase production in CRB.