Standardisation and evaluation of inhouse rapid carba-np and comparison of phenotypic methods for screening of carbapenemase producing gram negative bacterial isolates

Background: Identification of carbapenemase producer in routine laboratories is mandatory nowadays due to the increase in the prevalence of carbapenem resistant Gram negative bacteria. Most of the laboratories has to meet the challenge in identifying the carbapenemase producers from the clinical isolate due to non-availability of molecular diagnostics. Carba-NP test is recently added by CLSI for screening of carbapenemases is a rapid and reproducible test. Therefore, this study was done to standardize the rapid carba-NP test and to screen for carbapenemase production with other phenotypic tests in a tertiary care hospital, South India.
Methods: This is a prospective, cross-sectional study done with 122 nonduplicate Gram negative bacterial (GNB) isolates between February - September 2015.The isolates were identified using standard procedure and subjected to antibiotic susceptibility testing byclinical and laboratory standards institute (CLSI). The rapid Carba NP test was standardized and all the isolates were tested for carbapenemase production and screened by Modified Hodge test (MHT) and Imipenem (Imp) - Imp + EDTA combined disk test (CDT).
Results: Out of 122 GNB screened by disc diffusion technique, 19.67% (24/122) were carbapenem sensitive and 80.32% (98/122) were carbapenem resistant. The rapid carba-NP test showed that 21.42% (21/98) carbapenem resistant isolates were positive for rapid carba NP test and the results were compared with MHT and CDT.
Conclusion: The rapid detection of carbapenemase producer by Carba NP test helps to differentiate resistant pathogens from other mechanism of resistance.