Can phenotypic methods accurately identify carbapenemase production in Morganellaceae?

Abstract

AIM: We aimed to evaluate and compare the performance of two chromagenic media (CM) and the carbapenem-inactivation method (CIM) in identifying carbapenemase production in the Morganellaceae members. BACKGROUND: Prompt and rapid detection of carbapenemase production is crucial for selecting approppriate antimicrobial therapy. While the gold standard for detecting carbapenemase production is molecular identification of carbapenemase genes, not all laboratories have the capability to carry out these tests. Phenotypic methods provide a cheap and easy substitute for assessing carbapenemase production; however, data about their performance in Morganellaceae is scarce. METHODS: 123 Morganellaceae [Providencia spp.(n=61), Proteus spp.(n=46), M.morganii(n=16)]and 117 other Enterobacterales [Klebsiella spp.(n=39), E.coli(n=38), Enterobacter spp.(n=27), Serratia spp.(n=13)] isolates were evaluated. Carbapenemase genes for OXA-48, KPC, NDM, VIM, IMP, BIC and SPM were detected by multiplex-PCR. Two CM [CHROMAGAR KPC (RTA,Turkey), CHROMID Carba (Biomérieux,France)] and CIM test were performed on all isolates. Gram-positive bacteria and yeasts were used as negative-controls of growth on CM. RESULTS: 112(46.7%) isolates carried at least one carbapenemase gene (Table-1). CIM test performed well in identifying KPC- and NDM-producers, but was unsatisfactory in IMP-producers. Its performance in Morganellaceae was lower than other Enterobacterales (Tables-2,-3). All isolates irrespective of their carbapenemase production and all negative controls except S.aureus grew on both CM(Picture-1). Sensitivity, specificity and positive predictive value of CM were 100%, 0%, and 46%, respectively. CONCLUSIONS: CIM performs moderately for detection of carbapenemase production in Morganellaceae. CM are unreliable without further confirmation. Growth of VRE and C.auris on CM is worrisome as they are frequently used for screening purposes in hospitalized patients

Keywords

• Morganellaceae
• carbapenemase
• carbapenem inactivation method
• chromogenic medium
• multiplex PCR