Multi-centric study on the main carbapenem resistance mechanisms in the important members of Enterobacteriaceae family in Iran

Abstract Resistance to carbapenems has been increasingly reported from the Enterobacteriaceae family, with different mechanisms in different geographic parts of the world. This study was aimed to investigate the mechanisms of carbapenem resistance in Escherichia coli, Klebsiella pneumoniae, and Enterobacter spp. carried out as a multi-center study (n = 10). All third-generation cephalosporin-resistant E. coli, K. pneumoniae, and Enterobacter spp. that had been recovered from the selected provinces were included. Modified Hodge Test and Carba NP test were done as a phenotypical method for detection of carbapenemase, the most common carbapenemase was detected by PCR. We evaluated the presence of an active efflux pump by using Cyanide 3-chlorophenylhydrazone. Overexpression of AcrAB and presence of OqxAB was detected by real-time PCR and conventional PCR, respectively. Microorganisms in this study included 58 of E. coli, 95 of K. pneumoniae, and 60 of Enterobacter spp. MHT showed sensitivity 41%, specificity 83%, and the Carba NP test revealed a sensitivity of 26%, a specificity of 92% for detection of carbapenemase. OXA-48 was the most frequently detected carbapenemase seconded by NDM-1. 39% and 27% of positive CCCP test organisms included active AcrAB and OqxAB efflux pumps, respectively. The result showed the Carba NP test was more specific than MHT. Data confirmed the involvement of AcrAB and OqxAB efflux pump as a carbapenem resistance mechanism in selected bacteria. Similar to other reports from the Middle East, we found OXA-48 and NDM-1 as the most frequent carbapenemase.