Molecular epidemiology of carbapenem-resistant enterobacteriaceae from a north Indian tertiary hospital

Aim: To analyse the occurrence of bla genes (blaIMP, blaVIM, blaGIM, blaSIM, blaSPM, blaPER, blaKPC, and blaOXA) responsible for carbapenemresistance, as well as the presence of cephalosporin-resistance genes (blaCTX-M, blaTEM, blaSHV and blaampC ) by polymerase chain reactions (PCRs). Methods: The study was performed on routine samples subjected to culture and antibiotics susceptibility during September 2007 to April 2008. Bacterial cultures from 893 patients yielded growth of Gram-negative bacteria, and of which, sixteen isolates (E. coli= 10; Klebsiella pneumoniae= 6) were reported resistant to imipenem on primary antibiotic susceptibility testing. The minimum inhibitory concentration (MIC) for imipenem was detected as per the CLSI guidelines. These 16 isolates were further studied for the presence of carbapenem-resistance genes including blaIMP, blaVIM, blaGIM, blaSIM, blaSPM, blaPER, blaKPC, and blaOXA by PCR. Since the isolates were also reported resistant to third-generation cephalosporins, these 16 isolates were also screened for the presence of blaCTX-M, blaampC, blaTEM, and blaSHV. Results: Carbapenem-resistance was reported in 1.8% (16/893) isolates based on antibiotics susceptibility testing. However on detection of imipenem-MIC, only 7 (0.8%) isolates were found as imipenem-resistant. Of these 16 isolates, carbapenem-resistance gene, blaVIM, was detected in only 18.6% (3/16) isolates; all were K. pneumoniae. On cumulative analyses, any of the bla genes was detected in a total of 93.6% (15/16) isolates. blaCTX-M, blaampC, blaTEM and blaSHV were detected in 87.5% (14/16), 43.8% (7/16), 75% (12/16) and 31.3% (5/16) isolates, respectively. Maximum number (4/16; 25%) had a combination of blaCTX-M + blaTEM, followed by blaCTX-M, blaampC, blaTEM, and blaSHV in 3 (18.8%; 3/16) isolates. Conclusion: Resistance to carbapenem is quite low in our area; only blaVIM was detected responsible for carbapenem resistance in our isolates. This is among the premier reports from India looking extensively for the molecular epidemiology in carbapenem resistant isolates.

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