Evaluation of co-transfer of plasmid-mediated fluoroquinolone resistance genes and blaNDM gene in Enterobacteriaceae causing neonatal septicaemia

Abstract

BackgroundThe blaNDM-1 (New Delhi Metallo-β-lactamase-1) gene has disseminated around the globe. NDM-1 producers are found to co-harbour resistance genes against many antimicrobials, including fluoroquinolones. The spread of large plasmids, carrying both blaNDM and plasmid-mediated fluoroquinolone resistance (PMQR) markers, is one of the main reasons for the failure of these essential antimicrobials.MethodsEnterobacteriaceae (n = 73) isolated from the blood of septicaemic neonates, admitted at a neonatal intensive care unit (NICU) in Kolkata, India, were identified followed by PFGE, antibiotic susceptibility testing and determination of MIC values for meropenem and ciprofloxacin. Metallo-β-lactamases and PMQRs were identified by PCR. NDM-positive isolates were studied for mutations in GyrA & ParC and for co-transmission of blaNDM and PMQR genes (aac(6′)-Ib-cr, qnrB, qnrS) through conjugation or transformation. Plasmid types, integrons, plasmid addiction systems, and genetic environment of the blaNDM gene in NDM-positive isolates and their transconjugants/ transformants were studied.ResultsIsolated Enterobacteriaceae comprised of Klebsiella pneumoniae (n = 55), Escherichia coli (n = 16), Enterobacter cloacae (n = 1) and Enterobacter aerogenes (n = 1). The rates of ciprofloxacin (90%) and meropenem (49%) non-susceptibility were high. NDM was the only metallo-β-lactamase found in this study. NDM-1 was the predominant metallo-β-lactamase but NDM-5, NDM-7, and NDM-15 were also found. There was no significant difference in ciprofloxacin non-susceptibility (97% vs 85%) and the prevalence of PMQRs (85% vs 77%) between NDM-positive and NDM-negative isolates. Among the PMQRs, aac(6′)-Ib-cr was predominant followed by qnrB1 and qnrS1. Twenty-nine isolates (40%) co-harboured PMQRs and blaNDM, of which 12 co-transferred PMQRs along with blaNDM in large plasmids of IncFIIK, IncA/C, and IncN types. Eighty-two percent of NDM-positive isolates possessed GyrA and/or ParC mutations. Plasmids carrying only blaNDM were of IncHIB-M type predominantly. Most of the isolates had ISAba125 in the upstream region of the blaNDM gene.ConclusionWe hypothesize that the spread of PMQRs was independent of the spread of NDM-1 as their co-transfer was confirmed only in a few isolates. However, the co-occurrence of these genes poses a great threat to the treatment of neonates.