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

BackgroundThe bla(NDM-1) (New Delhi Metallo--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 bla(NDM) 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 ata 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--lactamases and PMQRs were identified by PCR. NDM-positive isolates were studied for mutations in GyrA & ParC and for co-transmission of bla(NDM) and PMQR genes (aac(6)-Ib-cr, qnrB, qnrS) through conjugation or transformation. Plasmid types, integrons, plasmid addiction systems, and genetic environment of the bla(NDM) 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--lactamase found in this study. NDM-1 was the predominant metallo--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 bla(NDM), of which 12 co-transferred PMQRs along with bla(NDM) 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 bla(NDM) were of IncHIB-M type predominantly. Most of the isolates had ISAba125 in the upstream region of the bla(NDM) 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.