Spread and exchange of bla NDM-1 in hospitalized neonates: role of mobilizable genetic elements

To investigate the mobilizable elements associated with bla (NDM-1) in Enterobacteriaceae isolated from septicaemic neonates at a NICU in India, during December, 2008-2011. An attempt was also made to understand whether there was a pattern in the temporal acquisition of bla (NDM-1) within the unit. Transferability of carbapenem resistance was tested by conjugation and transformation. Plasmid types and addiction systems were analysed. The genetic background of bla (NDM-1) and association with class 1 integron were evaluated by PCR mapping. RFLP was carried out to discriminate plasmids of same incompatibility group. Transfer of carbapenem resistance was successful in 13/15 cases. bla (NDM-1) was associated with different plasmid scaffolds (IncFII, IncL/M, IncN, IncR, IncHIB-M/FIB-M), IncF type being the prevalent one. Addiction systems ccdAB and hok/sok were associated with transferable plasmids. Genetic structures surrounding bla (NDM-1) showed its association with at least a remnant of ISAba125 at its 5'-end. The spread of NDM-1 was not related to class 1 integron which possessed resistance determinants against trimethoprim (dfrA12, dfrA1, dfrA5), streptomycin (aadA2, aacA4), and rifampicin (arr-3). RFLP showed that three isolates possessed the same FII/FIIs plasmid; two of these three isolates were from a single neonate, implying interspecies transfer of bla (NDM-1.) The predominance of FII plasmids and ISAba125 along with bla (NDM-1) was noted, but no specific pattern in the temporal acquisition of mobile genetic elements could be identified. To the best of our knowledge, this report is the first to inform the in-vivo interspecies plasmid transfer event of bla (NDM-1) in a neonate.