blaNDM-1-carrying Acinetobacter johnsonii detected in hospital sewage.

OBJECTIVES: This study screened hospital sewage for the presence of blaNDM.
METHODS: Colonies grown from plates containing meropenem streaked with hospital sewage were screened for blaNDM by PCR. Species identification was performed by sequencing 16S rRNA genes. Clonal relatedness of isolates was determined by Enterobacterial repetitive intergenic consensus sequence-PCR, sequencing recA and PFGE. Mating was attempted to obtain self-transmissible plasmids carrying blaNDM. The genetic context of blaNDM was investigated by PCR mapping using pNDM-BJ01, a blaNDM-1-carrying plasmid from Acinetobacter lwoffii as the reference.
RESULTS: Two Acinetobacter johnsonii isolates, designated XBB1 and XBC1, from sewage were found carrying blaNDM-1, but were of different clonal origins. In both cases, blaNDM-1 was carried by a self-transmissible plasmid. PCR mapping and sequencing revealed that the blaNDM-1-carrying plasmid of XBB1, pXBB1, was the same as pNDM-BJ01, whereas that of XBC1, pXBC1, was a variant of pNDM-BJ01. A large region downstream of blaNDM-1, including groES/groEL, ISCR27 and ISAba125, was absent from pXBC1. On pXBB1, blaNDM-1 was carried by Tn125, an ISAba125-formed composite transposon, which was inserted into a sequence downstream of aphA6.
CONCLUSIONS: Sewage of a hospital in China was found to contain blaNDM-1, suggesting that hospital sewage is an important but often overlooked reservoir of antimicrobial resistance determinants. A variety of Acinetobacter species in different locations have been found to harbour blaNDM-1, so the introduction of blaNDM-1 into Acinetobacter is unlikely to be a single event. The identification of blaNDM-1-carrying plasmid pNDM-BJ01/pXBB1 and its variants suggests that a common plasmid has been transferred among different host species at different locations.