DOES ACINETOBACTER BAUMANNII SERVES AS RESERVOIR FOR bla_NDM DISSEMINATION INTO ENTEROBACTERIACEAE?

Background

We aimed to describe the epidemiology and molecular features of NDM-producing Acinetobacter baumannii (NDMAb) and Enterobacteriaceae (NDME), and to explore the possibility of horizontal gene transfer (HGT) of the bla_NDM between these microbial families.

Methods

The study was done at the TASMC from 12/2014 until 8/2015. Surveillance rectal cultures were tested for NDME and NDMAb. Isolates were tested by PCR for bla_NDM and typing was done by PFGE. The locations of the bla_NDM within the ISAba125 transposon and on a plasmid were studied by PCR`s and S1-analysis, respectively. A transmission-event (TE) was determined if patients shared the same NDME or NDMAb PFGE type and were simultaneously in the same ward. Possible HGT-related TE was considered if the two isolates shared identical bla_NDM allele and transposon.

Results

The incidence of carbapenem-resistant A. baumannii-infected patients was 311, of which 15 (4.8%) were NDMAb (clinical-9, surveillance-4, both-2). The incidence of carbapenemase-producing Enterobacteriaceae-infected patients was 104, of which 13 (12.5%) were NDME (clinical-3, surveillance-8, both-2). All NDMAb isolate except one harbored bla_NDM-1 that was located on an ISAba125 transposon within a plasmid. The majority of patients (n=9) were infected by one NDMAb strain. NDME were either E. coli (n=4) or K. pneumoniae (n=9) of different PFGE types. Only 1 TE of NDME was identified. All NDME isolates harbored bla_NDM-1 on a transferable plasmid but the gene was located within an ISAba125 in only 3 isolates. One possible HGT-related TE from NDMAb to NDME was identified.

Conclusion

The incidences of NDMAb and NDME are similar. Whereas NDMAb appears to disseminate by clonal spread, the source of NDME remains elusive, and thus may be related to HGT from NDMAb.