Tn 125 -Related Acquisition of bla _NDM -Like Genes in Acinetobacter baumannii

Abstract

A multidrug-resistant Acinetobacter baumannii isolate recovered from a patient hospitalized in Switzerland after a transfer from Serbia produced the NDM-1 carbapenemase. The bla NDM-1 gene was part of a chromosomally located Tn125 composite transposon bracketed by two copies of the same insertion sequence, ISAba125. This transposon was also associated with the acquisition and expression of the bla NDM-2 gene in an A. baumannii isolate in Germany. Tn125 appears to be the main vehicle for dissemination of bla NDM genes in that species.T he carbapenemase NDM-1, initially identified in Escherichia coli and Klebsiella pneumoniae, has been found mostly in enterobacterial species (12,16,17). However, recent reports have described the occurrence of bla NDM genes in Acinetobacter baumannii. Several NDM-1-positive A. baumannii isolates have been identified in India (10), and two NDM-positive A. baumannii isolates have been recovered in Germany, one being from a patient transferred from a Serbian hospital and producing NDM-1 (6), whereas the other produced NDM-2 (one amino acid substitution with respect to NDM-1) and had been recovered from a patient transferred from an Egyptian hospital (isolate ML) (9). Although the Indian subcontinent is considered a reservoir of NDM-1 producers (17), recent reports indicate that at least the Balkan states and the Middle East regions could also be potential reservoirs (13,21).In a recent work, Pfeifer et al. (18) reported that the bla NDM-1 gene identified in A. baumannii isolate 161/07 from Germany (from a patient transferred from Serbia) (6) was located inside a composite transposon bracketed by two copies of insertion sequence ISAba125.A retrospective survey focusing on multidrug-resistant Gramnegative isolates identified several non-clonally related NDM-1-producing isolates from three patients who had been hospitalized in Geneva University Hospitals, Switzerland, from March 2009 to October 2010. One E. coli and one K. pneumoniae isolate were recovered from the same patient, who had been transferred from Serbia (22). In both isolates, the bla NDM-1 gene was identified on the same 150-kb IncA/C-type plasmid (20). Further investigations showed that this patient also carried a multidrug-resistant A. baumannii isolate that had been recovered from rectal swabs.A. baumannii isolate JH was resistant to all ␤-lactams, including carbapenems (MICs of imipenem, ertapenem, doripenem, and meropenem measured by Etest [AB bioMérieux; Solna, Sweden] were all Ͼ32 g/ml) according to the CLSI guidelines (3). It was also resistant to gentamicin, amikacin, chloramphenicol, tetracycline, and fluoroquinolones and remained susceptible to tobramycin and netilmicin, with MICs of colistin, rifampin, and tigecycline being at 0.5, 1, and 1 g/ml, respectively. PCR and sequencing revealed that A. baumannii JH harbored the bla NDM-1 gene. Screening for additional ␤-lactamase genes and for 16S RNA methylase genes as reported previously (1, 23) showed that A. baumannii JH was coharboring another carbapenemase gene, ...

Phenotypic, Biochemical, and Molecular Techniques for Detection of Metallo-β-Lactamase NDM in Acinetobacter baumannii

“…In a single case, as reported previously, two carbapenemase genes were identified that were bla OXA-23 and bla NDM-1 (20). Using these PCRbased techniques, all NDM producers were detected.…”

Transposition of Tn 125 Encoding the NDM-1 Carbapenemase in Acinetobacter baumannii

“…Tn125 is a 10,099-bp composite transposon bracketed by two copies of the insertion sequence (IS) ISAba125 orientated in the same direction (Fig. 1A) (4,7,8). The 1,087-bp ISAba125 element belongs to the IS30 family and encodes a 322-amino-acid-long DDE-type transposase surrounded by imperfect terminal inverted repeat sequences (IRR [inverted repeat right] and IRL [inverted repeat left], sharing 20/26 nucleotide identity) (9,10).…”

“…Multidrug-resistant A. baumannii isolates are of great concern (5,6). In Acinetobacter spp., the bla NDM-1 gene is embedded in transposon Tn125 (4,7,8). Tn125 is a 10,099-bp composite transposon bracketed by two copies of the insertion sequence (IS) ISAba125 orientated in the same direction (Fig.…”

The genetic analysis of Enterobacteriaceae plasmids to provide insights into the acquisition and spread of the blaNDM gene

“…Such events would result in the observation of the same genetic context on two different plasmid (184,200,241). It may be speculated that transposable elements have a degree of compatibility within a strain depending on their genera.…”

“…This Gene exchange events between plasmid types would be a mechanism to avert the plasmid types/genera compatibility. This event would possibly occur after a strain received a plasmid type that cannot be retained, where the AMR gene and any adjacent sequence would be transferred from said incompatible plasmid onto a plasmid type already co-resident and established within the strain.Such events would result in the observation of the same genetic context on two different plasmid (184,200,241). It may be speculated that transposable elements have a degree of compatibility within a strain depending on their genera.…”