NDM-1-Producing Escherichia coli in Germany

The bla_NDM-1 carbapenemase gene has now been identified among many different enterobacterial species from many countries (1, 7, 10-14). Its current spread has often been associated with importations from the Indian subcontinent.

Here we report the case of a 70-year-old man admitted to the intensive care unit of a hospital in Bonn, Germany, in December 2009. This patient had been hospitalized in India 3 months before as a consequence of a trauma that made him paraplegic. An acute appendicitis associated with paralytic ileus was diagnosed at the Bonn hospital. The surgical intervention was successful, but the patient remained on a ventilator and screening for colonization produced growth of a multidrug-resistant Escherichia coli isolate from his tracheal secretions. Since no symptoms of infection occurred, no antibiotic treatment was initiated, and the patient was shortly discharged.

Antimicrobial drug susceptibility testing of the E. coli RKI isolate was performed by broth microdilution according to the guidelines of the CLSI (3). E. coli RKI was resistant to all β-lactams, including carbapenems, with MICs of imipenem and meropenem being >32 μg/ml; to all aminoglycosides; and to nitrofurantoin and sulfonamides but remained susceptible to tigecycline and fosfomycin, and the MIC of colistin was 0.5 μg/ml. PCR and sequencing were performed in searching of different carbapenemase and extended-spectrum β-lactamase (ESBL) genes and also for bla_OXA genes as described previously (5, 9). These procedures showed that E. coli RKI harbored the bla_NDM-1, bla_CTX-M-15, bla_TEM-1, bla_OXA-1, and bla_OXA-2 genes.

In addition, PCR performed as described previously (4, 6, 11) revealed that E. coli RKI harbored the aac(6′)1b-cr gene, encoding resistance to aminoglycosides and reduced susceptibility to ciprofloxacin, together with the 16S rRNA methylase gene rmtC, conferring high-level resistance to all aminoglycosides, although no qnr gene was detected.

Transfer of the bla_NDM-1 gene was attempted by conjugation or electrotransformation (11) into a sodium azide-resistant E. coli J53 recipient strain, but the effort was unsuccessful. S1 nuclease pulsed-field gel electrophoresis (PFGE) analysis, performed as previously described (1), revealed two plasmids in E. coli RKI (120 and 70 kb, respectively) that did not hybridize with a bla_NDM-1-specific probe. Investigation of the bla_NDM-1 genetic environment by PCR mapping using primers designed according to previously identified bla_NDM-1-associated structures (11) revealed that the bla_NDM-1 genetic context in E. coli RKI was different from those previously identified, further underlining that the current dissemination of bla_NDM-1 was not associated with a single specific genetic structure.

Multilocus sequence typing (MLST) (http://mlst.ucc.ie/mlst/dbs/Ecoli) and PCR-based phylogroup analysis (2) identified E. coli RKI as an ST101 strain belonging to phylogroup B1. Interestingly, the NDM-1-positive E. coli 271 strain recently identified from Australia (11) with a link to the Indian subcontinent had also been identified as an ST101 strain. However, pulsed-field gel electrophoresis analysis (10) of E. coli RKI and E. coli 271 did not reveal any genetic relatedness.

This study further indicates that NDM-1-producing Enterobacteriaceae are currently spreading worldwide. Here we report a very likely chromosomal position of the bla_NDM-1 gene in E. coli, demonstrating that the genetic structures surrounding that gene might allow its integration in the bacterial chromosome.

Notably, the NDM-1-producing isolate also expressed other resistance determinants, in particular an ESBL and a 16S RNA methylase, leading to a panresistance phenotype. Our study is the first to evidence the occurrence of NDM-1-producing E. coli strains in Germany, with a link to previous hospitalization in India; this constitutes a warning to authorities to reinforce strict control measures for preventing the spread of such multidrug-resistant strains.