Antibiotic resistance: the emergence of plasmid-mediated colistin resistance enhances the need of a proactive one-health approach

For some years now, multi-resistant Gram-negative bacteria such as Escherichia coli or Klebsiella pneumoniae have been spreading globally, causing increasing difficulty in treating infectious diseases both in hospitals and the community at large. Of particular concern are carbapenemase-producing Enterobacteriaceae which are frequently resistant to nearly all antimicrobial drugs available. Up to now, both colistin (an antibiotic of the family of polymyxins), and tigecycline (a glycylcycline), have been regarded as a last resort drug. And although colistin-resistant Enterobacteriaceae have been isolated, such resistance to date has been chromosomally mediated, and hence less prone to be efficiently transferred by horizontal gene transfer. This situation, however, has suddenly significantly worsened, as reported in ‘Lancet Infectious Diseases’ in November last year. Liu et al. (2016) described in China the isolation from a pig of a resistant non-pathogenic E. coli strain whose resistance determinant (gene mcr-1) is encoded by a plasmid. This genetic element is transmissible, not only at rather high frequency by conjugation to E. coli, but also by transformation to both K. pneumoniae and Pseudomonas aeruginosa.