Clonal transmission of a colistin-resistantEscherichia colifrom a domesticated pig to a human in Laos: Table 1.

Sir, Colistin, recently reintroduced in human medicine, is one of the most important antibiotics currently used to treat severe Gram-negative bacterial infections in humans. Unfortunately, it is also extensively used in animal production, including in swine and poultry farming against Gram-negative bacterial pathogens.1,2 However, the extensive use of antibiotics in food-animal production has been shown to increase the risk of transferring resistant bacteria to humans.3 In this study, we investigated the possible link between colistin-resistant Escherichia coli isolated from domesticated pigs and humans in a rural area in Laos. In 2012, faecal samples were collected from 190 healthy individuals and 62 domesticated animals (44 free-range goats and 18 semi-free-range pigs) in Laksip, Laos (GPS coordinates of latitude: 19°50′55.615″N; longitude: 102°10′4.266″E). Approval was obtained from the Ministry of Health Council of Medical Sciences, National Ethics Committee for Health Research Laos, number 51/NECHR. The samples were screened for colistin-resistant E. coli using Cepacia Medium (Becton Dickinson, Heidelberg, Germany) and isolates identified using MALDI-TOF MS. Colistin and polymyxin B MICs were determined by Etest on Mueller–Hinton II agar (bioMérieux, France) and microdilution with cation-adjusted Mueller–Hinton II broth (Becton Dickinson, Le Pont de Claix, France) and interpreted using EUCAST4 and CLSI 2014 guidelines (M100-S24), respectively. Conjugation experiments were conducted as previously described using kanamycin.5 MLST was performed as described at http://mlst.warwick.ac.uk/mlst/dbs/Ecoli/documents/primersColi_html. Virulence typing was performed by targeting 10 virulence genes (kpsMTII, papC, sfa/foc, afa/dra, iutA, iss, tsh, sitAP, ompT and hlyF) and isolates classified as extraintestinal pathogenic E. coli (ExPEC) according to the criteria of Johnson et al.6 PFGE typing was performed as described previously7 using XbaI (Invitrogen, France) and 1.2% PFGE agarose gel (Sigma). Lastly, PCR and sequencing of the pmrAB, phoPQ and mgrB genes of colistin-resistant E. coli were carried out.8