Investigation of potential risk factors for the occurrence of Escherichia coli isolates from German fattening pig farms harbouring the mcr-1 colistin-resistance gene

Within the scope of a cross-sectional investigation on fattening pig farms conducted in 2011 and 2012, 48 fattening farms in different agricultural regions of Germany were sampled. Primary cultures of boot swabs and collective faecal samples were stored at −80 °C and screened for the presence of the mcr-1 colistin-resistance gene. The laboratory results were linked to farm-related data collected via questionnaire. Logistic regression models were used to investigate the association between occurrence of mcr-1 and farm-related data. Escherichia coli carrying the mcr-1 gene were isolated from 26 of 216 (12.0%) mixed bacterial cultures originating from 12 of 48 (25.0%) farms. Results of the logistic regression analyses indicate that the transmission between pigs or their direct environment is crucial for the occurrence of these resistant bacteria. However, there was no statistically significant association between antimicrobial use and the occurrence of the mcr-1 gene.