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Background and objectives: Soon after the finding of the plasmid-mediated colistin resistance gene mcr-1 in November 2015, working groups all over the world confirmed the presence of this gene in their strain collections. However, to date no analysis of factors associated with the occurrence of the mcr-1 gene in livestock has been published.
Materials and methods: Within the scope of a cross-sectional investigation on fattening pig farms conducted in 2011 and 2012, 48 fattening farms in Germany were investigated. Primary cultures of boot swabs and collective faecal samples were stored at 80°C and currently screened for the presence of the mcr-1 gene. Using logistic regression models the association between occurrence of mcr-1 and farm information were investigated.
Results: E. coli carrying the mcr-1 gene were isolated from 26 out of 216 mixed bacterial cultures (12.0%) originating from 12 out of 48 farms (25.0%). Farms and stables with low numbers of pigs were associated with a lower number of mcr-1-positive samples. The change of housing during fattening was associated with a higher number of mcr-1-positive samples. We found no statistically significant association between antimicrobial use and the occurrence of the mcr-1 gene.
Conclusion: Our results indicate that the transmission between pigs or their direct environment is crucial for the occurrence of resistant bacteria. Therefore, small animal groups, prevention of contact between animal groups and thorough application of hygiene measures should be recommended.