Investigation of livestock transport trailers as potential fomites for antibiotic-resistant Escherichia coli.

Dairy cattle and calves are regularly transported by calf buyers and to auctions and abattoirs by livestock transport vehicles from about 12,000 dairy farms in the United Kingdom (UK). UK Government guidelines require transport vehicles to be cleaned and disinfected within 24 hours of use or before re-use within that period. It is possible, however, that if cleaning fails to eradicate bacteria then transport vehicles can act as a carrier in the spread of antimicrobial-resistant (AMR) pathogens. The purpose of the pilot study by the authors cited, was to assess the contamination levels of trailers used for calf transport by Escherichia coli, a critically important foodborne pathogen, before and after the application of disinfection with FAM30. 

Calves were transported for 40-60 minutes from a dairy farm to the University of Liverpool. Within 20 minutes of unloading the trailer was cleaned with a pressure washer, and disinfected. Swab samples from five sites within the trailer were collected from a total of nine trailer-loads before and 30 minutes after application of the disinfectant. A bacterial count for E. coli was performed through growth on selective agar for each site and trailer-load. Species identification was confirmed by MALDI-TOF for a subset of twenty isolates selected for antibiotic susceptibility screening, and a broth micro-dilution minimum inhibitory concentration assay was performed for a selection of both veterinary and human antibiotics.

E. coli were recovered from all trailer-loads, both before and after disinfection. The sites with the highest level of contamination were underneath the side rails and the trailer ramp. However, the bacterial load was reduced for several sampled sites following disinfection. Furthermore, high levels of resistance to several antibiotic classes, namely β-lactams (21%), tetracyclines (42%) and sulphonamides (89%) were observed. Twenty percent of the screened isolates were also classified as multidrug-resistant (i.e. resistant to at least one antibiotic from three or more antibiotic classes).

The study demonstrated that livestock trailers can harbour zoonotic pathogens with AMR properties. Although disinfection is an important step to reducing bacterial populations in livestock trailers, it may not eliminate crucial pathogens.