Research Note: Tracing pathways of entry and persistence of facultative pathogenic and antibiotic-resistant bacteria in a commercial broiler farm with substantial health problems

On a commercial broiler farm with substantial health problems, shown by a reported loss rate of approx. 10% and regular antibiotic use, samples were taken at different locations in 2 barns, with the aim of analyzing possible entry routes and persistence of pathogens and antibiotic-resistant bacteria as well as revealing weak points in sanitation. Therefore, swab samples for biofilm and water samples from animal drinking water lines and the spray cooling system were taken twice immediately before restocking. In addition, swab samples from drain holes and air samples were collected. At restocking, hatchlings that died during transportation and chick paper were sampled. All samples were analyzed for the occurrence of Pseudomonas aeruginosa, total coliform count, and antibiotic-resistant bacteria, namely, methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli, Klebsiella spp., Citrobacter spp., Enterobacter spp., Acinetobacter baumannii, P. aeruginosa, and vancomycin-resistant Enterococci (VRE). No MRSA or VRE were detectable. In all samples from drinking water and sprinkler system pipes, P. aeruginosa was detectable; in most cases, antibiotic-resistant P. aeruginosa was also detected, with varying resistance profiles. Samples from the hatchlings and chick paper were contaminated with antibiotic-resistant Enterobacter spp., with resistance to piperacillin, fosfomycin, and the third-generation cephalosporins cefotaxime and ceftazidime. Therefore, the initial entry of antibiotic-resistant Enterobacteriaceae likely occurred via exposure at the hatchery, resulting in colonization of the chicks. Animals on the fattening farm were treated with colistin, amoxicillin, and lincomycin in the 3 production cycles before sampling. Owing to the frequent administration of several antibiotic classes during the fattening period via piped water in both barns, resistance of isolates from water pipes accumulated, showing additional resistance to chloramphenicol and frequently to ciprofloxacin and levofloxacin. To prevent the development of secondary diseases caused by the facultative pathogen P. aeruginosa in chicks with a weak immune status, the hygiene management for drinking water lines and the spray cooling system was changed. These changes resulted in an improvement in water line sanitation, shown by the absence of antibiotic-resistant bacteria and rare detection of P. aeruginosa.