Decontamination exterminates antibiotic-resistant bacteria from pig farm

The study involved a farm on which both pathogens had been discovered through routine monitoring. The farmer had approached the investigators for help. The Enterobacteriaceae were expressing resistance genes called extended-spectrum β-lactamases (ESBL-E). β-lactamases disable a broad, very important class of antibiotics called β-lactams, which inhibit bacterial wall synthesis.

For their part, the investigators wanted to find out whether intensive decontamination performed by a commercially available service would effectively expunge the pathogens contaminating the farm environment. They collected samples at different time points both before and after decontamination, from the pigs, the air, water, and manure, and from the farm personnel. "Later, we compared the time points and the different media to evaluate the efficacy and durability of the decontamination measures on the farm," said corresponding author Isabelle Bekeredjian-Ding, MD, MPH, Head of Microbiology, Paul-Ehrlich-Institut, the German Federal regulatory agency for Vaccines and Biomedicines, Langen, Germany.

Following decontamination, the investigators could no longer detect the MRSA and ESBL-E strains of bacteria in the farm environment, in the farm personnel, or on the new pigs that repopulated the stables, said Bekeredjian-Ding.

"However, we found a new MRSA strain that we had never detected previously, said Bekeredjian-Ding. "This strain colonized the pigs and contaminated the environment just two days after the arrival of the new pigs." The investigators also found the new strain colonizing the noses of farmworkers. Thus, the major challenge to farm hygiene may be preventing reintroduction of a new or old resistant strain from an external source, said first author Ricarda M. Schmithausen, MD, PhD, of the University Hospital Bonn Institute of Medical Microbiology, Immunology and Parasitology.

A year after decontamination, the farmer told the investigators that the farm had been able to greatly reduce use of antibiotics, that incidence of diarrhea among the animals had dropped to zero, and that the mortality rate among piglets had fallen below two percent. Thus, despite its high cost, decontamination had resulted in significant benefits to the farm, said coauthor Brigitte Petersen, Professor and Head of Preventive Health Management at the Agricultural Faculty, the University of Bonn.

Decontaminating the pig farm involved high pressure cleaning and then drying the stables, followed by treatment with a complex solution containing amphoteric surfactants and complexing agents. That was followed by a two day-long disinfection process using a complex formula that comprised formaldehyde and dimethyl ammonium chloride, as well as other compounds. Finally, the manure pit, ventilation system, and feeding installation were nebulized for 48 hours at 1,000o C. The process also included constructing new stables, from metal and plastic, which are more easily disinfected than wooden structures.

"Our results show that the control of MRSA colonization can be achieved with basic but rather aggressive infection control measures," the investigators conclude.