Pig farm successfully eradicates antibiotic-resistant bacteria

A German pig farm found to be contaminated with antibiotic-resistant bacteria has been successfully decontaminated.

A study in the journal Applied and Environmental Microbiology reports that routine monitoring had detected both methicillin-resistant Staphylococcus aureus (MRSA) and antibiotic-resistant, pathogenic intestinal bacteria, the Enterobacteriaceae, on a pig farm. 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.

The farmer approached the investigators for help and a study was designed to examine whether intensive decontamination performed by a commercially available service would effectively expunge the pathogens contaminating the farm environment.

Samples were collected 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.

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 colonised the pigs and contaminated the environment just two days after the arrival of new pigs.” The investigators also found the new strain colonising the noses of farmworkers. They conclude, therefore, that the major challenge to farm hygiene may be in preventing reintroduction of a new or old resistant strain from an external source.

A year after decontamination, the farmer reported that the farm had been able to greatly reduce use of antibiotics, that incidence of diarrhoea among the animals had dropped to zero and that the mortality rate among piglets had fallen below 2%. Thus, despite its high cost, decontamination had resulted in significant benefits to the farm, said co-author 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 nebulised for 48 hours at 1000°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 colonisation can be achieved with basic but rather aggressive infection control measures,” the investigators concluded.

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