New composting technique could reduce antibiotic resistance genes

Scientists at the University of York and the Fujian Agriculture and Forestry University in China have found that hyperthermophilic composting can kill most antibiotic resistant-carrying bacteria.

Compost on an industrial scale is traditionally made by combining animal and plant waste. Manure can contain antibiotic resistance genes if the animals were treated with the drug.

York University evolutionary biologist Dr Ville Friman said: “In modern animal husbandry, animals are reared in high density to maximize food production. However, in these circumstances diseases can spread very easily. To contain epidemics, antibiotics are used, which can then give rise to antibiotic resistance-carrying bacteria in the gut of the animals.”

Antibiotic resistance genes are not inherently harmful. However, they present a serious global health risk when transmitted to humans through compost and food.

“Antibiotic resistance genes are then transferred to the faeces of the animal, which is later used as manure in compost that is spread on fields to fertilise crops. Anitibiotic resistance is a significant global health issue, so we need to find ways of reducing the likelihood of these genes entering the food chain,” said Friman.

Traditional thermophilic composting heats the mixture to between 46-62°C. The minimum is known to kill pathogens in one week whereas the maximum kills pathogens in just one hour.

The joint study, however, found that hyperthermophilic composting–a process whereby the compost mixture is internally heated to a temperature of 90°C–can effectively kill the antibiotic-resistant bacteria in manure.

Treating compost with the hyperthermophilic technique destroys the majority of bacteria carrying the resistance genes. There is potential to make food products safer by significantly reducing the amount of antibiotic resistance genes in the composting stage.

“Developing safer ways to manufacture organic fertilisers can reduce our dependence of traditional chemical fertilisers, whilst at the same time ensuring that they do not impact on human health by enriching antibiotic resistance genes in agricultural environments.”

Hyperthermophilic composting is evidently successful on an industrial scale, and the cost of the process is similar to traditional methods.

Antibiotics resistance has been a prevalent concern in the UK recently, after a study by the Food Standards Agency (FSA) recorded a record amount of chickens sold in UK supermarkets were found to carry anti-microbial resistant superbugs.

ETH Zurich spatial epidemiologist Dr Thomas Van Boeckel, speaking at the Global Superbug Crisis event in London on 31 January, said that 73% of global antibiotics are used in the food processing supply chain, highlighting the necessity to limit the use of the drug in animal rearing worldwide.