Research identifies antibiotic resistance markers that make meat and milk safer

The World Health Organization (WHO) named resistance to antimicrobials one of the top 10 global public health threats because it decreases the effectiveness of medicines and makes infections more difficult to treat. The degree of threat this poses to the food supply is still unclear. Researchers at Pennsylvania State University led an international team that found that dairy cows in Brazil exposed for a few years to drinking water contaminated with heavy metals carry more pathogens loaded with antimicrobial-resistance genes able to tolerate and survive various antibiotics. These genes could potentially be passed to people through the food chain.

In 2015, the Fundao Tailings Dam in southeast Brazil suffered a catastrophic failure and released more than 11 billion gallons of iron ore waste. The huge wave of toxic mud flowed into the Doce River basin surrounding Mariana City, affecting drinking water supplies. Following this catastrophe, the research team analyzed the consequences of long-term exposure to contaminated drinking water on dairy cattle. They identified bacterial antimicrobial-resistance genes in the feces, rumen fluid and nasal passages of 16 dairy cattle in the area contaminated by iron ore waste four years after the environmental disaster. They compared samples taken from those animals to analogous samples from 16 dairy cattle on an unaffected Brazilian farm.

The microorganism community in the cattle continuously exposed to contaminated water differed in many ways from that of the control group of cows. Exposure to heavy metal contamination resulted in the selection of bacteria that have resistance genes to heavy metals, biocides and several drugs. They detected bacterial antimicrobial-resistance genes in fecal samples. This study was the first to show that the long-term persistence of heavy metals in the environment may trigger genetic changes and interfere with the microorganism communities that colonize dairy cows. If antibiotic resistance is transferred via milk or meat consumption, it could have substantial implications for human health, with the potential for an increase of so-called superbugs.

Project supported by Hatch funds.