Do plants really transmit superbugs to people?

Antibiotic-resistance infections are a big challenge to public health, food safety, and economy.

In their quest to find how antibiotic-resistance bacteria and their genes are transmitted from meat and plant-based foods, the researchers have found that plant-foods serve as vehicles for transmitting antibiotic resistance to the gut microbiome.

The study is presented at the 'ASM Microbe 2019' annual meeting.

"Our findings highlight the importance of tackling foodborne antibiotic-resistance from a complete food chain perspective that includes plant-foods in addition to meat," said Marlene Maeusli, the lead author on the study.

Spread of antibiotic-resistant superbugs from plants to humans is different from outbreaks of diarrheal illnesses caused immediately after eating contaminated vegetables. Superbugs can asymptomatically hide in (or 'colonise') the intestines for months or even years, when they then escape the intestine and cause an infection, such as a urinary infection.

The researchers developed a novel, lettuce-mouse model system that does not cause immediate illness to mimic the consumption of superbugs with plant-foods. They grew lettuce, exposed the lettuce to antibiotic-resistant E. coli, fed it to the mice and analysed their faecal samples over time.

"We found differences in the ability of bacteria to silently colonise the gut after ingestion, depending on a variety of host and bacterial factors. We mimicked antibiotic and antacid treatments, as both could affect the ability of superbugs to survive the passage from the stomach to the intestines," said Maeusli.

Exposure to one type of antibiotic did not increase the ability of superbugs to hide in the mouse intestines, whereas a second antibiotic resulted in stable gut colonisation after ingestion. Ingestion of bacteria with food also changed colonisation, as did administering an antacid before ingesting the bacteria.

"We continue to seek the plant characteristics and host factors that result in key microbial community shifts in the gut that put us at risk for colonisation and those that prevent it." The environment and human health - in this context via agriculture and microbiomes - are inextricably linked," said Maeusli.