Superbug warning as international travel resumes

International travellers have been warned returning from trips across the world they are likely to be bringing back new and potentially deadly strains of antimicrobial resistant superbugs.

A team from the Washington University School of Medicine in St. Louis have found that travellers often return home with an unexpected bounty of new bacterial strains jostling for position among the thousands that normally reside within the gut microbiome.

“Even before the COVID-19 pandemic, we knew that international travel was contributing to the rapid global increase and spread of antimicrobial resistance,” said Alaric D’Souza, an MD/PhD student at Washington University and a co-first author of the study. “But what’s new here is that we’ve found numerous completely novel genes associated with antimicrobial resistance that suggest a worrisome problem on the horizon.”

Poverty, poor sanitation and changing agricultural practices have turned many low-income, developing regions into hot spots for diseases spread by bacteria, including infections that are increasingly resistant to a range of antibiotic drug treatments.

The study found high-population densities make it easy for these bacteria to be shared among community residents and travellers through exposure to contaminated drinking water and food, or poorly sanitized restrooms, restaurants, hotel rooms and public transportation. Back at home, travellers run the risk of transferring these novel bacteria to family, friends and other community residents.

In conjunction with Maastricht University in the Netherlands, the team analysed bacterial communities in the gut microbiomes of 190 Dutch adults before and after travel to one of four international regions where the prevalence of resistance genes is high: South-eastern Asia, South Asia, North Africa and Eastern Africa.

Faecal samples analysed as part of the study were randomly selected from a larger, multicentre investigation of about 2,000 Dutch travellers, the majority of whom were tourists, known as the Carriage Of Multi-resistant Bacteria After Travel (COMBAT) study.

“We found significant travel-related increases in the acquisition of resistance genes, abundance and diversity encoded by bacteria that are endemic to the region visited,” D’Souza said. “These findings provide strong support for international travel as a vector for the global spread of clinically important antimicrobial resistance genes and highlight the need for broader surveillance of antimicrobial resistant bacteria in the gut microbiomes of returning travellers.”

The World Health Organization, the U.S. Centres for Disease Control and Prevention, and other agencies have described the rapid spread of antimicrobial resistance as one of the most serious public health threats now facing the world, a looming medical catastrophe that could outweigh the chaos created by the COVID-19 pandemic.

“While previous studies have scanned travellers’ stool samples for well-known antimicrobial resistant bacteria, we used a combination of whole metagenome shotgun sequencing and functional metagenomics to identify both known and novel genes that code for antimicrobial resistance,” Gautam Dantas, PhD, a professor of pathology & immunology at Washington University said.

Equally concerning, the study’s results confirmed that 56 unique antimicrobial resistance genes had become part of the travellers’ gut microbiomes during their trips abroad, including several mobile, high-risk resistance genes.

While bacteria may slowly evolve resistance from repeated exposures to antibiotics over time, diverse bacterial communities also share antimicrobial resistance genes through a more rapid process known as horizontal transfer, usually via the exchange of mobile genetic elements that allow snippets of DNA to jump from one bacterium to another.

“Since genes that code for resistance to different classes of antibiotics are often located on the same mobile elements, a single horizontal exchange has the potential to convert bacteria previously susceptible to antibiotics into a multi-drug resistant organism,” said Dantas.

He added: “Identifying new antimicrobial resistant bacteria and genes could play an important role in slowing the global spread of resistance and guide potential treatments for related diseases. Our study lays the groundwork for those efforts by offering new insight into the genetic mechanisms that underlie the rapid acquisition and sharing of antimicrobial resistance genes across people’s gut microbiomes during international travel.”