International travellers pick up ‘worrisome’ genes that promote microbial resistance, study says

New superbug genes which promote resistance to antimicrobial drugs are being picked up and spread by international travellers, according to a new study.

Scientists examined bacteria carried in the guts of tourists who returned from disease hotspots in southeastern Asia, south Asia, north Africa and east Africa.

Their findings appeared to confirm that global travel was contributing to the increase in antimicrobial resistance – but it also raised concerns about completely novel genes which could help spread potentially deadly superbugs.

"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, co-author of the study published in Genome Medicine.

"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."

The World Health Organisation has described the rapid spread of antimicrobial resistance as one of the most serious public health threats now facing the world and a looming medical catastrophe that could outweigh the chaos created by the Covid-19 pandemic.

Tourists can pick up gut bacteria through exposure to contaminated drinking water and food as well as poorly-cleaned restrooms, restaurants, hotel rooms and public transportation. On their return home they could then transfer them to family, friends and other members of the community.

For the study, researchers analysed bacterial communities in the gut microbiomes of 190 Dutch adults both before and after travel.

The research, conducted with Maastricht University in the Netherlands, also looked at stool samples randomly selected from about 2,000 Dutch travellers.

"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," said Mr D'Souza, a Phd student at Washington University.

"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 travelers.

"Though our study was unable to demonstrate resistance genes are carried by pathogenic bacteria, it's clear that this is possible.

"Additionally, international travelers have the potential to introduce resistance genes into their own communities when they return home, and future studies directly addressing this possibility are a priority."

The researchers detected a total 121 antimicrobial resistance genes across the gut microbiomes of the 190 Dutch travelers, including several mobile, high-risk resistance genes such as extended-spectrum β-lactamases (ESBL) and mcr-1.

Resistance to beta-lactam antibiotics protects bacteria from treatment with penicillin and other important antibiotics while mcr-1 genes guard against a antimicrobial drug called colistin, which is the last-resort treatment for infections by multidrug-resistant gram-negative bacteria.

The US Centre for Disease Control has warned that if colistin resistance spreads to bacteria that are resistant to other antibiotics it could result in truly untreatable infections.

Gautam Dantas, a professor of pathology and immunology at Washington University, said: "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."