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Travelers abroad can catch bacteria and other vectors containing genes conferring resistance to antimicrobials that remain in the gut when they return to their home country, according to a study published in Genome medicine.
A team of researchers from the University of Washington, USA and Maastricht University, the Netherlands, studied the presence of antimicrobial resistance (AMR) genes in the human gut microbiome by analyzing samples faeces from 190 Dutch travelers before and after their trip to destinations in North Africa, East Africa, South Asia and South East Asia. The gut microbiome consists of bacteria and other organisms that live in the digestive tract of humans. The participants and their samples were taken from a larger COMBAT study subset of data that also focused on antimicrobial resistance. Antimicrobial resistance genes have developed naturally in bacteria over millennia when exposed to antibiotics produced naturally by a few environmental bacteria, but the overuse and misuse of antibiotics in human medicine and animal agriculture is accelerating the process. Antimicrobial resistant bacteria do not respond to treatment with antibiotics to which they have developed resistance.
The authors found an increase in the amount and diversity of AMR genes in fecal samples from returning travelers, including high-risk AMR genes resistant to common and last-resort antibiotics ( antibiotics used when other antibiotics do not work). ).
The authors used fecal microbiome metagenome sequencing to identify AMR genes in samples by matching them to a database of known AMR genes. They also identified new genes for antimicrobial resistance by testing whether the genes in the samples, when added to an E. coli host, would allow those E. coli to acquire new resistance to antibiotics.
The diversity of AMR genes in the microbiome has increased dramatically in individuals returning from all destinations, with evidence of 56 different AMR genes acquired during travel. This diversity was highest among those who went to Southeast Asia. Genetic diversity in AMR was lower between travelers who traveled to the same destination, meaning they had more AMR genes in common with each other than with travelers from different destinations. This indicates that travelers have retrieved destination-specific RAM genes.
Extensive genetic analysis has identified high-risk antimicrobial resistance genes that are resistant to common and last-resort antibiotics. Six of the ten high-risk genes identified were present after the trip but not before, indicating that they were acquired during the trip. For example, the mcr-1 gene, which confers resistance to colistin, a treatment of last resort for infections such as pneumonia and meningitis, has only been found in samples after travel. The gene was found primarily in the microbiome of travelers in Southeast Asia; 18 of the 52 travelers (34.6%) included in the study who traveled to destinations in the region carried the gene on their return. The discovery indicates that travelers may have acquired the gene at their destination.
Fecal microbiome samples taken before the trip also contained AMR genes, and the authors acknowledge that it is possible that the travelers also spread AMR genes to the destinations they visited. The authors did not have samples of the contacts that the travelers interacted with, so they cannot be certain how the travelers acquired the AMR genes.
Lead author Alaric D’Souza said: “These findings strongly support that international travel risks spreading antimicrobial resistance globally. Upon their return, the travelers’ microbiomes had acquired a significant amount of antimicrobial resistance genes. Many of these genes were high risk antimicrobial resistance genes because they confer resistance to commonly used antibiotics. “
The authors conclude that understanding how AMR genes spread across countries will help target public health measures to prevent further spread. Future research could study the contacts that travelers interact with during their visits to understand how antimicrobial resistance genes are transmitted.
D’Souza said, “It is vital that we tackle antimicrobial resistance in low income countries with high rates of resistance and low public health funding. This comprehensive approach can not only help the respective countries, but it could also benefit others by reducing the international spread of resistance genes. “
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