London, Aug 21 (IANS): Even travelling, not just overuse of antibiotic, can make people vulnerable to antibiotic resistance if they eat contaminated food and water containing resistant bacteria, says a new study.

The researchers found that Swedish exchange students who studied in India and in central Africa returned from their sojourns with an increased diversity of antibiotic resistance genes in their gut microbiomes even though none of the students took antibiotics either before or during travel.

These resistance genes were not particularly abundant in the students prior to their travels, but the increases are nonetheless quite significant.

The increase seen in resistance genes could have resulted from ingesting food containing resistant bacteria, or from contaminated water, the investigators wrote.

"We asked students going abroad on exchange programmes to provide a sample of their feces before and after travelling," said one of the researchers Anders Johansson from Umea University in Sweden.

The use of metagenomics sequencing, a modern method, enabled the investigators to sample the entire microbiome of each student, and to sequence every resistance gene therein, rather than focusing on resistance genes in those few bacterial species that grow well on culture plates.

The researchers found a 2.6-fold increase in genes encoding resistance to sulfonamide, a 7.7-fold increase in trimethoprim resistance genes, and a 2.6-fold increase in resistance to beta-lactams -- all of this without any exposure to antibiotics among the 35 exchange students.

The research was published in the journal Antimicrobial Agents and Chemotherapy.