Abstract
BackgroundInternational travel contributes to the spread of antibiotic resistant bacteria over the world. Most studies addressing travel-related changes in the faecal flora have focused on specific mobile resistance genes, or depended on culturing of individual bacterial isolates. Antibiotic resistance can, however, also spread via travellers colonized by bacteria carrying chromosomal antibiotic resistance mutations, but this has received little attention so far. Here we aimed at exploring the abundance of chromosomal quinolone resistance mutations in Escherichia communities residing in the gut of Swedish travellers, and to determine potential changes after visiting India. Sweden is a country with a comparably low degree of quinolone use and quinolone resistance, whereas the opposite is true for India.MethodsMassively parallel amplicon sequencing targeting the quinolone-resistance determining region of gyrA and parC was applied to total DNA extracted from faecal samples. Paired samples were collected from 12 Swedish medical students before and after a 4–15 week visit to India. Twelve Indian residents were included for additional comparisons. Methods known resistance mutations were common in Swedes before travel as well as in Indians, with a trend for all mutations to be more common in the Indian sub group. There was a significant increase in the abundance of the most common amino acid substitution in GyrA (S83L, from 44 to 72 %, p = 0.036) in the samples collected after return to Sweden. No other substitution, including others commonly associated with quinolone resistance (D87N in GyrA, S80I in ParC) changed significantly. The number of distinct genotypes encoded in each traveller was significantly reduced after their visit to India for both GyrA (p = 0.0020) and ParC (p = 0.0051), indicating a reduced genetic diversity, similar to that found in the Indians.ConclusionsInternational travel can alter the composition of the Escherichia communities in the faecal flora, favouring bacteria carrying certain resistance mutations, and, thereby, contributes to the global spread of antibiotic resistance. A high abundance of specific mutations in Swedish travellers before visiting India is consistent with the hypothesis that these mutation have no fitness cost even in the absence of an antibiotic selection pressure.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-015-0574-6) contains supplementary material, which is available to authorized users.
Highlights
International travel contributes to the spread of antibiotic resistant bacteria over the world
After discarding reads that were too dissimilar from Escherichia and Shigella reference sequences, 53 % of the reads aligned to gyrA remained for further analysis, and 96 % of the reads aligned to parC (Additional file 1: Table S1)
There was a significant increase (0.28 increase in relative abundance, p = 0.036) in the abundance of the most commonly detected substitution, S83L, when comparing the Swedish samples collected before travel to India to the samples taken after return to Sweden (Fig. 2)
Summary
International travel contributes to the spread of antibiotic resistant bacteria over the world. International travel has been identified as one of the facilitators of the global spread of resistant bacteria, together with, e.g., trade and migration [1, 2]. The gene aac(6′)-lb-cr was only detected in isolates that possessed chromosomal mutations, and none of the studied isolates carried qnrA These results underline that chromosomal mutations in gyrA and parC are the main causes of clinical resistance to fluoroquinolones
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