Moving from a rural to a industrialized country may lead to an immediate and substantial increase in antibiotic resistance genes among immigrants, according to study results published in Clinical Infectious Diseases. The researchers found that women from 2 independent ethnic groups relocating from Thailand to the United States had a rapid increase in gut microbiome antibiotic resistance genes. 

A dataset of deep shotgun metagenomic DNA sequencing samples were used in this study. Samples originated from Hmong, Thailand (n=15), newly arrived Karen individuals (n=5) with samples collected 1 month before arrival in the US and approximately 6 months post-arrival), long-term (>30 years) US residents from Hmong (n=15), and healthy European American women who served as US controls (n=15).

Results of Principle Coordinate Analysis clearly showed that gut antibiotic resistance gene profiles clustered into 2 groups according to country of residency, rather than ethnic group (Adonis test R2=0.265; P =.001). Comparisons with healthy European American women found that immigrants who were long-term US residents were more similar to European American controls than to non-US residents (P <.001).

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Alpha diversity measures of fecal samples revealed significant difference between individuals living in Thailand and immigrants who were long-term US residents based on Shannon index of antibiotic resistance gene profiles (Mann-Whitney U-test, P =.006) and number of observed antibiotic resistance genes (ARG subtypes, Mann-Whitney U-test; P =.04). Of Hmong residents, 45% carried at least 1 antibiotic resistance gene, but 80% of immigrants who were long-term US residents from Hmong carried at least 1 antibiotic resistance gene in their gut (two-proportions z-test, P =.05). An extension of the analysis to the longitudinal cohort in an independent ethnic group, the Karen samples, showed a rapid increase in diversity and richness of antibiotic resistance gene between samples from this group collected before arrival and 6-months post-arrival.

The top 3 dominant antibiotic resistance gene subtypes in women from Hmong were tetracycline tetQ, beta−lactam CfxA2, and tetracycline tet37. In long-term US residents from Hmong, the top 3 were tetracycline tetQ, tetO and tetW. The differences in antibiotic resistance gene abundances between these groups were identified using Lefse, which found highly discriminative changes in 23 antibiotic resistance gene subtypes, all increased in long-term US residents, with a linear discriminant analysis score (log10) over an absolute value of 2, which represents a large size effect. The long-term US residents harbored gut resistomes with increased vancomycin (vanD, vanG, vanU, vanR, vanY), tetracycline (tet40, tetM, tetO, tetS, tetW), macrolide lincosamide streptogramin (ermF, macB, lsa), beta lactam classA, multidrug (mexB, cmeB, multidrug ABC transporter), aminoglycoside (aadE), bacitracin (bacA, bcrA), chloramphenicol and fosmidomycin antibiotic resistance genes.

There were also substantial differences in 41 antibiotic resistance gene subtypes when comparing longitudinal samples collected form Karen individuals 1-month pre- and 6-months post-arrival (Mann-Whitney U-test, False Discovery Rate corrected P <.10). After arrival these samples had increased beta-lactam, tetracycline, vancomycin, macrolide lincosamide streptogramin, aminoglycoside, and multidrug antibiotic resistance gene subtypes.

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The study was limited by the absence of a control group for antibiotic use upon arrival to the US. The exclusion criteria for participants included no antibiotic use within the previous 6 months, which would cover the short-term Karen individuals’ residence in the US. Also, investigators could not adequately evaluate antibiotic use in Thailand, where unregulated use may be problematic.

Investigators concluded that the overall findings suggest that moving to a modern industrialized country may lead to an immediate and substantial increase in antibiotic resistance genes. They recommend further investigations of this given the “looming global antimicrobial resistance crisis and increasing rates of global migration.”


Le Bastard Q, Vangay P, Batard E, Knights D, Montassier E. US immigration is associated with rapid and persistent acquisition of antibiotic resistance genes in the gut [published online November 4 2019]. Clin Infect Dis. doi:10.1093/cid/ciz1087

This article originally appeared on Infectious Disease Advisor