Photo Credit- CDC
The global spread of drug resistant pathogens has been a major topic of concern for years, but really gained prominence 3 and a half years ago when The Lancet published a study (see NDM-1: A New Acronym To Memorize) by Walsh, Toleman, Livermore, et al. that awakened the world to the emergence and growing prevalence of the NDM-1 (New Delhi metallo-β-lactamase) enzyme.
Widely found on the Indian sub-continent, but increasingly found around the globe, this enzyme can make many types of bacteria resistant to a wide spectrum of antibiotics.
Of particular concern, this enzyme (and others like it) can be carried by a plasmid – a snippet of portable DNA - that can be horizontally transferred to other types of bacteria (see Study: Adaptation Of Plasmids To New Bacterial Species), conveying resistance to them as well.
Six months after the first Lancet article - in April, 2011 - the same researchers published another study that found the NDM-1 enzyme in 4% of New Delhi’s sampled drinking water sources, and 30 per cent of the sewage tested. Most alarmingly, the researchers also identified 11 new species of bacteria carrying the NDM-1 gene, including strains which cause cholera and dysentery.
Since then we’ve seen the number and variety of these resistance-conveying enzymes increase, including the relatively recent arrivals of NDM-2, NDM-4, and NDM-5.
The constellation of Extended-spectrum beta-lactamases (ESBL) and Carbapenemase-resistant bacteria continues to expand, driven by these horizontally transferable genes which can be carried by both pathogenic and non-pathogenic bacteria (such as normal microflora found in our gut and on our skin).
Which means these genes can be easily picked up from the environment – and transported stealthily around the globe via international travel.
All of which serves as prelude to a study that appeared yesterday in the CDC’s EID Journal where researchers in the Netherlands tested 122 healthy travelers both before and after making an international trip for evidence that they carried one of (several) antimicrobial resistance-inducing genes.
They found a high rate of resistance genes in the commensal gut bacteria of returning travelers – particularly those visiting Southeast Asia and the Indian subcontinent .
While the risks are currently difficult to quantify, it points out that you don’t have to `pick up an infection’, or otherwise fall ill, in order to bring a resistance gene back home with you from your travels.
I’ve only excerpted the abstract and a small portion from the discussion, follow the link below to read the study in its entirety.
Author affiliations: Maastricht University Medical Center, Maastricht, the Netherlands (C.J.H. von Wintersdorff, J. Penders, E.E. Stobberingh, A.M.L. Oude Lashof, C.J.P.A. Hoebe, P. Savelkoul, P.H.M. Wolffs); South Limburg Public Health Service, Geleen, the Netherlands (C.J.P.A. Hoebe)
We investigated the effect of international travel on the gut resistome of 122 healthy travelers from the Netherlands by using a targeted metagenomic approach. Our results confirm high acquisition rates of the extended-spectrum β-lactamase encoding gene blaCTX-M, documenting a rise in prevalence from 9.0% before travel to 33.6% after travel (p<0.001). The prevalence of quinolone resistance encoding genes qnrB and qnrS increased from 6.6% and 8.2% before travel to 36.9% and 55.7% after travel, respectively (both p<0.001).
Travel to Southeast Asia and the Indian subcontinent was associated with the highest acquisition rates of qnrS and both blaCTX-M and qnrS, respectively. Investigation of the associations between the acquisitions of the blaCTX-M and qnr genes showed that acquisition of a blaCTX-M gene was not associated with that of a qnrB (p = 0.305) or qnrS (p = 0.080) gene. These findings support the increasing evidence that travelers contribute to the spread of antimicrobial drug resistance.
During our investigation of several targeted resistance genes, it became evident that resistance genes from foreign environments are being introduced into the gut resistome at high rates related to international travel. Although the consequences of these changes in the resistome are difficult to predict, the introduction of these genes into the genetic pool of resistance elements may create opportunities for the horizontal transfer to other organisms in the gut microbiota.
Our study data demonstrated an increasing prevalence of blaCTX-M, qnrB, and qnrS genes in the feces of healthy volunteers from the Netherlands immediately after they returned from international travel. These findings contribute to the increasing evidence that travelers contribute to the spread of antimicrobial drug resistance.
For more on the global spread of infectious disease, and the growing problem of antibiotic resistance, you may wish to revisit: