I trust you are enjoying a well-deserved summer break or packing your bags to take off. In case you missed this paper in the daily list of new ones on biorxiv, it tells you where to swim safely and where not. Elena Buelow, from Germany, a former PhD student in our lab in Utrecht and now post-doc in Limoges, France, reported. So, if you are floating quietly in a pittoresque small river and you see a hospital building on the hill near the next bend in the river, are you still in safe waters?

Elenas’ study is a nice follow-up of a much smaller study she did in the Netherlands (as such, l’histoire se repète en France). We all know, that human activity impacts the terrestrial and aquatic microbial ecosystems through chemical pollutants that are spread via urban, agricultural and industrial waste and that these may pose an important selective pressure for antimicrobial resistance. For instance, urban and hospital wastewaters (UWW and HWW) contain Antibiotic Resistance Genes (ARG), chemicals and other stuff, and that is why “clean” it in wastewater treatment plants (WWTP) before it reaches the environment (being the river in which we float and from which we drink).

The study nicely demonstrates that hospital waste and urban waste have very stable and markedly different resistomes and microbiomes. They are so different that even a “learned machine” could reliably predict where waste water came from. The hospital waste water resistome is loaded with ARGs (and Mobile Genetic Elements (MGEs)) for those antibiotics that are frequently used in hospitals: beta-lactams, quinolones, vancomycin and aminoglycosides. In fact, that “water” also contained high concentrations of ciprofloxacin, sulfamethoxazole and vancomycin. The qnr genes encoding quinolone resistance had the highest increase (161-fold) between HWW and UWW. These genes mainly reside in Enterobacteriales and the quantity of those species was also higher in HWW than in UWW.  ARGs for macrolides were more prevalent in urban waste water (and they are hardly used in French hospitals).

The good news is that waste water cleaning leads to a marked dilution of ARGs, as does the mixing of HWW and UWW. In fact, the river levels of ARGs, MGEs and microbiome markers (human gut bacteria) are comparable to treated UWW, and not measurably impacted by the HWW after treatment in the plant. So, if you plan to go floating in the Haute-Savoie (where the study was done) relax and keep on floating. In any other place in the world with rivers and hospitals, carefully check the local waste water plant map first. Enjoy.