Hotter Water, Less Superbugs

Antimicrobial resistance genes (ARGs) from wastewater can end up in natural biofilms in rivers, but they may not stick around very long. In a new research in mSphere, researchers report that after ARGs are introduced to a river they invade and initially join natural biofilms.

As river temperature rises, the prevalence of these introduced ARGs diminishes notably, indicating that the existing microbial community outcompetes the resistant newcomers. At 30°C (86°F), ARG levels reverted to baseline within just 2 weeks.

This discovery implies that rivers could serve as a natural barrier against disseminating ARGs from wastewater, contrary to the researchers' initial assumptions. Typically originating from human feces, most ARGs flourish at body temperature, which is higher than that of waterways. Microbiologists anticipated warm rivers to be conducive environments for ARG proliferation.

Klümper, Bagra, and their team initially submerged 27 glass slides in the Lockwitzbach River in eastern Germany for a month, noting its relatively pristine condition. Afterward, they retrieved the slides, now coated with natural biofilm, and immersed them into artificial river setups at three distinct temperatures. Following a week-long observation period, they noticed a rise in naturally occurring ARGs, particularly in the warmest water at 30°C.

Subsequently, all test slides were exposed to wastewater for a single day, and the team monitored ARG abundance—both natural and from wastewater—over the ensuing two weeks. The ARGs from the wastewater readily invaded the biofilm in all 3 cases, with no difference in abundance by temperature. 

However, the similarities ended there. In the warmest water, the abundance of invasive ARGs significantly decreased over two weeks. By the end of the experiment, the overall level of ARGs returned to its initial, natural abundance, and the invasive ARGs had nearly disappeared.

Klümper hopes the study will not only advance future research on how rivers might act as barriers to the spread of antimicrobial resistance but also enhance environmental surveillance of emerging risks.