[LUM#16] When the city puts pressure on

[LUM Magazine, Podcast] - Published on September 1, 2022 in Science-Society

All ecosystems bear the mark of human activity, and the bacterial communities in our rivers are no exception. Researchers have observed the presence of antibiotic-resistant bacteria in waterways that flow through cities. This "urban pressure" has been particularly evident in the Lez River in Montpellier.

They are naturally present in their millions in our rivers, representing an essential link in the aquatic ecosystem: bacteria. And they too are impacted by human activities, as shown by the work of Patricia Licznar-Fajardo. The researcher from the Hydrosciences Montpellier* laboratory studied the bacterial communities of the Lez, Verdanson, and Font d'Aurelle rivers, which flow through the Montpellier metropolitan area. "We were able to follow the entire continuum from the karstic source of the Lez to the lagoons, which allowed us to assess the impact of the urban environment on the bacterial communities in these rivers, " explains the specialist.

Shuttle

Together with her colleagues, she has been researching emerging antibiotic resistance . "We have shown that many indigenous bacteria, i.e., those naturally present in water, are antibiotic-resistant." How did they acquire this ability? While most waterborne bacteria naturally possess this ability, some forms of resistance are directly linked to human activities. "Initially, resistance is often acquired in the digestive microbiota of patients undergoing antibiotic treatment. These 'human' bacteria then become resistant and are eliminated in feces, with some ending up in the natural environment, " explains Patricia Licznar-Fajardo.

There, they will encounter bacteria that are naturally present in rivers. "These organisms are capable of exchanging genes with each other, so bacteria released into the water by humans can transfer the gene that gives them this resistance to native bacteria, which could then transfer it onward. We say that they act as a shuttle," explains Patricia Licznar-Fajardo.

One health

Researchers found more resistant and even multi-resistant bacteria in urban areas and downstream from the city than at the source. "We also observed variations in the composition of communities along the continuum, with an increase in human and potentially pathogenic bacteria, " adds the specialist. The causes? Urban runoff, wastewater, overflows linked to heavy rainfall, human activities, hospital activities, etc. "The city has a significant impact on bacterial communities and their resistance. In particular, we found greater resistance downstream from the hospital, " notes the researcher.

These findings are all the more worrying given that this phenomenon represents a major public health issue. "We need to take greater account of the role of the environment in antibiotic resistance. That is the whole point of the One Health approach, which considers human, animal, and environmental health as a single entity, " concludes Patricia Licznar-Fajardo.

* HSM (UM – CNRS – IRD)

Keywords: water, Environment, LUM#16, LumLu, Research, Health, Company