Since their discovery, antibiotics have saved millions of lives in the struggle against infectious diseases such as tuberculosis, pneumonia or meningitis.
Over the decades, the bacteria have mutated to resist them, and the phenomenon has become very worrying because of the intensive use of antibiotics, both in the field of public health and in the livestock sectors and agriculture.
” We are now at risk of a post-antibiotic era in which common infections and small wounds will be deadly again,”
the World Health Organization (WHO) warned last November.
Treatment plants, hot spots of dissemination
Several studies have highlighted the role of treatment plants in the spread of resistant bacteria in the environment.
Wastewater is, in fact, particularly loaded with urine and human waste is also packed with antibiotics. One question remains unresolved: do these bacteria become resistant, once in the wild, when exposed to low doses of antibiotics? Or are they already resistant when they come out of the intestines? The stakes are high because if resistance genes appear.
It means that new mechanisms of antimicrobial resistance, different from those known in intestinal bacteria, are likely to emerge.
The second hypothesis seems to be the right one, according to a Swedish study published January 8 in the journal Nature Communication. The researchers show that the amount of anti-resistant bacteria is closely correlated with the presence of crAssphage, a bacteriophage only present in the waste of human origin.
Which does not seem to develop outside the intestines? The other resistance genes detected are also all related to those found in humans.
The only notable exception is wastewater from antibiotic factories. In this case, the quantities of antibiotics released in nature are sufficiently significant for the bacteria to develop their resistance genes in the environment by natural selection.
Genetic crossings between fecal bacteria and biological wastewater treatment bacteria
These conclusions, which seem reassuring concerning the risk of new forms of antimicrobial resistance, are in contradiction with those of another study conducted last December by Eawag (Swiss Federal Institute for Water Science and Technology).
In it, the researchers explain that an increase in antimicrobial resistance accompanies the passage in the treatment plant. ” If 70% of the resistance genes arriving at the station with the wastewater are removed by treatment, others partially replace them.
“Nearly 40% of the resistance genes detected at the exit probably come from activated sludge,”