Estudi de la prevalença d’Escherichia coli adherent-invasiva (AIEC) en l’aigua residual de la ciutat de Girona

Abstract

The adherent-invasive Escherichia coli (AIEC) pathotype is closely associated with

inflammatory bowel diseases, such as Crohn’s disease. It is characterized by its ability

to adhere and invade intestinal epithelial cells, triggering an inflammatory response, as

well as its capacity to survive and replicate within macrophages, thereby evading

immune defenses.

In this study, we analyzed the presence and survival of AIEC in the wastewater of the

city of Girona (Campdorà wastewater treatment plant) in order to assess whether this

pathotype can be detected in wastewater as a first step toward conducting

epidemiological studies of Crohn’s disease through wastewater monitoring. In addition,

we evaluated the role of protozoa inhabiting the plant’s reactors as potential reservoirs

for AIEC.

We observed an increase in the proportion of potential AIEC strains in the plant’s effluent

(9.98%) compared to the influent water (5.35%). This finding contrasts with the overall

decrease in E. coli concentration between the two samples (6×104 CFU/mL at the inlet

versus 1.01×102 CFU/mL at the outlet), suggesting that AIEC strains may possess

resistance or protection mechanisms against the plant’s treatment processes.

Moreover, the presence of protozoa in the activated sludge raises the hypothesis that

AIEC could survive inside these microorganisms, similarly to how they survive within

human macrophages. Therefore, we examined the protozoan population in the sludge

and validated a protocol to isolate E. coli from within them. Finally, using an intestinal cell

assay, we assessed whether the intracellular isolates exhibited the adherent-invasive

phenotype. Although only one of the endosymbiotic E. coli isolates was identified as

AIEC, its detection opens new research avenues into the survival of AIEC pathotypes

within protozoa.

While it is still too early to definitively state that the AIEC pathotype is detectable in

wastewater, our results represent a starting point for future wastewater-based

epidemiological studies aimed at determining the community prevalence of these AIEC

strains, similar to what has been done with other pathogens (e.g., SARS-CoV-2). In any

case, the results suggest that wastewater treatment plants could act as reservoirs or

selection points for pathogenic and resistant strains, with broad environmental and public

health implications

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