ANTIMICROBIAL RESISTANCE: E. COLI UNDER THE LENS ACROSS ENVIRONMENT, ANIMALS AND HUMANS

A study carried out by the Istituto Zooprofilattico Sperimentale of Abruzzo and Molise, in collaboration with the Clinical Pathology and Microbiology Unit of Teramo Hospital, has examined the presence of antibiotic-resistant strains of Escherichia coli in different settings and species. In their scientific paper, published in Frontiers in Microbiology, the researchers focused on those strains that produce enzymes known as extended-spectrum beta-lactamases (ESBLs), which render some commonly used antibiotics ineffective in both human and veterinary medicine.

Drawing on analyses of almost one thousand samples collected in the Abruzzo region, the study employed advanced genomic tools to identify resistance genes and to better understand how they spread across environments and species, including farm animals, wildlife, pets, food and human patients.

“We found a significant presence of resistant strains both in livestock and companion animals, as well as in the environment - says Lisa Di Marcantonio, Bacteriology and Bacterial Antigen Development, IZS Teramo - while cases in wild animals were less frequent. This kind of comparison helps us to understand how human activities can influence the spread of resistance.”

The analyses indicate that resistant strains are more common in contexts closer to humans. In companion animals, for instance, the presence exceeds 16%, while in wild animals it is below 7%. This difference may be linked to two main factors: on the one hand, the direct use of antibiotics in pets and livestock, which can select increasingly resistant bacterial strains; on the other, the indirect spread of these bacteria through wastewater, contaminated soil or food. In other words, urban and agricultural environments appear to be more favourable to the circulation of resistance than natural habitats.

The study also found that some resistance genes, such as blaCTX-M-15 and blaCTX-M-1, tend to recur in specific host groups, suggesting possible adaptation to particular environments. However, the presence of these genes in very different strains also points to the key role of horizontal transfer - the direct exchange of genes between bacteria. This transfer takes place through molecular structures able to “carry” genetic information between microorganisms. Plasmids and other mobile genetic elements are fragments of DNA that bacteria can swap, even across species. This “genetic word of mouth” allows resistance genes to spread rapidly, making the problem harder to trace and control, as it involves entire bacterial populations across different environments rather than isolated strains.

“To combat resistance we cannot restrict our view to single cases - says Anna Janowicz, Bacteriology and Bacterial Antigen Development, IZS Teramo - we need to take into account the whole system: humans, farms, pets, wildlife, food and the environment.”

What emerges most strongly from this survey is the importance of an integrated approach to understand and counteract the spread of antibiotic resistance. The One Health perspective, which links human, animal and environmental health, proves once again to be an essential framework for addressing such a complex phenomenon, cutting across disciplinary and ecological boundaries.