Competitive exclusion strategies utilizing healthy caecal microbiota impair <i>Salmonella enterica</i> serovars colonization in broilers

Avian non-typhoidal <i>Salmonella</i> (NTS) is the second most prevalent foodborne zoonotic pathogen worldwide, which is transmitted through poultry products. Human-infecting serovars exhibit genotypic and phenotypic diversity, which affect bacterial virulence, such as susceptibility to antimicrobial drugs. The emergence of antimicrobial-resistant strains further reduces treatment efficacy, underscoring the need for alternatives in food-producing animals. One promising strategy is the use of competitive exclusion (CE) products, formulated with naturally occurring microorganisms derived from the gut microbiota of healthy adult birds. Although this approach has shown proven efficacy in controlling <i>Salmonella</i>, its application is still limited, primarily due to the incomplete understanding of the specific interactions among pathogen, host, and microbiota. Considering this scenario, we compared three CE products formulated under distinct conditions (aerobic, anaerobic, and a combination of both), being administered to newly hatched broiler chicks before challenging them with <i>Salmonella</i> Typhimurium (STM) or <i>Salmonella</i> Enteritidis (SE), evaluating faecal excretion and caecal colonization. Regarding caecal colonization, the combined formulation conferred the greatest reduction in STM-challenged birds, whereas the aerobic formulation conferred better reduction in SE-challenged birds. Bacterial adhesion factors, mainly associated with <i>Salmonella</i> Pathogenicity Island 10 (SPI-10), were also identified in the SE genome and may have contributed to the observed differences in outcomes. These findings suggest that CE products have the potential to aid in controlling <i>Salmonella</i> spp. in poultry production. Still, their effectiveness likely depends on pathogen virulence factors and the dynamics of the intestinal microbiota.