Introduction
Escherichia coli is one of the most important bacteria in animal production, showing great genotypic and pathogenic variability. Some strains are innocuous, and others can compromise animal and human health. Seven groups are included among the diarrheagenic E. coli : i) enteropathogenic (EPEC); ii) enteroinvasive (EIEC); iii) enterotoxigenic (ETEC); iv) enterohemorrhagic (EHEC); v) enteroaggregative (EAEC); vi) diffusely adherent (DAEC); and vii) adherent invasive (AIEC) [1].
Among the groups mentioned above, the ETEC strains stand out as one of the main causes of diarrhea, with pathogenic mechanisms that involve adhesion in the small intestine through colonization factors (mainly fimbriae and adhesins), and the production of toxins that affect intestinal homeostasis [2,3].
Within animal production, ETEC strains are of prime importance in swine production. They are mainly responsible for neonatal diarrhea, characterized by watery diarrhea, dehydration, electrolyte imbalance, apathy, and death. Different degrees of pathogenicity are found according to the type of fimbria expressed by the strains (mainly F4, F5, F6, F7, or F18). Of these, ETEC strains that express F4 fimbriae are more frequent and have a higher mortality rate[4].
Several strategies are used to prevent neonatal diarrhea, such as the vaccination of pregnant females for transfer of passive immunity via breastfeeding, or even the vaccination of the piglets themselves[5]. The use of antibiotics is also a common and widely used practice, but if used incorrectly it can lead to antimicrobial resistance, which is currently much discussed as it involves public health concerns [6].
Several alternatives are being developed to control diarrhea, especially lactic acid bacteria (LAB), widely used as probiotics and/or bioprotective agents, through competitive exclusion or production of antimicrobial substances, inhibiting the development of pathogens[7–9]. For example, studies have demonstrated that LAB isolated from cocoa (Theobroma cacao ) fermentation have inhibitory potential against Salmonella Typhimurium[10]. These studies corroborate the effective application of LAB against intestinal pathogens. Considering the principles of animal welfare and rational use of animals in research, preliminary laboratory in vitro tests that provide guidelines forin vivo research are required.
Thus, this study aims to evaluate the in vitro bioprotective potential of LAB isolated from fine cocoa fermentation, and their metabolites, against ETEC strains producing F4 fimbriae through cell culture and microbiological analysis, in order to support their application in feed for the realization of future in vivostudies.