Avaliação das alterações histopatológicas pós desafio com Escherichia coli patotipo STEC/ETEC em bezerros tratados por via oral com biopolímero imunomodulador

Abstract

Biopolymers are molecules that come from living organisms. Beta-glucans are a group of biopolymers that are among the main structural components of the cell walls of fungi, yeast, plants and some bacteria. They are called biological response modifiers (BRM) and have an immunomodulatory action. The susceptibility of calves during the weaning period to infections puts the herd's health as well as human health at risk by becoming a reservoir of harmful agents. The frequent use of antibiotics leads to antimicrobial resistance and difficult infection control. The search for new products thatallow for less use of antibiotics brings benefits and positive economic and environmental impacts. This study aimed to evaluate the action of beta-glucan on the immune system of calves, observing histopathological changes in the organs after oral infection by STEC/ETEC. The experiment is a parallel clinical study design with 6 replications per treatment and a control group. Groups of suckling calves were administered four oral dose levels of beta-glucan for 28 days after which the animals were challenged with STEC/ETEC. On the fifth day after experimental infection, six animals from each treatment were sacrificed to collect tissues for histological analysis.Based on the changes found in the gastrointestinal tract, it can be stated that the dailyadministration of 12 mg/kg of live weight of beta-glucan to suckling calves was effectivein reducing the intensity of lesions caused by an infection induced with 1010 CFU of E.coli (STEC/ETEC). The mechanism by which this effect occurred has not been evaluated. However, based on scientific literature and findings of increased frequencyof microabscesses, this effect is attributed to stimulation of the immune system. On theother hand, animals that received higher daily doses of beta-glucan (i.e. 36, 60 and 84mg/kg of body weight) showed intensity of the lesions caused by an infection induced with 1010 CFU of E. coli (STEC/ETEC) similar to the control group. In comparison to treatment with group 1, the mechanism by which higher daily doses of beta-glucan result in a reduction in the capacity to respond to E. coli challenge has not been evaluated, however it is hypothesized that beta-glucan overdose generates an exacerbated immune response, which in together with E. coli increases tissue damage;or that the beta- glucan overdose induces a slight immunosuppression of the animals in groups 2, 3 and 4 in relation to the animals in group 1, equaling the response capacity of groups 2, 3 and 4 to the control group. Future studies using refined techniques for biological analysis of the production and gene expression of cytokines and immune response receptors such as TLR4, together with clinical and morphological data, will be able to explain and confirm the hypotheses discussed here.