Avaliação do efeito protetor de Lactococcus lactis 4U em cultura fresca, liofilizada e seca em spray dryer em modelo murino de febre tifoide

Abstract

Typhoid fever causes mortality and morbidity worldwide. Within this issue, probiotics have emerged as a potential prophylactic option or as adjuvants in treatment. Lactic acid bacteria, widely used in dairy products, are commonly employed as probiotics, which are known as live microorganisms that, when administered in adequate amounts, confer a health benefit to the host. This study aimed to evaluate the potential probiotic mechanisms of action of the Lactococcus lactis 4U strain in a murine model of experimental infection with Salmonella enterica subsp. enterica serovar Typhimurium ATCC (14028). For this purpose, a murine infection model of S. Typhimurium, which mimics human typhoid fever, was used. A survival assay was conducted to monitor the animals weight variation, along with an assay to verify protective action mechanisms after pathogen challenge. In both assays, Balb/c mice received daily oral administration of the L. lactis 4U strain before and after the challenge. In the second assay, additional evaluations included bacterial translocation, histopathological lesions, myeloperoxidase (MPO) enzymatic activity, and the relative expression of pro and anti-inflammatory cytokine-coding genes. Oral administration of the L. lactis 4U strain (fresh, lyophilized, or spray-dried) resulted in stable weight gain and survival rates of 66.67% for 4U fresh + ST, 41.67% for 4U lyophilized + ST, and 75% for 4U spray + ST. Translocation of S. Typhimurium to the spleen and liver was observed in all experimental groups, with a colonization of 10⁵ CFU/g. Histopathological analysis showed normal levels and preservation of the ileum in the L. lactis 4U control and experimental groups, along with a reduction in liver microabscesses. MPO levels were higher in the liver for all groups except the L. lactis 4U control. The tested genes showed cytokine level regulation, highlighting the inflammatory process. It was concluded that the Lactococcus lactis 4U strain is safe, maintaining cell viability for administration in fresh, lyophilized, and spray-dried forms. It contributed to a higher survival rate, did not translocate, and helped preserve intestinal barrier integrity.