Lacticaseibacillus paracasei subsp. paracasei Q- 1 Exhibits Good Safety and Effectively Prevents Escherichia coli K99-Induced Diarrhea in Mice.

Escherichia is a common pathogen causing diarrhea in livestock and poultry, posing a serious threat to intestinal health and leading to significant economic losses in the animal husbandry industry. While antibiotics have been used to treat Escherichia coli diarrhea, their numerous drawbacks have led to increasing attention on probiotic interventions. In this study, Lacticaseibacillus paracasei subsp. paracasei Q-1 (L. paracasei subsp. paracasei Q-1) was isolated from fresh cow dung, and its in vitro and in vivo safety and probiotic properties were evaluated. In vitro experiments demonstrated that L. paracasei subsp. paracasei Q-1 exhibited good antimicrobial activity against Escherichia coli K99, along with key probiotic characteristics such as acid production, acid and bile salt tolerance, high-temperature resistance, hydrophobicity, and cell adhesion. Furthermore, it showed no hemolytic activity, gelatinase activity, or mucin-degrading activity, and it only exhibited decarboxylase activity for histamine. While resistant to certain antibiotics, no significant resistance genes were detected, indicating favorable probiotic and safety profiles. In vivo, acute toxicity tests in mice revealed no signs of acute poisoning after 14 days of high-dose oral administration. A 28-day oral toxicity test showed that different doses did not affect organ indices, cause bacterial translocation, alter blood biochemical parameters, or damage the ileum. In the infection protection experiment, oral administration of L. paracasei subsp. paracasei Q-1 significantly increased the survival rate of Escherichia coli K99-infected mice from 50 to 80%. In conclusion, L. paracasei subsp. paracasei Q-1 demonstrated excellent safety and probiotic properties both in vitro and in vivo and showed promising potential in preventing Escherichia coli K99 infections, with possible applications in animal health management.