Lactobacillus paracasei LCQ-1 Exhibits Good Safety and Effectively Prevents Escherichia coli K99-Induced Diarrhea in Mice

Escherichia coli 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, Lactobacillus paracasei LCQ-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 Lactobacillus paracasei LCQ-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 Lactobacillus paracasei LCQ-1 significantly increased the survival rate of Escherichia coli K99-infected mice from 50–80%. In conclusion, Lactobacillus paracasei LCQ-1 demonstrated excellent safety and probiotic properties both in vitro and in vivo, and shows promising potential in preventing and treating Escherichia coli K99 infections, with possible applications in animal health management.