Abstract
Simple SummaryCattle-yak milk is rich in numerous bioactive substances that function beyond their nutritive value. Given the high content of conjugated linoleic acid (CLA), this exponent suggests a potential role for cattle-yak milk in preventing cancer, heart disease, and metabolic disorders, such as diabetes. It is expected to isolate probiotic strains with natural and excellent characteristics in optimizing human health. However, little research data and much fewer studies on probiotics from cattle-yak milk are reported. Therefore, in the present study, the beneficial strains from cattle-yak milk were identified to evaluate probiotic characteristics of potential strains, and to screen potential probiotics with an emphasis on making better use of milk in such extreme climatic environments. These findings support the potential application of cattle-yak milk in human health, animal food processing, and drug production in the future as a potential candidate for probiotics.Cattle-yak milk is an important raw material and an indispensable source of high-quality food for local farmers and herdsmen to produce ghee, milk residue, yogurt, and other dairy products. In this study, Lactobacillus strains were isolated from cattle-yak milk for potential probiotic candidates using a series of in vitro tests, including probiotic characterization and safety evaluation (antibiotic susceptibility and hemolytic ability). The results found that the Lactobacillus rhamnosus CY12 strain showed a high survival rate in bile salts, under acid conditions, and in the gastrointestinal juice environment, as well as showing high antimicrobial activity and adhesive potential. The safety evaluation showed that all strains were considered non-hemolytic. In addition, the whole-genome sequencing indicated that the strain CY12 spanned 2,506,167 bp, with an average length of 881 bp; the GC content in the gene region (%) was 47.35, contained 1347 protein-coding sequences, and accounted for 85.72% of the genome. The genome annotation showed that genes mainly focused on the immune system process, metabolic process, carbohydrate utilization, carbon metabolism, galactose metabolism, and biological adhesion, etc. This study revealed that the Lactobacillus rhamnosus CY12 strain might be an excellent potential probiotic in the development of feed additives for animals and has the ability to promote health.
Highlights
In the past decades, antibiotic misuse and overuse in humans and livestock has led to the accelerated emergence of antibiotic-resistant organisms and the evolution of antibioticresistant strains, which have been serious risks to human security and animal health, as well as to the environment [1]
The results showed that CY12, CY2, and ATCC 7469 had higher antagonistic activity against pathogenic bacteria, including E. coli, S. aureus, S. typhii, and S. agalactis, than against other stains (p < 0.001)
We evaluated the antimicrobial susceptibility of seven selected strains using the disk diffusion method, and found that all studied strains were susceptible to antibiotics such as penicillin, chloramphenicol, erythrocin, tetracycline, ciprofloxacin, amoxicillin, ampicillin, and cefazolin, supporting most of the LAB strains exhibited sensitivity to tetracycline, penicillin, and chloramphenicol, indicating that lactic acid bacteria generally had low resistance to these antibiotics [13,31,45]
Summary
Antibiotic misuse and overuse in humans and livestock has led to the accelerated emergence of antibiotic-resistant organisms and the evolution of antibioticresistant strains, which have been serious risks to human security and animal health, as well as to the environment [1]. It is crucial to find an ideal substitute for antibiotics. The use of prebiotics as a second-generation substitute for antibiotics has been the hotspot in the research on animal nutrition. Probiotics are “living microorganisms with low or no pathogenicity, which exerts beneficial effects on the host health when ingested in sufficient amounts [2,3]”. As one of the most important bacterial groups in the food industry, the application of lactic acid bacteria (LAB) is considered to have beneficial effects on the health of animals and humans [4], such as improved digestion [5], strengthened mucosal immune barrier [6], treatment of diarrhea [7], anti-diabetic effects [8], improved immunity [9], maintenance of intestinal balance [10], management of inflammatory bowel diseases [10], and relieved constipation [11]. The mode of action of probiotics on the host is still not fully understood. Studying the in vitro characteristics and evaluating their probiotic properties are essential for the optimization and use of probiotics
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