In order to meet the increasing demand for food quality and safety, the control of pathogenic microorganisms from farms to consumers remains a continuous challenge. Disease has always been a critical issue in animal production, affecting animal health and wellbeing. For several decades, antibiotics and chemotherapeutic agents have been used in animal feed to treat and prevent infectious diseases or to promote growth. However, there are concerns about the risk of development of cross-resistance and multiple antibiotic resistance in pathogenic bacteria in both human and livestock. To slow the development of resistance, some countries have restricted or banned use of antibiotics in feeds. Therefore, the need to find alternatives to growth-promoting and prophylactic uses of antibiotics is of outmost importance in agriculture. Beneficial bacteria, mainly lactic acid bacteria have been effectively used previously as feed additives in livestock to manipulate the gut microbiota in order to support animal health.
Therefore, the current study focused on isolation and characterisation of probiotic bacteria from raw goats milk. The first part of the study aimed at isolating and identifying potential probiotic bacteria. Bacteria from raw milk were cultured onto selective media including, M17 agar and MRS agar supplemented with 0.05 g/L cysteine-hydrochloride. A total of seventeen lactic acid bacteria were isolated, and were then identified using phenotypic assays, 16S rDNA gene sequencing and matrix-assisted laser desorption ionization-time of flight (MALDI-TOF). Lactobacillus plantarum strains (KJ026587.1, KM207826.1, KC83663.1, and KJ958428.1) and Pediococcus acidalactici were obtained. Potential probiotic bacteria were identified based on their ability to survive in the gastrointestinal conditions that include growth at low pH and bile tolerance, production of antimicrobial compounds and adhesion to the intestinal mucosa. The second part of the study focused on in vitro screening of probiotic attributes in the isolates. Production of antimicrobial activity, ability to adhere to intestinal cells and survive in the gastrointestinal tract, as well as antibiotic susceptibility, were among the main probiotic properties that were analysed to assess functionality and safety of the isolates.
The in vitro studies revealed that the five isolates were tolerant to acidic pH and high concentrations of bile salts, which are characteristics necessary for the probiotics to survive in the gastrointestinal tract. These isolates were also found to exhibit antimicrobial activity against some of the pathogens affecting the goats industry. The five selected LAB strains displayed resistance to vancomycin, gentamycin and nalidixic acid, but were susceptible to a broad range of other antibiotics. However, the antibiotics to which the isolates were resistant might not pose problems as it is unlikely to be transmissible between bacteria cells. Fluorescent microscopy analysis, revealed strong adhesion of the isolates to the ileum mucus following their staining with BacLight viability probe.
This study is the first in South Africa that isolated and characterised probiotic bacteria from raw goats milk. Most studies on application of probiotics in ruminants have been performed in cows and calves, and there is very little information for lambs and goats. The results of this study suggest that the five selected bacteria could be used as potential candidates for the development of direct fed microbials and growth promoters that can be used in improving the overall health status of the goats. Formulation of the best cocktail and its use as direct fed microbials for goats will result in improved nutrition and productivity.