Isolation, screening and characterization of probiotic isolates from commercial dairy food and bovine rumen

Abstract

Probiotics are beneficial bacteria which either imparts overall general well being in the host or has intended specific applications such as treating selected health conditions for example; gut inflammation in humans, enhancing the feed conversion and body weight gain in livestock or suppressing transmissible dieases in poultry. There is increasing demand for probiotics; to meet this demand new sources for probiotic bacteria isolation and extensive routine screening studies carried out in laboratories are required. This leads to new candidates being selected and tested for efficacy in animal models for applications in the health, foods, food production and neutraceutical industries.

The key question investigated by this thesis was; can novel probiotic candidates be isolated from dairy food products and the bovine rumen?

Initially twenty dairy food isolates and thirty bovine rumen isolates were collected. Phenotypic characterization (Gram staining and colony morphology) of these isolates identified twenty- six isolates for further evaluation. All dairy food isolates were found to be Gram- positive and colony morphologies indicating they were likely to be lactic acid bacteria. Only six of the thirty bovine rumen isolates met these criteria, this was not surpising considering the vast range of microbial species present in the bovine rumen.

The twenty- six isolates (twenty from dairy food and six from the bovine rumen) were investigated for their survival at low pH and in the presence of bile salts. These conditions were selected as they are major challenges probiotic bacteria encounters during gastro- intestinal tract transit following injestion by farmed livestock or humans. Ten isolates (five each from dairy food and the bovine rumen) were identified as having good adhesion and survival at low pH and in the presence of bile salts. The high proportion of bovine rumen isolates (five of six) found to have good potential probiotic characteristics reflects perhaps their being isolated from an environment where such characteristics would be condusive to survival.

Species identification of these ten isolates confirmed all were Lactobacillus species. Extensive testing to further characterize the probiotic potential of the ten isolates included; inhibition of pathogens, resistance to antibiotics, biosafety (absence of haemolytic activity), adhesion (BATH test), carbohydrate fermentation, survival at low pH, and high bile salt concentrations. This testing identified two isolates (isolate MI 13 from dairy food and isolate RC 2 from the bovine rumen) for further evaluation.

The two isolates were characterized in terms of their adhesion to and permeability across gut Caco- 2 cells. These isolates were also characterized under standard and stressed (low pH and high bile salts) conditions by proteomic assessment of protein expression changes, production of volatile fatty acids and composition of fatty acid methyl esters.

A key conclusion from this research is that potential probiotic candidates can be isolated from commercial dairy food products and the bovine rumen. The data obtained from the screening tests indicates that overall the rumen isolates displayed better in vitro probiotic characteristics and isolates MI 13 and RC 2 shows promising potential for further development as a novel probiotic.