Partial characterization of probiotic lactic acid bacteria isolated from Chinese dairy products

A total of 246 bacterial isolates were collected from various food and animal sources within Nanning city, China. Sequencing of the 16S rRNA gene revealed that 24.4% of the isolates were lactic acid bacteria (LAB). Initial screens identified three isolates from semi-hard cheese: Lactobacillus plantarum subsp. plantarum strains K3 and K4 and Lb. paracasei subsp. tolerans K8; and one from raw buffalo milk: Lb. plantarum subsp. plantarum E41 as having the highest levels of cell surface hydrophobicity and auto-aggregation. Further characterization of these strains showed that all four isolates were completely stable after exposure to the pepsin and trypsin for 6 hours, and strains K8 and E41 remained viable after 6 hours of exposure to acidic conditions (pH 2.5) and bile salts (0.3%). In addition, strains K3 and K4 were shown to inhibit the growth of potential human pathogens, including methicillin resistant Staphylococcus aureus, Escherichia coli and Salmonella typhi, with inhibition zones being >14 mm for each bacterial target. Results from this study suggested that the four characterized LAB strains could survive passage through the gastrointestinal tract, thus supporting the need for additional studies to assess their potential as probiotics.