ASSOCIATIVE BEHAVIOUR OF SELECTED HUMAN STRAINS OF LACTOBACILLI WITH RESPECT TO THEIR ANTI-BACTERIAL ACTIVITY, INHIBITION PATTERN AND LACTASE ACTIVITY
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Date
1990
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AAU, Anand
Abstract
The present study was planned and conducted to examine the human strains of lactobacilli for their suitability in lactose malabsorption and their antibacterial abilities. Three human strains of lactobacilli - L. acidophilus LBKV and LBKI. and L. casei 4A isolated and maintained in Dairy. Microbiology Department, Dairy Science College, Anand were used in the present study. These three strains were mixed in equal proportion to get mixed lactobacilli culture. One strain each of Escherichia coli (mastitic), Salmonella typhosa, Pseudomonas aeruginosa. Bacillus cereus and Staphylococcus aureus used in the study were also from the Dairy Microbiology Department, Dairy Science College, GAU, Anand. Lactobacilli strains were maintained in MRS broth, while the strains of E. coli, Sal. typhosa, P. aeruginosa, B. cereus and S. aureus were maintained on nutrient agar slants Growth rates in terms of log viable counts and titratable acidity of mixed lactobacilli culture were determined in skim milk at 37°C Three different agars, MRS agar +0.5% bile, MRS agar +0.7% bile and MRS agar (devoid of glucose and beef extract) + 1% ribose were used for enumeration of individual strains L. acidophilus LBKV3 and LBKI4 and L. casei 4A in mixed population. These three individual strains as well as their combination were also tested for their antibacterial activity against E. coli (mastitic), S. typhosa, S. aureus, B. cereus and P. aeruginosa. Activated cultures of individual lactobacilli and their combination were inoculated in skim milk at 1.5 per cent level and incubated at 37°C for 12 to 72 hours. The cell-free culture filtrate5(CPC-filtrates) were obtained by centrifuging the curd at 3000 rpm for 40 minutes. The CFC-filtrates were assayed for antibacterial activity against above mentioned food spoilage and pathogenic organisms by cup-assay technique. Antibacterial activity of these three strains alone and in combination against mastitic E. coli and enterotoxigenic S. aureus during production and storage of acidophilus milk was compared. Cultures were inoculated in skim milk and their antibacterial activity was assessed at 37°C. Inhibitory activity was expressed in terms of reduction in viable counts of the pathogenic organisms at selected time intervals i.e. 12, 24, 36, 48, 60 and 72 hours of storage at 37°C. To determine the implantation properties, the milk fermented with mixed lactobacilli culture was fed to a group of four test subjects at the rate of 100 g per day for one week. The faecal samples of all the volunteers were examined immediately after collection for lactobacilli and coliform counts before starting the feeding and at the interval of 2 days and one week during feeding and one and two weeks after stopping the feeding. To assess suitability of these cultures in lactose intolerance, lactase activity was determined in skim milk inoculated with lactobacilli strains alone and in combination, by subjecting to ultrasonic disintegration at time interval of 4, 8, 12, 18 and 24 hours of incubation. The test solution was added with substrate O-nitrophenol D-galactopyranoside (ONPG) and the release of O-nitrophenol from the hydrolysis of ONPG was used as the parameter for measuring lactase activity. The absorbancy at 420 nm was measured in a Double Beam Hitachi 220 Spectrophotometer. For finding in vivo lactase activity, the level of blood glucose was estimated in two test subjects after fasting, immediately after ingestion (O h) of milk fermented with mixed lactobacilli and at the interval of 1, 2 and 3 hours. The results of this study have revealed that the mixed lactobacilli culture was superior in all desirable characteristics with respect to antibacterial activity and implantation property as compared to individual strains— L. acidophilus LBKV3, LBKI4 and L. casei 4A.
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DAIRY MICROBIOLOGY, A STUDY