lab report microbiology Essay

2906 Words Feb 19th, 2015 12 Pages
Dairy food staff such as soft cheese,cream cheese,raw milk,sour cream,yoghurt and probiotic yoghurt products can be a rich source of diverse lactic acid bacteria.The objective of this lab practical was to isolate lactic acid bacteria(LAB) form raw milk,establishment of pure cultures of LAB,identify LAB and phage recovery and enumeration of recoverd phage.Raw milk was chosen as a sample so as to have a more positive result.To identify bacteria Lab isolated from raw milk,biochemical,morphological ,physiological and cultural characteristics were employed. The purification of isolates was done by moving Gram +ve ro ds and cocci shaped bacteria to selective media MRS and M-17 plates. The isolates were sub cultured till pure
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Colonies were then selected randomly and the streak plating method employed to purify the stains. The strains were kept in 2 conditions including at 4°C (for MRS and M17 plates ) and at -20°C (for M17 and MRS broth) withh by 20% glycerol.

Identification of the bacterial strains:The strains were subjected to gram staining,catalase and spore formation tests. (Harrigan and McCance, 1976).All Colonies were characterized in MRS and M 17 agars.The strains that gave gram positive and catalse negative results were set aside for further identification.(Sharpe, 1979).The growth of the bacteria at different temperatures of between Growth 10-45°C for 3-6 days , resistance to 60°C for 30 min (Sherman test), growth in the presence of 2 to 6 % NaCl and different pHs (4.5 and 6.5) were used to identify the strains of LAB. Arginine and asculin hydrolysis,citrate utilistaion, acetone productionformation of gas from glucose and production of dextran from sucrose were also determined. The starins were then tested for fermentation of L-arabinose, D-xylose, galactose, D-fructose, sorbitol, lactose, melibiose, saccharose, D-raffinose, melezitose, mannose and glucose.Bacterial growth in the different temperatures were confirmed by turbidity change in MRS or M17 after incubation(after 24,48 and 72 hrs).Microbial

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