To isolate and identify the Lactobacillus spp. and Streptococcus lactis from the given curd sample.

AIM

            To isolate and identify the Lactobacillus spp.  and Streptococcus lactis from the given curd sample.

PRINCIPLE

            Milk contains high nutritive food value for the new borne mammal and human beings. It is also an ideal growth medium for the microbial proliferation. Fermented milk and milk based products at different formulation in different name are popular throughout the world for their taste as well as health benefits. Lactic acid bacteria (LAB) are widely distributed in nature; occur as natural adventitious contaminants in raw milk, yoghurt, etc. and sometimes with the coexistence of yeasts, moulds and some other pathogenic microorganisms. LAB as indigenous flora in raw milk acidifies the milk very slowly due to their low numbers. Hence most of the dairy industries now a day’s use LAB as starter culture for the manufacture of fermented products including milk products such as yoghurt, cheese; meat products, bakery products, wine, and vegetables        

MATERIALS REQUIRED

·         Curd sample

·         Man, Rogosa and Sharpe (MRS) agar media

·         Yeast Glucose Lemco Agar (YGLA).

·         Test tubes

·         Conical flask

·         Pipettes

·         Petri plates

·         Inoculation loop

PROCEDURE

·         10 ml of curd sample was homogenized with 90 ml of 0.85% (w/v) sterile sodium chloride solution to make an initial dilution (10⁻¹).

·         Serial dilutions upto 10⁻⁶ were made for each sample.

·         1 ml sample from each of the corresponding dilutions (10⁻⁵ and 10⁻⁶) were inoculated into various selective media such as MRS agar, and Yeast Glucose Lemco Agar (YGLA).

·         MRS agar (pH 6.2-6.6) used for the lactobacilli isolation, while YGLA (pH 7.0) for the isolation of streptococci of LAB origin.

·         Inoculated plates were then incubated at 37°C for 48-72 hours both at aerobic and anaerobic conditions.

·        

Total number of lactic acid bacterial population per ml=Average no. of                                                                                     colonies x dilution factor.

After incubation, plates with 30–300 colonies were enumerated and the calculated results were expressed as colony forming unit (cfu) per gm or ml by multiplying the average number of colonies with the reciprocal of dilution factor

·         Observe the colony morphologies such as form, elevation, margin, surface, color and consistency and isolated.

·         The isolated colonies were subjected to staining method to observe the morphology characteristics of Lactobacillus spp and Streptococcus lactis.

RESULTS

After incubation creamy to white color colonies were observed on the surface of MRS and YGLA agar plate. The morphological characteristics were further identified on the basis of microscopic observation. Microscopic examination shows the Gram