Composition
Ingredients | Gms/Ltr. |
Peptic digest of animal tissue | 5.00 |
Lactose | 5.00 |
Beef extract | 3.00 |
* Dehydrated powder, hygroscopic in nature, store in a dry place, in tightly -sealed containers below 25°C and protect from direct Sunlight.
Instructions for Use
Dissolve 13gms in 1000ml distilled water. Gently heat to boiling with gentle swirling and dissolve the medium completely. Dispense into tubes containing inverted Durham ’s tubes. Sterilize by autoclaving at 15 psi (121°C) for 15 minutes. Cool as quickly as possible.
Appearance: Pale to light yellow colour, clear with no to light precipitate.
pH (at 25°C): 6.9 ± 0.2
Principle
LACTOSE BROTH (FLUID LACTOSE MEDIUM) is used for the detection of coliform group in water, dairy and food products. The medium contains Beef extract and Peptic digest of animal tissue in quantities that allow to growth of non – fastidious microorganisms such as the coliforms. While preparing this medium it is important to avoid overheating and to distribute it into tubes before sterilization. Tubes of Lactose Broth are inoculated with dilutions of water or milk, etc. under test, and incubated at 35°C and examined for gas formation after 24 and 48 hours. Members of the coliform grou p are defined as aerobic and facultative anaerobic gram-negative and non -sporing bacilli, which ferment lactose with gas formation within 48 hours at 35°C. Mix 1, 10 or 100ml samples with specified volume s of lactose broth. The initial concentration of lactose broth must be increased so that the final conc entration of the components is maintained at the level of 13g/ l. Incubate the fermentation tubes at 35°C and take the first reading by shaking the tube slightly after 24 hours. If gas production is not evident in the D urham tubes, reinbate them for 24 hour s. Gas formation within 48 hours is a positive indication of coliforms. To confirm the presumptive test, subculture the positive lactose broth tubes into tubes of Brilliant Gr een Bile Broth 2% (TM 365).
Interpretation
Cultural characteristics observed afte r inoculating (10 3 CFU/ ml) , on incubation at 35ºC for 24 – 48 hours.
Microorganisms | ATCC | Inoculum (CFU/ml) | Growth |
Enterobacter aerogenes | 13048 | 103 | Luxuriant |
Escherichia coli | 25922 | 103 | Luxuriant |
Salmonella T yphimurium | 14028 | 103 | Good |
Enterococcus faecalis | 29212 | 103 | Good |
References
- A.E. Greenberg, R.R.Trussell, L.S. Clesceri (Eds.), Standard Methods for the Examination of Water an d Wastewater, 16th ed., APHA Washington, D.C. (1985).
- M. Speck (Ed.), APHA, Compendium of Methods for the Microbiological Examination of Foods, 3rd ed., Washington, DC. (1984).
- International Organiz ation for Standardization (ISOI , Draft ISO/ DIS 4831. (1991).
- APHA, American Water Works Association and Water Pollution Control Federation, Standard Methods for the Examination of Water and Wastewater 20th ed., Washington, (1998).
- European Pharmacopeia ll, Chapter Vlll, 10. United States Pharmacopeia XXlll, Chapter “Microbiol. Limit Test”, (1995).
- APHA, Prepared according to specifications in: Stand. Meths. for the Examin. of Water & Sewage, 9th Ed. 186 (1946).
- APHA, Stand. Meths. for the Examin. of Dairy Prods., 9th Ed. 133 (1948).
- Richardson (ed.), Stand. Meths. for the Examin. of Dairy Prods., APHA Washington, D.C. (1985).
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