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Dehydrated Culture Media

LACTOSE BROTH

Code: CM0137

A liquid medium for use in the performance or confirmation of the Presumptive Test for coliforms in water, milk, etc. as specified by the American Public Health Association.

Typical Formula

gm/litre

`Lab-Lemco’ powder

3.0

Peptone

5.0

Lactose

5.0

pH 6.9 ± 0.2 @ 25°C

 

* Adjusted as required to meet performance standards

Directions
Dissolve 13g in 1 litre of distilled water and distribute into containers with fermentation tubes (Durham). Sterilise by autoclaving at 121°C for 15 minutes.

Description
Lactose broth is recommended for use in the presumptive identification of coliform organisms in milk, water and foods as specified by the American Public Health Association1,2,3.

Tubes of Lactose Broth are inoculated with dilutions of the samples and incubated at 35°C. Examination for gas formation is carried out after 24 and 48 hours incubation. This presumptive evidence of coliform organisms must be confirmed by further tests.

Storage conditions and Shelf life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Store the prepared medium at room temperature (18-22°C).

Appearance
Dehydrated medium: Straw coloured, free-flowing powder
Prepared medium: Straw coloured solution

Quality control

Positive control:

Expected results

Escherichia coli ATCC® 8739 *

Turbid growth; acid and gas production

Negative control:

 

Uninoculated medium

No change

* This organism is available as a Culti-Loop®

Precautions
Ensure that the fermentation tubes are free from air bubbles before inoculation.
Large water samples may require double-strength lactose broth to reduce the final volumes. Do not overheat double- strength broth or inhibitory products will be produced.

References
1. American Public Health Association (1978) Standard Methods for the Examination of Dairy Products. 14th Edn. APHA Washington DC.
2. American Public Health Association (1980) Standard Methods for the Examination of Water and Wastewater. 15th Edn. APHA Inc. Washington DC.
3. American Public Health Association (1998) Compendium of Methods for the Microbiological Examination of Foods 3rd Edition. APHA Inc. Washington DC.

 
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