BROMOCRESOL PURPLE LACTOSE AGAR

A medium for the enumeration of spores of mesophilic and thermophilic Bacillus.

Code: CB1/1201

Typical formula g/l

Peptone mix	7.50
Lactose	8.50
Bromocresol purple	0.025
Agar	12.00

pH 6.8 ± 0.2

Directions

Suspend 28g in 1000ml of cold distilled water; heat to boiling with agitation and sterilise in the autoclave at 121°C for 15 minutes.

Description

Bromocresol Purple Agar is used for the enumeration of spores of Bacillus responsible for flat sour (especially B. stearothermophilus) in sugar, sweet desserts, spices, aromatic preparation and other foodstuffs.

Method

Destroy the vegetative cells by heating the sample.

Inoculate the plates with 1 ml of the sample or of its tenfold dilutions and pour 15 ml of medium into petri dishes

Incubate at 30°C for 5 days to enumerate Bacillus spores.

Incubate at 55°C for 5 days to enumerate thermophilic Bacillus spores. Pour several drops of sterile paraffin oil in the lid of the plate as a tight seal.

Bacteria acidifying the medium will grow with yellow colonies, bacteria not metabolising the glucose will grow with blue colonies.

User quality assurance

Productivity control

B.stearothermophilus ATCC 10149: growth, yellow colonies (55°C-72 h)

B.subtilis ATCC 6633: growth, yellow colonies (55°C-72 h)

Storage

Dehydrated medium: 15-30°C

User prepared flasks: 1 month at 2-8°C

Reference

National Canners Association (1993) Bacterial Standards for Sugar.