A1 BROTH

A liquid medium for the detection of faecal coliforms.

Code: CB1/8012

Typical formula  g/l

Tryptone	20.0
Lactose	5.0
Salicin	0.5
Sodium chloride	5.0
Triton X-100	1.0

pH 6.9 +/- 0.1

Directions

Suspend 32.5g in 1000ml of cold distilled water. Gently heat to dissolve completely and distribute 9 ml into test tubes with an inverted Durham tube. Sterilise by autoclaving at 121°C for 15 minutes. If required prepare multi-strength broth weighing the appropriate quantity of powdered medium.

Description

A1 Broth, is used for the detection of faecal coliforms in foods, treated wastewater and seawater bays as a most probable number (MPN) method.

Method

1ml of multiple dilutions of sample (3 or 5 replicates per dilution) is added to test tubes containing 10 ml of A1 Broth. After incubation at 37°C for 3 hours and at 44.5°C for 21 hours, tubes with gas accumulation in the Durham tubes are scored positive for faecal coliforms and, those with no gas as negative. A MPN table is consulted to determine the most probable number of faecal coliforms. From the positive tubes, subculture 0.1 ml to 10 ml of Peptone Tryptone Water. After incubation at 44°C for 18-24 hours, add 0.5 ml of Kovacs’ Reagent. The tubes, which develop a red-ring are considered positive for E.coli.

Quality Assurance (44 °C-24 hrs)

Productivity control

E.coli ATCC 25922: growth, gas production

Selectivity control

E.faecalis ATCC 19433: partially inhibited, no gas production

Storage

Dehydrated medium: 15-30°C

User prepared tubes: up to 7 days in the dark at 2-8°C

Reference

• Andrew, Presnell, (1972) App. Microb. 23: 521