Harlequin™ mLGA
(Membrane Lactose Glucuronide Agar)
HAL 9

Description
Traditionally, membrane Lauryl Sulphate Broth (mLSB) has been used as the standard media for isolating coliforms (including E. coli) from water potentially contaminated with sewage. Harlequin™ membrane Lactose Glucuronide Agar (mLGA) is a modification of mLSB aimed at reducing costs by reducing the number of filters used per test sample and aiding in the recovery and identification of coliforms and E. coli. The medium has been modified from the mLSB formulation by the incorporation of X-glucuronide, sodium pyruvate and agar. X-glucuronide is incorporated to allow for the presumptive isolation of E. coli, sodium pyruvate aids the recovery of chlorine stressed
organisms and agar is incorporated to remove the need for absorbent pads. This medium is recommended for the enumeration of coliform bacteria and E. coli by a single membrane filtration technique in The Microbiology of Drinking Water 2002 (previously Report 71).

Formula g/litre
Peptone 39.0
Yeast Extract 6.0
Lactose 30.0
Phenol Red 0.2
Sodium Lauryl Sulphate 1.0
Sodium Pyruvate 0.5
X-Glucuronide 0.2
Agar 10.0

Method for reconstitution
Weigh 87.0 grams of powder, disperse in 1 litre of deionised water and allow the mixture to soak for 10 minutes. Swirl to mix and sterilise at 121°C for 15 minutes. Cool to 47°C and pour into sterile Petri dishes.

Appearance:
Red, clear gel.

pH:
7.4 ± 0.2

Minimum Q.C. organisms:
Escherichia coli NCIMB 50034
Enterobacter aerogenes NCIMB 50029
Staphylococcus aureus NCIMB 50080 (inhibition)

Storage of Powdered Medium:
Plates - up to 7 days at 2-8°C in the dark.

Inoculation:
E. coli and coliform counts can be performed on the same sample of water. The volume and dilution of test sample should be chosen so as the number of colonies on the membrane lies between 20 and 80. With waters expected to contain low numbers of coliforms, a sample of 100ml should be filtered. For full methodology refer to The Microbiology of Drinking Water 2002 section 4 B - The enumeration of coliform bacteria and E. coli by a single membrane filtration technique.

Incubation:
4 hours at 30 °C followed by 14 hours at 37 °C

Interpretation:
Count all green-blue colonies as presumptive E. coli, and all green-blue and yellow colonies as presumptive coliforms.

References
Sartory, D.P. & Howard, L. (1992). A medium detecting B-glucuronidase for the simultaneous membrane filtration enumeration of Escherichia coli and coliforms from drinking water. Letters in Applied Microbiology 15, 273-276.
Calabrese, J.P. & Bisssonette, G.K. (1990). Improved membrane filtration method incorporating catalase and sodium pyruvate for detection of chlorine stressed coliform bacteria. Applied and Environmental Microbiology 56, 3558-3564. Microbiology of Drinking Water 2002 section 4 B – Environment Agency. The enumeration of coliform bacteria and E. coli by a single membrane filtration technique.