Sulphate API Agar w/o Sodium Lactate

Intended Use

Sulphate API Agar is used for detection and estimation of sulphate reducing bacteria.

Composition**

Final pH (at 25°C): 7.4±0.2

**Formula adjusted, standardized to suit performance parameters

Directions

Suspend 25.41 grams in 1000 ml distilled water. Add 4 ml of sodium lactate. Heat to boiling to dissolve the medium completely. Dispense preferably in screw-capped tubes in 9 ml amounts. Sterilize by autoclaving at 15 lbs pressure (121°C) for 10 minutes. Close the caps immediately while the medium is still hot.

Principle And Interpretation

Sulphate API Agar w/o Sodium Lactate is prepared according to the formulation described in the 'American Petroleum Institute Recommended Practice' (1) for detection of sulphate reducing bacteria. Sulphate-reducing bacteria cause corrosion of oil well systems resulting in perforations in the pipes. Sulphate-reducing bacteria convert sulphate to sulphide which with the ferrous ion gives black colour. The insoluble sulphide results in plugging.

Yeast extract in the medium provides nitrogen and other nutrients necessary to support bacterial growth. Ascorbic acid is the carbohydrate source. Dipotassium Phosphate buffers the medium. Sodium chloride, magnesium sulphate and ferrous ammonium sulphate provide essential ions. Desulfovibrio oxidizes reduced substrates i.e. sodium lactate, further with stepwise reduction of sulfate to sulfide. The detection and estimation of these bacteria is done on the basis of their ability to grow and produce sulphide in this medium. For the estimation, appropriate dilutions of water samples are inoculated.

Quality Control

Appearance Cream to yellow homogeneous free flowing powder

Gelling Firm, comparable with 1.4% Agar gel.

Colour and Clarity of prepared medium Light yellow coloured clear to slightly opalescent gel forms in Petri plates

Reaction Reaction of 2.54% w/v aqueous solution (containing 0.4% v/v sodium lactate) at 25°C. pH : 7.4±0.2

pH 7.20-7.60

Cultural Response M309: Cultural characteristics observed after an incubation at 30°C for upto 1 week, under anaerobic condition.

Storage and Shelf Life

Store dehydrated medium and the prepared medium at 2 - 8°C. Use before expiry date on the label.

Reference

1. American Petroleum Institute Recommended Practice 28, 1959, First ed.