SA Agar Base

SA Agar Base with Ampicillin Supplement is used for isolation, cultivation and differentiation of Aeromonas hydrophila from foods based on starch hydrolysis in accordance with APHA.

Composition**

Final pH (at 25°C): 7.4±0.2

**Formula adjusted, standardized to suit performance parameters

Directions

Suspend 31.02 grams in 1000 ml distilled water. Heat to boiling to dissolve the medium completely. Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes. Cool to 45-50°C. Aseptically add rehydrated contents of 1 vial of Ampicillin Supplement (FD082). Mix well before pouring into sterile Petri plates.

Principle And Interpretation

The isolation of Aeromonas hydrophila group has been extensively studied by clinical microbiologists and many media have been developed for their isolation. It was found that clinical media were not suitable because of lower recovery percentage and difficulties in distinguishing the A. hydrophila group from the background microflora.

To overcome these difficulties, Starch Ampicillin (SA) Agar was formulated as described by Palumbo et al (1) and is a slight modification of SA Agar recommended by APHA (2) for isolation and cultivation of A. hydrophila from foods.

Very few bacteria in food are capable of hydrolyzing starch. Starch hydrolysis is a differentiating character for A. hydrophila. SA Agar is also used for the quantitative detection of Aeromonas hydrophila, A. sobria and A. caviae in fresh foods of animal origin (2) and fresh vegetable (3). A. sobria and A. caviae are further identified by biochemical tests. Starch hydrolysis is determined by flooding 5 ml of Lugols Iodine solution per plate.

Casein enzymic hydrolysate in the medium provides essential growth nutrients. Sodium chloride maintains osmotic equilibrium. Ampicillin suppresses the contaminating microflora. Phenol red is the pH indicator.

Quality Control

Appearance Light yellow to pink homogeneous free flowing powder

Gelling Firm, comparable with 1.5% Agar gel

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

Reaction Reaction of 3.1% w/v aqueous solution at 25°C. pH: 7.4±0.2

pH 7.20-7.60

Cultural Response

M1177: Cultural characteristics observed after an incubation at 30°C for 24-48 hours with added Ampicillin Supplement (FD082).

Storage and Shelf Life

Store below 30°C in tightly closed container and the prepared medium at 2-8°C. Use before expiry date on the label.

Reference

1. Palumbo S. A., Maxino F., Williams A. C., Buchanan R. L., Thayer D. W., 1985, Appl. Environ. Microbiol., 50:1027.
2. Downes F. P. and Ito K., (Ed.), 2001, Compendium of Methods for the Microbiological Examination of Foods, 4th Ed. American Public Health Association, Washington, D.C.
3. Murray P. R., Baron J. H., Pfaller M. A., Jorgensen J. H. and Yolken R. H., (Ed.), 2003, Manual of Clinical Microbiology, 8th Ed., American Society for Microbiology, Washington, D.C.