Alicyclobacillus Detection Agar

Alicyclobacillus is a genus of Gram-positive, rod-shaped, spore-forming bacteria. The bacteria are able to grow in acidic conditions, while the spores are able to survive typical pasteurization procedures. Alicyclobacillus are strictly aerobic, acidophilic, thermophilic, soil-dwelling organisms, with an optimum growth at temperatures between 42-60 °C at a pH of 3.5-4.5 (growth range pH 2.2-5.8). Their spores survive for long periods in fruit concentrates and similar environments.

Spoilage of shelf-stable fruit juice products by Alicyclobacillus bacteria can be very costly. It is therefore important that concentrates and other raw materials are screened for spores of these taint producers to reduce the risk of spoilage of processed products.

Its presence in packaged products can cause flavor alterations. They do not produce gas or cause any change in the appearance of the beverage container, and therefore the spoilage is discovered only when the consumer opens and begins to consume the product. Fortunately, Alicyclobacillus are not pathogenic bacteria.

D(+) glucose is the fermentable carbohydrate providing carbon and energy. Yeast extract is a source of vitamins, particularly of the B-group. Monopotassium phosphate acts as a buffer system. The medium is especially characterized by the presence of many trace elements which supply all of the specific requirements for these bacteria. The pH value and the high incubation temperature inhibit the contaminating flora. Bacteriological agar is the solidifying agent.

A. acidoterrestris can be differentiated from A. acidocaldarius by incubating cultures at 30, 45 and 65 °C. A. acidoterrestris does not grow at 65 °C and A. acidocaldarius does not grow at 30 °C.

Typical formula in g/L, adjusted and/or supplemented as required to meet performance criteria.

Preparation

Suspend 29 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Dispense into appropriate containers and sterilize in autoclave at 121 °C for 15 minutes.

Note: the medium is manufactured with a pH of 5.3 ± 0.2 in order to maintain the gel strength during sterilization. Adjust the pH to 4.0 ± 0.2 after autoclaving, adding 1.7 mL of 1 N H₂SO₄ per liter of medium. Homogenize gently and pour into Petri plates.

Instructions for use

1. Incubate the medium for 3-5 days at 45 ± 1 °C.
2. Confirm the suspicious colonies by further testing.

• BAUMGART, J. and MENJE, S.: The Impact of Alicyclobacillus acidoterrestris on the Quality of Juices and Soft Drinks. Fruit Processing 7; 251-254 (2000).
• IFU Working Group Microbiology: First Standard IFU-Method on the Detection of Alicyclobacillus in Fruit Juices. (April 2003).
• Jensen Nancy, Evaluation of detection methods for alicyclobacilli in fruit juice concentrates in Australia. Food Science, Australia.
• Akira Yokota, Tateo Fujii, Keiichi Goto, Alicyclobacillus: Thermophilic Acidophilic Bacilli. Springer (2008).
• Chang SS, Kang DH. Alicyclobacillus spp. in the fruit juice industry: history, characteristics, and current isolation/detection procedures. Washington State University, Pullman, Washington, USA.