Media

There are two general types of media commonly used for the isolation or detection of the alicyclobacilli. The first type contains four specific mineral salts (ammonium sulfate, magnesium sulfate, calcium chloride, potassium phosphate) with minimal amounts of carbon and/or nitrogen sources (Table 7.3). Most of these media are similar in composition and are based upon early reports by Uchino and Doi [3] and Darland and Brock [5]. Modifications of these media have been published by Farrand et al. [23], Deinhard et al. [13], Yamazaki et al. [40], Wisse and Parish [44], and the Internationale Fruchtsaft-Union (IFU) [54]. Some of these media require addition of a trace mineral solution although the need for the full complement of minerals in a recovery medium is unclear.

The second class of media does not contain a complement of minerals and may be based on more traditional nutrient media with reduced pH. Examples are acidified versions of potato dextrose agar, orange serum agar, and plate count agar. YSG agar, recently advanced by Japanese organizations as part of a universal method for detection of the alicyclobacilli in juices, contains only yeast extract, soluble starch, and glucose. One particular nonmineral-containing medium, K agar, was developed specifically for the isolation of alicyclobacillus [55,56]. While nonmineral media may provide adequate recovery of alicyclobacilli in certain situations, some research suggests that mineral-containing media are more effective for enumeration or for situations where detection of small cell populations via enrichment is required. A recent study of more than 1500 environmental samples indicates that a minimal mineral medium, Ali agar [44], recovered significantly (a = 0.05) more alicyclobacillus strains than two nonmineral media, acidified potato dextrose agar and K agar, under the conditions of that study (Parish, unpublished data). Continued research to compare isolation media or investigate alternative media is warranted.

The official method of the IFU for detection of alicyclobacillus in fruit juices [54] depends upon the organisms' thermoacidophilic trait. A juice sample

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