IMPROVED RECOVERY OF STRESSED BIFIDOBACTERIUM FROM WATER AND FROZEN YOGURT

A roll-tube repair-detection procedure was developed to enumerate inju red and noninjured cells of Bifidobacterium species from water and foo d samples. This procedure combined the Virginia Polytechnic Institute and State University's anaerobic roll-tube procedure and the repair-de tection technique for detecting stressed cells. Mara and Oragui's huma n bifid sorbitol agar medium was modified for use in the roll-tube pro cedure by replacing the indicator bromocresol purple with phenyl red ( 0.027 g/l), adding 0.0006 g of methylene blue per 1, increasing the ag ar content to 25 g/l and adjusting the pH of the medium to 7.1 +/- 0.1 . The repair-detection roll-tube technique was shown to recover Bifido bacterium cells significantly (P < 0.01) better than pour plates, usin g the same medium incubated in anaerobe jars, even when a repair-detec tion system was used. Most repair in the roll tubes occurred in the fi rst hour. B. adolescentis had a poor survival rate after 96 hours in w ater. Glucose was substituted for sorbitol in the medium used for enum eration of B. longum added to frozen yogurt, because this organism can not utilize sorbitol. This medium, when used as part of a repair detec tion system, significantly (P < 0.01) recovered more cells than anaero bic pour plate techniques and was able to separate Bifidobacterium spe cies and Lactobacillus acidophilus by colony morphology. Bifidobacteri um cells were 1 mm or larger, round and yellow, while the L. acidophil us colonies were so small(< 1/4 mm) their detection and enumeration wa s difficult.