Development of detection medium for hard-to-culture beer-spoilage lactic acid bacteria.

Aims:  To develop a detection medium for hard-to-culture beer-spoilage lactic acid bacteria (LAB). Methods and Results:  Four hard-to-culture beer-spoilage strains of LAB, belonging to Lactobacillus paracollinoides and Lactobacillus lindneri, have been obtained by repeatedly subculturing the wild-type strains in beer. To develop a countermeasure against these hard-to-culture beer-spoilage LAB, a beer-based medium was modified. As a consequence, the supplementation of a small amount of de Man Rogosa Sharpe medium was found to enhance the growth of hard-to-culture beer-spoilage LAB strains obtained in this study. In addition, sodium acetate was shown to improve the selectivity of this beer-based medium. Further comparative study was performed with five other media widely used for the detection of beer-spoilage LAB in the brewing industry. This study revealed that the newly developed medium, designated advanced beer-spoiler detection (ABD) medium, possessed superior sensitivity for hard-to-culture beer-spoilage LAB and comparable sensitivity with easy-to-culture beer-spoilage LAB. Moreover, ABD medium was found to suppress the growth of nonspoilage micro-organisms, and thereby allow the selective growth of beer-spoilage LAB. Conclusions:  Advanced beer-spoiler detection medium is considered as an effective tool for comprehensive detection of beer-spoilage LAB in breweries. Significance and Impact of the Study:  The detection by ABD medium can be used as an indicator for differentiating the beer-spoilage ability of LAB without further confirmatory tests in breweries.