Analysis of brevibacteria on the surface of Gruyere cheese detected by in situ hybridization and by colony hybridization

From the surface microflora of three different mature Gruyere Suisse cheese s, only a minor part of the microscopically visible resident micro-organism s was culturable. This may be due to the selectivity of the medium and grow th conditions used, but also to dead or dormant cells. However, by use of f luorescent in situ hybridization (FISH) and the bacterial probe EUB338, a m ajor part (70% of 4'6-diamidino-2-phenylindole-stained cells) of the microb ial community was detectable. The analysis revealed that, with the aid of f urther specific nucleotide probes, most of the detectable micro-organisms w ere attributable to the Actinobacteria (76-90.3%), with comparable results obtained by colony hybridization (82-88%). The percentage of culturable bre vibacteria detected by colony hybridization was higher (15-35%) than the pe rcentage determined by in situ hybridization (10.6-14.3%), indicating that the numbers of brevibacteria are overestimated by the plating technique.