Twenty-nine Lactobacillus strains contaminating beers in different Czech breweries as well as representative type strains obtained from the Czech Collection of Microorganisms were characterized using ribotyping with EcoRI and a probe made complementary to 16S and 23S rRNA genes. Biochemical test results assigned the 29 strains to the species L. brevis, L. plantarum, L. buchneri and L. paracasei subsp. paracasei. Ribotyping separated L. brevis, L. plantarum and L. paracasei subsp. paracasei strains into species-specific ribogroups in full correspondence with biotyping; L. buchneri strains were split into two ribogroups. Characteristic band patterns for each species and even typical bands of certain sizes were observed.

Aims: To examine the resistance of beer isolates of lactic acid bacteria (LAB) towards a mixture of tetrahydroiso-aacids (Tetra) by growth experiments as well as by measurement of intracellular pH. Methods and Results: Beer LAB isolates were identified to species level by SDS-PAGE of whole-cell proteins. Beer isolates of Lactobacillus brevis showed better ability for growth in the presence of Tetra than nonbeer isolates of the L. brevis or other species of LAB including beer and nonbeer isolates. The antimicrobial effect of Tetra was also examined by noninvasive measurement of intracellular pH by fluorescence ratio imaging microscopy for selected beer isolates of L. brevis and Pediococcus inopinatus. Strains of L. brevis showing limited decrease of intracellular pH during exposure to Tetra also showed better ability for growth in the presence of these compounds as well as in commercial beer products. Conclusions: It was possible to apply a method for noninvasive measurement of intracellular pH to predict the resistance of beer spoilage LAB towards the Tetra hop analogue compounds. Significance and Impact of the Study: This study demonstrated the usability of a new rapid method for detecting hop-resistant variants of known beer spoilage LAB species.