Selection of Galactose-Fermenting Streptococcus thermophilus in Lactose-Limited Chemostat Cultures.

Stock cultures of Streptococcus thermophilus are essentially galactose negative (Gal). Although both galactose 1-phosphate uridyl transferase and uridine-5-diphospho-glucose 4-epimerase are present, suggesting that the genes for the Leloir pathway exist, cells cannot induce high levels of galactokinase. Therefore, galactose is largely excreted when cultures are grown on lactose, and most strains cannot be readily adapted to grow on free galactose.

DNA-DNA Homology Between Lactic Streptococci and Their Temperate and Lytic Phages.

Temperate phages were induced from Streptococcus cremoris R(1), BK(5), and 134. DNA from the three induced phages was shown to be homologous with prophage DNA in the bacterial chromosomes of their lysogenic hosts by the Southern blot hybridization technique. P-labeled DNA from 11 lytic phages which had been isolated on cheese starters was similarly hybridized with DNA from 36 strains of lactic streptococci.

Galactose fermentation and classification of thermophilic lactobacilli.

The ability to ferment galactose is a major characteristic which can be used to differentiate Lactobacillus helveticus (galactose positive) from Lactobacillus lactis and Lactobacillus bulgaricus (galactose negative). In milk cultures, galactose-positive strains produced d- and l-lactic acid with little galactose accumulation, whereas galactose-negative strains produced d-lactic acid, and galactose accumulated to high levels.

Carbohydrate Fermentation by Streptococcus cremoris and Streptococcus lactis Growing in Agar Gels.

When lactic streptococci were embedded in agar gels and incubated at 30 degrees C, the end products of carbohydrate fermentation depended on the initial cell density, which determined the subsequent distribution and size of colonies in the gel. With high initial cell densities, microcolonies formed close together and lactose and glucose were converted almost entirely to lactate. However, inoculation with a small number of cells, which then grew to form widely spaced and comparatively large colonies, resulted in up to 30% diversion of end product, usually to formate, ethanol, and acetate.

Purification and Some Properties of Diplococcin from Streptococcus cremoris 346.

Eleven of 150 Streptococcus cremoris strains examined produced the bacteriocin diplococcin. The diplococcin activity spectrum was restricted to S. cremoris and Streptococcus lactis strains, and none of a wide range of other gram-positive or gram-negative strains were inhibited.

Deoxyribonucleic Acid homology among lactic streptococci.

A comparison was made by deoxyribonucleic acid homology of 45 strains of lactic streptococci, using two strains of Streptococcus cremoris and three strains of Streptococcus lactis as reference strains. All S. cremoris strains were grouped together by deoxyribonucleic acid homology.

Grouping of lactic streptococci by gel electrophoresis of soluble cell extracts.

Soluble cell proteins obtained from 35 strains of lactic streptococci were examined by gel electrophoresis. A mathematical analysis of the densitometer scans of the gels enabled strains to be grouped according to their overall similarity. Strains which were known to be variants of the same parent strain fell into the same group, supporting the validity of the method.

Regulation of lactose fermentation in group N streptococci.

Group N streptococci, which have the lactose phosphoenolpyruvate (PEP)-dependent phosphotransferase system (PTS) and phospho-beta-d-galactosidase (beta-Pgal), grew rapidly on lactose and converted more than 90% of the sugar to l-lactate. In contrast, Streptococcus lactis 7962, which does not have a beta-Pgal, grew slowly on lactose and converted only 15% of the sugar to l-lactate. With glucose and galactose, this strain had growth rates and fermentation patterns similar to those of other S.

Improved medium for lactic streptococci and their bacteriophages.

Incorporation of 1.9% beta-disodium glycerophosphate (GP) into a complex medium resulted in improved growth by lactic streptococci at 30 C. The medium, called M17, contained: Phytone peptone, 5.

Typing of coagulase-positive staphylococci by proteolytic activity on buffered caseinate-agar, with special reference to bacteriophage nontypable strains.

The specificities of the proteinases produced by 136 strains of coagulase-positive staphylococci on a buffered caseinate-agar medium at 37 C were investigated. Five well-defined groups of staphylococci could be differentiated by the patterns of precipitation zones obtained as a result of proteolysis. Within these five groups, slight variations in zone types were observed.