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Strains of Lactobacillus bulgaricus and Streptococcus thermophilus isolated from yoghurt culture were used to study the cause of the synergistic effect on acid production by mixtures of the 2 cultures. The beneficial effect was essentially limited to the gradual accumulation of factors in the L. bulgaricus cultures that promoted more rapid acid production by Str. thermophilus. The active factors were identified as glycine and histidine.The starter culture employed in the manufacture of yoghurt is usually composed of a mixture of L. bulgaricus and Str. thermophilus. The studies conducted by Pette & Lolkema (1950 a) and Katrandziev (1954) have shown that acid production was more rapid when mixed cultures of L. bulgaricus and Str. thermophilus were inoculated in milk than when single strains were used. Pette & Lolkema (19506) also reported that the more rapid acid production by such cultures was attributable to water-soluble, heat-stable growth factors for the streptococcus produced by L. bulgaricus. They also indicated that these factors were ammo acids and that valine was the most stimulatory one.The present study was conducted to clarify further the symbiotic relationship existing between the 2 bacterial species in yoghurt starter cultures. ,. METHODS CulturesSingle strains of lactobacilli and streptococci were isolated from different yoghurt products or yoghurt starter cultures obtained from commercial sources by plating on lactic agar (Elliker, Anderson & Hannesson, 1956). The isolates were transferred daily in litmus milk using 1 % inoculum and incubating at 45 °C for about 5 h for the lactobacilli and about 6 h for the streptococci. Between transfers the cultures were stored in the refrigerator.

A collaborative study was conducted in 18 laboratories to assess the performance of the hydrophobic grid membrane filter method against that of the AOAC official first action method 46.013-46.016 for enumerating total and fecal coliforms and Escherichia coli. The study was carried out on frozen breaded fish, raw comminuted poultry, unroasted walnut pieces, ground black pepper, and cheddar cheese. The hydrophobic grid membrane filter method recovered significantly larger numbers of target bacteria in 7 of the food/analysis combinations: fecal coliforms in fish; E. coli in poultry; fecal coliforms and E. coli in walnuts; and total coliforms, fecal coliforms and E. coli in black pepper. Random error (Sr2) associated with the hydrophobic grid membrane filter method was significantly lower than that of the reference method in over 30% of the paired sample series. The hydrophobic grid membrane filter method for total coliform, fecal coliform, and E. coli enumeration in foods has been adopted official first action.

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DAHIYA, R. S. (North Carolina State College, Raleigh) AND M. L. SPECK. Identification of stimulatory factor involved in symbiotic growth of Streptococcus lactis and Streptococcus cremoris.