Strains Of Lactobacillus Bulgaricus Research Articles

Public Health Significance of Amines in Cheese

Research designed to identify factors which may contribute to elevated biogenic amines (e.g., histamine, tryptamine, tyramine) in cheese is described. Free tyrosine and histidine in market cheese ranged from 6 to 29 and 1.5 to 12 mg/100g. These concentrations of substrate would provide nontoxic quantities of corresponding amines, indicating that cheese proteolysis is important when toxic amounts occur. Pyridoxal phosphate concentration in 15 cheeses ranged from 42 to 215μg/100g, which appears to be sufficient to saturate amino acid decarboxylases required for amine production. Commercial preparations and cheese isolates of Propronibacterium species were tested for carbon dioxide production from histidine, tryptophan, and tyrosine in the presence and absence of pyriodoxal-5-phosphate. In the presence of cofactor, maximums were 10.9, 2.9, and 12.7μl of carbon dioxide per h/mg cell dry weight. Over 150 isolates from 15 cheeses were tested for amine producing potential by measuring carbon dioxide production from histidine, tryptophan, and tyrosine; isolates were most active on tyrosine, producing as much as 26μl of carbon dioxide per h/mg cell dry weight. Cheese slurries also were tested for carbon dioxide production from carboxyl carbon-14 labeled amino acids. Cheese isolates producing amines were tentatively identified as strains of Streptococcus faecium, Streptococcus mitis, Lactobacillus bulgaricus, Lactobacillus plantarum, and streptococci of the viridans group.

Transformation of amino acid composition in bacterial cells of Lactobacillus bulgaricus during freeze-drying.

Abstract In the course of freeze-drying of a Lactobacillus bulgaricus strain, denaturation of protein leads to the separation of amino acids and their further susceptibility to deamination. This deamination of free and some bound amino acids is a secondary process and its intensity depends on the degree of denaturation, i.e., on protein and peptide degradation. A decarboxylation process takes place as well. The rate of decarboxylation is as high as the free amino acid pool is rich in acids. Based on these findings, it is reasonable to conclude that denaturation, deamination, and decarboxylation are biochemical processes which greatly influence the transformation of the native stereostructure of the complex, upon which the effect of freeze-drying on the survival level of cell suspension is dependent.

Effect of Copper on Microorganisms in the Manufacture of Swiss Cheese1,2

Commercial strains of Lactobacillus bulgaricus, Streptococcus thermophilus, lactic streptococci, and propionibacteria were grown in the presence of 0, 2, 4, 8, and 16ppm copper to simulate conditions that might exist in Swiss cheese manufacture. In general, loss of viability and inhibition of acid production was hastened by an increase in copper concentration although genus, species, and strains differed. During the first 3h of incubation in milk, mixed-strain lactic cultures were not affected by the addition of copper up to 16ppm. Later, inhibition and increased death rates occurred depending upon copper concentration. S. thermophilus strains exhibited a wide variety of sensitivities to copper. However, they seemed to overcome partly their sensitivity to copper after about 16h incubation. Two of three strains of L. bulgaricus showed slight reduction in cell numbers and acid production with increasing copper concentration. The third strain more closely resembled the lactic streptococci in its greater sensitivity to copper. Two of four strains of propionibacteria were more sensitive to copper than were the other two. Carbon dioxide production in broth at pH 7.0 differed among the strains. Incubation periods up to 20 days, however, tended to overcome copper inhibition. At an initial broth pH of 5.4, carbon dioxide production was delayed markedly by 16ppm copper, but, with prolonged incubation, two of the four strains attained carbon dioxide production equal to copper-free controls.

SENSITIVITY OR RESISTANCE DAIRY STARTER AND ASSOCIATED MICROORGANISMS TO SELECTED ANTIBIOTICS

Forty-two strains of mesophilic lactic streptococci, enterococci, lactobacilli, leuconostoc, staphylococci, and other dairy- and food-related microorganisms were tested for their sensitivity to 30 antibiotic and antimicrobial agents. Elliker's lactic agar served as the growth medium; incubation temperature and times were varied according to individual culture growth requirements. Commercially available multitipped sensitivity discs were used. Almost all the microorganisms investigated, except for Streptococcus thermophilus, exhibited definite resistance to eight different sulfonamides. Most of the strains of starter streptococci and Lactobacillus bulgaricus were sensitive to all 16 antibiotic or antimicrobial agents (included in this survey) used for mastitis control. Strains of Leuconostoc dextranicum, Streptococcus faecalis, Streptococcus durans, and Brevibacterium linens were less affected.

LACTIC ACID FERMENTATION OF SOYBEAN MILK

Growth rates of 8 Lactobacillus acidophilus strains and four Lactobacillus bulgaricus strains were compared in soybean milk and soybean milk enriched with glucose, lactose, and sucrose. Four L. acidophilus strains grew well in soybean milk; the remainder grew better in soybean milk supplemented with glucose or lactose. In general, soybean milk was not an adequate media for strains of L. bulgaricus. Almost all these cultures, however, could adapt themselves to the environments of the media tested. A soybean milk drink fermented by L. acidophilus NRRL B-1910 was prepared and evaluated by a taste panel. The drink had a refreshing sweet-sour taste, and the beany flavor of soybeans was masked by the fermentation process.

Effect of beta-indolylacetic acid on the growth and the auxin catabolism of Lactobacillus bulgaricus.

ENDOGENOUS auxin may act in the regulation of bacteria growth1, although its precise role is as yet poorly understood2. For example, Lactobacillus can grow without auxin3; however, in the presence of β-indolylacetic acid (IAA), its multiplication can be strongly modified4. In the following experiments, Lactobacillus bulgaricus (strain 1416, Liebefeld Institute of Dairy Research) was used and the medium was Lactobacillus broth AOAC (Difco). For each series of growth measurements, tubes containing 10 ml. of medium (with IAA) were inoculated with 1 ml. of a young culture of Lactobacillus (standard: 0.416 ml. of protein). The cultures were incubated at 37° C and the growth was measured after 6 and 12 h. Two methods were found most satisfactory for the growth determinations. The first is related to a direct measurement of the increase in turbidity5, using the ‘Lumetron 402 E’ with a double photoelectric cell. The second is based on the analysis of the total protein content6. The protein was determined by precipitating the washed bacteria cells with trichloroacetic acid. Comparing the turbidity with a series of standard solutions of serum-albumin, precipitated with trichloroacetic acid, a good correlation was found. Further examination of this technique will be discussed elsewhere.

Factors Which Increase Acid Production in Milk by Lactobacilli

The stimulation by yeast extract of acid production in milk by various lactobacilli was studied. It was found that supplementing milk with purine and pyrimidine bases and amino acids allowed nearly maximal acid production by Lactobacillus bulgaricus strain 7994, L. acidophilus 4796, 4356, and 4357, and L. leichmannii 326 and 327. Further supplementation with deoxyribotides allowed maximal acid production by L. acidophilus 204, but L. acidophilus 207 required adenosine or adenylic acid. L. casei strain 7469 showed no appreciable response to the amino acids or purine and pyrimidine bases, and is presumed to require an unidentified factor in corn steep liquor.

The lack of correlation between sensitivity of bacteria to killing by mecrophages or acidic conditions.

SUMMARYSeveral species of bacteria have been tested for their sensitivity to the bactericidal action of both acidic conditions and mouse peritoneal macrophages, to see if there was any correlation between these two. It was found, on the contrary, that one of the most acid resistant strains of Lactobacillus bulgaricus was as susceptible to killing by macrophages as a strain of V. cholerae which was acutely acid sensitive.

Inhibitory Effect of Nisin upon Various Organisms1,2

Summary Two nisin-producing strains of Streptococcus lactis were found to vary in their ability to produce the antibiotic. In the milk medium containing 5% of nisin-broth, cell multiplication and acid production of two strains of Streptococcus thermophilus were delayed, but upon further incubation their total cell count and acid production were not affected appreciably. Nisin-broth did not inhibit three strains of S. lactis , two strains of Lactobacillus bulgaricus , two strains of S. thermophilus , a mixed lactic culture, and one strain each of Bacillus subtilis and Bacillus cereus . Nisin was not quite as inhibitory as several other antibiotics against the dairy cultures tested. Of 11 strains of Staphylococcus aureus Used, the antibiotic seemed to be active only against the coagulase-negative and weak coagulase-producing organisms. The data presented in this paper indicate that the antibiotic may be considered for use to inhibit certain staphylococci or lactic organisms. Additional work should be conducted to determine the applications of nisin and nisin-producing organisms in the dairy industry.

Fermentation Studies on Lactobacillus Acidophilus and Lactobacillus Bulgaricus

Since it is now a commonly accepted fact that strains of Lactobacillus acidophilus are implantable in the human intestinal tract and are of some therapeutic value whereas strains of Lactobacillus bulgaricus are not implantable and hence are of little or no therapeutic value, it is extremely important to have a reliable method for the differentiation of the two species. Obviously, proof of implantability would serve as the final criterion of a culture of Lactobacillus acidophilus, but as the carrying out of extensive implantation experiments is a laborious procedure, a number of presumptive methods have been proposed. A survey of recent literature shows that the final differentiation is frequently made by a study of the abilty of the organism to produce acid from maltose, sucrose and levulose, those strains that produce acid from the three sugars being considered L. acidophilus, and those strains that do not ferment these sugars, L. bulgaricus. The fermentation of maltose, levulose and sucrose by L. acidophilus has been generally agreed on. On the other hand, while L. bulgaricus was originally described by Grigoroff 1 as fermenting these three sugars, Rahe2 differentiated it from other acid-resisting organisms by its inability to ferment maltose. He found that some strains fermented sucrose and levulose. Kulp and Rettger3 and Kulp4 in extensive studies of L. acidophilus and L. bulgaricus were unable to secure any culture of typical L. bulgaricus that would ferment maltose, sucrose or levulose. They recognized the existence, however, of borderline strains that fermented maltose.