Strains Of Streptococcus Cremoris Research Articles

The origin of single strain starter culture usage for commercial Cheddar cheesemaking

The technology of using single strain starter cultures for commercial Cheddar cheesemaking is commonly believed to have originated in New Zealand in about 1934. However, W. S. Sutton of the New South Wales Department of Agriculture isolated pure strains of Streptococcus cremoris and, along with A. B. Shelton, conducted cheesemaking trials at the Hawkesbury Agricultural College, now the University of Western Sydney, from at least September 1930. Pure strains were being used in factories by October 1930 and, by July 1932, at least six factories were using pure single cultures. The technology was taken to New Zealand from New South Wales by Dr Moir.

Isolation and Characterization of the Bacteriophages of Lactic Streptococci

Four virulent phages of lactic streptococci were isolated from 245 samples of butter, buttermilk, curd, cheese, cheese whey, raw milk, and Srikhand Three of these phages, i.e., FRC1, FRC2, and FRC3 isolated from buttermilk, curd, and Srikhand, respectively, lysed Streptococcus cremoris strains, and phage FRC4 isolated from cheese whey was specific for Streptococcus lactis ssp. diacetylactis. Phages were examined by electron microscopy. Isolated phages comprised of two morphological types. Phages FRC1 and FRC3 possessed prolate head, whereas polyhedral capsids were exhibited by phages FRC2 and FRC4. Noncontractile tails of all phages were 2 to 2.5 times longer than the head diameter, exhibiting regular fine striations and 20 to 30 annuli. Base plates with three or four spikes were visible in all phages. A structure of plug type was observed in phages FRC1 and FRC3. All phages were classified into group B of Bradley. Phages FRC1, FRC2, and FRC3 exhibited a latent period of 40min, rise period of 20min, and average burst size of 70 to 110 phage particles. Phage FRC4 possessed a latent period of 45min, rise period of 15min, and average burst size of 100 to 150 phage particles. Further differentiation among these phages was on the basis of eclipse phases, which were in the range of 26 to 32min.

Whey Permeate as a Medium for Mesophilic Lactic Acid Streptococci

Streptococcus lactis C8 was inoculated into whey permeate, reconstituted skim milk permeate, two times (vol/vol) concentrated ultrafiltered whey, reconstituted skim milk, and reconstituted whey to compare growth and acid production. Permeate from reconstituted whey with .1% added yeast extract (BBL) was used as a growth medium for three different Streptococcus lactis ssp. diacetylactis strains and three Streptococcus cremoris strains. Acid development, generation time, and growth were determined for each culture in this medium during the 18-h incubation at 30°C.Streptococcus lactis C8 and Streptococcus cremoris SK11 were each propagated in permeate from reconstituted whey (3.5% total solids) and in RSM (9.0% total solids) over 7 d. Growth and acid production by the organisms in the two media were compared. All of the media in which S. lactis C8 was grown supported growth of the culture. Variations in acid development were observed among the different types of media and appeared to be related to the levels of solids and growth factors present. Permeate from reconstituted whey with .1% yeast extract added supported varying degrees of growth and activity by the six mesophilic lactic streptococci cultures that were inoculated into this medium. The results of propagating S. cremoris SK11 and S. lactis C8 in permeate from reconstituted whey and in RSM showed that growth increases by each culture were similar in the two types of media. The pH remained higher in the permeate than in RSM. The results of this study indicate that whey permeate may be suitable as a growth medium for mesophilic lactic acid streptococci.

Preparation of subcellular fractions from strains of Streptococcus cremoris

Preparation of subcellular fractions from strains of <i>Streptococcus cremoris</i>

Influence of pH, lactose and lactic acid on the growth of Streptococcus cremoris: a kinetic study

The effect of various culture conditions on growth kinetics of an homofermentative strain of the lactic acid bacterium Streptococcus cremoris were investigated in batch cultures, in order to facilitate the production of this organism as a starter culture for the dairy industry. An optimal pH range of 6.3–6.9 was found and a lactose concentration of 37 g·l-1 was shown to be sufficient to cover the energetic demand for biomass formation, using the recommended medium. The study of the effect of lactic acid concentration on growth kinetics revealed that the end-product was not the sole factor affecting growth. The strain was characterized for its tolerance towards lactic acid and a critical concentration of 70 g·l-1 demonstrated. With the product yield of 0.9 g·g-1 at non-lactose limiting conditions the lactic acid concentration of 33 g·l-1 could not explain the low growth rates obtained, implicating a nutritional limitation.

Development and use of a defined strain starter system for Cheddar cheese

Out of 210 strains of Streptococcus cremoris and Streptococcus lactis screened, 35 were suitable for inclusion in multiple strain starters for Cheddar cheese. The use of various combinations of these 35 strains and bacteriophage‐insensitive mutants isolated from some of them as cheese starters over six seasons is described. All cheese graded well for body, texture and flavour, with &lt;1% being downgraded due to starter failure. The system is now being used in all Cheddar cheese plants in Ireland producing ˜60,000 tonnes a year. The problems encountered in phage monitoring are also discussed.

Plasmid-encoded functions of ropy lactic acid streptococcal strains from Scandinavian fermented milk

Ropy Streptococcus (Lactococcus) cremoris strains isolated from a ropy Swedish sour milk (“longfil”) and a ropy Finnish milk product (“Viili”) were screened for their plasmid-encoded functions. Curing experiments strongly indicated that the ropy phenotype was linked to a 17-Md plasmid in the Swedish strains and to a 30 Md plasmid in the Finnish strains. Comparative restriction endonuclease analysis and DNA/DNA-hybridization studies revelead that plasmids from both strain families shared homologous DNA regions. Though be Swedish ropy strains harbored a conjugative 45-Md lactose plasmid, no cotransfer of the 17 Md plasmid occured.

β-Lactamase-Producing Mutants of Streptococcus cremoris

Penicillin-resistant mutants were isolated for six strains of Streptococcus cremoris used in commercial Cheddar cheese manufacture after treatment with N-methyl-N-nitro-N-nitrosoguanidine. The resistant mutants had an elevated minimal growth inhibitory concentration, 2.5μg (4.13 units)/ml, for penicillin G and other β-lactam antibiotics as compared with the penicillin-susceptible parent strains, which were each sensitive to .05μg (.08 units)/ml. Penicillin resistance was due to the production of β-lactamase. Plasmid DNA was not demonstrated in partially purified lysates of four mutants. Mutants had normal cellular morphology but altered phage sensitivity patterns. All except one strain were able to support complete phage adsorption. Resistance was retained after 20 passages in absence of penicillin.

Amino acid limited growth of starter cultures in milk

The specific growth rates of several Streptococcus cremoris strains were 10–40% lower in milk than in other growth in media. The growth rates in milk increased when an amino acid mixture or casein was added, whereas, when milk was diluted, the specific growth rate of the streptococci decreased. This decrease could be overcome by bringing the casein concentration in the diluted milk back to the normal value (3%). This indicates that casein-hydrolysis proceeded at a rate too low for the streptococci to reach their potential maximum specific growth rates in milk so that growth in milk is essentially amino acid-limited. This was subsequently demonstrated for S. cremoris by continuous cultivation in media with low casein concentrations. At a low dilution rate casein hydrolysis was fast enough to supply the cells with enough amino acids and lactose was growth-limiting, whereas at higher dilution rates amino acids became growth-limiting. In cultures exponentially growing in milk the concentration of free amino acids was measured to determine which amino acid(s) was(were) absent and could possibly limit growth. A number of essential amino acids (leucine, methionine, glutamate and in some cases phenylalanine) were not detected and addition of these, together, stimulated the growth of S. cremoris in milk. The amino acids leucine and phenylalanine appeared to play a particularly important role in this stimulation. These two are, supposedly, the first amino acids that become limiting during growth in milk. The effect of competition for casein and amino acids by different organisms was studied in continuous cultures. At different dilution rates different strains became dominant in these mixed cultures, suggesting that differences in apparent affinity constants (KS) for casein, leucine and glutamate existed between the strains.

Amino acid limited growth of starter cultures in milk

The specific growth rates of several Streptococcus cremoris strains were 10–40% lower in milk than in other growth in media. The growth rates in milk increased when an amino acid mixture or casein was added, whereas, when milk was diluted, the specific growth rate of the streptococci decreased. This decrease could be overcome by bringing the casein concentration in the diluted milk back to the normal value (3%). This indicates that casein-hydrolysis proceeded at a rate too low for the streptococci to reach their potential maximum specific growth rates in milk so that growth in milk is essentially amino acid-limited. This was subsequently demonstrated for S. cremoris by continuous cultivation in media with low casein concentrations. At a low dilution rate casein hydrolysis was fast enough to supply the cells with enough amino acids and lactose was growth-limiting, whereas at higher dilution rates amino acids became growth-limiting. In cultures exponentially growing in milk the concentration of free amino acids was measured to determine which amino acid(s) was(were) absent and could possibly limit growth. A number of essential amino acids (leucine, methionine, glutamate and in some cases phenylalanine) were not detected and addition of these, together, stimulated the growth of S. cremoris in milk. The amino acids leucine and phenylalanine appeared to play a particularly important role in this stimulation. These two are, supposedly, the first amino acids that become limiting during growth in milk. The effect of competition for casein and amino acids by different organisms was studied in continuous cultures. At different dilution rates different strains became dominant in these mixed cultures, suggesting that differences in apparent affinity constants ( K S) for casein, leucine and glutamate existed between the strains.

Cell surface proteins of encapsulated Streptococcus cremoris: identification and immunochemical characterization

Cell surface proteins of two slime-forming, encapsulated Streptococcus cremoris strains, MLS96 and T5 from the fermented milk product viili, were extracted with the non-ionic detergent Triton X-100. The isolated protein antigens were characterized by sodium dodecyl sulphate polyacrylamide gel electrophoresis and immunoblotting with antisera produced against whole Strep. cremoris cells. When protein profiles of these strains were compared, seven prominent polypeptides were found common to both and were recognized by both antisera. Five of these polypeptides with molecular weights of 70,000, 54,000, 50,000, 47,000 and 40,000 were identified as cell wall components. The remaining two polypeptides with molecular weights of 42,000 and 26,000 are being studied further in connection with slime formation for which modified Triton X-100 extraction provides a suitable method for isolation of the surface-associated antigens of lactic streptococci.

Mathematic model for lactic acid formation with Streptococcus cremoris from glucose

A strain of Streptococcus cremoris has been fermented on glucose at a fixed pH and temperature in a chemostat.

Identification of lactose fermentation plasmids of streptococcal dairy starter strains by Southern hybridization

Twenty-two strains of Streptococcus cremoris, seven strains of Streptococcus lactis and three strains of Streptococcus lactis subsp. diacetilactis, each with a different plasmid complement, were isolated from a starter culture used in a Finnish dairy plant. By using DNA-DNA hybridization, with cloned 6-P-s-galactosidase gene of the Strep, lactis plasmid pLP712 as a probe, the lactose fermentation genes were located, in each strain, in the large ( 30 MD) plasmid.

Cell wall associations of some antigenic proteins of slime-forming, encapsulated Streptococcus cremoris from the fermented milk product "viili"

Cell walls were isolated from mechanically disrupted cells of the slime-forming, encapsulated Streptococcus cremoris strains T5 and MLS96 by using sucrose gradient centrifugation as the last purification step. This cell wall isolation procedure was developed to obtain cell wall associated protein components. Sodium dodecyl sulfate – polyacrylamide gel electrophoresis revealed several polypeptide bands; the 50 kiloDalton band was major in strain T5 cell walls and the 26 and 30 kiloDalton bands were major in strain MLS96 cell walls. Both strains contained five antigenic polypeptides with molecular radius (Mr) values of 40, 47, 50, 54, and 70 kiloDaltons as analysed by immunoblotting and autoradiography. The polypeptides of strain MLS96 with molecular mass of 40 and 70 kiloDaltons reacted most strongly with homologous anti-whole cell serum. In addition, antigenic polypeptides with molecular mass of 100 and 160 kiloDaltons were also detected in strain T5.

Effects of Antibiotics on Proteinase-Positive and Proteinase-Negative Variants of Streptococcus cremoris

The growth and acid-producing ability of proteinase-positive and proteinase-negative starter cultures were studied in the presence of several antibiotics commonly used in treating bovine mastitis. Proteinase-positive and proteinase-negative variants of two different strains of Streptococcus cremoris were inoculated separately into heat-sterilized, reconstituted nonfat milk containing a range of concentrations of either dihydrostreptomycin, erythromycin, or penicillin G. Generation times and pH changes were determined for each sample following incubation at 38°C for 5h.At 2% inoculation, proteinase-positive cultures produced more pH change than their proteinase-negative counterparts at all concentrations of all three antibiotics. Proteinase-negative cultures at 8% inoculation produced more acid than proteinase-positives did when inoculated at 2%. Generation times for proteinase positives and proteinase negatives were the same when both cultures were inoculated at 2%, but 8% inoculation of proteinase negatives produced significantly shorter generation times. Increases in antibiotic concentrations affected proteinase-positives more than proteinase-negatives in both pH change and generation time. Penicillin affected both proteinase positives and negatives more than the other two antibiotics did but affected positives more than negatives.

Survey of antimicrobial resistance in lactic streptococci.

A total of 26 strains of Streptococcus cremoris and 12 strains of Streptococcus lactis were challenged with 18 antimicrobial agents and with nisin in the Bauer-Kirby disk susceptibility test. All strains were susceptible to ampicillin, bacitracin, cephalothin, chloramphenicol, chlortetracycline, erythromycin, penicillin G, tetracycline, and vancomycin. All strains were resistant to trimethoprim, and almost all strains were resistant to sulfathiazole. Variability in resistance to gentamicin, kanamycin, lincomycin, nafcillin, neomycin, nisin, rifampin, and streptomycin was observed. MICs of these substances for the less susceptible strains were determined, and high-level resistance factors could not be detected, except in the case of nisin. S. lactis ATCC 7962 was resistant to at least 40-fold-higher concentrations of nisin (greater than 64 micrograms/ml) than most other strains tested. This strain was a potent nisin producer.

Competition between different strains of Streptococcus cremoris

Competition between different strains of Streptococcus cremoris

Competition between different strains ofStreptococcus cremoris

Streptococcus cremoris strain HP was found to grow poorly on agar plates under aerobic conditions in comparison to several other strains of S. cremoris (Wg2, ML1, AM1, E8). This made it possible to determine the numbers of strain HP in mixed cultures with other strains under different culture conditions. None of the mixtures was stable in batch cultures as a result of differences in the maximum specific growth rate. In continuous culture under lactose limitation strain HP outcompeted strains E8 and ML1 at low dilution rates, but at high dilution rates and in batch culture the reverse was observed. This represents another example of crossing μ-s curves in anaerobic bacteria.

Aminopeptidase Profiles of Lactic Streptococci

Aminopeptidase activities of cell free extract from 11 strains of Streptococcus lactis and Streptococcus cremoris, used as starter bacteria in cheese manufacture, were determined with 54 synthetic substrates. Based on these aminopeptidase profiles, 11 strains were divided into three groups by cluster analysis. Enzymes involved in representative strains of each cluster (Streptococcus lactis 527, Streptococcus cremoris ML-14, and Streptococcus cremoris nTR) were separated partly by diethylaminoethyl-cellulose chromatography and compared for each enzyme's optimum pH and the effect of various metal ions and chemicals. These strains have at least six aminopeptidases (dipeptidase specific for hydrophobic amino acid-x, dipeptidase for basic amino acid-x, prolinediaminopeptidase, aminopeptidase-P (or prolidase), general aminopeptidase, and tripeptidase), although contents of enzymes vary among strains.

Conjugal transfer and characterization of bacteriocin plasmids in group N (lactic acid) streptococci.

Thirteen bacteriocin-producing strains of group N (lactic acid) streptococci were screened for their potential to transfer this property by conjugation to Streptococcus lactis subsp. diacetylactis Bu2-60. Bacteriocin production in three strains was plasmid encoded as shown by conjugal transfer and by analysis of cured, bacteriocin-negative derivatives of the donor strains and the transconjugants. With Streptococcus cremoris strains 9B4 and 4G6 and S. lactis subsp. diacetylactis 6F7 as donors, bacteriocin-producing transconjugants were isolated with frequencies ranging from ca. 2 X 10(-2) to 2 X 10(-1) per recipient cell. Bacteriocin-producing transconjugants had acquired a 39.6-megadalton plasmid from the donor strains 9B4 and 4G6, and a 75-megadalton plasmid from the donor strain 6F7. As shown by restriction endonuclease analysis, the plasmids from strains 9B4 and 4G6 were almost identical. The plasmid from strain 6F7 yielded some additional fragments not present in the two other plasmids. In hybridization experiments any of the three plasmids strongly hybridized with each other and with some other bacteriocin but nontransmissible plasmids from other S. cremoris strains. Homology was also detected to a variety of cryptic plasmids in lactic acid streptococci.