Strains Of Lactic Streptococci Research Articles

Iron and vanadium requirements of lactic acid streptococci

Lactic acid streptococci have an absolute requirement for magnesium and potassium and failed to grow in milk deionized with IRC 50 resin (sodium form) (Reiter unpublished; see also Fisons, 1958; Reiter, 1956). These findings were confirmed in preliminary experiments using the defined medium of Reiter & Oram (1962). Requirements for other metal ions have now been investigated. Two strains of Streptococcus lactis (ML3 and C10) and one of Streptococcus cremoris (HP) were used. They were maintained as milk cultures, and before use subcultured twice in the synthetic medium containing Ca, Mg, Fe, Zn, Mn, Co, Cu and Mo (cf. Reiter & Oram, 1962) and then finally in the synthetic medium containing only Mg and K (20 ppm.), and Fe (0·01 ppm.).

Acetaldehyde and diacetyl production by Streptococcus thermophilus and other lactic streptoccocci

SummaryThe quantities of acetaldehyde and diacetyl produced in skim-milk and MRS media are reported for strains of Streptococcus lactis, Str. cremoris, Str. diacetilactis, Str. faecalis and Str. thermophilus obtained from culture collections or freshly isolated from natural milk cultures used in cheese manufacture. The diacetyl: acetaldehyde ratio in skim-milk medium was found to be approximately 0·1:1 for Str. lactis and Str. cremoris, 0·5:1 for Str. diacetilactis (5:1 for Str. diacetilactis PIM 13 and K.2 strains) and for Str. thermophilus 0·3:1, in skim-milk medium, and 0·8:1, in MRS medium; in the latter species cultured in MRS medium the ratio varied from 3·5:1 to 0·04:1 and when cultured in milk from 1·2:1 to 0·03:1.In both media all strains of Str. thermophilus formed more acetaldehyde and diacetyl than other homofermentative lactic streptococci.The ratio diacetyl: acetaldehyde in 9 strains of Str. diacetilactis was found to be unsuitable for a good culture flavour.

Effect of heterophase admixtures on thermal decomposition of silver nitrite

The qualitative composition and quantitative relationships of amines in the volatile components of 6-, 24-, and 30-h cultures of a strain of Streptococcus lactis, in the logarithmic growth phase, was studied chromatographically using retention indices.The 21 amines found were identified as follows: primary amines—methylamine, ethylamine, isopropylamine, butylamine, isobutylamine, tert.-butylamine, amylamine, isoamylamine; secondary amines—dimethylamine, diethylamine, dipropylamine, diisopropylamine, diisobutylamine, n-butylisopropylamine, pyrrolidine, piperidine; tertiary amines—trimethylamine, triethylamine, tripropylamine. The qualitative composition of amines remained constant as the culture grew, but a sharp change in the quantities of the individual amines in the 6-, 24-, and 30-h cultures was observed. This pointed to the formation of amines during the metabolism of the bacterial cells and suggested the existence of special fermentative systems involved in the synthetic production of amines. Thus a fundamentally new phenomenon that of synthesis of secondary and tertiary amines by microorganisms has been discovered.

Flavor and Texture in Cheddar Cheese. I. Role of Mixed Strain Lactic Starter Cultures

Three commercial starters (A, B, and C) were selected for intensive study after several experimental cheese-making trials. Two of these were starters that produced cheeses with open texture and fruity-fermented flavor; the third culture consistently yielded normal-flavored, close-textured product. Comparisons were made with respect to culture survival patterns during manufacture, relative rates of sugar-and protein-degradation in ripening cheeses, and total carbonyl production in milk cultures. Taxonomie studies on the component strains also were conducted. No significant differences were observed in the rates of sugar- and protein-degradation between the normal (A) and detective cultures. Cultures associated with defective cheeses, however, survived the manufacturing process in greater numbers and dominated the cheese flora over longer periods of time. Furthermore, the defective cultures were found to contain high carbonyl-producing Streptococcus lactis and Streptococcus diacetilactis strains in contrast to Starter A, which was entirely made up of low carbonyl-producing Streptococcus cremoris strains and a few Leuconostoc strains. An apparent correlation between taxonomic and carbonyl-producing characteristics of specific starter cultures and the quality and grade of the corresponding cheeses was shown.

Lactic Streptococcal Phage-Associated Lysin. I. Lysis of Heterologous Lactic Streptococci by a Phage-Induced Lysin

This investigation concerns the study of a lactic phage-associated lysin released when Streptococcus lactis strain C10 cells were lysed by their homologous c10 phage. The lysin appeared in the medium when the cells lysed. A spreading halo surrounding the clear phage plaques was observed after prolonged incubation of double agar layer plates. Both living and sensitized C10 cells were lysed by the c10-lysin. All heterologous lactic streptococcal strains studied thus far were lysed by the c10-lysin. A lysozyme-sensitive strain of Sarcina lutea was very resistant to c10-lysin. Micrococcus lysodeikticus substrate cells (Difco) were lysed rapidly during the initial reaction period, but lysis diminished rapidly soon thereafter. The role of c10-lysin in the nascent phenomenon is discussed.

Identity of Additional Aroma Constituents in Milk Cultures of Streptococcus lactis var. Maltigenes

Gas chromatographic analyses of the headspace vapor over a series of milk cultures of malty and nonmalty strains of Streptococcus lactis revealed components in the malty strains tentatively identified as 2-methylpropanol and 3-methylbutanol. In a more detailed study the volatiles from milk cultures of a typical strain of S. lactis var. maltigenes were entrained and collected by an on-column trapping technique, chromatographed on l,2,3-tris(2-cyanoethoxy) propane and 1,2,4-butanetriol columns, and the separated components analyzed in a mass spectrometer. Ethanol, 2-methylpropanol, and 3-methylbutanol, as separated on both columns, were positively identified and the carbonyls including 2-methylpropanal and 3-methylbutanal were identified in the effluents from the former column.Although the culture volatiles contained more of the branched-chain alcohols than the corresponding aldehydes, organoleptic comparison of the aroma of an untreated culture with that in which the aldehydes had been removed by treatment with acidic hydroxylamine indicated that the typical malty aroma is due principally to the aldehydes.The presence of the alcohols in these cultures suggests that S. lactis var. maltigenes possesses a yeast-like alcohol dehydrogenase.

STUDIES WITH A BACTERIOPHAGE INHIBITORY MEDIUM: I. INHIBITION OF PHAGE AND GROWTH OF SINGLE STRAIN LACTIC STREPTOCOCCI AND LEUCONOSTOC

SummaryA phage resistant starter culture medium was examined for its ability to inhibit bacteriophages under several conditions. The medium also was tested for its ability to support growth of single strain starter culture organisms and for its effect on viability of starter bacteria during storage at 2 and −20 C. When prepared according to manufacturer's directions, the medium prevented phage proliferation and eliminated phages from infected cultures within three transfers. Preparation of the medium with water of 500 ppm hardness did not affect its phage-inhibiting properties. Single strains of Streptococcus lactis, Streptococcus cremoris and Streptococcus diacetilactis grew well in the medium though there was variation between strains; Leuconostoc species were not able to grow well. Storage survival of starter organisms in the phage resistant medium also revealed considerable variation between strains; Leuconostoc sp. and S. diacetilactis survived poorly when stored in the medium, especially at 2 C, while S. lactis and S. cremoris survived well when held at −20 C.

Phage-associated lysins affecting group N and group D streptococci.

SUMMARY Phage lysins were prepared from high titre phage lysates of 3 strains of Streptococcus lactis, one of which was purified 500-fold by treatment with cold acetone, chromatography on Amberlite CG50 ion-exchange resin, and fractional precipitation from potassium phosphate buffers. The lysins were activated by monovalent cations and were similar in physical properties. Viable streptococci of groups N and D were lysed, but not those in groups A, B and C. Different strains of group N streptococci were lysed at different rates, the rate of lysis being characteristic for individual phage lysins. A lytic enzyme, prepared from purified phage particles by freezing and thawing or by ultrasonic treatment, showed the same pH optimum and specificity as the corresponding phage lysin. Streptococci were lysed-from-without in the presence of high multiplicities of phage. The type of lysin produced in phage-infected culture was genetically determined by the phage. Lysis of streptococci by phage lysin was inhibited by an unidentified substance present in crude phage lysates. The lysis of different strains of streptococci by particulate phage, phage-tail enzyme and phage lysin occurred at the same relative rates. This is interpreted as evidence for the localization of the phage-lysin substrate within the phage receptor site. Possible reasons for the different specificities of phage lysins from streptococci of groups N and C are discussed.

Survival of strains of lactic streptococci during frozen storage

SummarySixteen single-strain cultures, 10 ofStreptococcus cremoris, 3 ofStr. lactisand 3 ofStr. diacetilactiswere examined for their ability to withstand freezing and storage at –17·8 and –23·3°C. The numbers of surviving bacteria decreased as storage time increased. For the majority of strains, the survival rate was greater at the lower temperature. At both storage temperatures there were differences between the percentages of surviving bacteria for different strains.The results suggest that the relative proportion of strains in mixed cultures would not remain constant under frozen storage.

Volatile Fatty Acids Produced by Some Lactic Acid Bacteria. I. Factors Influencing Production of Volatile Fatty Acids from Casein Hydrolysate

The effect of several conditions of substrate on total and individual volatile fatty acids (VFA) produced from casein hydrolysate by resting cells of three strains of lactic streptococci and two strains of lactobacilli has been studied. Fatty acids were steam-distilled from the reaction mixture and total and individual VFA determined by titration with alkali and by gas chromatography. Optimum pH of substrate was in the neutral or slightly alkaline range. Optimum temperature of incubation was 32C for streptococci and 42C for lactobacilli. Shaking incubation was more favorable to production of VFA than static incubation. There was no appreciable difference in total VFA production between incubations with air and with nitrogen atmosphere. Addition of sodium caseinate to casein hydrolysate stimulated VFA production, whereas addition of lactose or milk fat showed a slight inhibitory effect. Patterns of individual VFA varied from strain to strain, depending on the conditions of substrate.

SOME FACTORS WHICH GOVERN PLAQUE FORMATION BY LACTIC STREPTOCOCCAL BACTERIOPHAGE.: I. SEED LAYER REQUIREMENTS

SummaryA study was conducted of factors which may influence the accuracy of the plaque count obtained by the double-agar layer method as applied to lactic streptococcal bacteriophage. Host cell cultural media were skimmilk or hydrolyzed milk protein broth (Sobol's). Streptococcus lactis strains ML3, C10, C2 and Streptococcus cremoris strains C3, KH, R1, US3 and the homologous bacteriophages were used. Plaque formation on Trypticase Soy Agar was generally enhanced by: (a) modification of the cultural media or the seed layer agar by the addition of CaCl2, phenylalanine, proline, riboflavin, niacin, calcium pantothenate, and biotin; (b) using a six-hr culture of host cells rather than cells incubated for 18 or 24 hr; and (c) selection of the proper serial transfer system for reactivating the host cells from a frozen or lyophilized state. Sobol's broth yielded lower plaque counts than skimmilk irrespective of the modifications used. Responses to plaque enhancement factors were influenced by species and strain differences of S. lactis and S. cremoris. In general, strains of S. cremoris had a more exacting requirement for calcium, media enrichment, and length of incubation of host cells than S. lactis strains.

Occurrence of variants sensitive to agglutinins and to lactoperoxidase in a lactenin-resistant strain ofStreptococcus lactis

SummaryA strain ofStreptococcus lactis, C10, known to be resistant to lactenins, was found to be composed of 47% resistant cells, 10% cells sensitive to lactoperoxidase and 43% cells sensitive to both agglutinins and lactoperoxidase. By subculturing a strain composed of 100% resistant cells in different conditions of medium, temperature and incubation time, it was possible to obtain cultures composed of resistant and sensitive cells in various proportions. These findings help to explain how, after numerous subculturings in autoclaved milk, a resistant strain may become sensitive to the natural inhibitors of milk.

SOME FACTORS INFLUENCING ACID PRODUCTION BY AN OXYTETRACYCLINE-RESISTANT STRAIN OF STREPTOCOCCUS LACTIS.

Induction of oxytetracycline resistance in a strain of Streptococcus lactis caused this organism to display reduced acid production, salt tolerance, pyruvate synthesis, growth at alkaline pH, and a loss in ability to produce ammonia from arginine. alpha-Ketoglutaric and oxaloacetic acids were found to accumulate in the growth medium of resistant cells, in contrast to none in the medium of susceptible cells. No free arginine could be detected in the intracellular fraction of resistant cells, but arginine was present in the intracellular fraction of susceptible cells and decreased in concentration upon the addition of oxytetracycline to the growth medium. Depressed acid production in milk by the oxytetracycline resistant strain is evidently a consequence of the inability of this organism to metabolize arginine effectively.

Selective Plating Medium for Leuconostoc in Mixed Lactic Cultures

Summary Thirty-six strains of starter organisms ( Leuconostoc and Streptococcus ) were tested for their susceptibility to various antibiotics and sulfa drugs. Tetracycline hydrochloride was found to have less inhibitory effect on leuconostocs than on streptococci. Consequently, a simple selective plating medium containing tetracycline (0.15 μ g/ml) in a tomato juice agar base was developed. Five experimentally mixed starters of known composition and seven commercial multiple-strain lactic starters were used to evaluate the effectiveness of the medium. The mixed starters were plated in control and in the experimental agar and incubated at 30C for up to 72 hr. Representative colonies were isolated from the tetracycline agar after 48 hr and after 72 hr and were identified by growth in litmus milk and by biochemical tests. Results showed an incubation period of 48 hr to be optimum for best selectivity of leuconostocs, because a few strains of Streptococcus lactis were not inhibited on further incubation.

Some Factors Influencing Acid Production by an Oxytetracycline-Resistant Strain of Streptococcus lactis1

Induction of oxytetracycline resistance in a strain of Streptococcus lactis caused this organism to display reduced acid production, salt tolerance, pyruvate synthesis, growth at alkaline pH, and a loss in ability to produce ammonia from arginine. alpha-Ketoglutaric and oxaloacetic acids were found to accumulate in the growth medium of resistant cells, in contrast to none in the medium of susceptible cells. No free arginine could be detected in the intracellular fraction of resistant cells, but arginine was present in the intracellular fraction of susceptible cells and decreased in concentration upon the addition of oxytetracycline to the growth medium. Depressed acid production in milk by the oxytetracycline resistant strain is evidently a consequence of the inability of this organism to metabolize arginine effectively.

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.

Gas Production by Associated Swiss Cheese Bacteria

Summary Gas production in skimmilk cultures was markedly stimulated and inhibited by interactions of the late gas-formers with some but not all of the Swiss cheese lactic flora. The starter lactobacilli were markedly stimulatory for both Clostridium tyrobutyricum and Propionibacterium shermanii. Streptococcus thermophilus was very stimulatory for the Clostridium but without effect on the propionic, whereas Streptococcus faecalis generally had little effect on either gas-former. The nisin-producing strain of Streptococcus lactis was markedly inhibitory for the clostridium but without much effect on the propionic, whereas the ordinary strain of S. lactis had little effect on either. Gas production was stimulated when the clostridium and propionic were grown together. The stimulatory and inhibitory properties of the skimmilk cultures for the late gas-formers were at least in part dialyzable, heat- and acid-stable substances. The stimulatory activity of Lactobacillus helveticus was shown to be correlated with metabolic products rather than with the number of cells in the lactic culture.

Resistance of Certain Bacteria to Cottage Cheese Cooking Procedures

Summary Heat resistance in Cottage cheese whey at pH 4.6 was determined for selected strains of Pseudomonas fragi, Escherichia coli, Streptococcus cremoris , and Streptococcus lactis . Strains were selected for study on the basis of high heat resistance. Survivor curves in whey at various temperatures and thermal resistance curves were calculated. The time-temperature treatments used for cooking Cottage cheese curd in seven representative California plants and one hypothetical procedure were evaluated as to lethality for each of the selected cultures. Cooking procedures that did not have a maximum temperature of at least 130° F., and a holding time of at least 18min. at 130° F., proved unsatisfactory.

Domination among strains of lactic streptococci with attention to antibiotic production.

Domination among strains of lactic streptococci with attention to antibiotic production.

Peptides as Sources of Essential Amino Acids for Lactic Streptococci

Summary Two strains of Streptococcus lactis , one of Streptococcus cremoris , and one of Streptococcus lactis var. maltigenes were shown to possess peptidases capable of hydrolyzing a number of commercially available dipeptides and two tripeptides into the constituent amino acids. The four test cultures exhibited similar hydrolytic ability toward the peptides under examination. If the C-terminal amino acid of the peptide was of d configuration, no hydrolysis occurred. Dipeptides in which one of the constituent amino acids was l-Ieucine or l-valine, when substituted for these amino acids in chemically defined media, were shown to fulflll the nutritional requirements of each of the four cultures for these essential acids. S. lactis var. maltigenes degraded the freed leucine and valine from such peptides to 3-methylbutanal and 2-methylpropanal, respectively. The possible role of peptides as precursors of flavor compounds in dairy products is discussed.