Growth conditions that support bacteriocin (thermophilin T) production by Streptococcus thermophilus ACA-DC 0040 were identified. Synthesis of thermophilin T occurred during primary metabolic growth, while its specific rate of synthesis seemed to be optimal at T = 30 degrees C. Thermophilin T activity rapidly decreased in the stationary phase, especially at high growth temperature (i.e. T = 42 degrees C). In media with high content of complex nitrogen sources, high amounts of bacteriocin were detected in the growth environment, while about an 8-fold increase of thermophilin T titer and a 2-fold increase of specific synthesis rate was achieved when a fed-batch fermentation mode was applied.

The aim of this study was to assess the mode of carbohydrate catabolism by lactic acid bacteria isolated from traditional sourdoughs, as well as to study their effect on the metabolites produced. For this purpose, single cultures of the heterofermentative lactic acid bacteria Lactobacillus sanfranciscensis , Lactobacillus brevis , Weissella cibaria , and the homofermentative Lactobacillus paralimentarius and Pediococcus pentosaceus were grown in liquid media containing glucose, fructose, maltose and sucrose, either as a single carbon source or in combination with glucose. Carbon catabolism and the production of metabolites were determined by HPLC analysis. W. cibaria could ferment all carbon sources, L. sanfranciscensis , L. paralimentarius and P. pentosaceus could not ferment sucrose, while L. brevis could only ferment maltose. The presence of glucose did not influence the utilization of fructose and maltose by L. sanfranciscensis , while it repressed the fermentation of fructose, maltose and sucrose by W. cibaria , and fructose and maltose by L. paralimentarius and P. pentosaceus . Moreover, L. sanfranciscensis and L. brevis could obtain extra ATP through the reduction of fructose to mannitol, which favored the production of acetic acid against ethanol. The utilization of fructose as an electron acceptor has a decisive effect on the prevailing of L. sanfranciscensis and L. brevis in spontaneously fermented sourdough and in the scarce appearance of the other lactic acid bacteria studied .

The aim of this study was to assess the interactions between Saccharomyces cerevisiae and lactic acid bacteria that either form a stable consortium in Greek wheat sourdoughs (i.e. Lactobacillus sanfranciscensis and L. brevis) or occasionally constitute the secondary microbiota (i.e. Weissella cibaria, L. paralimentarius, Pediococcus pentosaceus and Enterococcus faecium). For this purpose, wheat dough was prepared by using strains of the above mentioned species either as single starters, or in combination of the yeast with each of the lactic acid bacteria strains. The determination of the metabolic products in sourdough samples was performed by HPLC analysis. Presence of lactic acid bacteria had no effect on S. cerevisiae final cell yield but affected negatively the maximum specific growth rate. Ethanol production was primarily affected negatively while the co-culture had a variable effect on glycerol production. On the other hand, the presence of S. cerevisiae favoured mannitol and acetic acid production, had a species-dependent effect on maximum specific growth rate and had no effect on final cfu/g sourdough and lactic acid production by the lactic acid bacteria and at the same time caused the depletion of glucose, fructose and maltose.

Dairy propionibacteria are present in Graviera Kritis, a traditional Gruyère-type cheese made without added propionic starter. Ten isolated strains were identified by a combination of SDS-PAGE, species-specific PCR and according to their ability to ferment lactose. They were all found to belong to the Propionibacterium freudenreichii subsp. shermanii species. Because of the stressing Gruyère technology, which includes cooking at 52 to 53 °C their thermotolerance was investigated at 55 °C. Thermotolerant and thermosensitive strains were clearly discriminated. Interestingly, the reference strain CIP 103027 belongs to the sensitive subset. One sensitive strain, ACA-DC 1305 and one tolerant, ACA-DC 1451, were selected for further study and compared to CIP 103027. For the sensitive strains ACA-DC 1305 and CIP 103027, heat pre-treatment at 42 °C conferred thermoprotection of cells at the lethal temperature of 55 °C, while there was less effect on the tolerant ACA-DC 1451. No cross-protection of salt-adapted cells against heat stress was observed for none of the strains. Differential proteomic analysis revealed distinct but overlapping cell responses to heat stress between sensitive and tolerant strains. Thermal adaptation upregulated typical HSPs involved in protein repair or turnover in the sensitive one. In the tolerant one, a distinct subset of proteins was overexpressed, whatever the temperature used, in addition to HSPs. This included enzymes involved in propionic fermentation, amino acid metabolism, oxidative stress remediation and nucleotide phosphorylation. These results bring new insights into thermoprotection in propionibacteria and the occurrence of divergent phenotypes within a same subspecies.

Lactobacillus plantarum ACA-DC 146 and L. paracasei subsp. tolerans ACA-DC 4037 were examined for their potential application as adjuncts in the production of traditional Greek set-type yoghurt. Both strains displayed low milk acidification activity, while no inhibition was observed towards or from the yoghurt starters used. Yoghurt produced with L. paracasei subsp. tolerans ACA-DC 4037 exhibited the best sensory properties, with a rich traditional smooth taste, and the strain was selected for further trials. Yoghurt produced with this strain as an adjunct had good physicochemical properties. After 2 weeks of refrigerated storage, microbial loads (>7.0logcfug−1) were in accordance with international recommendations and guidelines for probiotic and starter cultures in milk products. Increasing the microbial load further, using concentrated and encapsulated inocula (10–11logcfug−1), gave yoghurt with long fermentation times and poor organoleptic properties.

The metabolic interactions among the dominant Greek traditional wheat sourdough species Lactobacillus sanfranciscensis and Saccharomyces cerevisiae and the complementary species Lactobacillus brevis, Lactobacillus paralimentarius, Pediococcus pentosaceus and Weissella cibaria were examined. Their effect on the sensory properties of bread was evaluated as well. Wheat sourdough bread making was carried out according to a three-stage traditional procedure adjusted to semi-industrial scale. L. sanfranciscensis and S. cerevisiae were used as starter cultures either as such or in combination with L. brevis, L. paralimentarius, P. pentosaceus and W. cibaria. The determination of the metabolic products in sourdough samples was performed by HPLC analysis. L. brevis, W. cibaria and P. pentosaceus had basically no effect either on growth of the basal microflora or on the total metabolite production. On the other hand, L. paralimentarius seemed to have a negative effect on L. sanfranciscensis growth. All sourdough breads produced exhibited worthy organoleptic properties. Bread made with S. cerevisiae, L. sanfranciscensis and L. brevis ranked first in the sensory evaluation. The qualitative and quantitative differences observed in the metabolites’ profiles of the sourdoughs prepared with the different combinations of starters could not be correlated with the sensorial analysis of the respective breads produced.

Twenty-nine Lactobacillus strains of dairy origin were examined in vitro for their probiotic potential. Only a few strains were able to survive at pH 1 or in the presence of pepsin, while all were unaffected by pH 3, pancreatin and bile salts. Strains exhibited variable bile salt hydrolase activity. None was haemolytic. The majority of strains were resistant to vancomycin and teicoplanin, but sensitive to chloramphenicol and tetracycline. A few strains were able to adhere to Caco-2 cells. Although no bacteriocin activity was detected in vitro, strains L. casei Shirota ACA-DC 6002, L. plantarum ACA-DC 146 and L. paracasei subsp. tolerans ACA-DC 4037 were able to inhibit the adhesion of Escherichia coli and Salmonella typhimurium to Caco-2 cells. They also induced the secretion of pro- and anti-inflammatory cytokines by human peripheral blood mononuclear cells. These three strains were therefore found, in vitro, to possess desirable probiotic properties.

ABSTRACT We studied the potential inhibitory effect of Lactobacillus casei strain Shirota (from the fermented milk product Yakult [Yakult Ltd., Tokyo, Japan]) on Helicobacter pylori by using (i) in vitro inhibition assays with H. pylori SS1 (Sydney strain 1) and nine H. pylori clinical isolates and (ii) the in vivo H. pylori SS1 mouse model of infection over a period of 9 months. In vitro activity against H. pylori SS1 and all of the clinical isolates was observed in the presence of viable L. casei strain Shirota cells but not in the cell-free culture supernatant, although there was profound inhibition of urease activity. In vivo experiments were performed by oral administration of L. casei strain Shirota in the water supply over a period of 9 months to 6-week-old C57BL/6 mice previously infected with H. pylori SS1 (study group; n = 25). Appropriate control groups of H. pylori -infected but untreated animals ( n = 25) and uninfected animals given L. casei strain Shirota ( n = 25) also were included in the study. H. pylori colonization and development of gastritis were assessed at 1, 2, 3, 6, and 9 months postinfection. A significant reduction in the levels of H. pylori colonization was observed in the antrum and body mucosa in vivo in the lactobacillus-treated study group, as assessed by viable cultures, compared to the levels in the H. pylori -infected control group. This reduction was accompanied by a significant decline in the associated chronic and active gastric mucosal inflammation observed at each time point throughout the observation period. A trend toward a decrease in the anti- H. pylori immunoglobulin G response was measured in the serum of the animals treated with lactobacillus, although this decrease was not significant.

Citrate metabolism by Enterococcus faecium FAIR-E 198, isolated from Greek Feta cheese, was studied in various growth media containing citrate either in the presence of glucose, or as the sole carbon source, both under aerobic and anaerobic conditions. In de Man–Rogosa–Sharpe (MRS) broth with increasing citrate concentrations, cometabolism of citrate and glucose took place. Glucose was stoichiometrically converted into lactate, while citrate into acetate. Glucose consumption and biomass yield were enhanced with increasing initial citrate concentrations, even though maximum specific growth rate was not. When citrate was used as the sole carbon source in increasing initial concentrations, the main end product was acetate. Small amounts of lactate, formate, ethanol, and acetoin were also produced. In all cases, no significant differences were observed between aerobic and anaerobic conditions. However, when citrate was used as sole carbon source, formate production was favored in the absence of oxygen. The present work shows that E. faecium is able to utilize citrate in synthetic media, either in the presence of glucose or as the sole carbon source, resulting in energy production and the formation of aroma compounds.

Thermophilin ST-1 is produced by Streptococcus thermophilus ACA-DC 0001, a "wild" strain isolated from traditional Greek yogurt products. It exerts an inhibitory effect on lactic acid bacteria, several food spoilage and food-borne pathogenic microorganisms, and some Gram-negative phytopathogen bacteria, including Listeria innocua BL 86/20, Enterococcus faecalis EF1, Staphylococcus aureus ATCC 29996, Xanthomonas campestris BPIC 1660, Pseudomonas syringae BPIC 1549 and Erwinia rubrifasciens BPIC 1710. The crude antimicrobial compound is heat-labile (60 degreesC for 10 min) and sensitive to the proteolytic enzymes pronase and trypsin and high acidic and alkaline conditions, and shows a bactericidal mode of action against the indicator strain Lactococcus lactis ssp. cremoris CNRZ-117. Production of thermophilin ST-1 starts during the early growth of the producer strain and reaches a maximum titer of 2560 AU . mL(-1) at the end of the exponential growth. Thermophilin ST-1 was partially purified by ammonium sulfate precipitation, ionexchange and size-exclusion chromatography. SDS-PAGE electrophoresis of purified thermophilin ST-1 showed a single protein band with a molecular mass of 30 kg . mol(-1), classifying this novel bacteriocin with the large heat-labile proteins. Until now, however, the molecular mass of bacteriocins reported in the species of S. thermophilus was less than 10 kg . mol(-1) (small, heat-stable peptides). Curing experiments did not result in the loss of bacteriocin production, suggesting that the genetic determinant is probably located on the chromosome.

The X-prolyl-dipeptidyl aminopeptidase from Streptococcus macedonicus ACA-DC 191 was purified by anion exchange and hydrophobic interaction chromatography. A single band of a molecular mass of about 84 000 g.mol(-1) appeared in SDS-PAGE; by gel filtration it was shown that the native enzyme was dimeric. The enzyme showed optimum activity on glycyl-prolyl-4-nitroanilide at pH 7.0, with a K-M = 0.42 mmol.L-1 and a V-max = 12.8 mumol.mg(-1).min(-1). It was active over a temperature range of 10-60 degreesC. Over 60 degreesC, the enzyme activity declined rapidly. The peptidase was completely inactivated by PMSF, DTNB and Cu2+, while metal chelators had no effect on enzyme activity. By using the PCR technique with synthetic primers, the pepX gene was amplified, cloned and sequenced. This 2 289 nucleotide gene encodes a protein of 763 amino acids with a molecular mass of 86 866 g.mol(-1). The deduced amino acid sequence analysis of the pepX gene shows a high identity with PepX enzymes from other lactic acid bacteria and contains a motif around the active site serine (G-K-S-Y-L-G) that is well conserved among the PepX enzymes.

AIMS:To clone and sequence the pepX gene from Streptococcus thermophilus.METHODS AND RESULTS:Three pairs of primers were used in polymerase chain reactions using as template the total DNA from Strep. thermophilus ACA-DC 4 in order to amplify, clone and sequence the pepX gene. Sequence analysis revealed an open reading frame of 2268 nucleotides encoding a protein of 755 amino acids. The calculated molecular mass of 85 632 Da agreed well with the apparent molecular mass of 80 000 Da previously determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and gel filtration for the monomeric form of the purified enzyme.CONCLUSIONS:The pepX gene from Strep. thermophilus ACA-DC 4 was cloned and sequenced. The PepX protein showed significant sequence similarity with PepX enzymes from other lactic acid bacteria and contained a motif which was almost identical with the active site motif of the serine-dependent PepX family.SIGNIFICANCE AND IMPACT OF THE STUDY:There are economic and technological incentives for accelerating and controlling the process of cheese ripening. To achieve this, starters may be modified by introducing appropriate genes from other food-grade bacteria. New or additional peptidase activities may alter or improve the proteolytic properties of lactic acid bacteria.

ABSTRACT Streptococcus macedonicus ACA-DC 198, a strain isolated from Greek Kasseri cheese, produces a food-grade lantibiotic named macedocin. Macedocin has a molecular mass of 2,794.76 ± 0.42 Da, as determined by electrospray mass spectrometry. Partial N-terminal sequence analysis revealed 22 amino acid residues that correspond with the amino acid sequence of the lantibiotics SA-FF22 and SA-M49, both of which were isolated from the pathogen Streptococcus pyogenes. Macedocin inhibits a broad spectrum of lactic acid bacteria, as well as several food spoilage and pathogenic bacteria, including Clostridium tyrobutyricum. It displays a bactericidal effect towards the most sensitive indicator strain, Lactobacillus sakei subsp. sakei LMG 13558T, while the producer strain itself displays autoinhibition when it is grown under conditions that do not favor bacteriocin production. Macedocin is active at pHs between 4.0 and 9.0, and it retains activity even after incubation for 20 min at 121°C with 1 atm of overpressure. Inhibition of macedocin by proteolytic enzymes is variable.

Bacteriocin production by Enterococcus faecium FAIR-E 198, isolated from Greek Feta cheese, was studied in batch fermentations, under conditions simulating Feta cheese preparation. Maximum enterocin activity and growth rate was obtained in de Man–Rogosa–Sharpe (MRS) broth at 37 °C with controlled pH 6.5. The enterocin was produced throughout the growth phase of the microorganism, showing primary metabolite kinetics with a peak activity during the mid-exponential phase. The use of skimmed milk as substrate revealed low enterocin activity. When fermentations were performed in skimmed milk in the presence of rennet, CaCl2, and a mixed starter culture, no enterocin activity was observed, although the examined strain grew well under the above conditions. Finally, when E. faecium FAIR-E 198 was applied as adjunct starter in Feta cheese making, no enterocin activity was detected throughout ripening. Results obtained underline the frequently underestimated finding that in vitro production by novel bacteriocinogenic starter or co-cultures is no guarantee for in situ efficiency. It was concluded that the complex food environment thoroughly interferes with bacteriocin production levels.

Lactic acid bacteria (LAB) were isolated from Greek traditional wheat sourdoughs manufactured without the addition of baker's yeast. Application of sodium dodecyl sulfate-polyacrylamide gel electrophoresis of total cell protein, randomly amplified polymorphic DNA-PCR, DNA-DNA hybridization, and 16S ribosomal DNA sequence analysis, in combination with physiological traits such as fructose fermentation and mannitol production, allowed us to classify the isolated bacteria into the species Lactobacillus sanfranciscensis, Lactobacillus brevis, Lactobacillus paralimentarius, and Weissella cibaria. This consortium seems to be unique for the Greek traditional wheat sourdoughs studied. Strains of the species W. cibaria have not been isolated from sourdoughs previously. No Lactobacillus pontis or Lactobacillus panis strains were found. An L. brevis-like isolate (ACA-DC 3411 t1) could not be identified properly and might be a new sourdough LAB species. In addition, fermentation capabilities associated with the LAB detected have been studied. During laboratory fermentations, all heterofermentative sourdough LAB strains produced lactic acid, acetic acid, and ethanol. Mannitol was produced from fructose that served as an additional electron acceptor. In addition to glucose, almost all of the LAB isolates fermented maltose, while fructose as the sole carbohydrate source was fermented by all sourdough LAB tested except L. sanfranciscensis. Two of the L. paralimentarius isolates tested did not ferment maltose; all strains were homofermentative. In the presence of both maltose and fructose in the medium, induction of hexokinase activity occurred in all sourdough LAB species mentioned above, explaining why no glucose accumulation was found extracellularly. No maltose phosphorylase activity was found either. These data produced a variable fermentation coefficient and a unique sourdough metabolite composition.

Greek Feta cheese was prepared using as adjunct starter cultures Enterococcus faecium FAIR-E 198, E. faecium FAIR-E 243, and their combination. Numbers of enterococci in the control and in the batches containing E. faecium strains as adjunct starters rapidly increased until day 15 of ripening, and then remained constant. Both E. faecium strains positively affected the counts of non-starter lactic acid bacteria (NSLAB), micrococci and coliforms, while thermophilic cocci were not influenced. Moreover. E. faecium FAIR-E 243 enhanced the growth of mesophilic cocci and thermophilic bacilli. Physicochemical characteristics, such as pH, moisture, ash, salt in moisture and fat in dry matter (FDM) were not influenced by the addition of the E. faecium strains. The most pronounced effect was observed in the case of proteolysis. Both E. faecium strains, either as sole adjunct starter or in combination, increased the proteolytic index and the free amino groups concentration, and enhanced degradation of alpha(s1)- and beta-caseins in comparison to the control. Furthermore, the reverse-phase (RP)-HPLC peptide profiles of the water-soluble nitrogen (WSN) fractions were significantly affected by the addition of enterococci. The main volatile compounds produced were ethanol, acetate, acetone, acetaldehyde, acetoin and diacetyl, with highest amounts determined for ethanol, followed by acetate. Both E. faecium strains positively affected taste, aroma, colour and structure of the full-ripened cheeses, as well as the overall sensory profile. The present work emphasizes the technological significance of E. faecium strains and supports their use as adjunct cultures in the manufacture of Feta cheese.

The aim of this study was to develop a simple and specific method for the rapid detection and identification of Streptococcus macedonicus. The method was based on polymerase chain reaction (PCR) using species-specific primers derived from the 16S rRNA gene. Specific identification was proven on seven S. macedonicus strains, while 16 strains belonging to different lactic acid bacteria species were tested negative. The PCR assay was capable of detecting 100 pg of S. macedonicus DNA, and it was also efficient on single colonies of the bacterium. Furthermore, the same bacterial strains were used for the specificity evaluation of a S. macedonicus species-specific probe. Neither species-specific PCR nor DNA hybridisation experiments could differentiate Streptococcus waius from S. macedonicus, due to the identity of the 16S rRNA gene of the two species, indicating high phylogenetical relatedness. This was further confirmed by the comparative sequence analysis of the 16S–23S rRNA intergenic regions. It was thus clearly demonstrated that S. waius, recently described as a novel Streptococcus species, is phylogenetically identical to S. macedonicus.