Effects of carbon dioxide on cell growth and propionic acid production from glycerol and glucose by Propionibacterium acidipropionici

The effects of CO2 on propionic acid production and cell growth in glycerol or glucose fermentation were investigated in this study. In glycerol fermentation, the volumetric productivity of propionic acid with CO2 supplementation reached 2.94g/L/day, compared to 1.56g/L/day without CO2. The cell growth using glycerol was also significantly enhanced with CO2. In addition, the yield and productivity of succinate, the main intermediate in Wood-Werkman cycle, increased 81% and 280%, respectively; consistent with the increased activities of pyruvate carboxylase and propionyl CoA transferase, two key enzymes in the Wood-Werkman cycle. However, in glucose fermentation CO2 had minimal effect on propionic acid production and cell growth. The carbon flux distributions using glycerol or glucose were also analyzed using a stoichiometric metabolic model. The calculated maintenance coefficient (mATP) increased 100%, which may explain the increase in the productivity of propionic acid in glycerol fermentation with CO2 supplement.

[The use of real time PCR for quantitative determination of some propionic bacteria residing on human skin]

A test system has been developed for determination of propionic bacterial species residing on human skin. This system developed in the real time PCR format is applicable for quantitative determination and also detection of genomes of the following Propionibacterium species: P. acnes, P. granulosum and P. avidum. This system was used for analysis of wash samples from the skin of 17 pentathlon sportsmen and 16 students. All three species of propionic bacteria were found in all skin wash samples. However, contamination with P. acnes was two times higher in control group than in the group of pentathlon sportsmen.

Improved propionic acid production from glycerol with metabolically engineered Propionibacterium jensenii by integrating fed-batch culture with a pH-shift control strategy

Propionic acid (PA) production with metabolically engineered Propionibacterium jensenii (pZGX04-gldA) was improved by integrating fed-batch culture with a two-stage pH control strategy in a 3-L fermenter. The following two-stage pH control strategy was used: the pH was controlled at 5.9 for 0-36 h and shifted to 6.5 after 36 h. The PA titer was increased to 21.43 g/L. On the basis of pH control, the influence of fed-batch culture on PA production was further investigated and the maximum PA production (34.62 g/L) was obtained when glycerol was fed at a constant rate of 3.33 mL/h from 60 to 132 h with an initial glycerol concentration of 25 g/L. Crude glycerol was then used to produce PA using the optimized strategies, and maximal PA production reached 37.26 g/L. The strategies may be useful for the production of PA by other propionibacteria species.

An economical biorefinery process for propionic acid production from glycerol and potato juice using high cell density fermentation

An economically sustainable process was developed for propionic acid production by fermentation of glycerol using Propionibacterium acidipropionici and potato juice, a by-product of starch processing, as a nitrogen/vitamin source. The fermentation was done as high-cell-density sequential batches with cell recycle. Propionic acid production and glycerol consumption rates were dependent on initial biomass concentration, and reached a maximum of 1.42 and 2.30 g L(-1) h(-1), respectively, from 50 g L(-1) glycerol at initial cell density of 23.7 gCDW L(-1). Halving the concentration of nitrogen/vitamin source resulted in reduction of acetic and succinic acids yields by ~39% each. At glycerol concentrations of 85 and 120 g L(-1), respectively, 43.8 and 50.8 g L(-1) propionic acid were obtained at a rate of 0.88 and 0.29 g L(-1) h(-1) and yield of 84 and 78 mol%. Succinic acid was 13 g% of propionic acid and could represent a potential co-product covering the cost of nitrogen/vitamin source.

Enhancement of propionic acid fraction in volatile fatty acids produced from sludge fermentation by the use of food waste and Propionibacterium acidipropionici

Volatile fatty acids (VFA) can be used as the additional carbon source of biological nutrient removal (BNR), and the increase of propionic acid percentage in VFA has been reported to facilitate the performance of BNR. In this study a new method for significantly improving the propionic acid fraction in VFA derived from waste activated sludge was reported, which included (1) mixing food waste with sludge and pre-fermenting the mixture (first stage), and (2) separating the mixture, sterilizing the pre-fermentation liquid and fermenting it after inoculating Propionibacterium acidipropionici (second stage). By optimizing the first stage with response surface methodology, a propionic acid content of 68.4% with propionic acid concentration of 7.13 g COD/L could be reached in the second stage, which was much higher than that reported previously. Lactic acid was found to be the most abundant product of the first stage and it served as the substrate for propionic acid production in the second stage. Further investigation showed that during the first stage the addition of food waste to the pre-fermentation system of sludge significantly increased the generation of lactic acid due to the synergistic effect, which resulted in the improvement of propionic acid production in the second stage. Finally, the use of propionic acid-enriched VFA as a superior carbon source of BNR was tested, and its performance was observed to be much better than using acetic acid-enriched VFA derived from sludge by the previously documented method.

Production of propionic acid-enriched volatile fatty acids from co-fermentation liquid of sewage sludge and food waste using Propionibacterium acidipropionici

Volatile fatty acids (VFA), derived from sludge fermentation, have been used as one effective carbon source for biological nutrient removal, especially favorable with VFA containing with high levels of propionic acid. In this paper, a new fermentation method was employed to significantly produce the propionic acid-enriched VFA from the co-fermentation liquid of sewage sludge and food waste: including (1) mixing food waste with sludge in the anaerobic digester (the first stage) and (2) separating the mixture, sterilizing the first stage liquid and fermenting it after inoculation with Propionibacterium acidipropionici (the second stage). The effect of the key parameters including pH, the mixing ratio of the food waste and sludge, fermentation time and temperature of the first stage on the propionic acid-enriched VFA production (the second stage) was individually discussed. By the molecular weight distribution analysis, the comparison of the solubilisation and hydrolysis process in difference parameters was fully elaborated. The optimal combination of the parameters was then obtained. Finally, the propionic acid-enriched VFA fermentation was successfully conducted in a semi-continuous reactor using the first stage liquid from the optimal condition.

Formulation and evaluation of herbal anti-acne moisturizer

The moisture content present in human skin makes it look young and the use of moisturizer results in fastening the moisture with a surface film of oil. Acne vulgaris is one of the most commonly seen diseases among the youth. The present study is focused on the use of herbs as moisturizer for acne treatment. The anti-acne moisturizer was formulated from herbal crude extracts and investigated the physico-chemical parameters as well as antibacterial activity of the formulation. The study revealed that ethanol extract of Andrographis paniculata, Glycyrrhiza glabra, Ocimum sanctum, Azadiracta indica and Green tea possessed the potential for inhibiting acne. It was observed that the optimal formula of anti-acne moisturizer was satisfactorily effective to control acne inducing bacteria i.e., Staphylococcus epidermis and Propionibacterium. The physico-chemical parameters of the formulation were also optimal with no signs of irritation.

Assessment of the probiotic potential of a dairy product fermented by Propionibacterium freudenreichii in piglets

Dairy propionibacteria, including Propionibacterium freudenreichii , display promising probiotic properties, including immunomodulation. These properties are highly strain-dependent and rarely studied in a fermented dairy product. We screened 10 strains, grown in a newly developed fermented milk ultrafiltrate, for immunomodulatory properties in vitro. The most anti-inflammatory strain, P. freudenreichii BIA129, was further tested on piglets. P. freudenreichii -fermented product improved food intake and growth of piglets. Colonic mucosa explants of treated pigs secreted less interleukin 8 (-25%, P < 0.05) and tumor necrosis factor α (-20%, P < 0.05), either in basal conditions or after a lipopolysaccharide challenge. By contrast, the gut structure, barrier function (measured ex vivo in Ussing chambers), microbial diversity (assessed by 16S rRNA pyrosequencing), and colonic short-chain fatty acid content were unchanged, assuming maintenance of normal intestinal physiology. In conclusion, this work confirms in vivo probiotic properties of dairy propionibacteria-fermented products, which are promising for the prevention or healing of inflammatory bowel diseases.

Production of cis-9,trans-11-conjugated linoleic acid in camelina meal and okara by an oat-assisted microbial process

A method to obtain cis-9,trans-11-conjugated linoleic acid (c9,t11-CLA) into camelina meal and okara, the byproducts of plant oil processing, is described. The triacylglycerols in these materials were hydrolyzed with the aid of lipolytically active oat flour for 3 weeks at a water activity of 0.70. The resulting free linoleic acid was then isomerized predominantly to c9,t11-CLA by resting cells of Propionibacterium freudenreichii ssp. shermanii in 5% aqueous camelina meal and okara slurries. In camelina meal slurries, c9,t11-CLA content after 21 h of fermentation was 0.83 mg/mL and 96 mg/g of total lipids. In okara slurries, the content of c9,t11-CLA was 1.1 mg/mL and 78 mg/g of total lipids. Doubling the hydrolysis time in okara increased the subsequent content of c9,t11-CLA to 1.4 mg/mL, corresponding to 110 mg/g of total lipids. After isomerization, CLA was concentrated into a particulate material of the slurries by acidification. The results suggest that the method is applicable to a wide spectrum of lipid-containing plant materials to further increase their nutritional value.

Lactobacilli and dairy propionibacterium with potential as biopreservatives against food fungi and yeast contamination

Naturally fermented and raw foods contain a range of organisms that may have benefit as additives in some foods and food processing. In particular, potential anti-fungal properties of these organisms may be potentially utilised as natural alternatives to chemical additives used to delay and prevent spoilage by fungi and yeast. This study examined 12 novel bacteria previously isolated from food as possible biopreservatives. The bacteria from the lactobacilli and dairy propionibacterium groups were tested by agar overlay method for their ability to inhibit the growth of 10 fungi and one yeast commonly associated with food contamination. Eight among eleven tested lactic acid bacteria demonstrated broad spectrum of antifungal activity. Strong fungi inhibition was also demonstrated by the dairy propionibacterium, but efficacy was growth medium dependant. Only one fungi, Geotrichum candidum was highly resistant to the bacteria. Variation between the inhibition results for different bacteria identifies the importance of careful strain selection, and the benefits of strain combinations when selecting biopreservatives for foods.

[Effect of a corrinoid on Methanosarcina barkeri DNA synthesis]

Methanosarcina barkeri is capable of synthesizing large amounts of corrinoids, compounds of the vitamin B12 group, although not cobalamin. In the present work, exogenous cobalamin was demonstrated to upregulate DNA synthesis in M. harkeri cell suspensions incubated under air. The effect is similar to the one in Propionibacterium freudenreichii cells, though less pronounced. The growth of the archaeon under anaerobic conditions was shown to be suppressed by cobalamin and 5,6-dimethylbenzimidazole. The data obtained suggest the presence of a corrinoid-dependent ribonucleotide reductase in the archaeon cells which provides for deoxyribose precursors for DNA biosynthesis independently of the presence of molecular oxygen in the medium. Growth suppression under anoxic conditions by cobalamin and 5,6-dimethylbenzimidazole may be due to a decrease in the concentration of factor III, a polyfunctional corrinoid dominating in M. barkeri cells.

Propionibacterium jensenii produces the polyene pigment granadaene and has hemolytic properties similar to those of Streptococcus agalactiae

The red polyene pigment granadaene was purified and identified from Propionibacterium jensenii. Granadaene has previously been identified only in Streptococcus agalactiae, where the pigment correlates with the hemolytic activity of the bacterium. A connection between hemolytic activity and the production of the red pigment has also been observed in P. jensenii, as nonpigmented strains are nonhemolytic. The pigment and hemolytic activity from S. agalactiae can be extracted from the bacterium with a starch extraction solution, and this solution also extracts the pigment and hemolytic activity from P. jensenii. A partial purification of the hemolytic activity was achieved, but the requirement for starch to preserve its activity made the purification unsuccessful. Partially purified hemolytic fractions were pigmented, and the color intensity of the fractions coincided with the hemolytic titer. The pigment was produced in a soluble form when associated with starch, and the UV-visual spectrum of the extract gave absorption peaks of 463 nm, 492 nm, and 524 nm. The pigment could also be extracted from the cells by a low-salt buffer, but it was then aggregated. The purification of the pigment from P. jensenii was performed, and mass spectrometry and nuclear magnetic resonance analysis revealed that P. jensenii indeed produces granadaene as seen in S. agalactiae.

The growth of Propionibacterium cyclohexanicum in fruit juices and its survival following elevated temperature treatments

This study investigated the growth of Propionibacterium cyclohexanicum in orange juice over a temperature range from 4 to 40 degrees C and its ability to multiply in tomato, grapefruit, apple, pineapple and cranberry juices at 30 and 35 degrees C. Survival after 10 min exposure to 50, 60, 70, 80, 85, 90 and 95 degrees C in culture medium and in orange juice was also assessed. In orange juice the organism was able to multiply by 2 logs at temperatures from 4 to 35 degrees C and survived for up to 52 days. However, at 40 degrees C viable counts were reduced after 6 days and no viable cells isolated after 17 days. The optimum growth temperature in orange juice over 6 days was 25 degrees C but over 4 days it was 35 degrees C. The growth of P. cyclohexanicum was monitored in tomato, grapefruit, cranberry, pineapple and apple juices at 30 and 35 degrees C over 29 days. Cranberry, grapefruit and apple juice did not support the growth of P. cyclohexanicum. At 30 degrees C no viable cells were detected after 8 days in cranberry juice or after 22 days in grapefruit juice while at 35 degrees C no viable cells were detected after 5 and 15 days, respectively. However, in apple juice, although a 5 log reduction occurred, viable cells could be detected after 29 days. P. cyclohexanicum was able to multiply in both tomato and pineapple juices. In tomato juice, there was a 2 log increase in viable counts after 8 days at 30 degrees C but no increase at 35 degrees C, while in pineapple juice there was a 1 log increase in numbers over 29 days with no significant difference between numbers of viable cells present at 30 and 35 degrees C. The organism survived at 50 degrees C for 10 min in culture medium without a significant loss of viability while similar treatment at 60, 70 and 80 degrees C resulted in approximately a 3-4 log reduction, with no viable cells detected after treatment at 85 or 90 or 95 degrees C but, when pre-treated at intermediate temperatures before exposure to higher temperatures, some cells survived. However, in orange juice a proportion of cells survived at 95 degrees C for 10 min without pre-treatment and there was no significant difference between numbers surviving with and without pre-treatment. The results from this study demonstrate that P. cyclohexanicum is able to grow in a number of juices, other than orange juice, and able to survive a number of high temperature procedures. Therefore, if initially present in the raw materials P. cyclohexanicum might survive the pasteurization procedures used in the fruit juice industry, contaminate and consequently spoil the final product.

Development of New Probiotics by Strain Combinations: Is It Possible to Improve the Adhesion to Intestinal Mucus?

We evaluated the ability of commercial probiotic strains (Lactobacillus rhamnosus GG, L. rhamnosus LC705, Bifidobacterium breve 99, and Propionibacterium freudenreichii ssp. shermanii JS) to adhere alone or in different combinations to immobilized mucus. Probiotic combinations were clearly able to enhance the adhesion of L. rhamnosus GG, L. rhamnosus LC705, and P. freudenreichii ssp. shermanii JS. For L. rhamnosus GG and P. freudenreichii JS, all the combinations significantly improved adhesion to intestinal mucus, from 29.7 to 34.9% and from 1.9 to 2.3%, respectively. The adhesion of L. rhamnosus LC705 was improved from 0 to 46.4%. The adhesion of B. breve 99 was improved only in combination with L. rhamnosus GG and P. freudenreichii JS. Our results suggest that probiotic combinations could increase the beneficial health effects as compared with individual strains. Combinations of probiotic strains may therefore have synergistic adhesion effects, and such combinations also should be assessed in clinical studies.

Survival and metabolic activity of selected strains of Propionibacterium freudenreichii in the gastrointestinal tract of human microbiota-associated rats

In addition to their use in cheese technology, dairy propionibacteria have been identified as potential probiotics. However, to have a probiotic effect, propionibacteria have to survive and to remain metabolically active in the digestive tract. The aim of the present study was to investigate the survival and metabolic activity of Propionibacterium freudenreichii within the gastrointestinal tract of human microbiota-associated rats, and its influence on intestinal microbiota composition and metabolism. Twenty-five dairy Propionibacterium strains were screened for their tolerance towards digestive stresses and their ability to produce propionate in a medium mimicking the content of the human colon. Three strains were selected and a daily dose of 2 x 10(10) colony-forming units was fed to groups of human microbiota-associated rats for 20 d before microbiological, biochemical and molecular investigations being carried out. These strains all reached 8-log values per g faeces, showing their ability to survive in the gastrointestinal tract. Transcriptional activity within the intestine was demonstrated by the presence of P. freudenreichii-specific transcarboxylase mRNA. The probiotic efficacy of propionibacteria was yet species- and strain-dependent. Indeed, two of the strains, namely TL133 and TL1348, altered the faecal microbiota composition, TL133 also increasing the caecal concentration of acetate, propionate and butyrate, while the third strain, TL3, did not have similar effects. Such alterations may have an impact on gut health and will thus be taken into consideration for further in vivo investigations on probiotic potentialities of P. freudenreichii.

Antifungal compounds from cultures of dairy propionibacteria type strains

Antifungal compounds from cultures of five type strains of dairy propionibacteria, as well as from the cultivation medium, were studied. Cell-free supernatants and medium were fractionated by C(18) solid phase extraction. The aqueous 95% acetonitrile fractions were analyzed by GC-MS or subjected to reversed-phase HPLC, to identify, quantify or isolate antifungal substances. The resulting HPLC fractions were screened for antifungal activity against the mold Aspergillus fumigatus and the yeast Rhodotorula mucilaginosa. Active fractions were further separated by HPLC and the structures of the compounds were determined by spectroscopic and chromatographic methods. All five strains produced 3-phenyllactic acid, at concentrations ranging from 1.0 microg mL(-1) (Propionibacterium freudenreichii ssp. shermanii) to 15.1 microg mL(-1) (Propionibacterium thoenii), and at L/D -ratios ranging from 2 : 3 (Propionibacterium acidipropionici) to 9 : 1 (Propionibacterium freudenreichii). A number of active compounds found in cultures of propionibacteria were also present in noninoculated growth medium: two antifungal diketopiperazines, cyclo(L-Phe-L-Pro) and cyclo(L-Ile-L-Pro), and seven antifungal linear peptides. Three of the linear peptides corresponded to sequences found in the medium component casein, suggesting their origin from this component, whereas the diketopiperazines were suggested to be formed from medium peptides by heat treatment.

Antipropionibacterial activity of BAL19403, a novel macrolide antibiotic

BAL19403 exemplifies a new family of macrolide antibiotics with excellent in vitro activity against propionibacteria. MICs indicated that BAL19403 was very active against erythromycin-resistant and clindamycin-resistant propionibacteria with mutations in the region from positions 2057 to 2059 (Escherichia coli numbering) of the 23S rRNA, although it is less active against those rare clinical isolates in which a methyltransferase, ErmX, confers macrolide and lincosamide resistance by dimethylation of the adenine moiety at position 2058. BAL19403 was predominantly bacteriostatic toward the propionibacteria, and population analyses indicated resistance selection frequencies for BAL19403 and the comparator drugs (erythromycin, clindamycin) in the range 10(-8) to 10(-9) for cutaneous propionibacteria with diverse antibiotic resistance profiles. On the basis of its antipropionibacterial activity and its high anti-inflammatory activity, BAL19403 represents a promising topical treatment for mild to moderate inflammatory acne vulgaris.

Transcarboxylase mRNA: A marker which evidences P. freudenreichii survival and metabolic activity during its transit in the human gut

Dairy propionibacteria have recently been considered as probiotics which may beneficially modulate the intestinal ecosystem. However, appropriate vectors (food matrices containing the probiotic) which preserve their viability and offer good tolerance towards digestive stresses need to be developed. In addition, the development of efficient non-invasive methods which specifically monitor Propionibacterium freudenreichii concentration and activity within the human gut is required. To address this latter need, an enzyme involved in propionic fermentation, transcarboxylase, was evaluated in this study as molecular marker in P. freudenreichii. In vitro, the three transcarboxylase subunits were shown to be encoded by an operon and their expression regulated. It occurred during propionic fermentation, ceased in starved cells and was not affected by digestive stresses. The 5S subunit gene of transcarboxylase allowed specific detection of P. freudenreichii by real time PCR in the complex human faecal microbiota. A dairy vector harbouring P. freudenreichii was developed and afforded elevated probiotic faecal concentrations in humans. In vivo, this PCR method allowed rapid quantification of faecal P. freudenreichii in agreement with the cultural method (cfu counting). Moreover, real time Reverse Transcription (RT) -PCR evidenced transcription of the 5S subunit gene during transit through the human digestive tract. This work constitutes a methodological advance for survival and activity evaluation in human trials of the probiotics belonging to the P. freudenreichii species. It strongly suggests that this bacterium not only survives but remains metabolically active in the human gut.

Optimal aerobic cultivation method for 1,4-dihydroxy-2-naphthoic acid production by Propionibacterium freudenreichii ET-3

To investigate the effects of oxygen supply on Propionibacterium freudenreichii ET-3 metabolism and 1,4-dihydroxy-2-naphthoic acid (DHNA) production in detail, the strain was cultured by switching from anaerobic condition to aerobic condition at 72 h (termed anaerobic-aerobic switching culture hereafter) employing different oxygen transfer rates (OTRs) in the range of 0.08-0.90 mg/(l.h). It was found that a 0.08 mg/(l.h) OTR could not change the metabolism or improve the DHNA production of P. freudenreichii ET-3. When the OTR was in the range of 0.23-0.66 mg/(l.h), propionate, which inhibits DHNA production significantly, was consumed during the aerobic phase. Final DHNA concentration increased to 0.22 mM, irrespective of OTR. When the OTR was 0.90 mg/(l.h), a sudden increase in dissolved oxygen (DO) concentration during the aerobic phase resulted in a sudden decrease in DHNA concentration. To attenuate the stresses caused by propionate and oxygen exposure, we designed an optimal cultivation in which the anaerobic and aerobic phases were repeated three times alternately. As a result, propionate concentration was maintained below the level that inhibits DHNA production, and no DO concentration was detected throughout the culture. The final DHNA concentration in this culture was 0.33 mM, which is 2.7-fold that in the anaerobic culture and 1.5-fold that in the anaerobic-aerobic switching culture.

Use of DNA quantification to measure growth and autolysis of Lactococcus and Propionibacterium spp. in mixed populations

Autolysis is self-degradation of the bacterial cell wall that results in the release of enzymes and DNA. Autolysis of starter bacteria, such as lactococci and propionibacteria, is essential for cheese ripening, but our understanding of this important process is limited. This is mainly because the current tools for measuring autolysis cannot readily be used for analysis of bacteria in mixed populations. We have now addressed this problem by species-specific detection and quantification of free DNA released during autolysis. This was done by use of 16S rRNA gene single-nucleotide extension probes in combination with competitive PCR. We analyzed pure and mixed populations of Lactococcus lactis subsp. lactis and three different species of Propionibacterium. Results showed that L. lactis subsp. lactis INF L2 autolyzed first, followed by Propionibacterium acidipropionici ATCC 4965, Propionibacterium freudenreichii ISU P59, and then Propionibacterium jensenii INF P303. We also investigated the autolytic effect of rennet (commonly used in cheese production). We found that the effect was highly strain specific, with all the strains responding differently. Finally, autolysis of L. lactis subsp. lactis INF L2 and P. freudenreichii ISU P59 was analyzed in a liquid cheese model. Autolysis was detected later in this cheese model system than in broth media. A challenge with DNA, however, is DNA degradation. We addressed this challenge by using a DNA degradation marker. We obtained a good correlation between the degradation of the marker and the target in a model experiment. We conclude that our DNA approach will be a valuable tool for use in future analyses and for understanding autolysis in mixed bacterial populations.

Aerobic culture of Propionibacterium freudenreichii ET-3 can increase production ratio of 1,4-dihydroxy-2-naphthoic acid to menaquinone

This is the first report on the production of both 1,4-dihydroxy-2-naphthoic acid (DHNA) and menaquinone by Propionibacterium freudenreichii ET-3. DHNA can be a stimulator of bifidogenic growth, and menaquinone has important roles in blood coagulation and bone metabolism. During anaerobic culture, DHNA and menaquinone concentrations reached 0.18 mM and 0.12 mM, respectively. The molar ratio between these products was approximately 3:2, which was not affected by culture pH and temperature over the ranges of 6.0-7.0 and 31-35 degrees C, respectively. As for organic acid, propionate and acetate accumulated at concentrations of 0.3 M and 0.15 M, respectively, and the propionate accumulation particularly inhibited further production of DHNA. To improve DHNA production, we switched from anaerobic condition to aerobic condition during the culture when lactose was depleted. DHNA concentration continued to increase even after lactose exhaustion, reaching 0.24 mM. In contrast to DHNA production, menaquinone production stopped after the switch to aerobic condition. The total molar production of DHNA and menaquinone was 0.3 mM irrespective of aerobic culture and anaerobic-aerobic switching culture. Therefore, the anaerobic-aerobic switching culture could increase the production ratio of DHNA to menaquinone. The DHNA concentration obtained from the anaerobic-aerobic switching culture was 1.3-fold higher than that in the anaerobic culture, because P. freudenreichii ET-3 utilized propionate accumulated in the medium via the reversed methylmalonyl CoA pathway under aerobic condition. The culture method proposed in this study could be applicable to industrial-scale fermentation using 1000 l of media, by which 0.23 mM DHNA was produced.

Isolation of aminopeptidase N genes of food associated propionibacteria and observation of their transcription in skim milk and acid whey

In this study consensus oligonucleotides PN5/PN3 were designed by aligning the aminopeptidase N genes (pepN) of various actinobacteria and applied to the isolation of the pepN genes of dairy propionibacteria (PAB) and closely related species associated with food. This allowed sequencing of a pepN gene region from Propionibacterium jensenii LMG 16541. The sequence of this gene was completed by inverse PCR. Consensus primer pairs NU1/D1 and NU2/D1 were derived from the alignment of the new sequence with its homologues in Propionibacterium acnes and other actinobacteria; these were used to start sequencing of the pepN genes of Propionibacterium freudenreichii, Propionibacterium thoenii, Propionibacterium microaerophilum, Propionibacterium acidipropionici, Propioni bacterium cyclohexanicum and Propionibacterium microaerophilum. Reverse transcription coupled with PN5/PN3 and NU1/D1 PCR tests indicated that the pepN genes of P. jensenii and P. freudenreichii are expressed during growth in skim milk and acid whey.

Total bacterial and species-specific 16S rDNA micro-array quantification of complex samples

AIMS

We describe a novel DNA-micro-array-based method that targets 16S rDNA to quantify changes in both the total bacterial DNA and the species-specific DNA composition.

METHODS AND RESULTS

Quantifications were achieved by combining competitive PCR for quantifying total bacterial DNA with quantification of species-specific DNA composition based on signature 16S rDNA sequences. We constructed 11 different probes, which were evaluated on 21 different strains, in addition to complex samples. The signals obtained with sequence-specific labelling of the probes corresponded well with what should be expected based on 16S rDNA phylogenetic reconstruction. The quantification of species-specific DNA composition showed that the micro-array approach could be used to accurately determine differential growth of bacteria in mixed samples. We analysed samples containing mixtures of Lactococcus lactis and different species of propionibacteria during a 2-week incubation period. Lactococcus lactis grew fast, reaching a maximum after 12 h, Propionibacterium acidipropionici and Propionibacterium freudenreichii reached a maximum after 48 h, whereas Propionibacterium jensenii showed a slow increase during the whole growth period. The 16S rDNA total bacterial DNA quantification was compared with real-time PCR, absorbance measurements (ABS600) and colony forming units (CFU).

CONCLUSION

The accuracy of the array approach was in the same range or better than the alternative techniques. The potential of the 16S rDNA micro-array method was further demonstrated using a liquid cheese model.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is to our knowledge the first time quantification of the total bacterial DNA and the species-specific DNA compositions of mixed populations have been achieved in the same assay.

[A positive effect of Propionibacterium freudenreichii on the growth of Saccharomyces cerevisiae during their cocultivation]

The growth pattern of Saccharomyces cerevisiae and Propionibacterium freudenreichii ssp. shermanii (P. shermanii; propionic acid bacteria, PABs) during cocultivation in liquid media depended on the ratio of the cells in the inoculum. An increase in the growth rate of S. cerevisiae was observed at a PAB to yeast ratio of approximately 3 : 1; higher ratios exerted adverse effects on yeast growth. The culture liquid of 18- to 24-h (young) cultures of PABs stimulated yeast growth. Although yeast growth-stimulating exometabolites of PABs were not high-molecular-weight compounds, they were thermolabile. When present in the medium at concentrations of up to 1.5%, the antimicrobial agent sodium propionate did not interfere with S. cerevisiae growth; however, it completely inhibited the growth of B. subtilis at a concentration of 0.2%.

Fed-batch enhancement of jenseniin G, a bacteriocin produced by Propionibacterium thoenii (jensenii) P126

Jenseniin G is an antibotulinal bacteriocin (antimicrobial peptide) produced by the dairy culture, Propionibacterium thoenii (jensenii) P126. Activity from crude jenseniin G preparations isolated from static cultures was not detected in unconcentrated cultures before day 7. Activity was not detectable until the spent culture medium was concentrated 50-100 fold. Maximum activity (21 AU/ml) was observed in concentrated supernates at day 9. The production of bacteriocin jenseniin G was increased in fed-batch fermentations for 14 d at 32 degrees C in sodium lactate broth (NLB) containing 1.2% sodium lactate. Viable cell numbers in static and fed-batch cultures reached 1.2 and 5.4x10(9), respectively, during late exponential/early stationary phase (3 d). Concentrations of viable cells in fed-batch fermentations remained constant throughout the incubation period; those in static fermentations dropped after day 6 to a final concentration of 1.5x10(7). During fed-batch fermentations, jenseniin G was directly detected at day 5. In fed-batch fermentations, maximum activity in concentrated supernates (384 AU/ml) on day 12 provided an 18 fold increase over yields in static cultures and in fermenter without pH control, and 2.4 fold increase over yields in fermenter at controlled pH at 6.4. Fed-batch fermentation shows promise as a method to obtain high concentrations of industrially significant bacteriocins from dairy propionibacteria.

Production of Propionibacterium shermanii biomass and vitamin B12 on spent media

AIMS

The propionibacteria are commercially important due to their use in the cheese industry, and there is a growing interest for their probiotic effects. Stimulatory effects of lactic acid bacteria (LAB) on propionic acid bacteria have been observed. This study was designed to examine the possibility of using spent media previously used to grow LAB for the production of biomass and metabolites of Propionibacterium freudenreichii subsp. shermanii.

METHODS AND RESULTS

Seventeen MRS and vegetable juice media were prefermented by various LAB and evaluated for their ability to subsequently support the growth of Propionibacterium, using automated spectrophotometry (AS). Growth of Propionibacterium in spent media was strongly affected by the LAB strain used to produce the spent medium. The native MRS medium (not prefermented) yielded the highest optical density values followed by prefermented media by Lactobacillus acidophilus, Bifidobacterium longum and Lactococcus lactis. Prefermented cabbage juice enabled good growth of Propionibacterium. For the production of organic acids and vitamin B12, cells of Propionibacterium were concentrated and immobilized in alginate beads in the aim of accelerating the bioconversions. More propionic acid was obtained in spent media than in native MRS. The concentration of vitamin B12 was higher in media fermented with free cells than those with immobilized cultures; with the free cells, its concentration varied from 900 to 1800 ng ml(-1) of media.

CONCLUSIONS

It was demonstrated that spent media could be recycled for the production of Propionibacterium and metabolites, depending on the LAB strain that was previously grown. Media remediation is needed to improve the production of vitamin B12, especially with immobilized cells.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study presents an option for recycling of spent media generated by producers of LAB or producers of fermented vegetables. The propionic fermentation may result in three commercial products: biomass, vitamin B12 or organic acids, which may be used as starters, supplements or food preservatives. It is an attractive process from economical and environmental standpoints.

Protection mechanism of probiotic combination against human pathogens: in vitro adhesion to human intestinal mucus

In this study we evaluated the ability of commercial strains (L. rhamnosus GG, L. rhamnosus LC705, and P. freudenreichii ssp. shermanii JS) in combination with B. breve 99 or B. lactis Bb12 to inhibit, displace and compete with model pathogens in order to test their influence on the adhesion of selected pathogens to immobilized human intestinal mucus. Our results demonstrate that specific probiotic combinations are able to enhance the inhibition percentages of pathogens adhesion to intestinal mucus when compared to individual strains. This suggests that combinations of probiotic strains are useful and more effective in inhibition of pathogen adhesion than individual strains. Such combinations should be assessed in clinical studies in subjects where the intestinal microbiota aberrancies have been identified.

Conjugated linoleic acid content and organoleptic attributes of fermented milk products produced with probiotic bacteria

The effect of probiotic bacteria on the formation of conjugated linoleic acid (CLA), microbial growth, and organoleptic attributes (acidity, texture, and flavor) of fermented milk products was determined. Four probiotic bacteria, Lactobacillus rhamnosus, Propionibacterium freudenreichii subsp. shermanii 56, P. freudenreichii subsp. shermanii 51, and P. freudenreichii subsp. freudenreichii 23, were evaluated individually or in coculture with traditional yogurt cultures (Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus salivarius subsp. thermophilus). The lipid source was hydrolyzed soy oil. L. rhamnosus, in coculture with yogurt culture, resulted in the highest content of CLA. Growth and CLA formation of propionibacteria were enhanced in the presence of yogurt cultures. Texture and flavor attributes of fermented milks produced with propionibacteria were significantly different than the fermented milks processed with yogurt cultures. The fermented milks processed with probiotic bacteria in coculture with yogurt cultures demonstrated similar acidity, texture, and flavor as the fermented milk produced with yogurt cultures.

Enhancement of oxygen mass transfer in stirred bioreactors using oxygen-vectors 2. Propionibacterium shermanii broths

The previous works on simulated broths are continued and developed for Propionibacterium shermanii broths. The obtained results indicated the considerable increase of kLa in presence of n-dodecane as oxygen-vector and the existence of a certain value of hydrocarbon concentration that corresponds to the maximum mass transfer rate of oxygen. The magnitude of the positive effect of the oxygen-vector strongly depends on operational conditions of the bioreactor, on broth characteristics and on P. shermanii concentration.

The addition of Propionibacterium freudenreichii to Raclette cheese induces biochemical changes and enhances flavor development

Two mixtures of Propionibacterium freudenreichii commercial strains were tested as adjunct cultures in pasteurized milk Raclette cheese to investigate the ability of propionibacteria (PAB) to enhance flavor development. Cheese flavor was assessed by a trained sensory panel, and levels of free amino acids, free fatty acids, and volatile compounds were determined. The PAB level showed a 1.4 log increase within the ripening period (12 weeks at 11 degrees C). Eye formation, which was not desired, was not observed in PAB cheeses. PAB fermented lactate to acetate and propionate and produced fatty acids by lipolysis, branched chain volatile compounds derived from isoleucine and leucine catabolism and some esters. One of the experimental cheeses received the highest scores for odor and flavor intensity and was characterized by higher frequencies of detection for some minor notes ("propionic"and "whey" odor, "sweet" taste). PAB can therefore be considered as potential adjunct cultures to enhance or modify cheese flavor development.

Probiotic supplementation improves tolerance to Helicobacter pylori eradication therapy--a placebo-controlled, double-blind randomized pilot study

BACKGROUND

H. pylori is the major cause of chronic gastritis, and a risk factor for peptic ulcer and gastric cancer.

AIM

To investigate the effect of probiotic supplementation on the tolerance and efficacy of H. pylori eradication treatment in a randomized, double-blind, placebo-controlled trial.

METHODS

A total of 338 volunteers were screened for H. pylori infection. The eligibility criteria were met by 47 subjects whose H. pylori infection was verified at the outset and re-evaluated after the treatment by the 13C-urea breath test and by enzyme immunoassay serology. The subjects were randomized to receive probiotic therapy (Lactobacillus rhamnosus GG, L. rhamnosusLC705, Bifidobacterium breve Bb99 and Propionibacterium freudenreichii ssp. shermanii JS) or a placebo during H. pylori eradication and for 3 weeks following the treatment, and recorded their daily symptoms in a standardized diary.

RESULTS

When the frequencies of new or aggravated symptoms were evaluated, no significant differences were found between the two groups for individual symptoms. However, the probiotic group showed less treatment-related symptoms as measured by the total symptom score change (P = 0.038) throughout the H. pylori eradication therapy in contrast to the placebo group. The H. pylori eradication rate was non-significantly higher in the group receiving probiotic therapy (91% vs. 79%, P = 0.42). In this group the recovery of probiotic bacteria in the faeces increased significantly (P < 0.001).

CONCLUSIONS

In this pilot study, probiotic supplementation did not diminish significantly the frequency of new or aggravated symptoms during H. pylori eradication. However, our data suggest an improved tolerance to the eradication treatment when total symptom severity was taken into account. Furthermore, the results show that probiotic bacteria are able to survive in the gastrointestinal tract despite the intensive antimicrobial therapy.

An on-line technique for monitoring propionic acid fermentation

An on-line technique, based on measuring the increase in pressure due to CO(2) release in a closed air-tight reactor, was used to evaluate the fermentation of lactate by propionibacteria. The method was applied to batch cultures of Propionibacterium shermanii grown in yeast extract/sodium lactate medium containing lactate as a carbon source under micro-aerophilic conditions. Gas pressure evolution was compared both with substrate consumption and metabolites production and with acidification and growth. Linear relationships were found between gas pressure variation, lactate consumption and propionate and acetate production. The technique also enabled the evaluation of total CO(2) produced, by taking account of pressure, oxygen and pH measurements. These results tend to show that this simple and rapid method could be useful to monitor propionic acid bacteria growth.

Clarification of interactions among microorganisms and development of co-culture system for production of useful substances

Co-culture systems containing two microorganisms for the production of useful substances are described. We developed a novel co-culture system composed of two fermentors and two microfiltration modules. The proposed co-culture system allowed regulation of the dissolved oxygen concentration at a level suitable for an individual microorganism in each fermentor, as well as the successful exchange of culture medium between two fermentors. By co-culture, using a combination of Pichia stipitis and Saccharomyces cerevisiae, ethanol was produced efficiently from a mixture of glucose and xylose. Moreover, the useful probiotic cells were simultaneously produced with a high productivity by our co-culture using a combination of Bifidobacterium and Propionibacterium. Kefiran production by Lactobacillus kefiranofaciens alone under the culture conditions, established by mimicking the presence and activities of yeast cells in kefir grains, was also investigated. The results obtained showed that under the culture conditions established by mimicking the actions of yeast cells on L. kefiranofaciens in kefir grains, the amount of kefiran produced was enhanced, even when the lactic acid bacterium alone was used.

Enhancement of trehalose production in dairy propionibacteria through manipulation of environmental conditions

We have shown that the ability to produce trehalose is widespread within the genus Propionibacterium. Eighteen strains isolated from dairy sources were screened for trehalose synthesis; the effect of environmental conditions on trehalose production was evaluated in Propionibacterium freudenreichii ssp. shermanii NIZO B365, a strain that accumulated high amounts of this disaccharide. Lactose was the best carbohydrate source for trehalose production, whereas lactate, the substrate that led to the highest specific growth rate, was a poor precursor. Trehalose was consumed after exhaustion of the carbon source in the medium, suggesting its role as a reserve compound. The production of trehalose was not affected by lowering the growth temperature from 30 to 20 degrees C. On the other hand, the maximum trehalose accumulation increased from about 200 to 400 mg of trehalose/g of cell protein upon decreasing the pH from 7.0 to 4.7, by increasing the concentration of NaCl to 2% (w/v), or during growth under aerobic conditions (50% air saturation, 24 microM O(2), pH 7.0). In the absence of NaCl, trehalose accumulated concomitantly with growth, but an increase in salinity triggered a high trehalose production already in the early exponential growth phase. The data provide evidence for a dual function of trehalose as a reserve compound and as a stress-response metabolite. Moreover, P. freudenreichii ssp. shermanii NIZO B365 was able to produce high levels of trehalose in skim milk, which is promising for the implementation of fermented dairy products.

In vitro assessment of the upper gastrointestinal tolerance of potential probiotic dairy propionibacteria

This study aimed to assess the transit tolerance of potential probiotic dairy propionibacteria strains in human upper gastrointestinal tract in vitro, and to evaluate the effect of food addition on viability of these strains in simulated pH 2.0 gastric juices. The transit tolerance of 13 dairy propionibacteria strains was determined at 37 degrees C by exposing washed cell suspensions to simulated gastric juices at pH values at 2.0, 3.0, and 4.0, and simulated small intestinal juices (pH 8.0) with or without 0.3% bile salts. The viability of dairy propionibacteria in pH 2.0 simulated gastric juice with So-Good original soymilk or Up & Go liquid breakfast was also determined. The simulated gastric transit tolerance of dairy propionibacteria was strain-dependent and pH-dependent. All tested strains were tolerant to simulated small intestinal transit. The addition of So-Good original soymilk or Up & Go liquid breakfast greatly enhanced the survival of dairy propionibacteria strains in pH 2.0 simulated gastric juices. Dairy propionibacteria strains demonstrate high tolerance to simulated human upper gastrointestinal tract conditions and offer a relatively overlooked, yet alternative source for novel probiotics besides Lactobacillus and Bifidobacterium.

Adjunct starter properties affect characteristic features of Swiss-type cheeses

A large number of microorganisms, both starter microorganisms and non-starter lactic acid bacteria originating from the base milk, or from various contamination sources during cheese manufacture, is associated with cheese ripening and the formation of flavour, texture and aroma. Under controlled conditions, Emmental and Bergkäse, a Gruyère-type cheese variety, were produced from pasteurised milk with standard starters and defined strains of facultatively heterofermentative lactobacilli (FHL), and partly with addition of a defined mixture of enterococci. Lactobacillus casei subsp. casei and L. rhamnosus (two strains each) were selected with respect to their potential for the utilisation of citric acid and ribose as sole energy source. The FHL developed up to 10(8) cfu/g within the first weeks of ripening, and viable counts in mature cheeses were 10(7) cfu/g, independent of the cheese variety. Bergkäse made with addition of L. rhamnosus strains showed a more pronounced proteolysis, resulting in reduced firmness and elasticity values of the cheese body, and FHL strains able to utilise citric acid improved the appearance of the cheeses by increasing the number of small eyes to the desired level. In Emmental cheese, the citric acid (+) strains reduced the intensity of propionic acid formation as the FHL apparently competed with the propionibacteria, and enterococci disappeared completely during maturation. Although further work is needed the study shows that, depending on the cheese variety, particular properties of FHL adjunct starters significantly affect important quality attributes of the resulting cheeses.

The in vivo assessment of safety and gastrointestinal survival of an orally administered novel probiotic, Propionibacterium jensenii 702, in a male Wistar rat model

This study aimed to evaluate in vivo gastrointestinal survival and safety of orally administered probiotic bacterium, Propionibacterium jensenii 702, using a male Wistar rat model. A high dose of 10(10) cfu/rat/day of P. jensenii 702 was fed to each rat for 81 days. The repeated dose toxicity and translocation of P. jensenii 702 into rat tissues were evaluated, along with the rat faecal beta-glucuronidase activities and dairy propionibacteria counts. Results showed that P. jensenii 702 had no adverse effect on general health status, body weight gain, visceral organs and faecal beta-glucuronidase activities. No viable cells of P. jensenii 702 were recovered from blood and tissue samples (mesenteric lymph nodes, liver and spleen) of rats, and no treatment-associated illness or death was observed. Faecal dairy propionibacteria counts reached 10(8) cfu/g after 36 days treatment and remained between 10(8)-10(9) cfu/g till the end of 81 days treatment. The results indicate that P. jensenii 702 was able to survive the in vivo gastrointestinal tract transit of rats, with no adverse affects on the animals. However, further human clinical trials are required before strain P. jensenii 702 could be incorporated into food for human consumption as probiotics.

Fermentation of Five Sucrose Isomers by Human Dental Plaque Bacteria

Sucrose has five structural isomers: palatinose, trehalulose, turanose, maltulose and leucrose. Although these isomers have been reported to be noncariogenic disaccharides, which cannot be utilized by mutans streptococci, there is no information about their fermentability by other bacteria in dental plaque. The purpose of the present study was to examine whether these isomers were fermented by predominant bacteria in human dental plaque. Clinical bacterial isolates obtained from dental plaque from 3 children aged 22 months to 50 months (146 strains) were inoculated into 3 ml of peptone-yeast extract (PY medium) containing glucose for 1 day, then an aliquot of 20 microl of culture medium was inoculated into 1 ml of PY medium containing 1% (w/v) of the respective test carbohydrates. After incubation for 1 day, the pH values and the optical density at 660 nm of the cultures were measured. Fermentation ability was measured by pH <or=5.5, growth by an OD(660) of >or=0.5. Of the clinical isolates, 33% fermented palatinose, and 69% of these were Actinomyces species. All of the palatinose-fermenting bacterial strains fermented trehalulose, 25% fermented turanose, 70% fermented maltulose and 23% fermented leucrose. We therefore conclude that, in human dental plaque, there are significant numbers of bacteria that are able to ferment sucrose isomers.

Susceptibility and adaptive response to bile salts in Propionibacterium freudenreichii: physiological and proteomic analysis

Tolerance to digestive stresses is one of the main factors limiting the use of microorganisms as live probiotic agents. Susceptibility to bile salts and tolerance acquisition in the probiotic strain Propionibacterium freudenreichii SI41 were characterized. We showed that pretreatment with a moderate concentration of bile salts (0.2 g/liter) greatly increased its survival during a subsequent lethal challenge (1.0 g/liter, 60 s). Bile salts challenge led to drastic morphological changes, consistent with intracellular material leakage, for nonadapted cells but not for preexposed ones. Moreover, the physiological state of the cells during lethal treatment played an important role in the response to bile salts, as stationary-phase bacteria appeared much less sensitive than exponentially growing cells. Either thermal or detergent pretreatment conferred significantly increased protection toward bile salts challenge. In contrast, some other heterologous pretreatments (hypothermic and hyperosmotic) had no effect on tolerance to bile salts, while acid pretreatment even might have sensitized the cells. Two-dimensional electrophoresis experiments revealed that at least 24 proteins were induced during bile salts adaptation. Identification of these polypeptides suggested that the bile salts stress response involves signal sensing and transduction, a general stress response (also triggered by thermal denaturation, oxidative toxicity, and DNA damage), and an alternative sigma factor. Taken together, our results provide new insights into the tolerance of P. freudenreichii to bile salts, which must be taken into consideration for the use of probiotic strains and the improvement of technological processes.

Selective enumeration of Lactobacillus delbrueckii ssp. bulgaricus, Streptococcus thermophilus, Lactobacillus acidophilus, bifidobacteria, Lactobacillus casei, Lactobacillus rhamnosus, and propionibacteria

Nineteen bacteriological media were evaluated to assess their suitability to selectively enumerate Lactobacillus delbrueckii ssp. bulgaricus, Streptococcus thermophilus, Lactobacillus casei, Lactobacillus rhamnosus, Lactobacillus acidophilus, bifidobacteria, and propionibacteria. Bacteriological media evaluated included Streptococcus thermophilus agar, pH modified MRS agar, MRS-vancomycine agar, MRS-bile agar, MRS-NaCl agar, MRS-lithium chloride agar, MRS-NNLP (nalidixic acid, neomycin sulfate, lithium chloride and paramomycine sulfate) agar, reinforced clostridial agar, sugar-based (such as maltose, galactose, sorbitol, manitol, esculin) media, sodium lactate agar, arabinose agar, raffinose agar, xylose agar, and L. casei agar. Incubations were carried out under aerobic and anaerobic conditions at 27, 30, 37, 43, and 45 degrees C for 24, 72 h, and 7 to 9 d. S. thermophilus agar and aerobic incubation at 37 degrees C for 24 h were suitable for S. thermophilus. L. delbrueckii ssp. bulgaricus could be enumerated using MRS agar (pH 4.58 or pH 5.20) and under anaerobic incubation at 45 degrees C for 72 h. MRS-vancomycine agar and anaerobic incubation at 43 degrees C for 72 h were suitable to enumerate L. rhamnosus. MRS-vancomycine agar and anaerobic incubation at 37 degrees C for 72 h were selective for L. casei. To estimate the counts of L. casei by subtraction method, counts of L. rhamnosus on MRS-vancomycine agar at 43 degrees C for 72 h under anaerobic incubation could be subtracted from total counts of L. casei and L. rhamnosus enumerated on MRS-vancomycine agar at 37 degrees C for 72 h under anaerobic incubation. L. acidophilus could be enumerated using MRS-agar at 43 degrees C for 72 h or Basal agar-maltose agar at 43 degrees C for 72 h or BA-sorbitol agar at 37 degrees C for 72 h, under anaerobic incubation. Bifidobacteria could be enumerated on MRS-NNLP agar under anaerobic incubation at 37 degrees C for 72 h. Propionibacteria could be enumerated on sodium lactate agar under anaerobic incubation at 30 degrees C for 7 to 9 d. A subtraction method was most suitable for counting propionibacteria in the presence of other lactic acid bacteria from a product. For this method, counts of lactic bacteria at d 3 on sodium lactate agar under anaerobic incubation at 30 degrees C were subtracted from counts at d 7 of lactic bacteria and propionibacteria.

Monitoring of apheresis platelet bacterial contamination with an automated liquid culture system: a university experience

BACKGROUND

With 4 million platelet units transfused per year in the United States and with the current estimate of bacteria contamination rate in PLT units, it would be expected that 2000 to 4000 bacterially contaminated units are transfused and associated with 333 to 1000 cases of clinical sepsis.

STUDY DESIGN AND METHODS

Apheresis platelets were sampled on Day 2 of storage (collection day=Day 0) and issue (or following outdate, Days 6-8) using a sterile connection device (SCD) to attach a sampling bag. Using aseptic technique and a laminar flow hood, bottles were inoculated and placed onto an automated liquid culture system (BacT/ALERT 3D Microbial Detection System) for 7 days.

RESULTS

A total of 2397 apheresis PLT units were sampled. A triple apheresis collection was reactive within 14 hours of the Day 2 sampling (aerobic bottles) and the bags were removed from inventory. Staphylococcus epidermidis was identified in all three contaminated bags. Two double-apheresis collections were found to be contaminated with Proprionibacterium sp. after 6 days of incubation but had been transfused to four patients without discernible clinical sequelae. There was one false-positive aerobic bottle and one false-positive anaerobic result due to inadvertent contamination of a bottle. Thus, the overall true-positive rate was 7 of 2397 apheresis units (0.29%) with a true-positive rate for aerobic organisms of 0.13% and an anaerobic true-positive rate of 0.17%. The false-positive rate was 2 out of 4794 samplings (0.04%) or 2 out of 9588 bottles (0.02%).

CONCLUSION

This preliminary data suggests that the use of a SCD, aseptic technique, and a laminar flow hood is associated with a low rate of contamination. In no case did an issue (or outdate) detect contamination that was not detected by the Day 2 culture. Additional surveillance is necessary before we can conclude that a Day 2 sterile culture is truly predictive of an issue (or outdate) sterile culture. Bacterial culture surveillance of PLTs would be expected to save lives and may facilitate an extension in PLT storage.

Glucose fermentation by Propionibacterium microaerophilum: effect of pH on metabolism and bioenergetic

pH affected significantly the growth and the glucose fermentation pattern of Propionibacterium microaerophilum. In neutral conditions (pH 6.5-7.5), growth and glucose fermentation rate (qs) were optimum producing propionate, acetate, CO(2), and formate [which together represented 90% (wt/wt) of the end products], and lactate representing only 10% (wt/wt) of the end products. In acidic conditions, propionate, acetate, and CO(2) represented nearly 100% (wt/wt) of the fermentation end products, whereas in alkaline conditions, a shift of glucose catabolism toward formate and lactate was observed, lactate representing 50% (wt/wt) of the fermentation end products. The energy cellular yields ( Y(X/ATP)), calculated (i) by taking into account extra ATP synthesized through the reduction of fumarate into succinate, was 6.1-7.2 g mol(-1). When this extra ATP was omitted, it was 11.9-13.1 g mol(-1). The comparison of these values with those of Y(X/ATP) in P. acidipropionici and other anaerobic bacteria suggested that P. microaerophilum could not synthesize ATP through the reduction of fumarate into succinate and therefore differed metabolically from P. acidipropionici.

Genetic diversity in Swiss cheese starter cultures assessed by pulsed field gel electrophoresis and arbitrarily primed PCR

AIMS

To assess intraspecific genetic heterogeneity among commercial Swiss cheese starter culture strains of Lactobacillus helveticus, Streptococcus thermophilus and Propionibacterium freudenreichii and to compare the efficacy of two genetic typing methods.

METHODS AND RESULTS

Two genetic typing methods, pulsed field gel electrophoresis (PFGE) and arbitrarily primed PCR (AP-PCR), were used. Nine Strep. thermophilus strains revealed eight PFGE and five AP-PCR genotypes. Seventeen Lactobacillus strains yielded 16 and five genotypes by PFGE and AP-PCR, respectively. Eleven Propionibacterium strains yielded 10 PFGE genotypes. Cluster analysis of PFGE profiles generated similarity coefficients for Strep. thermophilus, Lact. helveticus and Prop. freudenreichii strains of 29.5%, 60.3%, and 30.5%, respectively. Milk acidification rates for Strep. thermophilus and Lact. helveticus were determined.

CONCLUSIONS

Pulsed field gel electrophoresis is more discriminatory than AP-PCR. The Lact. helveticus group is more homogeneous than the other species examined. Strains with > 87% similarity by PFGE consistently had the same acidification rate and AP-PCR profile.

SIGNIFICANCE AND IMPACT OF THE STUDY

Bacterial strains sold for Swiss cheese manufacture in the United States are genetically diverse. Clustering of genetically related bacteria may be useful in identifying new strains with industrially relevant traits.

A microbiological approach to acne vulgaris

The present article gives a concise survey of contemporary opinions on acne vulgaris, its etiopathogenesis, clinical forms and laboratory diagnostics. In particular, the value of microbiological diagnostics and possibilities of local as well as general therapy are discussed. Moreover, our experience is described with vaccinotherapy to manage serious clinical forms and cases when current therapy fails.

Cell-adhered conjugated linoleic acid regulates isomerization of linoleic acid by resting cells of Propionibacterium freudenreichii

The microbiological isomerization of linoleic acid (LA) to conjugated linoleic acid (CLA) was studied in resting cell suspensions of a propionibacterium and micellar LA to identify factors critical in the isomerization efficiency. These suspensions, containing cells 5x10(10) colony-forming units ml(-1) and 510 micro g LA ml(-1), isomerized about 90% of LA to CLA. However, the yield was not improved with higher amounts of micellar LA, suggesting that the cells had a fixed capacity to carry out the isomerization. This was explained by the fact that the CLA formed had a tendency to accumulate in the cell mass rather than in the aqueous micellar phase during the isomerization. Concomitantly, cell viability and isomerization rates were gradually reduced. Upon cessation of the reaction, about 46% of all the CLA formed was in the cell material. This accumulation to the cells was prevented by adding the detergent in excess to that required for micellization of LA. Then the cells remained viable, but the rate of isomerization was drastically lowered, due to impaired availability of LA from the fortified micellar phase to the cells. It was concluded that the phase distribution of substrate and product plays a critical role in the microbiological production of CLA.

Glucose metabolism of lactic acid bacteria changed by quinone-mediated extracellular electron transfer

It can be expected that extracellular electron transfer to regenerate NAD+ changes the glucose metabolism of the homofermentative lactic acid bacteria. In this work, the glucose metabolism of Lactobacillusplantarum and Lactococcus lactis was examined in resting cells with 2-amino-3-carboxy-1,4-naphthoquinone (ACNQ) as the electron transfer mediator and ferricyanide (Fe(CN)6(3-)) as the extracellular electron acceptor. NADH in the cells was oxidized by ACNQ with the aid of diaphorase, and the reduced ACNQ was reoxidized with Fe(CN)6(3-). The extracellular electron transfer system promoted the generation of pyruvate, acetate, and acetoin from glucose, and restricted lactate production. Diaphorase activity increased when cultivation was aerobic, and this increased the concentrations of pyruvate, acetate, and acetoin relative to the concentration of lactate to increase in the presence of ACNQ and Fe(CN)6(3-)

Diversion of first blood volume results in a reduction of bacterial contamination for whole-blood collections

BACKGROUND AND OBJECTIVES

In a previous study we established a reliable setpoint for the prevalence of bacteria in whole blood. In the present study we investigated the possible preventive effect, of diversion of the first 10 ml of a blood donation, on the bacterial contamination rate.

MATERIALS AND METHODS

To divert the first 10 ml of a whole-blood donation, we used a special five-bag system equipped with a Composampler device. After venepuncture, the first 10 ml of a donation was sampled into a vacutainer tube. This was followed by the collection of the whole-blood unit. The extra bag allowed direct sampling of the final donation in a closed system for BacT/Alert. Whole-blood samples were taken after storage (2-14 h at 20 degrees C) and subsequent mixing. BacT/Alert culture bottles were incubated until positive, or for 7 days if negative. Confirmation and identification of positive cultures was performed according to internationally recognized standard reference methods.

RESULTS

The prevalence of bacteria in whole blood, as determined by using standard collection techniques, was 0.35% (95% confidence interval 0.27-0.44%, n = 18 257). After diversion of the first 10 ml this value was significantly lower: 0.21% (P < 0.05, 95% confidence interval 0.12-0.35%, n = 7087). Most strikingly, a reduction in the frequency of staphylococcal species was observed (P < 0.02, reduction from 0.14 to 0.03%).

CONCLUSIONS

Diversion of the first 10 ml of blood was shown to contribute significantly to a reduction in the prevalence of superficial skin bacteria in whole-blood units. In our opinion, blood collection systems should be adapted to use the first 10-30 ml of a whole-blood donation for testing purposes.

Prevalence of antibiotic-resistant propionibacteria on the skin of acne patients: 10-year surveillance data and snapshot distribution study

BACKGROUND

Cutaneous propionibacteria are implicated in acne pathogenesis, although their exact role in the genesis of inflammation is still poorly understood. Agents, including antibiotics, that reduce the numbers of propionibacteria on skin are therapeutic. Resistance in the target organism is a well-recognized consequence of antibiotic therapy for acne but formal prevalence and distribution data are lacking.

OBJECTIVES

To monitor the prevalence of skin colonization by antibiotic-resistant propionibacteria in acne patients attending the dermatology out-patient clinic at Leeds General Infirmary over a 10-year period beginning in 1991, and to examine the distribution of resistant strains on acne-prone skin and in the nares.

METHODS

Propionibacterial samples were obtained from the skin surface of the worst affected site (usually the face) of 4274 acne patients using a moistened swab. The swab was used to inoculate agar plates with and without selective antibiotics. After anaerobic incubation at 37 degrees C for 7 days, the amount of growth in the presence of each antibiotic was scored on a scale from 0 to 5+. A small number of patients (72) were selected for more detailed quantitative sampling at six different sites to examine the distribution of resistant propionibacteria on acne-prone skin and in the anterior nares.

RESULTS

The proportion of patients carrying strains resistant to one or more commonly used antiacne antibiotics rose steadily from 34.5% in 1991 to a peak of 64% in 1997. The prevalence dropped to 50.5% during 1999 and then rose again to 55.5% in 2000. Resistance to erythromycin was the most common and the majority of erythromycin-resistant strains were cross-resistant to clindamycin. Resistance to tetracyclines was less common in all years and with little increase over time. The more detailed quantitative study in 72 patients showed that population densities of resistant propionibacteria varied considerably between sites and between individuals. Almost invariably, patients were colonized with resistant strains at multiple sites, including the nares.

CONCLUSIONS

Skin colonization with antibiotic-resistant propionibacteria is much more common now than a decade ago. Resistant propionibacteria are widely distributed on acne-prone skin and in the nares. This suggests that they will be very difficult to eradicate using existing therapeutic regimens, especially from the nasal reservoir.