Foodborne Yeasts Research Articles

Cyberlindnera jadinii and Kluyveromyces lactis, two fungi used in food processes, have potential probiotic effects on gut inflammation.

The food industry has always used many strains of microorganisms including fungi in their production processes. These strains have been widely characterized for their biotechnological value, but we still know very little about their interaction capacities with the host at a time when the intestinal microbiota is at the center of many pathologies. In this study, we characterized five yeast strains from food production which allowed us to identify two new strains with high probiotic potential and beneficial effects in a model of intestinal inflammation.

Perspectives on the Probiotic Potential of Indigenous Moulds and Yeasts in Dry-Fermented Sausages.

The role of indigenous fungi in the appropriate development of sensory properties and the safety of dry-fermented sausages has been widely established. Nonetheless, their applications as probiotic agents have not been elucidated in such products yet, despite their promising functional features. Thus, it should be interesting to evaluate the probiotic potential of native Debaryomyces hansenii isolates from dry-fermented sausages and their application in the meat industry, because it is the most frequently isolated yeast species from these foodstuffs and its probiotic effects for animals as well as its possible probiotic activity for human beings have been demonstrated. Within the functional ability of foodborne yeasts, anti-inflammatory, antioxidant, antimicrobial, antigenotoxic, and immunomodulatory properties have been reported. Similarly, the use of dry-fermented sausages as vehicles for probiotic moulds remains a challenge because the survival and development of moulds in the gastrointestinal tract are still unknown. Nevertheless, some moulds have been isolated from faeces possibly from their spores as a form of resistance. Additionally, their beneficial effects on animals and humans, such as the decrease in lipid content and the anti-inflammatory activity, have been reported, although they seem to be more related to their postbiotic capacity due to the generated bioactive compounds with profunctional attributes than to their role as probiotics. Therefore, further studies providing knowledge useful for generating dry-fermented sausages with improved functionality are fully necessary.

Investigation of the Chemical Composition of Myrtus communis L. and Gaultheria procumbens L. Essential Oils and their Effects on Foodborne Yeasts

This study investigates the antifungal activities of the essential oils (EO) obtained from Myrtus communis L. and Gaultheria procumbens L. leaves on foodborne yeasts, isolated from sourdough samples and the chemical compositions of the oils. The main constituents of the Myrtus communis L. EO. were 1,8-cineole (35.62 %), α-pinene (29.14 %) and α-terpineol (10.04 %). Methyl salicylate (96.87 %) and limonene (2.05 %) were identified as the major constituents in the G. procumbens L. EO. M. communis L. and G. procumbens L. EOs showed the highest antifungal activity against Torulaspora delbrueckii (27.86 mm zone diameter) and Pichia polymorpha (40.23 mm zone diameter) respectively. The minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of the M. communis L. and G. procumbens L. EOs were in the range of 46,87-562.50 μg/mL / 23.44-375.0 μg/mL and 4.39-562.50 μg/mL / 2.93-156.25 μg/mL, respectively.

Biological control of yeast contamination of industrial foods by propolis.

Bee glue (Propolis, PR), mixture of beeswax and resin is collected from honeybee (Apis mellifera) of different plant parts. The antimicrobial potential of PR against food borne yeast was reported. The experiment was designed to examine the way of antimicrobial impact of PR on food borne yeasts (Cryptococcus laurentii and Candida famata) and its usage use as biological strategy for the preservation of soft foods against microbial spoilage. The study also highlights, the ability of ethanol and water- PR extracts, discouraged growth of tested yeast. Antifungal properties were also determined using electron microscope while biochemical analysis was determined using free and proteinic amino acid technique and oxidative enzymes were determined using HPLC analysis. Antioxidant enzymes were determined using ELISA assay. The highest effect was recorded on C. laurentii however, the lowest effect shows on C. famata. The electron microscopic studies clearly disclosed the effect of water PR distillate on the external shape and internal organs of some tested yeast e.g. C. laurentii and C. famata. The result indicated some differences on concentrations of bio-chemical analyses for these tested yeasts treated with 70% water- PR extracts of different food materials. Moreover, biochemical analysis results also reported that the treated yeast indicated natural preservative to food products and considered as best alternative to the (chemical) preservatives currently employed.

Excision of endosymbiotic bacteria from yeast under aging and starvation stresses

Although infrequent in our laboratory, growth of bacterial colonies has been observed on top of the purified cultures of yeasts. In this study, the likelihood of bacterial excision from yeast under aging and starvation stresses was assessed using 10 gastric and 10 food-borne yeasts. Yeasts were identified as members of Candida or Saccharomyces genus by amplification and sequencing of D1/D2 region of 26S rDNA. For aging stress, yeasts were cultured on brain heart infusion agar supplemented with sheep blood and incubated at 30 °C for 3–4 weeks. For starvation stress, yeasts were inoculated into distilled water and incubated similarly. After seven days, starved yeasts were cultured on yeast extract glucose agar, incubated similarly and examined daily for appearance of bacterial colonies on top of the yeast's growth. Outgrowth of excised bacteria was observed on top of the cultures of 4 yeasts (Y1, Y3, Y13 and Y18) after 3–7 days. The excised bacteria (B1, B3, B13 and B18) were isolated and identified at the genus level according to their biochemical characteristics as well as amplification and sequencing of 16S rDNA. B1 (Arthrobacter) were excised from Y1 (Candida albicans) upon aging and B3 (Staphylococcus), B13 (Cellulomonas) and B18 (Staphylococcus) were excised from their respective yeasts; Y3 (Candida tropicalis), Y13 (Saccharomyces cerevisiae) and Y18 (Candida glabrata) upon starvation. DNA from yeasts was used for detection of 16S rDNA of their intracellular bacteria and sequencing. Amplified products from yeasts showed sequence similarity to those of excised bacteria. Under normal conditions, yeast exerts tight control on multiplication of its intracellular bacteria. However, upon aging and starvation the control is no longer effective and bacterial outgrowth occurs. Unlimited multiplication of excised bacteria might provide yeast with plenty of food in close vicinity. This could be an evolutionary dialogue between yeast and bacteria that ensures the survival of both partners.

Antimicrobial Activity of 4-O-methylgallic Acid Isolated from Phyllanthus polyphyllus L. against Foodborne Pathogenic Bacteria and Yeasts

The aim of this study was to evaluate the antimicrobial activity of 4-O-methylgallic acid isolated from Phyllanthus polyphyllus L. and examine its possible antimicrobial mode of action against food-borne pathogenic bacteria and yeast. The bioassay-guided fractionation of methanol extract of leaves led to the isolation of active compound 4-O-methylgallic acid (4-O-MGA). The antimicrobial activity were assessed against two Gram-positive (Staphylococcus aureus and Streptococcus faecalis), five Gram-negative (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus vulgaris and Salmonella typhimurium) bacteria and two yeasts (Candida albicans and Cryptococcus neoformans) using disk diffusion method followed by a standardized microdilution assay. 4-O-MGA exhibited antimicrobial activity against all tested bacteria with MIC ≥ 0.125 mg/mL and MBC ≥ 0.25 mg/mL. Among tested organisms, Gram-positive bacteria were more sensitive than Gram-negative, and yeasts showed more resistance with higher MIC 1.0 mg/mL and MFC ≥ 2.0 mg/mL. Much effort was focused on elucidating the mechanism of antimicrobial action of 4-O-MGA against S. aureus and E. coli by observing the changes in membrane integrity as confirmed by release of loss of 260 nm absorbing materials and leakage of potassium with outer membrane permeability, and against a yeast C. albicans as confirmed by inhibitory effects on biofilm formation and sterol content in the plasma membrane. The antimicrobial properties of 4-O-MGA suggest that, also considering its antioxidant and well known nutritional functions, it has potential for development as an antimicrobial agent for control of food-related pathogenic microbes.

Typing and virulence factors of food-borne Candida spp. isolates

Food-borne yeasts, excluding yeasts used as starter cultures, are commonly considered as food spoilage microorganisms. However, the incidence of non-C. albicans Candida (NCAC) infections has increased considerably over the past two decades. Although 15 Candida species are frequently identified as pathogens, a threat to human from food-borne Candida is poorly recognized. In the present study food-borne NCAC were characterized for the virulence factors, known to be associated with yeast pathogenicity. All food-borne strains in planktonic forms and 89% in biofilm structures represented biotypes established for C. albicans, and 61% demonstrated hemolytic activity. 56–94% of food-borne isolates formed biofilms on glass and biomaterials at a level comparable to clinical C. albicans. Nine out of eighteen tested food-borne NCAC strains (C. krusei, C. lusitaniae, C. famata, C. colliculosa, C. parapsilosis, C. tropicalis) showed similarity to clinical C. albicans in terms of their biotypes and the tested virulence factors, allocating them in a group of risk of potential pathogens. However, their capacity to grow at 37 °C seems to be the preliminary criterion in the study of potential virulence of food-borne yeasts.

Assessment of Multi Fragment Melting Analysis System (MFMAS) for the Identification of Food-Borne Yeasts.

Multi Fragment Melting Analysis System (MFMAS) is a novel approach that was developed for the species-level identification of microorganisms. It is a software-assisted system that performs concurrent melting analysis of 8 different DNA fragments to obtain a fingerprint of each strain analyzed. The identification is performed according to the comparison of these fingerprints with the fingerprints of known yeast species recorded in a database to obtain the best possible match. In this study, applicability of the yeast version of the MFMAS (MFMAS-yeast) was evaluated for the identification of food-associated yeast species. For this purpose, in this study, a total of 145 yeast strains originated from foods and beverages and 19 standard yeast strains were tested. The DNAs isolated from these yeast strains were analyzed by the MFMAS, and their species were successfully identified with a similarity rate of 95% or higher. It was shown that the strains belonged to 43 different yeast species that are widely found in the foods. A clear discrimination was also observed in the phylogenetically related species. In conclusion, it might be suggested that the MFMAS-yeast seems to be a highly promising approach for a rapid, accurate, and one-step identification of the yeasts isolated from food products and/or their processing environments.

MALDI-TOF MS as a tool to identify foodborne yeasts and yeast-like fungi

Since food spoilage by yeasts causes high economic losses, fast and accurate identifications of yeasts associated with food and food-related products are important for the food industry. In this study the efficiency of the matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) to identify food related yeasts was evaluated.A CBS in-house MALDI-TOF MS database was created and later challenged with a blinded test set of 146 yeast strains obtained from food and food related products. Ninety eight percent of the strains were correctly identified with log score values>1.7. One strain, Mrakia frigida, gained a correct identification with a score value<1.7. Two strains could not be identified at first as they represented a mix of two different species. These mixes were Rhodotorula babjevae with Meyerozyma caribbica and Clavispora lusitaniae with Debaryomyces hansenii. After separation, all four species could be correctly identified with scores>1.7. Ambiguous identifications were observed due to two incorrect reference mass spectra's found in the commercial database BDAL v.4.0, namely Candida sake DSM 70763 which was re-identified as Candida oleophila, and Candida inconspicua DSM 70631 which was re-identified as Pichia membranifaciens. MALDI-TOF MS can distinguish between most of the species, but for some species complexes, such as the Kazachstania telluris and Mrakia frigida complexes, MALDI-TOF MS showed limited resolution and identification of sibling species was sometimes problematic. Despite this, we showed that the MALDI-TOF MS is applicable for routine identification and validation of foodborne yeasts, but a further update of the commercial reference databases is needed.

Culture medium optimization for osmotolerant yeasts by use of a parallel fermenter system and rapid microbiological testing

In the present study, a culture medium for qualitative detection of osmotolerant yeasts, named OM, was developed. For the development, culture media with different concentrations of glucose, fructose, potassium chloride and glycerin were analyzed in a Biolumix™ test incubator. Selectivity for osmotolerant yeasts was guaranteed by a water activity (aw)-value of 0.91. The best results regarding fast growth of Zygosaccharomyces rouxii (WH 1002) were achieved in a culture medium consisting of 45% glucose, 5% fructose and 0.5% yeast extract and in a medium with 30% glucose, 10% glycerin, 5% potassium chloride and 0.5% yeast extract. Substances to stimulate yeast fermentation rates were analyzed in a RAMOS® parallel fermenter system, enabling online measurement of the carbon dioxide transfer rate (CTR) in shaking flasks. Significant increases of the CTR was achieved by adding especially 0.1–0.2% ammonium salts ((NH4)2HPO4, (NH4)2SO4 or NH4NO3), 0.5% meat peptone and 1% malt extract. Detection times and the CTR of 23 food-borne yeast strains of the genera Zygosaccharomyces, Torulaspora, Schizosaccharomyces, Candida and Wickerhamomyces were analyzed in OM bouillon in comparison to the selective culture media YEG50, MYG50 and DG18 in the parallel fermenter system. The OM culture medium enabled the detection of 102CFU/g within a time period of 2–3days, depending on the analyzed yeast species. Compared with YEG50 and MYG50 the detection times could be reduced. As an example, W. anomalus (WH 1021) was detected after 124h in YEG50, 95.5h in MYG50 and 55h in OM bouillon. Compared to YEG50 the maximum CO2 transfer rates for Z. rouxii (WH 1001), T. delbrueckii (DSM 70526), S. pombe (DSM 70576) and W. anomalus (WH 1016) increased by a factor ≥2.6. Furthermore, enrichment cultures of inoculated high-sugar products in OM culture medium were analyzed in the Biolumix™ system. The results proved that detection times of 3days for Z. rouxii and T. delbrueckii can be realized by using OM in combination with the automated test system even if low initial counts (101CFU/g) are present in the products. In conclusion, the presented data suggest that the OM culture medium is appropriate for the enrichment of osmotolerant yeasts from high-sugar food products.

Ultraviolet-C Light Effect on the Physicochemical and Antioxidant Properties of Blackberry, Blueberry, and Raspberry Nectars

The effect of UV-C light on foodborne microorganisms (mesophilic aerobic bacteria (MAB), molds, and yeasts), physicochemical characteristics (color, total soluble solids, pH, and acidity), and antioxidant properties (ascorbic acid, antioxidant capacity (AC), total monomeric anthocyanins (TMA), and total phenolic compounds (TPC)) in blackberry, blueberry, and raspberry nectars was evaluated. Nectars were UV-C light treated at five times (5, 10, 15, 20, and 25 minutes) at constant flow rate (16.48 mL/s). The best UV-C light treatment for the three nectars, from the microbiological point of view, was 25 min. A statistical difference (p &lt; 0.05) in TPC, within treatment times, was observed in nectars; their content was reduced as the treatment time increased, except for the blackberry nectar. The same effect was observed for the antioxidant capacity. The TMA content increased with the UV-C light treatment.

Killer toxin from several food-derived Debaryomyces hansenii strains effective against pathogenic Candida yeasts

Candida yeasts are the dominant fungi in the healthy human microbiome, but are well-known for causing disease following a variety of perturbations. Evaluation of fungal populations from the healthy human gut revealed a significant negative correlation between the foodborne yeast, Debaryomyces hansenii, and Candida species. D. hansenii is reported to produce killer toxins (mycocins) effective against other yeast species. In order to better understand this phenomenon, a collection of 42 D. hansenii isolates was obtained from 22 cheeses and evaluated for killer activity against Candida albicans and Candida tropicalis over a range of temperatures and pH values. Twenty three strains demonstrated killer activity against both C. albicans and C. tropicalis, which was pH- and temperature-dependent, with no killer activity observed for any strain at pH6.5 or higher, or at ≥35°C (physiological conditions in the human gastrointestinal tract). A cell-free mycocin preparation showed transient killer activity against C. albicans at 35°C and a cheese sample containing a killer D. hansenii strain demonstrated sustained killer activity against both C. albicans and C. tropicalis. Together, these observations raise the possibility that D. hansenii could influence Candida populations in the gut.

Potential of Lactobacillus reuteri from Spontaneous Sourdough as a Starter Additive for Improving Quality Parameters of Bread.

Retardation of microbial spoilage of bread can be achieved by the use of spontaneous sourdough with an antimicrobial activity. This study was undertaken to identify lactic acid bacteria naturally occurring in spontaneous sourdough and use them for quality improvement and prolonging shelf life of rye, wheat and rye with wheat bread. Identification of isolates from spontaneous sourdough by pyrosequencing assay showed that Lactobacillus reuteri were dominant lactic acid bacteria. The isolates showed a wide range of antimicrobial activity and displayed a synergistic activity against other lactobacilli, some lactococci and foodborne yeasts. The best application of spontaneous sourdough was noticed in the rye bread with the lowest crumb firmness of the final product, although the sensory results of wheat and rye with wheat bread did not statistically differ from control bread. L. reuteri showed a high preserving capacity against fungi during storage. This may be due to bacteriocins and various fatty acids secreted into the growth medium that were identified by agar well diffusion assay and gas chromatography. L. reuteri showing high antimicrobial activity have the potential to be used as a starter additive that could improve safety and/or shelf life of bread.

食品由来酵母の塩基配列解析法と市販同定キット（API 20C AUX）の同定結果の比較評価

食品由来酵母の塩基配列解析法と市販同定キット（API 20C AUX）の同定結果の比較評価

Comparison of New and Traditional Culture-Dependent Media for Enumerating Foodborne Yeasts and Molds

Fifty-six foods and food ingredients were analyzed for populations of naturally occurring yeasts and molds using Petrifilm rapid yeast and mold (RYM) count plates, Petrifilm yeast and mold (YM) count plates, dichloran rose bengal chloramphenicol (DRBC) agar plates, acidified potato dextrose agar (APDA) plates, and dichloran 18% glycerol (DG18) agar plates. Colonies were counted after incubating plates for 48, 72, and 120 h at 25°C. Of 56 foods in which either yeasts or molds were detected on at least one medium incubated for 120 h, neither yeasts nor molds were detected in 55.4, 73.2, 21.4, 19.6, and 71.4% of foods plated on the five respective media and incubated for 48 h; 10.7, 14.3, 3.6, 1.8, and 19.6% of foods were negative after 72 h, and 3.6, 1.8, 0, 0, and 0% of foods were negative after 120 h. Considering all enumeration media, correlation coefficients were 0.03 to 0.97 at 48 h of incubation; these values increased to 0.75 to 0.99 at 120 h. Coefficients of variation for total yeasts and molds were as high as 30.0, 30.8, and 27.2% at 48, 72, and 120 h, respectively. The general order of performance was DRBC = APDA > RYM Petrifilm > YM Petrifilm ≥ DG18 when plates were incubated for 48 h, DRBC > APDA > RYM Petrifilm > YM Petrifilm ≥ DG18 when plates were incubated for 72 h, and DRBC > APDA > RYM Petrifilm > YM Petrifilm > DG18 when plates were incubated for 120 h. Differences in performance among media are attributed to the diversity of yeasts and molds likely to be present in test foods and differences in nutrient, pH, and water activity requirements for resuscitation of stressed cells and colony development.

MALDI-TOF MS based identification of food-borne yeast isolates

In this study, food-borne yeast isolates (n=96), comprising at least 33 species, were identified using MALDI-TOF MS and conventional methods (API ID 32 C and Phoenix Yeast ID). Discrepancies of both methods were resolved by sequencing the ITS1–5.8S–rRNA–ITS2 region. For ten isolates, mainly classified to Rhodotorula and Trichosporon species, no clear final species identification was possible. 62 isolates were correctly identified to species level using either MALDI-TOF MS or conventional tests. 15 isolates were misidentified when applying conventional assays. In contrary, no species misidentifications were observed after MALDI-TOF MS based classification. In return, 16 isolates were not identifiable after matching their protein fingerprints against MALDI Biotyper 4.0.0.1 library. MALDI TOF MS in-house database update clearly improved the identification. In conclusion, the presented data suggest that MALDI-TOF MS is an appropriate platform for reliable classification and identification of food-borne yeast isolates.

UV‐C Irradiation of Freshly Squeezed Grape Juice and Modeling Inactivation Kinetics

AbstractUV inactivation kinetics of freshly squeezed turbid white grape juice (FSTGJ) treated with an annular flow UV reactor by applying UV dosages ranging from 0 to 116.7 J/mL, at three different flow rates (0.90, 1.75 and 3.70 mL/s), were modeled by using log‐linear, Weibull, Hom and modified Chick–Watson models. FSTGJ was circulated five times in the UV system, i.e., UV exposure time was 20.33 min during processing. The populations of Escherichia coli K‐12, lactic acid bacteria (LAB) and foodborne yeasts were reduced by 3.759, 4.133 and 1.604 log cfu/mL, respectively, after exposure to UV dosage of 116.7 J/mL at the lowest flow rate. The inactivation kinetics of foodborne yeasts were best described by the modified Chick–Watson model, with the least root mean squared error (RMSE = 0.001, R2 = 0.999). Besides, the inactivation kinetics of E. coli K‐12 and LAB were best fitted by Weibull model (R2 = 0.999). Additionally, when the UV exposure time was increased up to 32.5 min (i.e., eight cycles), UV‐C treatment of FSTGJ resulted in 5.341 log cfu/mL reduction in E. coli K‐12, which meets the Food and Drug Administration requirement of a 5 log reduction of microorganisms in fruit juices.Practical ApplicationsConsumer demand for high‐quality fruit juice with fresh‐like characteristics has markedly expanded in recent years. UV‐C irradiation is a nonthermal method and allows the processing of fruit juices with a minimal or no changes in flavor, essential nutrients and vitamins. Although thermal pasteurization is the most convenient way of increasing the shelf life of fruit juices, it causes a “cook taste” in grape juice. So, in this study, the application of UV‐C irradiation to process grape juice was investigated. The shape of the microbial inactivation curve is sigmoidal in UV treatment. Therefore, different kinetic models (e.g., log‐linear, Weibull, Hom and modified Chick–Watson) are applied to describe the inactivation kinetics of Escherichia coli K‐12, lactic acid bacteria and foodborne yeasts. Kinetic parameters (e.g., k and D) and models can be used for the development of UV‐C irradiation process to ensure microbial safety in juice products.

Vacuoles of Candida yeast as a specialized niche for Helicobacter pylori.

Helicobacter pylori (H. pylori) are resistant to hostile gastric environments and antibiotic therapy, reflecting the possibility that they are protected by an ecological niche, such as inside the vacuoles of human epithelial and immune cells. Candida yeast may also provide such an alternative niche, as fluorescently labeled H. pylori were observed as fast-moving and viable bacterium-like bodies inside the vacuoles of gastric, oral, vaginal and foodborne Candida yeasts. In addition, H. pylori-specific genes and proteins were detected in samples extracted from these yeasts. The H. pylori present within these yeasts produce peroxiredoxin and thiol peroxidase, providing the ability to detoxify oxygen metabolites formed in immune cells. Furthermore, these bacteria produce urease and VacA, two virulence determinants of H. pylori that influence phago-lysosome fusion and bacterial survival in macrophages. Microscopic observations of H. pylori cells in new generations of yeasts along with amplification of H. pylori-specific genes from consecutive generations indicate that new yeasts can inherit the intracellular H. pylori as part of their vacuolar content. Accordingly, it is proposed that yeast vacuoles serve as a sophisticated niche that protects H. pylori against the environmental stresses and provides essential nutrients, including ergosterol, for its growth and multiplication. This intracellular establishment inside the yeast vacuole likely occurred long ago, leading to the adaptation of H. pylori to persist in phagocytic cells. The presence of these bacteria within yeasts, including foodborne yeasts, along with the vertical transmission of yeasts from mother to neonate, provide explanations for the persistence and propagation of H. pylori in the human population. This Topic Highlight reviews and discusses recent evidence regarding the evolutionary adaptation of H. pylori to thrive in host cell vacuoles.

FOODBORNE YEASTS SERVE AS RESERVOIRS OF HELICOBACTER PYLORI

ABSTRACTIt is not clear where Helicobacter pylori establishes in the environment and how it is transmitted to humans. Fifteen yeasts were isolated from 15 food samples. Microscopic examination of yeasts revealed fast‐moving bacterium‐like bodies (BLBs) inside the vacuoles of yeasts. Yeasts were identified as Candida species. Polymerase chain reaction (PCR) was recruited to detect H. pylori‐specific ureAB (urease) and babAB (BabA/B adhesins) genes in the total DNAs of yeasts. The ureAB gene was amplified from 9/15 yeasts and babAB from 2/15. Sequencing of the PCR products of ureAB (406 bp) and babAB (980 bp) genes that were amplified from one yoghurt yeast showed 98% homology with those of control H. pylori. Fluorescent microscopy of stained yeasts showed live BLBs inside the vacuoles. It is proposed that foodborne yeast which originates from the environment could accommodate H. pylori in nature and act as a vehicle for its transmission to the human gastrointestinal tract.PRACTICAL APPLICATIONSHelicobacter pylori is a gastric pathogen and its entrance occurs through the ingestion of food. However, there is no strong evidence to show that food materials support the survival and growth of H. pylori and could play a crucial role in the bacterial transmission to humans. The intracellular existence of H. pylori in yeast could be important in the bacterial survival in the environment and its transmission. We propose that foodborne yeasts, which survive the stressful conditions during food processing, such as heat and sanitizers, could serve as potent reservoirs of H. pylori and facilitate its transmission to human. Occurrence of yeast in food materials could be considered as a possible marker for the bacterial contamination. Accordingly, reducing the yeast content of foods, through proper hygienic practice in food processing, might be crucial for the control of H. pylori and probably other bacterial infections.

Food borne yeasts as DNA-bioprotective agents against model genotoxins

Yeasts isolated from Italian beverages and foods (wine and cheeses) were identified as Saccharomyces cerevisiae and Debaryomyces hansenii by sequencing the D1/D2 domain of the 26S rRNA gene and differentiated, at strain level, by microsatellite PCR fingerprinting and RAPD-PCR. All the strains showed antioxidant activity, as demonstrated by their ability to scavenge the free radical diphenyl-1-picrylhydrazyl (DPPH). Furthermore, tested strains revealed high in vitro inhibitory activity against two model genotoxins, 4-nitroquinoline-1-oxide (4-NQO) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), as showed by short-term methods with different target cells: SOS-Chromotest with Escherichia coli PQ37 and Comet assay with HT-29 enterocytes. High inhibitory activity towards 4-NQO was associated with cell viability, while heat-inactivated cells showed a reduced antigenotoxic capability. Surprisingly, high inhibition of MNNG genotoxicity was observed even with heat-treated cells. Moreover, the strains able to inhibit the genotoxins induced some changes in the spectroscopic properties of the original compound. This result perfectly agrees with the information obtained by the two bioassays. Interestingly, strains characterized for antioxidant and antigenotoxic properties, also presented acid-bile tolerance, indicating that food autochthonous yeasts could be expected to reach gut in viable form and thus prevent genotoxin DNA damage in situ.