Food microbiology最新文献

A single strain of Candida anglica, isolated from cider, is available in international yeast collections. We present here seven new strains isolated from French PDO cheeses. For one of the cheese strains, we achieved a high-quality genome assembly of 13.7 Mb with eight near-complete telomere-to-telomere chromosomes. The genomes of two additional cheese strains and of the cider strain were also assembled and annotated, resulting in a core genome of 5966 coding sequences. Phylogenetic analysis showed that the seven cheese strains clustered together, away from the cider strain. Mating-type locus analysis revealed the presence of a MATa locus in the cider strain but a MATalpha locus in all cheese strains. The presence of LINE retrotransposons at identical genome position in the cheese strains, and two different karyotypic profiles resulting from chromosomal rearrangements were observed. Together, these findings are consistent with clonal propagation of the cheese strains. Phenotypic trait variations were observed within the cheese population under stress conditions whereas the cider strain was found to have a much greater capacity for growth in all conditions tested.

Gray mold, caused by Botrytis cinerea, is a prevalent postharvest disease of apple that limits their shelf life, resulting in significant economic losses. The use of antagonistic microorganisms has been shown to be an effective approach for managing postharvest diseases of fruit. In the present study, an endophytic yeast strain PGY-2 was isolated from apples and evaluated for its biocontrol efficacy against gray mold and its mechanisms of action. Results indicated that strain PGY-2, identified as Bullera alba, reduced the occurrence of gray mold on apples and significantly inhibited lesion development in pathogen-inoculated wounds. Gray mold control increased with the use of increasing concentrations of PGY-2, with the best disease control observed at 10⁸ cells/mL. Notably, Bullera alba PGY-2 did not inhibit the growth of Botrytis cinerea in vitro indicating that the yeast antagonist did not produce antimicrobial compounds. The rapid colonization and stable population of PGY-2 in apple wounds at 4 °C and 25 °C confirmed its ability to compete with pathogens for nutrients and space. PGY-2 also had a strong ability to form a biofilm and enhanced the activity of multiple defense-related enzymes (POD, PPO, APX, SOD, PAL) in host tissues. Our study is the first time to report the use of Bullera alba PGY-2 as a biocontrol agent for postharvest diseases of apple and provide evidence that Bullera alba PGY-2 represents an endophytic antagonistic yeast with promising biocontrol potential and alternative to the use of synthetic, chemical fungicides for the control of postharvest gray mold in apples.

One of the best-known Hungarian products on world wine market is Aszú, which belongs to the family of Tokaj wine specialties and is made from aszú berries. An important condition for the formation of aszú berries is the noble rot of technologically mature grapes, which is caused by Botrytis cinerea. At the same time botrytized sweet wines are produced not only in Hungary, but in many locations of wine-producing areas of Europe as well as in certain wine growing regions of other continents. The determination of botrytization is mostly based on sensory evaluations, which is a highly subjective procedure and largely depends on the training and experience of the evaluator. Currently, the classification of aszú berries (class I and class II) is based only on visual inspection and determination of sugar content.

Based on these facts the primary goal of our work was to develop a qPCR assay capable for objective rating and classification of aszú berries.

The developed qPCR is highly specific and sensitive as can clearly distinguish between B. cinerea and other filamentous fungi and yeast species occur on grapes. Moreover, it is suitable for categorizing berries colonized by B. cinerea to varying degrees. Thus, the developed qPCR method can be a useful technique for classification of the grape berries into four quality groups: healthy, semi-shrivelled, Aszú Class II and Aszú Class I.

The rot caused by pathogens during the storage of table grapes is an important factor that affects the development of the grape industry and food safety, and it cannot be ignored. The development of innovative methods for pathogen control should be based on a comprehensive understanding of the overall microbial community changes that occur during grape storage. The study aims to investigate the relationship between the native microbiota (including beneficial, pathogenic and spoilage microorganisms) on grape surfaces and the development of disease during grape storage. In this study, the bacteria and fungi present on grape surfaces were analyzed during storage under room temperature conditions using high-throughput sequencing. During the storage of grapes at room temperature, observable diseases and a noticeable decrease in quality were observed at 8 days. Microbial community analysis showed that 4996 bacterial amplicon sequence variants (ASVs) and 488 fungal ASVs were determined. The bacterial richness exhibited an initial increase followed by a subsequent decrease. However, the diversity exhibited a distinct pattern of gradual decrease. The fungal richness and community diversity both exhibit a gradual decrease during the storage of grapes. Fungal β-diversity analysis showed that despite the absence of rot and the healthy state of grapes on the first and fourth days, the fungal β-diversity exhibited a significant difference. The analysis of changes in genera abundances suggested that Candidatus Profftella and Aspergillus exhibited dominance in the rotting grape at 16 days, which are the main pathogens that caused disease in the present study. The co-occurrence networks among the microbial showed that the Candidatus proftella genera has a positive correlation with Aspergillus niger, indicating that they work together to cause disease and promote growth in grapes. Predicting the function of bacterial communities found that the microorganisms associated with lipid metabolism at 4 days play an important role in the process of postharvest decay of grapes.

Methicillin-resistant Staphylococcus aureus (MRSA) is a frequent cause of nosocomial and community infections, in some cases severe and difficult to treat. In addition, there are strains of MRSA that are specifically associated with food-producing animals. For this reason, in recent years special attention has been paid to the role played by foodstuffs of animal origin in infections by this microorganism. With the aim of gaining knowledge on the prevalence and types of MRSA in meat and meat products, a review was undertaken of work published on this topic since 2001, a total of 259 publications, 185 relating to meat samples from retail outlets and 74 to samples of animal origin collected in farms, slaughterhouses and meat processing facilities. Strains of MRSA were detected in 84.3% reports (156 out of 185) from retail outlets and 86.5% reports (64 out of 74) from farms, slaughterhouses and meat processing facilities, although in most of the research this microorganism was detected in under 20% of samples from retail outlets, and under 10% in those from farms, slaughterhouses and meat processing facilities. The meat and meat products most often contaminated with MRSA were pork and chicken. In addition to the mecA gene, it is crucial to take into consideration the mecB and mecC genes, so as to avoid misidentification of strains as MSSA (methicillin-susceptible Staphylococcus aureus). The great variety of methods used for the determination of MRSA highlights the need to develop a standardized protocol for the study of this microorganism in foods.

Daqu is used as the fermentation starter of Baijiu and contributes diversified functional microbes for saccharifying grains and converting sugars into ethanol and aroma components in Baijiu products. Daqu is mainly classified into three types, namely low (LTD), medium (MTD) and high (HTD) temperature Daqu, according to the highest temperatures reached in their fermentation processes. In this study, we used the PacBio small-molecule real-time (SMRT) sequencing technology to determine the full-length 16 S rRNA gene sequences from the metagenomes of 296 samples of different types of Daqu collected from ten provinces in China, and revealed the bacterial diversity at the species level in the Daqu samples. We totally identified 310 bacteria species, including 78 highly abundant species (with a relative abundance >0.1% each) which accounted for 91.90% of the reads from all the Daqu samples. We also recognized the differentially enriched bacterial species in different types of Daqu, and in the Daqu samples with the same type but from different provinces. Specifically, Lactobacillales, Enterobacterales and Bacillaceae were significantly enriched in the LTD, MTD and HTD groups, respectively. The potential co-existence and exclusion relationships among the bacteria species involved in all the Daqu samples and in the LTD, MTD and HTD samples from a specific region were also identified. These results provide a better understanding of the bacterial diversity in different types of Daqu at the species level.

The pied de cuve (PdC) technique involves using a portion of grape must to undergo spontaneous fermentation, which is then used to inoculate a larger volume of must. This allows for promoting autochthonous yeasts present in the must, which can respect the typicality of the resulting wine. However, the real impact of this practice on the yeast population has not been properly evaluated. In this study, we examined the effects of sulphur dioxide (SO₂), temperature, ethanol supplementation, and time on the dynamics and selection of yeasts during spontaneous fermentation to be used as PdC. The experimentation was conducted in a synthetic medium and sterile must using a multi-species yeast consortium and in un-inoculated natural grape must. Saccharomyces cerevisiae dominated both the PdC and fermentations inoculated with commercial wine yeast, displaying similar population growth regardless of the tested conditions. However, using 40 mg/L of SO₂ and 1% (v/v) ethanol during spontaneous fermentation of Muscat of Alexandria must allowed the non-Saccharomyces to be dominant during the first stages, regardless of the temperature tested. These findings suggest that it is possible to apply the studied parameters to modulate the yeast population during spontaneous fermentation while confirming the effectiveness of the PdC methodology in controlling alcoholic fermentation.

Cronobacter spp. are bacterial pathogens isolated from a wide variety of foods. This study aims at evaluating the occurrence of Cronobacter spp. in low water activity functional food samples, detect the presence of virulence genes, and determine the antibiotic susceptibility of strains. From 105 samples, 38 (36.2%) were contaminated with Cronobacter spp. The species identified by polymerase chain reaction (PCR) and sequencing analyses (rpoB and fusA genes, respectively) were C. sakazakii (60.3%), C. dublinensis (25.4%), C. turincensis (9.5%), and C. malonaticus (4.8%). Nineteen fusA alleles were identified, including four new alleles. The virulence genes were identified by PCR and all isolates were positive for ompX and sodA genes, 60.3% to cpa gene, and 58.7% to hly gene. Using the disk diffusion method, antibiotic susceptibility to twelve antibiotics was assessed twice, separated by a 19-month period. In the first test, the isolates showed diverse antibiotic susceptibility profiles, with nineteen isolates (30.2%) being multi-drug resistant (resistant to three or more antibiotic classes), in the second, the isolates were susceptible to all antibiotics. Cronobacter spp. in functional foods demonstrates the need for continued investigation of this pathogen in foods, and further research is needed to clarify the loss of resistance of Cronobacter strains.

Huangjiu is a spontaneously fermented alcoholic beverage, that undergoes intricate microbial compositional changes. This study aimed to unravel the flavor and quality formation mechanisms based on the microbial metabolism of Huangjiu. Here, metagenome techniques, chemometrics analysis, and headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC–MS) metabolomics combined with microbial metabolic network were employed to investigate the distinctions and relationship between the microbial profiles and the quality characteristics, flavor metabolites, functional metabolic patterns of Huangjiu across three regions. Significant variations (P < 0.05) were observed in metabolic rate of physicochemical parameters and biogenic amine concentration among three regions. 8 aroma compounds (phenethyl acetate, phenylethyl alcohol, isobutyl alcohol, ethyl octanoate, ethyl acetate, ethyl hexanoate, isoamyl alcohol, and diethyl succinate) out of 448 volatile compounds were identified as the regional chemical markers. 25 dominant microbial genera were observed through metagenomic analysis, and 13 species were confirmed as microbial markers in three regions. A metabolic network analysis revealed that Saccharomycetales (Saccharomyces), Lactobacillales (Lactobacillus, Weissella, and Leuconostoc), and Eurotiales (Aspergillus) were the predominant populations responsible for substrate, flavor (mainly esters and phenylethyl alcohol) metabolism, Lactobacillales and Enterobacterales were closely linked with biogenic amine. These findings provide scientific evidence for regional microbial contributions to geographical characteristics of Huangjiu, and perspectives for optimizing microbial function to promote Huangjiu quality.

This study aimed to determine the prevalence of V. parahaemolyticus in oysters from the northwestern coast of Mexico and to identify the serotypes, virulence factors, and antibiotic resistance of the strains. Oyster samples were collected from 2012 to 2020 from the northwest coast of Mexico; biochemical and molecular methods were used to identify V. parahaemolyticus from oysters; antiserum reaction to determine V. parahaemolyticus serotypes, and PCR assays were performed to identify pathogenic (tdh and/or trh) or pandemic (toxRS/new, and/or orf8) strains and antibiotic resistance testing. A total of 441 oyster samples were collected and tested for V. parahaemolyticus. Forty-seven percent of oyster samples were positive for V. parahaemolyticus. Ten different O serogroups and 72 serovars were identified, predominantly serotype O1:KUT with 22.2% and OUT:KUT with 17.3%. Twenty new serotypes that had not been previously reported in our region were identified. We detected 4.3% of pathogenic clones but no pandemic strains. About 73.5% of strains were resistant to at least one antibiotic, mainly ampicillin and ciprofloxacin; 25% were multi-drug resistant. In conclusion, the pathogenic strains in oysters and antibiotic resistance are of public health concern, as the potential for outbreaks throughout northwestern Mexico is well established.