Induction and Recovery of the Viable but Nonculturable State of Hop-Resistance Lactobacillus brevis

Formation and resuscitation of viable but non-culturable (VBNC) yeast in the food industry: A review

The viable but non-culturable (VBNC) state is a survival strategy adopted by microorganisms in response to unfavorable conditions in the environment. VBNC cells are unable to form colonies but still maintain a low level of activity, posing a potential threat to food safety and public health. Therefore, the development of effective strategies to prevent the formation and resuscitation of VBNC cells of microorganisms is a key challenge in food science and microbiology research. However, current research on VBNC cells has primarily focused on bacteria, with relatively limited reports on fungi. This paper provides a comprehensive and systematic review of yeast in the VBNC state, discussing various factors that induce and facilitate resuscitation, along with detection methods and formation and recovery mechanisms. A comprehensive understanding of the induction and resuscitation of yeast in the VBNC state and exploration of its molecular mechanism hold significant implications for food safety and public health. It is imperative to enhance our comprehension of the underlying mechanisms and contributory factors pertaining to VBNC yeast, thereby facilitating the efficient management of the food fermentation process and ensuring the integrity of food quality and safety.

Enhanced Biofilm Formation by Tetracycline in a Staphylococcus aureus Naturally Lacking ica Operon and atl

Staphylococcus aureus is a major, widespread pathogen, and its biofilm-forming characteristics make it even more difficult to eliminate by biocides. Tetracycline (TCY) is a major broad-spectrum antibiotic, the residues of which can cause deleterious health impacts, and subinhibitory concentrations of TCY have the potential to increase biofilm formation in S. aureus. In this study, we showed how the biofilm formation of S. aureus 123786 is enhanced in the presence of TCY at specific subinhibitory concentrations. S. aureus 123786 used in this study was identified as Staphylococcal Cassette Chromosome mec III, sequence type239 and naturally lacking ica operon and atl gene. Two assays were performed to quantify the formation of S. aureus biofilm. In the crystal violet (CV) assay, the absorbance values of biofilm stained with CV at optical density (OD)540 nm increased after 8 and 16 hr of incubation when the concentration of TCY was 1/2 minimum inhibitory concentration (MIC), whereas at the concentration of 1/16 MIC, the absorbance values increased after 16 and 24 hr of incubation. In tetrazolium salt reduction assay, the absorbance value at OD490 nm of S. aureus 123786 biofilms mixed with 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium solution increased after 8 hr when the concentration of TCY was 1/4 MIC, which may be correlated with the higher proliferation and maturation of biofilm. In conclusion, the biofilm formation of S. aureus 123786 could be enhanced in the presence of TCY at specific subinhibitory concentrations.

Viable but nonculturable (VBNC) state, an underestimated and controversial microbial survival strategy

As a unique microbial response to adverse circumstances, the viable but nonculturable (VBNC) state is characterized by the loss of culturability of microbial cells on/in nutrient media that normally support their growth, while maintaining metabolic activity. These cells can resuscitate to a culturable state under suitable conditions. Given the intrinsic importance of the VBNC state and recent debates surrounding it, there is a need to redefine and standardize the term, and to address essential questions such as 'How to differentiate VBNC from other similar terms?' and 'How can VBNC cells be standardly and accurately determined?'. This opinion piece aims at contributing to an improved understanding of the VBNC state and promoting its proper handling as an underestimated and controversial microbial survival strategy.

Methods for detection and identification of beer-spoilage microbes

It is critical that breweries of all sizes routinely monitor the microbiome of their process to limit financial losses due to microbial contamination. Contamination by beer-spoiling microbes (BSMs) at any point during the brewing process may lead to significant losses for breweries if gone undetected and allowed to spread. Testing and detection of BSMs must be routine and rapid, and because even small breweries need the capability of BSM detection and identification, the method also needs to be affordable. Lactic acid bacteria (LAB) are responsible for most spoilage incidents, many of which have been shown to enter the viable but nonculturable (VBNC) state under conditions present in beer such as cold or oxidative stress. These bacteria are invisible to traditional methods of detection using selective media. This article describes several methods of BSM detection and identification that may be useful in the majority of craft breweries. While there are several genomic methods that meet some or many qualifications of being useful in craft breweries, real-time quantitative polymerase chain reaction (qPCR) currently best meets the desired method characteristics and holds the most utility in this industry, specifically SYBR Green qPCR. qPCR is a targeted method of detection and identification of microbes that is affordable, rapid, specific, sensitive, quantitative, and reliable, and when paired with valid DNA extraction techniques can be used to detect BSMs, including those in the VBNC state.

Lactic acid bacteria biofilms and their antimicrobial potential against pathogenic microorganisms

The continuous growth of pathogenic microorganisms and associated biofilms poses severe public health challenges, particularly in food and clinical environments. However, these difficulties have enabled scientists to develop novel and safe methods for combating pathogens. The use of biofilms produced by lactic acid bacteria (LAB) against pathogenic bacteria has recently gained popularity. This review provides an in-depth look at LAB biofilms, their distribution, and mechanisms of action against pathogenic bacteria. More importantly, the bioactive substances produced by LAB-forming biofilm may be active against undesirable microorganisms and their products, which is of great interest in improving human health. Therefore, this review implies that a combination of LAB biofilms and other LAB products like bacteriocins could provide viable alternatives to traditional methods of combating pathogenic microorganisms and their biofilms.

Biofilm formation of two genetically diverse Staphylococcus aureus isolates under beta-lactam antibiotics

PURPOSE

Our aim was to evaluate the biofilm formation of 2 genetically diverse Staphylococcus aureus isolates, 10379 and 121940, under different concentrations of beta-lactam antibiotics on biomass content and biofilm viability.

METHODS

Biofilm formation and methicillin resistance genes were tested using PCR and multiplex PCR. PCR was combined with bioinformatics analysis to detect multilocal sequence typing (MLST) and SCCmec types, to study the genetical correlation between the tested strains. Then, the crystal violet (CV) test and XTT were used to detect biomass content and biofilm activity. Antibiotic susceptibility was tested using a broth dilution method. According to their specific MIC, different concentrations of beta-lactam antibiotics were used to study its effect on biomass content and biofilm viability.

RESULTS

Strain 10379 carried the icaD, icaBC, and MRSA genes, not the icaA, atl, app, and agr genes, and MLST and SCCmec typing was ST45 and IV, respectively. Strain 121940 carried the icaA, icaD, icaBC, atl, and agr genes, not the aap gene, and MLST and SCCmec typed as ST546 and IV, respectively. This suggested that strains 10379 and 121940 were genotypically very different. Two S. aureus isolates, 10379 and 121940, showed resistance to beta-lactam antibiotics, penicillin, ampicillin, meropenem, streptomycin and kanamycin, some of which promoted the formation of biofilm and biofilm viability at low concentrations.

CONCLUSION

Despite the large differences in the genetic background of S. aureus 10379 and 121940, some sub-inhibitory concentrations of beta-lactam antibiotics are able to promote biomass and biofilm viability of both two isolates.

Formic acid, an organic acid food preservative, induces viable-but-non-culturable state, and triggers new Antimicrobial Resistance traits in Acinetobacter baumannii and Klebsiella pneumoniae

Numerous human pathogens, especially Gram-negative bacteria, are able to enter the viable-but-non-culturable (VBNC) state when they are exposed to environmental stressors and pose the risk of being resuscitated and causing infection after the removal of the trigger. Widely used food preservatives like weak organic acids are potential VBNC inducers in food processing and packaging facilities but have only been reported for food-borne pathogens. In the present study, it is demonstrated for the first time that one such agent, formic acid (FA), can induce a VBNC state at food processing, storage, and distribution temperatures (4, 25, and 37°C) with a varied time of treatment (days 4-10) in pathogenic Gram-negative bacteria Acinetobacter baumannii and Klebsiella pneumoniae. The use of hospital-associated pathogens is critical based on the earlier reports that demonstrated the presence of these bacteria in hospital kitchens and commonly consumed foods. VBNC induction was validated by multiple parameters, e.g., non-culturability, metabolic activity as energy production, respiratory markers, and membrane integrity. Furthermore, it was demonstrated that the removal of FA was able to resuscitate VBNC with an increased expression of multiple virulence and Antimicrobial Resistance (AMR) genes in both pathogens. Since food additives/preservatives are significantly used in most food manufacturing facilities supplying to hospitals, contamination of these packaged foods with pathogenic bacteria and the consequence of exposure to food additives emerge as pertinent issues for infection control, and control of antimicrobial resistance in the hospital setting.

Overview of VBNC, a survival strategy for microorganisms

Microorganisms are exposed to a wide variety of stress factors in their natural environments. Under that stressful conditions, they move into a viable but nonculturable (VBNC) state to survive and maintain the vitality. At VBNC state, microorganisms cannot be detected by traditional laboratory methods, but they can be revived under appropriate conditions. Therefore, VBNC organisms cause serious food safety and public health problems. To date, it has been determined that more than 100 microorganism species have entered the VBNC state through many chemical and physical factors. During the last four decades, dating from the initial detection of the VBNC condition, new approaches have been developed for the induction, detection, molecular mechanisms, and resuscitation of VBNC cells. This review evaluates the current data of recent years on the inducing conditions and detection methods of the VBNC state, including with microorganisms on the VBNC state, their virulence, pathogenicity, and molecular mechanisms.

Transcriptome Analysis of Viable but Non-Culturable Brettanomyces bruxellensis Induced by Hop Bitter Acids

The viable but non-culturable (VBNC) state has been studied in detail in bacteria. However, it has received much less attention in eukaryotic cells. The induction of a VBNC beer-spoilage yeast (Brettanomyces bruxellensis) by hop bitter acids with different concentrations and its recovery were studied in this work. B. bruxellensis cells were completely induced into the VBNC state by treatment of 250 mg/L hop bitter acids for 2 h. The addition of catalase at a concentration of 2,000 U/plate on YPD agars enabled these VBNC cells to recover their culturability within 2 days. Moreover, the transcriptome profiling revealed that 267 and 197 genes were significantly changed upon VBNC state entry and resuscitation, respectively. The differentially expressed genes involved in the peroxisome activities, ABC transporter, organic acid metabolism, and TCA cycle were mainly downregulated in the VBNC cells. In contrast, the amino acid and carbohydrate metabolism, cell division, and DNA replication were promoted. This study supplies a theoretical basis for microbial risk assessment in the brewing industry.

Formation of viable but nonculturable state of Staphylococcus aureus under frozen condition and its characteristics

Viable but nonculturable (VBNC) state of microorganisms has attracted much attention due to its characteristics, including the difficulty in detection by culture-based methods, virulence retention, high resistance, and so on. As a foodborne pathogen, Staphylococcus aureus is widely distributed, and has been found to enter the VBNC state under some environmental stresses, posing a potential threat to human health. Freezing is a common condition for food storage. This study investigated whether citric acid, a common food additive, could induce S. aureus into the VBNC state at -20 °C. By measuring the number of culturable and viable cells, it was found that S. aureus entered the VBNC state after 72 days of induction in citric acid buffer at -20 °C. The VBNC cells were then successfully resuscitated at 37 °C in trypsin soybean medium (TSB) with or without heat shock treatment, and TSB supplemented with sodium pyruvate and Tween 80 after 48 h. Heat shock resulted in an excellent resuscitation effect. Observed by transmission electron microscopy, the internal structure of VBNC cells was found markedly changed, compared with that of exponential phase cells. API ZYM kit was used to compare the intracellular enzyme activity of S. aureus in the exponential phase with that in the VBNC state. The results showed that the enzyme activity decreased significantly in VBNC cells, and that the VBNC cells were more resistant to simulated gastrointestinal fluid through flow cytometry analysis. Quantitative reverse-transcription polymerase chain reaction results suggested that the ability of adhesion and biofilm formation of VBNC cells might be decreased due to the down-regulation of related genes. However, it should not be ignored the recovery potential of biofilm-forming ability of VBNC cells caused by the high expression of sarA. In conclusion, S. aureus could be induced into the VBNC state in citric acid buffer at -20 °C, which showed changes in some biological characteristics and could resuscitate successfully by many conditions. Food industry needs to pay attention to the potential hazard by VBNC S. aureus under frozen conditions.

Identification of Type II Toxin-Antitoxin Loci in Levilactobacillus brevis

Levilactobacillus brevis are present in various environments, such as beer, fermented foods, silage, and animal host. Like other lactic acid bacteria, L. brevis might adopt the viable but nonculturable (VBNC) state under unfavorable conditions. The toxin-antitoxin (TA) system, known to regulate cell growth in response to environmental stresses, is found to control the dynamic of the VBNC state. Here, we investigate the type II TA locus prevalence and compare the TA diversity in L. brevis genomes. Using the TAfinder software, we identified a total of 273 putative type II TA loci in 110 replicons of 21 completely sequenced genomes. Genome size does not appear to correlate with the amount of putative type II TA in L. brevis. Besides, type II TA loci are distributed differently among the chromosomes and plasmids. The most prevalent toxin domain is MazF-like in the chromosomes, and RelE/RelE-like in the plasmids; while for antitoxin, Xre-like and Phd-like domains are the most common in the chromosomes and plasmids, respectively. We also observed a unique GNAT-like/ArsR-like TA pair that presents only in the L. brevis chromosome. Detection of 273 putative type II TA loci in 21 complete genomes of Levilactobacillus brevis.

Systematic Understanding of the Mechanism of Baicalin against Gastric Cancer Using Transcriptome Analysis

BACKGROUND

Gastric cancer (GC) is the most common type of cancer. It is highly malignant and is characterized by rapid and uncontrolled growth. The antitumour activity of Baicalin was studied in multiple cancers. However, its mechanism of action has not been fully elucidated. We provided a systematic understanding of the mechanism of action of baicalin against GC using a transcriptome analysis of RNA-seq.

METHODS

Human GC cells (SGC-7901) were exposed to 200 μg/ml baicalin for 24 h. RNA-seq with a transcriptome, Gene Ontology (GO), and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were used to identify the antitumour effects of baicalin on SGC-7901 cells in vitro. A protein-protein interaction (PPI) network of differentially expressed genes (DEGs) was constructed. A competitive endogenous RNA (ceRNA) network was constructed and further analysed after validation using qRT-PCR.

RESULTS

A total of 68 lncRNAs, 20 miRNAs, and 1648 mRNAs were differentially expressed in baicalin-treated SGC-7901 GC cells. Three lncRNAs, 6 miRNAs, and 7 mRNAs were included in the ceRNA regulatory network. GO analysis revealed that the main DEGs were involved in the biological processes of the cell cycle and cell death. KEGG pathway analysis further suggested that the p53 signalling pathway was involved in the baicalin-induced antitumour effect on SGC-7901 cells. Further confirmation using qPCR indicated that baicalin induced an antitumour effect on SGC-7901 cells, which is consistent with the results of the sequencing data.

CONCLUSIONS

In summary, the mechanism of baicalin against GC involves multiple targets and signalling pathways. These results provide new insight into the antitumour mechanism of baicalin and help the development of new strategies to cure GC.

Viable but nonculturable bacteria and their resuscitation: implications for cultivating uncultured marine microorganisms

Culturing has been the cornerstone of microbiology since Robert Koch first successfully cultured bacteria in the late nineteenth century. However, even today, the majority of microorganisms in the marine environment remain uncultivated. There are various explanations for the inability to culture bacteria in the laboratory, including lack of essential nutrients, osmotic support or incubation conditions, low growth rate, development of micro-colonies, and the presence of senescent or viable but nonculturable (VBNC) cells. In the marine environment, many bacteria have been associated with dormancy, as typified by the VBNC state. VBNC refers to a state where bacteria are metabolically active, but are no longer culturable on routine growth media. It is apparently a unique survival strategy that has been adopted by many microorganisms in response to harsh environmental conditions and the bacterial cells in the VBNC state may regain culturability under favorable conditions. The resuscitation of VBNC cells may well be an important way to cultivate the otherwise uncultured microorganisms in marine environments. Many resuscitation stimuli that promote the restoration of culturability have so far been identified; these include sodium pyruvate, quorum sensing autoinducers, resuscitation-promoting factors Rpfs and YeaZ, and catalase. In this review, we focus on the issues associated with bacterial culturability, the diversity of bacteria entering the VBNC state, mechanisms of induction into the VBNC state, resuscitation factors of VBNC cells and implications of VBNC resuscitation stimuli for cultivating these otherwise uncultured microorganisms. Bringing important microorganisms into culture is still important in the era of high-throughput sequencing as their ecological functions in the marine environment can often only be known through isolation and cultivation.

Bioprocessing and integration of a high flux screening systematic platform based on isothermal amplification for the detection on 8 common pathogens

During a large variety of common pathogens, E. coli, P. aeruginosa, MRSA, MRCNS, V. parahaemolyticus, L. monocytogenes and Salmonella are the leading pathogens responsible for large number of human infections and diseases. In this study, a high flux screening based on nucleic acid isothermal amplification technique has been developed. For the 8 common pathogens, species-specific targets had been selected and analyzed for their unique specificity. After optimization, separate LAMP reaction assays had been bioprocessed and integrated into one systematic detection platform, including 8 strips (PCR tubes) and 96-well plates. Eight standard strains verified for the accuracy. Application of the established high flux screening platform was used for detection for 48 samples in 4 different 96-well plates, with 2 groups of 2 operators using double-blind procedure. The accuracy of 100% was obtained, with the total time consumption as 66-75 min (for 12 samples detection on 8 different pathogens). As concluded, through the bioprocess of the systematic platform based on LAMP technique, it's been demonstrated to be capable of simultaneous detection of 8 pathogens, with high sensitivity, specificity, rapidity and convenience.

Horseradish Peroxidase Labelled-Sandwich Electrochemical Sensor Based on Ionic Liquid-Gold Nanoparticles for Lactobacillus brevis

Lactobacillus brevis is the most common bacteria that causes beer spoilage. In this work, a novel electrochemical immunosensor was fabricated for ultra-sensitive determination of L. brevis. Gold nanoparticles (AuNPs) were firstly electro-deposited on the electrode surface for enhancing the electro-conductivity and specific surface area. Ionic liquid was used for improving the immobilization performance of the immunosensor. After optimization, a linear regression equation can be observed between the ∆current and concentration of L. brevis from 104 CFU/mL to 109 CFU/mL. The limit of detection can be estimated to be 103 CFU/mL.

Pathogenic and Virulence Factor Detection on Viable but Non-culturable Methicillin-Resistant Staphylococcus aureus

Food safety and foodborne infections and diseases have been a leading hotspot in public health, and methicillin-resistant Staphylococcus aureus (MRSA) has been recently documented to be an important foodborne pathogen, in addition to its recognition to be a leading clinical pathogen for some decades. Standard identification for MRSA has been commonly performed in both clinical settings and food routine detection; however, most of such so-called "standards," "guidelines," or "gold standards" are incapable of detecting viable but non-culturable (VBNC) cells. In this study, two major types of staphylococcal food poisoning (SFP), staphylococcal enterotoxins A (sea) and staphylococcal enterotoxins B (seb), as well as the panton-valentine leucocidin (pvl) genes, were selected to develop a cross-priming amplification (CPA) method. Limit of detection (LOD) of CPA for sea, seb, and pvl was 75, 107.5, and 85 ng/μl, indicating that the analytical sensitivity of CPA is significantly higher than that of conventional PCR. In addition, a rapid VBNC cells detection method, designated as PMA-CPA, was developed and further applied. PMA-CPA showed significant advantages when compared with PCR assays, in terms of rapidity, sensitivity, specificity, and accuracy. Compared with conventional VBNC confirmation methods, the PMA-CPA showed 100% accordance, which had demonstrated that the PMA-CPA assays were capable of detecting different toxins in MRSA in VBNC state. In conclusion, three CPA assays were developed on three important toxins for MRSA, and in combination with PMA, the PMA-CPA assay was capable of detecting virulent gene expression in MRSA in the VBNC state. Also, the above assays were further applied to real samples. As concluded, the PMA-CPA assay developed in this study was capable of detecting MRSA toxins in the VBNC state, representing first time the detection of toxins in the VBNC state.

Development of a Direct and Rapid Detection Method for Viable but Non-culturable State of Pediococcus acidilactici

Pediococcus acidilactici may significantly reduce the pH-value, and thus has different influence, including serving as a probiotic in human microbiota but a spoilage in human food as it could change the flavor. Pediococcus acidilactici is also capable of entering into the viable but non-culturable (VBNC) state causing false negative results of standard culture-based detection method. Thus, development of detection method for VBNC state P. acidilactici is of great significance. In this study, propidium monoazide (PMA) combined with cross priming amplification (CPA) was developed to detect the VBNC cells of P. acidilactici and applied on the detection in different systems. With detection limit of 10⁴ cells/ml, high sensitivity, and 100% specificity, PMA-CPA can successfully detect VBNC cells of P. acidilactici and be applied in with high robustness.

Morphological and physiological changes in Lentilactobacillus hilgardii cells after cold plasma treatment

Atmospheric cold plasma (ACP) inactivation of Lentilactobacillus hilgardii was investigated. Bacteria were exposed to ACP dielectric barrier discharge with helium and oxygen as working gases for 5, 10, and 15 min. The innovative approach in our work for evaluation of bacterial survival was the use in addition to the classical plate culture method also flow cytometry which allowed the cells to be sorted and revealed different physiological states after the plasma treatment. Results showed total inhibition of bacterial growth after 10-min of ACP exposure. However, the analysis of flow cytometry demonstrated the presence of 14.4% of active cells 77.5% of cells in the mid-active state and 8.1% of dead cells after 10 min. In addition, some of the cells in the mid-active state showed the ability to grow again on culture medium, thus confirming the hypothesis of induction of VBNC state in L .hilgardii cells by cold plasma. In turn, atomic force microscopy (AFM) which was used to study morphological changes in L. hilgardii after plasma treatment at particular physiological states (active, mid-active, dead), showed that the surface roughness of the mid-active cell (2.70 ± 0.75 nm) was similar to that of the control sample (2.04 ± 0.55 nm). The lack of considerable changes on the cell surface additionally explains the effective cell resuscitation. To the best of our knowledge, AFM was used for the first time in this work to analyze cells which have been sorted into subpopulations after cold plasma treatment and this is the first work indicating the induction of VBNC state in L. hilgardii cells after exposure to cold plasma.

Analysis on the virulomes and resistomes of multi-drug resistance clinical Escherichia coli isolates, as well as the interactome with gut microbiome

Escherichia coli is one of the most diverse microbial species. Pathogenic E. coli is capable of causing various diseases in humans, including several types of diarrhea, urinary tract infections, sepsis, and meningitis. This study focused on the antibiotic susceptibility profile and genomic analysis of a clinical E. coli Guangzhou-Eco330 isolated from a hospitalized 8-year-old female patient suffered from pulmonary infection in 2017. Susceptibility to 15 antibiotics were determined using Vitek2™ Automated Susceptibility System and Etest strips and interpreted based on CLSI guidelines. The genome was sequenced using Illumina Hiseq 2500 platform and assembled de novo using Velvet, followed by bioinformatics analysis. The genome has a length of 5,132,642 bp and contains 4989 predicted genes with an average GC content of 50.51%. The carriage of rfbE gene suggested the strain belonging to O157. In the genome, 70 non-coding RNAs, 50 repeat sequences, 18 transposons, 78 GIs, 9 CRISPRs, and 3 large prophages were identified. 37 PHI related genes and 108 virulence genes were determined to contribute to its pathogenicity. Specifically, the acquisition of multiple antibiotic resistance genes including bla_CTX-M-55, bla_OXA-10, bla_CMY-48, tetB, and qnrS1 contributed to its resistance to penicillins, telracyclines, cephalosporin, and quinolones. The understanding of the genome may aid in further study on the clinical control of multi-drug resistance E. coli.

Impact of Media Heat Treatment on Cell Morphology and Stability of L. acidophilus, L. johnsonii and L. delbrueckii subsp. delbrueckii during Fermentation and Processing

Manufacturers of starter cultures and probiotics aim to provide preparations with the highest possible amount of living cells and assurance of long-term storage stability. Thereby the industrial economy and thus an efficient outcome of the processes is of utmost importance. Earlier research has shown that the sterilization procedure of the microbial culture medium tremendously impacts growth performance of heating product-sensitive Lactobacillus strains. Thus, three different strains, i.e., L. acidophilus NCFM, L. johnsonii La-2801 and L. delbrueckii subsp. delbrueckii La-0704, were investigated for the influence of media heat pretreatment on cell morphology and stability during fermentation and further freeze drying and storage. The data indicate a relationship between the heating time of the culture medium, which is associated with an increase in browning reactions, and the cultural characteristics of the three strains. The resulting characteristic cell sizes of the cultures could be a major reason for the different stability properties during processing and storage that were observed. Besides the obvious relevance of the results for the production of starter cultures and probiotics, the pleomorphic phenomenon described here could also be a subject for other biotechnological processes, where heat-mediated media conversions, and thereby related cellular effects, could be a topic. Future studies have to show if further functional properties are influenced by the cell morphology and which cellular mechanisms lead to the observed pleomorphism.

Genomic analysis of a hop-resistance Lactobacillus brevis strain responsible for food spoilage and capable of entering into the VBNC state

BACKGROUND

Lactobacillus brevis is a major contaminant of spoiled beer. And it was able to enter VBNC state and cause false negative detection, which poses a major challenge to the brewing industry.

METHODS

The genomic DNA of L. brevis BM-LB13908 was extracted and purified to form a sequencing library that meets the quality requirements and was sequenced. The sequencing results were then screened and assembled to obtain the entire genome sequence of L. brevis. Predicted genes were annotated by GO database, KEGG pathway database and COG functional classification system.

RESULTS

The final assembly yielded 275 scaffolds of a total length of 2 840 080 bp with a G + C content of 53.35%. There were 2357, 701, 1519 predicted genes with corresponding GO functional, COG functional, and KEGG biological pathway annotations, respectively. The genome of L. brevis BM-LB13908 contains hop resistance gene horA and multiple genes related to the formation of VBNC state.

CONCLUSIONS

This report describes the draft genome sequence of L. brevis BM-LB13908, a spoilage strain isolated from finished beer sample. This study may support further study on L. brevis and other beer spoilage bacteria, and prevent and control beer spoilage caused by microorganisms.

Spoilage Lactic Acid Bacteria in the Brewing Industry

Lactic acid bacteria (LAB) have caused many microbiological incidents in the brewing industry, resulting in severe economic loss. Meanwhile, traditional culturing method for detecting LAB are time-consuming for brewers. The present review introduces LAB as spoilage microbes in daily life, with focus on LAB in the brewing industry, targeting at the spoilage mechanism of LAB in brewing industry including the special metabolisms, the exist of the viable but nonculturable (VBNC) state and the hop resistance. At the same time, this review compares the traditional and novel rapid detection methods for these microorganisms which may provide innovative control and detection strategies for preventing alcoholic beverage spoilage, such as improvement of microbiological quality control using advanced culture media or different isothermal amplification methods.

Effect of Biofilm Formation by Lactobacillus plantarum on the Malolactic Fermentation in Model Wine

Biofilm life-style of Lactobacillus plantarum (L. plantarum) strains was evaluated in vitro as a new and suitable biotechnological strategy to assure L-malic acid conversion in wine stress conditions. Sixty-eight L. plantarum strains isolated from diverse sources were assessed for their ability to form biofilm in acid (pH 3.5 or 3.2) or in ethanol (12% or 14%) stress conditions. The effect of incubation times (24 and 72 h) on the biofilm formation was evaluated. The study highlighted that, regardless of isolation source and stress conditions, the ability to form biofilm was strain-dependent. Specifically, two clusters, formed by high and low biofilm producer strains, were identified. Among high producer strains, L. plantarum Lpls22 was chosen as the highest producer strain and cultivated in planktonic form or in biofilm using oak supports. Model wines at 12% of ethanol and pH 3.5 or 3.2 were used to assess planktonic and biofilm cells survival and to evaluate the effect of biofilm on L-malic acid conversion. For cells in planktonic form, a strong survival decay was detected. In contrast, cells in biofilm life-style showed high resistance, assuring a prompt and complete L-malic acid conversion.

Viable but Nonculturable Escherichia coli O157:H7 and Salmonella enterica in Fresh Produce: Rapid Determination by Loop-Mediated Isothermal Amplification Coupled with a Propidium Monoazide Treatment

Escherichia coli O157:H7 and Salmonella enterica are leading causes of foodborne outbreaks linked to fresh produce. Both species can enter the "viable but nonculturable" (VBNC) state that precludes detection using conventional culture-based or molecular methods. In this study, we assessed propidium monoazide-quantitative PCR (PMA-qPCR) assays and novel methods combining PMA and loop-mediated isothermal amplification (LAMP) for the detection and quantification of VBNC E. coli O157:H7 and S. enterica in fresh produce. The performance of PMA-LAMP assays targeting the wzy gene of E. coli O157:H7 and the agfA gene of S. enterica and the performance of PMA-qPCR assays were compared in pure culture and spiked tomato, lettuce, and spinach. No cross-reaction was observed in the specificity tests. The values representing the limit of detection (LOD) seen with PMA-LAMP were 9.0 CFU/reaction for E. coli O157:H7 and 4.6 CFU/reaction for S. enterica in pure culture and were 5.13 × 103 or 5.13 × 104 CFU/g for VBNC E. coli O157:H7 and 1.05 × 104 or 1.05 × 105 CFU/g for VBNC S. enterica in fresh produce, representing results comparable to those obtained by PMA-qPCR. Standard curves showed correlation coefficients ranging from 0.925 to 0.996, indicating a good quantitative capacity of PMA-LAMP for determining populations of both bacterial species in the VBNC state. The PMA-LAMP assay was completed with considerable economy of time (30 min versus 1 h) and achieved sensitivity and quantitative capacity comparable to those seen with a PMA-qPCR assay. PMA-LAMP is a rapid, sensitive, and robust method for the detection and quantification of VBNC E. coli O157:H7 and S. enterica in fresh produce.IMPORTANCE VBNC pathogenic bacteria pose a potential risk to the food industry because they do not multiply on routine microbiological media and thus can evade detection in conventional plating assays. Both E. coli O157:H7 and S. enterica have been reported to enter the VBNC state under a range of environmental stress conditions and to resuscitate under favorable conditions and are a potential cause of human infections. PMA-LAMP methods developed in this study provide a rapid, sensitive, and specific way to determine levels of VBNC E. coli O157:H7 and S. enterica in fresh produce, which potentially decreases the risks related to the consumption of fresh produce contaminated by enteric pathogens in this state. PMA-LAMP can be further applied in the field study to enhance our understanding of the fate of VBNC pathogens in the preharvest and postharvest stages of fresh produce.

Characterization on gut microbiome of PCOS rats and its further design by shifts in high-fat diet and dihydrotestosterone induction in PCOS rats

Polycystic ovary syndrome (PCOS) is associated with gut microbiota disturbance. Emerging evidence has shown that gut microbiota plays a major role in the development of PCOS. To better understand how the gut microbiota contributes to the development of PCOS, we investigated the influences of high-fat diet and hyperandrogenism, independently or synergistically, have on the gut microbiota in rats. Furthermore, we explored the associations between gut microbiota and hyperandrogenism or other hallmarks of PCOS. Twenty female SD rats were randomized at aged 3 weeks into 4 groups (n = 5, each); HA: PCOS rats fed with ordinary diet; HF: rats with high-fat diet (HFD); HA-HF: PCOS rats fed with HFD; and C: control rats with ordinary diet. PCOS rat model was induced by 5α-dihydrotestosterone (DHT) injection for 6 weeks. The fasting blood glucose (FBG), plasma insulin, testosterone, free testosterone, TNF-α, MDA, SOD, LPS, TLR4, TG, TC, HDL-C, and LDL-C levels were measured. The molecular ecology of the fecal gut microbiota was analyzed by 16S rDNA high-throughput sequencing. The results showed that rats in the HA and HA-HF group displayed abnormal estrous cycles with increasing androgen level and exhibited multiple large cysts with diminished granulosa layers in ovarian tissues. Compare with the C group, relative abundance of the Bacteroidetes phylum decreased significantly in the other groups (P < 0.05). The Chao1 was the highest in the group C and significantly higher than the HA-HF group (P < 0.05). T, FT, insulin, MDA, LPS, and TNF-α levels had the negative correlation with the richness of community (Chao1 index) in the gut. The rats in the HF and HA-HF groups tended to have lower Shannon and Simpson indices than the C group (P < 0.01, respectively). However, there were no significant differences between C group and the HA group in the Shannon and Simpson values. Beta diversity analysis was then performed based on a weighted UniFrac analysis. The PCoA plots showed a clear separation of the C group from the other groups. ANOSIM analysis of variance confirmed that there were statistically significant separations between the C group and the HA, HA-HF, and HF groups (P < 0.01, respectively). These results showed that DHT with HFD could lower diversity of the gut microbial community. Both HFD and DHT could shift the overall gut microbial composition and change the composition of the microbial community in gut. Furthermore, our analyses demonstrated that the levels of TG, MDA, TNF-α, LPS, TLR4, T, FT, FINS, and HDL-C were correlated with the changes of in the gut microbiome. HFD and DHT were associated with the development and pathology of PCOS by shaping gut microbial communities.

A Plasmid-Encoded Putative Glycosyltransferase Is Involved in Hop Tolerance and Beer Spoilage in Lactobacillus brevis

Lactobacillus brevis beer-spoiling strains harbor plasmids that contain genes such as horA, horC, and hitA which are known to confer hop tolerance. The L. brevis beer-spoiling strain UCCLBBS124, which possesses four plasmids, was treated with novobiocin, resulting in the isolation of UCCLBBS124 derivatives exhibiting hop sensitivity and an inability to grow in beer. One selected derivative was shown to have lost a single plasmid, here designated UCCLBBS124_D, which harbors the UCCLBBS124_pD0015 gene, predicted to encode a glycosyltransferase. Hop tolerance and growth in beer were restored when UCCLBBS124_pD0015 was introduced in one of these hop-sensitive derivatives on a plasmid. We hypothesize that this gene modifies the surface composition of the polysaccharide cell wall, conferring protection against hop compounds. Furthermore, the introduction of this gene in trans in L. brevis UCCLB521, a strain that cannot grow in and spoil beer, was shown to furnish the resulting strain with the ability to grow in beer, while its expression also conferred phage resistance. This study underscores how the acquisition of certain mobile genetic elements plays a role in hop tolerance and beer spoilage for strains of this bacterial species.IMPORTANCE Lactobacillus brevis is a member of the lactic acid bacteria and is often reported as the causative agent of food or beverage spoilage, in particular, that of beer. Bacterial spoilage of beer may result in product withdrawal or recall, with concomitant economic losses for the brewing industry. A very limited number of genes involved in beer spoilage have been identified and primarily include those involved in hop resistance, such as horA, hitA, and horC However, since none of these genes are universal, it is clear that there are likely (many) other molecular players involved in beer spoilage. Here, we report on the importance of a plasmid-encoded glycosyltransferase associated with beer spoilage by L. brevis that is involved in hop tolerance. The study highlights the complexity of the genetic requirements to facilitate beer spoilage and the role of multiple key players in this process.

Development and Application of a Simple "Easy To Operate" Propidium Monoazide-Crossing Priming Amplification on Detection of Viable and Viable But Non-culturable Cells of O157 Escherichia coli

O157 Escherichia coli is one of the most important foodborne pathogens causing disease even at low cellular numbers. Thus, the early and accurate detection of this pathogen is important. However, due to the formation of viable but non-culturable (VBNC) status, the golden standard culturing methodology fails to identify O157 E. coli once it enters VBNC status. Crossing priming amplification (CPA) is a novel, simple, easy-to-operate detection technology that amplifies DNA with high speed, efficiency, and specificity under isothermal conditions. The objective of this study was to firstly develop and apply a CPA assay with propidium monoazide (PMA) for the rapid detection of the foodborne E. coli O157:H7 in VBNC state. Five primers (2a/1s, 2a, 3a, 4s, and 5a) were specially designed for recognizing three targets, which were rfbE, stx1, and stx2, and evaluated for its effectiveness in detecting VBNC cell of E. coli O157:H7 with detection limits of pure VBNC culture at 10³, 10⁵, and 10⁵ colony-forming units (CFUs)/ml for rfbE, stx1, and stx2, respectively, whereas those of food samples (frozen pastry and steamed bread) were 10³, 10⁵, and 10⁵ CFUs/ml. The application of the PMA-CPA assay was successfully used on detecting E. coli O157:H7 in VBNC state from food samples. In conclusion, this is the first development of PMA-CPA assay on the detection of VBNC cell, which was found to be useful and a powerful tool for the rapid detection of E. coli O157:H7 in VBNC state. Undoubtedly, the PMA-CPA method can be of high value to the food industry owing to its various advantages such as speed, specificity, sensitivity, and cost-effectiveness.

Effect of Environmental Conditions on the Formation of the Viable but Nonculturable State of Pediococcus acidilactici BM-PA17927 and Its Control and Detection in Food System

Objective: This study aimed to investigate the effect of environmental conditions including nutrient content, acetic acid concentration, salt concentration, and temperature on the formation of viable but nonculturable (VBNC) state of Pediococcus acidilactici, as well as its control and detection in food system. Methods: Representing various environmental conditions in different food systems, 16 induction groups were designed for the formation of VBNC state of P. acidilactici. Traditional plate counting was applied to measure the culturable cell numbers, and Live/Dead Bacterial Viability Kit combined with fluorescent microscopy was used to identify viable cells numbers. The inhibition of bacterial growth and VBNC state formation by adjusting the environmental conditions were investigated, and the clearance effect of VBNC cells in crystal cake system was studied. In addition, a propidium monoazide-polymerase chain reaction (PMA-PCR) assay was applied to detect the VBNC P. acidilactici cells in crystal cake food system. Results: Among the environmental conditions included in this study, acetic acid concentration had the greatest effect on the formation of VBNC state of P. acidilactici, followed by nutritional conditions and salt concentration. Reducing nutrients in the environment and treating with 1.0% acetic acid can inhibit P. acidilactici from entering the VBNC state. In the crystal cake system, the growth of P. acidilactici and the formation of VBNC state can be inhibited by adding 1.0% acetic acid and storing at -20°C. In crystal cake system, the PMA-PCR assay can be used to detect VBNC P. acidilactici cells at a concentration higher than 10⁴ cells/ml. Conclusion: The VBNC state of P. acidilactici can be influenced by the changing of environmental conditions, and PMA-PCR assay can be applied in food system for the detection of VBNC P. acidilactici cells.

First Report on the Rapid Detection and Identification of Methicillin-Resistant Staphylococcus aureus (MRSA) in Viable but Non-culturable (VBNC) Under Food Storage Conditions

Formation of viable but non-culturable (VBNC) status in methicillin-resistant Staphylococcus aureus (MRSA) has never been reported, and it poses a significant concern for food safety. Thus, this study aimed to firstly develop a rapid, cost-effective, and efficient testing method to detect and differentiate MRSA strains in the VBNC state and further apply this in real food samples. Two targets were selected for detection of MRSA and toxin, and rapid isothermal amplification detection assays were developed based on cross-priming amplification methodology. VBNC formation was performed for MRSA strain in both pure culture and in artificially contaminated samples, then propidium monoazide (PMA) treatment was further conducted. Development, optimization, and evaluation of PMA-crossing priming amplification (CPA) were further performed on detection of MRSA in the VBNC state. Finally, application of PMA-CPA was further applied for detection on MRSA in the VBNC state in contaminated food samples. As concluded in this study, formation of the VBNC state in MRSA strains has been verified, then two PMA-CPA assays have been developed and applied to detect MRSA in the VBNC state from pure culture and food samples.

Biofilm Formation of Staphylococcus aureus under Food Heat Processing Conditions: First Report on CML Production within Biofilm

This study aimed to evaluate the Staphylococcus aureus biofilm formation and Nε-carboxymethyl-lysine generation ability under food heat processing conditions including pH (5.0-9.0), temperature (25 °C, 31 °C, 37 °C, 42 °C and 65 °C), NaCl concentration (10%, 15% and 20%, w/v) and glucose concentration (0.5%, 1%, 2%, 3%, 5%, 10%, w/v). S. aureus biofilm genetic character was obtained by PCR detecting atl, ica operon, sasG and agr. Biofilm biomass and metabolic activity were quantified with crystal violet and methyl thiazolyl tetrazolium staining methods. S. aureus biofilm was sensitive to food heat processing conditions with 37 °C, pH 7.0, 2% glucose concentration (w/v) and 10% NaCl concentration (w/v) were favorable conditions. Besides, free and bound Nε-carboxymethyl-lysine level in weak, moderate and strong biofilm were detected by optimized high performance liquid chromatography tandem mass spectrometry. Nε-carboxymethyl-lysine level in S. aureus biofilm possessed a significant gap between strong, moderate and weak biofilm strains. This investigation revealed the biological and chemical hazard of Staphylococcus aureus biofilm to food processing environment.