Rapid detection of Oenococcus oeni in wine by real-time quantitative PCR

Fluorescence microscopy to monitor wine malolactic fermentation

Malolactic fermentation (MLF) is a natural and biological deacidification of wines and a required step for making premium red wines. MLF is carried out by lactic acid bacteria (LAB) that are present in the fermenting wines. Currently, real-time control of MLF is an issue of great interest as the classical plate count technique for assessing bacterial populations requires long incubation times that are not compatible with a tight control of MLF. The aim of this study was to apply fluorescence microscopy and the bacteria staining kit Live/Dead BacLight™ to quantify viable LAB populations in red wines undergoing MLF. This method proved to be a fast and reliable culture-independent method to monitor wine MLF. Moreover, comparison of bacterial population data obtained by fluorescence microscopy and classical plate counts of LAB populations allowed discriminating a population of fully active and culturable cells, from total viable cells that include cells in an intermediate unculturable state.

Direct and Rapid Detection and Quantification of Oenococcus oeni Cells in Wine by Cells-LAMP and Cells-qLAMP

Fast detection and enumeration of Oenococcus oeni in winemaking are necessary to determine whether malolactic fermentation (MLF) is likely to be performed or not and to decide if the use of a commercial starter is needed. In other wines, however, performing MLF can be detrimental for wine and should be avoided. The traditional identification and quantification of this bacteria using culture-dependent techniques in wine-related matrices require up to 14 days to yield results, which can be a very long time to perform possible enological operations. Loop-mediated isothermal amplification (LAMP) is a novel culture-independent technique that amplifies nucleic acid sequences under isothermal conditions with high specificity and efficiency in less than 1 h with inexpensive equipment. We designed LAMP primers for the specific detection and quantification of O. oeni cells. The developed LAMP method allows O. oeni to be detected directly from both grape musts and wines within 1 h from the time that the LAMP reaction begins, and without DNA extraction and purification requirements. The high sensitivity of LAMP methodology is achieved by previous mechanical cells lysis with no further purification by detecting one single cell per reaction in culture media, and in white/red grape musts and wines by avoiding reaction inhibition by ethanol, polyphenols, and other wine inhibitors. Cells can be concentrated prior to the LAMP reaction to further increase this sensitivity. Moreover, the LAMP method does not require expensive equipment and can be easily operated. The developed method is both economic and fast and offers high sensitivity and specificity.

Cells-qPCR as a direct quantitative PCR method to avoid microbial DNA extractions in grape musts and wines

A novel quantitative PCR assay called Cells-qPCR has been developed for the rapid detection and quantification of yeasts, lactic acid bacteria (LAB) and acetic acid bacteria (AAB) directly from grape must and wine that does not require DNA extraction. The assay was tested on Brettanomyces bruxellensis, Saccharomyces cerevisiae, Lactobacillus plantarum, Oenococcus oeni, Acetobacter aceti and Gluconobacter oxydans in culture media, and in white and red grape musts and wines. Standard curves were constructed from DNA and cells for the six target species in all the matrices. Good efficiencies were obtained for both when comparing DNA and cells standard curves. No reaction inhibition was observed between matrices for each species. Cells quantification was linear over a range of cell concentrations (7, 5 or 4 orders of magnitude) and detected as few as one cell per reaction in all the matrices. The developed Cells-qPCR assay is a robust, reliable, fast and specific method to detect and quantify different yeasts, LAB and AAB species in grape must and wine that avoids DNA extraction and overcomes the presence of inhibitors like polyphenols and ethanol.

A novel real-time PCR assay for the specific identification and quantification of Weissella viridescens in blood sausages

Weissella viridescens has been identified as one of the lactic acid bacteria (LAB) responsible for the spoilage of "morcilla de Burgos". In order to identify and quantify this bacterium in "morcilla de Burgos", a new specific PCR procedure has been developed. The primers and Taqman probe were designed on the basis of a sequence from the gene recN. To confirm the specificity of the primers, 77 strains from the genera Carnobacterium, Enterococcus, Lactobacillus, Leuconostoc, Pediococcus, Streptococcus, Vagococcus and Weissella were tested by conventional PCR. The specificity of the primers and the correct functioning of the probe was confirmed by performing real-time PCR (qPCR) with 21 W. viridescens strains and 27 strains from other LAB genera. The levels of detection and quantification for the qPCR procedure proposed herein were determined for a pure culture of W. viridescens CECT 283(T) and for "morcilla de Burgos" artificially inoculated with this species. The primers were specific for W. viridescens, with only one product of 91 bp being observed for this species. Similarly, the qPCR reactions were found to be specific, amplifying at a mean CT of 15.0±0.4 only for W. viridescens strains. The limit of detection (LOD) and quantification (LOQ) for this procedure was established in 0.082 pg for genomic DNA from W. viridescens. With regard to the artificially inoculated "morcilla", the limit of quantification was established in 80 CFU/reaction and the limit of detection in 8 CFU/reaction. Consequently, the qPCR developed herein can be considered to be a good, fast, simple and accurate tool for the specific detection and quantification of W. viridescens in meat samples.

Use of propidium monoazide for the enumeration of viable Oenococcus oeni in must and wine by quantitative PCR

Malolactic fermentation is an important step in winemaking, but it has to be avoided in some cases. It's carried out by lactic acid bacteria belonging mainly to the genus Oenococcus, which is known to be a slow growing bacterium. Classical microbiological methods to enumerate viable cells of Oenococcus oeni in must and wine take 7-9 days to give results. Moreover, RT-qPCR technique gives accurate quantitative results, but it requires time consuming steps of RNA extraction and reverse transcription. In the present work we developed a fast and reliable quantitative PCR (qPCR) method to enumerate cells of Oenococcus oeni, directly, in must and wine. For the first time we used a propidium monoazide treatment of samples to enumerate only Oenococcus oeni viable cells. The detection limit of the developed method is 0.33 log CFU/mL (2.14 CFU/mL) in must, and 0.69 log CFU/mL (4.90 CFU/mL) in wine, lower than that of the previously developed qPCR protocols.

Cytofluorometric detection of wine lactic acid bacteria: application of malolactic fermentation to the monitoring

In this study we report for the first time a rapid, efficient and cost-effective method for the enumeration of lactic acid bacteria (LAB) in wine. Indeed, up to now, detection of LAB in wine, especially red wine, was not possible. Wines contain debris that cannot be separated from bacteria using flow cytometry (FCM). Furthermore, the dyes tested in previous reports did not allow an efficient staining of bacteria. Using FCM and a combination of BOX/PI dyes, we were able to count bacteria in wines. The study was performed in wine inoculated with Oenococcus oeni (106 CFU ml−1) stained with either FDA or BOX/PI and analyzed by FCM during the malolactic fermentation (MLF). The analysis show a strong correlation between the numbers of BOX/PI-stained cells determined by FCM and the cell numbers determined by plate counts (red wine: R2 ≥ 0.97, white wine R2 ≥ 0.965). On the other hand, we found that the enumeration of O. oeni labeled with FDA was only possible in white wine (R2 ≥ 0.97). Viable yeast and LAB populations can be rapidly discriminated and quantified in simultaneous malolactic-alcoholic wine fermentations using BOX/PI and scatter parameters in a one single measurement. This rapid procedure is therefore a suitable method for monitoring O. oeni populations during winemaking, offers a detection limit of <104 CFU ml−1 and can be considered a useful method for investigating the dynamics of microbial growth in wine and applied for microbiological quality control in wineries.

The challenge to quantify Listeria monocytogenes--a model leading to new aspects in molecular biological food pathogen detection

In this work, we discuss the latest insights concerning advantages and disadvantages and the nature of microbiological and molecular methods for quantitative food pathogen detection. The assessment of molecular methods must be brought on a basis that considers the nature of molecular methods and their underlying mechanism. A potential approach to setting up the development, validation and structure of an analytical chain is presented based on quantitative real-time PCR (qPCR). This is analysed exemplary on the basis of recent work using the model organism Listeria monocytogenes. Several prerequisites for successful quantitative detection of this pathogen will be discussed. In particular, sample preparation, controls for all methodical steps and the validation of the core assay qPCR are addressed, which constitute the basis for a reliable analytical detection chain for molecular biological pathogen detection from food. Microbiological methods are analysed based on growth of the single cell, which is the fundament of these traditional methods.

Development of a sequence-characterized amplified region marker-targeted quantitative PCR assay for strain-specific detection of Oenococcus oeni during wine malolactic fermentation

Control over malolactic fermentation (MLF) is a difficult goal in winemaking and needs rapid methods to monitor Oenococcus oeni malolactic starters (MLS) in a stressful environment such as wine. In this study, we describe a novel quantitative PCR (QPCR) assay enabling the detection of an O. oeni strain during MLF without culturing. O. oeni strain LB221 was used as a model to develop a strain-specific sequence-characterized amplified region (SCAR) marker derived from a discriminatory OPA20-based randomly amplified polymorphic DNA (RAPD) band. The 5' and 3' flanking regions and the copy number of the SCAR marker were characterized using inverse PCR and Southern blotting, respectively. Primer pairs targeting the SCAR sequence enabled strain-specific detection without cross amplification of other O. oeni strains or wine species of lactic acid bacteria (LAB), acetic acid bacteria (AAB), and yeasts. The SCAR-QPCR assay was linear over a range of cell concentrations (7 log units) and detected as few as 2.2 × 10(2) CFU per ml of red wine with good quantification effectiveness, as shown by the correlation of QPCR and plate counting results. Therefore, the cultivation-independent monitoring of a single O. oeni strain in wine based on a SCAR marker represents a rapid and effective strain-specific approach. This strategy can be adopted to develop easy and rapid detection techniques for monitoring the implantation of inoculated O. oeni MLS on the indigenous LAB population, reducing the risk of unsuccessful MLF.

Molecular source tracking of predominant lactic acid bacteria in traditional Belgian sourdoughs and their production environments

AIMS

To investigate the circulation of predominant sourdough lactic acid bacteria (LAB) species in the production environment of two Belgian artisan sourdough bakeries.

METHODS AND RESULTS

Isolates were collected from sourdoughs, flour, hands of the baker and air in the bakery setting and taxonomically characterized using repetitive element sequence-based PCR fingerprinting, pheS and/or 16S rRNA gene sequencing and amplified fragment length polymorphism (AFLP) analysis. In parallel, PCR-DGGE (denaturing gradient gel electrophoresis) analysis of V3-16S rDNA amplicons was applied to visualize the predominant bacterial population in the sourdoughs and the corresponding bakery environment (flour, hands of the baker, air and bakery equipment). Both approaches revealed that sourdoughs produced at D01 and D10 were mainly dominated by Lactobacillus spicheri and L. plantarum and by L. sanfranciscensis, respectively, and that these LAB species also circulated in the corresponding bakery environment. Furthermore, AFLP fingerprinting demonstrated that sourdough and bakery environment isolates of these species were genetically indistinguishable. For more sensitive source-tracking, SYBR Green-based real-time PCR assays were developed using species-specific primers targeting the pheS gene of L. plantarum and L. sanfranciscensis, detected in air samples from D01 and D10, respectively.

CONCLUSIONS

The results obtained in this study indicate that specific strains of LAB persist in artisan doughs over years and circulate in the bakery environment. Furthermore, the importance of air as a potential carrier of LAB in artisan bakery environments was demonstrated.

SIGNIFICANCE AND IMPACT OF THE STUDY

PheS-based real-time PCR can be used to detect, quantify and/or monitor specific LAB species (e.g. starter cultures) in sourdough and bakery environment samples.

High frequency of histamine-producing bacteria in the enological environment and instability of the histidine decarboxylase production phenotype

Lactic acid bacteria contribute to wine transformation during malolactic fermentation. They generally improve the sensorial properties of wine, but some strains produce histamine, a toxic substance that causes health issues. Histamine-producing strains belong to species of the genera Oenococcus, Lactobacillus, and Pediococcus. All carry an hdcA gene coding for a histidine decarboxylase that converts histidine into histamine. For this study, a method based on quantitative PCR and targeting hdcA was developed to enumerate these bacteria in wine. This method was efficient for determining populations of 1 to 10(7) CFU per ml. An analysis of 264 samples collected from 116 wineries of the same region during malolactic fermentation revealed that these bacteria were present in almost all wines and at important levels, exceeding 10(3) CFU per ml in 70% of the samples. Histamine occurred at an often important level in wines containing populations of the above-mentioned bacteria. Fifty-four colonies of histamine producers isolated from four wines were characterized at the genetic level. All were strains of Oenococcus oeni that grouped into eight strain types by randomly amplified polymorphic DNA analysis. Some strains were isolated from wines collected in distant wineries. Moreover, hdcA was detected on a large and possibly unstable plasmid in these strains of O. oeni. Taken together, the results suggest that the risk of histamine production exists in almost all wines and is important when the population of histamine-producing bacteria exceeds 10(3) per ml. Strains of O. oeni producing histamine are frequent in wine during malolactic fermentation, but they may lose this capacity during subcultures in the laboratory.

A TaqMan-based real-time PCR assay for the specific detection and quantification of Leuconostoc mesenteroides in meat products

A new real-time PCR procedure was developed for the specific detection and quantification of Leuconostoc mesenteroides in meat products. It is a TaqMan assay based on 23S rRNA gene targeted primers and probe. Specificity was evaluated using purified DNA from 132 strains: 102 lactic acid bacteria (LAB), including 57 reference strains and 46 food isolates, belonging to genus Leuconostoc and related genera, and 30 non-LAB strains. Quantification was linear over at least 5 log units using both serial dilutions of purified DNA and calibrated cell suspensions from Leuconostoc mesenteroides ssp. dextranicum CECT 912T. This assay was able to detect at least five genomic equivalents, using purified DNA or 59 CFU per reaction when using calibrated cell suspensions. It performed successfully when tested on an artificially inoculated meat product, with a minimum threshold of 10(4) CFU g(-1) for the accurate quantification of Leuconostoc mesenteroides.

Monitoring of Saccharomyces and Hanseniaspora populations during alcoholic fermentation by real-time quantitative PCR

Real-time, or quantitative, PCR (QPCR) was developed for the rapid quantification of two of the most important yeast groups in alcoholic fermentation (Saccharomyces spp. and Hanseniaspora spp.). Specific primers were designed from the region spanning the internal transcribed spacer 2 (ITS2) and the 5.8S rRNA gene. To confirm the specificity of these primers, they were tested with different yeast species, acetic acid bacteria and lactic acid bacteria. The designed primers only amplified for the intended group of species and none of the PCR assays was positive for any other wine microorganisms. This technique was performed on reference yeast strains from pure cultures and validated with both artificially contaminated wines and real wine fermentation samples. To determine the effectiveness of the technique, the QPCR results were compared with those obtained by plating. The design of new primers for other important wine yeast species will enable to monitor yeast diversity during industrial wine fermentation and to detect the main spoilage yeasts in wine.

Evaluation of real-time PCR targeting the 16S rRNA and recA genes for the enumeration of bifidobacteria in probiotic products

The application of real-time PCR targeting the multicopy 16S rRNA gene and the single copy recA gene was evaluated for the enumeration of bifidobacteria in 29 probiotic products claimed to contain these organisms. Both assays relied on the use of genus-specific primers and the non-specific SYBR Green I chemistry. For both applications, the calibration curve was constructed using the type strain of Bifidobacterium animalis subsp. lactis. Upon correction with a factor corresponding to the 16S rRNA gene copy number, both assays generally produced comparable enumeration results. Only in exceptional cases, differences between both gene targets were found in probiotic products containing low amounts of bifidobacteria in which case the quantification of the multicopy 16S rRNA gene turned out to be more sensitive than the recA-based assay. On the other hand, the use of the latter single copy gene in real-time PCR quantification offers the advantage that no prior knowledge of bacterial content is required when using genus-specific primers, since no correction for multiple gene copies has to be performed. Only 11 of the analysed products (38%), including one dairy based product and ten dried products, contained a minimal Bifidobacterium concentration of 10(6) CFU per ml or g of product. Depending on the application, both assays proved to be rapid and reproducible alternatives for culture-based detection and quantification of bifidobacteria in probiotic products.

Direct quantitation and detection of salmonellae in biological samples without enrichment, using two-step filtration and real-time PCR

A new two-step filtration protocol followed by a real-time PCR assay based on SYBR green I detection was developed to directly quantitate salmonellae in two types of biological samples: i.e., chicken rinse and spent irrigation water. Four prefiltration filters, one type of final filter, and six protocols for recovery of salmonellae from the final filter were evaluated to identify an effective filtration protocol. This method was then combined with a real-time PCR assay based on detection of the invA gene. The best results were obtained by subsequent filtration of 100 ml of chicken rinse or 100 ml of spent irrigation water through filters with pore diameters of >40 mum to remove large particles and of 0.22 microm to recover the Salmonella cells. After this, the Salmonella cells were removed from the filter by vortexing in 1 ml of physiological saline, and this sample was then subjected to real-time quantitative PCR. The whole procedure could be completed within 3 h from sampling to quantitation, and cell numbers as low as 7.5 x 10(2) CFU per 100-ml sample could be quantified. Below this limit, qualitative detection of concentrations as low as 2.2 CFU/100 ml sample was possible on occasion. This study has contributed to the development of a simple, rapid, and reliable method for quantitation of salmonellae in food without the need for sample enrichment or DNA extraction.

Real-time quantitative PCR (QPCR) and reverse transcription-QPCR for detection and enumeration of total yeasts in wine

Real-time PCR, or quantitative PCR (QPCR), has been developed to rapidly detect and quantify the total number of yeasts in wine without culturing. Universal yeast primers were designed from the variable D1/D2 domains of the 26S rRNA gene. These primers showed good specificity with all the wine yeasts tested, and they did not amplify the most representative wine species of acetic acid bacteria and lactic acid bacteria. Numerous standard curves were constructed with different strains and species grown in yeast extract-peptone-dextrose medium or incubated in wine. The small standard errors with these replicas proved that the assay is reproducible and highly robust. This technique was validated with artificially contaminated and natural wine samples. We also performed a reverse transcription-QPCR (RT-QPCR) assay from rRNA for total viable yeast quantification. This technique had a low detection limit and was more accurate than QPCR because the dead cells were not quantified. As far as we know, this is the first time that RT-QPCR has been performed to quantify viable yeasts from rRNA. RT-QPCR is a rapid and accurate technique for enumerating yeasts during industrial wine fermentation and controlling the risk of wine spoilage.

Differential real-time PCR assay for enumeration of lactic acid bacteria in wine

Oenococcus oeni is often employed to perform the malolactic fermentation in wine production, while nonoenococcal lactic acid bacteria often contribute to wine spoilage. Two real-time PCR assays were developed to enumerate the total, and nonoenococcal, lactic acid bacterial populations in wine. Used together, these assays can assess the spoilage risk of juice or wine from lactic acid bacteria.

Real-time PCR detection of Biscogniauxia mediterranea in symptomless oak tissue

AIMS

Real-time PCR, based on TaqMan chemistry, was used to detect Biscogniauxia mediterranea, a fungal pathogen that after a long endophytic phase may cause charcoal disease in oak trees.

METHODS AND RESULTS

Specific primers and probe were designed and tested on axenic cultures of B. mediterranea and other fungi commonly colonizing oaks. Twig samples were collected in Tuscany from apparently healthy oaks (Quercus cerris, Quercus ilex and Quercus pubescens) growing near trees infected with the fungus. Twigs were divided into two groups: one for isolation in agar plates, and one for real-time PCR after DNA extraction. The detection limit of the assay was 0.01 pg/DNA, whereas the amounts of fungal DNA detected in asymptomatic tissue were >0.5 pg microg(-1) total DNA extracted. In the apparently healthy twigs the frequency of isolation found on agar was 25.0%, much lower than that with real-time PCR (96.4%).

CONCLUSIONS

Real-time PCR is a sensitive and fast technique able to specifically detect and quantify the DNA of B. mediterranea in oak tissue.

SIGNIFICANCE AND IMPACT OF THE STUDY

This diagnostic method is a precise tool to localize fungi in symptomless plant tissues and promises to advance our understanding of fungal infection during their latent phase.

Transcriptome analysis of bud burst in sessile oak (Quercus petraea)

Expression patterns of hundreds of transcripts in apical buds were monitored during bud flushing in sessile oak (Quercus petraea), in order to identify genes differentially expressed between the quiescent and active stage of bud development. Different transcriptomic techniques combining the construction of suppression subtractive hybridization (SSH) libraries and the monitoring of gene expression using macroarray and real-time reverse transcriptase polymerase chain reaction (RT-PCR) were performed to dissect bud burst, with a special emphasis on the onset of the process. We generated 801 expressed sequence tags (ESTs) derived from six developmental stages of bud burst. Macroarray experiment revealed a total of 233 unique transcripts exhibiting differential expression during the process, and a putative function was assigned to 65% of them. Cell rescue/defense-, metabolism-, protein synthesis-, cell cycle- and transcription-related transcripts were among the most regulated genes. Macroarray and real-time RT-PCR showed that several genes exhibited contrasted expressions between quiescent and swelling buds, such as a putative homologue of the transcription factor DAG2 (Dof Affecting Germination 2), previously reported to be involved in the control of seed germination in Arabidopsis thaliana. These differentially expressed genes constitute relevant candidates for signaling pathway of bud burst in trees.

Evaluation of intra-specific diversities in Oenococcus oeni through analysis of genomic and expressed DNA

In winemaking Oenococcus (O.) oeni is the most frequent species of lactic acid bacteria (LAB) associated with malolactic fermentation (MLF). Several studies have demonstrated that O. oeni is a quite homogeneous species and strains are difficult to differentiate especially when isolates from the same region are analyzed. In this study, the molecular biodiversity of O. oeni isolated from wines of the same region (Aglianico produced in Basilicata Region, Southern Italy) was evaluated with the aim of designing a molecular approach for discrimination and characterization of the isolates at the strain level. Three molecular techniques were applied: random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR), restriction endonucleases analysis-pulsed field gel electrophoresis (REA-PFGE) and differential display PCR (DD-PCR). The results obtained by RAPD-PCR confirmed the difficulty in differentiating isolates. By means of REA-PFGE a higher polymorphism, often related to the origin (winery) of strains, was revealed. However, on analyzing strains isolated from the same winery, only in some cases was more than one REA-PFGE pattern obtained. By analyzing dendrograms constructed on the basis of DD-PCR profiles differentiation of strains isolated from the same winery, in some cases, could be accomplished. The reliability of the DD-PCR in the differentiation of closely related strains suggests that this method could represent an alternative and/or additional tool to other molecular methods, such as REA-PFGE, for fine characterization of oenococcal strains.

Fast protocols for the 5S rDNA and ITS-2 based identification ofOenococcus oeni

To identify specific marker sequences for the rapid identification of Oenococcus oeni, we sequenced the 23S-5S internal transcribed spacer (ITS-2) region and the 5S rDNA of five different O. oeni strains and three phylogenetically related lactic acid bacteria (LAB). Comparative analysis revealed 100% identity among the ITS-2 region of the O. oeni strains and remarkable differences in length and sequence compared to related LAB. These results enabled us to develop a primer set for a rapid PCR-identification of O. oeni within three hours. Moreover, the comparison of the 5S rDNA sequences and the highly conserved secondary structure provided the template for the design of three fluorescence-labeled specific oligonucleotides for fluorescence in situ hybridization (FISH). These probes are partial complementary to each other. This feature promotes the accessibility to the target sequence within the ribosome and enhances the fluorescence signal. For the rapid identification of Oenococci both the 5S rRNA gene and the ITS-2 region are useful targets.

Real-time Fluorescent PCR Techniques to Study Microbial-Host Interactions

This chapter describes how real-time polymerase chain reaction (PCR) performs and how it may be used to detect microbial pathogens and the relationship they form with their host. Research and diagnostic microbiology laboratories contain a mix of traditional and leading-edge, in-house and commercial assays for the detection of microbes and the effects they impart upon target tissues, organs, and systems. The PCR has undergone significant change over the last decade, to the extent that only a small proportion of scientists have been able or willing to keep abreast of the latest offerings. The chapter reviews these changes. It discusses the second-generation of PCR technology-kinetic or real-time PCR, a tool gaining widespread acceptance in many scientific disciplines but especially in the microbiology laboratory.

A real-time polymerase chain reaction-based method for rapid and specific detection of spoilage Alicyclobacillus spp. in apple juice

AIMS

To develop a real-time PCR-based rapid detection method for spoilage Alicyclobacillus spp. in juice products.

METHODS AND RESULTS

The squalene-hopene cyclase-encoding gene was targeted for primer-and-probe development. Gene fragments from representative strains were cloned, and PCR primers and probe were designed by DNA sequence comparison. Selected bacteria were examined for cross-reactivity by the new method. Cells were serially diluted in apple juice and saline, and examined by the new method to establish detection sensitivity. Using the newly developed Taqman real-time PCR-based method, strains of Alicyclobacillus acidocaldarius and A. acidoterrestris were detected without cross reactivity with other common food-borne micro-organisms. Detection of <10 cells per PCR reaction from juice samples was accomplished within 3-5 h.

CONCLUSION

This is the first reported real-time PCR-based detection method for Alicyclobacillus spp. and its application in juice products is demonstrated.

SIGNIFICANCE AND IMPACT OF THE STUDY

As a favourable alternative for the laborious and time-consuming culture- or biochemical characterization-based techniques, the system has great potential for industrial applications from raw material screening to final product quality control.