Molecular diversity of leuconostoc mesenteroides and leuconostoc citreum isolated from traditional french cheeses as revealed by RAPD fingerprinting, 16S rDNA sequencing and 16S rDNA fragment amplification

The Controversial Nature of Some Non-Starter Lactic Acid Bacteria Actively Participating in Cheese Ripening

This mini review deals with some controversial non-starter lactic acid bacteria (NSLAB) species known to be both human and animal pathogens but also health-promoting and probiotic. The focus is on Lactococcus garvieae, two Streptococcus species (S. uberis and S. parauberis), four Weissella species (W. hellenica, W. confusa, W. paramesenteroides, and W. cibaria), and Mammalicoccus sciuri, which worldwide, are often found within the microbiotas of different kinds of cheese, mainly traditional artisanal cheeses made from raw milk and/or relying on environmental bacteria for their ripening. Based on literature data, the virulence and health-promoting effects of these bacteria are examined, and some of the mechanisms of these actions are reviewed. Additionally, their possible roles in cheese ripening are also discussed. The analysis of the literature data available so far showed that, in general, the pathogenic and the beneficial strains, despite belonging to the same species, show somewhat different genetic constitutions. Yet, when the safety of a given strain is assessed, genomic analysis on its own is not enough, and a polyphasic approach including additional physiological and functional tests is needed.

Anti-biofilm potential of Lactobacillus plantarum Y3 culture and its cell-free supernatant against multidrug-resistant uropathogen Escherichia coli U12

Uropathogens develop biofilms on urinary catheters, resulting in persistent and chronic infections that are associated with resistance to antimicrobial therapy. Therefore, the current study was performed to control biofilm-associated urinary tract infections through assaying the anti-biofilm ability of lactic acid bacteria (LAB) against multidrug-resistant (MDR) uropathogens. Twenty LAB were obtained from pickles and fermented dairy products, and screened for their anti-biofilm and antimicrobial effects against MDR Escherichia coli U12 (ECU12). Lactobacillus plantarum Y3 (LPY3) (MT498405), showed the highest inhibitory effect and biofilm production. Pre-coating of a microtitre plate with LPY3 culture was more potent than co-incubation. Pre-coating with LPY3 culture generated a higher anti-biofilm effect with an adherence of 14.5% than cell free supernatant (CFS) (31.2%). Anti-biofilm effect of CFS was heat stable up to 100 °C with higher effect at pH 4-6. Pre-coating urinary catheter with LPY3 culture reduced the CFU/cm2 of ECU12 attached to the catheter for up to seven days. Meanwhile, CFS reduced the ECU12 CFU/cm2 for up to four days. Scanning electron microscope confirmed the reduction of ECU12 adherence to catheters after treatment with CFS. Therefore, Lactobacillus plantarum can be applied in medical devices as prophylactic agent and as a natural biointervention to treat urinary tract infections.

Biodiversity and succession of lactic microbiota involved in Brazilian buffalo mozzarella cheese production

The biodiversity and succession of lactic acid bacteria (LAB) involved in the production and storage of Brazilian buffalo mozzarella cheese were evaluated. The isolates were characterized by Gram staining and catalase test, by the ability to grow at different conditions: temperatures, pH, concentrations of NaCl, and production of CO₂ from glucose. The biodiversity and succession of 152 LAB isolated during cheese production were evaluated by 16S rRNA gene sequencing, Random Amplified Polymorphic DNA (RAPD-PCR), and Restriction Fragment Length Polymorphism (RFLP-PCR) techniques. Most of the strains grow well at 30 °C and are tolerant to 6.5% of NaCl, and in general, the best pH for growing was 9.6. Leuconostoc mesenteroides, Lacticaseibacillus casei, Limosilactobacillus fermentum, and Enterococcus sp. were prevalent and present in almost all steps of production. The LAB strains are typically found in the traditional Italian cheese, except the Leuconostoc citreum species. Sixty clusters were obtained by RAPD-PCR with 85% of similarity (114 isolates) while most of the LAB was clustered with 100% of similarity by the RFLP-PCR technique. The applied techniques enabled a valuable elucidation of the LAB biodiversity and succession, contributing to a better understanding of the specific microbial cultures with a technological aptitude of this cheese.

A new Leuconostoc citreum strain discovered in the traditional sweet potato sour liquid fermentation as a novel bioflocculant for highly efficient starch production

Sour liquid fermentation is commonly used in the sedimentation process of traditional starch production, where bacteria play a critical role in starch flocculation. In this study, the dynamic changes of bacterial compositions during sweet potato sour liquid (SPSL) fermentation were profiled using the single-molecule real-time (SMRT) sequencing, unveiling that Leuconostoc citreum, Leuconostoc pseudomesenteroides, Lactococcus lactis, and Lactobacillus plantarum were the dominant microorganisms in the process, and Leuconostoc citreum exhibited a strong positive correlation with starch flocculation rate (FR). In total, 75 lactic acid bacterial (LAB) strains were isolated from the SPSL, but only 7 of them caused starch flocculation. For the first time, Leuconostoc citreum strains were reported with excellent starch-flocculating abilities (up to 55.56% FR in 20 min), which might be attributed to their ability to connect starch granules through the cell surface to form large aggregation. This study provides a comprehensive understanding of the bacterial dynamics in SPSL fermentation at the species level. A starch flocculation yield of 93.63% was achieved within 1 h by using the newly discovered Leuconostoc citreum SJ-57. The time required for total starch sedimentation was reduced from 10 h to 4 h, compared with the traditional process. These results suggest that this novel bioflocculant is more suitable for modernizing the traditional SPSL fermentation process and achieving rapid and highly efficient starch sedimentation.

Tracking of Intentionally Inoculated Lactic Acid Bacteria Strains in Yogurt and Probiotic Powder

The present work aimed at tracking intentionally inoculated lactic acid bacteria (LAB) strains in yogurt and probiotic powder. Leuconostoc (Leu.) mesenteroides (11251), Lactobacillus (L.) brevis (B151), and Lactobacillus plantarum (LB41^K) strains were tracked in yogurt, and L. plantarum (LB41^P) was tracked in a commercial probiotic powder. The yogurt was intentionally inoculated with the selected bacterial strains. Two types of yogurt with known and unknown bacterial pools were utilized. The standard 16S rRNA gene sequencing was used to evaluate the initial screening. The molecular typing tools, random amplified polymorphic DNA (RAPD), repetitive element palindromic PCR (rep-PCR), and comparative gene sequence analysis of selected housekeeping loci were used to track the inoculated dubious strains. Out of 30 random selections for each inoculation, the developed method identified seven (11251), nine (B151), and five (LB41^K) colonies in the yogurt. The validation was performed by identifying 7 colonies (LB41^P) out of 30 in the probiotic powder. The DNA banding profiles and the gene sequence alignments led to the identification of the correct inoculated strains. Overall, the study summarizes the use of molecular tools to identify the deliberately inoculated LAB strains. In conclusion, the proposed polyphasic approach effectively tracked the intentionally inoculated strains: Leu. mesenteroides, L. brevis, and L. plantarum (LB41^K) in yogurt and L. plantarum (LB41^P) in probiotic powder. The study demonstrates how to track industrially relevant misused LAB strains in marketable food products.

Lactobacillus plantarum P2R3FA Isolated from Traditional Cereal-Based Fermented Food Increase Folate Status in Deficient Rats

Folate deficiencies are widespread around the world. Promoting consumption of folate-rich foods could be a sustainable option to alleviate this problem. However, these foods are not always available. Cereals, being a staple food, could contribute to folate intake. They are fermented prior to consumption in many African countries, and fermentation can modify the folate content. In Ethiopia, injera is a widely consumed fermented flat bread. The main drivers of its fermentation are lactic acid bacteria (LAB). The aim of this work was to isolate and identify folate-producing LAB from injera fermented dough and to evaluate their ability to increase folate status after depletion in a rat model. Among the 162 strains isolated from 60 different fermentations, 19 were able to grow on a folate-free culture medium and produced 1 to 43 µg/L (24 h, 30 °C incubation). The four highest folate producers belonged to the Lactobacillus plantarum species. The most productive strain was able to enhance folate status after depletion in a rat model, despite the relatively low folate content of the feed supplemented with the strain. Folate-producing L. plantarum strain has potential use as a commercial starter in injera production.

Antibacterial and anti-adhesive efficiency of Pediococcus acidilactici against foodborne biofilm producer Bacillus cereus attached on different food processing surfaces

This study aimed to assess the biofilm formation by Bacillus cereus on two novel surfaces namely: aluminum and cold steel in comparison study with stainless steel and polystyrene. Also, it aimed to study the inhibitory effect of a new strain Pediococcus acidilactici against biofilm formation by B. cereus grown on these surfaces. In this study, B. cereus M50 isolated from milky machine surface was selected as the highest biofilm producer. The number of M50 cells adhered to aluminum and stainless steel surfaces were more than that adhered to polystyrene and cold steel, respectively. The antimicrobial, anti-adhesive and SEM studies revealed that the P. acidilactici P12 culture and its cell free filtrate showed a significant potential inhibition of biofilm formation of M50 on all tested surfaces under different conditions. These results demonstrated that P. acidilactici strain are considered a new biotreatment for biofilm destruction of food borne pathogens, food biopreservation and food safety.

Catalytic, Computational, and Evolutionary Analysis of the d-Lactate Dehydrogenases Responsible for d-Lactic Acid Production in Lactic Acid Bacteria

d-Lactate dehydrogenase (d-LDH) catalyzes the reversible reaction pyruvate + NADH + H⁺ ↔ lactate + NAD⁺, which is a principal step in the production of d-lactate in lactic acid bacteria. In this study, we identified and characterized the major d-LDH (d-LDH1) from three d-LDHs in Leuconostoc mesenteroides, which has been extensively used in food processing. A molecular simulation study of d-LDH1 showed that the conformation changes during substrate binding. During catalysis, Tyr101 and Arg235 bind the substrates by hydrogen bonds and His296 acts as a general acid/base for proton transfer. These residues are also highly conserved and have coevolved. Point mutations proved that the substrate binding sites and catalytic site are crucial for enzyme activity. Network and phylogenetic analyses indicated that d-LDH1 and the homologues are widely distributed but are most abundant in bacteria and fungi. This study expands the understanding of the functions, catalytic mechanism, and evolution of d-LDH.

Identification and Characterization of l-Malate Dehydrogenases and the l-Lactate-Biosynthetic Pathway in Leuconostoc mesenteroides ATCC 8293

One putative l-lactate dehydrogenase gene (l- ldh) and three putative d- ldh genes from Leuconostoc mesenteroides ATCC 8293 were overexpressed, and their enzymatic properties were investigated. Only one gene showed d-LDH activity, catalyzing pyruvate and d-lactate interconversion, whereas the other genes displayed l- and d-malate dehydrogenase (MDH) activity, catalyzing oxaloacetate and l- and d-malate interconversion, suggesting that strain ATCC 8293 may not harbor an l- ldh gene. Putative phosphoenolpyruvate carboxylase (PEPC)- and malolactic enzyme (MLE)-encoding genes were identified from strain ATCC 8293, and sequence analysis showed that they could exhibit PEPC and MLE activities, respectively. l-Lactate production and transcriptional expression of the mle gene in this strain were highly increased in the presence of l-malate. We propose that in strain ATCC 8293, which lacks an l- ldh gene, l-lactate is produced through sequential enzymatic conversions from phosphoenolpyruvate to oxaloacetate, then l-malate, and finally l-lactate by PEPC, l-MDH, and MLE, respectively.

Genetic diversity analysis of Leuconostoc mesenteroides from Korean vegetables and food products by multilocus sequence typing

In the present study, 35 Leuconostoc mesenteroides strains isolated from vegetables and food products from South Korea were studied by multilocus sequence typing (MLST) of seven housekeeping genes (atpA, groEL, gyrB, pheS, pyrG, rpoA, and uvrC). The fragment sizes of the seven amplified housekeeping genes ranged in length from 366 to 1414 bp. Sequence analysis indicated 27 different sequence types (STs) with 25 of them being represented by a single strain indicating high genetic diversity, whereas the remaining 2 were characterized by five strains each. In total, 220 polymorphic nucleotide sites were detected among seven housekeeping genes. The phylogenetic analysis based on the STs of the seven loci indicated that the 35 strains belonged to two major groups, A (28 strains) and B (7 strains). Split decomposition analysis showed that intraspecies recombination played a role in generating diversity among strains. The minimum spanning tree showed that the evolution of the STs was not correlated with food source. This study signifies that the multilocus sequence typing is a valuable tool to access the genetic diversity among L. mesenteroides strains from South Korea and can be used further to monitor the evolutionary changes.

Pan-genomic and transcriptomic analyses of Leuconostoc mesenteroides provide insights into its genomic and metabolic features and roles in kimchi fermentation

The genomic and metabolic features of Leuconostoc (Leu) mesenteroides were investigated through pan-genomic and transcriptomic analyses. Relatedness analysis of 17 Leu. mesenteroides strains available in GenBank based on 16S rRNA gene sequence, average nucleotide identity, in silico DNA-DNA hybridization, molecular phenotype, and core-genome indicated that Leu. mesenteroides has been separated into different phylogenetic lineages. Pan-genome of Leu. mesenteroides strains, consisting of 999 genes in core-genome, 1,432 genes in accessory-genome, and 754 genes in unique genome, and their COG and KEGG analyses showed that Leu. mesenteroides harbors strain-specifically diverse metabolisms, probably representing high evolutionary genome changes. The reconstruction of fermentative metabolic pathways for Leu. mesenteroides strains showed that Leu. mesenteroides produces various metabolites such as lactate, ethanol, acetate, CO₂, mannitol, diacetyl, acetoin, and 2,3-butanediol through an obligate heterolactic fermentation from various carbohydrates. Fermentative metabolic features of Leu. mesenteroides during kimchi fermentation were investigated through transcriptional analyses for the KEGG pathways and reconstructed metabolic pathways of Leu. mesenteroides using kimchi metatranscriptomic data. This was the first study to investigate the genomic and metabolic features of Leu. mesenteroides through pan-genomic and metatranscriptomic analyses, and may provide insights into its genomic and metabolic features and a better understanding of kimchi fermentations by Leu. mesenteroides.

Safety of Novel Microbes for Human Consumption: Practical Examples of Assessment in the European Union

Novel microbes are either newly isolated genera and species from natural sources or bacterial strains derived from existing bacteria. Novel microbes are gaining increasing attention for the general aims to preserve and modify foods and to modulate gut microbiota. The use of novel microbes to improve health outcomes is of particular interest because growing evidence points to the importance of gut microbiota in human health. As well, some recently isolated microorganisms have promise for use as probiotics, although in-depth assessment of their safety is necessary. Recent examples of microorganisms calling for more detailed evaluation include Bacteroides xylanisolvens, Akkermansia muciniphila, fructophilic lactic acid bacteria (FLAB), and Faecalibacterium prausnitzii. This paper discusses each candidate's safety evaluation for novel food or novel food ingredient approval according to European Union (EU) regulations. The factors evaluated include their beneficial properties, antibiotic resistance profiling, history of safe use (if available), publication of the genomic sequence, toxicological studies in agreement with novel food regulations, and the qualified presumptions of safety. Sufficient evidences have made possible to support and authorize the use of heat-inactivated B. xylanisolvens in the European Union. In the case of A. muciniphila, the discussion focuses on earlier safety studies and the strain's suitability. FLAB are also subjected to standard safety assessments, which, along with their proximity to lactic acid bacteria generally considered to be safe, may lead to novel food authorization in the future. Further research with F. prausnitzii will increase knowledge about its safety and probiotic properties and may lead to its future use as novel food. Upcoming changes in EUU Regulation 2015/2283 on novel food will facilitate the authorization of future novel products and might increase the presence of novel microbes in the food market.

Leuconostoc strains isolated from dairy products: Response against food stress conditions

A systematic study about the intrinsic resistance of 29 strains (26 autochthonous and 3 commercial ones), belonging to Leuconostoc genus, against diverse stress factors (thermal, acidic, alkaline, osmotic and oxidative) commonly present at industrial or conservation processes were evaluated. Exhaustive result processing was made by applying one-way ANOVA, Student's test (t), multivariate analysis by Principal Component Analysis (PCA) and Matrix Hierarchical Cluster Analysis. In addition, heat adaptation on 4 strains carefully selected based on previous data analysis was assayed. The strains revealed wide diversity of resistance to stress factors and, in general, a clear relationship between resistance and Leuconostoc species was established. In this sense, the highest resistance was shown by Leuconostoc lactis followed by Leuconostoc mesenteroides strains, while Leuconostoc pseudomesenteroides and Leuconostoc citreum strains revealed the lowest resistance to the stress factors applied. Heat adaptation improved thermal cell survival and resulted in a cross-resistance against the acidic factor. However, all adapted cells showed diminished their oxidative resistance. According to our knowledge, this is the first study regarding response of Leuconostoc strains against technological stress factors and could establish the basis for the selection of "more robust" strains and propose the possibility of improving their performance during industrial processes.

Genomic Characterization of Dairy Associated Leuconostoc Species and Diversity of Leuconostocs in Undefined Mixed Mesophilic Starter Cultures

Undefined mesophilic mixed (DL-type) starter cultures are composed of predominantly Lactococcus lactis subspecies and 1-10% Leuconostoc spp. The composition of the Leuconostoc population in the starter culture ultimately affects the characteristics and the quality of the final product. The scientific basis for the taxonomy of dairy relevant leuconostocs can be traced back 50 years, and no documentation on the genomic diversity of leuconostocs in starter cultures exists. We present data on the Leuconostoc population in five DL-type starter cultures commonly used by the dairy industry. The analyses were performed using traditional cultivation methods, and further augmented by next-generation DNA sequencing methods. Bacterial counts for starter cultures cultivated on two different media, MRS and MPCA, revealed large differences in the relative abundance of leuconostocs. Most of the leuconostocs in two of the starter cultures were unable to grow on MRS, emphasizing the limitations of culture-based methods and the importance of careful media selection or use of culture independent methods. Pan-genomic analysis of 59 Leuconostoc genomes enabled differentiation into twelve robust lineages. The genomic analyses show that the dairy-associated leuconostocs are highly adapted to their environment, characterized by the acquisition of genotype traits, such as the ability to metabolize citrate. In particular, Leuconostoc mesenteroides subsp. cremoris display telltale signs of a degenerative evolution, likely resulting from a long period of growth in milk in association with lactococci. Great differences in the metabolic potential between Leuconostoc species and subspecies were revealed. Using targeted amplicon sequencing, the composition of the Leuconostoc population in the five commercial starter cultures was shown to be significantly different. Three of the cultures were dominated by Ln. mesenteroides subspecies cremoris. Leuconostoc pseudomesenteroides dominated in two of the cultures while Leuconostoc lactis, reported to be a major constituent in fermented dairy products, was only present in low amounts in one of the cultures. This is the first in-depth study of Leuconostoc genomics and diversity in dairy starter cultures. The results and the techniques presented may be of great value for the dairy industry.

Mesophilic Lactic Acid Bacteria Diversity Encountered in Brazilian Farms Producing Milk with Particular Interest in Lactococcus lactis Strains

The milk produced in regions with different traditions in Brazil is used for artisanal product production, which is characterized by different sensorial characteristics. This study aimed to identify the bacterial ecosystem of farms located in a traditional dairy region in the state of Minas Gerais and to characterize Lactococcus lactis strains, the species of interest in this study, using a multilocus sequence typing (MLST) protocol and pulsed-field gel electrophoresis (PFGE) technique. Samples were collected from raw milk and dairy environment from six farms. A total of 50 isolates were analyzed using 16S rRNA sequencing and species-specific PCR. Five genera were identified: Lactobacillus, Leuconostoc, Lactococcus, Enterococcus, and Staphylococcus, from ten different species. MLST (with six housekeeping genes) and PFGE (with SmaI endonuclease) were used for the characterization of 20 isolates of Lactococcus lactis from a dairy collection in this study. Both methods revealed a high clonal diversity of strains with a higher discriminatory level for PFGE (15 pulsotypes), compared to MLST (12 ST). This study contributes to the preservation of the Brazilian dairy heritage and provides insights into a part of the LAB population found in raw milk and dairy environment.

Use of Potential Probiotic Lactic Acid Bacteria (LAB) Biofilms for the Control of Listeria monocytogenes, Salmonella Typhimurium, and Escherichia coli O157:H7 Biofilms Formation

Use of probiotic biofilms can be an alternative approach for reducing the formation of pathogenic biofilms in food industries. The aims of this study were (i) to evaluate the probiotic properties of bacteriocinogenic (Lactococcus lactis VB69, L. lactis VB94, Lactobacillus sakei MBSa1, and Lactobacillus curvatus MBSa3) and non-bacteriocinogenic (L. lactis 368, Lactobacillus helveticus 354, Lactobacillus casei 40, and Weissela viridescens 113) lactic acid bacteria (LAB) isolated from Brazilian’s foods and (ii) to develop protective biofilms with these strains and test them for exclusion of Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella Typhimurium. LAB were tested for survival in acid and bile salt conditions, surface properties, biosurfactant production, β-galactosidase and gelatinase activity, antibiotic resistance and presence of virulence genes. Most strains survived exposure to pH 2 and 4% bile salts. The highest percentages of auto-aggregation were obtained after 24 h of incubation. Sixty-seven percentage auto-aggregation value was observed in W. viridescens 113 and Lactobacillus curvatus MBSa3 exhibited the highest co-aggregation (69% with Listeria monocytogenes and 74.6% with E. coli O157:H7), while the lowest co-aggregation was exhibited by W. viridescens 113 (53.4% with Listeria monocytogenes and 38% with E. coli O157:H7). Tests for hemolytic activity, bacterial cell adherence with xylene, and drop collapse confirmed the biosurfactant-producing ability of most strains. Only one strain (L. lactis 368) produced β-galactosidase. All strains were negative for virulence genes cob, ccf, cylLL, cylLs, cyllM, cylB, cylA and efaAfs and gelatinase production. The antibiotic susceptibility tests indicated that the MIC for ciprofloxacin, clindamycin, gentamicin, kanamycin, and streptomycin did not exceed the epidemiological cut-off suggested by the European Food Safety Authority. Some strains were resistant to one or more antibiotics and resistance to antibiotics was species and strain dependent. In the protective biofilm assays, strains L. lactis 368 (bac-), Lactobacillus curvatus MBSa3 (bac+), and Lactobacillus sakei MBSa1 (bac+) resulted in more than six log reductions in the pathogens counts when compared to the controls. This effect could not be attributed to bacteriocin production. These results suggest that these potential probiotic strains can be used as alternatives for control of biofilm formation by pathogenic bacteria in the food industry, without conferring a risk to the consumers.

Pulsed-field gel electrophoresis for Leuconostoc mesenteroides and L. pseudomesenteroides

Pulsed-field gel electrophoresis (PFGE) is a technique using alternating electric fields to help the separation of high molecular weight DNA fragments with a high resolution. This method consists of the digestion of bacterial chromosomal DNA with rare-cutting restriction enzymes and of applying an alternating electrical current between spatially distinct pairs of electrodes. DNA molecules migrate at different speeds according to the size of the fragment. This method is considered as the "gold standard" for genotyping, genetic fingerprinting, epidemiological studies, genome size estimation, and studying radiation-induced DNA damage and repair.

A novel multi-locus sequence typing (MLST) protocol for Leuconostoc lactis isolates from traditional dairy products in China and Mongolia

BACKGROUND

Economically, Leuconostoc lactis is one of the most important species in the genus Leuconostoc. It plays an important role in the food industry including the production of dextrans and bacteriocins. Currently, traditional molecular typing approaches for characterisation of this species at the isolate level are either unavailable or are not sufficiently reliable for practical use. Multilocus sequence typing (MLST) is a robust and reliable method for characterising bacterial and fungal species at the molecular level. In this study, a novel MLST protocol was developed for 50 L. lactis isolates from Mongolia and China.

RESULTS

Sequences from eight targeted genes (groEL, carB, recA, pheS, murC, pyrG, rpoB and uvrC) were obtained. Sequence analysis indicated 20 different sequence types (STs), with 13 of them being represented by a single isolate. Phylogenetic analysis based on the sequences of eight MLST loci indicated that the isolates belonged to two major groups, A (34 isolates) and B (16 isolates). Linkage disequilibrium analyses indicated that recombination occurred at a low frequency in L. lactis, indicating a clonal population structure. Split-decomposition analysis indicated that intraspecies recombination played a role in generating genotypic diversity amongst isolates.

CONCLUSIONS

Our results indicated that MLST is a valuable tool for typing L. lactis isolates that can be used for further monitoring of evolutionary changes and population genetics.

Technological characterisation, antibiotic susceptibility and antimicrobial activity of wild-type Leuconostoc strains isolated from North Italian traditional cheeses

Genotypic and technological properties, antibiotic susceptibility and antimicrobial activity of 35 Leuconostoc strains, isolated from different Italian raw milk cheeses, were investigated. RAPD-PCR was used to study genetic variability and to distinguish closely related strains. The results showed a high degree of heterogeneity among isolates. All the strains had weak acidifying activity and showed low proteolytic and lipolytic activities. Reduction activity, was generally low. All the Leuconostoc were susceptible to ampicillin, mupirocin, erythromycin, quinupristin/dalfopristin and tetracycline. Many strains were classified as resistant to oxacillin, ciprofloxacin and nitrofurantonin, while all isolates were found resistant to vancomycin. PCR-based detection did not identify any of the common genetic determinants for vancomycin (vanA, vanB, vanC1, vanC2, vanC3, vanD, vanE, vanG) or erythromycin (ermB and ermC). Tetracycline resistance genes were detected in 25 tetracycline susceptible strains, the most frequent one being tetM. One strain, belonging to Ln. pseudomesenteroides species, was positive for the presence of the int gene of the Tn916/Tn1545 trasposon family. This is the first time the conjugative transposon Tn916 has been detected inside the Leuconostoc species. All strains showed antimicrobial activity against Enterococcus faecalis and Ent. faecium. The presence of genes encoding amino-acid decarboxylases (hdc and tdc) was not detected. Some strains are interesting in view of their use in cheese production as starter and non starter cultures.

Bacterial community dynamics, lactic acid bacteria species diversity and metabolite kinetics of traditional Romanian vegetable fermentations

BACKGROUND

Artisanal vegetable fermentations are very popular in Eastern European countries. Fresh vegetables undergo a spontaneous fermentation in the presence of salt, which is mainly carried out by lactic acid bacteria (LAB).

RESULTS

Culture-dependent and culture-independent analyses of end-samples of various spontaneous vegetable fermentations carried out in houses of the Chiodju region (central Romania) revealed Lactobacillus plantarum and Lactobacillus brevis as the most frequently isolated LAB species. Leuconostoc mesenteroides and Leuconostoc citreum were also found. Furthermore, the community dynamics of spontaneous cauliflower and mixed-vegetable (green tomatoes, carrots and cauliflower) fermentations revealed three steps: an initial phase characterised by the presence of Enterobacteriaceae and a wide LAB species diversity, encompassing Weissella species; a second phase from day 3 onwards wherein L. citreum and Lb. brevis occurred; and a final phase characterised by the prevalence of Lb. brevis and Lb. plantarum. Metabolite target analysis revealed that glucose and fructose were mostly depleted at the end of fermentation. The main products of carbohydrate metabolism were lactic acid, acetic acid, ethanol and small amounts of mannitol, indicating heterolactate fermentation.

CONCLUSION

Given their prevalence at the end of vegetable fermentations, Lb. brevis and Lb. plantarum appear to be good candidate starter cultures for controlled vegetable fermentation processes.

Prevalence and fate of Bacillus cereus in African traditional cereal-based foods used as infant foods

The objective of the present work was to estimate the prevalence of Bacillus cereus group species in traditional cereal-based lactic acid-fermented slurries and nonfermented flours used to prepare infant foods in an African context. High counts on mannitol-egg yolk-polymixin agar medium were determined for the fermented slurries (median, 4.5 × 10(4) CFU/ml of slurry) compared with the nonfermented flours, most of whose counts were lower than 10(-1) CFU/g. Virulence genes were characterized in 60 isolates from 26 traditional cereal-based foods in Ouagadougou (Burkina Faso). Seventy-two and 38 % of isolates were positive for the complete set of genes coding for hemolysin BL and nonhemolytic enterotoxin, respectively, suggesting a high enterotoxigenic potential for these foodborne isolates. No potentially emetic toxin-producing strains were detected. Because of the high counts found for fermented slurries, survival tests with vegetative cells inoculated in fermented slurries were performed, which showed that growth of B. cereus was inhibited. This result suggests that fermentation in traditional production units is presumably not adequately controlled, enabling growth during any unit operations before fermentation, or even during the fermentation step, when the process was poorly controlled. However, adding nisin (0.1 mg/ml) enabled a 5-log reduction in the B. cereus population in 5 h, suggesting that the use of nisin could be a way to upgrade the hygienic quality of this type of food.

Interaction between lactic acid bacteria and yeasts in airag, an alcoholic fermented milk

The interaction between nine lactic acid bacteria (LAB) and five yeast strains isolated from airag of Inner Mongolia Autonomic Region, China was investigated. Three representative LAB and two yeasts showed symbioses were selected and incubated in 10% (w/v) reconstituted skim milk as single and mixed cultures to measure viable count, titratable acidity, ethanol and sugar content every 24 h for 1 week. LAB and yeasts showed high viable counts in the mixed cultures compared to the single cultures. Titratable acidity of the mixed cultures was obviously enhanced compared with that of the single cultures, except for the combinations of Lactobacillus reuteri 940B3 with Saccharomyces cerevisiae 4C and Lactobacillus helveticus 130B4 with Candida kefyr 2Y305. C. kefyr 2Y305 produced large amounts of ethanol (maximum 1.35 g/L), whereas non-lactose-fermenting S. cerevisiae 4C produced large amounts of ethanol only in the mixed cultures. Total glucose and galactose content increased while lactose content decreased in the single cultures of Leuconostoc mesenteroides 6B2081 and Lb. helveticus 130B4. However, both glucose and galactose were completely consumed and lactose was markedly reduced in the mixed cultures with yeasts. The result suggests that yeasts utilize glucose and galactose produced by LAB lactase to promote cell growth.

Genetic screening of functional properties of lactic acid bacteria in a fermented pearl millet slurry and in the metagenome of fermented starchy foods

Lactic acid bacteria (LAB) (n = 152) in African pearl millet slurries and in the metagenomes of amylaceous fermented foods were investigated by screening 33 genes involved in probiotic and nutritional functions. All isolates belonged to six species of the genera Pediococcus and Lactobacillus, and Lactobacillus fermentum was the dominant species. We screened the isolates for the abilities to survive passage through the gastrointestinal tract and to synthesize folate and riboflavin. The isolates were also tested in vitro for their abilities to survive exposure to bile salts and to survive at pH 2. Because the ability to hydrolyze starch confers an ecological advantage on LAB that grow in starchy matrixes as well as improving the nutritional properties of the gruels, we screened for genes involved in starch metabolism. The results showed that genes with the potential ability to survive passage through the gastrointestinal tract were widely distributed among isolates and metagenomes, whereas in vitro tests showed that only a limited set of isolates, mainly those belonging to L. fermentum, could tolerate a low pH. In contrast, the wide distribution of genes associated with bile salt tolerance, in particular bsh, is consistent with the high frequency of tolerance to bile salts observed. Genetic screening revealed a potential for folate and riboflavin synthesis in both isolates and metagenomes, as well as high variability among genes related to starch metabolism. Genetic screening of isolates and metagenomes from fermented foods is thus a promising approach for assessing the functional potential of food microbiotas.

Stability of microbial communities in goat milk during a lactation year: Molecular approaches

The microbial communities in milks from one herd were evaluated during 1-year of lactation, using molecular methods to evaluate their stability and the effect of breeding conditions on their composition. The diversity of microbial communities was measured using two approaches: molecular identification by 16S and 18S rDNA sequencing of isolates from counting media (two milks), and direct identification using 16S rDNA from clone libraries (six milks). The stability of these communities was evaluated by counting on selective media and by Single Strand Conformation Polymorphism (SSCP) analysis of variable region V3 of the 16S rRNA gene and variable region V4 of the 18S rRNA gene. One hundred and eighteen milk samples taken throughout the year were analyzed. Wide diversity among bacteria and yeasts in the milk was revealed. In addition to species commonly encountered in milk, such as Lactococcus lactis, Lactococcus garvieae, Enterococcus faecalis, Lactobacillus casei, Leuconostoc mesenteroides, Staphylococcus epidermidis, Staphylococcus simulans, Staphylococcus caprae, Staphylococcus equorum, Micrococcus sp., Kocuria sp., Pantoea agglomerans and Pseudomonas putida, sequences were affiliated to other species only described in cheeses, such as Corynebacterium variabile, Arthrobacter sp., Brachybacterium paraconglomeratum, Clostridium sp. and Rothia sp. Several halophilic species atypical in milk were found, belonging to Jeotgalicoccus psychrophilus, Salinicoccus sp., Dietza maris, Exiguobacterium, Ornithinicoccus sp. and Hahella chejuensis. The yeast community was composed of Debaryomyces hansenii, Kluyveromyces lactis, Trichosporon beigelii, Rhodotorula glutinis, Rhodotorula minuta, Candida pararugosa, Candida intermedia, Candida inconspicua, Cryptococcus curvatus and Cryptococcus magnus. The analyses of microbial counts and microbial SSCP profiles both distinguished four groups of milks corresponding to four periods defined by season and feeding regime. The microbial community was stable within each period. Milks from winter were characterized by Lactococcus and Pseudomonas, those from summer by P. agglomerans and Klebsiella and those from autumn by Chryseobacterium indologenes, Acinetobacter baumanii, Staphylococcus, Corynebacteria and yeasts. However, the composition of the community can vary according to factors other than feeding. This study opens new investigation fields in the field of raw milk microbial ecology.

Phenotypic and genotypic identification of lactic acid bacteria isolated from ethnic fermented bamboo tender shoots of North East India

Mesu, soidon, soibum and soijim are ethnic fermented bamboo tender shoot products prepared by the people in North East India. Microbiological analysis of mesu, soidon, soibum and soijim showed the population dominated by lactic acid bacteria (LAB) ranging up to 10(8) cfu g(-1). The phenotypic characterisation of predominant LAB isolated from the fermented bamboo shoot products was based on general morphology, physiological tests, API and Biolog systems. The genotypic characterisation of LAB was based on RAPD-PCR, rep PCR, species-specific PCR techniques, 16S rRNA gene sequencing and DNA-DNA hybridisation. Predominant functional LAB strains associated with the fermented bamboo shoot products were identified as Lactobacillus brevis, Lb. plantarum, Lb. curvatus, Pediococcus pentosaceus, Leuconostoc mesenteroides subsp. mesenteroides, Leuc. fallax, Leuc. lactis, Leuc. citreum and Enterococcus durans.

Variability of bacterial biofilms of the "tina" wood vats used in the ragusano cheese-making process

Ragusano cheese is a "protected denomination of origin" cheese made in the Hyblean region of Sicily from raw milk using traditional wooden tools, without starter. To explore the Ragusano bacterial ecosystem, molecular fingerprinting was conducted at different times during the ripening and biofilms from the wooden vats called "tinas" were investigated. Raw milks collected at two farm sites, one on the mountain and one at sea level, were processed to produce Ragusano cheese. Raw milk, curd before and after cooking, curd at stretching time (cheese 0 time), and cheese samples (4 and 7 months) were analyzed by PCR-temporal temperature gel electrophoresis (PCR-TTGE) and by classical enumeration microbiology. With the use of universal primers, PCR-TTGE revealed many differences between the raw milk profiles, but also notable common bands identified as Streptococcus thermophilus, Lactobacillus lactis, Lactobacillus delbrueckii, and Enterococcus faecium. After the stretching, TTGE profiles revealed three to five dominant species only through the entire process of ripening. In the biofilms of the two tinas used, one to five species were detected, S. thermophilus being predominant in both. Biofilms from five other tinas were also analyzed by PCR-TTGE, PCR-denaturating gradient gel electrophoresis, specific PCR tests, and sequencing, confirming the predominance of lactic acid bacteria (S. thermophilus, L. lactis, and L. delbrueckii subsp. lactis) and the presence of a few high-GC-content species, like coryneform bacteria. The spontaneous acidification of raw milks before and after contact with the five tinas was followed in two independent experiments. The lag period before acidification can be up to 5 h, depending on the raw milk and the specific tina, highlighting the complexity of this natural inoculation system.

Differentiation and characterization by molecular techniques of Bacillus cereus group isolates from poto poto and dégué, two traditional cereal-based fermented foods of Burkina Faso and Republic of Congo

Poto poto (a maize sourdough) and dégué (a pearl millet-based food) are two traditional African fermented foods. The molecular biology of toxigenic and pathogenic bacteria found in those foods is largely unknown. The purpose of this study was to study the phylogenetic relatedness and toxigenic potential of 26 Bacillus cereus group isolates from these traditional fermented foods. The relatedness of the isolates was evaluated with repetitive element sequence-based PCR (REP-PCR) and 16S rDNA sequencing analysis. A multiplex real-time PCR assay targeting the lef and capC genes of B. anthracis pXO1 and pXO2 plasmids and the sspE chromosomal gene of B. cereus and B. anthracis also was carried out. Melting curve analysis of the sspE amplification product was used to differentiate B. cereus from B. anthracis, and the presence of the B. cereus enterotoxin genes was determined with PCR amplification. Isolates had 15 different REP-PCR profiles, according to which they could be clustered into four groups. 16S rDNA sequencing analysis identified 23 isolates as B. cereus or B. anthracis and three isolates as B. cereus or Bacillus sp. Multiplex real-time PCR amplification indicated the absence of the lef and capC genes of B. anthracis pXO 1 and pXO2 plasmids, and melting curve analysis revealed amplification of the 71-bp sspE product typical of B. cereus in all isolates instead of the 188-bp amplicon of B. anthracis, confirming the identity of these isolates as B. cereus. Four isolates had amylolytic activity. All isolates had lecithinase activity and beta-hemolytic activity. Enterotoxin production was detected in two isolates. The emetic toxin gene was not detected in any isolate. The nheB toxin gene was detected in 19 isolates by PCR amplification; one of these isolates also contained the hblD (L1) gene. The cytotoxin K cytK-1 gene was not detected, but the cytK-2 gene was clearly detected in six isolates.

Diversity of lactic acid bacteria associated with fish and the fish farm environment, established by amplified rRNA gene restriction analysis

Lactic acid bacteria have become a major source of concern for aquaculture in recent decades. In addition to true pathogenic species of worldwide significance, such as Streptococcus iniae and Lactococcus garvieae, several species have been reported to produce occasional fish mortalities in limited geographic areas, and many unidentifiable or ill-defined isolates are regularly isolated from fish or fish products. To clarify the nature and prevalence of different fish-associated bacteria belonging to the lactic acid bacterium group, a collection of 57 isolates of different origins was studied and compared with a set of 22 type strains, using amplified rRNA gene restriction analysis (ARDRA). Twelve distinct clusters were delineated on the basis of ARDRA profiles and were confirmed by sequencing of sodA and 16S rRNA genes. These clusters included the following: Lactococcus raffinolactis, L. garvieae, Lactococcus l., S. iniae, S. dysgalactiae, S. parauberis, S. agalactiae, Carnobacterium spp., the Enterococcus "faecium" group, a heterogeneous Enterococcus-like cluster comprising indiscernible representatives of Vagococcus fluvialis or the recently recognized V. carniphilus, V. salmoninarum, and Aerococcus spp. Interestingly, the L. lactis and L. raffinolactis clusters appeared to include many commensals of fish, so opportunistic infections caused by these species cannot be disregarded. The significance for fish populations and fish food processing of three or four genetic clusters of uncertain or complex definition, namely, Aerococcus and Enterococcus clusters, should be established more accurately.

Biodiversity of bacterial ecosystems in traditional Egyptian Domiati cheese

Bacterial biodiversity occurring in traditional Egyptian soft Domiati cheese was studied by PCR-temporal temperature gel electrophoresis (TTGE) and PCR-denaturing gradient gel electrophoresis (DGGE). Bands were identified using a reference species database (J.-C. Ogier et al., Appl. Environ. Microbiol. 70:5628-5643, 2004); de novo bands having nonidentified migration patterns were identified by DNA sequencing. Results reveal a novel bacterial profile and extensive bacterial biodiversity in Domiati cheeses, as reflected by the numerous bands present in TTGE and DGGE patterns. The dominant lactic acid bacteria (LAB) identified were as follows: Leuconostoc mesenteroides, Lactococcus garvieae, Aerococcus viridans, Lactobacillus versmoldensis, Pediococcus inopinatus, and Lactococcus lactis. Frequent non-LAB species included numerous coagulase-negative staphylococci, Vibrio spp., Kocuria rhizophila, Kocuria kristinae, Kocuria halotolerans, Arthrobacter spp./Brachybacterium tyrofermentans. This is the first time that the majority of these species has been identified in Domiati cheese. Nearly all the dominant and frequent bacterial species are salt tolerant, and several correspond to known marine bacteria. As Domiati cheese contains 5.4 to 9.5% NaCl, we suggest that these bacteria are likely to have an important role in the ripening process. This first systematic study of the microbial composition of Domiati cheeses reveals great biodiversity and evokes a role for marine bacteria in determining cheese type.

Safety and potential risks of enterococci isolated from traditional fermented capers

A collection of 17 enterococci isolates obtained from fermentations of capers (the fruits of Capparis sp.) were investigated for incidence of known virulence determinants, antibiotic resistance and production of biogenic amines. Molecular identification revealed the presence of Enterococcus faecium (nine isolates), Enterococcus faecalis (4), E. avium (3) and Enterococcus casseliflavus/flavescens (1). Alpha-haemolytic activity was detected in two E. avium and one E. faecalis isolates, and beta-haemolytic activity was detected in E. casseliflavus/flavescens. The haemolytic component cylB was detected by PCR amplification in three non-haemolytic isolates and in E. casseliflavus/flavescens. The collagen adhesin ace gene and the endocarditis associated antigen gene efaA(fm) were detected in two isolates each. Genes encoding sex pheromone precursors (cpd, cob, ccf) were detected in E. faecalis and E. casseliflavus/flavescens. Other presumed virulence genes (agg, gelE, cylM, cylA and efaA(fs)) were not detected. All isolates were resistant to rifampicin, erythromycin and ciprofloxacin, and some were also resistant to quinupristin/dalfopristin, tetracycline, levofloxacin, gentamicin and streptomycin. Vancomycin resistance was not detected. Tyrosine decarboxylation was detected in all E. faecium isolates. Given the high resistance of enterococci to environmental conditions, and their implication in opportunistic infections, the incidence of potential virulent enterococci in foods (especially those of a higher risk-like home-made foods) should be carefully studied.

Isolation of bacteriocinogenic Lactobacillus plantarum strains from ben saalga, a traditional fermented gruel from Burkina Faso

A collection of lactic acid bacteria isolated from ben saalga, a traditional fermented gruel from Burkina Faso, was screened for bacteriocin production. Seven isolates were selected for their broad antimicrobial spectra, which overall included strains of Bacillus cereus, Bacillus licheniformis, Enterococcus faecalis, Listeria innocua, Listeria monocytogenes, Staphylococcus aureus, Escherichia coli and Salmonella enterica. Cluster analysis of RAPD-PCR patterns revealed that six of the isolates represent different strains. The six selected strains were identified as Lactobacillus plantarum by 16S rDNA sequencing, species-specific PCR and multiplex PCR of the recA gene. PCR amplification revealed the presence of genes of the plantaricin cluster described in L. plantarum C11. Among them, strain 5.2.2 carried the largest number of genes from this cluster.

Microbiological study of lactic acid fermentation of Caper berries by molecular and culture-dependent methods

Fermentation of capers (the fruits of Capparis sp.) was studied by molecular and culture-independent methods. A lactic acid fermentation occurred following immersion of caper berries in water, resulting in fast acidification and development of the organoleptic properties typical of this fermented food. A collection of 133 isolates obtained at different times of fermentation was reduced to 75 after randomly amplified polymorphic DNA (RAPD)-PCR analysis. Isolates were identified by PCR or 16S rRNA gene sequencing as Lactobacillus plantarum (37 isolates), Lactobacillus paraplantarum (1 isolate), Lactobacillus pentosus (5 isolates), Lactobacillus brevis (9 isolates), Lactobacillus fermentum (6 isolates), Pediococcus pentosaceus (14 isolates), Pediococcus acidilactici (1 isolate), and Enterococcus faecium (2 isolates). Cluster analysis of RAPD-PCR patterns revealed a high degree of diversity among lactobacilli (with four major groups and five subgroups), while pediococci clustered in two closely related groups. A culture-independent analysis of fermentation samples by temporal temperature gradient electrophoresis (TTGE) also indicated that L. plantarum is the predominant species in this fermentation, in agreement with culture-dependent results. The distribution of L. brevis and L. fermentum in samples was also determined by TTGE, but identification of Pediococcus at the species level was not possible. TTGE also allowed a more precise estimation of the distribution of E. faecium, and the detection of Enterococcus casseliflavus (which was not revealed by the culture-dependent analysis). Results from this study indicate that complementary data from molecular and culture-dependent analysis provide a more accurate determination of the microbial community dynamics during caper fermentation.

1H nuclear magnetic resonance spectroscopy-based studies of the metabolism of food-borne carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline by human intestinal microbiota

2-Amino-3-methylimidazo[4,5-f]quinoline (IQ) is a mutagenic/carcinogenic compound formed from meat and fish during cooking. Following ingestion, IQ is metabolized mainly by liver xenobiotic-metabolizing enzymes, but intestinal bacteria may also contribute to its biotransformation. The aim of this study was to investigate the metabolism of IQ by the human intestinal microbiota. Following incubation of IQ (200 microM) under anoxic conditions with 100-fold dilutions of stools freshly collected from three healthy volunteers, we quantified residual IQ by high-pressure liquid chromatography (HPLC) analysis and characterized the production of IQ metabolites by in situ (1)H nuclear magnetic resonance ((1)H-NMR) spectroscopic analysis of crude incubation media. In addition, we looked for IQ-degrading bacteria by screening collection strains and by isolating new strains from the cecal contents of human-microbiota-associated rats gavaged with IQ on a regular basis. HPLC and (1)H-NMR analyses showed that the three human microbiota degraded IQ with different efficiencies (range, 50 to 91% after 72 h of incubation) and converted it into a unique derivative, namely, 7-hydroxy-IQ. We found 10 bacterial strains that were able to perform this reaction: Bacteroides thetaiotaomicron (n = 2), Clostridium clostridiiforme (n = 3), Clostridium perfringens (n = 1), and Escherichia coli (n = 4). On the whole, our results indicate that bacteria belonging to the predominant communities of the human intestine are able to produce 7-hydroxy-IQ from IQ. They also suggest interindividual differences in the ability to perform this reaction. Whether it is a metabolic activation is still a matter of debate, since 7-hydroxy-IQ has been shown to be a direct-acting mutagen in the Ames assay but not carcinogenic in laboratory rodents.

Enterocin AS-48RJ: a variant of enterocin AS-48 chromosomally encoded by Enterococcus faecium RJ16 isolated from food

The bacteriocinogenic strain RJ16 isolated from goat cheese has been identified as Enterococcusfaecium by species-specific PCR, DNA-rRNA hybridization and rDNA sequencing. Purified bacteriocin from strain RJ16 is a carboxypeptidase A-resistant peptide with a molecular mass (7125 Da) very close to the cyclic peptide enterocin AS-48. Bacteriocin from strain RJ16 and AS-48 show identical antibacterial spectra, although the former is slightly less active on strains of Listeria monocytogenes and Bacillus cereus. Producer strains show cross-immunity. PCR amplification of total DNA from strain RJ16 with primers for the AS-48 structural gene and sequencing of the amplified fragment revealed an almost identical sequence (99.5%), except for a single mutation that predicts the change of Glu residue at position 20 of AS-48 to Val. Therefore, bacteriocin produced by E. faecium RJ16 should be considered a variant of AS-48, which we call AS-48RJ. PCR amplification revealed that strain RJ16 contains the complete as-48. gene cluster. Hybridization with probes for as-48 gene cluster revealed a chromosomal location of as-48 genes in strain RJ16, being the first example of a chromosomal location of this bacteriocin trait. Strain RJ16 produced enzymes of interest in food processing (esterase, esterase lipase and phytase activities), and did not decarboxylate amino acids precursors for biogenic amines. Strain RJ16 did not exhibit haemolytic or gelatinase activities, and PCR amplification revealed the lack of genes encoding for known virulence determinants (aggregation substance, collagen adhesin, enterococcal surface protein, endocarditis antigens, as well as haemolysin and gelatinase production). Strain RJ16 was resistant to ciprofloxacin (MIC > 2 mgl(-1)) and levofloxacin (MIC > 4 mgl(-1)) and showed intermediate resistance to nitrofurantoin and erythromycin, but was sensitive to ampicillin, penicillin, streptomycin, gentamicin, rifampicin, chloramphenicol, tetracycline, quinupristin/dalfopristin, vancomycin and teicoplanin. Altogether, results from this study suggest that this broad-spectrum bacteriocin-producing strain may have a potential use in food preservation.

Molecular quantification of lactic acid bacteria in fermented milk products using real-time quantitative PCR

Real-time quantitative PCR assays were developed for the absolute quantification of lactic acid bacteria (LAB) (Streptococcus thermophilus, Lactobacillus delbrueckii, L. casei, L. paracasei, L. rhamnosus, L. acidophilus and L. johnsonii) in fermented milk products. The results of molecular quantification and classic bacterial enumeration did not differ significantly with respect to S. thermophilus and the species of the L. casei group which were detected in the six commercial fermented products tested, thus showing that DNA extraction was efficient and that genomic DNA solutions were free of PCR inhibitors. For L. delbrueckii, the results of bacterial enumeration were generally lower by a factor 10 to 100 than those of PCR quantification, suggesting a loss of viability during storage of the dairy products at 1-8 degrees C for most of the strains in this species. Real-time quantitative assays enabled identification of the species of lactic acid bacterial strains initially present in commercial fermented milk products and their accurate quantification with a detection threshold of 10(3) cells per ml of product.

Molecular characterization, technological properties and safety aspects of enterococci from 'Hussuwa', an African fermented sorghum product

AIMS

To identify enterococci from Hussuwa, a Sudanese fermented sorghum product, and determine their technological properties and safety for possible inclusion in a starter culture preparation.

METHODS AND RESULTS

Twenty-two Enterococcus isolates from Hussuwa were identified as Enterococcus faecium by using phenotypic and genotypic tests such as 16S rDNA gene sequencing, RAPD-PCR and restriction fragment length polymorphism of the 16S/23S intergenic spacer region fingerprinting. Genotyping revealed that strains were not clonally related and exhibited a considerable degree of genomic diversity. Some strains possessed useful technological properties such as production of bacteriocins and H2O2 or utilization of raffinose and stachyose. None produced alpha-amylase or tannase. A safety investigation revealed that all strains were susceptible to the antibiotics ampicillin, gentamicin, chloramphenicol, tetracycline and streptomycin, but some were resistant to ciprofloxacin, erythromycin, penicillin and vancomycin. Production of biogenic amines or presence of genes encoding virulence determinants occurred in some strains.

CONCLUSIONS

Enterococcus faecium strains are associated with fermentation of Sudanese Hussuwa. Some strains exhibited useful technological properties such as production of antimicrobial agents and fermentation of indigestible sugars, which may aid in stabilizing and improving the digestibility of the product respectively.

SIGNIFICANCE AND IMPACT OF THE STUDY

Enterococci were shown to play a role in the fermentation of African foods. While beneficial properties of these bacteria are indicated, their presence in this food may also imply a hygienic risk as a result of antimicrobial resistances or presence of virulence determinants.