Phenotypic and Genotypic Characterization of Lactic Acid Bacteria Isolated from Some Nigerian Traditional Fermented Foods

Detoxification of Aflatoxins in Fermented Cereal Gruel (Ogi) by Probiotic Lactic Acid Bacteria and Yeasts with Differences in Amino Acid Profiles

Toxigenic members of Aspergillus flavus contaminate cereal grains, resulting in contamination by aflatoxin, a food safety hazard that causes hepatocellular carcinoma. This study identified probiotic strains as aflatoxin detoxifiers and investigated the changes to the grain amino acid concentrations during fermentation with probiotics in the presence of either A. flavus La 3228 (an aflatoxigenic strain) or A. flavus La 3279 (an atoxigenic strain). Generally, higher concentrations (p < 0.05) of amino acids were detected in the presence of toxigenic A. flavus La 3228 compared to the atoxigenic A. flavus La 3279. Compared to the control, 13/17 amino acids had elevated (p < 0.05) concentrations in the presence of the toxigenic A. flavus compared to the control, whereas in systems with the atoxigenic A. flavus 13/17 amino acids had similar (p > 0.05) concentrations to the control. There were interspecies and intraspecies differences in specific amino acid elevations or reductions among selected LAB and yeasts, respectively. Aflatoxins B1 and B2 were detoxified by Limosilactobacillus fermentum W310 (86% and 75%, respectively), Lactiplantibacillus plantarum M26 (62% and 63%, respectively), Candida tropicalis MY115 (60% and 77%, respectively), and Candida tropicalis YY25, (60% and 31%, respectively). Probiotics were useful detoxifiers; however, the extent of decontamination was species- and strain-dependent. Higher deviations in amino acid concentrations in the presence of toxigenic La 3228 compared to atoxigenic La 3279 suggests that the detoxifiers did not act by decreasing the metabolic activity of the toxigenic strain.

Screening of Lactiplantibacillus plantarum Strains from Sourdoughs for Biosuppression of Pseudomonas syringae pv. syringae and Botrytis cinerea in Table Grapes

Grapes (Vitis vinifera L.) are an essential crop for fresh consumption and wine production. Vineyards are attacked by several economically important bacterial and fungal diseases that require regular pesticide treatment. Among them, Pseudomonas syringae pv. syringae (Ps. syringae) and Botrytis cinerea (B. cinerea) infections cause huge economic losses. The fresh fruit market has shifted to functional natural foodstuffs with clear health benefits and a reduced use of chemicals along the production chain. Lactic acid bacteria (LAB) have a biopreservative effect and are applied to ensure food safety in response to consumers' demands. In the present study, the possibilities of using microorganisms with a potential antimicrobial effect against Ps. syringae and B. cinerea in the production of table grapes were investigated. LAB of the genus Lactiplantibacillus can be a natural antagonist of pathogenic bacteria and fungi by releasing lactic acid, acetic acid, ethanol, carbon dioxide and bacteriocins in the medium. The present study focuses on the characterization of nine Lactiplantibacillus plantarum (Lp. plantarum) strains isolated from spontaneously fermented sourdoughs. Species-specific PCR identified the isolated LAB for partial recA gene amplification with an amplicon size of 318 bp. RAPD-PCR analysis showed the intraspecific diversity of the individual strains. Thirteen plantaricin-like peptides (PlnA, PlnB, PlnC, PlnD, PlnEF, PlnG, PlnI, PlnJ, PlnK, PlnN, PlnNC8, PlnS, and PlnW) produced by isolated Lp. plantarum strains were detected by PCR with gene-specific primers. The key features for future industrial applications were their antimicrobial properties. The culture medium and cell-free supernatant (CFS) were used to establish in vitro antimicrobial activities of Lp. plantarum strains against Ps. syringae and B. cinerea, and inhibition of phytopathogen development was observed. The inhibitory effect of the CFS (cell-free supernatant) of all strains was assessed by infecting table grapes with these pathogens in in vivo experiments. Lp. plantarum Q4 showed the most effective suppression of the pathogens both in vitro and in vivo, which indicates its potential use as a biocontrol agent against berry rot and grey rot on grapes, caused by Ps. syringae and B. cinerea.

Methicillin- and Vancomycin-Resistant Staphylococcus aureus and Vancomycin-Resistant Enterococci Isolated from Hospital Foods: Prevalence and Antimicrobial Resistance Patterns

This study aimed to investigate the prevalence of Methicillin- and Vancomycin-Resistant Staphylococcus aureus (MRSA, VRSA) and Vancomycin-Resistant Enterococcus (VRE) of hospital food samples in Mashhad, Iran. A total of 357 hospital food samples were collected from 13 hospitals. Enterococcus spp. and Staphylococcus aureus were identified using conventional cultural techniques following genotypic confirmation by PCR. The antibiotic resistance patterns of MRSA, VRSA, and VRE strains were analyzed using the disk diffusion methods. The prevalence of S. aureus and MRSA were 24.37% (87/357) and 22.98% (20.87), respectively. In addition, the vanB gene involved in vancomycin resistance was detected in 1.14% of the S. aureus strains. Enterococci and VRE had a prevalence of 15.4% (55/357) and 21.81% (12/55), respectively. Meat, chicken barbecues, and salad were the most commonly contaminated samples with S. aureus, MRSA, Enterococci, and VRE. PCR detected two vancomycin resistance genes, including vanA (1.81%, 1.55) and vanC2 (20%, 11.55) genes. MRSA strains revealed the highest resistance against penicillin, erythromycin, clindamycin, azithromycin, tetracycline, and gentamicin. The VRSA isolates were resistant to penicillin, ampicillin, oxacillin, cefoxitin, clindamycin, erythromycin, gentamicin, and trimethoprim-sulfamethoxazole. Furthermore, VRE isolates exhibited the highest resistance against quinupristin-dalfopristin, erythromycin, and tetracycline. The results of this study indicated that hospital foods might act as a reservoir of Enterococci spp. and S. aureus strains, which can transfer antibiotic resistance. Moreover, multidrug resistance (MDR) in some MRSA, VRSA, and VRE isolates represents a serious threat to susceptible persons in hospitals.

Novel Siphoviridae phage PMBT4 belonging to the group b Lactobacillus delbrueckii subsp. bulgaricus phages

A novel Lactobacillus delbrueckii bacteriophage PMBT4 was isolated from the Nigerian fermented milk product nono. The phage possesses a long and thin, non-contractile tail and an isometric head, indicating that it belongs to the Siphoviridae family. A neck passage structure (`collar`), previously hypothesized to be encoded by two genes located in the Lactobacillus delbrueckii phage LL-K insertion sequence (KIS) element, as well as in two additional Lb. delbrueckii phages Ld17 and Ld25A, could also be observed on an estimated 1-5% of phage particles by transmission electron microscopy. However, neither mapping of high throughput sequencing data to KIS element genes from Lb. delbrueckii phages LL-K, Ld17 and Ld25A nor PCR amplification of the KIS element genes could corroborate the presence of these genes in the PMBT4 genome. The PMBT4 genome consists of 31,399 bp with a mol% GC content of 41.6 and exhibits high (95-96%) sequence homologies to Lb. delbrueckii phages c5, Ld3, Ld25A and Ld17, which assigned PMBT4 as a new member of this genus, i.e. the Cequinquevirus genus.

Isolation and Characterization of Potential Starter Cultures from the Nigerian Fermented Milk Product nono

Nono, an important traditional fermented dairy food produced from cow’s milk in Nigeria, was studied for microbial diversity and for starter culture development for industrial production. On the basis of a polyphasic approach, including phenotypic and genotypic methods such as 16S rRNA gene sequencing, repetitive element PCR (rep-PCR) fingerprinting metagenomics, and whole genome sequencing, we identified Lactobacillus (Lb.) helveticus, Limosilactobacillus (L.) fermentum, Lb. delbrueckii, and Streptococcus (S.) thermophilus as predominant bacterial species involved with milk fermentation during traditional nono production in Nigeria, while the predominant yeast species in nono was identified as Saccharomyces cerevisiae. Using metagenomics, Shigella and potential pathogens such as enterobacteria were detected at low levels of abundance. Strains of the predominant lactic acid bacteria (LAB) were selected for starter cultures combination on the basis of their capacities for rapid growth in milk and reduction of pH below 4.5 and their gelling characteristic, which was demonstrated noticeably only by the S. thermophilus strains. Whole genome sequence analysis of selected bacterial strains showed the largest assembled genome size to be 2,169,635 bp in Lb. helveticus 314, while the smallest genome size was 1,785,639 bp in Lb. delbrueckii 328M. Genes encoding bacteriocins were not detected in all the strains, but all the LAB possessed genes potentially involved in diacetyl production and citrate metabolism. These bacteria isolated from nono can thus be used to improve the microbial safety quality of nono in Nigeria, in addition to improving technological parameters such as gelling viscosity, palatability, and product consistency.

Metataxonomic analysis of bacterial communities and mycotoxin reduction during processing of three millet varieties into ogi, a fermented cereal beverage

Ogi is a fermented cereal beverage, made primarily from maize (Zea mays) and rarely from millets. Unlike maize-based ogi, little is known about the bacterial community and mycotoxin profile during the production of millet-based ogi. Therefore, the bacterial community dynamics and mycotoxin reduction during ogi processing from three millet varieties were investigated using next-generation sequencing of the 16S rRNA gene and liquid chromatography-tandem mass spectrometry, respectively. A total of 1163 amplicon sequence variants (ASVs) were obtained, with ASV diversity across time intervals influenced by processing stage and millet variety. ASV distribution among samples suggested that the souring stage was more influenced by millet variety than the steeping stage, and that souring may be crucial for the quality attributes of the ogi. Furthermore, bacterial community structure during steeping and souring was significantly differentiated (PERMANOVA, P < 0.05) between varieties, with close associations observed for closely-related millet varieties. Taxonomically, Firmicutes, followed by Actinobacteria, Bacteroidetes, Cyanobacteria and Proteobacteria phyla were relatively abundant (>1%). Lactic acid bacteria, such as Burkholderia-Caballeronia-Paraburkholderia, Lactobacillus, Lactococcus and Pediococcus, dominated most fermentation stages, suggesting their roles as key fermentative and functional bacteria in relation to mycotoxin reduction. About 52-100%, 58-100% and 100% reductions in mycotoxin (aflatoxins, beauvericin, citrinin, moniliformin, sterigmatocystin and zearalenone) concentrations were recorded after processing of white fonio, brown fonio and finger millet, respectively, into ogi. This study provides new knowledge of the dominant bacterial genera vital for the improvement of millet-based ogi through starter culture development and as well, elucidates the role of processing in reducing mycotoxins in millet ogi.

Binding Capacities and Antioxidant Activities of Lactobacillus plantarum and Pichia kudriavzevii Against Cadmium and Lead Toxicities

The cadmium and lead binding capacities and antioxidant activities of Lactobacillus plantarum and Pichia kudriavzevii were evaluated in vitro and in vivo. Lactic acid bacteria and yeasts obtained from fermenting cassava mash and maize slurry were screened for tolerance to cadmium and lead at 500-1050 mg ml^-1 screened for probiotic potentials and antioxidant activities such as 2,2-diphenyl-1-picrylhydrazyl and ferric reducing antioxidant properties. The in vivo studies were carried out in male Wistar rats. The strains identified as Lactobacillus plantarum ML05 and Pichia kudriavzevii FY05 demonstrated the best probiotic potentials and antioxidant activities. Alterations in antioxidant capacities were positive in the treatment groups. The histopathology displayed positive changes in the renal tubules and glomeruli, hypertrophy, with normal capsular spaces without inflammation in the kidney, while the liver sinusoids appear normal in the rats administered with L. plantarum ML05 and P. kudriavzevii FY05 while the infected and not treated showed cell necrosis induced by toxicities. Our results provided new evidence that Lactobacillus plantarum and Pichia kudriavzevii have different biological actions on the heavy metals binding capacities and antioxidant activities in experimental animals. This study suggests that these microorganisms can be considered dietary therapeutics against cadmium and lead toxicities.

Sourdough Bread from the Blend of Cassava, Sweet Potato, and Soybean Flours Using Lactobacillus Plantarum and Pichia Kudriavzevii

Sourdough is specialty bread made from a combination of flour, lactic acid bacteria, and yeasts. Composite flour of cassava, sweet potato, and soybean was used for the production of sourdough bread employing autochthonous lactic acid bacteria and yeasts isolated from the composite dough. The flour samples were assessed for functional properties, while the sourdough breads were evaluated for nutritional composition and organoleptic properties. The flour samples possessed good proximate profiles and phenolic contents. The lactic acid bacterium and yeast with the most desirable properties were identified as Lactobacillus plantarum and Pichia kurdriazevii. Fermentation improved the nutritional indices of the composite sourdough bread samples. Lactobacillus plantarum SLC21 and P. kudriavzevii SYD17 bread had a shelf life of 7 days, while the control bread lasted for at least 4 days. Lactobacillus plantarum SLC21 and Pichia kudriavzevii SYD17 bread had the best overall acceptability. Utilisation of these local crops in a composite blend for sourdough will increase commercial profit for local farmers and developing economy. The composite blend will be of great importance in the preparation of pastries that do not require high gluten content. The strains exhibited great potentials for a better nutritional composition of the composite sourdough bread.

Microbial Profile Antibacterial Properties and Chemical Composition of Raw Donkey Milk

The human interest in donkey milk is growing due to its nutritional, functional properties and excellent microbiological quality according to published reports. However, more research needs to be conducted to assess the above variables from various breeds. In the present study, milk samples were collected from 17 Cypriot and six Arcadian healthy Greek donkeys. The microbiological quality, somatic cell counts (SCC), chemical composition analysis, and antimicrobial activity of the samples was assessed. In addition, clustering and identification of the bacterial composition was performed by RAPD-PCR and 16S rDNA sequencing, respectively. The good microbiological quality of the samples as estimated by the total aerobic mesophilic and psychrotrophic counts, which ranged from 2.18 to 2.71 log CFU/mL and from 1.48 to 2.37 log CFU/mL, respectively, was also verified. SCC were below 4.4 log CFU/mL. However, potential pathogenic species of Staphylococcus aureus, Bacillus cereus, and Clostridium spp. were enumerated in the milk of both breeds. The gross chemical composition showed mean values for fat, protein, and lactose from 0.82% to 1.24%, 1.22% to 1.87%, and 6.01% to 6.78%, respectively. All milk samples exhibited an antimicrobial activity against St. haemolyticus and Listeria monocytogenes, although quality control measures should be taken for health and safety prior to human consumption.

Traditional and Artisanal Beverages in Nigeria: Microbial Diversity and Safety Issues

A review of up to 90 articles on the microorganisms associated with important artisanal or traditional beverages in Nigeria was carried out. This resulted in an overview of the prevalent microorganisms associated with soymilk, nono (fermented cow milk), tiger nut milk, yoghurt, kunu, zobo, palm wine and the local beers pito and brukutu. The bacteria genera, namely Bacillus, Escherichia, Lactobacillus, Staphylococcus, and Streptococcus, were detected in all nine beverages. On the contrary, this survey resulted in finding that the genera Saccharomyces, Aspergillus, Candida, and Penicillium were the eukaryotic microorganisms isolated in all beverages. The occurrence of fungal isolates, which can be responsible for producing mycotoxins, is a concern and shows the need for post-production tests. Overall, there is a low prevalence of bacteria associated with hygiene, especially the Escherichia genus in alcoholic beverages such as palm wine, pito and burukutu, which may be due both to a low acidity and high ethanol content. However, the prevalence of hygiene indicator genera was higher in nonalcoholic drinks, probably because of incorrect practices during processing. The magnitude of the production and sales of unregulated local beverages in Nigeria has reached the stage where significant regulation and food safety standards are required to safeguard public health. An opportunity exists to monitor and characterize the microbial flora of the artisanal beverages using molecular methods at all stages of production and storage.

Bacterial Diversity and Mycotoxin Reduction During Maize Fermentation (Steeping) for Ogi Production

Bacterial diversity and community structure of two maize varieties (white and yellow) during fermentation/steeping for ogi production, and the influence of spontaneous fermentation on mycotoxin reduction in the gruel were studied. A total of 142 bacterial isolates obtained at 24-96 h intervals were preliminarily identified by conventional microbiological methods while 60 selected isolates were clustered into 39 OTUs consisting of 15 species, 10 genera, and 3 phyla by 16S rRNA sequence analysis. Lactic acid bacteria constituted about 63% of all isolated bacteria and the genus Pediococcus dominated (white maize = 84.8%; yellow maize = 74.4%). Pediococcus acidilactici and Lactobacillus paraplantarum were found at all steeping intervals of white and yellow maize, respectively, while P. claussenii was present only at the climax stage of steeping white maize. In both maize varieties, P. pentosaceus was found at 24-72 h. Mycotoxin concentrations (μg/kg) in the unsteeped grains were: white maize (aflatoxin B1 = 0.60; citrinin = 85.8; cyclopiazonic acid = 23.5; fumonisins (B1/B2/B3) = 68.4-483; zearalenone = 3.3) and yellow maize (aflatoxins (B1/B2/M1) = 22.7-513; citrinin = 16,800; cyclopiazonic acid = 247; fumonisins (B1/B2/B3) = 252-1,586; zearalenone = 205). Mycotoxins in both maize varieties were significantly (p < 0.05) reduced across steeping periods. This study reports for the first time: (a) the association of L. paraplantarum, P. acidilactici, and P. claussenii with ogi production from maize, (b) citrinin occurrence in Nigerian maize and ogi, and

Effect of ripening stage on the development of the microbial community during spontaneous fermentation of green tomatoes

BACKGROUND

Spontaneous fermentation of plant-derived material is mainly performed on a small scale, with the exception of fermented olives, cucumbers, sauerkraut and kimchi, which have met worldwide commercial significance.

RESULTS

This study of spontaneous fermentation of green tomatoes at different stages of ripening revealed a significant effect on the growth kinetics of lactic acid bacteria and the final pH value. Leuconostoc mesenteroides dominated spontaneous fermentation when the initial pH value ranged from 3.8 to 4.8 whereas at higher pH values (4.9-5.4) it co-dominated with Leu. citreum and Lactobacillus casei. Application of RAPD-PCR and rep-PCR allowed differentiation at sub-species level, suggesting a microbial succession at that level accompanying the respective at species level.

CONCLUSION

Ripening stage affected the development of the micro-ecosystem through the growth of lactic acid bacteria and concomitant pH value reduction; however, the outcome of the fermentation was only marginally different.

Technological properties and probiotic potential of Enterococcus faecium strains isolated from cow milk

AIM

To identify enterococci from the fermentation of milk for the production of nono, an African fermented dairy product, to determine the technological properties for suitability as starter cultures and safety as probiotics.

METHODS AND RESULTS

Enterococcus faecium CM4 and Enterococcus faecium 2CM1 were isolated from raw cow's milk. The strains were phenotypically and genotypically identified. Technological properties, safety investigations, in vitro adherence properties and antimicrobial characteristics were carried out. Strong acidification and tolerance to bile salts were recorded. The strains were bile salts hydrolytic positive and no haemolysis. There was no resistance to clinically relevant antibiotics. The strains exhibited adherence to human collagen type IV, human fibrinogen and fibronectin. The bacteriocins were active against Bacillus cereus DSM 2301, Bacillus subtilis ATCC 6633, Micrococcus luteus and Listeria monocytogenes. Bacteriocins were stable at pH 4-9 and on treatment with lipase, catalase, α-amylase and pepsin, while their activity was lost on treatment with other proteases. The bacteriocins produced were heat stable at 100°C for 10 min. The bacteriocin produced by the strains was identified as enterocin A.

CONCLUSIONS

The E. faecium strains in this study exhibited probiotic activity, and the safety investigations indicate their suitability as good candidates for a starter culture fermentation process.

SIGNIFICANCE AND IMPACT OF THE STUDY

The use of bacteriocin-producing E. faecium strains as starter cultures in fermented foods is beneficial but, however, their safety investigations as probiotics must be greatly emphasized.