Browsing by Author "Dicks, L. M. T."
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- ItemBiosensors for the detection of Escherichia coli(South African Water Research Commission, 2017-10) Maas, M. B.; Perold, W. J.; Dicks, L. M. T.ENGLISH ABSTRACT: The supply of safe potable water, free from pathogens and chemicals, requires routine analyses and the application of several diagnostic techniques. Apart from being expensive, many of the detection methods require trained personnel and are often time-consuming. With drastic climate changes, severe droughts, increases in population and pollution of natural water systems, the need to develop ultrasensitive, low-cost and hand-held, point-of-use detection kits to monitor water quality is critical. Although Escherichia coli is still considered the best indicator of water quality, cell numbers may be below detection limits, or the cells may be non-culturable and thus only detected by DNA amplification. A number of different biosensors have been developed to detect viable, dead or non-culturable microbial cells and chemicals in water. This review discusses the differences in these biosensors and evaluates the application of microfluidics in the design of ultra-sensitive nano-biosensors.
- ItemControl of malolactic fermentation in wine. a review(South African Society for Enology and Viticulture, 2004) Bauer, R.; Dicks, L. M. T.Malolactic fermentation (MLF) is conducted by lactic acid bacteria (LAB) and refers to the decarboxylation of Lmalate to L-lactate. This secondary fermentation is difficult to control and is mainly driven by Oenococcus oeni. Uncontrolled MLF, especially in wines with a high pH, which are typical of warmer viticultural regions, may render the wine unpalatable or even cause spoilage. In this review we focus on wine compounds and emphasise factors that affect the growth of 0. oeni and MLF, and discuss practical applications. We also explore alternative technologies that may enable better control over MLF.
- ItemIdentification of lactobacillus spp. isolated from different phases during the production of a South African fortified wine(South African Society for Enology and Viticulture, 2002) Stratiotis, A. L.; Dicks, L. M. T.Fortified wines contain a high level of unfermented sugars and are prone to spoilage by alcohol-tolerant lactic acid bacteria. A total of 62 strains were isolated from various production stages of one of the more popular fortified wines produced in South Africa. The strains were identified by using numerical analysis of total soluble cell protein patterns and 16S rRNA sequence analyses. The species most frequently isolated were Lactobacillus vermiforme (24 strains) and Lactobacillus casei subsp. casei (32 strains). Twenty-four of the strains of L. vermiforme, three strains of Lactobacillus buchneri, one strain of Lactobacillus plantarum and two strains of L. casei subsp. casei were isolated from spoiled fortified wine which contained 22% (vol/vol) ethanol. The majority of strains of L. casei subsp. casei (25 of the 32) and two strains of Lactobacillus zeae were isolated from wine before submerged fermentation. Five strains of L. casei subsp. casei were isolated from wine undergoing submerged fermentation, with an alcohol content of 11.92% (vol/vol). No strain was isolated from unbottled wine which underwent the complete fermentation process and with an alcohol content of 17.20% (vol/vol). Three distinct phenotypic groups of L. vermiforme were identified at r ≥ 0. 70, separate from Lactobacillus brevis,' L. buchneri and Lactobacillus hilgardii. Three phenotypic clusters have been identified for L. casei subsp. casei. This is the first report of the presence of L. vermiforme, L. zeae, L. casei subsp. casei and L. plantarum in fortified wines.
- ItemIsolation, identification and changes in the composition of lactic acid bacteria during the malting of two different barley cultivars(2002) Booysen, C.; Dicks, L. M. T.; Meijering, I.; Ackermann, A.Malt has a complex microbial population, which changes as the malting process commences. Little is known about the proliferation of lactic acid bacteria (LAB) in each of the malting phases. In this study, we determined the number of LAB present in the different phases of malting with Clipper and Prisma barley cultivars. The strains were identified to species level by using numerical analysis of total soluble cell protein patterns, RAPD-PCR banding patterns and 16S rRNA sequencing. The number of viable LAB in the barley before steep was higher in Prisma than Clipper (7.6×104 and 1.2×103 cfu/g, respectively). Despite this, the number of viable cells recorded in the first steep water was slightly higher for Clipper (9.0×105 cfu/g) than Prisma (5.5×105 cfu/g). More or less, the same cell numbers were recorded for the two barley cultivars after the first and second dry stands. Both cultivars displayed more or less the same cell numbers (3.7×107 for Clipper and 3.2×107 cfu/g for Prisma) after the third day of germination. However, a higher number of LAB were detected in the kilned Prisma malt (6.9×104 cfu/g) than the Clipper malt (1.5×104 cfu/g). Leuconostoc argentinum, Le. lactis and Weissella confusa were the most predominant in both cultivars. A few strains were identified as W. paramesenteroides (four strains), Lactobacillus casei (five strains), Lactococcus lactis (five strains) and Lb. rhamnosus (two strains). Lb. casei and Lb. rhamnosus were not isolated from the Prisma cultivar, while W. paramesenteroides and Lc. lactis were absent in the Clipper cultivar. Kilned malt of the Clipper cultivar contained predominantly Le. argentinum, whereas the Prisma cultivar contained mainly Lc. lactis. To our knowledge, this is the first report of LAB in Clipper and Prisma barley and the various malting phases. The influence of the various groups of lactic acid bacteria on the fermenting ability of brewers' yeast is currently being determined. Copyright © 2002 Elsevier Science B.V.
- ItemMarket and product assessment of probiotic/prebiotic - containing functional foods and supplements manufactured in South Africa(Health & Medical Publishing Group, 2005) Brink, M.; Senekal, M.; Dicks, L. M. T.Objectives. Probiotic and prebiotic products manufactured in South Africa were identified and health and content claims stated on the labels were evaluated according to available scientific evidence, the proposed South African regulations in the Foodstuffs, Cosmetics and Disinfectants Act (Act No. 54 of 1972, www.doh.gov.za), and microbial assessment. Results. The range of products identified included probiotic-and/or prebiotic-containing supplements (capsules), food items fortified with probiotics and/or prebiotics, and fermented food containing probiotics, e.g. dairy products. Most of the health-related claims on the labels of the identified products do not comply with proposed South African regulations. However, results also indicate that the proposed South African regulations should be reconsidered to include an additional 5 claims, for which scientifically sound evidence is available. The claims regarding probiotic strains, viable cell numbers, prebiotic type and concentration stated on the labels of the products are mostly in line with the proposed South African regulations. The actual viable cell content of 3 out of 5 probiotic supplements readily available on the South African market did not comply with the content claim stated on the label. However, this problem did not seem to affect the inhibitory activity of the probiotic strains against indicator strains isolated from faeces of patients diagnosed with AIDS. To validate this finding in vivo assessments should be implemented before considering the need to include a wider range of prescribed viable cell numbers in the proposed South African regulations. Conclusions. The proposed South African regulations regarding probiotic- and prebiotic-containing products should be revised based on the results of this research, and the manufacturers of these products should be held responsible for providing the consumer with scientifically sound and legally correct information.
- ItemOptimized production of bacteriocin ST11BR, generated by Lactobacillus paracasei subsp. paracasei ST11BR isolated from traditional South African beer(Academy of Science for South Africa, 2005) Todorov, S. D.; Van Reenen, C. A.; Dicks, L. M. T.Little is known about the production of antimicrobial peptides (bacteriocins) by lactic acid bacteria in traditional South African beer and their inhibition of food spoilage or pathogenic bacteria. In this paper, we report on bacteriocin ST11BR, produced by Lactobacillus paracasei subsp. paracasei ST11BR isolated from beer made with maize, barley, soy flour and sugar (sucrose). Bacteriocin ST11BR is a 3.2-kDa peptide with activity against Lactobacillus casei, L. sakei, Pseudomonas aeruginosa and Escherichia coli. The peptide is sensitive to proteinase K and pronase, but not to α-amylase. Glycerol in the growth medium repressed bacteriocin production. Tween 80 suppressed production by more than 50%, irrespective of the initial pH of the medium. MRS broth adjusted to pH 4.50 yielded 3200 AU/ml bacteriocin. The corresponding value at pH 5.0, 5.5, 6.0 and 6.5 was 12 800 AU/ml. The highest yield (25 600 AU/ml) was recorded in MRS broth without Tween 80, and with meat extract as the only nitrogen source, or a combination of meat extract and tryptone, or yeast extract and tryptone. Growth in the presence of tryptone as sole nitrogen source achieved only 12 800 AU/ml bacteriocin. Yeast extract, or a combination of yeast extract and meat extract, yielded 6400 AU/ml. A growth medium comprising 20.0 g/l maltose, sucrose or mannose yielded bacteriocin levels of 25 600 AU/ml, whereas the corresponding values for the same concentration of glucose or fructose were 12 800 AU/ml and 1 600 AU/ml, respectively. Lactose did not stimulate bacteriocin production - the highest yield (6 400 AU/ml) was generated in the presence of 10.0 g/l. No difference in bacteriocin activity was recorded when strain ST11BR was grown in the presence of 2.0 g/l KH2PO4 and 2.0-10.0 g/l K2HPO 4. However, cyanocobalamin, thiamine and DL-6,8-thioctic acid (1.0 ppm), but not L-ascorbic acid, stimulated peptide production. This study provided valuable information on the optimal production of bacteriocin by a strain of L. paracasei naturally present in a traditional beer.
- ItemSafety assessment of antibiotic and probiotic feed additives for Gallus gallus domesticus(Nature Research, 2017) Neveling, D. P.; Van Emmenes, L.; Ahire, J. J.; Pieterse, E.; Smith, C.; Dicks, L. M. T.Antibiotics in feed select for resistant strains and is thus a threat to human health. In this study, the effect of a multi-strain probiotic and antibiotics on the growth and health of broilers was studied. Equal numbers of broilers received on a daily basis either a multi-strain probiotic or a combination of sulphadiazine, colistin and trimethoprim, whereas the control group received standard feed. The villi of immature broilers (19 days old) administered antibiotics had a larger surface area and their lymphocyte and basophil counts were higher compared to broilers from the probiotic and control groups. The cecal microbiomes of mature broilers (29 days old) that received probiotics had higher levels of Enterobacteriaceae, but lower numbers of Clostridiales, Brucellaceae, Synergistaceae, Erysipelotrichaceae and Coriobacteriaceae compared to the antibiotic-treated group. A decline in the bioluminescence of Listeria monocytogenes observed for broilers on probiotics suggested that the probiotic may be used to control bacterial infections. No significant differences in total red blood cell, haemoglobin and haematocrit content, and mean values for corpuscular volume, corpuscular haemoglobin and corpuscular haemoglobin numbers were recorded amongst broilers from the different treatment groups. This study provides valuable information on the health and performance of broilers when administered probiotics and antibiotics as additives.
- ItemStrains of lactobacillus plantarum in grape must are also present in the intestinal tract of vinegar flies(South African Society for Enology and Viticulture, 2006) Groenewald, W. H.; Van Reenen, C. A.; Dicks, L. M. T.Twenty-one lactic acid bacteria isolated from the intestinal tract of Drosophila simulans Stuvervant and nine from Merlot noir grapes were identified as L. plantarum by PCR with species-specific primers and 16S rDNA sequencing. The 30 isolates grouped into four clusters based on RAPD-PCR banding patterns, suggesting that they belong to at least four genotypic groups. Thirteen isolates from grape must and five from the flies yielded identical RAPDPCR banding patterns and grouped into one cluster, suggesting that they are descendants from the same strain. Concluded from these results, L. plantarum (or at least descendants from a specific strain) has the ability to use vinegar flies as a host and vector to infect grape must. Further research is needed to determine the role of this specific strain in wine fermentations.
- ItemTaxonomic status of lactic acid bacteria in wine and key characteristics to differentiate species(SASEV, 2009) Dicks, L. M. T.; Endo, A.Oenococcus oeni is the best malolactic bacterium adapted to low pH and the high SO2 and ethanol concentrations in wine. Leuconostoc mesenteroides and Leuconostoc paramesenteroides (now classified as Weissella paramesenteroides) have also been isolated from wine. Pediococcus damnosus is not often found in wine and is considered a contaminant of high pH wines. Pediococcus inopinatus, Pediococcus parvulus and Pediococcus pentosaceus have occasionally been isolated from wines. Lactobacillus brevis, Lactobacillus plantarum, Lactobacillus buchneri, Lactobacillus hilgardii (previously Lactobacillus vermiforme), Lactobacillus fructivorans (previously Lactobacillus trichoides and Lactobacillus heterohiochii) and Lactobacillus fermentum have been isolated from most wines. Lactobacillus hilgardii and L. fructivorans are resistant to high acid and alcohol and have been isolated from spoiled fortified wines. Lactobacillus vini, Lactobacillus lindneri, Lactobacillus nagelii and Lactobacillus kunkeei have been described more recently. The latter two species are known to cause sluggish or stuck alcoholic fermentations in wine. Although Lactobacillus collinoides and Lactobacillus mali (previously Lactobacillus yamanashiensis) decarboxylate L-malic acid, they are more often found in cider and fruit juices. Lactobacillus curvatus, Lactobacillus delbrueckii, Lactobacillus diolivorans, Lactobacillus jensenii and Lactobacillus paracasei are seldomly isolated from wines. Some strains of Lactobacillus casei may be closer related to Lactobacillus paracasei or a distant relative, Lactobacillus zeae. Oenococcus kitaharae, isolated from compost is genetically closely related to Oenococcus oeni, but does not decarboxylate malate, prefers higher growth pH and is phenotypically well distinguished from O. oeni. This review summarises the current taxonomic status of malolactic bacteria and lists key phenotypic characteristics that may be used to identify the species.
- ItemXenorhabdus khoisanae SB10 produces Lys-rich PAX lipopeptides and a Xenocoumacin in its antimicrobial complex(BMC (part of Springer Nature), 2019-06-13) Dreyer, J.; Rautenbach, Marina; Booysen, E.; Van Staden, A. D.; Deane, S. M.; Dicks, L. M. T.Background: Xenorhabdus spp. live in close symbiosis with nematodes of the Steinernema genus. Steinernema nematodes infect an insect larva and release their symbionts into the haemocoel of the insect. Once released into the haemocoel, the bacteria produce bioactive compounds to create a semi-exclusive environment by inhibiting the growth of bacteria, yeasts and molds. The antimicrobial compounds thus far identified are xenocoumacins, xenortides, xenorhabdins, indole derivatives, xenoamicins, bicornutin and a number of antimicrobial peptides. The latter may be linear peptides such as the bacteriocins xenocin and xenorhabdicin, rhabdopeptides and cabanillasin, or cyclic, such as PAX lipopeptides, taxlllaids, xenobactin and szentiamide. Thus far, production of antimicrobial compounds have been reported for Xenorhabdus nematophila, Xenorhabdus budapestensis, Xenorhabdus cabanillasii, Xenorhabdus kozodoii, Xenorhabdus szentirmaii, Xenorhabdus doucetiae, Xenorhabdus mauleonii, Xenorhabdus indica and Xenorhabdus bovienii. Here we describe, for the first time, PAX lipopeptides and xenocoumacin 2 produced by Xenorhabdus khoisanae. These compounds were identified using ultraperformance liquid chromatography, linked to high resolution electrospray ionisation mass spectrometry and tandem mass spectrometry. Results: Cell-free supernatants of X. khoisanae SB10 were heat stable and active against Bacillus subtilis subsp. subtilis, Escherichia coli and Candida albicans. Five lysine-rich lipopeptides from the PAX group were identified in HPLC fractions, with PAX1’ and PAX7 present in the highest concentrations. Three novel PAX7 peptides with putative enoyl modifications and two linear analogues of PAX1’ were also detected. A small antibiotic compound, yellow in colour and λmax of 314 nm, was recovered from the HPLC fractions and identified as xenocoumacin 2. The PAX lipopeptides and xenocoumacin 2 correlated with the genes and gene clusters in the genome of X. khoisanae SB10. Conclusion: With UPLC-MS and MSe analyses of compounds in the antimicrobial complex of X. khoisanae SB10, a number of PAX peptides and a xenocoumacin were identified. The combination of pure PAX1’ peptide with xenocoumacin 2 resulted in high antimicrobial activity. Many of the fractions did, however, contain labile compounds and some fractions were difficult to resolve. It is thus possible that strain SB10 may produce more antimicrobial compounds than reported here, as suggested by the APE Ec biosynthetic complex. Further research is required to develop these broad-spectrum antimicrobial compounds into drugs that may be used in the fight against microbial infections.