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Biomedical subjects

G H Fleet

Publications and source records attributed to G H Fleet.

At least 19 recordsLinked to original sources
PubMed2006

Lactic acid bacteria associated with wine grapes from several Australian vineyards.

AIMS: The detection and isolation of lactic acid bacteria by enrichment methods from wine grapes cultivated in vineyards located in New South Wales, Australia. METHODS AND RESULTS: Enrichment cultures in de Man, Rogosa and Sharpe (MRS) broth, MRS + ethanol (5%), MRS broth supplemented with 15% (v/v) tomato juice (MRST), pH 5.5 and 3.5 and autoenrichment in grape juice homogenate were used to detect lactic acid bacteria on wine grapes. Bacteria were isolated from enrichment cultures by plating onto MRS and MRST agar and identified by 16S rDNA sequence analysis and phenotypical methods. A molecular method, PCR-denaturing gradient gel electrophoresis (DGGE) was also used to examine the bacteria that developed in enrichment cultures. Species of Lactobacillus, Enterococcus, Lactococcus and Weissella were detected in enrichments by plating and PCR-DGGE. Other bacteria (Sporolactobacillus, Asaia, Bacillus ssp.) were also found in some enrichment cultures. The principal malolactic bacterium, Oenococcus oeni, was not isolated. CONCLUSIONS: The incidence and populations of lactic acid bacteria on wine grapes were very low. Damaged grape berries showed a greater presence of these bacteria than undamaged berries. The diversity of bacterial species isolated from the grapes was greater than those previously reported and represented both lactic acid bacteria and nonlactic acid bacteria. Some of these bacteria (i.e. Lactobacillus lindneri, Lactobacillus kunkeei) could be detrimental to wine production. Oenococcus oeni was not found on grapes, but its recovery could be obscured by overgrowth from other species. SIGNIFICANCE AND IMPACT OF THE STUDY: Lactic acid bacteria are significant in wine production because they conduct the malolactic fermentation and cause stuck or sluggish alcoholic fermentation and wine spoilage. This study investigates wine grapes as a potential source of these bacteria.

Culture Media↗
PubMed2004

Microsatellite PCR profiling of Saccharomyces cerevisiae strains during wine fermentation.

AIMS: Use of microsatellite PCR to monitor populations of Saccharomyces cerevisiae strains during fermentation of grape juice. METHOD AND RESULTS: Six commercial wine strains of S. cerevisiae were screened for polymorphism at the SC8132X locus using a modified rapid PCR identification technique. The strains formed four distinct polymorphic groups that could be readily distinguished from one another. Fermentations inoculated with mixtures of three strains polymorphic at the SC8132X locus were monitored until sugar utilization was complete, and all exhibited a changing population structure throughout the fermentation. CONCLUSIONS: Rapid population quantification demonstrated that wine fermentations are dynamic and do not necessarily reflect the initial yeast population structure. One or more yeast strains were found to dominate at different stages of the fermentation. SIGNIFICANCE AND IMPACT OF THE STUDY: The population structure of S. cerevisiae during mixed culture wine fermentation is dynamic and could modify the chemical composition and flavour profile of wine.

Carbohydrate Metabolism↗
PubMed2003

Spoilage of bottled red wine by acetic acid bacteria.

AIMS: To determine the bacterial species associated with an outbreak of spoilage in commercially bottled red wine where the bottles had been stored in an upright vertical compared with horizontal position. METHODS AND RESULTS: Bottled wines comprising Cabernet Sauvignon, Pinot Noir, Shiraz, Merlot and blended red varieties were examined for visible spoilage. Analysis of visibly affected and non-affected wines revealed a spectrum of aroma and flavour defects, ranging from loss of fruity aroma, staleness, oxidized character to overt volatile acidity. Only acetic acid bacteria, and not yeast or lactic acid bacteria, could be isolated from both spoiled and unspoiled wines and were found to grow only on Wallerstein Nutrient (WL) medium supplemented with 10% red wine or 1-2% ethanol. Analysis of the 16S rRNA region and RAPD-PCR analysis showed the isolates to be a closely related group of Acetobacter pasteurianus, but this group was differentiated from the group comprising beer, vinegar and cider strains. CONCLUSIONS: A. pasteurianus was the species considered responsible for the spoilage but the isolates obtained had atypical properties for this species. In particular, they failed to grow on WL nutrient medium without ethanol or wine supplementation. Storage of the bottles of wine containing A. pasteurianus in an upright vertical position specifically induced growth and spoilage in a proportion of the bottles under conditions that were inhibitory for horizontally stored bottles. We hypothesize that the upright position created a heterogeneous environment that allowed the growth of bacteria in only those bottles sealed with cork closures that had upper limit for the natural permeability to oxygen. Such a heterogeneous environment would not exist in horizontally stored bottles as the larger volume of wine adjacent to the cork would strongly compete with the bacteria for the oxygen as it diffuses through the cork closure. SIGNIFICANCE AND IMPACT OF THE STUDY: A low level of bacteria (acetic acid bacteria) in wine can proliferate and cause wine spoilage in bottles stored in an upright vertical as opposed to an horizontal position under conditions that would normally limit bacterial development.

Acetic Acid↗
PubMed2001

The growth, properties and interactions of yeasts and bacteria associated with the maturation of Camembert and blue-veined cheeses.

The growth of yeasts and bacteria were monitored during the maturation of Camembert and blue-veined cheese produced in Australia. Yeasts were prominent throughout maturation, growing to 10(5)-10(9)/g, depending on the manufacturer. Debaryomyces hansenii predominated, but there were lesser, inconsistent contributions from Yarrowia lipolytica. Of the non-lactic acid bacteria, Acinetobacter species were significant during the maturation of Camembert but not blue-veined cheeses, and grew to 10(6)-10(8) cfu/g. Staphylococcus and Micrococcus species were consistently isolated from the cheeses with Staphylococcus xylosus growing to 10(5)-10(9) cfu/g, depending on the product. Lactic acid bacteria (10(7)-10(9) cfu/g) were present throughout maturation but were not identified. Interactions between the various yeasts and bacterial isolates were examined. Several strains of D. hansenii exhibited killer activity but not against Y. lipolytica. None of the yeasts were antagonistic towards the bacteria but some strains of D. hansenii enhanced the growth of Y. lipolytica and S. xylosus. The yeast and bacterial isolates exhibited various degrees of extracellular proteolytic and lipolytic activities.

Bacteria↗
PubMed2001

Growth of fungi and mycotoxin production on cheese under modified atmospheres.

The use of modified atmospheres to prevent fungal growth and mycotoxin production in cheese was evaluated. Eight fungal species: Mucor plumbeus, Fusarium oxysporum, Byssochlamys fulva, B. nivea, Penicillium commune, P. roqueforti, Aspergillus flatus and Eurotium chevalieri were inoculated onto cheese and incubated under conditions of decreasing concentrations of O2 (5% to < 0.5%) and increasing concentrations of CO2 (20-40%). Fungal growth was measured by colony diameter and ergosterol content. All fungi examined grew in atmospheres containing 20% and 40% CO2 with 1% or 5% O2, but growth was reduced by 20-80%, depending on species, compared with growth in air. The formation of aflatoxins B1 and B2, roquerfortine C and cyclopiazonic acid was greatly decreased but not totally inhibited in these atmospheres. At 20% or 40% CO2 with < 0.5% O2, only B. nivea exhibited growth, which was very slow. Growth of F. oxysporum, B. fulca, P. commune and A. flavus showed good correlations between colony diameter and ergosterol content. However, for the other species correlations were inconsistent.

Carbon Dioxide↗
PubMed2000

Microbial species associated with different sections of broccoli harvested from three regions in Australia.

The microbial populations associated with the different sections of broccoli harvested from three locations in Australia were studied during storage at 5, 15 and 20 degrees C. Bacterial and yeast populations associated with the outer florets and cut surfaces of the stem were generally 10-fold or more higher than those associated with inner florets or non-cut stems, respectively. The predominating bacterial species varied with the origin of the broccoli. Pseudomonas fluorescens, Ps. corrugata and Ps. viridiflava predominated at populations of 10(5)-10(7) cfu/g on broccoli harvested from Victoria, Ps. fluorescens, Ps. mendocina and Ps. fragii and Arthrobacter spp. (10(-3) 10(6) cfu/g) were prevalent on broccoli harvested from Queensland. Broccoli harvested from New South Wales exhibited a predominance of Ps. fluorescens, Arthrobacter spp. and Enterobacteragglomerans (10(3)-10(5) cfu/g). Most species grew on broccoli during storage. Similar species were found at the different sections of broccoli, although, for some species there was evidence of strain variation at the different locations and for different temperature of storage.

Australia↗
PubMed2000

Foodborne viral illness--status in Australia.

Norwalk-like virus contamination of oysters and orange juice, and hepatitis A virus contamination of oysters have been responsible for large outbreaks of foodborne viral disease in Australia. Rotavirus, adenovirus, astrovirus, parvovirus and other enteroviruses also contribute to the incidence of gastroenteritis in this country but the role of foods and waters in transmitting these viruses is unclear. Protocols for the investigation, surveillance and reporting of foodborne viral illness require further development to enable a more accurate description of the problem. Few laboratories have the capability to analyse foods for viruses and specific training in this technology is needed. Management of food safety in Australia largely relies on the implementation of HACCP principles, but these need to be adapted to address the specific risks from viruses.

Adenoviridae↗
PubMed1998

Composition of the cell walls of several yeast species.

Cell walls, representing 26%-32% of the cell dry weight, were prepared from several strains of the yeasts Kloeckera apiculata, Debaryomyces hansenii, Zygosaccharomyces bailii, Kluyveromyces marxianus and Saccharomyces cerevisiae. Extraction of the walls with potassium hydroxide at 4 degrees C, followed by saturation of the alkali-soluble extract with ammonium sulphate gave fractions of mannoprotein, alkali-soluble glucan and alkali-insoluble glucan. Chitin was associated with the alkali-insoluble glucan. The proportions of the different fractions within the walls varied with the species and strain. Mannoprotein comprised between 25% and 34% of the walls, the content of alkali-insoluble glucan ranged from 15% to 48%, and the content of alkali-soluble glucan ranged from 10% to 48%. There was significant variation in the physical appearance of the alkali-soluble glucans and the relative viscosity of suspensions of these glucans. The yeasts could represent novel sources of polysaccharides with industrial and medical applications.

Cell Wall↗
PubMed1997

Effect of diluent type on viability of yeasts enumerated from foods or pure culture.

The effects of seven diluent types on the viability of yeasts enumerated from foods and in pure culture were studied. The diluents were laboratory glass distilled water; saline water (0.85% NaCl), sodium phosphate buffer (0.1 M, pH 7.0), 0.1% peptone, 0.1% yeast extract, 0.1% peptone in 0.1 M sodium phosphate buffer, pH 7.0, and 0.1% malt extract. For all foods studied, dilution in 0.1% peptone gave the highest counts, with saline and phosphate buffer diluents giving lower counts than those obtained with distilled water. When seven species of yeast were enumerated in pure culture, highest counts were obtained using 0.1% peptone as the diluent and, with three exceptions, all species gave higher counts when diluted in diluents other than distilled water. When yeast suspensions were held in diluents for up to 2 h before plating, cell death occurred. The extent of death was highest in distilled water, saline and phosphate buffer diluents. Cell death also occurred in 0.1% peptone, yeast extract and malt extract, but to a lesser degree.

Beverages↗
PubMed1997

Evaluation of the Biolog system for the identification of food and beverage yeasts.

The inconvenience of conventional yeast identification methods has resulted in the development of rapid, commercial systems, mainly for clinical yeast species. The Biolog system (Biolog Inc., Hayward, CA, USA) is a new semi-automated, computer-linked technology for rapid identification of clinical and non-clinical yeasts. The system is based around a microtitre tray and includes assimilation and oxidation tests. This paper evaluates the Biolog system for the identification of 21 species (72 strains) of yeasts of food and wine origin. Species correctly identified included Saccharomyces cerevisiae, Debaryomyces hansenii, Yarrowia lipolytica, Kluyveromyces marxianus, Kloeckera apiculata, Dekkera bruxellensis and Schizosaccharomyces pombe. Zygosaccharomyces bailii and Zygosaccharomyces rouxii were identified correctly 50% of the time and Pichia membranaefaciens 20% of the time.

Beverages↗
PubMed1996

The occurrence and growth of yeasts in Camembert and blue-veined cheeses.

Yeast populations greater than 10(6) cfu/g were found in approximately 54% and 36%, respectively in surface samples of retail Camembert (85 samples) and Blue-veined (45 samples) cheeses. The most predominant species isolated were Debaryomyces hansenii, Candida catenulata, C. lipolytica, C. kefyr, C. intermedia, Saccharomyces cerevisiae, Cryptococcus albidus and Kluyveromyces marxianus. The salt concentration of the surface samples of the cheeses varied between 2.5-5.5% (w/w) (Camembert) and 7.5-8.3 (Blue-veined), depending upon brand, and influenced the yeast ecology, especially the presence of S. cerevisiae. Yeasts grew to populations of 10(6)-10(8) cfu/g when cheeses were stored at either 25 degrees C or 10 degrees C. These populations decreased on continued storage at 25 degrees C, but such decreases were not so evident on storage at 10 degrees C. The properties of yeasts influencing their occurrence and growth in cheese were: fermentation/assimilation of lactose; production of extracellular lipolytic and proteolytic enzymes, utilisation of lactic and citric acids; and growth at 10 degrees C.

Candida↗
PubMed1996

Effect of diluents on the enumeration of Vibrio vulnificus.

Peptone (0.1%) solution containing 3% NaCl (PS) was a more suitable diluent than phosphate buffered saline (PBS) solution for the enumeration of Vibrio vulnificus in both broth cultures and oyster homogenates. PBS caused significant underestimation of the viable population of the species by plate counts on either selective or non-selective media. Dilution in PS is recommended in methods for the enumeration of V. vulnificus.

Food Microbiology↗
PubMed1996

Growth of yeasts in milk and associated changes to milk composition.

The growth of several yeast species in milk containing added sodium chloride (0-15%, w/v) at 25 degrees C and 10 degrees C was examined in conjunction with yeast metabolism of milk constituents. Depending on conditions, all yeasts grew to maximum populations of 10(7)-10(8) cfu/ml. Kluyveromyces marxianus gave strong utilisation of lactose and weak metabolism of citrate, protein and fat with the production of ethanol, glycerol, lactic acid and propionic acid. As measured by the production of free amino acids and free fatty acids, Candida lipolytica and Candida catenulata gave strong proteolytic and lipolytic reactions, the specificities of which appeared to be influenced by temperature and the presence of NaCl. These species also metabolised organic acids. Although giving strong growth responses, Debaryomyces hansenii and Saccharomyces cerevisiae did not metabolise lactose and gave only very weak lipolytic and proteolytic reactions. Citrate was metabolised by D. hansenii but not by S. cerevisiae. Both species produced small amounts of ethanol, glycerol and lactic acid.

Amino Acids↗
PubMed1991

The occurrence and growth of microorganisms during the fermentation of fish sausage.

Minced fish (mullet) sausage mixes containing added sugar, salt, nitrate, nitrite and spices were fermented (48 h, 30 degrees C) by indigenous flora or by a starter culture (Pediococcus acidilactici) and the microbial ecology and behaviour of various bacteria was monitored. Pediococcus pentosaceus and Lactobacillus plantarum dominated the indigenous fermentation, achieving populations of 10(7)-10(8) cfu/g by 48 h, and decreasing the pH of the mix to 4.5-4.7. Significant growth (10(5)-10(7) cfu/g) of Staphylococcus warneri, Staphylococcus aureus, Staphylococcus epidermidis. Micrococcus varians and Micrococcus luteus also occurred during this fermentation. Less growth was exhibited by Bacillus megaterium and yeasts. Pediococcus acidilactici dominated the fermentation when it was inoculated as a starter culture, but indigenous lactic acid bacteria (P. pentosaceus and L. plantarum) also grew to 10(7)-10(8) cfu/g. The growth of other bacteria and yeasts was restricted during fermentation with starter culture. Inoculated Escherichia coli, Salmonella typhimurium, Salmonella sofia, and Staphylococcus aureus grew to 10(6)-10(7) cfu/g in the sausage mix during indigenous fermentation. Lesser growth occurred for Bacillus cereus, Clostridium perfringens and Vibrio parahaemolyticus. Growth of these bacteria was significantly inhibited in sausage mix fermented with P. acidilactici.

Animals↗