Effect of germicidal UVC light on fungi isolated from grapes and raisins

AIMS

To examine how UVC affects the different genera of fungi commonly isolated from grapes, with the aim of understanding changes in mycobiota during grape ripening and possible applications for preventing grape decay during storage.

METHODS AND RESULTS

Spores of Aspergillus carbonarius, Aspergillus niger, Cladosporium herbarum, Penicillium janthinellum and Alternaria alternata (between 100-250 spores/plate agar) were UVC irradiated for 0 (control), 10, 20, 30, 60, 300 and 600 s. Plates were incubated at 25 degrees C and colonies were counted daily up to 7 days. Alternaria alternata and Aspergillus carbonarius were the most resistant fungi. Conidial germination in these species was reduced by approx. 25% after 10 s of exposure, compared with greater than 70% reduction for the remaining species tested. Penicillium janthinellum spores were the most susceptible at this wavelength. UVC exposures of 300 s prevented growth of all isolates studied, except for Alternaria alternata.

CONCLUSIONS

UVC irradiation plays a major role in selecting for particular fungi that dominate the mycobiota of drying grapes.

SIGNIFICANCE AND IMPACT OF THE STUDY

The UVC irradiation of harvested grapes could prevent germination of contaminant fungi during storage or further dehydration.

Ochratoxin A-producing Aspergilli in Vietnamese green coffee beans

AIMS

To determine the incidence and severity of infection by ochratoxin A (OA)-producing fungi in Vietnamese green coffee beans.

METHODS AND RESULTS

Aspergillus carbonarius, A. niger and yellow Aspergilli (A. ochraceus and related species in section Circumdati) were isolated by direct plating of surface-disinfected Robusta (65 samples) and Arabica (11 samples) coffee beans from southern and central Vietnam. Significantly, more Robusta than Arabica beans were infected by fungi. Aspergillus niger infected 89% of Robusta beans, whereas A. carbonarius and yellow Aspergilli each infected 12-14% of beans. OA was not produced by A. niger (98 isolates) or A. ochraceus (77 isolates), but was detected in 110 of 113 isolates of A. carbonarius, 10 isolates of A. westerdijkiae and one isolate of A. steynii. The maximum OA observed in samples severely infected with toxigenic species was 1.8 microg kg(-1); however, no relationship between extent of infection and OA contamination was observed.

CONCLUSIONS

Aspergillus niger is the dominant species infecting Vietnamese coffee beans, yet A. carbonarius is the likely source of OA contamination.

SIGNIFICANCE AND IMPACT OF STUDY

Vietnamese green coffee beans were more severely infected with fungi than the levels reported for beans from other parts of the world, yet OA contamination appears to be infrequent.

Opportunistic, human-pathogenic species in the Herpotrichiellaceae are phenotypically similar to saprobic or phytopathogenic species in the Venturiaceae

Although morphologically similar, species of Cladophialophora (Herpotrichiellaceae) were shown to be phylogenetically distinct from Pseudocladosporium (Venturiaceae), which was revealed to be synonymous with the older genus, Fusicladium. Other than being associated with human disorders, species of Cladophialophora were found to also be phytopathogenic, or to occur as saprobes on organic material, or in water, fruit juices, or sports drinks, along with species of Exophiala. Caproventuria and Metacoleroa were confirmed to be synonyms of Venturia, which has Fusicladium (= Pseudocladosporium) anamorphs. Apiosporina, based on A. collinsii, clustered basal to the Venturia clade, and appears to represent a further synonym. Several species with a pseudocladosporium-like morphology in vitro represent a sister clade to the Venturia clade, and are unrelated to Polyscytalum. These taxa are newly described in Fusicladium, which is morphologically close to Anungitea, a heterogeneous genus with unknown phylogenetic affinity. In contrast to the Herpotrichiellaceae, which were shown to produce numerous synanamorphs in culture, species of the Venturiaceae were morphologically and phylogenetically more uniform. Several new species and new combinations were introduced in Cladophialophora, Cyphellophora (Herpotrichiellaceae), Exophiala, Fusicladium, Venturia (Venturiaceae), and Cylindrosympodium (incertae sedis).

Aspergillus species producing ochratoxin A: isolation from vineyard soils and infection of Semillon bunches in Australia

AIMS

The incidence of toxigenicity among Australian isolates of Aspergillus niger and Aspergillus carbonarius was assessed. Aspergillus rot and concomitant production of ochratoxin A (OA) in bunches inoculated with A. carbonarius were also investigated.

METHODS AND RESULTS

Aspergillus niger and A. carbonarius were isolated from vineyard soils. Aspergillus niger was more widespread than A. carbonarius, and two restriction fragment length polymorphism types of A. niger, N and T, were present. Three of 113 A. niger isolates and all 33 A. carbonarius isolates produced OA. Aspergillus carbonarius was inoculated onto Semillon bunches with and without damage in the month before harvest. Damaged berries at greater than 12.3 (o) Bx were particularly susceptible to Aspergillus rot and production of OA, which was concentrated in severely mouldy berries.

CONCLUSIONS

OA in Australian grapes results mainly from infection of berries by A. carbonarius. It is concentrated in discoloured, shrivelled berries. The potential for Aspergillus rot and OA production appears to commence after veraison and increase with berry damage and ripeness.

SIGNIFICANCE AND IMPACT OF THE STUDY

Minimizing damage to grapes between veraison and harvest significantly reduces Aspergillus rot and OA formation. Monitoring the extent of Aspergillus rot in bunches infected with toxigenic Aspergillus spp. may give some indication of OA contamination.

Australian research on ochratoxigenic fungi and ochratoxin A

The presence of the mycotoxin, ochratoxin A (OTA), has been reported in Australian grape products. Comprehensive surveys of Australian wines have determined that the frequency and level of OTA contamination are low. Aspergillus carbonarius is the primary OTA-producing species associated with grapes in Australia, and all isolates tested to date produce OTA. Aspergillus niger is isolated more frequently from vineyards, however, few strains produce OTA. A. carbonarius and A. niger exist as saprophytes in the top layer of soil beneath vines, from where they are thought to be blown onto bunches. The level of A. carbonarius in soil may be reduced by temperatures above or below the optimum temperature for survival (25 degrees C), by high soil moisture content, and by modifications to tillage and mulching practices. A. carbonarius is an opportunistic pathogen of damaged berries. In the absence of damage, spores may exist on berry surfaces without causing visible rots. Aspergillus rots are associated with black Aspergillus species, primarily A. niger, A. carbonarius and A. aculeatus. The potential for such rots is increased with berry damage, inoculum coverage and berry maturity. Susceptibility to berry splitting is related, in part, to bunch structure, and may be variety-dependent or influenced by rainfall, irrigation and canopy management. Black Aspergillus spp. are closely associated with berries near the main stem of the bunch. During winemaking, around 80% of the OTA initially present in grapes is removed, primarily with the skins and pulp during pressing. Additional reductions occur with the removal of precipitated grape and yeast solids. Bentonite in white wine and yeast hulls in red wine were the most effective non-carbonaceous fining agents for the removal of OTA.

Effects of water activity and temperature on the survival of Aspergillus carbonarius spores in vitro

AIMS

To determine the effect of water activity (a(w)) and temperature on the survival of Aspergillus carbonarius spores.

METHODS AND RESULTS

Spores of A. carbonarius were dried onto filter membranes. These filters were held at 1.0, 0.9, 0.8, 0.6 and 0.4 a(w) and at 1, 15, 25 and 37 degrees C for up to 618 d. At intervals, spores were recovered from filters and assessed for viability by enumeration on dichloran rose bengal chloramphenicol agar. Survival and subsequent growth of spores was prolonged at low temperatures and at a(w) below 0.6. Above 15 degrees C, 0.6-0.9 a(w) were often more deleterious than 1.0. However, at 1 degrees C and 1.0 a(w), spores lost viability more rapidly than at lower a(w).

CONCLUSIONS

Increased incidence of black Aspergillus spp. in dry soils and from grapes in dry conditions may result partly from prolonged survival of spores.

SIGNIFICANCE AND IMPACT OF THE STUDY

Delineating the direct effect of a(w) and temperature on survival of A. carbonarius spores may aid in understanding the incidence of this ochratoxin A-producing species in vineyard soils and on grapes.

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.

Effects of personal exposures on pulmonary function and work-related symptoms among sawmill workers

Three green mills and two dry mills were studied for personal exposure to wood dust and biohazards associated with wood dust and their correlation to lung function and work-related symptoms among sawmill workers. The levels of exposure to endotoxin, (1-->3)-beta-D-glucan, bacteria and fungi were high in green mills compared with dry mills. Compared with dry mill workers, green mill workers had significantly high prevalence of regular cough, chronic bronchitis, regular blocked nose, regular sneezing, sinus problems, flu-like symptoms, and eye and throat irritation. Significant positive correlations were found among endotoxin and Gram (-)ve bacteria, (1-->3)-beta-D-glucan and fungi, and endotoxin and (1-->3)-beta-D-glucan exposure levels. Significant dose-response relationships were found for personal exposures and lung function, and lung function and work-related respiratory symptoms. The significant correlations found for respirable fractions show that not only inhalable but also respirable fractions are important in determining potential health effects of exposure to wood dust. The management and employees of the sawmilling industry should be educated on the potential health effects of wood dust. Wood dust should be controlled at the source.

Exposure to biohazards in wood dust: bacteria, fungi, endotoxins, and (1-->3)-beta-D-glucans

Personal exposure to fungi, bacteria, endotoxin, and (1-->3)-beta-D-glucan was determined at different woodworking sites--logging sites, sawmills, woodchipping sites, and joineries. Exposure levels to fungi at logging sites and sawmills were in the range of 10(3)-10(4) cfu/m3, at the woodchipping mill, 10(3)-10(5) cfu/m3, and at joineries, 10(2)-10(4) cfu/m3. Although mean endotoxin levels were lower than the suggested threshold value of 20 ng/m3, some personal exposures at sawmills and a joinery exceeded the standard. The geometric mean personal (1-->3)-beta-D-glucan exposure level at the woodchipping mill was 2.32 ng/m3, at sawmills, 1.37 ng/m3, at logging sites, 2.02 ng/m3, and at joineries, 0.43 ng/m3. Highly significant associations were found between mean personal inhalable endotoxin exposures and Gram-negative bacteria levels (p < 0.0001), and mean personal inhalable (1-->3)-beta-D-glucan exposures and fungi levels (p = 0.0003). The prevalence of cough, phlegm, chronic bronchitis, nasal symptoms, frequent headaches, and eye and throat irritations was significantly higher among woodworkers than controls. Dose-response relationships were found between personal exposures and work-related symptoms among joinery workers and sawmill and chip mill workers.

Dust exposures in the wood processing industry

Workers at four different woodworking processes--two logging sites, four sawmills, one major woodchipping operation, and five joineries situated in the state of New South Wales in Australia--were studied for personal inhalable dust exposures (N = 182). The geometric mean exposure at logging sites was 0.6 mg/m3 (N = 7), sawmills 1.6 mg/m3 (N = 93), woodchipping 1.9 mg/m3 (N = 9), and joineries 3.7 mg/m3 (N = 66). Overall, 62% of the exposures exceeded the current standards. Among joineries, 95% of the hardwood exposures and 35% of the softwood exposures were above the relevant standards. A majority of workers (approximately 90%) did not wear appropriate respirators approved for wood dust, while the ones who did wear them, used them on average less than 50% of the time. The significant determinants of personal wood dust exposures (n = 163) were found to be local exhaust ventilation, job title, use of handheld tools, cleaning method used, use of compressed air, and green or dry wood processed. Type of wood processed (softwood or hardwood) was not found to be statistically significant.

Work-related symptoms and dose-response relationships for personal exposures and pulmonary function among woodworkers

BACKGROUND

Four sawmills, a wood chipping mill, and five joineries in New South Wales, Australia, were studied for the effects of personal exposure to wood dust, endotoxins. (1-->3)-beta-D-glucans, Gram-negative bacteria, and fungi on lung function among woodworkers.

METHODS

Personal inhalable and respirable dust sampling was carried out. The lung function tests of workers were conducted before and after a workshift.

RESULTS

The mean percentage cross-shift decrease in lung function was markedly high for woodworkers compared with the controls. Dose-response relationships among personal exposures and percentage cross-shift decrease in lung function and percentage predicted lung function were more pronounced among joinery workers compared with sawmill and chip mill workers. Woodworkers had markedly high prevalence of regular cough, phlegm, and chronic bronchitis compared with controls. Significant associations were found between percentage cross-shift decrease in FVC and regular phlegm and blocked nose among sawmill and chip mill workers. Both joinery workers and sawmill and chip mill workers showed significant relationships between percentage predicted lung function (FVC, FEV1, FEV1/FVC, FEF25-75%) and respiratory symptoms.

CONCLUSIONS

Wood dust and biohazards associated with wood dust are potential health hazards and should be controlled.

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.

Alternaria toxins in weather-damaged wheat and sorghum in the 1995-1996 Australian harvest

Weather-damaged wheat from northern New South Wales in 1995-96 was heavily infected with the fungus Alternaria alternata. The mycotoxins tenuazonic acid, alternariol, and alternariol monomethyl ether were detected at low levels which corresponded with the degree of A. alternata infection and the geographical location. Sorghum and undamaged wheat from the same region also showed moderate levels of A. alternata infection and low levels of tenuazonic acid but none of the other toxins. These mycotoxins were not found in weather-damaged wheat from other areas of Australia where the primary infection was by A. infectoria rather than A. alternata.

Media for preservative resistant yeasts: a collaborative study

An international collaborative study was carried out to determine the most effective medium for selective isolation and enumeration of preservative resistant yeasts. Such a medium should prevent the growth of other yeasts such as Saccharomyces cerevisiae that are tolerant to lower levels of commonly used food preservatives, and sensitive yeasts such as Rhodotorula species. The study compared two non-selective media that are in common use for cultivation of yeasts from foods, Malt Extract agar (MEA) and Tryptone Glucose Yeast extract agar (TGY) with media made selective for preservative resistant yeasts by addition of 0.5% acetic acid to these two basal media (MEAA and TGYA). A fifth medium, Zygosaccharomyces bailii medium (ZBM) was also included in the study. These media were compared for their efficacy in selective isolation and enumeration of the preservative resistant yeasts Zygosaccharomyces bailii, Schizosaccharomyces pombe and Pichia membranaefaciens. MEA and TGY without acetic acid were used as control, non-selective media, and Rhodotorula glutinis was the preservative sensitive control culture. Seven laboratories in six countries took part in the study. Of the non-selective media, TGY generally gave the highest counts, and TGY amended with 0.5% acetic acid (TGYA) was the best medium for recovery of all three preservative-resistant yeasts. ZBM was found to be selective for Z. bailii, but counts of this yeast on ZBM were significantly lower than on TGYA. R. glutinis did not grow on any of the selective media.

The normal mycoflora of commodities from Thailand. 2. Beans, rice, small grains and other commodities

Part of a comprehensive study of fungi occurring in commodities in Thailand, this paper reports results from 276 samples of mung beans, rice, sorghum and soybeans as well as other minor crops. Samples for major commodities were taken from farmers' stocks, middlemen and retail outlets, while those for minor crops were mostly from retail. Each sample was divided into two portions, one being examined in Bangkok and the second at North Ryde. Mycological examinations were carried out by direct plating after surface disinfection in chlorine. Media used were dichloran rose bengal chloramphenicol agar, dichloran 18% glycerol agar, Aspergillus flavus and parasiticus agar and dichloran chloramphenicol peptone agar. Fungi were identified to species level and percentage infection of samples calculated. The dominant fungus found in mung beans was Fusarium semitectum, which was present in 40% of samples and at a high level (18% of all seeds) overall. Aspergillus flavus was also found in 40% of samples, but only in 2% of seeds overall. Lasiodiplodia theobromae was the only other fungus exceeding 1% total infection. The major fungi found in soybeans were A. flavus (67% of samples; 6% overall) and Cladosporium cladosporioides (49% of samples; 9% overall). Storage fungi were more common in soybeans than the other commodities, indicating longer or adverse storage. Paddy rice contained high levels of a wide variety of field fungi, notably Fusarium semitectum, Bipolaris oryzae, and Curvularia, Phoma and Colletotrichum species. However, probably due to the heat generated by milling, milled rice contained very few fungi, which were mostly of storage origin. Only 3% of particles examined contained internal fungi. Infection in sorghum was typical of oilseeds, dominated by Aspergillus flavus, which was present in 86% of samples, with an overall infection rate of 12%. Beans other than soybeans were infected by a wide range of field fungi, but at low levels, with less than half of seeds examined being infected internally. With the exception of sorghum, the levels of mycotoxigenic fungi encountered were much lower than observed previously in nuts and oilseeds.

The normal mycoflora of commodities from Thailand. 1. Nuts and oilseeds

A comprehensive study was carried out of the fungi occurring in commodities normally traded in Thailand. Samples of major commodities were obtained from farmers' stocks and middlemen in major producing areas throughout the country. Retail samples were obtained from outlets in and around Bankok. Samples were divided into two portions, one being examined in Bangkok, and the second in Sydney. After surface disinfection, fungi were enumerated by direct plating on dichloran rose bengal chloramphenicol agar, dichloran 18% glycerol agar, Aspergillus flavus and parasiticus agar and dichloran chloramphenicol peptone agar. Figures for percentage infection were calculated, and fungi were isolated and identified to species level. In all 602 samples were examined, and at North Ryde about 18,000 fungal isolates identified. Data obtained from 329 samples are reported here, comprising maize (154), peanuts (109), cashews (45) and copra (21). Major fungi in maize included Fusarium moniliforme (present in 97% of samples), Aspergillus flavus (85%), Penicillium citrinum (67%), Aspergillus niger (64%), Lasiodiplodia theobromae (58%) and Fusarium semitectum (45%). In peanuts, the major fungi were Aspergillus flavus (95% of samples), Aspergillus niger (86%), Rhizopus oryzae (60%), Eurotium rubrum (51%), Macromina phaseolina (49%), Penicillium citrinum (46%) and Eurotium chevalieri (46%). Invasion in cashews was lower, major fungi being Aspergillus flavus (60%), Nigrospora oryzae (58%), Aspergillus niger (53%), Chaetomium globosum (47%) and Eurotium chevalieri (40%). Aspergillus flavus (86% of samples) was again dominant in copra, with Rhizopus oryzae (52%), Aspergillus niger (43%), Eurotium chevalieri (43%) the only other species exceeding 40% infection. Aspergillus parasiticus was rarely seen, and Aspergillus nomius was reported from foods for the first time.

Interactions among xerophilic fungi associated with dried salted fish

Interactions were investigated among five xerophilic fungi, Polypaecilum pisce, Basipetospora halophila, Eurotium rubrum, Aspergillus wentii and A. penicillioides, isolated from Indonesian dried salted fish. A range of water activities (aw) (0.98, 0.95, 0.90 and 0.84) and temperatures (15 degrees, 25 degrees and 30 degrees C) were studied on agar media in Petri dishes, and with dried fish as a substrate at 0.90 and 0.84 aw at 30 degrees C. Generally, the fungi exhibited one of two interaction types: mutual inhibition on contact, or inhibition of one or both species on contact, with the inhibited species continuing to grow at a significantly reduced rate. On glucose-based agar media A. wentii and E. rubrum were most competitive at all aw values and temperatures studied, while on NaCl media P. pisce and B. halophila were usually most competitive. The Petri dish system was a useful model, but did not completely simulate the interactions observed on dried fish. Polypaecilum pisce and B. halophila were able to compete more strongly on fish than on agar media, especially at 0.90 aw. This study provides some evidence that each species examined had a niche in which it was dominant, and that species interactions as well as environmental factors are important in determining the dominant fungal species on dried salted fish.

Production of trichothecene mycotoxins by Australian Fusarium species

Australian isolates of Fusarium species were grown on potato dextrose agar. Trichothecenes produced by these species were extracted by ethyl acetate followed by methanol and a silica gel column was used to clean-up the extract. The extracted samples were derivatized by acetylation with trifluoroacetic anhydride and the derivatives analysed by gas chromatography/mass spectrometry (GC/MS). Multiple ion detection was used to trace ions characteristic of the trichothecenes expected to be present. Quantitation of those found was based on a known mass of pentabromophenol that was added as an internal standard. Eight species of Fusarium (nineteen strains) were surveyed, of which three species, F. acuminatum, F. equiseti and F. sporotrichioides, produced the trichothecenes scirpentriol, diacetoxyscirpenol, neosolaniol, HT-2 toxin, T-2 toxin, T-2 tetraol and deoxynivalenol. Wheat samples were inoculated with four different species of Fusarium, F. acuminatum, F. equiseti, F. graminearum and F. sporotrichioides, and in these samples diacetoxyscirpenol, neosolaniol, HT-2 toxin and T-2 toxin were found.

Fungi causing thread mould spoilage of vacuum packaged Cheddar cheese during maturation

Thread mould is a defect which occurs sporadically in maturing vacuum packaged Cheddar cheese, caused by the growth of fungi in folds and wrinkles of the plastic film in which the cheese is packaged. Fungi were isolated and identified from 110 Cheddar cheese blocks exhibiting typical thread mould defects. The major causative species were found to be Cladosporium cladosporioides, Penicillium commune, C. herbarum, P. glabrum and a Phoma species. Yeasts were also frequently isolated from the cheese, the majority belonging to the genus Candida. Fungal species which can cause thread mould defects were also found in the cheese factory environment, on cheesemaking equipment, in air, and in curd and whey, providing a wide range of potential sources of contamination.

Strategies for microbial growth at reduced water activities

Microorganisms that are capable of growth at reduced water activities all rely on a common strategy for survival, i.e. the intracellular accumulation of a solute or solutes to balance the external water activity (aw), thus preventing the mass movement of water out of the cell. Understanding the physiological mechanisms that enable solutes to be accumulated and retained against strong concentration gradients, and the genetic controls on these processes may, in future, lead to the genetic manipulation of crop plants to increase their drought resistance.

Water relations of Paecilomyces variotii, Eurotium amstelodami, Aspergillus candidus and Aspergillus sydowii, xerophilic fungi isolated from Indonesian dried fish

The water relations of four xerotolerant fungi, Paecilomyces variotii, Eurotium amstelodami, Aspergillus candidus and Aspergillus sydowii, isolated from dried salt fish, were examined at 25 degrees C, on media in which water activity (aW) was controlled by NaCl or a glucose/fructose mixture. All fungi were less tolerant of NaCl than glucose/fructose at low aW. P. variotii grew 2 to 3 times faster on glucose/fructose media than on NaCl. The minimum aW permitting germination varied from 0.753 for E. amstelodami and, 0.776 for A. candidus and A. sydowii to 0.793 for P. variotii. At low aW germination was not always followed by growth. In most cases the minimum for growth was 0.02 aW units above that for germination.

Intoxication by tremorgenic mycotoxin (penitrem A) in a dog

A 1-year-old Siberian Husky dog presented with severe muscle tremors after ingestion of a mouldy hamburger bun. Penicillium crustosum and the tremorgenic mycotoxin penitrem A were isolated from the remaining portion of the hamburger bun. When grown in pure culture, the isolate of P. crustosum produced large amounts of penitrem A, along with other penitrem compounds. This is the first reported Australian case of toxicosis by naturally occurring penitrem A.

Systemic mycotic disease of captive crocodile hatchling (Crocodylus porosus) caused by Paecilomyces lilacinus

The sudden death occurred of a captive Estuarine crocodile hatchling (Crocodylus porosus). On autopsy, granuloma-like lesions were seen in the liver, left lung and spleen, and branching, septate fungal hyphae were observed in sections of liver and spleen. The fungus isolated from the liver showed characteristics of both Paecilomyces lilacinus and Paecilomyces marquandii but was closer to the former species. This is apparently the first report of the isolation of this fungus from a reptile in Australia.

An improved medium for the detection of Aspergillus flavus and A. parasiticus

An effective selective medium for the enumeration of Aspergillus flavus and Aspergillus parasiticus has been developed by modification of Bothast and Fennell's Aspergillus Differential Medium. Results can be obtained with the new medium, Aspergillus flavus and parasiticus Agar (AFPA), after 42 h incubation at 30 degrees C. The medium is thus suitable for use in quality control as a guide to the presence of A. flavus and, potentially, of aflatoxins. AFPA has been extensively tested on peanuts and soils. Results were reproducible and comparable with those on standard fungal enumeration media incubated for much longer periods. A very low percentage of false positive or negatives was found.

Trichosporonoides nigrescens sp. nov., a new xerophilic yeast-like fungus

A new yeast-like fungus isolated from jam on two occasions is described as Trichosporonoides nigrescens. It is a true xerophile, able to grow at water activities at least as low as 0.75. For this reason, its carbon assimilation pattern was examined using both dilute (standard) and concentrated carbon sources: six to nine compounds not assimilated at the standard concentrations of 0.5% (0.001 to 0.1 mol/kg) were assimilated at 1.5 to 2.0 mol/kg. Cell wall and septal ultrastructure, DNA base ratios, and the nuclear cycle were examined to determine the generic and higher taxonomic affinities of this microorganism. All properties were consistent with its assignment to Trichosporonoides Haskins et Spencer. However, while ultrastructure indicated an affinity with the Basidiomycetes, the mitotic nuclear cycle and the xerophilic nature of this fungus suggested an Ascomycete affinity. The GC content (57%) is consistent with assignment to either. No teleomorphic state was found.

Dichloran-glycerol medium for enumeration of xerophilic fungi from low-moisture foods

A low water activity (alpha omega) medium (0.95 alpha omega) containing 18% (wt/wt) glycerol and 2 micrograms of dichloran per ml was developed for enumerating the fungal flora of dried and semidried foods. The medium, designated DG18, was shown to be significantly better than Christensen malt salt agar when both media were tested with foodstuffs and with pure culture inocula. The need for a medium of reduced alpha omega for enumerating xerophilic fungi from low-moisture foods was demonstrated by comparing fungal counts obtained on both high-alpha omega and low-alpha omega media.

Dichloran-rose bengal medium for enumeration and isolation of molds from foods

Overgrowth by spreading molds such as Rhizopus and Mucor species is a problem with fungal enumeration media used for foods. Thirty-one antifungal compounds were surveyed for their ability to selectively inhibit such fungi while allowing growth of mycotoxigenic molds and other species of significance in food spoilage. Dichloran (2,6 dichloro-4-nitroaniline) restricted growth of Rhizopus stolonifer while allowing satisfactory growth of the other test molds. Three Rhizopus and Mucor species were encountered that were not inhibited by dichloran; these were controlled by the addition of rose bengal. The optimal medium, designated DRBC, contained 2 micrograms of dichloran and 25 micrograms of rose bengal per ml. DRBC, in pure culture tests and with food samples, restricted the colony size of spreading molds and recovered a wider range of species in higher numbers than other enumeration media.

Influence of solute and hydrogen ion concentration on the water relations of some xerophilic fungi

Germination and growth of six xerophilic fungi, Aspergillus flavus, Aspergillus ochraceus, Eurotium chevalieri, Chrysosphorium fastidium, Wallemia sebi and Xeromyces bisporus were examined on media of a wide range of water activities (aw). The influence of three solutes, NaCl, glycerol and a glucose/fructose mixture, was studied at pH 4-0 and pH 6-5 using a plate-slide technique. Germination times and growth rates were affected by solute type, but the influence of pH was less marked. Except for Wallemia sebi, the fungi grew most strongly on glucose/fructose and were partially or completely inhibited by NaCl. The results showed that a universal isolation medium for xerophilic fungi could be based on glycerol or glucose/fructose but not on NaCl as aw-limiting solute.