Morphological and molecular identification of filamentous Aspergillus flavus and Aspergillus parasiticus isolated from compound feeds in South Africa

Aspergillus population diversity and its role in aflatoxin contamination of cashew nuts from coastal Kenya

Cashew nuts are among the main cash crops in coastal Kenya, due in large part to their high nutritional value. Unfortunately, they also make them highly susceptible to mold contamination, resulting in biodeterioration of the nutritional value and potential contamination with toxic secondary metabolites, such as aflatoxins, that cause them to be rejected for sale at the market. We determined the population diversity of the Aspergillus species and their role in aflatoxin contamination in cashew nuts in selected coastal regions of Kenya. Fifty raw cashew nut samples were collected from post-harvest storage facilities across three counties in Kenya's coastal region and examined for moisture content and the presence of Aspergillus fungi. About 63 presumptive isolates were recovered from the cashew nuts. ITS and 28S rDNA regions were sequenced. The aflD, aflM and aflR genes were amplified to identify the potentially aflatoxigenic from the Aspergillus isolates. The Aflatoxins' presence on the isolates was screened using UV and the ammonia vapour test on coconut milk agar and validated using ELISA assay. A comparison of cashew moisture content between the three counties sampled revealed a significant difference. Sixty-three isolates were recovered and identified to section based on morphological characters and their respective ITS regions were used to obtain species identifications. Three sections from the genus were represented, Flavi and Nigri, and Terrei with isolates from the section Nigri having slightly greater abundance (n = 35). The aflD, aflM and aflR genes were amplified for all isolates to assess the presence of the aflatoxin biosynthesis pathway, indicating the potential for aflatoxin production. Less than half of the Aspergillus isolates (39.68%) contained the aflatoxin pathway genes, while 22.22% isolates were aflatoxigenic, which included only the section Flavi isolates. Section Flavi isolates identification was confirmed by calmodulin gene. The presence of species from Aspergillus section Flavi and section Nigri indicate the potential for aflatoxin or ochratoxin in the cashew nuts. The study established a foundation for future investigations of the fungi and mycotoxins contaminating cashew nuts in Kenya, which necessitates developing strategies to prevent infection by mycotoxigenic fungi, especially during the storage and processing phases.

Seasonal and Geographical Impact on the Mycotoxigenicity of Aspergillus and Fusarium Species Isolated from Smallholder Dairy Cattle Feeds and Feedstuffs in Free State and Limpopo Provinces of South Africa

This study evaluated the impact of seasonal and geographical variations on the toxigenicity of Aspergillus and Fusarium strains previously isolated from smallholder dairy cattle feeds and feedstuffs sampled during summer and winter in the Free State and Limpopo provinces of South Africa (SA). In total, 112 potential toxigenic fungal species were obtained and determined for their capability to produce mycotoxins on solid Czapek Yeast Extract Agar (CYA); followed by liquid chromatography-mass spectrometry (LC-MS/MS) analysis. Our result revealed that 41.96% of the fungal species produced their respective mycotoxins, including aflatoxin B₁ (AFB₁), aflatoxin B₂ (AFB₂), and zearalenone (ZEN), with higher levels of AFB₁ (0.22 to 1045.80 µg/kg) and AFB₂ (0.11 to 3.44 µg/kg) produced by fungal species isolated from summer samples than those in winter [(0.69 to 14.44 µg/kg) and (0.21 to 2.26 µg/kg), respectively]. The same pattern was also observed for AFB₁ and AFB₂ in Limpopo (0.43 to 1045.80 µg/kg and 0.13 to 3.44 µg/kg) and Free State (0.22 to 576.14 µg/kg and 0.11 to 2.82 µg/kg), respectively. More so, ZEN concentrations in summer (7.75 to 97.18 µg/kg) were higher than in winter (5.20 to 15.90 µg/kg). A similar observation was also noted for ZEN in Limpopo (7.80 to 97.18 µg/kg) and Free State (5.20 to 15.90 µg/kg). These findings were confirmed via Welch and Brown-Forsythe tests with significantly (p ≤ 0.05) higher mycotoxin levels produced by fungal strains obtained in samples during summer than those in winter. In contrast, the concentrations of mycotoxins produced by the fungal species from both provinces were not significantly (p > 0.05) different.

Seasonal Diversity and Occurrence of Filamentous Fungi in Smallholder Dairy Cattle Feeds and Feedstuffs in South Africa

This study investigated 65 (35 in summer and 30 in winter) smallholder dairy cattle feeds from Free State and Limpopo provinces in South Africa from 2018 to 2019 for fungal contamination and assessed the impacts of seasonal variation on fungal contamination levels, isolation frequency, and diversity. Samples were examined for fungal contamination using macro- and microscopic approaches, and their identities were confirmed by molecular means. A total of 217 fungal isolates from 14 genera, including Aspergillus, Fusarium, and Penicillium, were recovered from feeds from both seasons. The most prevalent fungal species recovered were A. fumigatus and P. crustosum. Mycological analyses showed that 97% of samples were contaminated with one or more fungal isolates, with the summer fungal mean level (6.1 × 103 to 3.0 × 106 CFU/g) higher than that of feeds sampled during winter (mean level: 1.1 × 103 to 4.1 × 105 CFU/g). Independent sample t-test revealed that the isolation frequencies of the genera Aspergillus and Fusarium were significantly (p ≤ 0.05) higher in summer than winter, while Penicillium prevalence in both seasons was not statistically (p > 0.05) different. Furthermore, the Shannon−Weiner diversity index (H′) revealed a higher fungal diversity in summer (H′ = 2.8) than in winter (H′ = 2.1). This study on fungal contamination could be used for future fungal control and mycotoxin risk management in South Africa.

Occurrence of Mycotoxins and Toxigenic Fungi in Cereals and Application of Yeast Volatiles for Their Biological Control

Fungal infections in cereals lead to huge economic losses in the food and agriculture industries. This study was designed to investigate the occurrence of toxigenic fungi and their mycotoxins in marketed cereals and explore the effect of the antagonistic yeast Cyberlindnera jadinii volatiles against key toxigenic fungal strains. Aspergillus spp. were the most frequent contaminating fungi in the cereals, with an isolation frequency (Fr) of 100% in maize, followed by wheat (88.23%), rice (78.57%) and oats (14.28%). Morphological and molecular identification confirmed the presence of key toxigenic fungal strains in cereal samples, including A. carbonarius, A. flavus, A. niger, A. ochraceus and A. parasiticus. Aflatoxins (AFs) were detected in all types of tested cereal samples, with a significantly higher level in maize compared to wheat, rice, oats and breakfast cereals. Ochratoxin A (OTA) was only detected in wheat, rice and maize samples. Levels of mycotoxins in cereals were within EU permissible limits. The volatiles of Cyberlindnera jadinii significantly inhibited the growth of A. parasiticus, A. niger and P. verrucosum. The findings of this study confirm the presence of toxigenic fungi and mycotoxins in cereals within the EU permissible limits and the significant biocontrol ability of Cyberlindnera jadinii against these toxigenic fungi.

Aflatoxin M1 in Brazilian goat milk and health risk assessment

Contamination of goat milk with aflatoxin M₁ (AFM₁) is a public health concern. This study investigated filamentous fungi in goat feed and quantified AFM₁ in milk samples (n = 108) from goat fed forage and concentrate. Based on the detected AFM₁ concentration, risk assessment analyses were performed concerning the Estimated Daily Intake (EDI) for one-year-old children and adults. Filamentous fungi were found in goat feed samples in a range of 3.1 ± 1.9 to 4.2 ± 0.2 log CFU/g. Five genera were identified, to cite Aspergillus, Penicillium, Fusarium, Rhizopus and Acremonium. Aspergillus species comprised A. flavus, A. niger, and A. ochraceus. All goat milk samples were contaminated with AFM₁ (5.60-48.20 ng/L; mean 21.90 ± 10.28 ng/L) in amounts below the limits imposed by regulatory agencies. However, EDI values for AFM₁ through goat milk estimated for one-year-old children were above the Tolerable Daily Intake. The calculated Hazard Index for one-year-old children indicated potential risk of liver cancer due to goat milk consumption. The Margin of Exposure values to AFM₁ in one-year-old children and adults consuming goat milk as the unique milk source indicated increased health risk. Therefore, contamination of goat milk with AFM₁ should be considered a high priority for Brazil's risk management actions.

Effects of cold plasma on wheat grain microbiome and antimicrobial efficacy against challenge pathogens and their resistance

The safety and quality of cereal grain supplies are adversely impacted by microbiological contamination, with novel interventions required to maximise whole grains safety and stability. The microbiological contaminants of wheat grains and the efficacy of Atmospheric Cold Plasma (ACP) for potential to control these risks were investigated. The evaluations were performed using a contained reactor dielectric barrier discharge (DBD) system; samples were treated for 0-20 min using direct and indirect plasma exposure. Amplicon-based metagenomic analysis using bacterial 16S rRNA gene and fungal 18S rRNA gene with internal transcribed spacer (ITS) region was performed to characterize the change in microbial community composition in response to ACP treatment. The antimicrobial efficacy of ACP against a range of bacterial and fungal contaminants of wheat, was assessed to include individual isolates from grains as challenge pathogens. ACP influenced wheat microbiome composition, with a higher microbial diversity as well as abundance found on the untreated control grain samples. Culture and genomic approaches revealed different trends for mycoflora detection and control. A challenge study demonstrated that using direct mode of plasma exposure with 20 min of treatment significantly reduced the concentration of all pathogens. Overall, reduction levels for B. atrophaeus vegetative cells were higher than for all fungal species tested, whereas B. atrophaeus spores were the most resistant to ACP among all microorganisms tested. Of note, repeating sub-lethal plasma treatment did not induce resistance to ACP in either B. atrophaeus or A. flavus spores. ACP process control could be tailored to address diverse microbiological risks for grain stability and safety.

Screening of Fungi Isolates for C-4 Hydroxylation of R-2-Phenoxypropionic Acid Based on a Novel 96-Well Microplate Assay Method

R-2-(4-Hydroxyphenoxy)propionic acid (R-HPPA) is a pivotal intermediate for the synthesis of aryloxyphenoxypropionate (APP) herbicide. To rapidly screen microbial isolates with the capacity of hydroxylating R-2-phenoxypropionic acid to R-HPPA from various environmental samples, a convenient and safe 96-well microplate assay method with sodium nitrite (NaNO₂) as chromogenic reagent was proposed and optimized. The optimum assay conditions were as follows: the detection wavelength was 420 nm, the concentration of NaNO₂ solution was 6.0 g/L, color reaction temperature was 60 °C, the pH of the NaNO₂ solution was 2.4, and the reaction time was 40 min. With the aid of this method, screening for microorganisms with C-4-specific hydroxylation activity of R-PPA was conducted. As a result, 23 strains among 3744 single colonies isolated from various samples exhibited the hydroxylation activity. Among these strains, the highest bioconversion rate was achieved by Penicillium oxalicum A5 and Aspergillus versicolor A12, respectively. After 72-h cultivation in shake flask, their conversion rates of R-HPPA from 10 g/L R-PPA reached 21.18% and 40.24%, respectively. The established method was effective in rapid screening of microbes capable of biosynthesizing R-HPPA through hydroxylation of R-PPA, and the obtained two fungi species could be potentially used for R-HPPA production.

Mycoremediation: a treatment for heavy metal-polluted soil using indigenous metallotolerant fungi

Bioleaching of heavy metals from industrial contaminated soil using metallotolerant fungi is the most efficient, cost-effective, and eco-friendly technique. In the current study, the contaminated soil samples from Hattar Industrial Estate revealed a total lead (Pb) and mercury (Hg) concentration of 170.90 mg L^-1 and 26.66 mg L^-1, respectively. Indigenous metallotolerant fungal strains including Aspergillus niger M1, Aspergillus fumigatus M3, Aspergillus terreus M6, and Aspergillus flavus M7 were isolated and identified by pheno- and genotyping. A. fumigatus and A. flavus of soil sample S1 showed higher efficiency for Pb removal (99.20% and 99.30%, respectively), in SDB medium. Likewise, A. niger and A. terreus of soil sample S2 showed higher efficiency for Hg removal (96% and 95.50%, respectively), in YPG medium. Furthermore, the maximum uptake efficiency for Pb removal (8.52 mg g^-1) from soil sample S1 was noticed for A. fumigatus in YPG medium, while the highest uptake efficiency (4.23 mg g^-1) of A. flavus M2 strain was observed with CYE medium. Similarly, the maximum uptake efficiency of 0.41 mg g^-1 and 0.44 mg g^-1 for Hg removal from soil sample S2 was found for A. niger and A. terreus strains, respectively, in CYE medium. Thus, in order to address the major issue of industrial waste pollution, indigenous fungal strains A. fumigatus (M1) and A. terreus (M7), isolated in this study, could be used (ex situ or in situ) to remediate soils contaminated with Pb and Hg.

Analysis of Mycotoxins Contamination in Poultry Feeds Manufactured in Selected Provinces of South Africa Using UHPLC-MS/MS

A total of 105 different types of poultry feed samples from South Africa were simultaneously analysed for the presence of 16 mycotoxins using ultra-high-performance liquid chromatography coupled to a triple quadrupole mass spectrometer (UHPLC-MS/MS). The data revealed the presence of 16 mycotoxins in the various poultry feed samples. Fumonisin B₁ (FB₁) was the most dominant recovered from 100% of samples analysed at concentrations ranging between 38.7 and 7125.3 µg/kg. This was followed by zearalenone (ZEN) (range: 0.1–429 µg/kg) and deoxynivalenol (DON) (range: 2.5–154 µg/kg). Samples were also found to be contaminated with fumonisin B₂ (FB₂) (range: 0.7–125.1 µg/kg), fumonisin B₃ (FB₃) (range: 0.1–125.1 µg/kg), α-zearalenol (α-ZEL) (range: 0.6–20 µg/kg ), β-zearalenol (β-ZEL) (range: 0.2–22.1 µg/kg), 3-acetyldeoxynivalenol (3-ADON) (range: 0.1–12.9 µg/kg) and 15-acetyldeoxynivalenol (15-ADON) (range: 1.7–41.9 µg/kg). Alternaria mycotoxin, i.e., Alternariol monomethyl ether (AME) was recovered in 100% of samples at concentrations that ranged from 0.3–155.5 µg/kg. Aflatoxins (AFs) had an incidence rate of 92% with generally low concentration levels ranging from 0.1–3.7 µg/kg. Apart from these metabolites, 2 type A trichothecenes (THs), i.e., HT-2 toxin (HT-2) (range: 0.2–5.9 µg/kg) and T-2 toxin (T-2) (range: 0.1–15.3 µg/kg) were also detected. Mycotoxin contamination in South African poultry feed constitutes a concern as correspondingly high contamination levels, such as those observed herein are likely to affect birds, which can be accompanied by severe health implications, thus compromising animal productivity in the country. Such exposures, primarily to more than one mycotoxin concurrently, may elicit noticeable synergistic and or additive effects on poultry birds.

Aspergillus terreus (Trichocomaceae): A Natural, Eco-Friendly Mycoinsecticide for Control of Malaria, Filariasis, Dengue Vectors and Its Toxicity Assessment Against an Aquatic Model Organism Artemia nauplii

Vector-borne diseases like malaria, filariasis, and dengue are transmitted by mosquitoes and they cause global mortality and morbidity due to an increased resistance against commercial insecticides. The present study was aimed to evaluate the neurobehavioral toxicity, knock-down effect, histopathology, ovicidal, adulticidal, and smoke toxicity effect of Aspergillus terreus extract against three mosquito species, namely Anopheles stephensi, Culex quinquefasciatus, and Aedes aegypti (Diptera: Culicidae). The isolated fungal strain was identified as A. terreus (GenBank accession no: KX694148.1) through morphological and molecular (phylogenetic) analysis. The morphological changes in the treated fourth instar larvae shown the demelanization of cuticle and shrinkage of the internal cuticle of anal papillae. The time duration of extract exposure against the larvae determines the level of toxicity. The extract treated larvae were displayed excitation, violent vertical and horizontal movements with aggressive anal biting behavior as the toxic effect on the neuromuscular system. The results of the biochemical analysis indicated that a decrease in the level of acetylcholinesterase, α-carboxylesterase, and β-carboxylesterase in extract treated fourth instar larvae of all tested mosquito species. The findings of histopathological investigation shown the disorganization of the abdominal region, mainly in mid, hindgut, and gastric caeca, loss of antenna, lateral hair, caudal hair, upper and lower head hairs in the mycelium extract treated An. stephensi, Cx. quinquefasciatus, and Ae. aegypti. The ovicidal bioassay test results showed the mosquito hatchability percentage was directly related to the concentrations of mycelium extract. Nil hatchability of mosquito eggs was noticed at 500 μg/ml concentration. The adulticidal activity of fungal mycelia ethyl acetate extract resulted in a dose-dependent activity (15 and 30 min recovery periods). The higher concentration of extract (1000 mg/L) acted as a repellent, the adult mosquitoes showed restless movement, uncontrolled/anesthetic flight at last died. The better adulticidal activity was observed in the ethyl acetate extract against An. stephensi, Cx. quinquefasciatus followed by Ae. aegypti with the best score of LD50 and LD90 values and nil mortality was found in the control. The results of smoke toxicity assay of the mycelia extract exhibited significant mortality rate against Ae. aegypti (91%), Cx. quinquefasciatus (89%), and An. stephensi (84%). In addition, the present investigation reported the stability and toxic effects of A. terreus mycelium ethyl acetate extract on Artemia nauplii. The swimming speed (0.88 mm s-1) of A. terreus was reduced with ethyl extract 24 h treatment whereas, the control A. nauplii showed the normal speed of 2.96 mm s-1. Altered behavior and swimming movement were observed in the 8 h A. terreus mycelium extract treated A. nauplii. A pale yellow color substance (metabolites) was found in the mid-gut region of the mycelial extract exposed A. nauplii. The outcome of the present study, suggest that the A. terreus metabolites might serve as an alternative, cost-effective, eco-friendly, and target specific mosquitocidal agent in the future.

Inactivation of Vibrio parahaemolyticus by antimicrobial photodynamic technology using methylene blue

BACKGROUND

Vibrio parahaemolyticus is the leading causative pathogen of gastroenteritis often related to contaminated seafood. Photodynamic inactivation has been recently proposed as a strategy for killing cells and viruses. The objective of this study was to verify the bactericidal effects caused by photodynamic inactivation using methylene blue (MB) over V. parahaemolyticus via flow cytometry, agarose gel electrophoresis and sodium dodecyl sulfate polyacrylamide gel electrophoresis. Vibrio parahaemolyticus counts were determined using the most probable number method. A scanning electron microscope and a transmission electron microscope were employed to intuitively analyze internal and external cell structure.

RESULTS

Combination of MB and laser treatment significantly inhibited the growth of V. parahaemolyticus. The inactivation rate of V. parahaemolyticus was >99.99% and its counts were reduced by 5 log10 in the presence of 0.05 mg mL(-1) MB when illuminated with visible light (power density 200 mW cm(-2)) for 25 min. All inactivated cells showed morphological changes, leakage of cytoplasm and degradation of protein and DNA.

CONCLUSION

Results from this study indicated that photodynamic technology using MB produced significant inactivation of V. parahaemolyticus mainly brought about by the degradation of protein and DNA.