Mixing postharvest fungicides and sanitizers results in unpredictable survival of microbes that affect cantaloupes.

Postharvest treatments with sanitizers and fungicides are applied to increase the quality, safety and shelf life of fresh produce including cantaloupes (also known as rockmelons). The primary role of sanitizers during cantaloupe washing is to prevent cross contamination of potentially pathogenic bacteria in washwater. Postharvest fungicide sprays or dips are employed to inhibit spoilage-causing fungi. While assessing the compatibility of these antimicrobials based on the measurement of active ingredients levels provides some indication of antimicrobial capacity, there is limited data on whether the interaction between these chemicals in wash water modifies their overall efficacy against relevant microorganisms. The aim of this research was to determine how chlorine- and peroxyacetic acid-based sanitizers interact with commercial guazatine- and imazalil-based fungicide formulations used on cantaloupes, and whether mixing these augments or suppresses anti-microbial activity against relevant human pathogens and spoilage fungi in wash water. The results were unpredictable: while most combinations were antimicrobial, the chlorine-based sanitizer when mixed with the guazatine-based fungicide had significantly reduced efficacy against pathogenic Salmonella spp. (~2.7 log) and the fungal spoilage organisms, Trichothecium roseum and Rhizopus stolonifera. Mixing the chlorine-based sanitizer with an imazalil-based fungicide produced a range of outcomes with antagonistic, indifferent and synergistic interactions observed for the fungal species tested. The peroxyacetic acid-based sanitizer led to indifferent interactions with the guazatine-based fungicide, while antagonism and synergy were observed when mixed with the imazalil-based fungicide. This study demonstrates that mixing postharvest agrichemicals used in the cantaloupe industry may increase the risk of microbial contamination and thereby potentially compromise food safety and quality.

Environmental Drivers for Persistence of Escherichia coli and Salmonella in Manure-Amended Soils: A Meta-Analysis.

ABSTRACT: Application of organic amendments to agricultural land improves soil quality and provides nutrients essential for plant growth; however, they are also a reservoir for zoonotic pathogens whose presence poses a significant risk to public health. The persistence of bacteria in manure-amended soil, and differences in manure handling practices, are important issues from a food safety perspective. The primary objective of this study was to quantitatively summarize the variations in the rate of decline of Escherichia coli and Salmonella spp. in manure-amended soil under laboratory and field conditions, and to assess the impact of environmental factors. Available literature data on persistence of E. coli and Salmonella spp. in manure-amended soil from 42 primary research studies were extracted and statistically analyzed using a mixed-effect regression model. The results indicated that temperature (soil and air combined) was the most prominent factor affecting persistence of both E. coli and Salmonella spp. under laboratory conditions (P < 0.001), and of E. coli under field conditions (P < 0.05). The time required for a log reduction of E. coli under field conditions was significantly higher at low temperature (0 to 10°C) than at high temperature (greater than 20°C) (P < 0.05). In addition, application method was identified as a significant factor, with manure incorporation to soil inducing longer survival compared with surface application by approximately 1.2 times. The significant variation observed among primary research studies of bacterial persistence has highlighted that mitigation strategies associated with the use of manures in fresh produce production need to be improved by addressing factors such as climate, soil management, application method, and initial microbial levels. These findings may be used to support guidelines establishing exclusion periods between manure fertilization and the grazing or harvesting of crops, and may be useful for the generation of quantitative microbial risk models for fresh produce.

Diversity and guaiacol production of Alicyclobacillus spp. from fruit juice and fruit-based beverages.

Alicyclobacillus acidoterrestris is an acido-thermophilic, spore-forming bacterial species that can spoil acidic fruit juice and fruit-based beverages. The metabolism of taint compounds by this bacterial species has led to its status as a targeted microorganism in the fruit juice industry. This study aims to assess the genetic diversity of Alicyclobacillus spp. including A. acidoterrestris and its correlation to spoilage taint metabolism. Alicyclobacillus cultures, which were previously isolated from a wide range of domestic and international products including fruit juice, fruit drinks and fruit juice concentrates, were subjected to DNA fingerprint analysis by using randomly amplified polymorphic DNA (RAPD) - polymerase chain reaction. Isolates were classified on the basis of their RAPD profile and the results were used to select representative strains to undergo taint production assessment. The taint guaiacol produced by Alicyclobacillus spp. was measured by headspace gas chromatography and mass spectrometry. From produced RAPD profiles, two genotypic groups and two sub-groups were identified. The groups were independent of product types and geographical origins. A significant number of isolates were clustered in genotypic group I, including A. acidoterrestris ATCC 49025. These isolates produced significant levels of guaiacol, 8.7 mg/L on average. A smaller number of isolates was found in genotypic group II including A. acidocaldarius and they produced no guaiacol. Primer F-64 was useful to identify Alicyclobacillus at the species level, and permitted rapid identification of strains producing fruit juice taint compounds such as guaiacol.

Aspergillus hancockii sp. nov., a biosynthetically talented fungus endemic to southeastern Australian soils.

Aspergillus hancockii sp. nov., classified in Aspergillus subgenus Circumdati section Flavi, was originally isolated from soil in peanut fields near Kumbia, in the South Burnett region of southeast Queensland, Australia, and has since been found occasionally from other substrates and locations in southeast Australia. It is phylogenetically and phenotypically related most closely to A. leporis States and M. Chr., but differs in conidial colour, other minor features and particularly in metabolite profile. When cultivated on rice as an optimal substrate, A. hancockii produced an extensive array of 69 secondary metabolites. Eleven of the 15 most abundant secondary metabolites, constituting 90% of the total area under the curve of the HPLC trace of the crude extract, were novel. The genome of A. hancockii, approximately 40 Mbp, was sequenced and mined for genes encoding carbohydrate degrading enzymes identified the presence of more than 370 genes in 114 gene clusters, demonstrating that A. hancockii has the capacity to degrade cellulose, hemicellulose, lignin, pectin, starch, chitin, cutin and fructan as nutrient sources. Like most Aspergillus species, A. hancockii exhibited a diverse secondary metabolite gene profile, encoding 26 polyketide synthase, 16 nonribosomal peptide synthase and 15 nonribosomal peptide synthase-like enzymes.

Analysis of the Listeria monocytogenes Population Structure among Isolates from 1931 to 2015 in Australia.

Listeriosis remains among the most important bacterial illnesses, with a high associated mortality rate. Efforts to control listeriosis require detailed knowledge of the epidemiology of the disease itself, and its etiological bacterium, Listeria monocytogenes. In this study we provide an in-depth analysis of the epidemiology of 224 L. monocytogenes isolates from Australian clinical and non-clinical sources. Non-human sources included meat, dairy, seafood, fruit, and vegetables, along with animal and environmental isolates. Serotyping, Multi-Locus Sequence Typing, and analysis of inlA gene sequence were performed. Serogroups IIA, IIB, and IVB comprised 94% of all isolates, with IVB over-represented among clinical isolates. Serogroup IIA was the most common among dairy and meat isolates. Lineage I isolates were most common among clinical isolates, and 52% of clinical isolates belonged to ST1. Overall 39 STs were identified in this study, with ST1 and ST3 containing the largest numbers of L. monocytogenes isolates. These STs comprised 40% of the total isolates (n = 90), and both harbored isolates from clinical and non-clinical sources. ST204 was the third most common ST. The high prevalence of this group among L. monocytogenes populations has not been reported outside Australia. Twenty-seven percent of the STs in this study contained exclusively clinical isolates. Analysis of the virulence protein InlA among isolates in this study identified a truncated form of the protein among isolates from ST121 and ST325. The ST325 group contained a previously unreported novel mutation leading to production of a 93 amino acid protein. This study provides insights in the population structure of L. monocytogenes isolated in Australia, which will contribute to public health knowledge relating to this important human pathogen.

Draft Genome Sequences of 15 Isolates of Listeria monocytogenes Serotype 1/2a, Subgroup ST204.

Listeria monocytogenes sequence type 204 (ST204) strains have been isolated from a range of food, environmental, and clinical sources in Australia. This study describes the draft genome sequences of 15 isolates collected from meat and dairy associated sources.

Comparative Genomics of the Listeria monocytogenes ST204 Subgroup.

The ST204 subgroup of Listeria monocytogenes is among the most frequently isolated in Australia from a range of environmental niches. In this study we provide a comparative genomics analysis of food and food environment isolates from geographically diverse sources. Analysis of the ST204 genomes showed a highly conserved core genome with the majority of variation seen in mobile genetic elements such as plasmids, transposons and phage insertions. Most strains (13/15) harbored plasmids, which although varying in size contained highly conserved sequences. Interestingly 4 isolates contained a conserved plasmid of 91,396 bp. The strains examined were isolated over a period of 12 years and from different geographic locations suggesting plasmids are an important component of the genetic repertoire of this subgroup and may provide a range of stress tolerance mechanisms. In addition to this 4 phage insertion sites and 2 transposons were identified among isolates, including a novel transposon. These genetic elements were highly conserved across isolates that harbored them, and also contained a range of genetic markers linked to stress tolerance and virulence. The maintenance of conserved mobile genetic elements in the ST204 population suggests these elements may contribute to the diverse range of niches colonized by ST204 isolates. Environmental stress selection may contribute to maintaining these genetic features, which in turn may be co-selecting for virulence markers relevant to clinical infection with ST204 isolates.

Draft Genome Sequence of Clostridium sp. Maddingley, Isolated from Coal-Seam Gas Formation Water.

Clostridium sp. Maddingley was isolated as an axenic culture from a brown coal-seam formation water sample collected from Victoria, Australia. It lacks the solventogenesis genes found in closely related clostridial strains. Metabolic reconstructions suggest that volatile fatty acids are the main fermentation end products.