Browsing by Author "Death RG"

Now showing 1 - 4 of 4
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    Detecting genes associated with antimicrobial resistance and pathogen virulence in three New Zealand rivers
    (PeerJ, Inc, 2021-12-03) Davis M; Midwinter AC; Cosgrove R; Death RG; Oehlmann J
    The emergence of clinically significant antimicrobial resistance (AMR) in bacteria is frequently attributed to the use of antimicrobials in humans and livestock and is often found concurrently with human and animal pathogens. However, the incidence and natural drivers of antimicrobial resistance and pathogenic virulence in the environment, including waterways and ground water, are poorly understood. Freshwater monitoring for microbial pollution relies on culturing bacterial species indicative of faecal pollution, but detection of genes linked to antimicrobial resistance and/or those linked to virulence is a potentially superior alternative. We collected water and sediment samples in the autumn and spring from three rivers in Canterbury, New Zealand; sites were above and below reaches draining intensive dairy farming. Samples were tested for loci associated with the AMR-related group 1 CTX-M enzyme production (bla CTX-M) and Shiga toxin producing Escherichia coli (STEC). The bla CTX-M locus was only detected during spring and was more prevalent downstream of intensive dairy farms. Loci associated with STEC were detected in both the autumn and spring, again predominantly downstream of intensive dairying. This cross-sectional study suggests that targeted testing of environmental DNA is a useful tool for monitoring waterways. Further studies are now needed to extend our observations across seasons and to examine the relationship between the presence of these genetic elements and the incidence of disease in humans.
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    Freshwater invertebrate responses to fine sediment stress: A multi-continent perspective
    (John Wiley and Sons Ltd, 2024-01) McKenzie M; Brooks A; Callisto M; Collins AL; Durkota JM; Death RG; Jones JI; Linares MS; Matthaei CD; Monk WA; Murphy JF; Wagenhoff A; Wilkes M; Wood PJ; Mathers KL
    Excessive fine sediment (particles <2 mm) deposition in freshwater systems is a pervasive stressor worldwide. However, understanding of ecological response to excess fine sediment in river systems at the global scale is limited. Here, we aim to address whether there is a consistent response to increasing levels of deposited fine sediment by freshwater invertebrates across multiple geographic regions (Australia, Brazil, New Zealand and the UK). Results indicate ecological responses are not globally consistent and are instead dependent on both the region and the facet of invertebrate diversity considered, that is, taxonomic or functional trait structure. Invertebrate communities of Australia were most sensitive to deposited fine sediment, with the greatest rate of change in communities occurring when fine sediment cover was low (below 25% of the reach). Communities in the UK displayed a greater tolerance with most compositional change occurring between 30% and 60% cover. In both New Zealand and Brazil, which included the most heavily sedimented sampled streams, the communities were more tolerant or demonstrated ambiguous responses, likely due to historic environmental filtering of invertebrate communities. We conclude that ecological responses to fine sediment are not generalisable globally and are dependent on landscape filters with regional context and historic land management playing important roles.
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    Nitrate enrichment does not affect enteropathogenic Escherichia coli in aquatic microcosms but may affect other strains present in aquatic habitats
    (PeerJ, Inc, 2022-09-27) Davis MT; Canning AD; Midwinter AC; Death RG; Oehlmann J
    Eutrophication of the planet's aquatic systems is increasing at an unprecedented rate. In freshwater systems, nitrate-one of the nutrients responsible for eutrophication-is linked to biodiversity losses and ecosystem degradation. One of the main sources of freshwater nitrate pollution in New Zealand is agriculture. New Zealand's pastoral farming system relies heavily on the application of chemical fertilisers. These fertilisers in combination with animal urine, also high in nitrogen, result in high rates of nitrogen leaching into adjacent aquatic systems. In addition to nitrogen, livestock waste commonly carries human and animal enteropathogenic bacteria, many of which can survive in freshwater environments. Two strains of enteropathogenic bacteria found in New Zealand cattle, are K99 and Shiga-toxin producing Escherichia coli (STEC). To better understand the effects of ambient nitrate concentrations in the water column on environmental enteropathogenic bacteria survival, a microcosm experiment with three nitrate-nitrogen concentrations (0, 1, and 3 mg NO3-N /L), two enteropathogenic bacterial strains (STEC O26-human, and K99-animal), and two water types (sterile and containing natural microbiota) was run. Both STEC O26 and K99 reached 500 CFU/10 ml in both water types at all three nitrate concentrations within 24 hours and remained at those levels for the full 91 days of the experiment. Although enteropathogenic strains showed no response to water column nitrate concentrations, the survival of background Escherichia coli, imported as part of the in-stream microbiota did, surviving longer in 1 and 3 mg NO3-N/Lconcentrations (P < 0.001). While further work is needed to fully understand how nitrate enrichment and in-stream microbiota may affect the viability of human and animal pathogens in freshwater systems, it is clear that these two New Zealand strains of STEC O26 and K99 can persist in river water for extended periods alongside some natural microbiota.
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    Nutrient criteria to achieve New Zealand's riverine macroinvertebrate targets
    (PeerJ, Inc, 2021) Canning AD; Joy MK; Death RG; Brauns M
    Waterways worldwide are experiencing nutrient enrichment from population growth and intensive agriculture, and New Zealand is part of this global trend. Increasing fertilizer in New Zealand and intensive agriculture have driven substantial water quality declines over recent decades. A recent national directive has set environmental managers a range of riverine ecological targets, including three macroinvertebrate indicators, and requires nutrient criteria be set to support their achievement. To support these national aspirations, we use the minimization-of-mismatch analysis to derive potential nutrient criteria. Given that nutrient and macroinvertebrate monitoring often does not occur at the same sites, we compared nutrient criteria derived at sites where macroinvertebrates and nutrients are monitored concurrently with nutrient criteria derived at all macroinvertebrate monitoring sites and using modelled nutrients. To support all three macroinvertebrate targets, we suggest that suitable nutrient criteria would set median dissolved inorganic nitrogen concentrations at ~0.6 mg/L and median dissolved reactive phosphorus concentrations at ~0.02 mg/L. We recognize that deriving site-specific nutrient criteria requires the balancing of multiple values and consideration of multiple targets, and anticipate that criteria derived here will help and support these environmental goals.