Browsing by Author "Stone, Wendy"

Now showing 1 - 4 of 4
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    Canary in the coliform mine : exploring the industrial application limits of a microbial respiration alarm system
    (Public Library of Science, 2021-03-04) Stone, Wendy; Louw, Tobi M.; Booysen, Marthinus J.; Wolfaardt, Gideon M.; Zhang, Dawei
    Fundamental ecological principles of ecosystem-level respiration are extensively applied in greenhouse gas and elemental cycle studies. A laboratory system termed CEMS (Carbon Dioxide Evolution Measurement System), developed to explore microbial biofilm growth and metabolic responses, was evaluated as an early-warning system for microbial disturbances in industrial settings: in (a) potable water system contamination, and (b) bioreactor inhibition. Respiration was detected as CO₂ production, rather than O₂ consumption, including aerobic and anaerobic metabolism. Design, thresholds, and benefits of the remote CO₂ monitoring technology were described. Headspace CO₂ correlated with contamination levels, as well as chemical (R² > 0.83–0.96) and microbiological water quality indicators (R² > 0.78–0.88). Detection thresholds were limiting factors in monitoring drinking water to national and inter- national standards (0 CFU/100 mL fecal coliforms) in both open- (>1500 CFU/mL) and closed-loop CO₂ measuring regimes (>100 CFU/100 mL). However, closed-loop detection thresholds allow for the detection of significant contamination events, and monitoring less stringent systems such as irrigation water (<100 CFU/mL). Whole-system respiration was effectively harnessed as an early-warning system in bioreactor performance monitoring. Models were used to deconvolute biological CO₂ fluctuations from chemical CO₂ dynamics, to optimize this real-time, sustainable, low-waste technology, facilitating timeous responses to biological disturbances in bioreactors.
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    Disinfectant, Soap or Probiotic Cleaning? Surface Microbiome Diversity and Biofilm Competitive Exclusion
    (MDPI [Commercial Publisher], 2020-11-04) Stone, Wendy; Tolmay, Janke; Tucker, Keira; Wolfaardt, Gideon M.
    This study extends probiotic cleaning research to a built environment. Through an eight-month cleaning trial, we compared the e ect of three cleaning products (disinfectant, plain soap, and a probiotic cleaner containing a patented Bacillus spore consortium), and tap water as the control, on the resident microbiome of three common hospital surfaces (linoleum, ceramic, and stainless steel). Pathogens, Escherichia coli and Staphylococcus aureus, were deposited and desiccated, and competitive exclusion was assessed for each microbiome. Cell survival was shown to be an incomplete tool for measuring microbial competitive exclusion. Biofilm competition offered a fuller understanding of competitive dynamics. A test for culturable cell survival showed that both plain soap and probiotic cleaner regimes established a surface microbiome that outcompeted the two pathogens. A different picture emerged when observing biofilms with a deposited and desiccated GFP-labeled pathogen, Pseudomonas aeruginosa. Competitive exclusion was again demonstrated. On surfaces cleaned with disinfectant the pathogen outcompeted the microbiomes. On surfaces cleaned with plain soap, the microbiomes outcompeted the pathogen. However, on surfaces cleaned with probiotic cleaner, despite the exponentially higher surface microbial loads, the microbiome did not completely outcompete the pathogen. Thus, the standard culturable cell test for survival on a surface confirmed the competitive advantage that is typically reported for probiotic cleaners. However, observation of competition in biofilms showed that the more diverse microbiome (according to alpha and beta indices) established on a surface cleaned with plain soap had a better competitive advantage than the monoculture established by the probiotic cleaner. Therefore, microbial diversity appears to be as critical to the competitive exclusion principle as cell numbers. The study showed that both plain soap and probiotic cleaner fostered competitive exclusion far more effectively than disinfectant. Probiotic cleaners with microbial diversity could be worth considering for hospital cleaning.
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    An external ecological niche for Candida albicans within reducing, oxygen-limited zones of wetlands and riverbanks
    (Stellenbosch : Stellenbosch University, 2011-03) Stone, Wendy; Botha, Alfred; Wilsenach, Jac; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: The ascomycetous yeast, Candida albicans, has been almost exclusively studied in a clinical context, due to the medical risk and costs associated with the yeast. Most environmental research into the external survival of this opportunistic pathogen has been concerned with short-term, severe pollution challenges. However, a study of literature indicates that the habitat characteristics of the oxygenlimited zones in wetlands and riverbanks are comparable to those of the gastrointestinal source of sewage-borne C. albicans. Interestingly, these are the external, environmental regions to which sewage-borne C. albicans is often exposed. In addition, oxygen-limitation is the predominant parameter in stimulating conjugation of C. albicans. Based on these observations, this study aimed to assess polluted river bank and wetland environments in the Western Cape of South Africa as potential habitats to accommodate a niche for C. albicans, particularly comparing the presence of this yeast in oxygen-limited, plant debris-rich zones and aerobic, clear, flowing zones. The second objective was to employ in vitro microcosm studies to investigate the survival and growth of C. albicans in various microhabitats similar to those comprising the oxygen-limited zones of wetlands. These included the rhizosphere of wetland flora, various soil and mud types and decomposing plant debris. The final objective was to establish the presence of sufficient nutrient and energy sources within this environment for the growth of C. albicans. In particular, cellulosic substrates and mono- and disaccharides released by the natural degradation of wetland plant debris were investigated as potential energy sources for this human commensal in the wetland environment. These study objectives combined to demonstrate the potential of such an oxygen-limited, plant debris-rich environment as a niche for C. albicans external to its human host. Both semi-quantitative culturing techniques and quantitative Real-Time PCR demonstrated the improved survival of C. albicans in oxygen-limited, plant debris-rich zones in wetland and river bank environments, in comparison to aerobic, clear subsurface water zones in the same environments. These zones were compared in the Plankenburg and Diep Rivers, situated in the Western Cape of South Africa. Correlations between coliform concentrations and total yeast concentrations were demonstrated in each of the different river zones, with higher pollution levels characteristic of the dry season. Candida albicans numbers in flowing water (zone W), rock-filtered (zone R) and plant-filtered water (zone P) were compared during the progress of the rainy and dry seasons. No C. albicans was observed in clear, flowing water throughout the analysis. Early in the rainy season, both rock-filtered (aerobic, poor in plant debris) and plant-filtered (oxygen-limited, rich in plant debris) water demonstrated C. albicans numbers at approximately equivalent levels of 10²-10³ cells/100 mL. However, as the rainy season progressed and total yeast and coliform numbers in all zones of the rivers dropped to negligible levels, C. albicans could no longer be detected in aerobic, rock-filtered zones; but its numbers remained at constant levels in oxygen-limited, plant-filtered zones. This suggests that oxygen-limited wetland and river bank zones rich in plant matter, analogous to the human gastrointestinal tract, may provide an ideal habitat in which C. albicans could establish a niche external to its host. The survival of this yeast in the various microhabitats that comprise this anaerobic, reducing wetland environment was evaluated with in vitro microcosms. The rhizosphere of wetland plants had no influence on C. albicans growth and survival in comparison to bulk soil away from the plant, and wetland mud microbiota was demonstrated to be inhibitory to its survival. However, decaying plant debris was shown to increase the survival of the yeast in this inhibitory mud environment. Candida albicans was shown to compete well saprophytically in anaerobic plant debris microcosms. In addition, the tendency of C. albicans to associate with plant matter in an aquatic environment was demonstrated by inoculating the yeast in water containing Hydrilla, a submerged macrophyte found in South African aquatic environments. Plate and liquid analyses, as well as an ANKOM NDF analysis, indicated unequivocally that the C. albicans strains evaluated in this work were unable to utilise the complex carbohydrates of the wetland habitat, including cellulose and fibre. However, HPLC, along with GCMS, demonstrated the anaerobic assimilation by C. albicans of monosaccharides released by natural lignocellulose degradation of wetland plant matter. An analysis of total nitrogen by digestion in a nitrogen analyser, as well as evaluation of ammonium, nitrate and nitrite in a KCL extract, also showed that C. albicans assimilates nitrogenous compounds released by the decomposition of wetland plant matter. This decay process occurs constantly in wetland and river bank habitats. It may therefore provide energy and nutrients for C. albicans, particularly in the anaerobic zones where conjugation may possibly occur and a niche may be established, as indicated by the results obtained for the Plankenburg and Diep Rivers.
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    Microbes at surface-air interfaces : the metabolic harnessing of relative humidity, surface hygroscopicity, and oligotrophy for resilience
    (Frontiers, 2016) Stone, Wendy; Kroukamp, Otini; Korber, Darren R.; McKelvie, Jennifer; Wolfaardt, Gideon M.
    The human environment is predominantly not aqueous, and microbes are ubiquitous at the surface-air interfaces with which we interact. Yet microbial studies at surface-air interfaces are largely survival-oriented, whilst microbial metabolism has overwhelmingly been investigated from the perspective of liquid saturation. This study explored microbial survival and metabolism under desiccation, particularly the influence of relative humidity (RH), surface hygroscopicity, and nutrient availability on the interchange between these two phenomena. The combination of a hygroscopic matrix (i.e., clay or 4,000 MW polyethylene glycol) and high RH resulted in persistent measurable microbial metabolism during desiccation. In contrast, no microbial metabolism was detected at (a) hygroscopic interfaces at low RH, and (b) less hygroscopic interfaces (i.e., sand and plastic/glass) at high or low RH. Cell survival was conversely inhibited at high RH and promoted at low RH, irrespective of surface hygroscopicity. Based on this demonstration of metabolic persistence and survival inhibition at high RH, it was proposed that biofilm metabolic rates might inversely influence whole-biofilm resilience, with ‘resilience’ defined in this study as a biofilm’s capacity to recover from desiccation. The concept of whole-biofilm resilience being promoted by oligotrophy was supported in desiccation-tolerant Arthrobacter spp. biofilms, but not in desiccation-sensitive Pseudomonas aeruginosa biofilms. The ability of microbes to interact with surfaces to harness water vapor during desiccation was demonstrated, and potentially to harness oligotrophy (the most ubiquitous natural condition facing microbes) for adaptation to desiccation.