Traditional Microbial Indicators Research Articles

Assessment of Human Health Risks in Tropical Environmental Waters with Microbial Source Tracking Markers

Human specific microbial source tracking (MST) markers which are highly specific to human waste contamination offer the advantage of better association with human pathogens than traditional microbial indicators. However, the performance of these MST markers may vary across different geographical regions. The magnitude of MST markers also plays an important role in interpreting the health risks. This study aims to (i) validate the specificity and sensitivity of human markers for tropical urban catchments; (ii) identify the threshold concentrations of MST markers, i.e. human polyomaviruses (HPyVs), Bacteroides thetaiotaomicron (B. theta) and Methanobrevibacter smithii (M. smithii), that correspond to the acceptable gastrointestinal (GI) illness risks associated with swimming using the QMRA approach; and (iii) validate the threshold concentrations of MST markers using the surveillance data obtained from the tropical urban environment. Among the three MST markers, HPyVs showed the highest specificity (100%) to sewage samples, followed by M. smithii (97%) and B. theta (90%). All MST markers showed 100% sensitivity towards sewage contamination, with B. theta present in highest abundance in sewage, followed by HPyVs and M. smithii. This study demonstrates a risk-based framework to identify the threshold concentrations of MST markers associated with GI illness risks in environmental waters by considering two main influencing factors (i.e. decay and dilution factors). This study successfully validated the B. theta threshold concentration range (581 to 8073 GC/100 mL) with field data (370 to 6500 GC/100 mL) in estimating GI illness risks with an Enterococcus model. Field data showed that the MST markers at threshold concentrations were able to classify the safe level in more than 83% of the samples, according to GI illness risks from Enterococcus and adenovirus. The study also highlighted the lack of associations between MST markers and GI illness risks from norovirus. With comprehensive information on specificity, sensitivity and threshold concentrations of MST markers, increasing confidence can be placed on identifying human source contamination and evaluating the health risks posed in environmental waters in Singapore.

A Structural Equation Model to Decipher Relationships among Water, Sanitation, and Health in Colonias-Type Unincorporated Communities.

The colonias along the United States-Mexico border are generally self-built neighborhoods of low-income families that lack basic infrastructure. While some government assistance has provided roads and electricity, water and wastewater services are still lacking in many colonias. This research is the first to collect a comprehensive dataset on water, sanitation, health, and living conditions in these unincorporated neighborhoods through collection of water samples and surveys; 114 households in 23 colonias across three geographically diverse Texas counties are studied. Water quality is assessed via traditional microbial indicators, chlorine, and arsenic. This complex dataset requires an advanced statistical tool to disentangle relationships among diverse factors. Structural equation modeling is utilized to identify relationships among surveyed and measured variables. The model reveals that colonias residents with well/hauled water accurately predict their water quality, while those with treated+piped water tend to think that their water is worse than it actually is. Dwelling quality and connection to sanitary sewers influence perceived health risks and household health, respectively. Furthermore, these communities have an overwhelming need and desire for point-of-use water treatment. This model can inform decision making and may be adapted to probe other questions and social dynamics for water and sanitation in unincorporated communities elsewhere.

Assessing the microbial quality of a tropical watershed with an urbanization gradient using traditional and alternate fecal indicators

Urbanization affects the microbial loading into tropical streams, but its impact on water quality varies across watersheds. Rainfall in tropical environments also complicates microbial dynamics due to high seasonal and annual variations. Understanding the dynamics of fecal contamination in tropical surface waters may be further hindered by limitations from the utilization of traditional microbial indicators. We measured traditional (Enterococcus spp. and Escherichia coli), as well as alternate (enterophages and coliphages) indicators of fecal contamination in a tropical watershed in Puerto Rico during a 1-year period, and examined their relationship with rainfall events across an urbanization gradient. Enterococcus spp. and E. coli concentrations were 4 to 5 logs higher in non-urbanized or pristine sites when compared to enterophages and coliphages, suggesting that traditional fecal indicator bacteria may be natural inhabitants of pristine tropical waters. All of the tested indicators were positively correlated with rainfall and urbanization, except in the most urbanized sites, where rainfall may have had a dilution effect. The present study indicates that utilizing novel indicators of microbial water quality may improve the assessment of fecal contamination and pathogen risk for tropical watersheds.

Alternative fecal indicators and their empirical relationships with enteric viruses, Salmonella enterica, and Pseudomonas aeruginosa in surface waters of a tropical urban catchment.

The suitability of traditional microbial indicators (i.e., Escherichia coli and enterococci) has been challenged due to the lack of correlation with pathogens and evidence of possible regrowth in the natural environment. In this study, the relationships between alternative microbial indicators of potential human fecal contamination (Bacteroides thetaiotaomicron, Methanobrevibacter smithii, human polyomaviruses [HPyVs], and F+ and somatic coliphages) and pathogens (Salmonella spp., Pseudomonas aeruginosa, rotavirus, astrovirus, norovirus GI, norovirus GII, and adenovirus) were compared with those of traditional microbial indicators, as well as environmental parameters (temperature, conductivity, salinity, pH, dissolved oxygen, total organic carbon, total suspended solids, turbidity, total nitrogen, and total phosphorus). Water samples were collected from surface waters of urban catchments in Singapore. Salmonella and P. aeruginosa had significant positive correlations with most of the microbial indicators, especially E. coli and enterococci. Norovirus GII showed moderately strong positive correlations with most of the microbial indicators, except for HPyVs and coliphages. In general, high geometric means and significant correlations between human-specific markers and pathogens suggest the possibility of sewage contamination in some areas. The simultaneous detection of human-specific markers (i.e., B. thetaiotaomicron, M. smithii, and HPyVs) with E. coli and enterococcus supports the likelihood of recent fecal contamination, since the human-specific markers are unable to regrow in natural surface waters. Multiple-linear-regression results further confirm that the inclusion of M. smithii and HPyVs, together with traditional indicators, would better predict the occurrence of pathogens. Further study is needed to determine the applicability of such models to different geographical locations and environmental conditions.

Degradation of faecal sterols in urine for assessment of faecal cross-contamination in source-separated human urine and urine storage tank sediment

The degradation of the faecal sterol coprostanol and its precursor cholesterol, were determined in source-separated human urine and urine tank sediment. The aim was to assess their potential as biomarkers of faecal cross-contamination in source-separated waste systems since traditional microbial indicators have been shown not to be reliable in this context. Investigations were performed at 4 and 20°C in collected human urine and urine tank sediment to which human faeces and synthetic cholesterol and coprostanol were added. The individual degradation experiments were performed over periods of up to 118 days and represented a wide concentration range both for the urine and the urine tank sediment. Coprostanol showed no significant degradation in either the urine or urine tank sediment when faeces or synthetic coprostanol were added. Neither the normalised variance for the individual slopes, nor the combined regression analysis showed any significant difference from the common slope of zero. For cholesterol no significant degradation was found in the urine tank sediment, but based on pooled data, a moderate decrease occurred in the urine. This was most evident for endogenous cholesterol in the urine at low concentrations where 38 and 55% of the original amounts were lost at 4 and 20°C, respectively. The daily rate of loss of cholesterol based on the regression analysis was 0.73 μg l −1 per day. It is concluded that amounts of coprostanol in urine collection tanks can be used as an indicator of faecal cross-contamination cumulatively occurring over the collection period. Together with die-off data of indicator organisms and pathogens, establishment of a baseline risk assessment would now be possible in relation to storage, handling and reuse of the urine.

Use of lux-based biosensors for rapid diagnosis of pollutants in arable soils

A field trial, in Central Scotland, demonstrated that crop yields were reduced with increased application of paper mill sludge to land. A suite of ecotoxicity assays, including, luminescence response of lux-marked bacteria, respirometry and enzyme activity was used to assess toxicity of the paper mill sludge to the soil microbial biomass. The results from the use of the lux based biosensors correlated well with more traditional microbial indicators of soil pollution (respiration and enzyme activity). Concentrations of metals and organic contaminants in samples were confirmed using GFAAS and GC-MS, respectively. The main pollutant components of paper mill sludge were found to be Cd, Cu and PCP (pentachlorophenol). The range of environmental bioassays used, with chemical verification, was shown to offer a rapid and comprehensive battery test for rapid assessment of the ecotoxicity associated with papermill sludge application to land.

Inactivation of Health-Related Microorganisms in Water by Disinfection Processes

The recent literature on disinfection of health-related microorganisms in water and wastewater is reviewed. There is now considerable evidence that traditional microbial indicators of water and wastewater quality, such as total and fecal coliform bacteria, are inadequate to predict the presence or disinfection responses of several important, newly recognized bacterial, viral and protozoan pathogens. This review emphasizes the response to disinfection of waterborne microbial pathogens and potential indicators of recent recognition and public health concern. These organisms include heterotrophic plate count (HPC) bacteria, frank and opportunistic bacterial pathogens, such as Campylobacter jejuni, Yersinia enterocolytica, non-tubercular mycobacteria, Legionella spp. and pseudomonads; coliphage indicators and enteric viral pathogens, such as hepatitis A virus, rotaviruses and Norwalk virus; and protozoan pathogens, such as Giardia lamblia, Cryptosporidium, and the free-living amoeba (e.g., Acanthamoeba spp. and Negleria spp.). The responses of these organisms to widely used, traditional disinfectants, such as free and combined chlorine, and to disinfectants of more recent interest, such as ozone, chlorine dioxide and ultraviolet light, are reviewed. This review also attempts to identify the variety of factors influencing disinfection efficiency, especially those that interfere with disinfection. It is apparent that traditional microbial indicators, such as total and fecal coliforms, are more sensitive to disinfection than such pathogens of recent concern as mycobacteria, enteric viruses and protozoan cysts. Therefore, efforts must be continued to find more reliable indicators of disinfection efficiency and microbial water quality and improved methods for water and wastewater disinfection.