Microbiological safety of drinking water: United States and global perspectives

Legionella: A Promising Supplementary Indicator of Microbial Drinking Water Quality in Municipal Engineered Water Systems

Opportunistic pathogens (OPs) are natural inhabitants and the predominant disease causative biotic agents in municipal engineered water systems (EWSs). In EWSs, OPs occur at high frequencies and concentrations, cause drinking-water-related disease outbreaks, and are a major factor threatening public health. Therefore, the prevalence of OPs in EWSs represents microbial drinking water quality. Closely or routinely monitoring the dynamics of OPs in municipal EWSs is thus critical to ensuring drinking water quality and protecting public health. Monitoring the dynamics of conventional (fecal) indicators (e.g., total coliforms, fecal coliforms, and Escherichia coli) is the customary or even exclusive means of assessing microbial drinking water quality. However, those indicators infer only fecal contamination due to treatment (e.g., disinfection within water utilities) failure and EWS infrastructure issues (e.g., water main breaks and infiltration), whereas OPs are not contaminants in drinking water. In addition, those indicators appear in EWSs at low concentrations (often absent in well-maintained EWSs) and are uncorrelated with OPs. For instance, conventional indicators decay, while OPs regrow with increasing hydraulic residence time. As a result, conventional indicators are poor indicators of OPs (the major aspect of microbial drinking water quality) in EWSs. An additional or supplementary indicator that can well infer the prevalence of OPs in EWSs is highly needed. This systematic review argues that Legionella as a dominant OP-containing genus and natural inhabitant in EWSs is a promising candidate for such a supplementary indicator. Through comprehensively comparing the behavior (i.e., occurrence, growth and regrowth, spatiotemporal variations in concentrations, resistance to disinfectant residuals, and responses to physicochemical water quality parameters) of major OPs (e.g., Legionella especially L. pneumophila, Mycobacterium, and Pseudomonas especially P. aeruginosa), this review proves that Legionella is a promising supplementary indicator for the prevalence of OPs in EWSs while other OPs lack this indication feature. Legionella as a dominant natural inhabitant in EWSs occurs frequently, has a high concentration, and correlates with more microbial and physicochemical water quality parameters than other common OPs. Legionella and OPs in EWSs share multiple key features such as high disinfectant resistance, biofilm formation, proliferation within amoebae, and significant spatiotemporal variations in concentrations. Therefore, the presence and concentration of Legionella well indicate the presence and concentrations of OPs (especially L. pneumophila) and microbial drinking water quality in EWSs. In addition, Legionella concentration indicates the efficacies of disinfectant residuals in EWSs. Furthermore, with the development of modern Legionella quantification methods (especially quantitative polymerase chain reactions), monitoring Legionella in ESWs is becoming easier, more affordable, and less labor-intensive. Those features make Legionella a proper supplementary indicator for microbial drinking water quality (especially the prevalence of OPs) in EWSs. Water authorities may use Legionella and conventional indicators in combination to more comprehensively assess microbial drinking water quality in municipal EWSs. Future work should further explore the indication role of Legionella in EWSs and propose drinking water Legionella concentration limits that indicate serious public health effects and require enhanced treatment (e.g., booster disinfection).

Structure and Functional Attributes of Bacterial Communities in Premise Plumbing Across the United States

Microbes that thrive in premise plumbing can have potentially important effects on human health. Yet, how and why plumbing-associated microbial communities vary across broad spatial scales remain undetermined. We characterized the bacterial communities in 496 showerheads collected from across the continental United States. The overall community structure, determined by 16S rRNA gene amplicon sequencing, revealed high levels of bacterial diversity. Although a large fraction of the observed variation in community composition could not be explained, differences in bacterial community composition were associated with water supply (private well water vs public municipal water), water source (groundwater vs surface water), and associated differences in water chemistry (pH and chlorine). Most notably, showerheads in homes supplied with public water had higher abundances of Blastomonas, Mycobacterium, and Porphyrobacter, while Pseudorhodoplanes, Novosphingobium, and Nitrospira were more abundant in those receiving private well water. We conducted shotgun metagenomic analyses on 92 of these samples to assess differences in genomic attributes. Public water-sourced showerheads had communities enriched in genes related to lipid and xenobiotic metabolisms, virulence factors, and antibiotic resistance. In contrast, genes associated with oxidative stress and membrane transporters were over-represented in communities from private well water-sourced showerheads compared to those supplied by public water systems. These results highlight the broad diversity of bacteria found in premise plumbing across the United States and the role of the water source and treatment in shaping the microbial community structure and functional potential.

Green sol-gel synthesis of novel nanoporous copper aluminosilicate for the eradication of pathogenic microbes in drinking water and wastewater treatment

We used a green sol-gel synthesis method to fabricate a novel nanoporous copper aluminosilicate (CAS) material. Nanoporous CAS was characterized using X-ray powder diffraction (XRD), field emission transmission and scanning electron microscopies (FE-TEM/FE-SEM), Fourier transform infrared (FTIR) spectroscopy, and optical analyses. The CAS was also evaluated for use as a promising disinfectant for the inactivation of waterborne pathogens. The antimicrobial action and minimum inhibitory concentration (MIC) of this CAS disinfectant were determined against eight microorganisms (Escherichia coli, Salmonella enterica, Pseudomonas aeruginosa, Listeria monocytogenes, Staphylococcus aureus, Enterococcus faecalis, Candida albicans, and Aspergillus niger). An antimicrobial susceptibility testing of CAS was measured. Results of disc diffusion method pointed out that the diameters of the zone using well diffusion were wider than disc diffusion methods, and the findings also showed that the MIC of the CAS disinfectant against E. coli, S. enterica, and P. aeruginosa was 100 mg/L within 20 min of contact time. Meanwhile, the MIC of the CAS disinfectant was 100 mg/L within 40 min of contact time for the other strains. The efficacy of antimicrobial action (100%) reached within 20 to 40 min against all tested microbes. Herein, the antimicrobial susceptibility testing of CAS disinfectant showed no toxicity for human and bacterial cells. It can be concluded that nanoporous CAS is a promising, economically, and worthy weapon for water disinfection.

Cross-Resistance of UV- or Chlorine Dioxide-Resistant Echovirus 11 to Other Disinfectants

The emergence of waterborne viruses with resistance to disinfection has been demonstrated in the laboratory and in the environment. Yet, the implications of such resistance for virus control remain obscure. In this study we investigate if viruses with resistance to a given disinfection method exhibit cross-resistance to other disinfectants. Chlorine dioxide (ClO₂)- or UV-resistant populations of echovirus 11 were exposed to five inactivating treatments (free chlorine, ClO₂, UV radiation, sunlight, and heat), and the extent of cross-resistance was determined. The ClO₂-resistant population exhibited cross-resistance to free chlorine, but to none of the other inactivating treatments tested. We furthermore demonstrated that ClO₂ and free chlorine act by a similar mechanism, in that they mainly inhibit the binding of echovirus 11 to its host cell. As such, viruses with host binding mechanisms that can withstand ClO₂ treatment were also better able to withstand oxidation by free chlorine. Conversely, the UV-resistant population was not significantly cross-resistant to any other disinfection treatment. Overall, our results indicate that viruses with resistance to multiple disinfectants exist, but that they can be controlled by inactivating methods that operate by a distinctly different mechanism. We therefore suggest to utilize two disinfection barriers that act by different mechanisms in order to control disinfection-resistant viruses.

The influence of biofilm structure and total interaction energy on Escherichia coli retention by Pseudomonas aeruginosa biofilm

The retention of a surrogate pathogenic bacterium, Escherichia coli(T) , in Pseudomonas aeruginosa biofilms (with various EPS excreting capacities) was investigated using a laboratory flow cell system. The structural characteristics of the biofilm, as well as the quantity of E. coli(T) retained in the biofilm, were assessed using confocal laser scanning microscopy coupled with image analysis. In addition, the total interaction energy between E. coli(T) and the P. aeruginosa biofilm was computed with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, which provided an additional context to explain the pathogen interaction in aquatic biofilms. The correlations between the quantity of detained E. coli(T) cells and the structural characteristics of the biofilm were analysed and the results indicated that the heterogeneity of the biofilm could create a quiescent zone leading to temporary retention of E. coli(T) within the biofilm. Overall, this study provided insights toward understanding the retention of pathogenic bacteria in environmental biofilms.

High throughput, real-time detection of Naegleria lovaniensis in natural river water using LED-illuminated Fountain FlowTMCytometry

AIMS

To test Fountain Flow Cytometry (FFC) for the rapid and sensitive detection of Naegleria lovaniensis amoebae (an analogue for Naegleria fowleri) in natural river waters.

METHODS AND RESULTS

Samples were incubated with one of two fluorescent labels to facilitate detection: ChemChrome V6, a viability indicator, and an R-phycoerytherin (RPE) immunolabel to detect N. lovaniensis specifically. The resulting aqueous sample was passed as a stream in front of a light-emitting diode, which excited the fluorescent labels. The fluorescence was detected with a digital camera as the sample flowed toward the imager. Detections of N. lovaniensis were made in inoculated samples of natural water from eight rivers in France and the United States. FFC enumeration yielded results that are consistent with other counting methods: solid-phase cytometry, flow cytometry, and hemocytometry, down to concentrations of 0.06 amoebae ml(-1), using a flow rate of 15 ml min(-1).

CONCLUSIONS

This study supports the efficacy of using FFC for the detection of viable protozoa in natural waters and indicates that use of RPE illuminated at 530 nm and detected at 585 nm provides a satisfactory means of attenuating background.

SIGNIFICANCE AND IMPACT OF THE STUDY

Because of the severe global public health issues with drinking water and sanitation, there is an urgent need to develop a technique for the real-time detection of viable pathogens in environmental samples at low concentrations. FFC addresses this need.

The role of water use patterns and sewage pollution in incidence of water-borne/enteric diseases along the Ganges river in Varanasi, India

In Varanasi, India, an estimated 200 million liters daily or more of untreated human sewage is discharged into the Ganges River. River water monitoring over the past 12 years has demonstrated faecal coliform counts up to 10(8) MPN (most probable number) per 100 ml and biological oxygen demand levels averaging over 40 mg/l in the most polluted part of the river in Varanasi. A questionnaire-based survey was used to estimate water-borne and enteric disease incidence and study river use among resident users of the Ganges River in Varanasi. The overall rate of water-borne/enteric disease incidence, including acute gastrointestinal disease, cholera, dysentery, hepatitis-A, and typhoid, was estimated to be about 66% during the one-year period prior to the survey. Logistic regression analysis revealed significant associations between water-borne/enteric disease occurrence and the use of the river for bathing, laundry, washing eating utensils, and brushing teeth. Thirty-three cases of cholera were identified among families exposed to washing clothing or bathing in the Ganges while no cholera cases occurred in unexposed families. Other exposure factors such as lack of sewerage and toilets at residence, children defecating outdoors, poor sanitation, low income and low education levels also showed significant associations with enteric disease outcome. This study provides an estimate of water-borne/enteric disease incidence and identifies possible risk factors for residents who live by and use the Ganges River in Varanasi.

Chromosome damage in peripheral lymphocytes of sheep induced by chlorine in drinking water

The potential of chromosomal damage associated with the effects of chlorine in drinking water was evaluated using chromosome aberrations and micronuclei as cytogenetic endpoints in the lymphocytes of peripheral blood of ewe lambs. The study assessed the in vivo effects of high chlorine doses (1.8 mg l(-1), based on Savo-Super disinfectant) in drinking water on the peripheral lymphocytes of sheep after 30 days. The frequency of aberrant cells (AB.C.) in the experimental and control groups was 31.80+/-13.68% AB.C. and 4.50+/-2.07% AB.C. respectively, and the increased AB.C. in the treated group was highly significant (P=/<0.001). In the experimental group chromatid breaks (26.20+/-10.47%) and gaps (24.20+/-13.94%) were the dominant types of aberrations, but statistically significant chromosome gaps and exchanges were also present. The frequency of micronuclei in peripheral lymphocytes of sheep in the control group was 21.17+/-4.36 per 1,000 binucleated cells and 64.20+/-22.51 per 1,000 binucleated cells in the experimental group. A significant increase in the frequency of micronuclei in peripheral lymphocytes of sheep was observed between the two groups (P=0.001).

Water usage patterns in low-income urban communities in Uganda: implications for water supply surveillance

The selection of water sources by poor households in three urban areas in Uganda is shown to be complex, with a range of communal water sources used. In all towns, significant numbers of households used multiple sources. An aggregated estimate of the level of use in the largest town, Kampala, showed little difference in the number of households collecting water from piped and non-piped sources. In the other towns, households in Soroti were more likely to use point sources than piped water and in Masaka most households used piped water, with unprotected sources the most common subsidiary source. Differentiation in use by source type was evaluated. In two of the towns no differentiation in use is seen. In Soroti, some differentiation in use is seen as the water from boreholes is widely used for drinking and that from other sources less frequently consumed. Supplemental water purchased from vendors was relatively uncommon in the towns, but two towns showed that many households collect rainwater for domestic use. The implications of these findings for the drinking water surveillance programme are discussed.