Sensitivity of Legionella pneumophila to sunlight in fresh and marine waters

Effects of water turbidity on the survival of Staphylococcus aureus in environmental fresh and brackish waters

Staphylococcus aureus is an opportunistic pathogen frequently detected in environmental waters and commonly causes skin infections to water users. S. aureus concentrations in fresh, brackish, and marine waters are positively correlated with water turbidity. To reduce the risk of S. aureus infections from environmental waters, S. aureus survival (stability and multiplication) in turbid waters needs to be investigated. The aim of this study was to measure S. aureus in turbid fresh and brackish water samples and compare the concentrations over time to determine which conditions are associated with enhanced S. aureus survival. Eighteen samples were collected from fresh and brackish water sources from two different sites on the east side of O'ahu, Hawai'i. S. aureus was detected in microcosms for up to 71 days with standard microbial culturing techniques. On average, the greatest environmental concentrations of S. aureus were in high turbidity fresh waters followed by high turbidity brackish waters. Models demonstrate that salinity and turbidity significantly predict environmental S. aureus concentrations. S. aureus persistence over the extent of the experiment was the greatest in high turbidity microcosms with T90 's of 147.8 days in brackish waters and 80.8 days in freshwaters. This study indicates that saline, turbid waters, in the absence of sunlight, provides suitable conditions for enhanced persistence of S. aureus communities that may increase the risk of exposure in environmental waters. PRACTITIONER POINTS: Staphylococcus aureus concentrations, survival, and persistence were assessed in environmental fresh and brackish waters. Experimental design preserved in situ conditions to measure S. aureus survival. Higher initial S. aureus concentrations were observed in fresh waters with elevated turbidity, while sustained persistence was greater in brackish waters. Water turbidity and salinity were both positively associated with S. aureus concentrations and persistence. Climate change leads to more intense rainfall events which increase water turbidity and pathogen loading, heightening the exposure risk to S. aureus.

Legionella Occurrence beyond Cooling Towers and Premise Plumbing

Legionella is an environmental pathogen that is responsible for respiratory disease and is a common causative agent of water-related outbreaks. Due to their ability to survive in a broad range of environments, transmission of legionellosis is possible from a variety of sources. Unfortunately, a disproportionate amount of research that is devoted to studying the occurrence of Legionella in environmental reservoirs is aimed toward cooling towers and premise plumbing. As confirmed transmission of Legionella has been linked to many other sources, an over-emphasis on the most common sources may be detrimental to increasing understanding of the spread of legionellosis. This review aims to address this issue by cataloguing studies which have examined the occurrence of Legionella in less commonly investigated environments. By summarizing and discussing reports of Legionella in fresh water, ground water, saltwater, and distribution system drinking water, future environmental and public health researchers will have a resource to aid in investigating these pathogens in relevant sources.

Solar and Climate Effects Explain the Wide Variation in Legionellosis Incidence Rates in the United States

Legionellosis, an infection caused by the environmental bacteria Legionella spp., has become a significant public health problem in the United States in recent years; however, among the states, the incidence rates vary widely without a clear explanation. This study examined environmental effects on the 2014-to-2016 average annual legionellosis incidence rates in the U.S. states through correlative analyses with long-term precipitation, temperature, solar UV radiation, and sunshine hours. The continental states west of ∼95°W showed low incidence rates of 0.51 to 1.20 cases per 100,000 population, which corresponded to low precipitation, below 750 mm annually. For the eastern states, where precipitation was higher, solar effects were prominent and mixed, leading to wide incidence variation. Robust regressions suggested a dividing line at 40°N: north of this line, rising temperature, mainly from solar heat, raised legionellosis incidence to a peak of 4.25/100,000 in Ohio; south of the line, intensifying sunlight in terms of high UV indices and long sunshine hours prevailed to limit incidence gradually to 0.99/100,000 in Louisiana. On or near the 40°N line were 15 eastern states that had leading legionellosis incidence rates of >2.0/100,000. These states all showed modest environmental parameters. In contrast, the frigid climate in Alaska and the strong year-round solar UV in Hawaii explained the lowest U.S. incidences, 0.14/100,000 and 0.47/100,000, respectively, in these states. The findings of solar and climate effects explain the wide variation of legionellosis incidence rates in the United States and may offer insights into the potential exposure to and prevention of infection.IMPORTANCE Legionellosis, caused by the environmental bacteria Legionella spp., has become a significant public health problem in the United States in recent years, with ∼6,000 cases annually. The present study showed, through a series of correlative analyses with long-term precipitation, temperature, solar UV radiation, and sunshine hours, that these environmental conditions strongly influence the legionellosis incidence rates across the United States in mixed and dynamic fashions. The incidence rates varied remarkably by region, with the highest in Ohio and New York and the lowest in Alaska. A precipitation threshold above 750 mm was required for elevated legionellosis activity. Regression models and dividing lines between regions were established to show the promotive effect of temperature, as well as the inhibitive effects of solar UV and sunshine hours. These findings explain the wide variation of legionellosis incidence rates in the United States. They may also offer insights into potential exposure to and prevention of infection.

Sunlight-mediated inactivation of health-relevant microorganisms in water: a review of mechanisms and modeling approaches

Health-relevant microorganisms present in natural surface waters and engineered treatment systems that are exposed to sunlight can be inactivated by a complex set of interacting mechanisms. The net impact of sunlight depends on the solar spectral irradiance, the susceptibility of the specific microorganism to each mechanism, and the water quality; inactivation rates can vary by orders of magnitude depending on the organism and environmental conditions. Natural organic matter (NOM) has a large influence, as it can attenuate radiation and thus decrease inactivation by endogenous mechanisms. Simultaneously NOM sensitizes the formation of reactive intermediates that can damage microorganisms via exogenous mechanisms. To accurately predict inactivation and design engineered systems that enhance solar inactivation, it is necessary to model these processes, although some details are not yet sufficiently well understood. In this critical review, we summarize the photo-physics, -chemistry, and -biology that underpin sunlight-mediated inactivation, as well as the targets of damage and cellular responses to sunlight exposure. Viruses that are not susceptible to exogenous inactivation are only inactivated if UVB wavelengths (280-320 nm) are present, such as in very clear, open waters or in containers that are transparent to UVB. Bacteria are susceptible to slightly longer wavelengths. Some viruses and bacteria (especially Gram-positive) are susceptible to exogenous inactivation, which can be initiated by visible as well as UV wavelengths. We review approaches to model sunlight-mediated inactivation and illustrate how the environmental conditions can dramatically shift the inactivation rate of organisms. The implications of this mechanistic understanding of solar inactivation are discussed for a range of applications, including recreational water quality, natural treatment systems, solar disinfection of drinking water (SODIS), and enhanced inactivation via the use of sensitizers and photocatalysts. Finally, priorities for future research are identified that will further our understanding of the key role that sunlight disinfection plays in natural systems and the potential to enhance this process in engineered systems.

Viable Legionella pneumophila bacteria in natural soil and rainwater puddles

AIMS

For the majority of sporadic Legionnaires' disease cases the source of infection remains unknown. Infection may possible result from exposure to Legionella bacteria in sources that are not yet considered in outbreak investigations. Therefore, potential sources of pathogenic Legionella bacteria--natural soil and rainwater puddles on roads--were studied in 2012.

METHODS AND RESULTS

Legionella bacteria were detected in 30% (6/20) of soils and 3·9% (3/77) of rainwater puddles by amoebal coculture. Legionella pneumophila was isolated from two out of six Legionella positive soil samples and two out of three Legionella positive rainwater samples. Several other species were found including the pathogenic Leg. gormanii and Leg. longbeachae. Sequence types (ST) could be assigned to two Leg. pneumophila strains isolated from soil, ST710 and ST477, and one strain isolated from rainwater, ST1064. These sequence types were previously associated with Legionnaires' disease patients.

CONCLUSIONS

Rainwater and soil may be alternative sources for Legionella.

SIGNIFICANCE AND IMPACT OF THE STUDY

The detection of clinically relevant strains indicates that rainwater and soil are potential sources of Legionella bacteria and future research should assess the public health implication of the presence of Leg. pneumophila in rainwater puddles and natural soil.

Effects of Japan Sea Proper Water on the growth ofLegionella pneumophila, Escherichia coli, andStaphylococcus aureus

OBJECTIVE

To assess whetherLegionella pneumophila serogroup 1 and serogroup 6,Escherichia coli, andStaphylococcus aureus can survive in Japan Sea Proper Water (JSPW).

METHODS

The inhibitory effects of JSPW, surface seawater (SSW), phosphate buffer solution with 3.5% NaCl of pH 7.0 (3.5% NaCIPBS), and the 10(2)- and 10(4)-fold dilute solutions with purified water or phosphate buffer solution of pH 7.0, and purified water were investigated. Survival cells were counted immediately after the water and the bacteria were mixed, and at 1,3,5, and 7 days after incubation at 37°C. If the number of surviving cells was decreased more than 2 log units compared with the starting value, we judged the medium to have had an inhibitory effect on the growth of the bacteria.

RESULTS

The survival cells of the bacteria in JSPW had decreased more than 2 log units compared with the starting value at 1 day after incubation. After 1 day of incubation, the cells ofLegionella pneumophila serogroup 6 andStaphylococcus aureus were found to have decreased more than 2 log units in purified water (PW) used as a control. Furthermore,Legionella pneumophila serogroup 1 in the 10(2)-fold dilute solution of JSPW was only 1.04 log units lower than the starting value at 7 days after incubation. In the 10(2)- and 10(4)-fold dilute solutions of JSPW,Escherichia coli survived for 7 days after incubation. These results were almost similar to the results in SSW and 3.5% NaCIPBS.

CONCLUSIONS

The present findings demonstrate thatLegionella pneumophila serogroup 1 andEscherichia coli cannot survive in undiluted JSPW for over a day at 37°C, suggesting the inhibitory effects may be due to the sodium chloride contained in JSPW.

Amoebae and Legionella pneumophila in saline environments

Amoeboid protists that harbor bacterial pathogens are of significant interest as potential reservoirs of disease-causing organisms in the environment, but little is known about them in marine and other saline environments. We enriched amoeba cultures from sediments from four sites in the New England estuarine system of Mt. Hope Bay, Massachusetts and from sediments from six sites in the Great Salt Lake, Utah. Cultures of amoebae were enriched using both minimal- and non-nutrient agar plates, made with fresh water, brackish water or saltwater. Recovered amoeba cultures were assayed for the presence of Legionella species using nested polymerase chain reactions (PCR) and primers specific for the genus. Positive samples were then screened with nested amplification using primers specific for the macrophage infectivity potentiator surface protein (mip) gene from L. pneumophila. Forty-eight percent (185 out of 388) of isolated amoeba cultures were positive for the presence of Legionella species. Legionella pneumophila was detected by PCR in 4% of the amoeba cultures (17 out of 388), and most of these amoebae were growing on marine media. Our results show that amoebae capable of growing in saline environments may harbor not only a diverse collection of Legionella species, but also species potentially pathogenic to humans.