Patricia A. Rusin

Risk Assessment of Opportunistic Bacterial Pathogens in Drinking Water

This study was undertaken to examine quantitatively the risks to human health posed by heterotrophic plate count (HPC) bacteria found naturally in ambient and potable waters. There is no clear-cut evidence that the HPC bacteria as a whole pose a public health risk. Only certain members are opportunistic pathogens. Using the four-tiered approach for risk assessment from the National Academy of Sciences, hazard identification, dose-response modeling, and exposure through ingestion of drinking water were evaluated to develop a risk characterization, which estimates the probability of infection for individuals consuming various levels of specific HPC bacteria. HPC bacteria in drinking water often include isolates from the following genera: Pseudomonas, Acinetobacter, Moraxella, Aeromonas, and Xanthomonas. Other bacteria that are commonly found are Legionella and Mycobacterium. All these genera contain species that are opportunistic pathogens which may cause serious diseases. For example, the three nonfermentative gram-negative rods most frequently isolated in the clinical laboratory are (1) Pseudomonas aeruginosa, (2) Acinetobacter, and (3) Xanthomonas maltophilia. P. aeruginosa is a major cause of hospital-acquired infections with a high mortality rate. Aeromonas is sometimes associated with wound infections and suspected to be a causative agent of diarrhea. Legionella pneumophila causes 4%-20% of cases of community-acquired pneumonia and has been ranked as the second or third most frequent cause of pneumonia requiring hospitalization. The number of cases of pulmonary disease associated with Mycobacterium avian is rapidly increasing and is approaching the incidence of M. tuberculosis in some areas. Moraxella can cause infections of the eye and upper respiratory tract. The oral infectious doses are as follows in animal and human test subjects: P. aeruginosa, 10(8)-10(9); A, hydrophila, > 10(10); M. avium, 10(4)-10(7); and X. maltophilia, 10(6)-10(9). The infectious dose for an opportunistic pathogen is lower for immunocompromised subjects or those on antibiotic treatment. These bacteria have been found in drinking water at the following frequencies: P. aeruginosa, < 1%-24%; Acinetobacter, 5%-38%; X. maltophilia, < 1%-2%; Aeromonas, 1%-27%; Moraxella, 10%-80%; M. avium, < 1%-50%; and L. pneumophila, 3%-33%. These data suggest that drinking water could be a source of infection for some of these bacteria. The risk characterization showed that risks of infection from oral ingestion ranged from a low of 7.3 x 10(-9) (7.3/billion) for low exposures to Aeromonas to higher risks predicted at high levels of exposure to Pseudomonas of 9 x 10(-2) (98/100). This higher risk was only predicted for individuals on antibiotics. Overall, the evidence suggests that specific members of HPC bacteria found in drinking water may be causative agents of both hospital- and community-acquired infections. However, the case numbers may be very low and the risks represent levels generally less than 1/10,000 for a single exposure to the bacterial agent. Future research needs include (1) determining the seasonal concentrations of these bacteria in drinking water, (2) conducting adequate dose-response studies in animal subjects or human volunteers, (3) determining the health risks for an individual with multiple exposures to the opportunistic pathogens, and (4) evaluating the increase in host susceptibility conferred by antibiotic use or immunosuppression.

Reduction of faecal coliform, coliform and heterotrophic plate count bacteria in the household kitchen and bathroom by disinfection with hypochlorite cleaners

Fourteen sites evenly divided between the household kitchen and bathroom were monitored on a weekly basis for numbers of faecal coliforms, total coliforms and heterotrophic plate count bacteria. The first 10 weeks comprised the control period, hypochlorite cleaning products were introduced into the household during the second 10 weeks, and a strict cleaning regimen using hypochlorite products was implemented during the last 10 weeks. The kitchen was more heavily contaminated than the bathroom, with the toilet seat being the least contaminated site. The highest concentrations of all three classes of bacteria were found on sites that were moist environments and/or were frequently touched; these included the sponge/dishcloth, the kitchen sink drain area, the bath sink drain area, and the kitchen faucet handle(s). The implementation of a cleaning regimen with common household hypochlorite products resulted in the significant reduction of all three classes of bacteria at these four sites and other household sites.

Solubilization of plutonium hydrous oxide by iron-reducing bacteria

The removal of plutonium from soils id challenging because of its strong sorption to soils and limited solubility, Microbial reduction of metals is known to affect the speciation and solubility of sparingly soluble metals in the environment, notably iron and manganese. The similarity in reduction potential for [alpha]-FeOOH(s) and hydrous PuO[sub 2](s) suggests that iron-reducing bacteria may also reduce and solubilize plutonium. Bacillus strains were used to demonstrate that iron-reducing bacteria mediate the solubilization of hydrous PuO[sub 2](s) under anaerobic conditions. Up to [approximately]90% of the PuO[sub 2] was biosolubilized in the presence of nitrilotriacetic acid (NTA) within 6-7 days. Biosolubilization occurred to a lesser extent ([approximately] 40%) in the absence of NTA. Little PuO[sub 2] solubilization occurred in sterile culture media or in the presence of a non-iron-reducing Escherichia coli. These observations suggest a potentially attractive, environmentally benign strategy for the remediation of Pu-contaminated soils. 26 refs., 5 figs., 2 tabs.

Quantitative assessment of risk reduction from hand washing with antibacterial soaps

The Centers for Disease Control and Prevention have estimated that there are 3,713,000 cases of infectious disease associated with day care facilities each year. The objective of this study was to examine the risk reduction achieved from using different soap formulations after diaper changing using a microbial quantitative risk assessment approach. To achieve this, a probability of infection model and an exposure assessment based on micro-organism transfer were used to evaluate the efficacy of different soap formulations in reducing the probability of disease following hand contact with an enteric pathogen. Based on this model, it was determined that the probability of infection ranged from 24/100 to 91/100 for those changing diapers of babies with symptomatic shigellosis who used a control product (soap without an antibacterial ingredient), 22/100 to 91/100 for those who used an antibacterial soap (chlorohexadine 4%), and 15/100 to 90/100 for those who used a triclosan (1.5%) antibacterial soap. Those with asymptomatic shigellosis who used a non-antibacterial control soap had a risk between 49/100,000 and 53/100, those who used the 4% chlorohexadine-containing soap had a risk between 43/100,000 and 51/100, and for those who used a 1.5% triclosan soap had a risk between 21/100,000 and 43/100. The adequate washing of hands after diapering reduces risk and can be further reduced by a factor of 20% by the use of an antibacterial soap. Quantitative risk assessment is a valuable tool in the evaluation of household sanitizing agents and low risk outcomes.

Rapid reduction of Legionella pneumophila on stainless steel with zeolite coatings containing silver and zinc ions

Aims: To determine the rate of reduction of Legionella pneumophila by stainless steel surfaces with zeolite ceramic coatings containing 2·5% (w/w) silver (Ag) and 14% zinc (Zn) ions.

Health significance of pigmented bacteria in drinking water

The purpose of this study was to determine the relative health risks of pigmented bacteria found in drinking water samples. These pigmented bacteria include opportunistic pathogens such as Flavobacterium, Pseudomonas, Corynebacterium, Nocardia, Mycobacterium, Erwinia, Enterobacter, Serratia, and Micrococcus. Flavobacterium meningosepticum is the most clinically important of the flavobacteria but causes Pseudomonas aeruginosa is an important opportunistic pathogen causing >10% of nosocomial infections. Human feeding tests show that oral doses of 10 6 to 10 8 CFU results in colonisation of the gastrointestinal (GI) tract but do not produce any morbidity in healthy volunteers. Corynebacteria rarely cause disease except for toxigenic C. diphtheriae which is non-pigmented on R2A agar. The most important member of Nocardia is N. asteroides which is an opportunistic pathogen for certain immunocompromised population segments. National surveys show that only 9.2–19.2% of mycobacterial clinical isolates are pigmented with M. kansasii being the most frequent (4–10%). This bacterium is associated with disease but would not be detected as part of the HPC bacteria using a 7d incubation period. Pigmented strains of Erwinia, Enterobacter, Serratia , and Micrococcus can cause disease but they are relatively unimportant compared to other pathogenic bacteria as shown in ranking studies.

Microbiological damage of cellulose acetate RO membranes

Abstract Based on the data presented in this study, microorganisms can degrade wet cellulose acetate (CA) reverse osmosis (RO) membranes during shutdown periods or under storage conditions. Fungal (and perhaps bacterial) metabolism of the membranes was measured from CA membranes using the 14 C isotope. Using uniformly labeled 14 C cellulose as the starting compound, CA polymer was synthesized, casting solutions were made, and CA membranes were produced. After inoculating membrane samples with the microorganisms, the metabolism of the membranes was confirmed by measuring isotopically enriched carbon dioxide gas produced either by the respiration under aerobic or anaerobic conditions using the Krebs metabolic cycle or by fermentation. Results show that the dense zone of the asymmetric membrane, where desalting occurs, could be compromised in 3 months or less. Membrane samples that were treated by sanding and hydrolyzing the surface to simulate a “used” membrane, degraded at a faster rate than new membranes. Removing oxygen from the system failed to slow or stop the rate of growth. Data showed that no “special” fungus from the RO industry is unique in degrading CA membrane. Instead, all organisms tested degraded these membranes, including microorganisms found in the biofilms from a field RO system and microorganisms present as laboratory contaminates.

Physiology and kinetics of manganese‐reducing bacillus polymyxa strain D1 isolated from manganiferous silver ore

Abstract Manganese‐reducing bacteria were isolated from a manganiferous silver ore mining site using enrichment procedures. The most rapid Mn(IV) reducer was identified as Bacillus polymyxa and was designated as strain D1. Isolate D1 has no growth‐factor requirements and is mesophilic and neutrophilic. D1 respires glucose aerobically, under which conditions cyanide is bactericidal. Nonfermentable substrates such as lactate, acetate, citrate, and succinate cannot serve as sole carbon sources. D1 ferments glucose anaerobically, producing acetic acid, ethanol, and butanediol as major metabolic end products. Both anaerobic conditions and direct physical contact with pyrolusite (MnO2) particles were necessary for manganese reduction. Strain D1 is unique in that manganese serves as an ancillary electron acceptor during anaerobic fermentation. Kinetic experiments showed that D1 reduced manganese three to five times as rapidly as the widely studied Mn(IV)/Fe(III)‐reducing microorganisms Shewanella putrefaciens MR...

Microbial source tracking of Escherichia coli in a constructed wetland.

Little information has been gathered on the effect of avian species on the microbial water quality in constructed wetlands. To address this concern, fecal pollution from nonpoint and point sources was evaluated in a constructed wetland in Tolleson, Arizona. Antibiotic resistance profiling and biochemical fingerprinting were performed on 325 Escherichia coli isolates, collected from key points in the wetlands. Multivariate statistical analysis was used to interpret the data for samples collected on October 3 and December 12, 2000, and January 16, 2001. It was found that the passerine population was the major source of the Escherichia coli in the water samples collected in the wetlands on October 3 and December 12, 2000, whereas the regrowth in the treated municipal wastewater was the main source on January 16, 2001. This information is useful in providing data for operators in the monitoring of wetlands created for wastewater treatment and wildlife habitat.

Isolation and physiology of a manganese-reducing Bacillus polymyxa from an Oligocene silver-bearing ore and sediment with reference to Precambrian biogeochemistry

Abstract Samples from an Oligocene silver-bearing manganese ore mining site in Saguochi country, Colorado were screened for bacteria which solubilize manganese in the refractory ore thus making the silver more amenable to standard extraction techniques. Over 300 bacterial isolates were tested. Manganese reduction was detected by growing the organisms in a mineral salts medium supplemented with the insoluble MnO2 (pyrolusite). Reduction of the black MnO2 resulted in the formation of colorless solubilized Mn2+. One of the most efficient manganese reducers was a Bacillus polymyxa strain D1. This bacterium was isolated from the ore heap and from a zone 5 cm below the sediment surface of the inlet which drained ore heap leachate into a holding pond. Isolate D1 has a unique mode of manganese reduction as shown by the following combination of characteristics: (1) anaerobiosis is absolutely necessary; (2) direct surface contact with the mineral particle is required; (3) facultative fermentation occurs concomitantly with manganese reduction; and (4) Mn4+ does not substitute for O2 at the end of the respiratory electron transport chain. Although the ore deposit is approximately 35-30 Ma old, D1 probably have first appeared at the site contemporaneous with mining activities as evidenced by its resistance to exogenous zinc used in the silver extractive process. If organisms such as D1 were present > 600 Ma ago they could have played a role in the Precambrian manganese cycle as they do in the Holocene. Encrustations of MnO2 have been found in Precambrian sediments which are thought to be biogenic in origin. Solubilized reduced Mn2+ must also have been present to serve as a substrate. Anaerobic conditions alone are insufficient for the reduction of manganese dioxide, therefore, it is likely that manganese reduction was due, in part, to microbial activity. Solubilization of manganese occurs via microbial dissimilatory reduction as seen with isolate D1. Precipitation results from oxidation of manganese coupled to ATP synthesis as described by Ehrlich (1976, 1983).