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Eugene W Rice

Publications and source records attributed to Eugene W Rice.

13 recordsLinked to original sources
PubMed2006

Persistence of Klebsiella pneumoniae on simulated biofilm in a model drinking water system.

Persistence of Klebsiella pneumoniae on corroded iron surfaces in drinking water was studied using biofilm annular reactors operated under oligotrophic conditions. Reactors were inoculated with K. pneumoniae, and persistence was monitored in the bulk and biofilm phases. Initial cell concentration of 10(6) MPN/mL in the bulkwater phase resulted in significantly longer adhesion than initial concentrations 1 and 2 orders of magnitude lower. K. pneumoniae cultured in low nutrient growth medium persisted longer in dechlorinated tap water than those cultured in full strength medium. Cell surface charge was more negative under low nutrient conditions, and this influenced electrostatic attraction between the cells and the oxidized iron surface. Cells grown in full strength media persisted longer in water with both low (<0.2 mg/L) and high (>0.5 mg/L) free chlorine residuals. Growth media injected with the cells dechlorinated the water allowing adhesion without inactivation. Microelectrode measurements showed a 40-70% drop in free chlorine from the bulk to the coupon surface, which decreased disinfectant potency against adhered cells. Growth and injection conditions clearly influenced cell adhesion and persistence, but permanent colonization of the corroded iron surface by K. pneumoniae was not observed.

Biofilms↗
PubMed2006

The widespread occurrence of the enterohemolysin gene ehlyA among environmental strains of Escherichia coli.

The putative virulence factor enterohemolysin, encoded by the ehlyA gene, has been closely associated with the pathogenic enterohemorrhagic Escherichia coli (EHEC) group. Escherichia coli isolates from effluents from seven geographically dispersed municipal wastewater treatment plants were screened for the presence of enterohemolysin. A total of 338 E. coli isolates were found to express the ehlyA gene. However, none of the isolates contained the toxin-encoding genes (stxA or stxB) associated with EHEC. Two of the 338 isolates possessed the virulence factor intimin, encoded by the eae gene. These findings suggest that the ehlyA gene may be widely distributed among non-EHEC isolates in the environment.

Bacterial Toxins↗
PubMed2006

Persistence of nontuberculous mycobacteria in a drinking water system after addition of filtration treatment.

There is evidence that drinking water may be a source of infections with pathogenic nontuberculous mycobacteria (NTM) in humans. One method by which NTM are believed to enter drinking water distribution systems is by their intracellular colonization of protozoa. Our goal was to determine whether we could detect a reduction in the prevalence of NTM recovered from an unfiltered surface drinking water system after the addition of ozonation and filtration treatment and to characterize NTM isolates by using molecular methods. We sampled water from two initially unfiltered surface drinking water treatment plants over a 29-month period. One plant received the addition of filtration and ozonation after 6 months of sampling. Sample sites included those at treatment plant effluents, distributed water, and cold water taps (point-of-use [POU] sites) in public or commercial buildings located within each distribution system. NTM were recovered from 27% of the sites. POU sites yielded the majority of NTM, with >50% recovery despite the addition of ozonation and filtration. Closely related electrophoretic groups of Mycobacterium avium were found to persist at POU sites for up to 26 months. Water collected from POU cold water outlets was persistently colonized with NTM despite the addition of ozonation and filtration to a drinking water system. This suggests that cold water POU outlets need to be considered as a potential source of chronic human exposure to NTM.

Colony Count, Microbial↗
PubMed2005

Chlorine inactivation of bacterial bioterrorism agents.

Seven species of bacterial select agents were tested for susceptibility to free available chlorine (FAC). Under test conditions, the FAC routinely maintained in potable water would be sufficient to reduce six species by 2 orders of magnitude within 10 min. Water contaminated with spores of Bacillus anthracis spores would require further treatment.

Bacillus anthracis↗
PubMed2004

Effect of alfalfa seed washing on the organic carbon concentration in chlorinated and ozonated water.

The bioassays assimilable organic carbon (AOC) and coliform growth response are better indexes than biological oxygen demand to determine water quality and water's ability to support the growth of bacteria. Ozonated (5 mg/liter) and chlorinated tap water were used to wash alfalfa seeds for 30 min. After washing in the ozonated tap water, the AOC concentration increased 25-fold, whereas the dissolved ozone decreased to undetectable levels. The AOC levels for the chlorinated water after washing the seeds also increased. These increases are due to ozone's strong oxidizing ability to break down refractory, large-molecular-weight compounds, forming smaller ones, which are readily used as nutrient sources for microorganisms. This same phenomenon was observed when using ozone in the treatment of drinking water. The AOC value increased from 1,176 to 1,758 micrograms C-eq/liter after the reconditioned wastewater was ozonated. When the ozonated wastewater was inoculated with Salmonella serotypes, the cells survived and increased generation times were observed. The increased nutrients would now become more readily available to any pathogenic microorganisms located on alfalfa seed surface as seen with the increase in the inoculated levels of Salmonella in the ozonated wastewater. If the washing process using ozonated water is not followed by the recommended hypochlorite treatment or continually purged with ozone, pathogen growth is still possible.

Area Under Curve↗
PubMed2003

Development of a Ct equation for the inactivation of Cryptosporidium oocysts with chlorine dioxide.

Cryptosporidium parvum, a protozoan parasite, has been implicated in a number of waterborne disease outbreaks and is difficult to inactivate using free chlorine. It appears, however, to be inactivated more easily by other oxidants such as chlorine dioxide or ozone. A major element of the EPA (US EPA) strategy for controlling C. parvum (oocysts) in drinking water is the possible use of Ct (concentration of disinfectant in mg/L times time in minutes) values. To support this strategy a Ct equation, based on first-order kinetics, is proposed to provide guidance to drinking water utilities for the application of chlorine dioxide for controlling C. parvum oocysts. The equation is based on standard statistical techniques using available bench scale data. It can predict mean inactivation levels as well as a statistically conservative upper bound Ct value. This upper bound could be used to insure an appropriate safety factor for the protection of public health.

Animals↗
PubMed2003

A Bayesian method of estimating kinetic parameters for the inactivation of Cryptosporidium parvum oocysts with chlorine dioxide and ozone.

The main objective of this paper is to use Bayesian methods to estimate the kinetic parameters for the inactivation kinetics of Cryptosporidium parvum oocysts with chlorine dioxide or ozone which are characterized by the delayed Chick-Watson model, i.e., a lag phase or shoulder followed by pseudo-first-order rate of inactivation. As the length of the lag phase (CT(lag)) is not known, Bayesian statistics provides a more accurate approach than traditional statistical methods to fitting the delayed Chick-Watson kinetics. Markov Chain Monte Carlo method is used to estimate CT(lag) and first-order rate constant values. This method is also used to estimate the minimum CT requirement (with safety factor) for 99% inactivation of C. parvum oocysts.

Animals↗
PubMed2003

Detection of intrinsic vancomycin resistant enterococci in animal and human feces.

Fecal samples from animal species and humans were analyzed by quantitative culture for enterococci and vancomycin resistant enterococci (VRE). Each host species carried enterococci which exhibited intrinsic intermediate resistance to vancomycin and sensitivity to teicoplanin (Van C phenotype). The carriage rate in humans was 9%. Carriage rates varied among animal species with the highest percentages being found in deer, duck, goose, horse and turkey.

Animals↗
PubMed2003

Estimation of Giardia Ct values at high pH for the Surface Water Treatment Rule.

The U.S. Environmental Protection Agency currently recommends Ct (disinfectant concentration multiplied by the exposure time) values to achieve required levels of inactivation of Giardia lamblia cysts by different disinfectants including free chlorine. Current guidance covers inactivation levels in the pH range between 6 and 9. Subsequent to the publication of these criteria, studies on the inactivation kinetics of Giardia cysts by chlorine have been performed at pH levels greater than 9. It has been shown that the chlorine inactivation process for Giardia cysts is pH dependent. The objective of this paper is to extend the current Ct values for higher pH levels. The Chick-Watson first order kinetics model was used to develop Ct values for pH levels from 6 to 11.5. A formula is provided to calculate a 100(1 - alpha)% upper confidence bound for these values.

Animals↗
PubMed2003

Survival of Salmonella in waste egg wash water.

Waste wash waters from chicken egg-processing facilities can harbor high densities of bacteria, including salmonellae. For this study, we enumerated total coliforms, Escherichia coli, and Salmonella spp. in the egg wash waters of a large egg producer. We then determined how long these organisms would survive at temperatures of 5, 15, and 25 degrees C. We found that the fraction of salmonellae surviving over time at a given temperature was comparable to the fraction of indicator organisms that survived. We also found that the survival of these organisms varied with temperature, with 16, 8, and < 2 days being required for a 90% reduction of Salmonella in waste wash water held at 5, 15, and 25 degrees C, respectively. Finally, we noted that the response of laboratory-derived cultures to environmental stresses mimics the response of the indigenous microbial population, but individual cells within that population may survive for longer periods than laboratory-cultured strains.

Animals↗
PubMed2002

Development of a Ct equation for the inactivation of Cryptosporidium oocysts with ozone.

Cryptosporidium parvum, a protozoan parasite, has been implicated in a number of waterborne disease outbreaks. It is difficult to inactivate using free chlorine, but appears to be easily inactivated by ozone. Therefore, the US EPA has promulgated the Interim Enhanced Surface Water Treatment Rule, which for the first time, addresses the control of C. parvum in drinking water. The use of Ct (concentration of disinfectant in mg/L times, time in minutes) values is being considered as one of the options for controlling this organism. This paper proposes a Ct equation, based on first order kinetics, to provide guidance to drinking water utilities for the application of ozone for controlling C parvum oocysts in drinking water. The equation, which provides mean estimates of inactivation, was developed using standard statistical techniques and currently available field and bench scale data. In addition, the possibility of using a statistically conservative upper bound Ct value in order to insure an appropriate safety factor is explored.

Animals↗
PubMedDate not supplied

The role of flushing dental water lines for the removal of microbial contaminants.

OBJECTIVES: This study was designed to determine the role of flushing dental water lines for the removal of heterotrophic plate count bacteria, Legionella spp., and free-living protozoa. METHODS: Forty dental offices were surveyed in the study. An initial sample and a sample taken after three minutes of flushing were obtained from the air/water syringe at each location. All samples were quantitatively analyzed for heterotrophic bacteria using three bacteriological procedures. The samples were analyzed for the presence of Legionella spp. using cultural, immunological, and molecular procedures and for the occurrence of free-living protozoa using a killed bacteria plate procedure. RESULTS: The flushing process reduced the level of heterotrophic plate count bacteria by 1.1 to 1.5 log10 CFU/ml. Compliance with recommendations for bacterial levels varied depending on the methodology employed in the analysis. The flushing process did not reduce the occurrence of Legionella spp. or free-living protozoa. CONCLUSION: The results support recent U.S. Centers for Disease Control and Prevention recommendations that the process of flushing dental water lines cannot be relied upon as a sole means of reliably improving the quality of water used in dental treatment.

Bacteriological Techniques↗