Enumeration, Occurrence, and Significance of Injured Indicator Bacteria in Drinking Water

Rapid diagnosis and precision treatment of Helicobacter pylori infection in clinical settings

Helicobacter pylori is a gram-negative bacterium that colonizes the stomach of approximately half of the worldwide population, with higher prevalence in densely populated areas like Asia, the Caribbean, Latin America, and Africa. H. pylori infections range from asymptomatic cases to potentially fatal diseases, including peptic ulcers, chronic gastritis, and stomach adenocarcinoma. The management of these conditions has become more difficult due to the rising prevalence of drug-resistant H. pylori infections, which ultimately lead to gastric cancer and mucosa-associated lymphoid tissue (MALT) lymphoma. In 1994, the International Agency for Research on Cancer (IARC) categorized H. pylori as a Group I carcinogen, contributing to approximately 780,000 cancer cases annually. Antibiotic resistance against drugs used to treat H. pylori infections ranges between 15% and 50% worldwide, with Asian countries having exceptionally high rates. This review systematically examines the impacts of H. pylori infection, the increasing prevalence of antibiotic resistance, and the urgent need for accurate diagnosis and precision treatment. The present status of precision treatment strategies and prospective approaches for eradicating infections caused by antibiotic-resistant H. pylori will also be evaluated.

Natural inactivation of Escherichia coli in anaerobic and reduced groundwater

AIMS

Inactivation rates of Escherichia coli in groundwater have most often been determined in aerobic and oxidized systems. This study examined E. coli inactivation rates in anaerobic and extremely reduced groundwater systems that have been identified as recharge zones.

METHODS AND RESULTS

Groundwater from six artesian wells was diverted to above-ground, flow-through mesocosms that contained laboratory grown E. coli in diffusion chambers. All groundwater was anaerobic and extremely reduced (ORP < -300 mV). Cells were plated onto mTEC agar during 21-day incubation periods. All data fit a bi-phasic inactivation model, with >95% of the E. coli population being inactivated <11·0 h (mean k = 0·488 ±0·188 h(-1) ).

CONCLUSIONS

The groundwater geochemical conditions enhanced the inactivation of E. coli to rates approx. 21-fold greater than previously published inactivation rate in groundwater (mean k = 0·023 ± 0·030 h(-1) ). Also, mTEC agar inhibits E. coli growth following exposure to anaerobic and reduced groundwater.

SIGNIFICANCE AND IMPACT OF THE STUDY

Aquifer recharge zones with geochemical characteristics observed in this study complement above-ground engineered processes (e.g. filtration, disinfection), while increasing the overall indicator micro-organism log-reduction rate of a facility.

Microbial indicators, pathogens and methods for their monitoring in water environment

Water is critical for life, but many people do not have access to clean and safe drinking water and die because of waterborne diseases. The analysis of drinking water for the presence of indicator microorganisms is key to determining microbiological quality and public health safety. However, drinking water-related illness outbreaks are still occurring worldwide. Moreover, different indicator microorganisms are being used in different countries as a tool for the microbiological examination of drinking water. Therefore, it becomes very important to understand the potentials and limitations of indicator microorganisms before implementing the guidelines and regulations designed by various regulatory agencies. This review provides updated information on traditional and alternative indicator microorganisms with merits and demerits in view of their role in managing the waterborne health risks as well as conventional and molecular methods proposed for monitoring of indicator and pathogenic microorganisms in the water environment. Further, the World Health Organization (WHO) water safety plan is emphasized in order to develop the better approaches designed to meet the requirements of safe drinking water supply for all mankind, which is one of the major challenges of the 21st century.

Spatial distribution and physiological state of bacteria in a sand column experiment during the biodegradation of toluene

Toxic organic contaminants frequently serve as growth substrates for bacteria. However, long-term exposure to the organic contaminants can result in significant stress or "injury" to bacterial cells such that bacteria may lose, either temporarily or permanently, their capacity to degrade a specific toxic organic contaminant. In order to understand the relationship between biodegradability and physiological conditions of bacteria after a prolonged exposure to a contaminant, biomass samples collected from a sand column experiment, with toluene as the carbon source, were analyzed for bacterial physiology and spatial population distribution in the porous media. The column was seeded with three bacterial isolates that perform aerobic (Pseudomonas putida F1), denitrifying (Thauera aromatica T1), and facultative (Ralstonia pickettii PKO1) degradation of toluene were analyzed. Total, viable but not culturable with toluene, and toluene-culturable cells were enumerated using 4'6-diamidino-2-phenylindole (DAPI) staining and plate counting methods. Comparison of three types of cell counts showed that toluene-culturable cells were less than 40% of the total cell numbers. However, viable colonies transferred to a toluene media after cultivation on rich media regained their ability to degrade toluene. This implies that the temporary loss of their toluene degradation capacity is either due to an intracellular accumulation of degradation by-products, which have to be consumed in order for the cells to degrade toluene, or it is possible that cells have shifted to degrade other substrates such as toluene degradation intermediates or organic materials resulting from cell turnover. Comparison of cell counts with toluene concentration showed no exponential increase in total and viable cell numbers, as reported for flat bed biofilm reactor experiments. The overall fraction of toluene-culturable cells was highest at the highest toluene concentration near the column inlet, which indicates that the observed temporary loss of toluene culturability was not solely caused by a direct toxic effect from the long-term exposure to toluene.

Effect of oxygen on survival of faecal pollution indicators in drinking water

AIMS

The aim of this study was to determine the effect of oxygen on the survival of faecal pollution indicators including Escherichia coli in nondisinfected drinking water.

METHODS AND RESULTS

Aerobic and anaerobic drinking water microcosms were inoculated with E. coli ATCC 25922 or raw sewage. Survival of E. coli was monitored by membrane filtration combined with cultivation on standard media, and by in situ hybridization with 16S rRNA-targeted fluorescent oligonucleotide probes. Anaerobic conditions significantly increased the survival of E. coli in drinking water compared with aerobic conditions. Escherichia coli ATCC 25922 showed a biphasic decrease in survival under aerobic conditions with an initial first-order decay rate of -0.11 day(-1) followed by a more rapid rate of -0.35 day(-1). In contrast, the first-order decay rate under anaerobic conditions was only -0.02 day(-1). After 35 days, <0.01% of the initial E. coli ATCC 25922 population remained detectable in aerobic microcosms compared with 48% in anaerobic microcosms. A poor survival was observed under aerobic conditions regardless of whether E. coli ATCC 25922 or sewage-derived E. coli was examined, and regardless of the detection method used (CFU or fluorescent in situ hybridization). Aerobic conditions in drinking water also appeared to decrease the survival of faecal enterococci, somatic coliphages and coliforms other than E. coli.

CONCLUSIONS

The results indicate that oxygen is a major regulator of the survival of E. coli in nondisinfected drinking water. The results also suggest that faecal pollution indicators other than E. coli may persist longer in drinking water under anaerobic conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

The effect of oxygen should be considered when evaluating the survival potential of enteric pathogens in oligotrophic environments.

Rapid detection of respiring Escherichia coli O157:H7 in apple juice, milk, and ground beef by flow cytometry

BACKGROUND

Rapid and simple methods to detect viable pathogenic microbes in foods and drinks are required. Flow cytometry was used for the rapid detection of respiring Escherichia coli O157:H7 cells in apple juice, milk, and ground beef.

METHODS

CTC (5-cyano-2,3-ditolyl tetrazolium chloride) was used to estimate the respiratory activity of bacteria. Fluorescein isothiocyanate (FITC)-labeled anti-E. coli O157:H7 direct antibody (FA) was used for the specific detection of target cells. Food samples were inoculated with starved E. coli O157:H7 and E. coli K-12 cells, and analyzed by both fluorescent microscopy and flow cytometry after double staining with FA and CTC.

RESULTS

Respiring E. coli O157:H7 cells in food samples showed strong fluorescence of both FA (green) and CTC (red); thus, they could be clearly and specifically distinguished from respiring E. coli K-12 or inactive cells. A good correlation was achieved in flow cytometric analysis between the numbers of inoculated viable E. coli O157:H7 and those detected in milk and apple juice. The detection threshold for this flow cytometry for E. coli O157:H7 in milk, apple juice, and ground beef was 10(3) cells/ml (milk and apple juice) or 10(3) cells/g (ground beef) of sample when the total bacterial number in the sample was 10(6) cells/ml.

CONCLUSIONS

Respiring E. coli O157:H7 in food samples can be detected specifically within a few hours. Flow cytometry with FA-CTC double staining can be used to examine food contamination with various pathogenic microbes demonstrating physiologic activity through the use of a suitable fluorescent antibody.

Synthesis and evaluation of novel fluorogenic substrates for the detection of bacterial beta-galactosidase

AIMS

A widely used coumarin derivative is 7-hydroxy-4-methylcoumarin-beta-D-galactoside (4-methylumbelliferone-beta-D-galactoside; 4-MU-GAL). This galactoside is utilized as a substrate for the detection of the beta-galactosidase activity of coliform bacteria in water analysis. The intense fluorescence of coumarin-based molecules has enabled them to be incorporated into enzyme-based tests for the quantitative assay of indicator bacteria. The aim of this present study was to evaluate the potential of other coumarin derivatives, by synthesis of a selection of core coumarin molecules.

METHODS AND RESULTS

Several coumarin derivatives were found to be more promising than 4-MU, with ethyl-7-hydroxycoumarin-3-carboxylate (EHC) giving a combination of greater fluorescence over a broad pH range and reduced growth inhibition with 12 representative coliform strains. On conversion to a beta-galactoside derivative, EHC-GAL generated a more rapid fluorescence than any other tested substrate.

CONCLUSIONS

When tested in a broth assay format, based on most probable number (MPN), low numbers of coliforms were detected with EHC-GAL around 1 h earlier than with 4-MU-GAL.

SIGNIFICANCE AND IMPACT OF THE STUDY

The present study suggests that EHC-GAL should be evaluated as a substrate for the detection of coliforms in water analysis, due to a combination of the following favourable features: (i) reduced toxicity; (ii) increased fluorescence; (iii) pH stability of fluorescence; and (iv) rapid detection.

Recovery of hydrogen peroxide-sensitive culturable cells of Vibrio vulnificus gives the appearance of resuscitation from a viable but nonculturable state

The viabilities of five strains of Vibrio vulnificus were evaluated during the storage of the organisms in sterile seawater at 5 degrees C. The number of CFU was measured by plate count methods on rich media. The total cell numbers were determined by direct microscopic count methods. The titer of CFU declined logarithmically to undetectable levels over a period of 2 to 3 weeks, while the total cell numbers were unchanged. Midway through each study, higher culturable cell counts began to be observed on plates containing catalase or sodium pyruvate; during the latter stages of the study, the plate counts on such media were up to 1,000-fold higher than those on unsupplemented plates. Because autoclaving is known to generate hydrogen peroxide in rich media, and because catalase and sodium pyruvate are known to eliminate hydrogen peroxide, it appears that the conditions of the experiments led to the selection of a hydrogen peroxide-sensitive culturable cell subpopulation. At the time of the final stage of the decline in viability of each culture, hydrogen peroxide-sensitive cells were the only culturable cells present. Warming samples of the cultures to room temperature led to the growth of these residual culturable cells, utilizing nutrients provided by the nonculturable cells. The cells that grew recovered hydrogen peroxide resistance. When mixtures of culturable and nonculturable cells were diluted to the point where only nonculturable cells were present, or when the hydrogen peroxide-sensitive culturable cells had declined to undetectable levels, warming had no effect; no culturable cells were recovered. Warming has been reported to "resuscitate" nonculturable cells. Recognition of the existence of hydrogen peroxide-sensitive culturable cell populations, as well as their ability to grow to high levels in the warmed seawater microcosms, leads instead to the conclusion that while warming permits culturable cells to grow, it has no effect on nonculturable cells.

Bacterial growth state distinguished by single-cell protein profiling: does chlorination kill coliforms in municipal effluent?

Municipal effluent is the largest reservoir of human enteric bacteria. Its public health significance, however, depends upon the physiological status of the wastewater bacterial community. A novel immunofluorescence assay was developed and used to examine the bacterial growth state during wastewater disinfection. Quantitative levels of three highly conserved cytosolic proteins (DnaK, Dps, and Fis) were determined by using enterobacterium-specific antibody fluorochrome-coupled probes. Enterobacterial Fis homologs were abundant in growing cells and nearly undetectable in stationary-phase cells. In contrast, enterobacterial Dps homologs were abundant in stationary-phase cells but virtually undetectable in growing cells. The range of variation in the abundance of both proteins was at least 100-fold as determined by Western blotting and immunofluorescence analysis. Enterobacterial DnaK homologs were nearly invariant with growth state, enabling their use as permeabilization controls. The cellular growth states of individual enterobacteria in wastewater samples were determined by measurement of Fis, Dps, and DnaK abundance (protein profiling). Intermediate levels of Fis and Dps were evident and occurred in response to physiological transitions. The results indicate that chlorination failed to kill coliforms but rather elicited nutrient starvation and a reversible nonculturable state. These studies suggest that the current standard procedures for wastewater analysis which rely on detection of culturable cells likely underestimate fecal coliform content.

Effect of u.v. light irradiation, starvation and heat on Escherichia coli beta-D-galactosidase activity and other potential viability parameters

The effect of u.v. light irradiation and two other types of stress (heat and starvation) on cellular functions of Escherichia coli have been studied. The severe reduction of the culturable cell number (cfu) and the direct viable count (DVC) after exposure to moderate u.v. light doses (48 mWs cm-2), was not reflected by the dehydrogenase activity (5-cyano-2,3-ditolyl tetrazolium chloride (CTC)-positive cells), the membrane integrity (SYTOX Green-negative cells), the membrane potential (bis-(1,3-dibutylbarbituric acid) trimethine oxonol (DiBAC4[3]) (OXONOL)-negative cells), and the beta-D-galactosidase activity. All parameters were affected by high u.v. light doses. Cellular activities (CTC, SYTOX, OXONOL, beta-D-galactosidase activity) were intact in non-culturable cells with presumably severe damage to DNA, and the activities seemed not to be appropriate for detection of viable E. coli after u.v. light irradiation. Heating for 20-30 min at 63 degrees C was required to cause a severe loss of the beta-D-galactosidase activity and the numbers of CTC-positive, SYTOX Green-negative or OXONOL-negative cells. A large portion (> or = 38%) of pre-irradiated (190 mWs cm-2) cells maintained their ability to reduce CTC and exclude SYTOX Green and OXONOL after 51 d of starvation (dark, 7 degrees C) in phosphate-buffered saline.

The use of multiple indices of physiological activity to access viability in chlorine disinfected Escherichia coli O157:H7

A suite of fluorescent intracellular stains and probes was used, in conjunction with viable plate counts, to assess the effect of chlorine disinfection on membrane potential (rhodamine 123; Rh123 and bis-(1,3-dibutylbarbituric acid) trimethine oxonol; DiBAC4(3)), membrane integrity (LIVE/DEAD BacLight kit), respiratory activity (5-cyano-2,3-ditolyl tetrazolium chloride; CTC) and substrate responsiveness (direct viable counts; DVC) in the commensal pathogen Escherichia coli O157:H7. After a 5 min exposure to the disinfectant, physiological indices were affected in the following order: viable plate counts > substrate responsiveness > membrane potential > respiratory activity > membrane integrity. In situ assessment of physiological activity by examining multiple targets, as demonstrated in this study, permits a more comprehensive determination of the site and extent of injury in bacterial cells following sublethal disinfection with chlorine. This approach to assessing altered bacterial physiology has application in various fields where detection of stressed bacteria is of interest.

Sensitive detection of Escherichia coli O157:H7 in food and water by immunomagnetic separation and solid-phase laser cytometry

Rapid, direct methods are needed to assess active bacterial populations in water and foods. Our objective was to determine the efficiency of bacterial detection by immunomagnetic separation (IMS) and the compatibility of IMS with cyanoditolyl tetrazolium chloride (CTC) incubation to determine respiratory activity, using the pathogen Escherichia coli O157:H7. Counterstaining with a specific fluorescein-conjugated anti-O157 antibody (FAb) following CTC incubation was used to allow confirmation and visualization of bacteria by epifluorescence microscopy. Broth-grown E. coli O157:H7 was used to inoculate fresh ground beef (<17% fat), sterile 0.1% peptone, or water. Inoculated meat was diluted and homogenized in a stomacher and then incubated with paramagnetic beads coated with anti-O157 specific antibody. After IMS, cells with magnetic beads attached were stained with CTC and then an anti-O157 antibody-fluorescein isothiocyanate conjugate and filtered for microscopic enumeration or solid-phase laser cytometry. Enumeration by laser scanning permitted detection of ca. 10 CFU/g of ground beef or <10 CFU/ml of liquid sample. With inoculated meat, the regression results for log-transformed respiring FAb-positive counts of cells recovered on beads versus sorbitol-negative plate counts in the inoculum were as follows: intercept = 1.06, slope = 0.89, and r2 = 0. 95 (n = 13). The corresponding results for inoculated peptone were as follows: intercept = 0.67, slope = 0.88, and r2 = 0.98 (n = 24). Recovery of target bacteria on beads by the IMS-CTC-FAb method, compared with recovery by sorbitol MacConkey agar plating, yielded greater numbers (beef, 6.0 times; peptone, 3.0 times; water, 2.4 times). Thus, within 5 to 7 h, the IMS-CTC-FAb method detected greater numbers of E. coli O157 cells than were detected by plating. The results show that the IMS-CTC-FAb technique with enumeration by either fluorescence microscopy or solid-phase laser scanning cytometry gave results that compared favorably with plating following IMS.

Comparison of the recoveries of Escherichia coli and total coliforms from drinking water by the MI agar method and the U.S. Environmental Protection Agency-approved membrane filter method

Drinking water regulations under the Final Coliform Rule require that total coliform-positive drinking water samples be examined for the presence of Escherichia coli or fecal coliforms. The current U.S. Environmental Protection Agency-approved membrane filter (MF) method for E. coli requires two media, an MF transfer, and a total incubation time of 28 h. A newly developed MF method, the MI agar method, containing indoxyl-beta-D-glucuronide and 4-methylumbelliferyl-beta-D-galactopyranoside for the simultaneous detection of E. coli and total coliforms, respectively, by means of their specific enzyme reactions, was compared with the approved method by the use of wastewater-spiked tap water samples. Overall, weighted analysis of variance (significance level, 0.05) showed that the new medium recoveries of total coliforms and E. coli were significantly higher than those of mEndo agar and nutrient agar plus MUG (4-methylumbelliferyl-beta-D-glucuronide), respectively, and the background counts were significantly lower than those of mEndo agar (< 5%). Generally, the tap water source, overall chlorine level, wastewater source, granular activated carbon treatment of the tap water, and method of grouping data by E. coli count for statistical analysis did not affect the performance of the new medium.

Factors affecting the determination of respiratory activity on the basis of cyanoditolyl tetrazolium chloride reduction with membrane filtration

Deficiencies in traditional bacterial enumeration techniques which rely on colony formation have led to the use of total direct counting methods, such as the acridine orange direct count technique for the enumeration of planktonic bacteria. As total direct counts provide no information on the viability or activity of the organisms, demonstration of respiratory activity with the fluorochrome cyanoditolyl tetrazolium chloride (CTC) has been employed. We have modified this technique by performing filtration prior to CTC incubation. Cells captured on a polycarbonate membrane were incubated on absorbent pads saturated with medium containing CTC. Following counterstaining with DAPI (4(prm1),6-diamidino-2-phenylindole) total and respiring cells were enumerated by epifluorescence microscopy. Factors affecting CTC reduction by Klebsiella pneumoniae, Salmonella typhimurium, and Escherichia coli K-12 were investigated. With K. pneumoniae, nutrient additions to the CTC medium did not increase the number of respiring cells detected. CTC reduction by all three organisms decreased in response to an increase of the pH of the CTC medium above pH 6.5. Increasing phosphate concentrations contributed to this inhibitory effect. CTC-membrane filter counts of K. pneumoniae, S. typhimurium, and E. coli K-12 and of bacteria in well water corresponded closely with plate counts (r = 0.987). The results show that careful attention should be given to the composition of CTC-containing media which are used to enumerate respiring bacteria. With an appropriate medium, reliable enumeration of respiring bacteria can be achieved within a few hours.

A rapid, direct method for enumerating respiring enterohemorrhagic Escherichia coli O157:H7 in water

Simple, rapid methods for the detection and enumeration of specific bacteria in water and wastewater are needed. We have combined incubation using cyanoditolyl tetrazolium chloride (CTC) to detect respiratory activity with a modified fluorescent-antibody (FA) technique, for the enumeration of specific viable bacteria. Bacteria in suspensions were captured by filtration on nonfluorescent polycarbonate membranes that were then incubated on absorbent pads saturated with CTC medium. A specific antibody conjugated with fluorescein isothiocyanate was reacted with the cells on the membrane filter. The membrane filters were mounted for examination by epifluorescence microscopy with optical filters designed to permit concurrent visualization of fluorescent red-orange CTC-formazan crystals in respiring cells which were also stained with the specific FA. Experiments with Escherichia coli O157:H7 indicated that both respiratory activity and specific FA staining could be detected in logarithmic- or stationary-phase cultures, as well as in cells suspended in M9 medium or reverse-osmosis water. Following incubation without added nutrients in M9 medium or unsterile reverse-osmosis water, the E. coli O157:H7 populations increased, although lower proportions of the organisms reduced CTC. Numbers of CTC-positive, FA-positive cells compared with R2A agar plate counts gave a strong linear regression (R = 0.997). Differences in injury did not appear to affect CTC reduction. The procedure, which can be completed within 3 to 4 h, has also been performed successfully with Salmonella typhimurium and Klebsiella pneumoniae.

Comparison of respiratory activity and culturability during monochloramine disinfection of binary population biofilms

Biofilm bacteria challenged with monochloramine retained significant respiratory activity, even though they could not be cultured on agar plates. Microbial colony counts on agar media declined by approximately 99.9% after 1 h of disinfection, whereas the number of bacteria stained by a fluorescent redox dye experienced a 93% reduction. Integrated measures of biofilm respiratory activity, including net oxygen and glucose utilization rates, showed only a 10 to 15% reduction. In this biofilm system, measures of microbial respiratory activity and culturability yielded widely differing estimates of biocide efficacy.

Survival ofEscherichia coli andYersinia enterocolitica in stream water: Comparison of field and laboratory exposure

Experiments were done to compare the influence of three aquatic exposure methods on the behavior of pathogenic and nonpathogenic enteric bacteria (Yersinia enterocolitica andEscherichia coli). Bacterial suspensions were exposed to stream water in membrane diffusion chambers in situ as well as in the laboratory using a large vessel of stream water and in enclosed bottles. The persistence of culturability of the bacterial suspensions was dependent upon the method of aquatic exposure. This difference was most apparent during the initial six days of each experiment. A steady decline in colony forming units was seen after a short stationary period in chambers in situ, while there was an abrupt increase in bacteria within chambers exposed in the laboratory. A rapid initial decrease was observed in the experimental variation using bottles, accompanied by higher levels of injury inE. coli and reduced expression of plasmid-borne virulence phenotypes inY. enterocolitica. However, there were no changes in the plasmid profiles of either organism throughout the 21-day duration of the experiments. In addition, the survival and injury of pathogenic and nonpathogenic strains of both test bacteria was very similar with aquatic exposure. These results suggest that the response of enteric bacteria in aquatic environments is influenced by experimental design as well as other factors and that the comparison of survival data should only be attempted when similar methods are used.