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Biomedical subjects

M D Sobsey

Publications and source records attributed to M D Sobsey.

At least 19 recordsLinked to original sources
PubMed2006

F+ RNA coliphage typing for microbial source tracking in surface waters.

AIMS: The utility of coliphages to detect and track faecal pollution was evaluated using South Carolina surface waters that exceeded State faecal coliform standards. METHODS AND RESULTS: Coliphages were isolated from 117 surface water samples by single agar layer (SAL) and enrichment presence/absence (EP/A) methods. Confirmed F+ RNA coliphages were typed for microbial source tracking using a library-independent approach. Concentrations of somatic coliphages using 37 and 44.5 degrees C incubation temperatures were found to be significantly different and the higher temperature may be more specific for faecal contamination. The EP/A technique detected coliphages infecting Escherichia coli Famp in 38 (66%) of the 58 surface water samples negative for F+ coliphages by the SAL method. However, coliphages isolated by EP/A were found to be less representative of coliphage diversity within a sample. Among the 2939 coliphage isolates tested from surface water and known source samples, 813 (28%) were found to be F+ RNA. The majority (94%) of surface water F+ RNA coliphage isolates typed as group I. Group II and/or III viruses were identified from 14 surface water stations, the majority of which were downstream of wastewater discharges. These sites were likely contaminated by human-source faecal pollution. CONCLUSIONS: The results suggest that faecal contamination in surface waters can be detected and source identifications aided by coliphage analyses. SIGNIFICANCE AND IMPACT OF THE STUDY: This study supports the premise that coliphage typing can provide useful, but not absolute, information to distinguish human from animal sources of faecal pollution. Furthermore, the comparison of coliphage isolation methods detailed in this study should provide valuable information to those wishing to incorporate coliphage detection into water quality assessments.

Animals↗
PubMed2006

Characterisation of the biosand filter for E. coli reductions from household drinking water under controlled laboratory and field use conditions.

More than a billion people in the developing world lack access to safe and reliable sources of drinking water. Point of use (POU) household water treatment technology allows people to improve the quality of their water by treating it in the home. One emerging POU technology is the biosand filter (BSF), a household-scale, intermittently operated slow sand filter. Laboratory and field studies examined Escherichia coli reductions achieved by the BSF. During two laboratory studies, mean E. coli reductions were 94% and they improved over the period of filter use, reaching a maximum of 99%. Field analysis conducted on 55 household filters near Bonao, Dominican Republic averaged E. coli reductions of 93%. E. coli reductions by the BSF in laboratory and field studies were less than those typically observed for traditional slow sand filters (SSFs), although as for SSFs microbial reductions improved over the period of filter use. Further study is needed to determine the factors contributing to microbial reductions in BSFs and why reductions are lower than those of conventional SSFs.

Colony Count, Microbial↗
PubMed2006

Detection and occurrence of antimicrobially resistant E. coli in groundwater on or near swine farms in eastern North Carolina.

The use of antibiotics for growth promotion and disease treatment by the commercial swine industry has led to high proportions of multiple antibiotic-resistant enteric bacteria being shed by these animals and concerns about the environmental spread of these bacteria. A study was conducted to quantify the extent of release of antibiotic-resistant E. coli from swine farms into groundwater. Four study sites, two swine farms and two reference sites (crop farms), with known groundwater flow paths were screened for E. coli four times over the course of one and a half years. A total of 100 biochemically-confirmed E. coli were collected from the four sites. There were statistically significantly higher E. coli levels at the two swine farm sites than at the reference sites. The bacterial isolates were tested for antibiotic resistance using a panel of 17 drugs that are typical of human and veterinary use. There were 19 and 71 E. coli isolates from swine farms #1 and #2, respectively, with most (68%) being resistant to 1 -6 antimicrobials. Only one E. coli isolate from each of the reference sites showed antimicrobial resistance traits. The results of this study demonstrate that antibiotic-resistant E. coli strains are present in groundwaters of swine farms with a typical lagoon and land application system for waste management.

Animals↗
PubMed2004

Inactivation of enteric microbes in water by electro-chemical oxidant from brine (NaCl) and free chlorine.

Oxidant solutions of mostly free chlorine can be electrochemically produced on-site from brine (NaCl) solution and used to disinfect water at the household or community level. In this study electrochemical oxidant (ECO) from brine and free chlorine were evaluated under laboratory conditions for inactivation of test microbes. Purified suspensions of Escherichia coli, the rugose strain of Vibrio cholerae, Clostridium perfringens spores, MS2 coliphage and Cryptosporidium parvum oocysts were treated with 2 mg/L or 5 mg/L solutions of ECO or free chlorine at 5 degrees C and 25 degrees C and pH 6, 8, and 10 (pH 7 and 25 degrees C only for C. parvum oocysts) for contact times <60 min. Under nearly all conditions, inactivation kinetics were more rapid for E. coli, V. cholerae, C. perfringens spores and MS2 coliphage with ECO than with free chlorine. ECO reduced E. coli, V. cholerae and MS2 by >4 log10 within 30 min and C. perfringens spores by >2 log10 within 10 min at pH 8 and 25 degrees C. Contrary to previous results, however, C. parvum oocysts were not inactivated by ECO, and the reasons for this difference are uncertain. The on-site electrolytic generation of oxidants from brine provided a convenient and inexpensive disinfectant containing free chlorine that was effective against many enteric microbes, for the treatment of household and community drinking-water supplies worldwide. However, the effectiveness of such oxidants for inactivating C. parvum oocysts was variable and sometimes ineffective.

Animals↗
PubMed2004

Development and evaluation of methods to detect coliphages in large volumes of water.

New and improved methods have been developed to detect somatic and male-specific coliphages in large volumes of water by single agar layer (SAL), enrichment and membrane filter methods. Somatic coliphages were detected efficiently on E. coli hosts C and CN13, male-specific coliphages were detected more efficiently on E. coli Famp than on Salmonella typhimurium WG49 and both types of coliphages were detected simultaneously on E. coli C3000. For water volumes of up to 100 ml, the SAL method was efficient and reliable. For water volumes of <1 L and as many as 10 multiple 1 L volumes, the enrichment method was efficient in detecting very low numbers of coliphages. Membrane filter methods, in which coliphages were adsorbed to and eluted from filters, also were relatively efficient, but they were less efficient than SAL and enrichment methods and were considered to be more cumbersome. For filter adsorption-elution methods, coliphage recoveries were most efficient for cellulose ester filters, less efficient for electropositive 1 MDS filters and least efficient for a direct membrane filter method. Overall, the enrichment method was preferred because of its ability to easily and rapidly detect low levels of coliphages in large sample volumes by either presence-absence or most probable number quantification.

Cellulose↗
PubMed2003

Comparative reduction of Norwalk virus, poliovirus type 1, F+ RNA coliphage MS2 and Escherichia coli in miniature soil columns.

Norwalk-like viruses (NLVs) are important agents of waterborne illness and have been linked to several groundwater-related outbreaks. The presence of human enteric viruses, in particular the presence of NLVs, is difficult to detect in the environment. Consequently, surrogate organisms are typically used as indicators of viruses from faecal contamination. Whether traditional bacterial indicators are reliable indicators for viral pathogens remains uncertain. Few studies have directly compared mobility and reduction of bacterial indicators (e.g. coliforms, Escherichia coli) and other surrogate indicators (coliphages) with pathogenic human viruses in soil systems. In this study the mobility and comparative reduction of the prototype NLV, Norwalk Virus (NV), was compared to poliovirus 1 (PV1), a bacterial indicator (E coli, EC) and a viral indicator (coliphage MS2) through miniature soil columns. Replicate, 10 cm deep, miniature columns were prepared using three soils representing a range of soil textures (sand, organic muck, and clay). Columns were initially conditioned, then incubated at 10-14 degrees C, dosed twice weekly for 8 weeks with one column pore volume of virus-seeded groundwater per dose, followed by 8 weeks of dosing with one column pore volume per dose of unseeded, simulated rainwater. Columns were allowed to drain after each dosing until an effluent volume equivalent to an applied dose was collected. Column effluents and doses were assayed for all viruses and EC. Rapid mobility with minimal reduction was observed for all organisms in the sand. Similar reductions were observed in organic muck for most organisms but NV showed a greater reduction. No organisms were shown to pass through the clay columns. Elution of viruses, in particular PV1, from the columns was gradual. After cessation of microbe dosing, E. coli was less detectable than viruses in column effluents and, therefore, unreliable as a virus indicator.

Aluminum Silicates↗
PubMed2003

A chemiluminescent immunofocus assay (CIFA) for non-microscopic enumeration of Cryptosporidium parvum infectivity in cell culture.

As Cryptosporidium parvum continues to cause waterborne disease, despite extensive efforts by drinking water suppliers and regulators, it is important to have reliable and convenient methods for detection of this pathogen in wastewater discharges, environmental source waters and finished drinking water supplies. In order to better understand the health risks of this organism, it is necessary that detection methods be able to distinguish between infectious and non-infectious Cryptosporidium oocysts in these environmental samples. Cryptosporidium infectivity assay systems based on infections in mice and on in vitro infections in continuous mammalian cell lines are available. Currently, these methods are impractical for routine analysis of water samples because they are tedious, lengthy and costly. These methods rely on careful microscopic examination or further analysis by PCR and then characterisation of the amplified DNA. Practical and affordable non-microscopic methods to determine Cryptosporidium infectivity are much needed for environmental analysis. A cell culture infectivity detection system was developed for infectious Cryptosporidium oocysts that does not rely on microscopic examination of samples to score results, is applicable to a variety of samples and has the potential to be used for routine water monitoring and other environmental or biomedical analysis. Using a chemiluminescent immunoassay, the discrete foci of developmental stages of Cryptosporidium in cell cultures are clearly visible as discrete objects in an image of the entire cell culture layer in a dish or on a slide. These objects are directly countable with the unaided eye and their identity can be further confirmed or verified by microscopic examination.

Animals↗
PubMed2003

Factors influencing faecal contamination in coastal marinas.

Recreational pleasure and fishing boats are potential sources of human faecal contamination because the sanitary wastes from boat occupants may be discharged into the surrounding water. The impacts of such faecal contamination from boats is potentially high in marinas where boats are often kept and occupied for varying periods of time. The nature and extent of such faecal contamination from boats in marinas of different design and use is still inadequately understood. In this study the levels of faecal coliform (FC) bacteria were measured in the waters of a confined and an open water marina over a 6 d period encompassing a holiday weekend. Levels of FC rose with increasing occupancy by boats and boaters during the study period and then declined again. FC levels were higher in waters of a confined or basin marina than in waters of an open or unconfined marina. In both confined and open water marinas, FC levels were highest in water samples collected near boats but they also became elevated on occasion in water samples taken a distance of 305 m from boats. Concentrations of FC in marina waters exceeded the standards and guidelines for shell-fishing and primary contact recreation waters. Therefore, greater consideration of human health risks from enteric microbes in marina waters and shellfish is recommended.

Animals↗
PubMed2003

Chlorination and safe storage of household drinking water in developing countries to reduce waterborne disease.

Simple, effective and affordable methods are needed to treat and safely store non-piped, gathered household water. This study evaluated point-of-use chlorination and storage in special plastic containers of gathered household water for improving microbial quality and reducing diarrhoeal illness of consumers living under conditions of poor sanitation and hygiene. Community families were recruited and randomly divided into intervention (household water chlorination and storage in a special container) and control (no intervention) households. Microbes in stored household water were extensively inactivated by 1-5-mg/L doses of hypochlorite. Escherichia coli levels in stored household waters were < 1/100 mL in most intervention households but readily detectable at high levels in control households. Stored water of intervention households was also lower in Clostridium perfringens and heterotrophic plate count bacteria than in control households. The intervention reduced household diarrhoeal illness. In Bolivia, monthly episodes of household diarrhoeal illness were 1.25 and 2.2 in intervention and control families, respectively (P = < 0.002) indicating that 43% of community diarrhoea was preventable by using the intervention. In Bangladesh, mean episodes of child diarrhoea/1,000 d were 19.6 and 24.8 in intervention and control groups respectively (P = < 0.03) indicating that about 24% of observed diarrhoea was preventable by using the intervention. Chlorine disinfection and storage in an appropriate container significantly improved the microbiological quality of non-piped household drinking water and reduced community diarrhoeal disease. Widespread use of this simple treatment and storage system for non-piped domestic water has the potential to dramatically reduce the global burden of waterborne diarrhoeal disease.

Adult↗
PubMed2002

F-specific RNA coliphages: occurrence, types, and survival in natural waters.

A small, well-defined watershed was investigated over a 2-year period to determine the prevalence of F-specific RNA coliphage (F + RNA) serotypes as indicators of animal fecal contamination. Sampling sites collected runoff from areas of urban and agricultural land use patterns. F-specific coliphages were concentrated from 2-L freshwater samples by polyethylene glycol precipitation, isolated using the double agar layer (DAL) method, confirmed as F + RNA by RNAse suppression, and serotyped. A subset of serotyped F + RNA were confirmed by genotyping. To determine relative survival, 10 confirmed F + RNA field isolates and 5 prototypic F + RNA were spiked into surface water and incubated at 25 degrees C for 36 days. F-specific coliphage isolation was strongly associated with rainfall events and was infrequent from primarily animal impacted surface waters. Field isolates were predoffiinantly Type I F + RNA (81%) and raw sewage isolates were predominantly Type III F + RNA (57%). Genotyping from either the watershed or raw sewage samples never positively identified Type IV F + RNA. Results from laboratory studies showed that F + RNA differ in their survival in water and that Type IV strains were the least persistent. Type III F + RNA were found to be reliably related to the release of uncontrolled human fecal material in the watershed, but the results of this study suggest that further study is required before utilizing for fecal source identification in natural waters.

Agriculture↗
PubMed2002

Enteric bacteriophages as potential fecal indicators in ground beef and poultry meat.

Recovery efficiencies of enteric bacteriophages (F+ RNA coliphages, somatic coliphages, and Salmonella phages) as alternative fecal indicators were determined from ground beef and chicken breast meat using amino acid eluants (glycine and threonine) and a complex eluant (3% beef extract). Levels of F+ RNA coliphages (MS2, GA, Qbeta, FI, and SP), the somatic coliphage phiX174, and three environmental isolates of Salmonella phages (isolated from raw sewage) were assayed using three respective hosts: Escherichia coli Famp, E. coli C, and Salmonella Typhimurium. When 8% polyethylene glycol and 0.1 M NaCl were used to precipitate bacteriophages eluted with five different eluants, the highest recoveries of the three phage groups were with 0.5 M threonine and 0.25 M glycine-threonine. The average recoveries of F+ RNA coliphages, somatic coliphages, and the Salmonella phages from ground beef and chicken meat were 100, 69, and 65%, respectively, with threonine (0.5 M, pH 9.0) as the eluate. Of eight market food samples tested, F+ RNA coliphages were detected in five (63%) and somatic coliphages were detected in seven (88%). The overall detection sensitivity of the method was 3 PFU/100 g of ground beef or chicken meat. Levels of bacteriophages and bacterial indicators on chicken carcass surfaces were determined at identified critical control points at a poultry plant. Through the processing steps of evisceration, washing, and chilling, the levels of F+ RNA coliphages and fecal coliforms were reduced by 1.6 and 1.9 log10 PFU or CFU/100 g, respectively. F+ RNA coliphages and perhaps other enteric bacteriophages may be effective candidate indicators for monitoring the microbiological quality of meat, poultry, and perhaps other foods during processing. The bacteriophage concentration method developed provides a simple, rapid, and practical tool for the evaluation of fecal contamination levels in ground beef and processed chicken meat.

Animals↗
PubMed2001

Improved method for the recovery of hepatitis A virus from oysters.

Hepatitis A is one of the major infectious diseases epidemiologically associated with worldwide shellfish consumption. Molecular detection using polymerase chain reaction (PCR) to detect hepatitis A virus (HAV) in contaminated shellfish can be hindered by low virus recoveries during the concentration process and by natural PCR inhibitors in shellfish. This study evaluated and modified two major steps of a processing procedure for virus concentration from oysters: acid adsorption-elution and solvent extraction. With the addition of second and third elutions, the acid adsorption-elution step doubled the recovery to 46% of HAV seeded initially. Extraction with chloroform or chloroform-butanol resulted in lower HAV detection limits by reverse transcription-PCR (RT-PCR)-oligoprobing than extraction with the fluorocarbon, Freon. These results led to the following modified procedure: HAV was acid adsorbed at pH 4.8, eluted first with 0.05 M glycine, second with 0.5 M threonine, PEG-precipitated twice, chloroform-extracted twice, RNA-extracted, and RT-PCR (single round) amplified. Using the modified procedure, HAV was detected by RT-PCR in all trials with a seeding density of > or = 1 plaque forming unit (PFU)/g of oyster, and in which the equivalent detection limit was 0.33 PFU of HAV seeded per RT-PCR reaction (corresponding to 111 PCR units). The method developed is capable of detecting low levels of HAV in oysters environmentally contaminated.

Animals↗
PubMed2001

Concentration and detection of cryptosporidium oocysts in surface water samples by method 1622 using ultrafiltration and capsule filtration.

The protozoan parasite Cryptosporidium parvum is known to occur widely in both source and drinking water and has caused waterborne outbreaks of gastroenteritis. To improve monitoring, the U.S. Environmental Protection Agency developed method 1622 for isolation and detection of Cryptosporidium oocysts in water. Method 1622 is performance based and involves filtration, concentration, immunomagnetic separation, fluorescent-antibody staining and 4',6-diamidino-2-phenylindole (DAPI) counterstaining, and microscopic evaluation. The capsule filter system currently recommended for method 1622 was compared to a hollow-fiber ultrafilter system for primary concentration of C. parvum oocysts in seeded reagent water and untreated surface waters. Samples were otherwise processed according to method 1622. Rates of C. parvum oocyst recovery from seeded 10-liter volumes of reagent water in precision and recovery experiments with filter pairs were 42% (standard deviation [SD], 24%) and 46% (SD, 18%) for hollow-fiber ultrafilters and capsule filters, respectively. Mean oocyst recovery rates in experiments testing both filters on seeded surface water samples were 42% (SD, 27%) and 15% (SD, 12%) for hollow-fiber ultrafilters and capsule filters, respectively. Although C. parvum oocysts were recovered from surface waters by using the approved filter of method 1622, the recovery rates were significantly lower and more variable than those from reagent grade water. In contrast, the disposable hollow-fiber ultrafilter system was compatible with subsequent method 1622 processing steps, and it recovered C. parvum oocysts from seeded surface waters with significantly greater efficiency and reliability than the filter suggested for use in the version of method 1622 tested.

Animals↗
PubMed2001

Low-pressure UV inactivation and DNA repair potential of Cryptosporidium parvum oocysts.

Because Cryptosporidium parvum oocysts are very resistant to conventional water treatment processes, including chemical disinfection, we determined the kinetics and extent of their inactivation by monochromatic, low-pressure (LP), mercury vapor lamp UV radiation and their subsequent potential for DNA repair of UV damage. A UV collimated-beam apparatus was used to expose suspensions of purified C. parvum oocysts in phosphate-buffered saline, pH 7.3, at 25 degrees C to various doses of monochromatic LP UV. C. parvum infectivity reductions were rapid, approximately first order, and at a dose of 3 mJ/cm(2) (=30 J/m(2)), the reduction reached the cell culture assay detection limit of approximately 3 log(10). At UV doses of 1.2 and 3 mJ/cm(2), the log(10) reductions of C. parvum oocyst infectivity were not significantly different for control oocysts and those exposed to dark or light repair conditions for UV-induced DNA damage. These results indicate that C. parvum oocysts are very sensitive to inactivation by low doses of monochromatic LP UV radiation and that there is no phenotypic evidence of either light or dark repair of UV-induced DNA damage.

Animals↗
PubMed2001

Comparative survival of enteric viruses and bacteria in Atlantic Ocean seawater.

The survival of Escherichia coli, Salmonella typhi, Shigella sonnei, poliovirus type 1 and a parvovirus (Minute Virus of Mice) was determined in seawater. Seeded seawater was incubated in the laboratory at 6, 12, 20 and 28 degrees C for up to 40 d. In-situ survival studies were done seasonally (winter, spring, summer and fall) using seeded microbial dialysis equipment placed in the Atlantic Ocean off coastal North Carolina at water depths of 3-10 m. In laboratory studies all test microbes survived longer at lower temperatures with typical times for 90% inactivation (T90) of 1-3 d at the highest temperature and > 10 d at the lowest temperature. Of the microbes tested, E. coli survived least well while S. typhi and Sh. sonnei survived similar to or greater than enteric viruses. Parvovirus survival was similar to that of poliovirus. Under in-situ conditions, E. coli also survived least well of all microbes tested with T90 values of 0.9-3.9 d depending upon season. All other test microbes had generally similar survivals. Overall, microbial survival in seawater was greater under laboratory conditions than under in-situ conditions. There was no clear association between microbial survival and water temperature. The lower survival of E. coli compared to the bacterial and viral pathogens under laboratory conditions raises concerns because it is a key microbial indicator of faecal contamination.

Animals↗
PubMed2001

Comparative effectiveness of UV wavelengths for the inactivation of Cryptosporidium parvum oocysts in water.

Cryptosporidium parvum oocysts in water were exposed to distinct wavelength bands of collimated beam ultraviolet (UV) radiation across the germicidal UV wavelength range (210-295 nm) that were emitted from a medium pressure (MP) mercury vapour lamp. The dose of UV radiation transmitted though each narrow bandpass filter was measured utilising potassium ferrioxalate actinometry. Oocyst infectivity was determined using a cell culture assay and titre was expressed as an MPN. The log10 inactivation for each band of radiation was determined for a dose of 2 mJ/cm2. Doses from all wavelengths between 250-275 nm resulted in approximately 2 log10 inactivation of Cryptosporidium parvum oocyst infectivity while doses with wavelengths higher and lower than this range were less effective. Because polychromatic radiation from MP UV lamps had about the same germicidal activity between the wavelengths of 250-275 nm for inactivation of oocyst infectivity, there was no unique advantage of MP UV over low pressure (LP) UV except for the simultaneous delivery of a wide range of germicidal wavelengths.

Animals↗