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Biomedical subjects

D Schoenen

Publications and source records attributed to D Schoenen.

At least 19 recordsLinked to original sources
PubMed1992

Photoreactivation of E. coli depending on light intensity after UV irradiation.

Interest in the disinfection of drinking water by UV rays has been growing in recent years. Since the beginning of the 40's it has been known that, by means of certain repair mechanism, microorganisms are able to restore lesions on DNA. These processes are more or less clarified. However there is no secure knowledge about the degree of possible repair. Photoreactivation induced by light of 350-600 nm is one of these repair mechanisms. Thus the effect of light exposure on disinfection results with E. coli after UV disinfection was examined. E. coli ATCC 11229 were cultivated, washed, suspended and irradiated by means of UV rays from a mercury low-pressure lamp. After UV disinfection, the bacterial suspension was illuminated by fluorescent light. The degree of photoreactivation could be influenced by illumination intensity. The speed of reactivation decreased with the distance of the probes to the illumination source and increased with the period of time of illumination. After a 4 log reduction of the colony count (10(6)/ml-10(2)/ml) through UV rays, the reduction rate could be decreased to only 1 log (10(5)/ml) after UV disinfection and illumination. In probes kept in darkness for the same period there was no change in the count of reproductive bacteria. It seems to be necessary to take photoreactivation into consideration with the UV disinfection of drinking water.

Colony Count, Microbial↗
PubMed1991

Studies on the lethal effect of ultraviolet light on Trichomonas vaginalis.

Following cultivation in Asami medium, centrifugation and resuspension in saline or in water from a medicinal spring, Trichomonas vaginalis trophozoites were exposed to well-defined doses of ultraviolet (UV) light (254 nm). We used 24- and 48-h-old trichomonads at concentrations of 1 x 10(5) and 5 x 10(4) trophozoites/ml in a total volume of 20 ml for these studies. The apparatus for UV irradiation was especially constructed for batch experiments. After irradiation at doses ranging from 80 to 160 mJ/cm2, the mobility of the parasites was reduced and morphological alterations appeared: rounding of the cells, vacuolization of the cytoplasm and even cytolysis. A dose of 401.7 mJ/cm2 killed 99.8% of the 48-h-old trichomonads when irradiation occurred in saline at a cell density of 1 x 10(5) trichomonads/ml and 98.9% when irradiation was done at a cell density of 5 x 10(4) trichomonads/ml. A dose of 362.1 mJ/cm2 killed only the more sensitive 24-h-old trichomonads. In mineral water, 241 mJ/cm2 was sufficient to kill up to 99.5% of the 48-h-old trichomonads. When 48-h-old trichomonads that had been exposed to a radiation dose of 160-240 mJ/cm2 were subcultured, they lost their ability to propagate. At a dose of 80 mJ/cm2, both the trichomonads that had been harvested during the log phase and the 48-h-old organisms suspended in mineral water lost their ability to propagate on subculture. These results indicate that 24-h-old trichomonads were more sensitive than 48-h-old organisms. Furthermore, the experiments demonstrated that a higher dose of UV radiation must be applied to T. vaginalis trophozoites than to the more sensitive bacterial strain Escherichia coli ATCC 11229 so as to achieve comparable killing results.

Animals↗
PubMed1991

[Effect of the reflection of UV rays in the disinfection of drinking water].

The disinfection of drinking water by means of UV-rays represents an interesting alternative to chemical disinfection. However, several questions still remain to be answered, making the disinfection of drinking water by means of UV-radiation appear unsafe. The regulations concerning the disinfection performance of UV-systems are still presenting difficulties. Within the course of comparative experiments in the laboratory and using a flow-through reactor on the disinfection effectiveness of UV-radiation, it has been shown that the reflection of UV-rays can have a considerable influence on the disinfection effectiveness. In order to be able to make reliable statements on the dose-effect relation it is necessary, therefore, to record exactly the radiation applied, including the reflected proportion.

Bacteria↗
PubMed1990

Ultraviolet disinfection of drinking water. 1. Communication: Inactivation of E. coli and coliform bacteria.

The inactivation of E. coli and coliform bacteria by UV rays was tested in a laboratory unit. The strains investigated were E. coli ATCC 11229, C. freundii ATCC 8090, E. cloacae ATCC 13047 and K. pneumoniae ATCC 4352. The irradiation dose was determined by a modified potassium ferrioxalate actinometer according to Calvert and Pitts. In consequence with the investigations E. cloacae ATCC 13047 proved to be the most UV resistant and K. pneumoniae ATCC 4352 to be the most UV sensitive microorganism.

Colony Count, Microbial↗
PubMed1990

[Solvents in drinking water from a thermostatic mixing battery].

In a hospital an odour of organic solvent could be smelled when a special thermostatic water mixer has been used. At no other water tap in the house a similar smell could be recognized. After stagnation overnight or after weekends the disgusting smell has been rather strong. The odour of organic solvent disappeared when the water had been running for some time. The organic compound in the drinking water has been identified and the thermostatic water mixer could be revealed as the source of the contamination. Further investigations of other thermostats showed a variety of alcoholic compounds which were used as thermostatic fluids.

Odorants↗
PubMed1989

[Microbial contamination of drinking water by a polyamide feedpipe].

An incident is described with high colony counts in the drinking water from a well. The well was disinfected with sodium hypochlorite for several times, but without permanent success. After that the search for the reason of the high colony counts started. It turned out that the polyamide rising-pipe produced the microbial growth. Besides the colony increase in the water there was a microbial growth upon the surface of the polyamide pipe as well. When a high grade steel pipe was installed instead of the polyamide pipe there was no colony increase in the water any more.

Germany, West↗
PubMed1989

[Microbial contamination of water by pipe and tube materials. 3. Behavior of E. coli, Citrobacter freundii and Klebsiella pneumoniae].

Materials water comes into contact with can promote the microbial growth as it could be shown before. The reaction of an unspecific microorganism flora and of Legionella pneumophila in pipes and hoses has been described in the two previous communications. The investigation with L. pneumophila has shown that even a pathogen organism can grow upon the materials. Therefore it was of special interest to prove whether indicator organisms for the testing of drinking water can grow in pipes and hoses as well. Escherichia coli, Citrobacter freundii and Klebsiella pneumoniae grew after the experimental contamination for many weeks on the rubber hose until the test was finally stopped, in the other pipes and hoses (glass, high-grade steel, PVC, PE, PA, PTFE and silicone) E. coli could be found for maximal 7 weeks, Citrobacter freundii for 1 week and Klebsiella pneumoniae for maximal 3 weeks. In the copper pipe the organisms could be found only for a few days.

Citrobacter↗
PubMed1988

[Pseudomonas aeruginosa contamination of disinfectant solutions from central disinfectant dispensing devices in swimming pools].

The disinfectant solutions from central dosing operators in swimming-bathes were microbiologically tested. The disinfectant solutions in all but one of the tested swimming-bathes showed a microbial colonization. The number of colonies ranged to 3 X 10(5) Col/ml and in 11 of the 24 tested bathes Pseudomonas aeruginosa could be isolated from the disinfectant solutions. Especially the occurrence of P. aeruginosa is quite unfavourable. Due to the results special restorations seem to be necessary.

Disinfectants↗
PubMed1988

[Microbial contamination of water by pipe and hose material. 1. Detection of colony count changes].

Materials may produce a growth of microorganisms by contact with water. Pipes and hoses with a narrow diameter have not yet been tested on their influence on the microbial colonization of the water. A harmful change has been discussed especially in dental treatment units. Pipes and hoses were tested in their influence on the microbial growth for half a year. Glass, high grade steel, copper and PTFE showed no increase in microorganisms or only a little in the beginning. The other tested materials, PVC, PE, PA, silicon and rubber, produced an intensive microbial growth.

Bacteria↗
PubMed1988

[Microbial contamination of water by pipe and tubing material. 2. Growth of Legionella pneumophila].

In the 1st communication it was possible to show that some hoses and insufficiently cleaned high grade steel pipe can produce a microbial growth. The growth-promoting effect of materials in the water distribution system for Legionella pneumophila has been discussed before. In this investigation it was tested how L. pneumophila behaves in pipes and hoses with narrow diameter, at temperatures from 35 degrees C to 40 degrees C and over a time of half a year. L. pneumophila could be found in high numbers in the water from PVC, PE, PTFE, rubber and silicon hoses all over the time and regularly in low numbers or occasionally in glass, high-grade steel pipes and PA hose. L. pneumophila could be found only for the first 4 weeks in the copper pipe.

Copper↗
PubMed1987

Microbiological evaluation of drinking water construction materials--comparison of two test procedures.

Materials used in contact with drinking water can impair water quality by supporting the growth of aquatic microorganisms. In order to prevent this problem several different test procedures have been developed but to date no comparative study of the performance of these methods has been published. During collaborative studies between the regional laboratories of the Thames Water Authority, London, and the Institute of Hygiene, University Bonn, duplicate samples of 11 PVC materials were exchanged and evaluated by the standard methods used in the United Kingdom (UK) and the Federal Republic of Germany (FRG). There was a good agreement between the results as assessed by the published criteria. When a stricter criterion for interpreting the results of the UK method was applied to the findings, a complete agreement between the methods was observed.

Bacteria↗
PubMed1987

[Increase in the colony count in drinking water tanks caused by solvents from the coating material].

As a freshly coated storage tank was put into operation a permanent colony increase in the drinking water (up to 7400 cfu/ml) could be detected. By chlorine dosage (30 mg/l) colony counts were reduced. From a second storage tank which had been coated at the same time bituminous coating material and air samples could be taken. After the exposure of the bituminous coating material in aqua bidest. 48 organic compounds were found by GC/MS-analysis. The main compounds were xylene, ethylbenzene and 1,2,4-trimethylbenzene. These compounds were also found by GC-investigations of the air-samples. The dependence between the used organic solvents and the colony increase could be demonstrated by biodegradation tests of solvent compounds. It was found that about 50 per cent of the identified compounds could be degraded by microorganisms and therefore caused a colony increase in drinking water.

Bacteriological Techniques↗
PubMed1986

[Decontamination of drinking water taps colonized with Pseudomonas aeruginosa].

Water taps in hospitals are quite often contaminated with Pseudomonas aeruginosa. It is possible that Pseudomonas aeruginosa is disseminated with the water. It seems necessary to disinfect the water taps in order to prevent an endangering of the patients and a contamination of wetted areas. It has been looked for a method of decontamination which could be used under practical conditions. The experimentally contaminated taps could be disinfected in a short time when hot water was lead into the taps. The taps could not be disinfected by heating with a flexible electric heating ribbon.

Disinfection↗
PubMed1986

[Recent studies on the recolonization of drinking water].

About the re- or aftergrowth in drinking water there are some reports. But there are still no real ideas about the reasons and the colony counts to which the water may rise under practical conditions when there is no external influence. In these investigations drinking water was stored in a reservoir for 3-6 weeks and the increase of colonies was observed. In all six tests there was an increase in the colony count. The maximum counts fluctuated between 8-2000 colonies/ml. The water, a mixture of surface- and groundwater, had not a homogeneous tendency of re- or aftergrowth. The chemical parameters gave no indications to these differences.

Bacteria↗