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Three different soil types (two sandy materials and one till soil type) were sterilized with 14 different sterilization methods or variations. The cation-exchange capacity and specific surface of the soil samples were chosen as control parameters of physico-chemical modifications in the soils. Incubation of soil samples in the presence of Na-azide and HgCl2, in addition to tyndallization and fractionated heating of soil lead to a significant reduction of microorganisms. UV radiation and alternating freezing and thawing of soil had no influence on the number of microorganisms. The application of mercury-II-chloride did not lead to the expected sterilization, especially with till. A sterilization of soil is possible by using formaldehyde and ethylene oxide gassing, in addition to autoclaving and gamma radiation. No microorganisms could be detected in the soils after application of these sterilization methods. The cation exchange capacity of the soils was only slightly influenced with these methods. The use of gamma radiation seems to be the best method for sterilization of soils.

Using three UV-plants of different technical designs for water disinfection, we studied the conformity between experimental germ reduction using standard test organisms and calculated UV-doses under various water flow conditions. Taking into consideration the style of construction of the UV-plants, the irradiation area and the layer thickness were used as constant parameters for dose calculations. This was also employed for the irradiation intensity, since the experiments were performed for a relatively short period compared of the life span of the UV-irradiators. Both exposure time and water transmission were employed as variable parameters in the dose calculations and experimental procedures respectively. The calculated UV-dose and experimentally obtained germ reduction values were comparatively the same for two of the three UV-plants studied. However, no correlation was observed between the reduction of E. coli and the corresponding calculated UV-dose values. Therefore, the calculated UV-dose values for any given UV-plant should be considered to be relative and by no means absolute values. We are of the opinion that within a certain range of water flow rate and transmission, antimicrobial effectiveness of different UV-plants should be demonstrated independent of dose values, technical and other construction characteristics. The applicability of the UV-plants studied is discussed.

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.

Pasteurized milk was treated with microwaves for 2.5 minutes (2450 MHz, 650 W). Important chemical components (vitamin A, beta-carotin, vitamins B1, B2, C, E; activity of peroxidase, xanthinoxidase; content of fat and peroxides, percentage of solids, content of raw protein, content of all microorganisms and storage stability were examined. Ascorbic acid (reduction of 36%) and alpha-tocopherol (reduction of 17%) were influenced by microwave treatment, whereas other chemical parameters, odor and flavor remained unchanged. The content of microorganisms was reduced from about 10(4) to 10(2) per milliliter. Untreated milk had a content of 10(7) microorganisms per milliliter after 10 days storage at 8 degrees C and a taste of acidity, whereas in milk treated with microwaves only 10(4) microorganisms per ml were identified and no organoleptic changes could be observed after 14 days storage at 8 degrees C.

The u.v.-susceptibility of E. cloacae, E. coli and E. faecium was tested with a flow-through u.v. light treatment apparatus. Drinking water of three ranges of temperature (ca. 13 degrees C, ca. 33 degrees C, and ca. 48 degrees C) was used. The u.v.-susceptibility was tested with bacteria harvested in the exponential phase of growth as well as with bacteria harvested in the stationary phase. In all ranges of temperature and both phases of growth reductions of at least 99.9999% of E. cloacae and E. coli were obtained by a dosage of less than or equal to 25 mWs/cm2. For E. faecium harvested in the exponential phase of growth this could be confirmed in cold water of 13 degrees C, while in warm water of 48 degrees C a dosage of ca. 47 mWs/cm2 for a reduction of 99.9999% was necessary. To kill E. faecium-cells, which were harvested in the stationary phase, dosage between 39 and 45 mWs/cm2 were necessary in water of the three ranges of temperature.

With a flow-through u.v. light treatment apparatus the u.v.-susceptibility of E. faecium, E. coli and P. aeruginosa in drinking water was tested. The investigations were done with cells harvested in the exponential phase of growth. One part of the suspensions was used immediately (= 0 days old cells), two other parts were stored for 5 and 7 days in sterilised drinking water in the dark at room temperature (= 5 and 7 days old cells). In either case--0 or 5 and 7 days old cells--reductions of at least 99.999% were obtained by a dosage of 25 mWs/cm2. No difference concerning the u.v.-susceptibility could be noticed between the different kind of cells of E. faecium, E. coli, and P. aeruginosa.

UV-Inactivation of Escherichia coli, Bacillus subtilis spores, Staphylococcus-Phage A 994, Poliovirus type Mahoney and Rotavirus SA 11 was tested under controlled physical conditions. B. subtilis-spores were found to be the most resistant of these microorganisms, followed by Rotavirus, Bacteriophage and Poliovirus. E. coli required the lowest irradiation dose for inactivation. Causes and meaning of these dose-survival-reactions are discussed.

Reported in this paper is the use of 60Co gamma radiation to inactivate mycoplasmas in calf serum, newborn calf serum, and fetal calf serum. A dose of 3 kGy, independent of dose rate, was found to be sufficient for inactivation in the above sera of several mycoplasmas, including Acholeplasma laidlawii, Mycoplasma (M.) orale, M. arginini, M. hyorhinis, and M. bovis. The critical dose proved to be at 2 kGy. No difference was found to exist between the above species in susceptibility to irradiation in diluted sera (50%) and 10% in Eagle MEM). Sensibility of wild mycoplasma strains was found to be identical with that of laboratory strains. Hence, 60Co gamma irradiation of sera appears to be a safe method by which to make sera mycoplasma-free. Bacillus subtilis in calf serum was inactivated by doses above 18 kGy, with the critical dose being 15 kGy.

The kinetics of inactivation and the resistance to gamma radiation of microorganisms usually to be found in raw sludge were examined with five viruses, three bacteria and a fungus serving as prototypes in comparative studies. All these infectious agents could reliably be inactivated by gamma rays in raw sewage sludge but they were clearly more resistant to gamma rays compared to irradiation in a liquid suspension. The reduction of the virus content required a much higher radiation dose compared to bacteria and the fungus used, excluding Streptococcus faecalis which was exceptionally resistant. Considering the content of pathogenic viruses and other agents in raw sewage sludge, the required radiation dose necessary to comply with average to strict demands for the hygienisation of sewage sludge is discussed. The radiation dose of 500 to 1,000 krad seems therefore to be sufficient.

Untreated surface water of a total bacterial count of approximately 10(4) cfu/ml was contaminated additionally with suspensions of E. coli and S. faecium, which contained about 10(6) cfu/ml. At flow rates of 7.2 m3/h, 4.0 m3/h and 2.0 m3/h the survival of bacteria as a function of exposure to radiation was measured with two different U.V.-disinfection units. In surface water, -without an additional contamination -minimum doses of radiation up to 74 mWs/cm2 were necessary to cause a reduction of 99.99% for total bacterial counts and counts of lactose-positive colonies. When suspensions of E. coli or S. faecium were added, a reduction of 99.99% for total bacterial count was attainable with minimum doses up to 71 mWs/cm2. To reduce the number of lactose-positive colonies or the number of D-streptococci to 99.99% a minimum dose up 56 mWs/cm2 or 18 mWs/cm2 was necessary.

UV-radiation of 254 nm wavelength produces in the genetic material (desoxyribonucleic acid, (DNA) of bacteria photochemical alterations (lesions) which can lead to cellular death or mutation induction. The biologically most important class of these lesions is the one of the pyrimidine dimers. Bacteria possess three groups of enzymatic mechanisms which can eliminate such lesions under certain circumstances: elimination in situ; removal from the nucleotide chain (prereplication repair); ignoring the lesion (postreplication repair). The biological effect and the importance of these so-called repair mechanisms is reviewed and the occurrence in other organisms is briefly discussed. On the one hand, organisms are exposed to UV-radiation of 254 nm wavelength only under artificial conditions; on the other hand, long-wave solar UV-radiation (between approximately 300 nm and visible light) which amounts to about three per cent of the total energy output, represents the most powerful radiation to which organisms can be exposed under natural conditions to any larger extent. As outlined in the second part of this review, this radiation also induces lesions which may act as substrate for the above mentioned repair mechanisms. With increasing wavelength, lesions may also occur in cellular components other than DNA. The complexity of biological responses arising thereby is discussed.

The presence of 5-bromouracil (BU) as well as 5-bromo-2-deoxyuridine (BUdR) in the cultivation media of bacteria results in the distinct increase of UV sensitivity. With the nucleic acid base analogue 8-azaadenine (8-AA) a similar effect was confirmed, however, not so pronounced. In the experiments reported here the combined action of BU or BUdR and 8-AA on Escherichia coli, Proteus mirabilis, Bacillus subtilis and Bacillus cereus was investigated. The sensitization effect of BUdR does not increase if 8-AA is present additionally during cultivation. On the contrary, a decrease of sensibilization occurs. This result may be caused by the protective effect of the adenine derivative against UV irradiation, if it is present in the cell, but not incorporated into the DNA.

The effect of cobalt-60 gamma irradiation was investigated on the concentration of Salmonella (S.) typhimurium in artificial contaminated chicken carcasses and on the number of S. tennessee and S. agona in artificial contaminated spray-dried whole egg powder and liquid whole egg. Irradiation of carcasses and of liquid whole egg was carried out at deep frozen conditions between -10 degrees C and -18 degrees C and whole egg powder at 15-20 degrees C. The irradiation doses used where between 0.05 and 8.0 KGy. The D10-value of S. typhimurium in broiler chicks ranged between 0.57 and 0.74 and of S. agona respectively S. tennessee amounted to 0.95 and 1.07 in spray dried whole egg powder and 0.47 respectively 0.53 in whole egg content. Irradiation causes drastic reduction of physiological microflora in chicken carcasses. By radiation treatment using a dose of 4.0 KGy, germ count reductions by 3-5 decimal powers were achieved. Resistance of microbes increases in following succession: Pseudomonas spp., Salmonella spp., other Enterobacteriaceae spp., Micrococcus spp., Flavobacterium spp., yeasts, Bacillus spp., Streptomyces spp., fungi. Results of microbiological and sensorial examinations allow following conclusions: 1. Irradiation is highly effective against Salmonella. 2. Irradiation dose of 4.0 KGy is able to kill about 1 Million Salmonella bacteria per chicken. This guarantees safe elimination of natural occurring Salmonella bacteria in broiler chicken carcasses. 3. Irradiation of chicken carcasses up to 4.0 KGy causes no injury of quality, however storage longer than 4 months deteriorates sensorial qualities more than of unirradiated carcasses.(ABSTRACT TRUNCATED AT 250 WORDS)

As a physical disinfection method without chemicals required the ultraviolet irradiation was tested for disinfection of drinking water. The survival was measured as a function of exposure to radiation for S. enteritidis, E. cloacae, C. freundii, S. marcescens, E. coli, K. pneumoniae und S. faecium. The bacteria were grown in trypton soya broth until they were well into the exponential phase. Two different UV-disinfection units were tested. Both consist of cylindrical shaped chambers with one low-pressure mercury-discharge lamp with their longitudinal axis parallel to the chambers. With 10(6) cfu/ml the experiments were done with three different rates of flow of 7,2 m3/h, 4,0 m3/h and 2,0 m3/h. The minimum exposures to radiation necessary to cause a 99.999% reduction were 10-86 mWs/cm2 depending on the test bacterium and on the UV-disinfection unit. The minimum doses ranged for S. enteritidis up to 13 mWs/cm2, for E. coli up to 21 mWs/cm2, for K. pneumoniae up to 39 mWs/cm2, for S. faecium up to 42 mWs/cm2, for E. cloacae up to 43 mWs/cm2, for C. freundii up to 72 mWs/cm2, and for S. marcescens up to 86 mWs/cm2.