In favorable conditions, many bacteria form resistant lasting/permanent spores (these spore-producing bacteria are also collectively termed as bacilli (germs). Generally, spores are more resistant to high temperatures and UV-radiation than bacteria, which is why it is necessary to choose ten times the dose that would be necessary for the destruction of bacteria. Under favorable conditions, the spore develops into a new bacterial cell.
Yeast fungi are uni-cellar plant-like microorganisms (Sacharmyces and other relatives to snake fungi). They do not contain chlorophyll and differentiate themselves from the mold by multiplying in a different way. Like some kinds of bacteria, yeast fungi can also form spores. In practice, yeast fungi are widely applied. The most important applications are beer yeast fungi (lower and upper yeast fungi), yeast fungi for raising bread, wine and food items (dried, pressed yeast fungus).
The pattern of yeast fungi reaction to UV-radiation is similar to that of mold fungi in which processes the aim is the destruction of the “wild” yeast fungi.
This description covers a group of microorganisms, spread through spores. Mold fungi form cotton wool-like, entangled and puffball -like expenses on plant or animal matter (material), causing a putrefying (rotting) process. Mold fungi are also seen as parasites causing illness in humans and animals.
Some kinds are:
- Head mold (mucor) on fruit and bread
- Flask (spadix) or pouring jugs (Aspergillus), on moist plant matter, fruit, bread, leather
- Brush mold (botrytis cinera), perishable fruit, especially strawberries and half ripening grapes
Other kinds of molds serve as the basis for antibiotics. This includes penicillin and streptomycin.
First mold fungi (and yeast fungi) show activation when radiated with small doses of UV. With larger doses, they are killed, in which process the spectral effect is approximately the same as with the bacteria. Also here the spores are essentially more resistant than vegetative kinds.
This term covers a group of micro-organisms of largely unknown nature, all of which cause illnesses in humans, animals, and plants. Viruses are so small that bacteria-impermeable filters cannot trap them. Not until the use of the electron microscope, has it became possible to observe all kinds of viruses. All viruses have the characteristic of not thriving on dead matter, which is why they can only be cultivated in living substances. Viruses are stopped in their action when exposed to UV-C 253.7.
There are important differences in the resistance towards UV-C radiation for the various kinds of micro-organisms. The percentage for dead bacteria is not proportional with the dose of radiation, where, however, they increase with an increasing dose. In the list, a collection of the necessary doses for a certain effect of disinfection is given. The information is from the current literature.
The values from various authors are at present remarkably deviant. This may be due to the different types of bacteria – different growth conditions and the temperatures concerned. Calculations based on the inactivation of micro-organisms show a variation in the interpretation of the conditions of radiation for necessary dose values.
This means that with e.g. a radiation value E, which over a certain progress of time T, reaches a certain effect of disinfection, arrive at the same result when the two factors vary, but their result E multiplied by T is the same. However, it is only possible to change the time T within certain boundaries, as the micro-organisms by excessively prolonged radiation and at a too low radiation value E, in the beginning, will only be able to multiply, due to the fact that the UV-dose is too small. For these reasons, the desired effect of inactivation is achieved much later than this law stipulates. The surroundings, in which microorganisms are found, greatly influence the desired level of disinfection. In water e.g. there are coli-bacteria, which are 10 times more resistant than in air. Increased moisture content in the air greatly increases the necessary dose.