Bacterial disinfection methods

Fecal organism inactivation was also studied in nonchlorinated secondary wastewater and raw wastewater by Kurucz et al. (1991). Fecal organisms are absorbed in a dose-dependent manner, and four to five log units of inactivation can be expected as the dose approaches 6 kGy. The total bacterial flora was inactivated at approximately the same level as the coliform for each absorbed dose, as opposed to other disinfectant methods. The fact that the total fecal organisms are inactivated at approximately the same rate indicates that high-energy electrons are indiscriminate disinfectants. 

The roots of environmental microbiology also lie in urban waste management and treatment. The field originally focused on monitoring the movement of pathogens and treating them within natural and urban environments to protect municipal water quality and public health. As the world became more urbanized in the late nineteenth century, the incidence of communicable diseases such as typhoid fever and cholera increased. To combat the spread of diseases, cities and communities began to treat water with various filtration and disinfectant methods. For the most part, such approaches to water treatment were instrumental in the elimination of waterborne bacterial diseases in developed countries, and disinfection processes continue to be widely used. 

During the last few years, the European Standardization Committee 216 has begun to harmonize disinfection methods. It has been shown that precision and test reproducibility can be improved by rigorous standardization of methods for preparation of the disinfectant solutions and bacterial suspensions. These tests can be classified into three levels, as follows. 

While the precise reasons for the higher bacterial growth in the electronic faucets still need clarification, the researchers say it appears that standard hospital water disinfection methods, which complement treatments by public utilities, did not work well on the complex valve components of the newer faucets. They suspect that the valves simply offer additional surfaces for bacteria to become trapped and grow. 

Phenol Coefficient Test. The first important attempt at standardizing testing methods was known as the phenol coefficient test (96). It has been modified several times, and is an official AO AC screening test recognized by EPA and PDA. The phenol coefficient test compares the activity of disinfectants to that of phenol, under specific conditions, to give a number that measures the activity of the chemical tested with respect to that of phenol, ie, the phenol coefficient. The AO AC method employs visual examination of bacterial growth in a nutrient medium. The Kelsey-Sykes test (1969) is a modified method popular in British circles. 

In all antiseptic testing, it is recognized that skin and mucous membranes to which products ate appHed cannot be disinfected or sterilized but it is possible to significantly reduce the population of transient and resident pathogenic bacterial flora. AH in vivo test methods requite a deterrnination of the bacteria on the skin before and after treatment. Because of the normal variation in bacterial population of the skin of different people, a number of people must be tested in order to make a statistical analysis of the results. Different parts of the body are used for different tests. In aH of the tests the details of the protocol ate extremely important and must be strictly adhered to in order to obtain reproducible results. 

The Kelsey-Sykes (KS) test. Having regard to the many disadvantages alleged against the RW and CM tests, attempts were made and published in the early 1960s to find improved test methods. The foundations for the new test were laid by Kelsey et al. in 1965, and with the collaboration of the late G. Sykes and ofisobel M. Maurer, the Kelsey-Sykes test was evolved. This test embodied several principles. Firstly, it was a capacity test. Here a bacterial inoculum was added to the disinfectant in three successive lots at 0, 1 and 5 minutes. This is the principle of a capacity test where the capacity or lack of capacity ofthe disinfectant to destroy successive additions of a bacterial culture is tested. 

At the well field adjacent to Terrieu Creek in southern France, a large proportion of fecal coliform bacteria was associated with suspended sediment, at times up to 90%. Bacterial concentrations associated with sediment in surface water and in the subsurface were very similar, indicating a close connection between the two. The association of bacteria with sediment has important implications for public health. The bacteria may be protected from predation, may be able to use the substrate as a food source, and are less susceptible to standard methods of disinfection. 

Some methods, based on standard disinfectant protocols, state a requirement for reduction of bacterial cells in a one hour period (e.g., a 2 log reduction - a 99% decrease in the number of viable bacteria). Others... 

The application of nanosilver in medicine is particularly an important issue. The method of production of nanosilver-coated polymers, which are used as plastic catheters, has been developed. A coating with silver nanoparticies acts as an antibacterial and disinfectant. The in vitro tests confirmed growth inhibition in the bacterial layer which was sustained for 72 h (Roe et al., 2008). In patent... 

The AO AC use-dilution method is most commonly used to register disinfectant products. In this test, bacterial inocula are dried onto stainless steel penicylinders before exposure to disinfectant. The penicylinders, with dried organisms, are exposed to the disinfectant for 10 min and are then transferred to a subculture containing a germicide neutralizer. The product passes the test if no more than 1 sample out of 60 replicates gives a positive growth [13]. 

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