Type Disinfectant

Compound (example) Spectrum of disinfection (types of organisms killed) pH range for effective kill Typical concentration needed Typical formulation concentration (%) Chemical incompatibilities/ comments... 

This formulation has not been registered with the Environmental Protection Agency (EPA). Any formulation which you might choose to market with germicidal, disinfectant type claims must be registered with the EPA as required by the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA). 

Disinfection. Ozone is a more effective broad-spectmm disinfectant than chlorine-based compounds (105). Ozone is very effective against bacteria because even concentrations as low as 0.01 ppm are toxic to bacteria. Whereas disinfection of bacteria by chlorine involves the diffusion of HOGl through the ceU membrane, disinfection by ozone occurs with the lysing (ie, mpture) of the ceU wall. The disinfection rate depends on the type of organism and is affected by ozone concentration, temperature (106), pH, turbidity, clumping of organisms, oxidizable substances, and the type of contactor employed (107). The presence of oxidizable substances in ordinary water can retard disinfection until the initial ozone demand is satisfied, at which point rapid disinfection is observed. 

The threat of accidental misuse of quaternary ammonium compounds coupled with potential harmful effects to sensitive species of fish and invertebrates has prompted some concern. Industry has responded with an effort to replace the questionable compounds with those of a more environmentally friendly nature. Newer classes of quaternaries, eg, esters (206) and betaine esters (207), have been developed. These materials are more readily biodegraded. The mechanisms of antimicrobial activity and hydrolysis of these compounds have been studied (207). AppHcations as surface disinfectants, antimicrobials, and in vitro microbiocidals have also been reported. Examples of ester-type quaternaries are shown in Figure 1. 

Alkylbenzyldimethyl quaternaries (ABDM) are used as disinfectants (49) and preservatives. The most effective alkyl chain length for these compounds is between 10 and 18 carbon atoms. Alkyltrimethyl types, alkyl dimethylbenzyl types, and didodecyl dimethyl ammonium chloride [3401-74-9] exhibit excellent germicidal activity (151—159). Dialkyldimethyl types are effective against anaerobic bacteria such as those found in oil wells (94—97). One of the most effective and widely used biocides is didecyl dimethyl ammonium chloride [7173-57-5]. 

Sodium bisulfate, NaHSO, is a convenient mild acid and is safe for uses as a household toilet-bowl cleaner, automobile-radiator cleaner, and for swimming pool pH adjustment. It is used for metal pickling, as a dye-reducing agent, for soil disinfecting, and as a promoter in hardening certain types of cement. 

Liquid sterilants are known to corrode the metal parts of articles and instmments that are to be sterilized, although articles composed exclusively of glass or certain type of corrosion-resistant metal alloys can be safely processed. Because the degree of corrosion is related to length of exposure, many articles are merely disinfected in a shorter exposure time. Disinfection may be suitable for certain appHcations. The safety of using Hquid sterilants must be judged by a qualified microbiologist. 

Disinfection tests can be classified according to the test organism, ie, whether the test employs certain species of bacteria, fungi, or vimses classified as to whether it is a static test or a cidal test, as in a bactericidal vs bacteriostatic test or sporicidal vs sporistatic test or classified as to whether it is a microbial reduction test or an end-point test where all the organisms in the test are apparently killed. Procedures may be distinguished by in vitro or in vivo testing. Another way to consider tests is whether they are screening tests, practical type laboratory tests, or field tests. 

Available Chlorine Test. The chlorine germicidal equivalent concentration test is a practical-type test. It is called a capacity test. Under practical conditions of use, a container of disinfectant might receive many soiled, contaminated instniments or other items to be disinfected. Eventually, the capacity of the disinfectant to serve its function would be overloaded due to reaction with the accumulated organic matter and organisms. The chlorine germicidal equivalent concentration test compares the load of a culture of bacteria that a concentration of a disinfectant will absorb and still kill bacteria, as compared to standard concentrations of sodium hypochlorite tested similarly. In the test, 10 successive additions of the test culture are added to each of 3 concentrations of the hypochlorite. One min after each addition a sample is transferred to the subculture medium and the next addition is made 1.5 min after the previous one. The disinfectant is then evaluated in a manner similar to the phenol coefficient test. For equivalence, the disinfectant must yield the same number of negative tubes as one of the chlorine standards. 

Tuberculocidal Test. The tubercle bacillus is resistant to disinfectants because the cells are protected with a waxy coating that is not readily penetrated. The tuberculocidal test is a use dilution practical type test that employs porcelain cylinders. The bacteria are different from those in the use dilution method (Table 10), the incubation time is longer, and the details of the procedure are different. For example, in the tuberculocidal test the test is divided into two parts, a presumptive test and a confirmatory test. The former employs Mycobacterium smegmatis and the latter employs Mycobacterium bovis (BCG). For the presumptive test the incubation time is 12 days, as against 48 hours for other bacteria used in the use-dilution method. For the confirmatory test the incubation time is 60 days, with an additional 30 days in case there is no growth. As shown in Table 10, the concentrations of the phenol standard are higher than used with other bacteria. 

In order to ensure the destruction of pathogens, the process of chlorination must achieve certain control of at least one factor and, preferably two, to compensate for fluctuations that occur. For this reason, some authorities on the subject stress the fact that the type and concentration of the chlorine residual must be controlled to ensure adequate disinfection. Only this way, they claim, can chlorination adequately take into account variations in temperature, pH, chlorine demand and types of organisms in the water. While possible to increase minimum contact times, it is difficult to do so. Five to ten minutes is normally all the time available with the type of pressure systems normally used for small water supplies. Many experts feel that satisfactory chlorine residual alone can provide adequate control for disinfection. In their opinion, superchlorination-dechlorination does the best job. Briefly, what is this technique and how does it operate ... 

It is only very recently that organic componnds synthesized by humans have begun to exert a selection pressure upon natural populations, with the consequent emergence of resistant strains. Pesticides are a prime example and will be the principal subject of the present section. It should be mentioned, however, that other types of biocides (e.g., antibiotics and disinfectants) can produce a similar response in microbial populations that are exposed to them. 

The more usual pattern found experimentally is that shown by B, which is called a sigmoid curve. Here the graph is indicative of a slow initial rate of kill, followed by a faster, approximately linear rate of kill where there is some adherence to first-order reaction kinetics this is followed again by a slower rate of kill. This behaviour is compatible with the idea of a population of bacteria which contains a portion of susceptible members which die quite rapidly, an aliquot of average resistance, and a residue of more resistant members which die at a slower rate. When high concentrations of disinfectant are used, i.e. when the rate of death is rapid, a curve ofthe type shown by C is obtained here the bacteria are dying more quickly than predicted by first-order kinetics and the rate constant diminishes in value continuously during the disinfection process. 

The testing of disinfectants for virucidal activity is not an easy matter. As pointed out earlier (Chapter 3), viruses are unable to grow in artificial culture media and thus some other system, usually employing living cells, must be considered. One such example is tissue culture, but not all virus types can propagate under such circumstances and so an alternative approach has to be adopted in specific instances. The principles of such methods are given below. 

This type of procedure may thus suggest that an unnecessarily high disinfectant concentration (so-called overkill) may be employed in practice to achieve a virucidal effect. 

The human immunodeficiency virus (HIV lymphadenopathy-associated virus, LAV human T-cell lymphotrophic virus type 3, HTLV III) is responsible for acquired immune deficiency syndrome (AIDS see Chapter 3). Because of the hazard and difficulties of growing the virus outside humans, a different approach has to be examined for determining viral sensitivity to disinfectants. 

The clinical relevance of biocide resistance of antibiotic-resistant staphylococci is, however, unclear. It has been claimed that the resistance of these organisms to cationic-type biocides confers a selective advantage, i.e. survival, when such disinfectants are employed clinically. However, the in-use concentrations are several times higher than those to which the organisms are resistant. 

Most contact lenses are worn for optical reasons as an alternative to spectacles. Contact lenses are of two types, namely hard lenses, which are hydrophobic, and soft lenses, which may be either hydrophilic or hydrophobic. The surfaces of lenses mnst be wetted before nse, and wetting solntions (section 4.5.1) are nsed for this pnrpose. Hard and, more especially, soft lenses become heavily contantinated with protein material dnring nse and must therefore be cleaned (section 4.5.2) before disinfection (section 4.5.3). Contact lenses are potential sonrees of eye infection and conseqnentiy nticroorganisms should be removed before the lens is again inserted into the eye. Lenses mnst also be clean and easily wettable by the lacrimal secretions. Contact-lens solntions are thns sterile solutions of the varions types described below. Apart fiom... 

Finally, heat m be utilized as an alternative method to disinfect soft contact lenses, especially the hydrophilic type. Lenses are boiled in isotonic saline. 

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