Sporicidal effects

A very commonly used disinfectant is ethanol-water in neutral or, preferably, in acidic conditions. Aqueous ethanol displays its best germicidal efficiency at a concentration of 60 to 70%. However, the most commonly used concentration in industry is about 20%, because higher concentrations require specific explosion-proof facilities. At 20%, ethanol has no sporicidal effect, its effect on viral inactivation is only partial and it does not destroy pyrogens (it only tends to destabilize large molecular aggregates of lipopolysaccharide molecules). For these reasons, 20% ethanol can only be considered as a bacteriostatic agent. Mixtures of ethanol with bases or acids are somewhat more sporicidal, but are not sufficient to provide sterilization at short incubation times and low temperatures. 

The presence of water is essential for the activity of isopropanol, too. Most effective are concentrations of approx. 50%. Isopropanol and n-propanol are the highest alcohols which are miscible with water. The sporicidal effectiveness of isopropanol is poor. 

Because of the mechanism mentioned above the aldehydes with microbicidal effect are distinguished by broad spectra of effectiveness which also cover viri and spores. Since only few sporicides are found among microbicides, the sporicidal effect of aldehydes, particularly that of glutaric aldehyde is of special interest. Aldehydes are above all used for disinfecting purposes but also for preservation, then chiefly in the form of so-called aldehyde releasing compounds (see Sections 3 and 4). 

Formaldehyde is well established as a bactericidal agent [13], although most of the research has focused on its sporicidal effects [24, 74] which are therefore considered in more detail in the following section. 

Some commercial formulations have combined aldehydes with other compounds to enhance sporicidal effects. Gigasept (succinaldehyde plus formaldehyde) has been recommended for the disinfection of endoscopes [123]. The formulation effects a 2-log and 5-log reduction at concentrations of 5% and 10% respectively against aqueous suspensions of B. subtilis spores [8] and is therefore more effective than formaldehyde alone. 

The use of peracetic acid (PAA) for sterilization has received increasing attention due to deepening concerns about environmental impacts as well as increased needs for cold sterilization. PAA attacks a wide spectrum of microbes [19-22] and maintains sporicidal effects at temperatures even lower than room temperature [23] further it leaves only nontoxic residues [24]. Therefore, PAA-based disinfectants have been widely used in the food and healthcare industries as an effective means of sterilization [25, 26]. PAA is an ideal disinfectant in sterile clean-in-place (CIP) packing systems for plastic bottle beverages because of its rapid sporicidal effect and low-temperature sterilization [26]. 

A number of aldehydes possess antimicrobial properties, including sporicidal activity however, only two, formaldehyde and glutaraldehyde, are used for disinfection. Both these aldehydes are highly effective biocides and their use as chemosterilants reflect this. 

The acridine dyes, including proflavine, acriflavine and aminacrine, have also been employed for skin disinfection and treatment of infected wounds or burns. They are slow-acting and mainly bacteriostatic in effect, with no useful fungicidal or sporicidal... 

Yeasts (including Candida albicans) and dermatophytes are usually sensitive, although chlorhexidine fungicidal action is subject to species variation, as are other agents. The effective concentrations of chlorhexidine agents for bactericidal, bacteriostatic, sporicidal, and sporostatic organisms are listed in Table 2.13. 

Phenols (Fig. 17.7) are widely used as disinfectants and preservatives. They have good antimicrobial activity and are rapidly bactericidal but generally are not sporicidal. Their activity is markedly diminished by dilution and is also reduced by organic matter. They are more active at acid pH. The main disadvantages of phenols are their caustic effect on skin and tissues and their systemic toxicity. The... 

Bacterial spores of the genera Bacillus and Clostridium are invariably the most resistant of all types of bacteria to biocides. Many biocides, e.g. biguanides and QACs, will kill (or at low concentrations be bacteriostatic to) non-sporulating bacteria but not bacterial spores. Other biocides such as alkaline glutaraldehyde are sporicidal, although higher concentrations for longer contact periods may be necessary than for a bactericidal effect. 

These data clearly demonstrated that the antifungal activity of HMTP was due to its sporicidal action, and the antibacterial activity was attributed to its bactericidal property. We also investigated the effects on the cellular... 

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