Tuesday, 21 April 2015

Introduction to Disinfectants


A disinfectant is a chemical agent that is used to reduce the number of viable microorganisms on pharmaceutical surfaces to an acceptable level. Disinfectants have a variety of properties that include spectrum of activity, mode of action, and effectiveness. Some are bacteriostatic, where the ability of the bacterial population to reproduce is halted. In this case, the disinfectant can cause selective and reversible changes to microbial cells by interacting with nucleic acids and inhibiting enzymes, or permeating into the cell wall. Once the disinfectant is removed from contact with bacterial cells, the surviving bacterial population can potentially grow. Other disinfectants are bactericidal in that they destroy bacterial cells and cause irreversible damage through different mechanisms that include structural damage to the cell, cell lysis, and autolysis, resulting in leakage or coagulation of cytoplasm. The destruction of bacterial and fungal spores is a property which a given disinfectant may or may not possess. This type of chemical agent is called a sporicide. A chemical agent does not have to be sporicidal in order to be classified as a 'disinfectant' or as a 'biocide'. The bacteriostatic, bactericidal and sporicidal properties of a disinfectant is influenced by many variables.

Disinfectants can be categorized into groups by chemical nature, spectrum of activity, or mode of action. Some disinfectants, on entering the microbial cell either by disruption of the membrane or through diffusion, proceed to act on intracellular components. Actions against the microbial cell include: acting on the cell wall, the cytoplasmic membrane (where the matrix of phospholipids and enzymes provide various targets) and the cytoplasm. This section provides a summary some of the more common disinfectants used the pharmaceutical environment. The two principle categories consist of non-oxidizing and oxidizing disinfectants.

Non-Oxidizing Disinfectants: The majority of disinfectants in this group have a specific mode of action against microorganisms and generally have a lower spectrum of activity compared to oxidizing disinfectants. These disinfectants include alcohols. Alcohols have an antibacterial action against vegetative cells. The effectiveness of alcohols against vegetative bacteria increases with their molecular weight (i.e., ethanol is more effective than methanol and in turn isopropyl alcohols are more effective than ethanol). Alcohols, where efficacy is increased with the presence of water, act on the bacterial cell wall by making it permeable. This can result in cytoplasm leakage, denaturation of protein and eventual cell lysis (alcohols are one of the so called 'membrane disrupters'). The advantages of using alcohols include a relatively low cost, little odor and quick evaporation. However, alcohols have very poor action against bacterial and fungal spores and can only inhibit spore germination at best.

Oxidizing Disinfectants: This group of disinfectants generally has non-specific modes of action against microorganisms. They have a wider spectrum of activity than non-oxidizing disinfectants with most types able to damage bacterial endospores. The disinfectants in this group pose greater risks to human health. This group includes oxygen-releasing compounds like peracetic acid and hydrogen peroxide. They are often used in the gaseous phase as surface sterilants for equipment. These peroxygens function by disrupting the cell wall causing cytoplasm leakage and can denature bacterial cell enzymes through oxidation. Oxidizing agents are clear and colorless, thereby eliminating staining, but they do present significant health and safety concerns particularly in terms of causing respiratory difficulties to unprotected users.

Posted by Tim Sandle

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