Definition of Terms

Definition of Terms

Gerald McDonnell

Words are meant to convey meaning, but we cannot be sure that any word will convey the same meaning to every person under every situation. People have different backgrounds and outlooks and derive different meanings from the same word. Furthermore, language is, in a sense, a living organism, and words can change their meaning with time. Consider the English language alone and the difference between reading a modern novel in comparison to the works of Shakespeare and Chaucer. In modern usage, the definition of words can make a difference to their general and legal use. In previous edition of this book,1 as example was given with the word “whiskey” (or for those such inclined, “whisky”). Most people think they know what the term whiskey means, but they could be wrong, for it is a word with a legal as well as a popular meaning. Legally, whiskey is strictly a spirit distilled from a fermented mash of grain at less than 95% alcohol by volume (190 proof) having the taste, aroma, and characteristics generally attributed to whisky and bottled at not less than 40% alcohol by volume (80 proof). This term can be further subdivided into other subterms, such as Irish whiskey and Scotch whisky, that are related to spirits made in certain countries, according to laws of those specific countries. A product having the same color, odor, taste, and chemical composition might not satisfy the legal definition and its associated label claims.

Definitions are man-made and can therefore range considerably depending on different parts of the world and under different situations. Consider terms such as disinfection, sterilization, and preservation, which are often used in common practice but can have different legal requirements under different situations. Definitions attempt to make boundaries around terms, but these boundaries are often become vague and indistinct to accommodate different situations. Yet, we must work with them as best we can. A good example is trying to define what we mean when we use the term dead. We understand, no doubt, the term, but how do we define this? It is hard to be exact. When is a person physically or legally dead? When they are no longer breathing? When he or she is brain dead? When all the cells in his or her body are dead? It is no different when we use terms such as sterilization and sterile. When is a product sterile? When all life in or on it has been killed, when it has been heated at x temperature for y minutes, or when its microbial population is reduced by a given number or scale? It is what we say it is, according to the way we construct our definition.

Definitions by lexicographers and lawyers serve the useful purpose of giving all people the opportunity of common understanding of what they mean when they use a word. When manufacturers label a product as an antiseptic, as disinfectant, or as “sterile,” it is imperative that their product does or is what these terms imply. The legal implication of these terms became a focus in the 1920s in certain countries such as the United States. An initial judicial decision at this time in the United States stated that “language used in the label is to be given the meaning ordinarily conveyed by it to those to whom it was addressed.” This was difficult to do if there was not clear and defined meanings (and expectations) for these various terms. Legal definitions therefore began to clarify their meanings. It was in 1925 that the US Bureau of Chemistry (now the US Food and Drug Administration [FDA]) deemed it necessary to give drug manufacturers a legal definition of the word antiseptic so that this class of drugs could be controlled by the government. Words such as antiseptic, disinfectant, and sanitizer were early examples of words that had loosely accepted meanings until they were more strictly defined during these times. Austin M. Patterson, a lexicographer of scientific terms, made a thorough study of many of these words in 1932, which served to further harmonize their meanings in the new era of antimicrobial controls.2 Others such as those published by McCulloch,3 Reddish,4 Spaulding,5 and earlier editions of this book, to name but a few, continued to evolve these growing series of definitions. In recent
years, there has been much progress made on harmonizing many of the definitions that we use in the application of disinfection, sterilization, and preservation technologies internationally (eg, as defined in ISO 111396). Despite that, different countries (or even regulatory agencies) can still use specific terms to represent legal requirements in their jurisdiction that can vary from their general or harmonized usage.

Overall, definitions are further discussed in this chapter. An initial consideration is given to four main terms, disinfection, antisepsis (as a specific type of disinfection application), sterilization, and preservation, with some discussion. This is followed by an alphabetic list of definitions that may be a useful reference during the reading of the subsequent chapters of this book. This list should not be considered strict or exclusive, and it is important to note that the general and, more importantly, legal requirements in the use of these terms for product labeling can vary from country (or area) to country.


Disinfection is a process to inactivate viable microorganisms to a level previously specified as being appropriate for a defined purpose. It can be achieved using a variety of physical (eg, heat or radiation) and chemical methods or indeed a combination of both. Chemical disinfection, for example, can therefore be defined as the reduction of microorganisms achieved by the action of one or more chemicals. Note that processes such as cleaning and filtration can also physically remove viable microorganisms from surfaces or the air, others gases, or liquids but do not necessarily inactivate microorganisms. A disinfectant may be simply defined as the technology used for the purpose of disinfection. This can include the use of hot water, steam, or ultraviolet (UV) light, but the common use of the term disinfectant generally refers to a chemical or combination of chemicals used for disinfection. A harmonized term used is disinfecting agent, which refers to any physical or chemical agent used for disinfection.

The origin of the term is from the French des- and the verb infecter, to essentially mean the reversal of or to rid from infection. The word disinfectant was first recorded in writing in 1598, with the meaning of “to cure, to heal,” but in 1658, it was used in the more modern sense, to remove infection. At this time, it was already appreciated that there was a benefit to burning the belongings used of those “that died of the pestilence to dis-infect them.” In those days, it was believed that contagious diseases arose from effluvia, a flowing out of invisible particles from the diseased person or corpse, or from miasmas, which were noxious disease-bearing exhalations from putrefying organic matter emanating from damp, unhealthful places like malarial swamps. Miasmas were referred to in medical writing as early as 1665. But we can find earlier evidence of the importance of disinfection methods in earlier times, such as in the use of chemical substances such as burning sulfur, the earliest reference for which can be at least traced back to the practice being described in Homer’s Odyssey in approximately 800 bc, calling on his nurse to bring sulfur for fumigation following the massacre of suitors. The purifying effects of chemicals such as sulfur has been cited for many similar uses, such as in the 4th century for rooms used for surgery in India and during the Middle Ages in Europe during the plague epidemics. Because disease was associated with foul odors, disinfectants were expected to destroy or mask the odors to get rid of the infection.

The term became more widespread in its use during the 1800s in parallel with a greater understanding of microorganisms. Patterson2 studied 143 definitions of disinfectant used from 1854 to 1930. Of these, 25, mostly of earlier date, made no mention of microorganisms. Of the rest, 95 defined disinfectants as germ destroyers. In this respect, the term germ refers to any microorganism. But the word disinfectant still carries with it much of its original connotation, namely, the cleaning of sickrooms, clothing, bedding, lavatories, stables, and so forth. Even the more legal definition4 is similar but more detailed. It refers to an agent that frees from infection; usually a chemical agent that destroys disease germs or other harmful microorganisms or inactivates viruses. So, even at this time, the term was most commonly used to designate chemicals that kill the growing (or vegetative) forms of microorganisms but not necessarily the more resistant forms (such as the endospores of bacteria). Proper use of a disinfectant could therefore be contingent on the purpose for which it is used or the type of infectious (or contaminating) agent there is reason to suspect may (or is known) be present.

Block,1 in a previous edition of this book, discussed in more detail the various medical, chemical, legal, and general definitions at the time. But the subsequent harmonization of the terms disinfection and disinfectant negates the need for further debate. But he also highlighted five elements in these definitions of disinfection. These were that a disinfectant (1) removes infection (or microbial contamination); (2) is ordinarily a chemical but can be a physical agent; (3) kills, not just inhibits, microorganisms in the vegetative stage; (4) does not necessarily kill spores (or other, more resistant forms of microbial life); and (5) is typically used only on inanimate objects, not on the human or animal body. These are useful in discussing disinfection further and other associated definitions.

As already discussed, a disinfectant in the past was often associated with ensuring the concept of being “free from infection” but should be more generally considered as any agent that destroys pathogenic (disease-causing) and other kinds of unwanted microorganisms by chemical or physical means. In many applications, disinfection is not only required to reduce pathogens but may also be just as concerned with other unwanted microorganisms
(such as those leading to food or other product spoilage). We have also considered that this can encompass a wide range of chemical and/or physical methods, many of which are considered in greater detail in this book. But the types of microorganisms that are (or maybe) present can vary from situation to situation, ranging in their structures and levels of resistance to disinfectants. This is considered in detail in chapter 3, Microorganisms and Resistance, but a summary of their hierarchy of resistance (or sensitivity) to disinfectants is given in Figure 2.1.

This is important because a disinfectant may be capable of inactivating few or many types of microorganisms based on this hierarchy. From a labeling (and therefore legal) point of view, the disinfectant may be further defined based on the ability to inactivate different groups of microorganisms using specific terms. It is important to note that these terms can vary in their usage and requirements for the test methodology to be used to support such claims. This can vary from country to country, many of which require the demonstration (and often registration) of disinfectants or disinfection processes in different countries. Unfortunately, at the time of writing, there are no harmonized requirements for the claims and test methods used to support disinfectant efficacy internationally. The two most commonly cited systems are those based on disinfectant labeling requirements in the United States (eg, by the FDA, Environmental Protection Agency, and US Department of Agriculture, depending on the application) and the European Union (EU).7 A common way is to refer to the specific ability to inactivate certain classes of microorganisms. Examples include the use of the suffix -cidal, such as in bactericidal (ability to kill vegetative bacteria), mycobactericidal (to kill mycobacteria, which are considered more difficult to kill than other types of bacteria), viricidal (to kill viruses), and sporicidal (the ability to kill spores, generally indicated by confirming efficacy against bacterial endospores). So, for example, a sporicidal disinfectant (which is some countries may be labeled a liquid chemical sterilants) is considered effective against bacterial spores and, when appropriate in some jurisdictions, may also be considered to be effective against other types of microorganisms given the hierarchy of resistance of microorganisms to disinfectants shown in Figure 2.1. But overall, the term sporicidal indicates the ability of a disinfectant or disinfection process to inactivate bacterial spores but does not directly indicate that all other forms of microorganisms are inactivated or that these products/processes can render a “sterile” situation (see the discussion on sterilization and sterile in the following text). It is important to understand the regulatory use of these terms to ensure the appropriate use of the disinfectant and the desired outcome. For example, in the United States, the term germicide is limited to the ability of the disinfectant to demonstrate bactericidal efficacy against certain vegetative bacteria (eg, Staphylococcus aureus and Escherichia coli). This does not ensure efficacy of the disinfectant against all germs, all bacteria (eg, mycobacteria are not included), or bacterial endospores (although the vegetative forms of spore-forming genus such as Bacillus would be included). Also, because the test methods used to verify such claims can vary from area to area, it is important to review the labeling and claims carefully to ensure the effectiveness of the disinfectant for any specific application.

FIGURE 2.1 The estimated hierarchy of microorganism resistance to disinfection. The figure is given as a guide, and the specific resistance profile can vary depending on the disinfectant and the specific target microbial strain.

A similar, yet distinct, designation using the suffix “-static” refers to the ability to inhibit the growth of a certain class of microorganisms (eg, fungistatic, bacteriostatic, and sporistatic). Note that strictly speaking, these terms would not meet the requirement of the definition of a disinfectant and may be considered more forms of preservation in some situations.

Another way is to define disinfectants based on their ability to inactivate a more general group of microorganisms based on their similar profile of resistance to inactivation. A commonly used system, as an example, defines disinfectants into three classes: low-level, intermediate-level, and high-level disinfectants (Table 2.1).

There is a range of other terms that may be considered to fall under the general definition of disinfection but in more specific ways. Many of these terms are often used interchangeable with disinfection or disinfectant. These include the following:

Sanitization is the removal or inactivation of microorganisms that pose a threat to public health, and therefore, sanitizers would be considered as types
of disinfectants. These terms are particular widely used in food and brewing industries for hard surface disinfection. The term sanitizer first appeared in the 1950s but became more widely used when published in the first edition of this book. Today, sanitization is a regulated term and is widely used in the United States to define disinfectants used to reduce, but not necessarily eliminate, microorganisms from the inanimate environment to levels considered safe as determined by public health codes or regulations. In this context, they can include a wide range of food-contacting surfaces and non-food-contacting surfaces as well as air sanitizers. The typical efficacy tests used to support such product claims are essentially bactericidal tests (eg, a specific hard surface carrier test demonstrating efficacy against a gram-positive and/or gram-negative bacteria, such as S aureus or Salmonella enterica [formerly typhi]). But the term is also often used in general terms, such as in the case of hand sanitizers, referring to liquids used to disinfect the hands (eg, alcohol-containing gels or solutions).

Fumigation may be defined as the delivery of an antimicrobial process (typically based on a liquid or gas) that is applied indirectly to an area for the purpose of disinfection. Although the typical use of disinfectant to a large area and its associated surfaces (such as in a room) is by a manual method (eg, spray and wiping), fumigation is achieved by applying the antimicrobial gas, liquid, or aerosol into the area for a given time for disinfection. The process may need to be followed by the active removal of residual disinfectant from the air/surface (or allowing the biocide to naturally degrade overtime) to allow for the safe entry into the area. Fogging or aerosolizing of disinfectants into an area is therefore considered methods of fumigation. Applications can include the use of disinfectants such as formaldehyde, hydrogen peroxide, or chlorine dioxide in high-risk areas to control pathogens; such as biosafety level 2, 3, or 4 laboratories; contaminated hospital wards; and controlled manufacturing environments.

Pasteurization is a very familiar term used to describe the antimicrobial reduction of microorganisms that can be harmful or cause product spoilage. The traditional and most common use of the term is in the heating of liquids, such as in treatment of foods and liquid (eg, milk and juices). The process was named after one of the founding fathers of modern microbiology, Louis Pasteur, based on his demonstration for the successful use of the use of heat in the prevention of beer and wine spoilage during the 19th century. It is important to note that the effects of heating of various liquid foodstuffs in preventing spoilage or extending shelf life had been described and used by many others for centuries before this time. Although the term is most widely used in food industry, it has often been used to describe the use of hot water (typically above 65°C or 149°F) for many surface disinfection purposes (eg, the disinfection of medical devices or manufacturing equipment).

Sterilant may be generically defined as an agent used to destroy microorganisms (ie, a disinfectant), but the term more specifically is used in the United States to define a liquid chemical sterilants as disinfectants that can destroy all forms of microbiological life, including high numbers of bacterial spores. This definition may appear to be similar to that of a high-level disinfectant, discussed earlier, but note that the FDA further defines a sterilant as a high-level disinfectant used under the same contact conditions except typically for a longer contact time. Therefore, such products can have a specified contact time for high-level disinfection but may have a much longer contact time for sterilant activity. The term sterilant begins to crossover to our understanding of our use of the term sterilization or rendering a surface “sterile,” but note that although a sterilant has the ability to inactivate microorganisms, this does not necessarily mean that it achieves a sterile end point. A good example is the use of a liquid chemical sterilant to treat a surface, but then how is it removed following its use to ensure the surface is safe and without recontaminating the surface? Consider it
this way: A sterilant on its own may have the ability to sterilize but only as part of a controlled process. This is discussed further under “sterilization.”

Biocide (or more specifically microbicide) is a general term to describe any physical or (more commonly) chemical agent that inactivates a broad spectrum of microorganisms. It typically refers to the specific antimicrobial agent being used (eg, heat, hydrogen peroxide, or UV light) in comparison to “disinfectant” that can refer to the antimicrobial agent and the various product formulations that use the agent in combination with other ingredients (see following text for further definitions).

A further specific term is antisepsis. Antisepsis is defined as the destruction or inhibition of microorganisms in or on living tissue, for example, on the skin or mucous membranes. The word antiseptic is traditionally credited to John Pringle in his experiments published in the 1750s studying the effects of various substance to inhibit putrefaction. He was familiar with the word septic, first recorded in 1605, which means “putrefying.” As a physician, he had written, “The miasma or septic ferment being received into the blood,” and when he found chemicals (eg, salts, acids, and alkalis) that prevented putrefaction, the word antiseptic was generated.9 In the EU, the term is specifically defined as application of an antiseptic on living tissues causing an action on the structure or metabolism of microorganisms to a level judged to be appropriate to prevent and/or limit and/or treat an infection of those tissues.7 Therefore, antiseptics are types of products and antimicrobial agents (excluding antibiotics) that are used for that purpose. These include products such as preoperative preparations (used in the disinfection of skin prior to surgical intervention), surgical scrubs (used for the washing or treatment of hands prior to the donning of gloves by surgeons and other operating room staff), health care personal hand washes (used for routine disinfection of hands in health care facilities), and general or surgical hand disinfectants (or sanitizers defined earlier). Other terms such as hygienic hand rubs or hand washes are widely used in the EU. The regulatory (and labeling) requirements for products making such claims are controlled in many countries, including the United States, Canada, and the EU. Due to the sensitive nature of the target tissues in comparison to the air or hard surfaces, only a limited number of disinfectant types are used due to the balance of antimicrobial efficacy but in the absence of significant damage or irritation. These include biocides such as alcohols, iodine-releasing agents, chlorhexidine, and triclosan. An important consideration to note is the ability of many of these actives to be effective antimicrobials when initially applied to the skin (or other tissue) but then also to retain some (often bacteriostatic or even bactericidal) activity over time. This may be referred to as residual activity, persistence, or substantively. Biocides that include this attribute include chlorhexidine and other biguanides.

TABLE 2.1 A general classification of disinfection (and disinfectants), as defined by the US Food and Drug Administrationa



Expected Efficacy

Low level

A lethal process using an agent that kills vegetative forms of bacteria, some fungi, and lipid viruses

Bactericidal, virucidal (enveloped viruses)

Intermediate level

A lethal process using an agent that kills viruses, mycobacteria, fungi, and vegetative bacteria but no bacterial spores

Mycobactericidal, fungicidal, virucidal, bactericidal

High level

A lethal process using a sterilant under less than sterilizing conditions. The process kills all forms of microbial life except for large numbers of bacterial spores.

Sporicidal (but often over an extended period), mycobactericidal, fungicidal, virucidal, bactericidal

a From US Food and Drug Administration.8

The word antiseptic is derived from the Greek language to mean “against putrefaction.” The term was first used by Pringle in the 1750s to record the ability of substances to prevent the spoilage of organic matter such as egg and meat. After Lister’s research in the use of antimicrobial agents in surgery, the term acquired a second meaning, that of a substance used to destroy pathogenic microorganisms. Patterson,2 in his detailed review of definitions published in 1932, found some difference of opinion regarding the true meaning of the term—whether an antiseptic merely inhibited the growth of microorganisms, killed them, or both. Essentially, antiseptics can provide microbicidal and/or microbiostatic activity, depending on the target microorganisms, the biocide itself, and the product formulation. The mode of action will, of course, depend on such criteria as concentration used, time of contact, temperature, pH, and organic matter present. The antimicrobial efficacy of antiseptics is typically verified against bacteria but can also include fungi and viruses. Furthermore, the label efficacy claims associated with antiseptics are often controlled based on certain in vitro (and on skin) test criteria to ensure they meet the intended need. Although widely used in the EU, the use of term disinfectant for antimicrobial products used on the body, as in the case of “skin disinfectant,” has traditionally been frowned on in the United States. The over-the-counter antimicrobial drug review panel10 stated that disinfection properly referred to the use of such chemicals on inanimate objects and not on the human body. A hard distinction insofar as US governmental regulations is concerned is that disinfectants or antimicrobial chemicals labeled for use on inanimate objects (“hard surfaces”) are considered economic poisons under the Federal Environmental Pesticide Control Act (7 USC §136), whereas agents such as antiseptics labeled for use on human or animal tissue are regulated as drugs under the Federal Food, Drug, and Cosmetic Act. The specific regulatory status in other countries or economic areas can also vary.

Overall, a disinfection process or disinfectant may have different antimicrobial designations depending on its application (eg, foods, food contact surfaces, devices, agricultural, veterinary). An example was given by Fraser11 in writing about the antimicrobial properties of peracetic acid, although this could easily be applied to other chemical or physical disinfectants. The chemical product may be referred to as a “sanitizer” being particularly used in the food and brewing industries, “terminal disinfectants” in the dairy industry, as “biocides” in municipal water treatment, as “ovicides” in agricultural waste treatment, and as “high-level disinfectants” or “sterilants” in medical and pharmaceutical applications. Of course, a biocide such as peracetic acid may be bacteriostatic under certain (low concentration/temperature) conditions with short contact time, bactericidal at longer time, and sporicidal at even longer time. Each can be a proper designation for the conditions of use and its label. On the other hand, some industries may use terminology particular to that
industry with no regard to any properly accepted definitions. It would be desirable to have definitions accepted internationally in all cases, but they are not; therefore, there may be different interpretations of the terms as they are used in different industries and countries.

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May 9, 2021 | Posted by in MICROBIOLOGY | Comments Off on Definition of Terms
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