Choosing disinfectants

Cleaning and disinfection of surfaces are essential steps for maintaining the cleanliness of pharmaceutical manufacturing operations. The USP, for example, requires stringent procedures to be followed during the manufacture of pharmaceutical preparations (as stated in USP Chapter <797>).¹ One step towards achieving microbial control within a cleanroom is the use of defined cleaning techniques for walls, ceilings, floors and surfaces at working height together with the application of suitable detergents and disinfectants.

One of the more difficult tasks facing pharmaceutical organisations is with the selection of disinfectants, particularly in ensuring that those chosen are appropriate and that their effectiveness is periodically assessed.² The need for a scientific rationale for the selection is outlined in the USP chapter <1072> ‘Selection of a Disinfectant for Use in a Pharmaceutical Manufacturing Environment’.³

Disinfectant suppliers, such as schülke, can work with pharmaceutical companies to help them to determine the most suitable types of disinfectants. The selection of a disinfectant involves the careful consideration of a number of factors and this article outlines some of the most important.

A disinfectant is one of a diverse group of chemicals that reduces the number of micro-organisms present (normally on an inanimate object). There are various “official” definitions of the process of disinfection and disinfectant agents; one of the most straightforward is from the ISO standard on Aseptic Processing (ISO 13408–11), where a disinfectant is defined as “[a] chemical or physical agent that inactivates vegetative micro-organisms but not necessarily highly resistant spores”.⁴

Disinfectants vary in their spectrum of activity, modes of action and efficacy. Some are bacteriostatic, where the ability of the bacterial population to grow is halted. Here, the disinfectant can cause selective and reversible changes to cells by interacting with nucleic acids, inhibiting enzymes or permeating into the cell wall. Once the disinfectant is removed from contact with bacteria cells, the surviving bacterial population could potentially grow.

Other disinfectants are bactericidal, in that they destroy bacterial cells through different mechanisms including: causing structural damage to the cell; autolysis; cell lysis and the leakage or coagulation of cytoplasm.⁵

Within these groupings the spectrum of activity varies, with some disinfectants being effective against vegetative Gram-positive and Gram-negative micro-organisms only, while others are effective against fungi. Some disinfectants are sporicidal, in that they can cause the destruction of endospore-forming bacteria (these are the most difficult forms of micro-organisms to eliminate from cleanroom surfaces). However, a chemical agent does not have to be sporicidal in order to be classed as a “disinfectant” or as a “biocide”.⁶ The bacteristatic, bactericidal and sporicidal properties of a disinfectant are influenced by many variables, not least their active ingredients.

Points to consider

There are many different types of disinfectants for use within the pharmaceutical industry,⁷ with different spectrums of activity and modes of action. The mechanisms of action are not always completely known and continue to be investigated. A range of different factors needs to be considered as part of the process of selection including the mode of action, efficacy, compatibility, cost and with reference to current health and safety standards.⁸

In examining these criteria further, the main points to consider when selecting a disinfectant are:

• A disinfectant must have a wide spectrum of activity. This refers to the ability of the disinfectant to kill micro-organisms of varying types and in different physiological states.
• Is there a requirement for the disinfectant to be sporicidal? This requirement influences the type of disinfectant purchased. Sporicidial disinfectants tend to have greater health and safety considerations and some, particularly chlorine-based disinfectants, are aggressive to certain types of surfaces and will cause discolouration and abrasion.
• The disinfectant must be rapid in action with an ideal contact time of less than 10min. The contact time is the time taken for the disinfectant to bind to the micro-organism, traverse the cell wall and membrane and to reach its specific target site. The longer the contact time, then the longer the surface or article needs to be left, prior to reuse.
• The disinfectants selected must have different modes of action. Various types of disinfectants and their different modes of action are discussed below. The emphasis on different modes of action is also tied to the regulatory expectation that disinfectants are rotated, which is also discussed later.
• Some disinfectants require certain temperature and pH ranges to function correctly. One type of disinfectant, for example, may not be effective in a coldroom due to the lower temperature. The reason for this is that the validation standards for disinfectants measure the bactericidal activity at 20°C and therefore the disinfectant may not be as effective at higher or lower temperatures.
• Prior to the use of disinfectants it is essential that as much dirt and soil is removed as possible. This requires the application of a detergent. Some disinfectants are not compatible with certain detergents. In such instances, detergent residues could neutralise the active ingredient in the disinfectant. Any disinfectant purchased should be compatible with the detergent used.
• Other disinfectants leave residues on surfaces. While this can mean a continuation of an antimicrobial activity, residues can also lead to sticky surfaces and or the inactivation of other disinfectants.
• Different disinfectants are not compatible with all types of surfaces. The disinfectants must not damage the material to which they are applied (although it is recognised that repeated applications over several years may cause some corrosion). For more aggressive disinfectants, a wipe down using water or a less aggressive disinfectant such as an alcohol is sometimes necessary to remove the residues. In addition to some disinfectants having a corrosive effect, others may be absorbed by fabrics, rubber etc, which lessens their bactericidal properties.⁹
• The disinfectants must meet the requirements of the validation standards to measure bactericidal, fungicidal and, if appropriate, sporicidal and virucidal activity. There are detailed standards that describe how disinfectants should be validated against a range of different surfaces, parts of which are undertaken by the manufacturer and some by the pharma organisation that purchases the disinfectants.
• The presentation of the disinfectant is an important choice, whether as a pre-diluted preparation in a trigger spray or as a ready-to-use concentrate or an impregnated wipe, which is why many disinfectant suppliers, including schülke, provide a wide range of different presentations of disinfectants.
• The disinfectants must be relatively safe to use, in terms of health and safety standards. Here, the main concern is with operator welfare. A related concern is the impact upon the environment.
• The cost of the disinfectant is also a factor to consider, especially if it is to be used over a large surface area.
• If the disinfectant is required for use in an aseptic filling area then it will need to be sterile filtered or supplied sterile in a suitably wrapped container. For example, schülke supplies disinfectants that have been sterile filtered through a 0.2μm filter and are provided in gamma-irradiated containers with outer wrapping.

Carrying out such a review, based on the above factors prior to purchasing a disinfectant, does not guard against the incorrect use of the disinfectant within the pharmaceutical manufacturing facility. Any disinfectant will be effective only if it is used at the correct concentration, applied to relatively clean surfaces using appropriate cleanroom grade mops or cloths and left for the correct contact time.

In addition to surface disinfectants, hand sanitisers are also required (for cleanroom staff to apply either to skin or to gloved hands) as part of a comprehensive disinfection programme.

Modes of action

Disinfectants have varying modes of action against microbial cells due to their chemical diversity. Different disinfectants can target different sites within the microbial cell. These include the cell wall, the cytoplasmic membrane (where the matrix of phospholipids and enzymes provide various targets) and the cytoplasm. Some disinfectants, on entering the cell either by disruption of the membrane or through diffusion, then proceed to act on intracellular components. There are different approaches to the categorisation and sub-division of disinfectants, including grouping by chemical nature, mode of activity or by bacteristatic and bactericidal effects on micro-organisms.¹⁰

The different types of disinfectant include:

Non-oxidising disinfectants – The majority of this group of disinfectants have specific modes of action against micro-organisms, but generally they have a narrower spectrum of activity compared with oxidising disinfectants.

This group includes: alcohols, such as schülke’s Perform Sterile Alcohol EP, which disrupts the bacterial cell membrane and has a one minute contact time; aldehydes, which have a non-specific effect in the denaturing of bacterial cell proteins and can cause coagulation of cellular protein; amphoterics that have both anionic and cationic character and possess a relative wide spectrum of activity; phenolics (some phenols cause bacterial cell damage through disruption of proton motive force, while others attack the cell wall and cause leakage of cellular components and protein denaturation); and quaternary ammonium compounds (QAC), which are among the most commonly used disinfectants in the pharmaceutical industry and include preparations such as schülke’s Perform Concentrate QB (available in convenient single-use bottles, which reduces the preparation time). The mode of action of QACs is on the cell membrane leading to cytoplasm leakage and cytoplasm coagulation through interaction with phospholipids.¹¹

Oxidising disinfectants – These materials generally have non-specific modes of action against micro-organisms. They have a wider spectrum of activity than non-oxidising disinfectants, with most types able to damage endospores, but they can pose greater risks to human health and therefore require greater control. This group includes: halogens, such as iodine, and oxidising agents, such as peracetic acid (e.g. schülke’s sporicidal Perform Concentrate PAA), a chemical containing oxygen deposits (Perform Concentrate OXY, available in single-use sachets) and hydrogen peroxide. Perform Concentrate OXY has an excellent material compatibility and does not damage most surfaces.

Hand sanitisers – There are many commercially available hand sanitisers, the most commonly used types being alcohol-based gels or alcoholic hand rubs, such as desderman pure from schülke. With hand sanitisers the most important factor is the hand rubbing technique, since the sanitisers are made effective through the act of agitation by rubbing them into the hands.¹²

Perform Sterile Alcohol EP is gamma-irradiated, microbial filtered and ready to use in a sterile 500ml spray

In selecting disinfectants many pharma manufacturers will opt to have two ‘in-use’ disinfectants, and sometimes to have a third disinfectant as a reserve in case a major contamination incident arises – such as a bioburden contamination build-up that appears resistant or difficult to eliminate using the routinely used disinfectants. The reserve disinfectant will often be more powerful and sporicidal, such as an oxidising agent, the routine use of which is restricted because of likely damage to the equipment and premises.

Typically, the two primary disinfectants are rotated. This is a requirement of regulatory bodies and the strongest pressure for it has come from Europe with the EU GMP Guide stating that, “where disinfectants are used, more than one type should be employed” (Annex 1). This quotation is normally interpreted as a requirement for two different types of disinfectant to be rotated. The USP (<1072>), in contrast, is less exacting and poses some questions about the scientific need for rotation.

Reducing resistance

The argument for rotating two disinfectants is to reduce the possibility of resistant strains of micro-organisms developing. While the phenomenon of microbial resistance is an issue of major concern for antibiotics there are few data to support development of resistance to disinfectants.¹³

This is particularly so when applied to dry environments such as cleanrooms, where microbial replication as a primary process for gaining resistance is minimal.

While there is limited scientific evidence to support disinfectant resistance,¹⁴ there is a need to meet regulatory expectations and many pharmaceutical organisations adopt policies for disinfectant rotation. When using disinfectants with different modes of activity more often one of the selected disinfectants is sporicidal.

The frequency of rotation tends to be based on the environmental monitoring data. Given that environ-mental monitoring data should be reviewed for trends on a regular basis, this allows the frequency of cleaning and disinfection to be based on risk.

In summary, this article has examined some of the key criteria for the selection of disinfectants in the pharmaceutical industry and has examined some of the main types of disinfectants available. While selection is important, it will matter little how careful the selection of disinfectants has been if disinfectants are not applied and used according to Standard Operating Procedures because the efficacy of the disinfectant will decrease.

It is also important to emphasise that once a disinfectant is selected its performance should be periodically reviewed. Such a review is in relation to the effect that the disinfectant has on the surface material and in relation to the environmental monitoring data collected.

Given that the objective of the disinfectant is to kill micro-organisms and to reduce the surface bioburden, then the real test of its effectiveness is with the numbers of micro-organisms recovered through environmental monitoring and the types found (the ‘microflora’).

Thus the selection of disinfectants is not a one-off decision; it must remain part of the on-going quality reviews undertaken by pharmaceutical organisations and for this the expertise provided by disinfectant manufacturers, such as schülke, will be of great value.

1. United States Pharmacopoeial Convention, Inc. United States Pharmacopeia 28-National Formulary 23. Rockville, MD: US Pharmacopoeial Convention, Inc. Chapter <797>

2. Sandle, T., PharMIG News, No. 15, March / April 2004, pp10-15

3. United States Pharmacopoeial Convention, Inc. United States Pharmacopeia 28-National Formulary 23. Rockville, MD: US Pharmacopoeial Convention, Inc, Chapter <1072>

4. ISO 13408 Aseptic processing of health care products – Part 1: General Requirements, 2008, International Standards Organisation, Geneva, Switzerland

5. Cooper MS., The Microbiological Update, June 2000, 18(3): 1–4.

6. Sandle, T., : ‘Selection and use of cleaning and disinfection agents in pharmaceutical manufacturing’ in Hodges, N and Hanlon, G. (2003): ‘Industrial Pharmaceutical Microbiology Standards and Controls’, Euromed Communications, England

7. Block S. 1977; Disinfection, Sterilisation and Preservation, Third Edition, Lea and Febiger, Philadelphia.

8. Sandle, T., The Journal, Institute of Science Technology, Summer 2006, pp16-18

9. Pharmig. A Guide to Disinfectants and their Use in the Pharmaceutical Industry. Pharmaceutical Microbiology Interest Group, 2006, England.

10. Denyer SP and Stewart GSAB., International Biodeterioration and Biodegradation, 1998; 41: 261-268

11. McDonnell G and Russell A., Clinical Microbiology Reviews, Jan. 1999; 147–179.

12. Namura S, Nishijima S, McGinley J and Leyden J., The Journal of Dermatology, 1993; 20: 88–93

13. Anon. Bacteriotherapy: the time has come, British Medical Journal, 18th August 2001, 353–354

14. Madigan M, Martinko J and Parker J. Brock Biology of Micro-organisms, 8th edition, 1997, Prentice Hall, 408–409.

About the author

A pharmaceutical microbiologist with more than 20 years of experience, Tim Sandle has managed a large pharmaceutical microbiology laboratory, undertaken several consultation projects with healthcare and pharmaceutical organisations, and has written many papers and technical articles. He is the communications lead for the UK and Ireland Pharmaceutical Microbiology Interest Group, an honorary consultant with the University of Manchester School of Pharmacy and is employed as Head of Microbiology for the Bio Products Laboratory.