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Philip B Hunt
BSc CBiol MIBiol EurProBiol
Head of Microbiology
Pharmacy Practice Unit
Quality Control North West
National Health Service
Why is decontamination of cleanroom surfaces important There are a number of reasons why it is important to control contamination on cleanroom surfaces, which include surfaces in and on isolators and laminar-flow cabinets, workbenches, floors, walls and ceilings. Reasons include the following:
Sources of contamination
Contamination can be in the form of microbes. These can be introduced by personnel and by components and materials transferred into the cleanroom. Microbes can also enter via the air supply to the facility, or arise from the fabric of the building due to damp or exposed plaster or woodwork.
Sampling and detection
To be able to monitor the efficiency of the cleaning programme, it is necessary to determine the extent of surface contamination.
A number of methods can be used; however, the most common sampling techniques are the use of swab samples or contact plates (such as RODAC plates). Assessment of the optimum technique is quite complex and has been the subject of much discussion; however, recent work on this subject has clarified the situation.(3)
In brief, contact plates generally achieve better recovery of microbes from surfaces than swab samples, but only work well on flat, accessible areas. Contact plates also leave residual culture medium on the surface after sampling. This must be removed immediately using a validated cleaning technique to avoid microbial growth.
Swab samples achieve better recovery from irregular surfaces, corners, joins and seams. ï¿½However, some microbes may be lost in the matrix of the swab. Microbes may also be lost in the semi-solid transport medium in which the swab is immersed to preserve viability of microbes if culture cannot be performed at the time of sampling – for example, if the microbiology laboratory is distant from the cleanroom, as is often the case.
A further point to consider when deciding whether to monitor cleanroom cleanliness with contact plates or swabs is that contact plate limits are tabulated in GMP requirements, but swab sample limits are not. This means that data from swab sampling require careful interpretation.
Principles of cleanroom cleaning
Microbes cannot proliferate without moisture and a suitable source of nutrient.
If surfaces such as laminates, stainless steel, and vinyl floor, wall and ceiling finishes are dry and free from nutrients, vegetative forms of microbes cannot survive and will lose viability in a short time. However, some microbes are able to form spores that are capable of surviving for long periods of time without water and nutrients and are highly resistant to disinfectant agents.
There are a number of theories surrounding best practice for cleanroom surface decontamination in pharmaceutical cleanrooms. These cover a broad spectrum of concepts, ranging from regular application of powerful sporicidal agents to much less aggressive cleaning programmes using mild disinfectants or even detergents.
The sporicidal agents most commonly used in cleanroom applications are chlorine-releasing agents such as sodium hypochlorite or chlorine dioxide, or oxidising agents such as hydrogen peroxide. The benefit of using these agents is that they have the ability to rapidly destroy virtually all vegetative forms of microbe, and given adequate contact time can destroy spores that may be present on cleanroom surfaces.
This may confer a certain level of peace of mind, arising from the belief that a powerful sporicidal agent will be able to cope with almost any microbiological challenge that could arise. This may be true, but is often unnecessary in correctly managed pharmaceutical cleanroom environments, where the level of microbiological challenge encountered should be very low.
One of the consequences of using chlorine-releasing and oxidising agents in cleanroom environments is that they can be quite aggressive and may be damaging to surface finishes (see Figure 1). Most cleanroom surface finishes are designed to be as smooth as possible.
This is because surface imperfections can retain traces of nutrients, perhaps in the form of medicines spilled during preparation or the breakdown products of disinfectant residue. Surface imperfections can also harbour microbes, reduce the contact of disinfectant agents and make physical removal for example, by wiping – less effective. Wiping is considered an important aspect of surface decontamination in cleanrooms and during transfer or components and materials into cleanroom environments.(4)
Nonaggressive cleaning agents
An alternative to using powerful antimicrobial agents and sporicides is to use much milder agents. This could include amphoteric surfactants or mixtures of quaternary ammonium compounds and biguanide. These are not powerful antimicrobial agents when compared to chlorine-releasing agents, but they have adequate activity for use in cleanroom applications, where heavy soiling of surfaces is generally not a problem. They are also surface-active agents that are effective in removing spilled medicines and biofilms. The action of these agents in conjunction with the physical action of suitable wiping also acts to remove microbes and spores.
A cleaning programme utilising these nonaggressive agents confers a number of very significant benefits, such as:
In order to comply with GMP requirements, disinfectants for use in grade A & B areas must be sterile before use and agents for use in GMP C & D areas must be monitored to control microbial contamination.(5)
Alcohols in surface decontamination
Alcohols have many benefits when used in cleanroom environments, the most effective concentration being 60-70% for ethanol.
Application of disinfectant agents
When cleaning agents or disinfectants are applied to surfaces, some important aspects of the process must be considered.