Safe selection of biocides

Consideration of the antimicrobial efficacy of different biocides is an important basis on which to choose an effective disinfectant regime appropriate to the hygiene requirements in a production plant. Alcohols act rapidly and effectively against bacteria, mycobacteria, fungi and viruses but do not possess sporicidal efficacy. Quaternary ammonium compounds have no effect against bacterial spores or mycobacteria, while guanidines have better efficacy against Gram-negative bacteria, but are poorer against yeasts and moulds. Sources of contamination are also a crucial factor.

Choosing an effective disinfectant regime can be a complex process

Production hygiene relates directly to the quality and safety of pharmaceutical products, and in line with the rising significance of hygiene in production processes, international hygiene standards are becoming ever more important. An example is the growing influence of the US Food and Drug Administration (FDA) in international pharmaceutical manufacturing. At the same time, the harmonisation of international testing regulations (e.g. European Norms, EN) opens up new options for disinfectant risk assessment.

Choosing an effective disinfectant regime appropriate to the hygiene requirements in a production plant can be a complex process. In this context, consideration of the antimicrobial efficacy of different biocides is an important basis on which to make such decisions. Not all disinfectant actives have the same spectrum of effect and when systematically using disinfectants, it is vital to take into account the effect of different disinfectants. Table 1 gives an overview of the spectrum of antimicrobial efficacy of different biocides on selected actives, with a distinction being made between bactericidal, fungicidal, sporicidal, mycobactericidal and virucidal efficacy.1

Table 1 shows that alcohols, which act rapidly and effectively against bacteria, mycobacteria, fungi and viruses, do not possess sporicidal efficacy. Quaternary ammonium compounds (quats) likewise have no effect against bacterial spores or mycobacteria that are significant infection pathogens, especially in the medical area.

This is also true of guanidines; compared with quaternary ammonium compounds, these have rather better efficacy against Gram-negative bacteria, but are poorer against yeasts and moulds.

Aldehydes and active oxygen compounds and peracetic acid have a broad antimicrobial spectrum of action. However, the fungicidal and virucidal efficacy of aldehydic compounds tends to be rather poorer than that of active oxygen compounds and peracetic acid.2

Table 1: Illustrative presentation of the microbicidal efficacy of biocidal actives
BactericidiaMyco
bactericidia
SporicidiaFungicidiaVirucidia
Spectrum of actionGram+ bacteriaGram– bacteriaMyco
bacteria
Bacterial sporesYeastsMouldsViruses
Alcohols+++++++++++++++
Quats+++++++++++++
Guanidines++++++++++++
Aldehydes++++++++++++++++++
Active oxygen+++++++++++++++++++++
Peracetic acid+++++++++++++++++++++
The ratings used are: +++ = good efficacy; ++ = moderate efficacy; - = inadequate efficacy

Sources of contamination: In addition to antimicrobial efficacy, consideration of microbial contamination plays a crucial role when choosing suitable and effective disinfectants in the production plant. Packaging material, for example, is a typical source of contamination with spore-forming bacteria, moulds and yeasts. In areas where cardboard materials are used extensively, and spore-forming bacteria, yeasts and moulds have been detected during monitoring, it is sensible to ensure the use of disinfectants with bactericidal, fungicidal and sporicidal efficacy.

Figure 1: Detection of Staphylococcus epidermidis on the inner side of a ring that comes into contact with the skin. The illustration shows the microbiological contamination of a ring as a result of the intensive skin contact, constituting a potential contamination danger in the production process. Staphylococcus epidermidis is a Gram-positive bacterium, and can be effectively combated by the use of bactericidal disinfectants

Employees are also a source of microbial contamination, especially Gram-positive bacteria, e.g. the microbiological flora of humans and other mammals3 (see Figure 1).

Raw materials are a further common source of contamination. For example, when raw materials of plant origin are used, entry of Gram-negative bacteria, such as Enterobacteriaceae or spore-forming Clostridium spp. can occur. If a risk of entry of spore-forming Clostridium spp. or the spore-forming Bacillus spp. is identified, appropriate sporicidal disinfection measures are necessary. However, if the risk can be excluded, use of sporicidally effective disinfectants is not necessary.

Microbiological monitoring: Regular microbiological monitoring is of crucial importance. On the one hand the monitoring findings form an important basis for the selection of suitable disinfection measures, and on the other hand the monitoring has a decisive control function – enabling the efficacy of the disinfectants used to be repeatedly checked.

In this way any changes in the microbiological spectrum are detected immediately and, in turn, form the basis for appropriate adaptation of the disinfection regime. For example, exceeding the microbiological warning values (limit values) in combination with a changed microbiological spectrum of the contamination is a clear indication of altered conditions, which must be taken into account in a systematic adaptation of the hygiene regime. An example of this would be the sudden occurrence of mould spores as a result of a newly installed composting facility in the proximity of the production site.

The microbiological monitoring is also of essential importance with regard to checking that the disinfection measures are being applied correctly. It also enables a regular check of whether the selected hygiene regimen is being followed correctly, and this is documented by the warning limit (action limit) being within the specified limits when the microbiological spectrum is unchanged.

If, however, the warning limit (action limit) is exceeded when there has been no change in the microbiological spectrum of the contaminants, it is reasonable to suppose errors in the application of the disinfection measures used, an immediate response to which must be made, for example by the training of those responsible.

Reports based on efficacy tests according to European standards: Using the example of efficacy against spore-forming bacteria, in the following discusion it should be seen how the results from the monitoring, together with the specific tests of efficacy of a disinfectant in accordance with European norms (ENs) can be used for a systematic analysis of the risks.

For verification of the sporicidal efficacy of disinfectants, the following tests can be used: EN 14347 (phase 1), EN 13704 (phase 2/step 1), EN 13697 (phase 2/step 2).4, 5, 6

The test for sporicidia according to EN 13704 is a quantitative suspension test (phase 2/step 1), in which the sporicidal efficacy of a disinfectant is tested in the presence of an organic load. In addition, the test on surfaces simulating practical conditions (EN 13697) can be modified and also used to prove sporicidal efficacy.

In both cases Bacillus subtilis ATCC 6633 is the standard test organism. However, Bacillus cereus ATCC 12826 or Clostridium sporogenes 51 CIP 7939 may also be used.

Example of a systematic risk analysis on the basis of taxonomic classification of microbial contamination (spore-forming bacteria) detected during monitoring
Detection of spore-forming bacteria in the monitoring:
-> hygienically relevant spore-forming bacteria are Bacillus spp. or Clostridium spp.
Taxonomic classification of Bacillus spp.:
Bacteria; Firmicutes; Bacilli; Bacillales; Bacillaceae; Bacillus
Test organisms in EN tests
EN 13704 (Phase 2/step 1), quantitative suspension test with organic load
EN 13697 mod. (phase 2/step 2), quantitative surface test
Bacillus subtilis ATCC 6633 (obligatory)
Bacillus cereus ATCC 12826 (additional)

The example above shows how systematic risk analysis can be achieved by means of the taxonomic classification of the micro-organisms detected during monitoring.

As a result of the monitoring, spore-forming bacteria were detected. The spore-forming bacteria with hygienic relevance were limited to the genera Bacillus and Clostridium. Bacillus subtilis ATCC 6633 is used in EN 13704 as an obligatory test organism in the form of endospores, and can also be used in EN 13797 mod. as a standard test organism in testing for sporicidia.

Schülke & Mayr’s own lab tests have also shown that the resistance of Bacillus subtilis endospores to various biocides is greater than that of Clostridium sporogenes endospores (Steinhauer, K. et al. (2010) unpublished). As a result of the reduction of at least 103–104 micro-organisms per test surface (3–4 log steps) required in the efficacy tests, from the point of view of practical use there is also a considerable safety margin in the case of disinfectants tested to EN 13697.1,7

References

1. Steinhauer, K. (2010): Antimicrobial efficacy and systematic use of disinfectants, In: Mendez-Vilas, A. (ed.), Current Research, Technology and Education Topics in Applied Microbiology and Microbial Biotechnology, Volume 1, pp. 369–376, Formatex Research Center, Badajoz, Spain, ISBN (13): 978-84-614-6194-3

2. Assadian, O. und Kramer, A. (2008): Wallhäußers Praxis der Sterilisation, Desinfektion, Antiseptik und Konservierung. 1st ed. Georg Thieme Verlag, Stuttgart

3. Bannerman, T. L. and Peacock, S. J. (2007): Manual of clinical microbiology, 9th ed., ASM press, Washington, D.C.

4. European Committee for standardization (2005): European standard EN 14347

5. European Committee for standardization (2002): European standard EN 13704

6. European Committee for standardization (2002): European standard EN 13697

7. Steinhauer, K. (2006): Nutzen der EN-Prüfungen von Desinfektionsmitteln. Reinraumtechnik 03: 20-24, GIT-Verlag

Footnote

This article is a summary of the article Steinhauer, K. (2010): Antimicrobial efficacy and systematic use of disinfectants, In: Mendez-Vilas, A. (ed.), Current Research, Technology and Education Topics in Applied Microbiology and Microbial Biotechnology, Vol. 1, pp. 369–376, Formatex Research Center, Badajoz, Spain, ISBN (13): 978-84-614-6194-3

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