Biocides (antiseptics and disinfectants) (work in progress)#

First version: 2020-02-09
Last update: 2022-03-02
Persistent link to latest version:

1 Nomenclature

Biocides are chemical substances that in low concentrations are enough to kill viruses and inactivate bacteria. A vague distinction is made in practice between antiseptics which are biocides suitable for use on living beings and disinfectants which are biocides suitable for use on inanimate objects.

2 Targets

WHO (2016), p. 79 give the resilience of microorganisms to antiseptics as follows, in decreased order of resilience:

  1. Prions
  2. Bacterial spores
  3. Parasites of the taxon Coccidia
  4. Mycobacteria
  5. Small non-enveloped viruses
  6. Vegatative bacteria
  7. Lipid enveloped viruses

An early version of this ranking appeared of McDonnell, Russel (1999) and Russell (1999).

Note that resilience is not an indicator of pathogenicity nor vice-versa. For example: The lowest category, lipid enveloped viruses, includes HIV and the Ebola virus which have caused highly lethal epidemics; bacterial spores include Geobacillus stearothermophilus which is not pathogenic to humans; Coccidia monocellular parasites include Toxoplasma gondii, which can cause infection in humans, usually asymptomatic.

2.1 Prions

Prions are a specific class of abnormally folded proteins that can induce the same misfolding on proteins of the same type. Prions are the causative agent of transmissible spongiform encephalopathie (TSEs) including bobine spongiform encephalopathy (“mad cow disease”). TSEs are among the few transmissible diseases that can emerge spontaneously in healthy organisms without prior contamination. Prions accumulate especially in the central nervous system of affected organisms and are not common in the outdoor environment, unlike spore-forming bacteria.

2.2 Bacterial spores

Bacterial spores are structures that contain the genetic material of the parent bacterium in a dormant state; when exposed to favorable conditions, they regenerate the vegatative (active) form. Bacterial spores are resilient to extreme conditions including high temperature and most biocides. Only some bacterial species can form spores. Leggett et al. (2001) reviewed the mechanism at the biochemical level known or suspected to be responsible for the resilience of bacterial spores.

Spore-forming bateria are common in outdoor environments. Some species are part of the normal flora of the digestive tract of humans and other animals. A few species cause localized cutaneous infection; examples include Clostridium perfringens (gas gangrene) and Bacillus anthracis (cutaneous anthrax).

Biocides that can inactivate bacterial spores are called sporicides. Sporicides used in practice can be divided in 2 disjoint groups: alkylating agents and oxidizing agents (Maillard (2011) writes: “There is only a limited number of chemical biocides that possess sporicidal activity. These biocides are all highly reactive and theycan be divided into alkylating and oxidising agents”). Oxidizing agents are generally faster to inactivate spores than alkylating agents and can harm metal objects. Alkylating agents are suitable for use with metal objects. Neither class is suitable for use on living tissue. Alkylating agents tend to be mutagenic in in vitro assays; therefore, exposure of operators to their vapors should be minimized as a precautionary measure material disinfected with such agents should be thoroughly rinsed before use.

3 Cleaning

Material should be devoid of macroscopic contamination prior to disinfection. Residues of bodily fluids and solid tissue decrease the effectiveness of biocides through chemical reaction, dilution and hindering penetration of the biocide. This contamination can be removed by manual scrubbing with a brush using clean water and a detergent or an enzymatic cleaner, then rising with water. The water used for cleaning needs not be sterile. Brushes should be discarded or cleaned and disinfected between uses to avoid cross-contamination. Cleaning is not a substitute for disinfection. WHO (2016) contains extensive discussion of recommended practices for cleaning.

4 Agents

4.1 Benzalkonium chloride

Benzalkonium chloride is a quaternary ammonium salt. It is suitable as an antiseptic. It is suitable as a surgical disinfectant provided that contamination with resilient pathogens (especially bacterial spores) can be ruled out. Benzalkonium chloride solutions in water have a slight tendency to foam like soapy water. It is not and oxidant and therefore does not tarnishes stainless steel. It has a mild sweet odor, especially when dry.

Sebben (1983) recommend against benzalkonium chloride because of its narrow spectrum and that it is easily inactivated by ordinary conditions including contact with blood. Acosta-Gío et al. (2001) found that benzalkonium chloride at a mass concentration[1] of 0.12 % did not inactivate Bacillus subtilis spores.

Wood, Payne (1998) found that a solution of 2 g/l of benzalkonium chloride inactivates non-enveloped viruses and coxsackie virus but not poliovirus in 1 minute in an assay made to simulate contamination with bodily fluids.

4.2 Benzene-1,2-dicarbaldehyde

Benzene-1,2-dicarbaldehyde is an alkylating sporicidal. In medical practice it is more commonly known under the archaic name “o-phthalaldehyde”. Cabrera-Martinez et al. (2002) examined the sporicidal mechanism of action of benzene-1,2-dicarbaldehyde.

4.3 Chlorhexidine

Chlorhexidine is a broad-spectum biocidal with activity against Gram-positive and Gram-negative bacteria, fungi and viruses but not spores. It has limited activity against spores. Neutral chlorhexidine has low solubility in water. In medical used it is used in the form of chlorhexidine acetate, chloride dichloride or chlorhexidine digluconate in solution with an alcohol (Karpiński, Szkaradkiewicz 2015 for paragraph so far). Chlorhexidine is partially tolerant to autoclaving; it releases small amounts of 4-chloroaniline (Russel 1993 for sentence). Its activity is reduced by blood serum (Russel 1993 for sentence).

4.4 Ethaneperoxoic acid

Ethaneperoxic acid is the linear single-ended peroxic acid with 2 carbon atoms. In medical practice it is more commonly known under the archaic name “peroxyacetic acid”. March et al. (2015) found that a solution with a mass fraction[1] of 0.25 % ethaneperoxic acid is effective in inactivating bacterial spores; among the species tested, they found that spores of Bacillus anthracis required the longest time to inactivating (6 decades of reduction) at 4 minutes. A solution of 1.3 % ethaneperoxic acid achieved the same level of inactivation at less than 1 minute.

Black et al. (2017) found that ethaneperoxic acid is suitable for use with steel of alloy AISI 304 but not suitable for use with steel of type AISI 430 because it causes corrosion of the later alloy and is quickly inactivated. Alloy AISI 304 is representative of the stainless steel used for surgical instruments; however surgical instruments almost never state the specific alloy they are made of.

4.5 Pentanedial

Pentanedial is the linear, unsubstituted dialdehyde with 5 carbon atoms. In medical practice it is more commonly known under the archaic name “glutaraldehyde”. Acosta-Gío et al (2001) is found that a solution with (presumed mass) fraction of 2 % pentanedial inactivates Bacillus subtilis spores after 10 h. March et al. (2015) found that a solution of glutaraldehyde at 2.4 % (not specified whether by mass or volume) is effective in inactivating bacterial spores; among the species tested, they found that spores of Bacillus subtilis requied the longest time to inactivate (6 decades of reduction) at 214 minutes.

4.6 Sodium hypochlorite

Sodium hypochlorite is the the active component of household bleach. It is a powerful disinfectant. The United States Center for Disease Control (CDC) includes immerson in sodium hypochlorite among the recommended means of disinfection for instruments contaminated with prions. Brown et al. (2004) examined the effect of concentrated aqueous solution of sodium hypochlorite mass fraction[1] of 5.25 % to 6 % on medical instruments. Instruments were immersed in sodium hypochlorite for 1 h, then washed in water for 30 min; this was repeated 5 times. They found that some instruments were not harmed at all, some had cosmetic blackening of the surface not affecting the functionality and others had patent corrosion.

Solutions of sodium hypochlorite are degraded with time because chlorine escapes as a gas. To minimize inactivation, solutions of sodium hypochlorite should be kept in a air-tight closed container and diluted only prior to use.

Kampf et al. (2020) found that 0.1 % sodium hypochlorite[1] inactivates SARS-CoV-2 after 1 minute.

5 Autoclave

Autoclaves are the standard means to disinfect heat-resistant instruments in well-equiped medical facilities. Usual treatment is 30 min of exposure to steam at 121 °C. Validation can be performed by exposing spores of Geobacillus stearothermophilus –a particullarly heat-resistant species– to an autoclave cycle. The exposed sample and an untreated control sample are cultivated. The proccess is deemed valid if there is germination in the control sample and not in the exposed sample. An autoclave proccess cerified in this manner will inactivate most pathogens with the notable exception of prions. The WHO recommend methods for the reprocessing of instruments contaminated with prions, some of which involve combination of autoclave treatment with sodium hypochlorite or sodium hydroxide; see WHO (1999).

Swenson et al. (2018) found that some commercially available pressure cookers are suitable for disinfection up to inactivation of Geobacillus stearothermophilus.

6 Other resources

The WHO published a book on recommended practices for reprocessing of medical devices including biocides for reprocessing surgical instruments (WHO 2016). Rutala, Weber (2004) wrote an introduction to disinfection of medical equipment with chemical products.

7 Notes

  1. Not specified whether mass fraction, volume fraction or amount of substance fraction in source. Assumed to be mass fraction.

  2. of 0.12 % did not inactivate

8 References

  • E. Acosta-Gío et al. (2001) “El cloruro de benzalconio: inaceptable para esterilizar o desinfectar instrumental médico o dental” [in Spanish]. DOI: 10.1590/S0036-36342001000600008. Open access.
  • E. Black et al. (2017) “Evaluation of AISI Type 304 stainless steel as a suitable surface material for evaluating the efficacy of peracetic acid-based disinfectants against Clostridium difficile spores”. DOI: 10.1371/journal.pone.0187074 . Open access.
  • S. Brown et al. (2004) “Effects on instruments of the World Health Organization–recommended protocols for decontamination after possible exposure to transmissible spongiform encephalopathy–contaminated tissue”. DOI: 10.1002/jbm.b.30125. Open access.
  • R. M. Cabrera-Martinez et al. (2002) “Studies on the mechanisms of the sporicidal action of ortho-phthalaldehyde”. DOI: 10.1046/j.1365-2672.2002.01572.x. Open access.
  • G. Kampf et al. (2020) “Persistence of coronaviruses on inanimate surfaces and its inactivation with biocidal agents” DOI: 10.1016/j.jhin.2020.01.022.
  • T. M. Karpiński, A.K. Szkaradkiewicz (2015) “Chlorhexidine – pharmaco-biological activity and application”. No DOI found.
  • M. J. Leggett et al. (2011) “Bacterial spore structures and their protective role inbiocide resistance”. DOI: 10.1111/j.1365-2672.2012.05336.x. Open access.
  • J. K. March et al. (2015) “The differential effects of heat-shocking on the viability of spores from Bacillus anthracis, Bacillus subtilis, and Clostridium sporogenes after treatment with peraceticacid- and glutaraldehyde-based disinfectant”. DOI: 10.1002/mbo3.277. Open access.
  • J. Y. Maillard (2011) “Innate resistance to sporicides and potential failure to decontaminate”. DOI: 10.1016/j.jhin.2010.06.028.
  • G. McDonnell, A. D. Russell (1999) “Antiseptics and Disinfectants: Activity, Action, and Resistance”. DOI: 10.1128/cmr.12.1.147 . Open access.
  • A. D. Russell (1993) “Antibacterial activity of chlorhexidine”. DOI: 10.1016/0195-6701(93)90109-d.
  • Russell, A. D. (1999) “Bacterial resistance to disinfectants: present knowledge and future problems”. DOI: 10.1016/s0195-6701(99)90066-x.
  • W. A. Rutala, D. A. Weber (2004) “Disinfection and Sterilization in Health Care Facilities: What Clinicians Need to Know”. DOI: 10.1086/423182.
  • J. E. Sebben (1983) “Surgical antiseptics”. DOI: 10.1016/s0190-9622(83)70192-1.
  • V. A. Swenson et al. (2018) “Assessment and verification of commercially available pressure cookers for laboratory sterilization”. DOI: 10.1371/journal.pone.0208769 .
  • Cited as “WHO (1999)”. World Health Organization (1999) “WHO Infection Control Guidelines for Transmissible Spongiform Encephalopathies”. Open access.
  • Cited as “WHO (2016)”. World Health Organization (2016) “Decontamination and reprocessing of medical devices for health-care facilities” (version in English). ISBN: 9789241549851. Open access.
  • A. Wood, D. Payne (1998) “The action of three antiseptics/disinfectants against enveloped and non-enveloped viruses”. DOI: 10.1016/s0195-6701(98)90077-9.