Resistance of microorganism against disinfectant
The use of antiseptics and disinfectants are the essential part for infection control. The main purpose of disinfection is to reduce the number of targeted microorganisms on surface or instrument to the levels where it is safe to the public. According to European regulation, the standards to which disinfectants have to conform in order to support the claims for microbial activity is guided by EN 14885:2018. According to EN 14885, there are seven different microbial activity that can be claimed, including bactericidal, fungicidal, yeasticidal, tuberculocidal, mycobactericidal, virucidal and sporicidal activities.
Different types of microorganisms have vary resistance against disinfectant, depending on the active substance of disinfectants. Generally, the resistance of the microorganisms against disinfectant has been shown in Figure 1 (2-3).
Bacterial endospore (Bacillus, Clostridium)
↓
Mycobacteria (M. tuberculosis)
↓
Small non-enveloped viruses (Poliovirus)
↓
Gram-negative bacteria (Pseudomonas)
↓
Fungi (Candida, Aspergillus)
↓
Large non-enveloped viruses (Entero, Adeno)
↓
Gram-positive bacteria (Staphylococcus, Enterococci)
↓
Lipid enveloped viruses (HIV, HBV)
Figure 1. Resistance of microorganisms against disinfectant in descending order.
Bacterial endospore
Bacterial endospore is the hardest organism to be killed by disinfectant. During stress condition, some of the bacteria will undergo sporulation and form spore coat to protect themselves from dying. The endospore remains dormant until the environment is favourable for it to grow. Bacillus and Clostridium have been widely used as the model to study the properties of bacterial endospore. Bacterial endospore can be permanently deactivated by disinfectant containing chloride compounds, glutaraldehyde or peracetic acid. In contrast, alcohol, phenolics, QACs and chlorhexidine are not effective in eliminating bacterial endospore (3).
Mycobacteria
Mycobacteria is the second hardest organism to be eliminated by disinfectant. This might due to their complex cell walls that provide effective barrier against the active substance. Phenol, peracetic acid, hydrogen peroxide, alcohol and glutaraldehyde are active substances that exhibit mycobactericidal activity. In contrast, chlorhexidine, glutaraldehyde and QACs are weak in mycobactericidal activity.
Small non-enveloped viruses
Small non-enveloped viruses, including norovirus and poliovirus, are the most resistant virus group against disinfectant. The size for small non-enveloped virus is less than 50nm. This virus group contains a very resistant viral capsid.
Gram-negative bacteria
Gram-negative bacteria contains cell wall which is composed of lipopolysaccharide and proteins. This type of cell wall limits the entry of antibacterial agents to the cell, and thus gram-negative bacteria is considerably more resistant to most of the active substances of disinfectant, including chlorhexidine and QACs, compared to gram-positive bacteria.
Fungi
Fungi can be divided into yeast and mold. Yeast reproduce asexually through mitosis, while mold reproduce through spores. Mold’s spore is the most resistant form within this group against disinfectants. Chlorine compounds, glutaraldehyde, iodophors, phenolic compounds and hydrogen peroxide can exhibit fungicidal activity.
Large non-enveloped viruses
Similar as small non-enveloped viruses, large non-enveloped viruses, including rotavirus and adenovirus, also contain a very resistant viral capsid. As they have larger size (70-100nm) than small non-enveloped viruses, they are more susceptible to disinfectant.
Gram-positive bacteria
Gram-positive bacteria contains cell wall which is composed of peptidoglycan and teichoic acid. This cell wall is not able to form an effective barrier against the disinfectant, as the high molecular weight substances can easily penetrate into the cells through this cell wall. Most of the active substances of disinfectant, including alcohol, QACs and chlorhexidine, are effective in killing the bacteria.
Lipid enveloped viruses
The enveloped viruses, such as vaccinia virus and HIV, contain lipid envelope, which is easily dissolved by disinfectants. Once it is dissolved, the core is exposed and virus is inactivated. Thus, lipid enveloped viruses are the most susceptible microorganism against disinfectants.
Reference
1) EN 14885:2018 Chemical disinfectants and antiseptics. Application of European Standards for chemical disinfectants and antiseptics
2) Russell, A.D., 1999. Bacterial resistance to disinfectants: present knowledge and future problems. Journal of Hospital infection, 43, pp.S57-S68.
3) McDonnell, G. and Russell, A.D., 1999. Antiseptics and disinfectants: activity, action, and resistance. Clinical microbiology reviews, 12(1), pp.147-179.