Introduction
Effective disinfection is crucial for infection control as it helps to control potentially hazardous microorganisms, especially in laboratory environments. It is crucial to use validated decontamination protocols to effectively inactivate pathogens as this reduces the likelihood of pathogen exposure, resulting in laboratory-acquired infections and contamination of laboratory and outside environments. The selection of a disinfectant is often based on various factors, including the pathogens to be manipulated, compatibility with laboratory surfaces and efficacy of inactivation [
1]. This is particularly important in low-resource settings, where cost, availability, and concentration influence decisions.
Laboratory personnel consistently face significant hazards when exposed to hazardous and potentially lethal pathogens. The routine handling of pathogenic biological agents by laboratory personnel necessitates adherence to stringent safety protocols due to the inherent risk of infection.
P. aeruginosa is an opportunistic bacterium classified as risk group 2 [
2] that frequently causes nosocomial infections, particularly in patients with burn wounds, cystic fibrosis, acute leukaemias, organ transplantation, and intravenous drug addiction [
3]. Inadequate infection control protocols can contribute to its persistence. They can survive under various environmental conditions, such as storage tanks, disinfectant solutions, and urinals in hospital environments [
4]. According to the Centers for Disease Control and Prevention (CDC),
P. aeruginosa causes 51,000 healthcare-associated infections in US hospitals annually, with 13% of cases exhibiting multidrug resistance, leading to 440 deaths each year [
5]. Similarly, Methicillin-Resistant
Staphylococcus aureus (MRSA) infection is a significant source of nosocomial and community-associated infections, potentially leading to mortality due to its resistance to conventional beta-lactam antibiotics [
6]. The manipulation of
S. aureus necessitates adherence to Biosafety Level 2 practices and procedures [
7]. Specific populations, including athletes, daycare and school children, military personnel residing in barracks, and individuals undergoing inpatient medical care, surgery, or using medical devices, are more susceptible to MRSA infection [
8].
Burkholderia pseudomallei is a gram-negative bacterium classified as risk group 3 and causes melioidosis infection [
9,
10]. Patients infected with this bacterium often experience symptoms that can be easily confused with other diseases, such as tuberculosis [
11].
B. pseudomallei infection can lead to local infection, bacteremia, pulmonary infection, and disseminated infection, with a mortality rate of approximately 21% [
9].
Escherichia coli is mostly harmless to humans; however, some strains, such as enterotoxigenic
E. coli O157:H7 [
12,
13], can cause serious illness. These pathogenic strains are known to contaminate food and water sources, leading to symptoms such as diarrhoea and poisoning in people who come into contact with them.
Umonium
38 has been reported as a broad-spectrum disinfectant for laboratory purposes for a wide range of bacteria, viruses, and fungi. The active ingredient of Umonium
38 is isopropyl-tridecyl-dimethyl-ammonium, a surfactant that breaks the bonds between water molecules and penetrates deeper into micro-asperities, allowing it to dissolve other molecules [
14]. Studies have demonstrated that Umonium
38 is a highly effective disinfectant against avian influenza virus (AIV) subtype H5N1 and Newcastle disease virus (NDV) [
15]. Furthermore, Umonium
38, when combined with other active compounds, exhibits anti-mycobacterial and antibacterial properties [
16]. Umonium
38 offers several advantages, such as its broad antibacterial properties, relative affordability, and user safety since it contains no carcinogenic or endocrine-disrupting components [
14]. It is also compatible with several industrial and equipment surfaces, thanks to its neutral pH, non-flammability, and lack of toxic gas emissions [
14].
This study aimed to assess the bactericidal efficacy of various concentrations of Umonium38 against four bacterial species: B. pseudomallei, E. coli, MRSA and Pseudomonas aeruginosa. We also examined the bactericidal efficacy of Umonium38 and determined its stability over 14 days post-treatment. Furthermore, we aimed to compare the bactericidal efficacy of Umonium38 with Virkon®, a widely employed and currently available laboratory disinfectant.
Discussion
This study is the first to determine the most effective Umonium38 concentration and duration of contact for inactivation of P. aeruginosa, E. coli, B. pseudomallei, and MRSA under optimal conditions. 1% Virkon® was also effective against the four bacterial strains following a 30-minute contact time.
The results presented in this study reflected those of the Umonium
38 manufacturer (summarised in Table
3) on
P. aeruginosa and
E. coli using European Standards EN 1276:2019 and EN 1040:2006 [
19]. They reported a contact time of > 10 min, and a 0.5% Umonium
38 solution resulted in a reduction of over 10
5 in both bacteria; however, after a 1-minute contact, the reduction reported was < 10
5 [
19]. The report also mentioned that a higher concentration of 2.5% Umonium
38 required a minimum contact time of only 1 min to achieve the same bactericidal effect as 0.5% Umonium
38 following 10 min of contact [
19]. Similar results were achieved for inactivating
P. aeruginosa and
E. coli using 0.5% and 2.5% Umonium
38 following 15 min of contact following the European Standard EN13697:2001 [
16].
Table 3
Summary of the manufacturer’s (Huckert’s International, Belgium) antibacterial validation results and the results of studies on P. aeruginosa (ATCC 27,853) and E. coli (ATCC 25,922).
Adapted from [
19]. Numbers in bold are the results from this study.
P. aeruginosa (ATCC 27,853) | 0.5 | 10 | > 5 | Dilution/neutralisation | EN 1276 |
2.5 | 1 | > 5 | Dilution/neutralisation | EN 1276 |
0.5 | 1 | < 5 | Glass/ PVC | EN 1040 |
0.5 | 10 | > 5 | Glass/ PVC | EN 1040 |
0.5 | 30 | > 5 | Glass/ PVC | EN 1040 |
2.5 | 1 | > 5 | Glass/ PVC | EN 1040 |
2.5 | 10 | > 5 | Glass/ PVC | EN 1040 |
2.5 | 30 | > 5 | Glass/ PVC | EN 1040 |
0.5 | 15 | 8 | This study | |
E. coli (ATCC 25,922) | 0.5 | 10 | > 5 | Dilution/neutralisation | EN 1276 |
2.5 | 1 | > 5 | Dilution/neutralisation | EN 1276 |
0.5 | 1 | < 5 | Glass/ PVC | EN 1040 |
0.5 | 10 | > 5 | Glass/ PVC | EN 1040 |
0.5 | 30 | > 5 | Glass/ PVC | EN 1040 |
2.5 | 1 | > 5 | Glass/ PVC | EN 1040 |
2.5 | 10 | > 5 | Glass/ PVC | EN 1040 |
2.5 | 30 | > 5 | Glass/ PVC | EN 1040 |
0.5 | 15 | 8 | This study | |
Our results demonstrated that 0.5% Umonium
38 can effectively inactivate MRSA within 15 min, sustained for 14 days, and underscores its potential for safely and effectively disinfecting equipment surfaces and laboratory environments. MRSA inactivation currently focuses on light utilisation, such as far-UVC LEDs with a wavelength below 240 nm [
20,
21] and antimicrobial photodynamic therapy with a porphyrinic formulation [
22] for antiseptic purposes on the skin. In addition, the efficacy of octenidine hydrochloride has been assessed for the inactivation of MRSA biofilm formation on medical implants and laboratory equipment within hospital settings [
23].
Our study demonstrated that
B. pseudomallei required 1% Umonium
38 with contact for 15 min for effective inactivation. Other chemical treatments, heat exposure, autoclaving, and radiation are also effective for
B. pseudomallei inactivation. Chemical agents, including chlorine dioxide solution [
24], pH-adjusted bleach, ethanol solution (70%), quaternary ammonium compounds, and PineSol
® [
25] have been proven effective.
B. pseudomallei can be effectively inactivated by heat treatment at 80
oC for 1 h [
26] or 121
oC for 15 min [
27]. Exposure to sunlight with wavelengths ranging from 295 to 305 nm can inactivate
B. pseudomallei concentrations from 10
4 to 10
6 CFU/ml in 60 to 180 min [
28]. Furthermore, ultraviolet (UV) light with a wavelength of 365 nm, emitting a radiant flux of 90,000 mWs/cm
2 at a flow rate of 5 L/min, resulted in the inactivation of
B. pseudomallei 10
6 CFU/mL [
29].
A limitation of the results presented in this study is that it has been performed under optimal conditions, and the results should be interpreted as such. The effectiveness of chemical disinfectants under different background conditions, including pH, and in the presence of significant biological matrices, including culture media or organic contamination, may affect the efficacy of the inactivation of Umonium
38. Raffo et al. [
16] investigated the impact of “clean” and “dirty” conditions on the effectiveness of 0.5% and 2.5% Umonium
38 for inactivating
P. aeruginosa and
E. coli. The “clean” condition involved 0.3 g of bovine serum albumin per liter of water, while the “dirty” condition involved the combination of 3.3 g of bovine serum albumin with 3.0 ml of red blood cells per liter of water. The study found that for both
P. aeruginosa and
E. coli. under “clean” conditions, 0.5% Umonium
38 treatment gave a 4-log
10 reduction in infectivity after 15 min; however, 60 min was required under “dirty” conditions [
16]. Interestingly, 2.5% Umonium
38 achieved a 4-log
10 reduction in infectivity of both pathogens after 15-minute exposure for both “clean” and “dirty” conditions [
16]. Therefore, additional studies are required to determine the optimal concentrations for the inactivation of
B. pseudomallei and MRSA under sub-optimal conditions, including organic loads or varied pH.
The results presented here demonstrate the effectiveness of Umonium38 and Virkon® for a selected group of bacteria under optimal conditions. When used correctly, Umonium38 offers laboratory staff an alternative for effective disinfection and provides an affordable and practical method for routine disinfection. Further work is required to determine the effectiveness of this and other disinfectants under the practical circumstances of everyday use.
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