AT
In 2023, reports on antibiotic resistance in the EU showed declined rates of bloodstream infections by methicillin-resistant Staphylococcus aureus (MRSA) and third-generation cephalosporin-resistant Escherichia coli compared with 2019 [1]. Unfortunately, there was over a 50% increase in Klebsiella pneumoniae bloodstream infections in 2023 compared to 2019, which impacted the 5% reduction target by 2030 [1]. Despite the decreased rates observed for certain bloodstream infections, the increased rate of K. pneumoniae bloodstream infections raises public health concerns and if rates continue to rise, the EU will not reach their antimicrobial resistance (AMR) targets by 2030 [1].
Unfortunately, bloodstream infections are not the only microbial infections that are impacting AMR rates in the EU; oral and throat infections are among the leading causes of inappropriate antibiotic use, with most infections treatable with topical therapies but instead are being treated with antibiotics, which is increasing rates of AMR [2]. One example is pharyngitis, which is colloquially known as a sore throat, and is often treated using antibiotics where alternative therapies can be successful [2]. Orally administered octenidine-containing lozenges are one of the alternatives that can be used to treat pharyngitis and are pharmacodynamically advantageous due to their easy administration and prolonged mucosal exposure [2]. On the other hand, their impact on the oral, throat and intestinal microbiome is unclear including whether they disrupt the commensals which are vital for maintaining homeostasis [2]. It is important for clinicians to have data on the impact of octenidine-containing lozenges in terms of their antimicrobial activity and impact on commensals, as without this they are unable to make decisions on the administration and comment on their microbiological safety to patients.
Junka et al. explored the antimicrobial activity of octenidine dihydrochloride against 106 microbial strains, including pathogenic and commensal microorganisms of the oral cavity, colon and pharynx. Among the panel of microorganisms were MRSA, Streptococcus pyogenes, E. coli, Candida albicans, as well as Bacteroides spp., which is an obligate anaerobe that resides in the gut and requires strict anaerobic conditions – this was achieved using the Whitley A35 Anaerobic Workstation under an atmosphere of 85% N2, 10% H2, and 5% CO2. Initial antimicrobial activity was assessed using a modified disk diffusion method and minimal biocidal concentration (MBCs) were determined using broth microdilution. Along different contact times and physiologically relevant concentrations, octenidine dihydrochloride gave MBCs of less than 260 mg/L against microorganisms representing the oral cavity and throat but no biocidal effect was seen against intestinal commensals at 0.05 mg/L octenidine dihydrochloride. Octenidine dihydrochloride was successful in eliminating pathogenic species, but there was a non-specific effect on commensals such as Streptococcus mitis. However, due to the short-term use of this treatment, as observed in octenidine dihydrochloride mouthwash, the impact on dysbiosis is easily reversible, given a healthy microbiome. Intestinal impact of octenidine dihydrochloride in terms of the impact on the gut microbiota is also minimal; there was no negative effect observed on the intestinal strains, including Bacteroides spp. Ultimately, these results support that antiseptic treatments are successful in eradicating pathogenic microorganisms from the oral cavity and throat, whilst not impacting the gut microbiome. This is incredibly promising as it provides an alternative therapy for sore throats from antibiotics and subsequently will halt the progression of AMR [2].
Whilst we endeavour to reduce antibiotic use, it is important to identify effective alternative treatments. In the interest of public health, data regarding microbiological impact on the microbiome is imperative, so research of this kind is highly regarded. With additional public awareness and increased research into alternative treatments, clinicians and patients will not have to rely on antibiotic use and the pandemic of AMR can be slowed.
Written by DWs Microbiologist Kirsty McTear
References
- European Centre for Disease Prevention and Control. Antimicrobial resistance in the EU/EEA (EARS-Net) - Annual Epidemiological Report 2023 [Internet]. European Centre for Disease Prevention and Control. 2024. Available from: https://www.ecdc.europa.eu/en/publications-data/antimicrobial-resistance-eueea-ears-net-annual-epidemiological-report-2023
- Junka A, Malwina Brożyna, Paweł Krzyżek, Tomczyk M, Krasucki K, Matys T, et al. Octenidine Lozenges Intended for Oral Administration Display In Vitro Activity Against Oropharyngeal Pathogens and Safety Toward Intestinal Microbiota. International Journal of Molecular Sciences. 2025 Oct 15;26(20):10045–5.
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