Understanding the risk of emerging bacterial resistance from the use of sore throat over-the-counter topical antibiotics

Robertson, Andrew ORCID: https://orcid.org/0000-0001-5345-7846 2023. Understanding the risk of emerging bacterial resistance from the use of sore throat over-the-counter topical antibiotics. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Within Europe, antibiotics are available in over-the-counter (OTC) topical sore throat medications. As sore throats are mainly of viral aetiology, antibiotics in these medications is poor antimicrobial stewardship. It is unknown what role OTC antibiotics (bacitracin, gramicidin, neomycin and tyrothricin) play in antimicrobial resistance. This study aims to understand whether the use of OTC antibiotics could contribute to resistance development in bacteria. OTC antibiotics at during-use concentrations were tested against a panel of bacteria and mainly Gram-negative bacteria could resist their effects, with the exception of neomycin. After OTC exposure, clinical cross-resistance was gained to beta-lactam antibiotics (including ampicillin, cefotaxime, aztreonam and imipenem) and gentamicin and this resistance was mainly stable. Phenotypic and genotypic changes after OTC antibiotic exposure were assessed and many changes occurred including, increased beta-lactamase activity, increased efflux activity, morphological changes, metabolic changes and mutation in membrane protein genes. It is thought that the increase in beta-lactamase activity is due to induction of AmpC, which is predominantly responsible for the clinical cross-resistance to the beta-lactam antibiotics. Co-exposure assays were done to evaluate the impact OTC antibiotics have on aminoglycoside efficacy. It was found that gramicidin and tyrothricin both impacted the efficacy of aminoglycoside treatment, although bacitracin did not. The study concluded that gramicidin and tyrothricin depolarize the cell membrane by potassium leakage, inhibiting aminoglycoside uptake into the cell. Along with experimental lab work, a survey was constructed to understand OTC antibiotic usage. It also sought to understand how sore throat is managed, and the knowledge of pharmacists on OTC antibiotic-containing products. Although the survey has not yet been distributed, responses from pretesting indicate that some pharmacists are unaware of OTC antibiotic-containing products. This study highlights the development of clinical cross-resistance from exposure to OTC antibiotics, and therefore should not be used for sore throat products for patients seeking symptomatic relief.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Pharmacy
Subjects:	Q Science > Q Science (General)
Date of First Compliant Deposit:	17 April 2024
Last Modified:	17 Apr 2024 10:31
URI:	https://orca.cardiff.ac.uk/id/eprint/168012

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