Evaluating of the effect of sub-inhibitory concentrations of alcohol on Pseudomonas aeruginosa across different biofilm models

Lench, Elizabeth (2023) Evaluating of the effect of sub-inhibitory concentrations of alcohol on Pseudomonas aeruginosa across different biofilm models. Masters by Research thesis (MPhil), Manchester Metropolitan University.

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Abstract

Pseudomonas aeruginosa is a major cause of life-threatening nosocomial infections, especially in immunocompromised individuals, and therefore poses a significant threat to public health. This is largely due to its ability to form biofilms which reduces its susceptibility to antimicrobials and host immune defences. Whilst antibiotic resistance (ABR) in P. aeruginosa biofilm has been studied extensively, less attention has been paid to the relationship between biofilm and alcohol-based disinfectants. This project aims to explore the extent to which alcohols contribute to biofilm formation in hospital settings by investigating the effect of sub-inhibitory concentrations of ethanol (EtOH) and isopropyl alcohol (propan-2-ol), both common active ingredients in hand sanitisers, on P. aeruginosa biofilm growth. This was achieved by establishing the tolerance of 58 clinical P. aeruginosa isolates to low concentrations of EtOH and propan-2-ol, quantifying biofilm formation in sub-inhibitory levels of EtOH and determining the effect of sub-inhibitory concentrations of EtOH on established biofilm. Results demonstrate that bacteria were more susceptible to propan-2-ol than EtOH (mean MBC=8.17% and 11.02% respectively), and statistically significant (P< 0.05) variation in response to low levels of alcohol exists between P. aeruginosa isolates belonging to ST111 and ST235. Most significantly, 19 isolates showed significant (P< 0.05) increases in biofilm formation in the presence of 1-3% EtOH compared to 0% EtOH. Finally, P. aeruginosa in established biofilms (post 24-hour incubation at 37°C) were able to withstand greater concentrations of EtOH than in the initial stages of biofilm formation. This suggests diluted alcohol-based disinfectants are capable of stimulating biofilm formation in hospital water systems.