Development of a predictive in-vitro model to study preservative resistance development in Pseudomonas aeruginosa

Lead Research Organisation: University of Liverpool
Department Name: Institute of Infection and Global Health


Chemical preservatives, essential tools in the context of food, nutrition and health, are added to home and personal care (HPC) products to prevent microorganism growth and ensure products remain safe to use by the millions of consumers that utilise these products daily. The nature of how consumers use HPC products results in potential microbial inoculation e.g. skin creams and many of the HPC products Unilever sells rely on preservatives to prevent microbial spoilage. As a result, future-proofing preservative systems for HC and PC liquid formulations is one of the biggest technical challenges faced by R&D over the past couple of years.

Chemical preservatives are undergoing intense scrutiny for consumer safety, environmental impact and public relation opinion. The HPC industry is responding by removing fast acting preservatives such as formaldehyde donors and isothiazolinones and replacing them with milder chemicals that have a slower kill efficacy, such as organic acids; which introduces greater risk of preservative resistance. Resistance to preservatives can occur due to: sub-effective concentrations or microorganism bioburden overwhelming the preservative. A leading facilitator of antimicrobial resistance for industrial manufacturing is the formation of biofilms that slough transiently giving variable contamination of manufactured batches. Biofilms occlude the diffusion of chemicals resulting in a concentration gradient across the biofilm and microorganisms exposed to sub-lethal concentration of antimicrobials giving an opportunity to develop resistance.

Combatting antimicrobial resistance is an increasing global challenge; HPC products recalled due to microbial contamination has increased over the past 3 years. A microbiological contamination incident for a public recall costs >750K euro and a trade recall >50K euro; the reputational damage to a brand can be a significantly greater cost to the business. In the financial year 2014/15 two public and one trade recall in HPC due to microbiological contamination cost Unilever >1.5 million euros.

Pseudomonas spp are the most common industrial microbial contaminants of HPC products. Pseudomonas spp are a ubiquitous genus of microorganisms routinely isolated from water. Consequently, P. aeruginosa is a leading microorganism of concern for product spoilage and an excellent model organism to develop understanding of preservative resistance. Understanding preservative resistance mechanisms and the importance of biofilm formation of Pseudomonas spp is very important to optimise new preservation strategies.

This project will develop in-vitro resistance to a range of preservatives in Pseudomonas isolates, elucidating mechanisms of resistance against new, progressive kill preservation chemicals. A comparison of in-vitro resistant Pseudomonas isolates and naturally occurring resistant industrial contamination Pseudomonas isolates will be performed by genomic and transcriptomic analysis to identify if in-vitro resistance mechanisms reflect those generated in Unilever factories.

In particular, we aim to achieve the following:

Validation of selected methods for generating resistance to a range of preservation chemicals to determine the preferred methodology for further resistance development utilising a wider range of preservation chemicals and isolates.

Generation of resistance to strategic preservation chemicals including binary and tertiary combinations in Pseudomonas isolates.

Use of next generation sequencing analysis of in-vitro and ex-vivo resistant Pseudomonas isolates to determine genomic and transcriptomic basis for resistance. Comparison of resistance mechanisms to determine whether resistance generated in-vitro is representative of resistance occurring naturally within an industrial environment.

Evaluation of in-vitro resistance generation model capability as an investigative tool for preservative resistance development.


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Studentship Projects

Project Reference Relationship Related To Start End Student Name
BB/S506904/1 01/10/2018 30/09/2022
2105572 Studentship BB/S506904/1 01/10/2018 30/09/2022 Lewis Fisher