Crossman, L. | bioRxiv Science

bioRxiv2025

Plasticity in a bacterial global regulatory switch that drives a shift in antibiotic resistance and virulence

Antibiotic resistance and expression of virulence factors can impact the outcome of infection by Pseudomonas aeruginosa. Pathogenesis is often modelled using the P. aeruginosa PAO1 reference strain but laboratory lineages vary in the sequence and activity of MexT, a global regulator impacting virulence, biofilm formation and ciprofloxacin resistance. We defined the impact of active versus inactive MexT in PAO1 and observed global transcriptomic changes affecting the expression of 900 genes. Phenotyping revealed altered metabolism, antibiotic resistance and virulence - resulting in striking variation across a single model organism. We propose that antibiotic-resistance, introduced during work with the original PAO1 strain, has caused plasticity in mexT that accounts for variation across lineages. To test this, we introduced antibiotic resistance into clinical P. aeruginosa isolates and observed downstream mutations in mexT when selective pressure was removed, supporting the proposed evolutionary pathway. Overall, we have demonstrated the transcriptomic basis of MexT as a phenotypic switch in PAO1 and implicated antibiotic resistance as a cause of downstream changes in mexT in P. aeruginosa. Furthermore, MexS/MexT-regulated efflux is implicated in the antibiotic stress response and virulence, helping identify the mechanisms for rapid phenotypic switching through mexT and confirming that PAO1 is a very different organism compared to most isolates. Improved understanding of the regulatory changes linked to antibiotic resistance is particularly relevant to P. aeruginosa where cycles of antibiotic treatment are common.

microbiology↗

bioRxiv2024

Sticking together: Independent evolution of biofilm formation in different species of staphylococci has occurred multiple times via different pathways

Various species of staphylococci cause a wide range of infections, including implant-associated infections which are often difficult to treat due to the presence of biofilms. Whilst some proteins involved in biofilm formation are known, the differences in biofilm production between staphylococcal species remains understudied. Currently biofilm formation by Staphylococcus aureus is better understood than for other members of the genus as more research effort has focused on this species. We assembled a panel of 385 non-aureus Staphylococcus isolates of 19 species from prosthetic joint infection as well as other clinical sources and reference strains. We assessed the biofilm forming ability of all strains using a high-throughput crystal violet assay. This identified distinct biofilm formation categories and we then compared the prevalence of Pfam domains and identified those which distinguished the categories as well as using machine learning to identify amino acid 20-mers linked to biofilm formation. This identified some domains within proteins already positively linked to biofilm formation but we also identified important domains not previously linked to biofilm formation. RT-qPCR confirmed the expression of selected genes predicted to encode important domains within biofilms in Staphylococcus epidermidis. The prevalence and distribution of biofilm associated domains showed a link to phylogeny, suggesting different Staphylococcus species have independently evolved different mechanisms of biofilm production. This work has identified different routes to biofilm formation in diverse species of Staphylococcus as well as suggesting independent evolution of biofilm has occurred multiple times across the genus. Understanding the mechanisms of biofilm formation in any given species is likely to require detailed study of relevant strains and the ability to generalise across the genus may be limited.

microbiology↗