Browsing by Author "Howlin, R. P."

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    Antimicrobial activity of the quinoline derivative HT61 against Staphylococcus aureus biofilms
    (American Society for Microbiology, 2020-03-02) Frapwell, C. J.; Skipp, P. J.; Howlin, R. P.; Angus, E. M.; Hu, Y.; Coates, A. R. M.; Allan, Raymond N.; Webb, J. S.
    Staphylococcus aureus biofilms are a significant problem in healthcare settings, in part, owing to the presence of a non-dividing, antibiotic tolerant sub-population. Here we evaluated treatment of S. aureus UAMS-1 biofilms with HT61, a quinoline derivative shown to be effective against non-dividing Staphylococcal spp. HT61 was effective in reducing biofilm viability, associated with increased expression of cell wall stress and division proteins, confirming its potential as a treatment for S. aureus biofilm infections.
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    Cephalosporin nitric oxide-donor prodrug DEA-C3D disperses biofilms formed by clinical cystic fibrosis isolates of Pseudomonas aeruginosa
    (Oxford University Press, 2019-09-17) Soren, O.; Rineh, A.; Silva, D. G.; Cai, Y.; Howlin, R. P.; Allan, Raymond N.; Feelisch, M.; Davies, J. C.; Connett, G. J.; Faust, S. N.; Kelso, M. J.; Webb, J. S.
    Objectives: The cephalosporin nitric oxide (NO)-donor prodrug DEA-C3D (DiEthylAmin-Cephalosporin-3’- Diazeniumdiolate) has been showed to initiate the dispersal of biofilms formed by Pseudomonas aeruginosa laboratory strain PAO1. In this study, we investigated whether DEA-C3D disperses biofilms formed by clinical cystic fibrosis isolates of P. aeruginosa and its effect in combination with two anti-pseudomonal antibiotics, tobramycin and colistin, in vitro. Methods: -lactamase-triggered release of NO from DEA-C3D was confirmed using a gas-phase chemiluminescence detector. MICs against P. aeruginosa clinical isolates were measured using the broth microdilution method. A crystal violet staining technique and confocal laser scanning microscopy were used to evaluate the effects of DEA-C3D on P. aeruginosa biofilms alone and in combination with tobramycin and colistin. Results: DEA-C3D was confirmed to selectively release NO in response to contact with bacterial -lactamase. Despite lacking direct, cephalosporin/-lactam-based antibacterial activity, DEA-C3D was able to disperse biofilms formed by three P. aeruginosa clinical isolates. Confocal microscopy revealed that DEA-C3D in combination with tobramycin produces similar reductions in biofilm to DEA-C3D alone, whereas the combination with colistin causes near complete eradication of P. aeruginosa biofilms in vitro. Conclusions: DEA-C3D is effective in dispersing biofilms formed by multiple clinical isolates of P. aeruginosa and could hold promise as a new adjunctive therapy to patients with CF.
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    D-methionine interferes with non-typeable Haemophilus influenzae peptidoglycan synthesis during growth and biofilm formation
    (Microbiology Society, 2017-07-12) Dawe, H.; Berger, E.; Sihlbom, C.; Angus, E. M.; Howlin, R. P.; Laver, J. R.; Tebruegge, M.; Hall-Stoodley, L.; Stoodley, P.; Faust, S. N.; Allan, Raymond N.
    Non-typeable Haemophilus influenzae (NTHi) is an opportunistic pathogen that plays a major role in a number of respiratory tract infections, including otitis media, cystic fibrosis and chronic obstructive pulmonary disease. Biofilm formation has been implicated in both NTHi colonization and disease, and is responsible for the increased tolerance of this pathogen towards antibiotic treatment. Targeting metabolic pathways that are important in NTHi biofilm formation represents a potential strategy to combat this antibiotic recalcitrance. A previous investigation demonstrated increased expression of a putative D-methionine uptake protein following exposure of NTHi biofilms to the ubiquitous signalling molecule, nitric oxide. We therefore hypothesized that treatment with exogenous D-methionine would impact on NTHi biofilm formation and increase antibiotic sensitivity. Treatment of NTHi during the process of biofilm formation resulted in a reduction in biofilm viability, increased biomass, changes in the overall biofilm architecture and the adoption of an amorphous cellular morphology. Quantitative proteomic analyses identified 124 proteins that were differentially expressed following D-methionine treatment, of which 51 (41 %) were involved in metabolic and transport processes. Nine proteins involved in peptidoglycan synthesis and cell division showed significantly increased expression. Furthermore, D-methionine treatment augmented the efficacy of azithromycin treatment and highlighted the potential of D-methionine as an adjunctive therapeutic approach for NTHi biofilm-associated infections.
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    Parallel evolution in Streptococcus pneumoniae biofilms
    (Oxford University Press, 2016-04-15) Churton, N. W. V.; Mirsa, R.; Howlin, R. P.; Allan, Raymond N.; Ghabria, S. E.; Edwards, R. J.; Clarke, S. C.; Webb, J. S.
    Streptococcus pneumoniae is a commensal human pathogen and the causative agent of various invasive and noninvasive diseases. Carriage of the pneumococcus in the nasopharynx is thought to bemediated by biofilm formation, an environment where isogenic populations frequently give rise to morphological colony variants, including small colony variant (SCV) phenotypes. We employed metabolic characterization and whole-genome sequencing of biofilm-derived S. pneumoniae serotype 22F pneumococcal SCVs to investigate diversification during biofilm formation. Phenotypic profiling revealed that SCVs exhibit reduced growth rates, reduced capsule expression, altered metabolic profiles, and increased biofilm formation compared to the ancestral strain. Whole-genome sequencing of 12 SCVs from independent biofilm experiments revealed that all SCVs studied had mutations within the DNA-directed RNA polymerase delta subunit (RpoE). Mutations included four large-scale deletions ranging from 51 to 264 bp, one insertion resulting in a coding frameshift, and seven nonsense single-nucleotide substitutions that result in a truncated gene product. This work links mutations in the rpoE gene to SCV formation and enhanced biofilm development in S. pneumoniae and therefore may have important implications for colonization, carriage, and persistence of the organism. Furthermore, recurrent mutation of the pneumococcal rpoE gene presents an unprecedented level of parallel evolution in pneumococcal biofilm development.
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    Targeting microbial biofilms: current and prospective therapeutic strategies
    (Macmillan Publishers Limited, 2017-09-25) Koo, H.; Allan, Raymond N.; Howlin, R. P.; Stoodley, P.; Hall-Stoodley, L.
    Biofilm formation is now recognized as a key virulence factor for a wide range of chronic microbial infections. While it has been well known for decades that bacteria and fungi in biofilms become highly tolerant of antibiotics, the development of effective therapeutics has lagged behind our growing understanding of biofilm biology. The multifactorial nature of biofilm development and drug tolerance imposes significant challenges to conventional antimicrobials, and indicates the need for multi-targeted or combinatorial therapies. In light of the discrepancy between the explosion of papers presenting multitude of methods to control biofilms and the sparsity of biofilm specific treatments available to the clinician, in this review, we focus on current therapeutic strategies and those in development for the treatment of biofilm infections, which target vital structure-function traits and drug tolerance mechanisms, including the extracellular matrix and dormant cells. We emphasize strategies that are supported by in vivo or ex vivo studies, highlight emerging anti-biofilm technologies, and provide a rationale for multi-targeted therapies aimed at disrupting the complex biofilm microenvironment.