Combating Antibacterial Resistance through Novel Cationic Biocides Restricted; Files Only
Sanchez, Christian (Summer 2024)
Abstract
Cationic biocides serve as the first level of defense against human pathogens in the effort towards infection prevention and control. Through poor management and overuse, bacterial pathogens have begun to develop resistance mechanisms to overcome cationic disinfectant treatment. The investigations contained herein focus on the development and study of novel cationic biocides as they relate to bacterial pathogens. Through our efforts, we have built upon previous structure- activity relationships for quaternary ammonium compounds (QACs) and quaternary phosphonium compounds (QPCs) as amphiphilic disinfectants. In the evaluation of nearly 200 novel cationic biocides, we have uncovered potent scaffolds that inhibit growth in gram-positive and gram- negative species. Narrowing in on a QPC from a previous campaign, P6P-10,10 displays a high degree of potency against cationic biocide resistant clinical isolates of Acinetobacter baumannii surpassing the efficacy of commercial and previously reported, experimental QACs. Similar studies in Pseudomonas aeruginosa revealed a similar efficacy. Mechanistic studies uncovered a distinct mode of action in P. aeruginosa and other gram-negative species, which is hypothesized to be based on specific structural features—namely the presence of delocalized lipophilic cations. Further investigations into whether the disinfectant mechanism of action affects the virulence phenotype of resistant strains revealed no substantial differences between the resistance phenotypes of commercial disinfectant benzalkonium chloride (BAC) and P6P-10,10. However, our results illustrate the significant consequences that cationic biocide resistance exerts on virulence-associated phenotypes of P. aeruginosa.
Table of Contents
Chapter 1 Introduction.............................................................................. 1
1.1 The Bacterial Problem ..................................................................................1
1.2 Addressing Bacterial Pathogens......................................................................1
1.2.1 Overview of Strategies..........................................................................2
1.2.2 Antibiotics.......................................................................................2
1.2.3 Vaccines.........................................................................................3
1.2.4 Disinfectants....................................................................................4
1.3 Conclusion.................................................................................................4
1.4 References.................................................................................................5
Chapter 2 Exploring Novel Classes of Cationic Biocides.................................... 10
2.1 Previous Research into Novel Classes of Cationic Biocides as Disinfectants...............10
2.2 Exploring Novel Classes of Cationic Biocides as Bacterial Disinfectants ..................16
2.2.1 BAC Derivatization Strategy...............................................................16
2.2.2 Atom Economic Alkyl Phosphonium Biocides ..........................................22
2.2.3 Rigidity Effects on Phosphorus Biocide Scaffolds.......................................30
2.2.4 “Soft” QPC Amphiphiles....................................................................34
2.2.5 Evaluation of Cationic Biocides against a Panel of Acinetobacter baumannii
Clinical Isolates...............................................................................42
2.3 Conclusion and Future Work........................................................................47
2.4 References.................................................................................................49
Chapter 3 Highly effective biocides against Pseudomonas aeruginosa reveal new mechanistic insights across gram-negative bacteria...........................58
3.1 Introduction to the problem.........................................................................58
3.2 Uncovering Novel Mechanistic Insights of Cationic Biocides.................................59
3.2.1 Pseudomonas aeruginosa clinical isolates are broadly cationic biocide resistant...59
3.2.2 Next-generation QPCs are effective against highly antibiotic resistant Pseudomonas aeruginosa strains............................................................62
3.2.3 The outer membrane of P. aeruginosa is not appreciably influenced by the presence of P6P-10,10.......................................................................62
3.2.4 P6P-10,10 selectively targets the inner membrane of P. aeruginosa..................64
3.2.5 Antagonism assays support an inner membrane-specific mechanism of action......65
3.2.6 Distinct mechanism of resistance to cationic biocides..................................66
3.2.7 SmvA is a major P6P-10,10 resistance determinant.....................................67
3.2.8 Cationic biocides possess distinct mechanism in gram-negative bacteria that are structurally predictable............................................................70
3.3 A Mechanistic Distinction in Cationic Biocides Revealed......................................71
3.3.1 Discussion.......................................................................................71
3.4 Conclusion................................................................................................74
3.5 References................................................................................................75
Chapter 4 Investigating the influence of cationic biocides on virulence and pathogenicity in Pseudomonas aeruginosa.......................................82
4.1 Cationic Biocide Resistance Phenotype and Introduction.....................................82
4.1.1 Overview of virulence and pathogenicity...................................................82
4.1.2 Disinfectants and Virulence-Associated Phenotypes......................................83
4.1.3 Aim of Present Investigation into Disinfectant Resistance...............................85
4.2 Cationic Biocides Resistance and its Effect on Defensive Strategies..........................86
4.2.1 Cationic Biocide Resistance in P. aeruginosa Influences Antibiotic Susceptibility..86
4.2.2 Cationic Biocide Resistance Increases Alginate Production in P. aeruginosa.........89
4.2.3 Quantification of biofilm in CB-resistant strains of P. aeruginosa.....................90
4.2.4 Pellicle Formation is Increased in the BAC-resistant but not in the P6P-10,10-Resistant Strain Derived from PAO1........................................................92
4.3 Cationic Biocide Resistance and its Effect on Offensive Strategies..........................93
4.3.1 BAC Adaptation Reduces Swimming Behavior in Clinical Isolates....................93
4.3.2 BAC Resistance Results in an Increase in Virulence-Associated Pigment Production .......................................................................................95
4.3.3 Lysis of S. aureus by Disinfectant-Resistant Pseudomonas aeruginosa PAO1........96
4.3.4 CB-Resistant Mutants Show Competitive Disadvantage Compared to the PAO1 Parental Strain................................................................................98
4.3.5 Evaluation of P. aeruginosa virulence in Galleria mellonella infection model.......99
4.4 Conclusion.............................................................................................100
4.5 References..............................................................................................101
5.0 Supporting Information.............................................................................110
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