Mechanisms of Antibacterial Activity for Polymyxins

Transcription

1 Mechanisms of Antibacterial Activity for Polymyxins Brian T. Tsuji, Pharm.D. Assistant Professor of Pharmacy School of Pharmacy and Pharmaceutical Sciences University at Buffalo, State University of New York Laboratory for Antimicrobial Pharmacodynamics Mechanisms of Action Important in Polymyxins Self Promoted Uptake Theory Pictures of Mechanism of Action Impact of Inoculum Two component regulatory system Cell density dependent regulation Gooderham WJ and Hancock REW FEMS microbiology reviews. ;() 1

2 A) Neutralization Polymyxin s (Positively charged) cationic peptides interact with surface of the outer membrane (Negatively charged) to either neutralize and competetively displace Calcium and magnesium. Creates Cracks. B) Or Binding to LPS Or Direct Binding to the divalent cation binding sites on LPS to cause membrane disruption.

3 C) Binding to Cytoplasmic Membrane Once across, polymxyin binds to the negatively charged surface (CM) created by phospholipd headgroups and insert itself into the membrane. Changes form. D) Micelle Formation Insertion into the membrane interface and are proposed to then either aggregate into a micelle like complex which spans the membrane.

4 E) Or Flip Flop across the membrane under the influence of the large transmembrane electrical potential gradient F) Channels & Leakage: Micelles form channels for the movement of ions across the membrane and leakage of larger water soluble molecules. Increase in cell permeability.

5 Polymyxin Mechanism of Action P. aeruginosa ot t w ob ith e ou co t t pi he ed pe an rm d is dis si tr on ib of ute th d t e o au ot th he or rs A) Untreated B) Polymxyin B Low mg/l cracks and streaming content C) Colistin. Projections D) Polymyxin B High Projection derived from outer layer of cell wall Numerous projections appear. Bacterial cytoplasmic membrane to be damaged Cytoplasmic material released in fibrous forms through cracks Koike M, Iida K, Natsui. J. Bacteriology. 1. Pictures of the Inner & Outer Leaflet of the Outer Membrane N Untreated Salmonella typhimurium Concave closely packed cells, smooth shallow groves Treated S. typhimurium with Colistin Pit like depressions Small, cone like elevations projections Lounatmaa K, and Nanninga N. J. Bacteriology. 1.

6 Atomic Force Microscopy A. baumannii (S) Mid Log Phase & Stationary after minutes treatment SHAPE MORPHOLOGY SURFACE ROUGHNESS Soon et. al. AAC.. Maintenance shape small pits and indentations across bacterial surface No Change (. ±. nm) Vs. (. ±1. nm) Loss of shape numerous grooves and incisions presence of debris surrounding some cells Increase (1. ±. nm) Vs. (. ±1. nm) Smooth topography Clumping Mechanims of Polymyxin Action Production of fibrous structures and the possible induction of lytic bacteriophage are indicators of cellular stress Compromised cell membrane integrity with some cells completely lysed in the presence of colistin at 1 mg/l Boinett CJ, Cain AK, Ellington MJ et. al. 1 st International Conference 1 on Polymyxins. 1

7 Polymyxin s Exhibit Rapid Bactericidal Activity: How are bacterial cells finally killed? Log CFU/mL Time (h) Control Regimen 1 Regimen Regimen Regimen Extremely rapid bactericidal activity, difficult to quantify Complete Killing Process is unknown Killing process is not dependant of bacterial metabolic activity Li J, Rayner CR, Nation RL et. al. AAC.. Additional Mechanisms Important in Polymyxin Killing in P. aeruginosa Impact of Inoculum Two component regulatory system Regulation antibiotics tolerance in response to external environment stimuli Cell density dependent regulation Cell to cell communication which known as quorum sensing system Bacteria sensing their own population via a diffusible signal molecule Gooderham WJ and Hancock REW FEMS microbiology reviews. ;()

8 Log CFU ml -1 Log CFU ml -1 Impact of Initial Inocula on Colistin Killing Sensor Kinases Time (h) Growth Cntrl.1xMIC.xMIC.xMIC 1 1 Growth Cntrl.XMIC 1XMIC XMIC XMIC XMIC 1XMIC XMIC XMIC 1 1 Time (h) Two-Component Regulatory System: PhoPQ and PmrAB Bulitta JB et. al. AAC. Response Regulators Response Addition of aminoarabinose to lipid A of lipopolysaccharide (LPS) involved in colistin resistance Gooderham WJ and Hancock REW FEMS microbiology reviews. ;:

9 Colistin against P. aeruginosa Isogenic strains: Low inoculum Log (CFU/mL) Wild Type 1 1 pmra mutant 1 1 Ly NS et al. Antimicrob Agents Chemother 1 April. Log (CFU/mL) 1 1 phop mutant 1 1 Time (h) Colistin Growth Control. mg/l. mg/l 1. mg/l. mg/l. mg/l. mg/l 1 mg/l PA1 and Mutants from Drs. McPhee, Bains and Hancock Colistin against P. aeruginosa Isogenic strains: High Inoculum Wild Type 1 1 pmra mutant Time (h) phop mutant 1 1 Colistin GC. mg/l. mg/l 1. mg/l. mg/l. mg/l. mg/l 1 mg/l mg/l mg/l 1 mg/l mg/l Ly NS et al. Antimicrob Agents Chemother 1 April. PA1 and Mutants from Drs. McPhee, Bains and Hancock

10 Quorum Sensing: Cell to cell Communication Antibiotic tolerance has been hypothesized to result from the QS regulatory system, at high inocula Allow bacteria to act as a community rather as individual bacteria and to release virulence factors at specific cell density There are three quorum sensing signaling systems in P. aeruginosa Las system rhl system -oxo-c 1 -HSL C -HSL -heptyl--hydroxy--quinolone Control of biofilm infections by signal manipulation, Springer, New York, Pearson et al. Infect Immun., :1- Rumbaugh et al. Infect Immun. 1, :- Acknowledgements Pseudomonas quinolone system US Australia Alan Forrest Roger L. Nation Neang Ly Jian Li Gauri Rao Juergen Bulitta Samira Garonzik Cornelia Landersdorfer Jenny C. Yang John Boyce Patty N. Holden Hongmei Xu Mark Sutton Robert Hancock Peter E. Greenberg Funding: NIAID/NIH: R1AI to RL Nation SUNY Interdisciplinary Award AFPE Fellowship to NSL

11 Thank you for your attention 1 11