Mechanisms of Antibiotic Evasion in Pseudomonas aeruginosa by Biofilm Formation and the Use of Phage Therapy to Combat Infection
Vinayika Papineni
Introduction. Antibiotic resistance is a major issue that leads to 35,000 deaths annually in the US.1 Pseudomonas aeruginosa is an opportunistic pathogen which evades antibiotics through the formation of a biofilm. A biofilm is composed of bacterial cells that adhere to each other in a matrix of extracellular polymeric substance (EPS).1,2 The EPS poses a diffusion barrier for antibiotics impeding their capacity to kill rapidly dividing bacteria.2,3 Persister cells within the biofilm are not metabolically active, and thus, are not affected by antibiotics.1 Cystic fibrosis (CF) patients harbor a high number of persister cells in their lungs contributing to chronic infections.1 A novel antimicrobial therapy is the use of bacteriophages, which are viruses that inject their DNA into bacteria, create proteins, assemble new phages, and lyse the bacteria.2 Phages have EPS degrading enzymes such as lysins, depolymerases, and quorum quenching lactonase that disrupt biofilms rendering them effective against biofilm associated cells.1,3 However, bacteria can develop resistance to single phages via mutations prompting the study of combinations of antibiotics and phages or phage cocktails.4 Methods. Chang et al. combined bacteriophage therapy and ciprofloxacin at various minimum inhibitory concentrations (MICs) and compared the biofilm viability and killing of P. aeruginosa.5 Forti et al. compared the biofilm viability when treated with a single phage versus a phage cocktail.6 Waters an colleagues intranasally infected mice with P. aeruginosa strains and compared phage cocktail treatments given at various time points.7 Cafora and colleagues focused on inducing a CFTR-loss of function in zebrafish, then infected them with P. aeruginosa strains, and compared combination treatments of phage therapy and ciprofloxacin.8 A clinical trial is currently studying bacteriophage therapy in adult CF patients in which the treatment group receives nebulized phage therapy for 7 days compared to the control group with placebo. Sputum bacterial culture, lung function, and quality of life will be measured.10 Results. When single phage therapy was utilized, there was an initial reduction in biofilm viability.4 However due to bacterial mutations against bacteriophages, the biofilm expanded over time.4 Usage of phage cocktails increase the efficiency at killing the host, reducing biofilm viability, and preventing the emergence of phage resistant mutants. 4,5,6,8 Bacteriophage are synergistic with antibiotics, because phages break down the biofilm EPS exposing the bacteria to higher concentrations of antibiotics.6,7,8 Conclusion. These studies showcase how phage therapy, when used in cocktails and as adjuncts with antibiotics, effectively kill drug resistant P.aeruginosa.
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- Principi N, Silvestri E, Esposito S. Advantages and Limitations of Bacteriophages for the Treatment of Bacterial Infections. Front Pharmacol. 2019;10:513. Published 2019 May 8. doi:10.3389/fphar.2019.00513
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- Yang Y, Shen W, Zhong Q, et al. Development of a Bacteriophage Cocktail to Constrain the Emergence of Phage- Resistant Pseudomonas aeruginosa. Front Microbiol. 2020; 11:327. Published 2020 Mar 4. doi:10.3389/fmicb.2020.00327
- Chang RYK, Das T, Manos J, Kutter E, Morales S, Chan HK. Bacteriophage PEV20 and Ciprofloxacin Combination Treatment Enhances Removal of Pseudomonas aeruginosa Biofilm Isolated from Cystic Fibrosis and Wound Patients. AAPS J. 2019;21(3):49. Published 2019 Apr 4. doi:10.1208/s12248-019-0315-0
- Forti F, Roach DR, Cafora M, et al. Design of a Broad-Range Bacteriophage Cocktail That Reduces Pseudomonas Aeruginosa Biofilms and Treats Acute Infections in Two Animal Models. Antimicrob Agents Chemother. 2018;62(6):e02573-17. Published 2018 May 25. doi:10.1128/AAC.02573-17
- Waters EM, Neill DR, Kaman B, et al. Phage therapy is highly effective against chronic lung infections with Pseudomonas aeruginosa. Thorax. 2017;72(7):666-667. doi:10.1136/thoraxjnl-2016-209265
- Cafora, M., Deflorian, G., Forti, F. et al. Phage therapy against Pseudomonas aeruginosa infections in a cystic fibrosis zebrafish model. Sci Rep 9, 1527 (2019).
- Law, N., Logan, C., Yung, G. et al. Successful adjunctive use of bacteriophage therapy for treatment of multidrug- resistant Pseudomonas aeruginosa infection in a cystic fibrosis patient. Infection 47, 665–668 (2019). https://clinicaltrials.gov/ct2/show/NCT04684641