Accurate Methods For In Vitro Antimicrobial Susceptibility Testing Of Bacterial Pathogens
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Respiratory infections caused by the opportunistic bacterial pathogen Pseudomonas aeruginosa are a common cause of mortality in patients with cystic fibrosis (CF). These infections are difficult to eradicate with conventional antibiotic treatment as P. aeruginosa is often innately resistant to many antibiotics. In clinical practice, diagnostic labs test P. aeruginosa strains in vitro (outside of a living organism) in order to determine an appropriate antibiotic to prescribe to each patient. However, these test results can be misleading because antibiotic resistance is highly dependent on the chemical environment in which the bacteria grow. Therefore, it is essential that in vitro models used to assess antibiotic resistance resemble in vivo growth conditions as closely as possible. In this thesis, I compared the antibiotic resistance of P. aeruginosa in two growth conditions: within a complex media commonly used in diagnostic labs, and a chemically defined synthetic sputum media (SCFM2) constructed to closely mimic the lung fluid of cystic fibrosis patients. I tested P. aeruginosa in both media, using three clinically relevant antibiotics (tobramycin, gentamicin, and polymyxin B), and found that the bacteria produce significantly different antimicrobial susceptibility profiles depending on the media in which they are cultured. Ultimately, the data presented here have the potential to help guide diagnostic labs to create more accurate in vitro models to predict more effective treatments for individual patients.