Antibiotic Efficacy in Treating Variant Pseudomonas aeruginosa and Staphylococcus aureus Biofilms

Abstract

This study investigates antibiotic efficacy against planktonic vs biofilm bacteria in vitro, using eight different antibiotics: carbenicillin, ciprofloxacin, colistin, gentamicin, meropenem, rifampicin, tobramycin, and vancomycin. The main aim is to see which antibiotic can best clear the biofilm, which antibiotics correlate to the appearance of variant colonies, and which antibiotics can eradicate variant colonies. Biofilms are resilient toward chemical and physical challenges due to the secretion of extracellular polymeric substance and high cellular density. This makes biofilm infections difficult to treat. Some examples of biofilm infections are osteomyelitis and cystic fibrosis pneumonia most commonly caused by S. aureus and P. aeruginosa respectively. This study uses bioluminescent bacteria, S. aureus SAP231 and P. aeruginosa Xen41 as the test subjects for antibiotic efficacy. There are four major components to this study: first, the minimum inhibitory concentration of planktonic cells against antibiotics were found. Second, the antibiotic delivery mechanism was tested to see if mode of antibiotic delivery has an effect on biofilm clearance. Third, antibiotics and combinations of antibiotics are tested against biofilms. Lastly, the variant colonies are quantified to see which antibiotics correlate to variant colony formation. The results show that biofilm infections are more difficult to treat than planktonic bacteria, and the use of multi-combinatory antibiotics are effective at treating biofilm. A combination of antibiotic with vancomycin was very effective in reducing biofilm and variant colonies in S. aureus. A combination of antibiotic with ciprofloxacin was very effective in reducing biofilm and variant colonies in P. aeruginosa.