Different Compositions of Biofilm Extracellular Polymeric Substance Reveals Contrasting Antibiotic Resistance Profiles in Pseudomonas aeruginosa

Abstract

Pseudomonas aeruginosa biofilms are more resistant to antibiotics than their planktonic counterparts. Current antibiotics used for therapy to treat P. aeruginosa infections are ciprofloxacin and gentamicin, both of which are bactericidal; however, cystic fibrosis patients often become infected by extremely resistant strains that overproduce alginate in the extracellular polymeric substances. It has been shown that strains producing different levels of alginate display different carbohydrate profiles, such as upregulated glucose and galactose. To determine if these varying carbohydrate profiles contribute to different levels of antibiotic resistance, three strains were obtained producing different amounts of alginate: wild-type producing a normal amount of alginate, algA producing no alginate, and mucA overproducing alginate. The strains were grown for 5 days to obtain mature biofilms which were then homogenized and incubated with gentamicin or ciprofloxacin and compared to a control. The percent survival for ciprofloxacin in all strains was less than 1%. The gentamicin treated mucA and wild-type strains showed no significant difference at 27% and 31% survivability, respectively. However, the gentamicin treated algA strain showed 75% survival, suggesting that the carbohydrate composition of this strain leads to increased resistance to gentamicin, but not to ciprofloxacin. Further studies may be needed to determine which carbohydrates are responsible for conferring increased resistance to gentamicin.