Results and discussion - Essay Example

A biofilm structure hinders antibiotic entry to cells, and at the same time, increases oxidative damage, which increases the mutation rate. To show that mutation frequency in response to the antibiotics mupirocin and rifampicin is due to oxidative stress in planktonic and biofilm cultures, Staphylococcal aureus strains SH 1000 and UAMS-1 were grown in media supplemented with hydrogen peroxide and antioxidants. Planktonic cultures that were supplemented with antioxidants did not differ in their mutation frequency.

However, the addition of hydrogen peroxide to the growth media significantly increased mutation frequencies under antibiotic selection. The mutation frequencies declined significantly with the addition of antioxidants, together with hydrogen peroxide, to the culture media significantly. Biofilm cultures, that were not treated with oxidising agent, showed high levels of mutation frequencies, equal to that obtained for planktonic culture in hydrogen peroxide alone. In cultures growing in rifampicin selection plates, the bacterial have mutation frequency of 10-5, which was indicative of a mutator phenotype.

The increase in mutation frequency indicates defects in the methyl-mismatch repair system during biofilm formation. Similar to planktonic cultures, the addition of antioxidants to the culture media reduced the mutation frequency to levels between 10-7 and 10-8. A bacterial biofilm is a structured community of bacterial cells enclosed within a self-produced extracellular polymeric matrix attached to surface (Costerton, Stewart & Greenberg 1999). Bacterial biofilms are present mostly on wet surfaces and are mostly visible to the naked eye.

The biofilms consist of microcolonies on a surface and develop into organized communities with functional heterogeneity. Different bacterial species specifically attach to different surfaces and could aggregate with other species or a combination of species. The organization and structure of