The effect of subminimal inhibitory concentrations of antibiotics on virulence factors expressed by Staphylococcus aureus biofilms

R. N. S. Haddadin, S. Saleh, I. S. I. Al-Adham, T. E. J. Buultjens, Phillip J. Collier

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Aims: The effect of subminimal inhibitory concentrations (sub-MICs) of cefalexin, ciprofloxacin and roxithromycin was investigated on some virulence factors [e.g. coagulase, Toxic Shock Syndrome Toxin 1 (TSST-1) and biofilm formation] expressed by Staphylococcus aureus biofilms. Methods and Results: Biofilms were grown with and without the presence of 1 ⁄ 16 MIC of antibiotics on Sorbarod filters. Eluate supernatants were collected, and coagulase and TSST-1 production were evaluated. Coagulase production was reduced in eluates exposed to roxithromycin when compared to control, while TSST-1 production was reduced in biofilms exposed to cefalexin and to a lesser extent, ciprofloxacin. In addition, the ability of Staph. aureus to produce biofilm in microtitre plates in the presence of sub-MIC antibiotics indicated that cefalexin induced biofilm formation at a wide range of sub- MICs. TSST-1 produced from the challenged and control biofilms was purified, and its proliferative activity was studied on single cell suspension of mouse splenocytes using MTS⁄PMS assay. No significant difference in the activity between the treated toxin and the control has been observed. Conclusions: Antibiotics at sub-MIC levels interfere with bacterial biofilm virulence expression depending on the type and concentration of antibiotic used. Significance and Impact of the Study: The establishment of sub-MICs of antibiotics in clinical situations may result in altered virulence states in pathogenic bacteria.
Original languageEnglish
Pages (from-to)1281-1291
Number of pages11
JournalJournal of Applied Microbiology
Issue number4
Publication statusPublished - Apr 2010


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