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.
Haddadin, R. N. S., Saleh, S., Al-Adham, I. S. I., Buultjens, T. E. J., & Collier, P. J. (2010). The effect of subminimal inhibitory concentrations of antibiotics on virulence factors expressed by Staphylococcus aureus biofilms. Journal of Applied Microbiology, 108(4), 1281-1291. https://doi.org/10.1111/j.1365-2672.2009.04529.x