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


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.


CONCLUSIONS
The establishment of sub-MICs of antibiotics in clinical situations may result in altered virulence states in pathogenic bacteria.
School of Contemporary Sciences, University of Abertay Dundee, Dundee, UK.
R N S
RN
Haddadin
S
S
Saleh
I S I
IS
Al-Adham
T E J
TE
Buultjens
P J
PJ
Collier
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D018441:Biofilms / Q000187:drug effects; D002478:Cells, Cultured; D005260:Female; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D051379:Mice; D008826:Microbial Sensitivity Tests; D013203:Staphylococcal Infections / Q000382:microbiology; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000378:metabolism / Q000472:pathogenicity / Q000502:physiology*; D014774:Virulence / Q000187:drug effects; D037521:Virulence Factors / Q000378:metabolism*
D000900:Anti-Bacterial Agents; D037521:Virulence Factors