Interplay of antibiotics and bacterial inoculum on suture-associated biofilms.
BACKGROUND
Biofilms are often antibiotic resistant, and it is unclear if prophylactic antibiotics can effectively prevent biofilm formation. Experiments were designed to test the ability of high (bactericidal) concentrations of ampicillin (AMP), vancomycin (VAN), and oxacillin (OXA) to prevent formation of suture-associated biofilms initiated with low (10(4)) and high (10(7)) numbers of Staphylococcus aureus.


METHODS
S. aureus biofilms were cultivated overnight on silk suture incubated in biofilm growth medium supplemented with bactericidal concentrations of AMP, VAN, or OXA. Standard microbiological methods were used to quantify total numbers of viable suture-associated S. aureus. Crystal violet staining followed by spectroscopy was used to quantify biofilm biomass, which includes bacterial cells plus matrix components. To observe the effects of antibiotics on the microscopic appearance of biofilm formation, biofilms were cultivated on glass slides, then stained with fluorescent dyes, and observed by confocal microscopy.


RESULTS
In the presence of a relatively low inoculum (10(4)) of S. aureus cells, bactericidal concentrations of AMP, VAN, or OXA were effective in preventing development of suture-associated biofilms. However, similar concentrations of these antibiotics were typically ineffective in preventing biofilm development on sutures inoculated with 10(7)S. aureus, a concentration relevant to contaminated skin. Confocal microscopy confirmed that bactericidal concentrations of AMP, VAN, or OXA inhibited, but did not prevent, development of S. aureus biofilms.


CONCLUSIONS
Bactericidal concentrations of AMP, VAN, or OXA inhibited formation of suture-associated biofilms initiated with low numbers (10(4)), but not high numbers (10(7)), of S. aureus cells.
Department of Surgery, University of Minnesota, Minneapolis, USA. hessx006@tc.umn.edu
Donavon J
DJ
Hess
Michelle J
MJ
Henry-Stanley
Carol L
CL
Wells
D000667:Ampicillin / Q000494:pharmacology / Q000627:therapeutic use; D000900:Anti-Bacterial Agents / Q000494:pharmacology / Q000627:therapeutic use*; D018441:Biofilms / Q000187:drug effects*; D008826:Microbial Sensitivity Tests; D018613:Microscopy, Confocal; D010068:Oxacillin / Q000494:pharmacology / Q000627:therapeutic use; D013203:Staphylococcal Infections / Q000517:prevention & control*; D013211:Staphylococcus aureus / Q000187:drug effects*; D013530:Surgical Wound Infection / Q000517:prevention & control*; D013537:Sutures / Q000382:microbiology*; D014640:Vancomycin / Q000494:pharmacology / Q000627:therapeutic use
D000900:Anti-Bacterial Agents; D014640:Vancomycin; D000667:Ampicillin; D010068:Oxacillin