In vitro activity of vancomycin, quinupristin/dalfopristin, and linezolid against intact and disrupted biofilms of staphylococci.
Shed cells or disrupted parts of the biofilm may enter the circulation causing serious and very hard to treat biofilm-associated infections. The activity of antimicrobial agents against the shed cells/disrupted biofilms is largely unknown.


METHODS
We studied the in vitro susceptibility of intact and disrupted biofilms of thirty clinical isolates of methicillin-resistant and methicillin-susceptible Staphylococcus aureus (MRSA and MSSA) and Staphylococcus epidermidis to vancomycin, quinupristin/dalfopristin, and linezolid and compared it to that of the suspended (planktonic) cells.


RESULTS
Bacteria in the disrupted biofilms were as resistant as those in the intact biofilms at the minimum inhibitory concentrations of the antibiotics. At higher concentrations, bacteria in the disrupted biofilms were significantly (P < 0.001) less resistant than those in the intact biofilms but more resistant than the planktonic cells. Quinupristin/dalfopristin showed the best activity against cells of the disrupted biofilms at concentrations above MICs and vancomycin, at 500 and 1,000 microg/ml, was significantly more active against the biofilms of MRSA and S. epidermidis


CONCLUSIONS
The difficulty of treating biofilm-associated infections may be attributed not only to the difficulty of eradicating the biofilm focus but also to the lack of susceptibility of cells disrupted from the biofilm to antimicrobial agents.
El-Azizi
Mohamed
M
Division of Infectious Diseases, Southern Illinois University School of Medicine, Springfield, IL 62794, USA. mel-azizi@siumed.edu <mel-azizi@siumed.edu>
Rao
Suma
S
Kanchanapoom
Termkiat
T
Khardori
Nancy
N
D000081:Acetamides; D018441:Biofilms / Q000187:drug effects*; D006801:Humans; D000069349:Linezolid; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests; D023303:Oxazolidinones; D013210:Staphylococcus / Q000187:drug effects*; D013211:Staphylococcus aureus / Q000187:drug effects; D013212:Staphylococcus epidermidis / Q000187:drug effects; D014640:Vancomycin / Q000494:pharmacology*; D014769:Virginiamycin / Q000494:pharmacology*
D000081:Acetamides; D023303:Oxazolidinones; D014769:Virginiamycin; C062940:quinupristin-dalfopristin; D014640:Vancomycin; D000069349:Linezolid