A Comparative Study of the In Vitro Activities of Various Antibacterial Drugs Alone and in Combination with Voriconazole (VCZ) against monomicrobial (MM) and polymicrobial (PM) biofilms of Staphylococcus aureus (SA) and Aspergillus fumigatus (AF)

J. A. Vazquez, D. L. Vager, E. K. Manavathu

Author address: 

Henry Ford Hosp., Detroit, MI.



SA and AF are frequently isolated from the respiratory tracts of cystic fibrosis (CF) patients with prevalence as high as 58% and 60%, respectively. PM infections of the respiratory tracts of CF patients with these microorganisms are associated with biofilms. The biofilm-bound cells and thus the infections are less susceptible to conventional antimicrobial therapy. To study the efficacy of antimicrobials alone or in combination against these biofilms, we developed an in vitro model and examined the effect of several antimicrobials alone and in combinations with VCZ against MM &PM biofilms of SA & AF.


MM & PM biofilms of SA and AF were developed in 24-well Costar tissue culture plates in Sabouraud’s dextrose broth at 35 °C. The activity of different concentrations (0-64 µg/ml) of ciprofloxacin (CIP), cephalexin (CEP), linezolid (LIN) and vancomycin (VAN) alone, and in combination with VCZ on MM & PM biofilms were examined by colony forming units (CFUs) assay after a 24-hr drug exposure.


VCZ alone and in combination with several antibacterial drugs provided a 1 to 1.5 log reduction of AF CFUs in both MM & PM biofilms indicating that both biofilm-embedded cells are equally susceptible. The addition of antibacterial drug to VCZ did not affect its activity against AF. All antibacterial drugs examined showed similar activity against MM & PM biofilms in a drug concentration dependent manner reducing the SA CFU from 2 - 3 logs at 64 µg/ml. However, the PM biofilm-bound SA CFUs were significantly lower than those of the MM biofilm-bound. Addition of VCZ to antibacterial drug produced no reduction of their activities.


Antibacterial drugs such as CIP, CEP, LIN and VAN were equally effective alone and in combination with VCZ against SA in MM & PM biofilms. Likewise, VCZ was equally effective against AF in MM & PM biofilms with and without the antibacterial drug.


abstract No: 


Full conference title: 

111th General Meeting American Society for Microbiology
    • ASM 111th (2011)