Effects of ampicillin and vancomycin on Staphylococcus aureus biofilms

Abstract

The collection of 23 coagulase-positive Staphylococcus aureus strains isolated mainly from food in the Czech Republic were tested on the ability to form biofilms in the presence of ampicillin and vancomycin. The antimicrobial sensitivity (16 antibiotics) was determined in all strains by the standard disc diffusion method on Mueller-Hinton agar plates (NCCLS). The resistance to ampicillin was found in 16 strains (69.5%), all strains being susceptible to vancomycin. The formation of biofilm was conducted in 96-well, polystyrene microtiter plates COSTAR 3797 in tryptic soy broth (TSB) with 1% of glucose for 24 h at 30°C. Staining with crystal violet (0.1%) was used for biofilm quantification. Ampicillin (0.5, 2, and 4 mg/l) and vancomycin (32, 64 and 128 mg/l) were added: (i) direct addition of the agent to the well at zero time, (ii) after 24 h to washed well, (iii) after 24 h directly to well with the cell suspension. The tested types of ampicillin treatment did not confirm the impact of resistance on the biofilm production among the strains tested. The addition of vancomycin at zero time of cultivation effectively suppressed the biofilm production. Other types of treatment showed unequal strain dependent response. Planktonic cells demonstrated a higher sensitivity to antibiotics than the biofilm forming cells.