Antimicrobial action of carvacrol at different stages of dual-species biofilm development by Staphylococcus aureus and Salmonella enterica serovar Typhimurium.

The effects of carvacrol, a natural biocide, on dual-species biofilms formed by Staphylococcus aureus and Salmonella enterica serovar Typhimurium were investigated with a constant-depth film fermentor. Biofilm development reached a quasi-steady state in 12 days at 25 degrees C with S. aureus predominance ( approximately 99%). Cryosectional analysis detected viable S. aureus and S. enterica serovar Typhimurium at depths of 320 and 180 mum from the film surface, respectively. Carvacrol pulses (1.0 mmol/h) inhibited S. aureus by 2.5 log CFU/biofilm during the early stages of film formation, ultimately causing a significant reduction (P < 0.001) of the staphylococcal population at quasi-steady state. Initial carvacrol pulsing elicited a 3 log CFU/biofilm reduction in viable S. enterica serovar Typhimurium, and additional periodic carvacrol pulses instigated significant inhibition of salmonellae (1 to 2 log CFU/biofilm) during biofilm development. Carvacrol pulsing reduced protein levels fivefold (P < 0.001) during initial biofilm development. Comparative studies with a peroxide-based commercial sanitizer (Spor-Klenz RTU) revealed that this commercial sanitizer was more biocidal than carvacrol during early biofilm development. When the biofilm reached quasi-steady state, however, periodic pulses with 1 mmol of carvacrol per h (P = 0.021) elicited a significantly higher inhibition than Spor-Klenz RTU (P = 0.772). Dual-species microcolonies formed under the influence of continuously fed low carvacrol concentrations (1.0 mmol/h) but failed to develop into a mature quasi-steady-state biofilm and did not reach any stage of film formation in the presence of high concentrations (5.0 mmol/h). These data show that carvacrol is an effective natural intervention to control dual-species biofilm formation.