Efficacy of oregano and rosemary essential oils to affect morphology and membrane functions of non‐cultivable sessile cells of Salmonella Enteritidis 86 in biofilms formed on stainless steel

AIMS: This study evaluated the efficacy of essential oil from Origanum vulgare L. (oregano; OVEO) and Rosmarinus officinalis L. (rosemary; ROEO) to inactivate sessile cells of Salmonella enterica serovar Enteritidis 86 (SE86) in young and mature biofilms formed on stainless steel. METHODS AND RESULTS: Ultrastructural alterations and damage in different physiological functions caused by OVEO and ROEO in noncultivable sessile cells of SE86 were investigated using scanning electron microscopy and flow cytometry. OVEO (2.5 mul ml(-1) ) and ROEO (40 mul ml(-1) ) were effective to eradicate young and mature biofilms formed by SE86 sessile cells on stainless steel surfaces; however, the efficacy varied with exposure time. OVEO and ROEO caused alterations in morphology of SE86 sessile cells, inducing the occurrence of bubbles or spots on cell surface. OVEO and ROEO compromised membrane polarization, permeability and efflux activity in noncultivable SE86 sessile cells. These findings show that OVEO and ROEO act by a multitarget mechanism on SE86 membrane functions. CONCLUSIONS: ROEO and OVEO showed efficacy to eradicate SE86 sessile cells in preformed biofilms on stainless steel, displaying a time-dependent effect and multitarget action mode on bacterial cell membrane. SIGNIFICANCE AND IMPACT OF THE STUDY: The study provides for the first time the effects of OVEO and ROEO on morphology and physiological functions of noncultivable sessile cells of S. Enteritidis biofilms preformed on stainless steel surfaces.