Efeito antilisterial de compostos majoritários de óleos essenciais contra células planctônicas e sésseis

Abstract

Microbial biofilms represent a major problem for the food industry, and their disposal has been the subject of several studies. The use of essential oils and their major compounds has shown to be effective in removing biofilms of several species, such as Listeria monocytogenes (LM). However, little is known about the effect of sublethal concentrations of these compounds in bacterial cells. The first stage of this research was conducted with the objective of evaluating the antilisterial activity of citral (CIT) essential oils’ constituents, thymol, cinnamaldehyde (CIN), eugenol, α-terpineol, carvacrol and terpinen-4-ol against planktonic cells of ATCC 19117, 7644 and 15313 strains. Minimum Inhibitory Concentrations (MICs) were determined by broth microdilution, subsequently determining the Bactericidal Minimum Concentrations (BMCS). All constituents show antibacterial activity. Citral and cinnamaldehyde solutions, constituents which showed the lowest BMCS, were tested against biofilms formed on # AISI 304 stainless steel. The CMBBs values ranged from 0.42 to 1.2% (v/v). Citral and cinnamaldehyde also showed antibacterial effect against sessile cells, and may be new alternatives for sanitizer development. The second stage of this research aimed at evaluating the effect of the exposure of the LM biofilm during its formation, to sublethal concentrations of CIN and CIT. The biofilms were formed on a AISI 304 stainless steel, in contact with tryptone soy broth supplemented with 0.6 % (w /v) of yeast extract (TSB-YE) and incubated at 37 °C, treated every 48 hours with solutions containing sublethal concentrations (1/3 of lethal concentration) of CIN and CIT for 15 minutes, in addition to a control solution (without antibiotics). We developed three types of biofilm for each strain: BC (control biofilm), BECIN (biofilm exposed to sublethal concentrations of cinnamaldehyde during its formation) and BECIT (biofilm exposed to sublethal concentrations of citral biofilm during its formation). After 240 hours, the number of viable cells was determined immediately after treatment with the solutions, and the log reduction was calculated. With the number of sessile cells after 240 hours, we verified that the exposure to sublethal concentrations of ash and CIT affect biofilm formation. Exposure to sublethal concentrations of CIN and CIT affected biofilm formation. The exposure to sublethal concentrations of CIN and CIT affected the LM biofilm, and may cause it to be more resistant to these compounds as well as more sensitive, of cross- way or not, with the occurrence of these effects dependent on the strain and the compound used.