Atividade antibacteriana de extrato de butiá (Butia odorata Barb. Rodr.): mecanismo de ação, aplicação em sistema alimentar e em biofilme bacteriano

Abstract

Foodborne bacteria constitute a danger to human health. As a result, interest in new antimicrobials is increasing. The aim of this study was to evaluate the antibacterial activity of Butia odorata extract (BOE) against selected foodborne pathogens, characterize it chemically, investigate the mechanism of the action in Staphylococcus aureus and Escherichia coli, used as Gram-positive and Gram-negative bacterial models, as well as apply the BOE in sliced mozzarella cheese contaminated experimentally with E. coli and study the effect of BOE on S. aureus cells in biofilm. According to agar disc diffusion test all bacterial strains tested, both Gram-positive and Gram-negative bacteria (Listeria monocytogenes, S. aureus, E. coli O157:H7 and Salmonella Typhimurium) are susceptible to the BOE (inhibition zone of 30±2.0 mm, 22±0.8 mm, 16±3.9 mm and 15±3.2 mm, respectively). The minimum inhibitory concentration (MIC) varied of 4 to 8 mg.mL-1 and minimum bactericidal concentration (MBC) of 16 to 33 mg.mL-1. Regarding to chemical characterize, the major compounds present in the extract were Z-10-Pentadecenol (80.1 %) and Palmitic acid (19.4 %). In relation to the mechanism of action, BOE caused cell membrane damage, which can be viewed in scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM), resulting in release of DNA to the extracellular environment. The fluorescence spectrophotometry analysis showed that BOE caused S. aureus and E. coli DNA damage. In cheese contaminated experimentally with E. coli isolate, there was significant difference (p<0.05) between control (2.8 log CFU.cm-2) and treated samples with MIC, 2 x MIC, 4 x MIC and 8 x MIC (1.3, 1.4, 1.6 and 0.5 log CFU.cm-2, respectively). Regarding the effect of EBO on S. aureus isolate cells in biofilm, when 4 x MIC was used, there was a significant difference (p<0.05) between control and treated samples at all evaluated times (15, 30 and 60 min), and at 30 and 60 min there was a reduction of 99.9% in the number of biofilm cells. At 60 min of contact and addition of 2 x MIC there was a decrease of 4.21 log CFU.cm-2 (99.99%) in relation to the control, and with addition of MIC value the difference was 1.1 log CFU.cm-2. BOE showed antibacterial activity against foodborne microorganisms, having potential to be used as alternative to synthetic preservatives. In addition, this study demonstrated that the mechanism of action of BOE against S. aureus and E. coli, used as models of Gram-positive and Gram-negative bacteria, occurs by dual mechanism, causing damage in the bacterial membrane and in the genomic DNA. BOE, consisting mainly of Z-10- Pentadecenol and Palmitic acid, showed antibacterial activity in sliced mozzarella cheese contaminated experimentally with E. coli, indicating that it can be an alternative for inhibit the growth of this microorganism in sliced cheese. In addition, BOE reduced the number of S. aureus biofilm cells, having the potential to be used as a sanitizer.