Adaptação e adaptação cruzada de Escherichia coli enterotoxigênica e enteropatogênica a componentes majoritários de óleos essenciais e ao estresse ácido

Abstract

Pathogenic bacteria such as Escherichia coli Enteropathogenic and Enterotoxigenic may cause diarrhea or even death in children and immunoincompetent patients. As a foodborne disease, mostly from animal resources, the microbiological control is from great relevance. Food preservatives usually control these bacteria by inhibition or death. Although, these additives may cause negative impacts on public health. Natural compounds shows up as alternative to common chemical substances. Major compound of essential oils has known and broad-spectrum antimicrobial activity against foodborne pathogens. However, when used in sublethal doses it may induce physiological response in bacteria, which reduce susceptibility to these compounds or even other stressor agents. By these reasons, it becomes necessary to verify EPEC and ETEC adaptive and/or cross-adaptive capacity to major compounds of essential oils. Initially, pH of minimum inhibition and growth were determinated and minimum bactericidal concentration (MBC) of cinnamaldehyde, eugenol and citral against EPEC and ETEC. Adaptive capacity of EPEC and ETEC exposed to major compounds and acid stress were tested and cross-adaptation between major compound and acid stress were evaluated as well. EPEC and ETEC cells were grown in major compound or pH of minimum growth exposition during 6 hours at 37ºC on adaptation and cross-adaptation tests. After this, 10 8 CFU/mL standard suspensions of EPEC and ETEC were centrifuged and resuspended in Brain-heart infusion broth (BHI). In adaptation tests, sublethal doses of 1/4, 1/8 and 1/16 MBC of cinnamaldehyde, eugenol or citral and 0.5% of Tween 80 were added on BHI for previous exposition. EPEC and ETEC standard suspension cells were incubated at 37ºC for 24 hours under 0.5; 1.0; 1.2; 1.4; 1.6; 1.8 and 2.0 MBC of major compounds. After this period, cells were plated on Tryptic soy agar (TSA) and incubated at 37ºC for 24h to evaluate adaptive response. In cross-adaptation tests between acid stress and major compounds, EPEC and ETEC standard cells were grown in BHI with addition of 0.5% Tween 80 and major compounds at 0.5 to 2.0 MBC concentrations for 24h at 37ºC. Then, cells were plated on TSA and incubated at 37ºC for 24h. ETEC and EPEC previously exposed to major compound and pH were grown in BHI with pH of: 6.0; 5.0; 4.5; 4.0; 3.5; 3.0; 2.5; 2.0 using lactic acid as adjustment, followed by TSA plating and incubation. The pH of minimum inhibition and growth were 4.0 and 4.5, respectively for EPEC and ETEC. Cinnamaldehyde, eugenol and citral MBC were 0.125, 1.0 and 1,0%, respectively, for both pathotypes. Adaptation and cross-adaptation tests demonstrated that EPEC and ETEC pre-exposition to sublethal doses of major compound and pH of minimum growth promoted bacterial resistance. Therefore, cinnamaldehyde, eugenol and citral are potential option to be used as industrial antimicrobial sanitizers while in appropriate concentrations.