Influence of the native microbiota and of physical- chemical factors in adhesion of Salmonella Enteritidis in lettuces of hydroponic and conventional sistems / Influência da microbiota natural e de fatores físico-químicos na adesão de Salmonella Enteritidis em alface de cultivo hidropônico e convencional

Priscilla Macedo Lima

Adhesion of Salmonella Enteritidis in lettuces leaves of hidroponic and convencional systems was evaluated in reason of the native microbiota, with or without sanitization with chlorinated organic compound and vegetal roughness, using Atomic Force Microscopy. Besides, surfaces hydrophobicities of the lettuce leaves and S. Enteritidis were determined, through water contact angle and free energy. Also, a thermodynamic study was accomplished based on the quantification of the total free energy of interaction of the surfaces to foresee the pathogen adhesion on the leaf surfaces. The presence of Salmonella sp. Was not observed in none of the lettuces samples. Except filamentous fungi and yeasts counts, the lettuce cultivars grown hydroponically presented smaller counts (P <0,05) for aerobic mesophilic, lactic bacteria and coliforms at 35C. Sanitization with 200mg.L-1 of total residual chlorine, pH 6.8, during 15 min reduced (P <0,05) the counts of all of the microbial groups, altering the native microbiota of the lettuces surface. The adhesion of S. Enteritidis was larger (P <0,05) in the Hydroponic lettuce and in both types of lettuces after the sanitization procedure (P <0,05). Images obtained by Scanning Electron Microscopy showed that the leaf surface presented different micro photographic characteristics and that the present stomats in surfaces served as entrance and shelter for the pathogen cells. The roughness values showed that the surface of lettuces cultivars qrown hydropomically was more wrinkled (P <0,05), with average of 1211.2 nm. The lettuce of conventional cultivaiton presented a mediumroughness of 293.3 nm. The qualitative analysis of hydriohobicity revealed that the surface S. Enteritidis was hydrophilic and that the surfaces of the hydroponic and conventional lettuces can be classified as hydrophobic and slightly hydrophilic,respectively. Free energies values were positive (Δgsws >0) for the surface of conventional cultivaion lettuce, and for S. Enteritidis surface, indicating hydrophilic surface, while for the lattuce cultivas grown hydroponically the value of the free energy was nagative (Δgsws <0), in other words, hydrophonic. The main factors involved in the adhesion of the pathogen in this research were superfaces roughness and competitor microbiota. Adhesion of S. Enteritidis to the leave surface was thermodynamically unfarvirable, independent of the cultivation way (ΔgAdesão >0). Thus, the termodynamic evaluation explains the low number of S. Enteritidis cells adhered to the leave surface. Results show the importance of the vegetables sanitization processe and of the sppropriate production practices and suggest that the recontamination is an important factor to be considered. In that sense, the biological preservation should be considered as an additional measure a not like a substitution of the hygienic-sanitarium processes. Besides, the study of factors that involve the bacterial adhesion in foods surfaces is of great importance for the control of this process and the obtaining of safe foods from the microbiological point of view.

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