Fresh produce has been identified as an important vehicle for the transmission of foodborne pathogens. This study evaluated the behavior of vegetative cells and spores of Bacillus thuringiensis, one of the main biological control agents (BCAs) used in the world, and Salmonella enterica on spinach plants (pre-harvest) and spinach cut leaves (post-harvest) at 12°C, experimentally inoculated as single or co-cultures. The results evidenced that spray-inoculated commercial BCA containing Bacillus thuringiensis subsp. aizawai ABTS-1857 (BTa ABTS-1857) spores persisted well on spinach leaves in both pre- and post-harvest simulations. However, when BTa ABTS-1857 vegetative cells were spray-inoculated, more than 2 log reductions in the counts of B. thuringiensis were observed during 20 days pre- and 5 days post-harvest simulations, respectively. The counts of S. Montevideo on the spinach cut leaves during post-harvest storage at 12°C for 5 days remained unchanged, whereas 1 log reduction was noted during pre-harvest. Moreover, during pre-harvest simulation, when co-inoculated with BTa ABTS-1857 vegetative cells or spores, additional 0.5 or 1.0 log reductions were detected on the counts of S. Montevideo in the spinach leaves on the 10th day. These results were obtained under laboratory conditions, and further findings in longitudinal studies from farm (in the agricultural field) to retail (end of shelf life) will contribute to understanding of the role of B. thuringiensis as a BCA on growth/survival of Salmonella spp. in fresh produce.

Aims: To gather data on agricultural practices in organic farms in Sao Paulo, Brazil, and evaluate their relationship with the microbiological characteristics of samples collected along the production chain.Methods and Results: Practices data were based on field observations and interviews with farmers in 10 selected organic lettuce producing farms. Counts of Enterobacteriaceae and surveys for Salmonella were performed in samples of lettuce (before and after washing), fertilizers, irrigation and washing water, all collected in the same farm. Water samples were also tested for total coliforms and generic Escherichia coli. Isolated Enterobacteriaceae were identified by MALDI-TOF MS.Contamination of lettuce was influenced by some agricultural practices: chicken manure-based fertilization resulted in higher Enterobacteriaceae counts in lettuce when compared to other types of manure, whereas pre-washed lettuces presented lower microbial counts than non-pre-washed samples. Salmonella was detected in one lettuce sample by qPCR. Escherichia coli was detected in all irrigation water samples. All sample types contained Enterobacteriaceae species commonly reported as opportunistic human pathogens. Conclusions:The data highlight the need for improvement in the good agricultural practices in the studied farms. Significance and Impact of the Study:This study provides information on agricultural practices and microbiological characteristics of organic lettuce, contributing to the development of more accurate risk assessments.

À minha família, minha base, apoio e inspiração para seguir em frente. Minha mãe Cleyde e meu irmão Marcos, por terem me motivado a ir em busca dos meus sonhos e enfrentar as adversidades da vida com garra, ética e resistência; Meus sogros Ivone e Milton pelo carinho de sempre; E meu companheiro Diogo, pela paciência, pelos conselhos, por acreditar e me mostrar que sou capaz de ir além. À Profª Drª Bernadette D.G.M. Franco, pela orientação e oportunidades de aprendizado e desenvolvimento profissional durante o mestrado. A Profª Drª Mieke Uyttendaele, por ter me recebido na Ghent University e compartilhado seu conhecimento, me orientado em parte desta pesquisa. À Profª Drª Daniele Fernanda Maffei, pelos ensinamentos, experiências compartilhadas, oportunidades de parcerias e amizade. Às Professoras Mariza Landgraf, Elaine Martinis e Cynthia Kunigk pela participação no exame de qualificação e sugestões para enriquecimento deste trabalho. À Profª Drª Evelise Telles, pela oportunidade de participar como monitor PAE na disciplina Higiene e Segurança Alimentar da FMVZ/USP. À Universidade de São Paulo, que tem possibilitado o meu desenvolvimento científico desde a graduação. Assim como aos professores desta instituição, pelo aprendizado nas aulas e empenho pelo desenvolvimento científico do País. À equipe do Laboratório de Microbiologia de Alimentos da FCF/USP, professores, pesquisadores, técnicas e estagiários, pelo auxílio no desenvolvimento dos experimentos, aprendizado e pelos bons momentos compartilhados. À equipe do Laboratório de Microbiologia e Preservação de Alimentos da Ghent University, professores, técnicos e pesquisadores, pelo acolhimento caloroso, troca de experiências e amizade.