This book reports on activities carried out at the Centro de Estudos Superiores de Caxias of the Universidade Estadual do Maranhao - CESC/UEMA, with funding from the Fundacao de Amparo a Pesquisa e ao Desenvolvimento Cientifico e Tecnologico do Maranhao - FAPEMA. This research was carried out during my stay in the Postgraduate Program in Biodiversity, Environment and Health. Under the guidance of Prof. Dr. Francisco Laurindo da Silva, the research focused on carrying out tests to verify the efficiency of plants used by the community against Gram-negative bacteria, but with an antibacterial purpose that has not yet been proven. This work was carried out in the Microbiology Laboratory at CESC/UEMA. It was necessary to count on the help of collaborators in the day-to-day laboratory activities such as the FACID Laboratory Technician - Esmeralda and academics Francilene de Sousa Vieira and Gleciane Costa de Sousa. This research is extremely important given the large number of people who are increasingly becoming resistant to the antibiotics available on the market.