Prospecção de óleos essenciais em combinação com florfenicol frente aeromonas móveis isoladas de tambaqui (Colossoma macropomum)

Abstract

With the current growth of fish farming on the national and international scene, there is an intensification of production systems. Although more profitable, this system must be accompanied by good management practices, otherwise it acts as a facilitator for the installation of diseases. Among the diseases that can affect fish, bacteriosis stand out. As they are considered productivity limiting, they are commonly treated with antimicrobials and chemotherapy indiscriminately. As a result, an increase in bacterial resistance to antimicrobials has been observed. In this sense, the search for natural products with antimicrobial activity and their association with synthetic antibiotics of interest to fish farming is necessary. Therefore, the aim of this study was to evaluate the antimicrobial, antibiofilm and synergistic activities of five essential oils (EOs) with florfenicol against Aeromonas hydrophila and Aeromonas jandaei isolated from tambaqui (Colossoma macropomum). Bacterial strains were identified by sequencing the 16S rRNA¸ gene and from these, three A. hydrophila and one A. jandaei strains were selected for the study. The EOs of the species of Aloysia triphylla, Croton cajucara morphotype red, Croton cajucara morphotype white, Cymbopogon citratus and Lippia gracilis had as major constituent the compound β-pinene (22.1%), germacrene D (11.5%), linalool ( 23%), geranial (45.7%) and carvacrol (42.2%), respectively. To determine the minimal inhibitory concentrations (MIC) the microdilution technique in 96-well plates was used, and to determine the minimal bactericidal concentration (CBM) of the EOs, platings were performed in Muller Hinton agar (MHA). For the synergistic activity, the checkerboard technique was used. The five EOs evaluated were classified as having weak antimicrobial activity, showing bactericidal action against target pathogens, with MIC ranging from 5,000 to 640,000 ug mL−1. The EOs of L. gracilis and C. citratus showed the lowest concentrations against the investigated pathogens (MIC and CBM of 5,000 ug mL-1). The EOs interfered in the initial and consolidated biofilm when compared to the negative control (E. coli), going from weak producers to non-producers. The EOs of A. triphylla, C. Citratus, C. cajucara white morphotype and L. gracilis combined with florfenicol reduced the MIC, and the fractional inhibitory concentration index varied between 0.38 and 0.50, indicating a synergistic effect. In this dissertation, it was possible to demonstrate the synergistic effect of four EOs with florfenicol, reducing the dose of this antimicrobial and EOs. Considering the cost of treatments in fish farming that are still high, this work contributed to reducing the amount of drugs used (synthetic and natural) and, consequently, reducing the cost of treatment. In addition, the reduction of synthetic antimicrobials in the water makes the treatment more sustainable for the environment, even reducing the selection of bacterial strains resistant to the antimicrobial.