RESUMO: O uso de produtos naturais, como óleos essenciais (OEs), é uma nova abordagem potencial para o tratamento de infecções bacterianas em peixes com um baixo risco de desenvolvimento de resistência. Existem estudos reportando a atividade de OEs como aqueles obtidos das espécies Achyrocline satureioides, Aniba parviflora, Aniba rosaeodora, Anthemis nobilis, Conobea scoparioides, Cupressus sempervirens, Illicium verum, Lippia origanoides e Melaleuca alternifolia contra bactérias. Porém, existem poucos estudos investigando o efeito desses OEs supracitados contra bactérias isoladas de peixes. Portanto, o objetivo desse estudo foi avaliar a atividade antibacteriana in vitro desses OEs contra bactérias isoladas de peixes (Aeromonas hydrophila, Citrobacter freundii e Raoultella ornithinolytica). Assim como avaliar a atividade antibacteriana in vivo do OE de L. origanoides contra uma infecção por A. hydrophila experimentalmente induzida em jundiá (Rhamdia quelen). O OE de L. origanoides foi escolhido porque apresentou a melhor atividade antibacteriana in vitro, com concentrações inibitórias mínimas variando de 0,2 a 0,8 mg mL-1. Esse OE apresentou sucesso terapêutico de 58,33% no dia 30 pós-infecção. Portanto, sugerimos que o OE de L. origanoides possa ser uma alternativa viável no tratamento da infecção por A. hydrophila em peixes.

ABSTRACT: The use of natural products, such as essential oils (EOs), is a potential novel approach to treat fish bacterial infections with a lower risk of developing resistance. There has been a number of studies reporting the activity of EOs as those obtained from the species Achyrocline satureioides, Aniba parviflora, Aniba rosaeodora, Anthemis nobilis, Conobea scoparioides, Cupressus sempervirens, Illicium verum, Lippia origanoides, and Melaleuca alternifolia against bacteria. However, there are few studies investigating the effect of these EOs against fish bacteria. Therefore, the aim of this study was to evaluate the in vitro antibacterial activity of EOs against the following fish bacteria, Aeromonas hydrophila, Citrobacter freundii, and Raoultella ornithinolytica. Additionally, the in vivo antibacterial activity of the EO L. origanoides was evaluated against experimentally induced A. hydrophila infection of silver catfish (Rhamdia quelen). The EO of L. origanoides was chosen as it showed the highest in vitro antibacterial activity, with minimum inhibitory concentrations ranging from 0.2 to 0.8 mg mL-1. This EO also presented a therapeutic success of 58.33%, on a 30 day A. hydrophila infection. Therefore, we suggested that the EO of L. origanoides may be a viable alternative as a treatment for A. hydrophila infection.

The invasin gimB (genetic island associated with human newborn meningitis) is usually found in ExPEC (Extraintestinal Pathogenic Escherichia coli) such as UPEC (uropathogenic E. coli), NMEC (neonatal meningitis E. coli) and APEC (avian pathogenic E. coli). In NMEC, gimB is associated with the invasion process of the host cells. Due to the importance of E. coli as a zoonotic agent and the scarce information about the frequency of gimB-carrying strains in different animal species, the aim of this study was to investigate the presence of gimB in isolates from bovine, swine, canine and feline clinical samples. PCR was conducted on 196 isolates and the identity of the amplicons was confirmed by sequencing. Of the samples tested, only E. coli SB278/94 from a bovine specimen was positive (1/47) for gimB, which represents 2.1% of the bovine isolates. The ability of SB278/94 to adhere to and invade eukaryotic cells was confirmed by adherence and gentamicin-protection assays using HeLa cells. This is the first study that investigates for gimB in bovine, canine and feline E. coli isolates and shows E. coli from the intestinal-bovine samples harboring gimB.

The aim of this study was to determine the differences in the antimicrobial susceptibility profiles of Moraxella bovis, M. bovoculi and M. ovis. Thirty-two strains of Moraxella spp. isolated from cattle and sheep with infectious keratoconjunctivitis were tested via broth microdilution method to determine their susceptibility to ampicillin, cefoperazone, ceftiofur, cloxacillin, enrofloxacin, florfenicol, gentamicin, neomycin, oxytetracycline and penicillin. The results demonstrated that Moraxella spp. strains could be considered sensitive for most of the antimicrobials tested in this study, but differences between the antimicrobial susceptibility profiles of these three Moraxella species were found. M. bovis might differ from other species due to the higher MIC and MBC values it presented.