Activity of biogenic silver nanoparticles against isolates of Prototheca species from bovine mastitis.

Prototheca spp. cause numerous infections in a wide variety of species, including treatment-unresponsive mastitis. Thus, the search for an effective therapy is essential. Silver nanoparticles are compounds with high therapeutic potential. This study aimed to evaluate the susceptibility profile and morphological changes in Prototheca spp. treated with biogenic silver nanoparticles (Bio-AgNP). The algaecide activity was evaluated in microplates by microdilution method, resulting in a MIC50 of 30 µg ml-1 and a MIC90 of 60 µg ml-1 . Scanning electron microscopy demonstrated changes in the surface of Prototheca bovis cells following treatment. The algaecide activity of Bio-AgNP suggests a therapeutic potential as a novel approach for the control of Prototheca spp. in bovine mastitis.

Moraxella bovis, Moraxella ovis and Moraxella bovoculi: biofilm formation and lysozyme activity.

AIMS: This study aimed to verify the formation of biofilms by Moraxella bovis, Moraxella ovis and Moraxella bovoculi isolates from ruminants. In addition, the lysozyme activity against the isolates of M. bovis, M. ovis and M. bovoculi in free form and in biofilms was determined. METHODS AND RESULTS: In this study, 54 isolates of Moraxella sp. obtained from bovine and ovine clinical samples were evaluated in vitro for capacity of biofilm formation and lysozyme susceptibility in planktonic and sessile cells. In addition, biofilms produced by four Moraxella sp. isolates were visualized under scanning electron microscope (SEM). It was possible to demonstrate, for the first time, the ability to form biofilms by M. ovis and M. bovoculi. The isolates of Moraxella sp. have the capacity to form biofilms in different intensities, varying among weak, moderate and strong. It was verified that the lysozyme shows activity on Moraxella sp. in planktonic form. However, on biofilms there was a reduction in the production, but without impairing its formation, and on consolidated biofilms the lysozyme did not have the capacity to eradicate the preformed biofilms. CONCLUSIONS: This work shows the capacity of biofilm formation by Moraxella sp. of veterinary importance. The lysozyme susceptibility of Moraxella sp. in planktonic form shows that this enzyme has bacteriostatic activity on this micro-organism and it reduced the production of biofilms. SIGNIFICANCE AND IMPACT OF THE STUDY: Based on the results, it is possible to infer that the biofilm formation capacity by Moraxella sp. and the resistance to lysozyme concentrations equal to or greater than the physiological levels of the ruminant tear may be linked not only to the capacity to colonize the conjunctiva, but also to remain in this place even after healing of the lesions, being a reservoir of Moraxella sp. in a herd.

Antibacterial potential of phytochemicals alone or in combination with antimicrobials against fish pathogenic bacteria.

AIMS: This study investigated the antibacterial activity of five phytochemicals (carvacrol, citral, eugenol, linalool and thymol) alone or in combination with florfenicol or oxytetracycline against bacteria isolated from silver catfish (Rhamdia quelen). We also analysed the potential of these compounds to inhibit biofilm formation and haemolysis caused by the bacteria. METHODS AND RESULTS: Bacteria were tested with antimicrobials to calculate the multiple antibiotic resistances. The checkerboard assay was used to evaluate a putative synergy between five phytochemicals and antimicrobials against the strains isolated. The biofilm formation inhibition assay was performed with phytochemicals and antimicrobials, and the haemolysis inhibition assay was performed with the phytochemicals. Carvacrol, eugenol and thymol were the most effective phytochemicals. Three combinations (linalool with florfenicol or oxytetracycline against Aeromonas hydrophila and citral with oxytetracycline against Citrobacter freundii) demonstrated synergy in the checkerboard assay. All phytochemicals inhibited biofilm formation and haemolysis activity. CONCLUSION: The tested phytochemicals showed satisfactory activity against fish pathogenic bacteria. SIGNIFICANCE AND IMPACT OF THE STUDY: The phytochemicals did not present antagonistic interactions with the antimicrobials, allowing their combined use, which may contribute to a decrease in the use of conventional drugs and their residues in aquatic environment.