In vitro activity of conventional drugs and natural essences against Prototheca

Background: Bovine mastitis caused by Prototheca can assume high significance because of economic losses and the potential risk to public health. Many studies highlighted the high level of antibiotic resistance of Prototheca, as well as the unsuccessful therapies. Objectives: To determine the in vitro susceptibility of Prototheca isolates to different antibiotics and alternative treatments based on essential oils. Methods: Sixteen isolates of Prototheca were identified by multiplex PCR reaction, typed using RAPD-PCR, and tested by the disk diffusion method for their susceptibility to 28 antibiotics. The efficacy tests to essential oils (thymol, carvacrol and cinnamaldehyde) were performed using emitters releasing compounds in a controlled way in jars, containing the Prototheca strains streaked on Sabouraud agar. Results: All the strains were resistant to Amikacin, Ampicilin, Aztreonam, Cefepime, Ceftazidime, Chloramphenicol, Ciprofloxacin, Erythromycin, Fosfomycin, Imipenem, Levofloxacin, Meropenem, Mupirocin, Nitrofurantoin, Oxacillin, Penicilin G, Piperacillin, Quinupristin/Dalfopristin, Rinfamicin, Streptomycin, Tetracycline, Ticarcillin/clavulanic acid, Tobramycin and Vancomicin. In contrast, Colistin sulphate, Gentamicin, Kanamycin and Netilmicin were effective against all the strains tested. The growth of P. zopfii genotype 1- 2, and P. blasckeae was completely inhibited by thymol, carvacrol and cinnamaldehyde. Conclusions: The results of the study revealed 4 out of 28 antibiotics tested efficient against Prototheca spp. while all the strains were inhibited by the tested essential oils Thus, in vivo studies are needed to evaluate if these compounds could rise as alternative treatments for bovine mastitis caused by Prototheca spp.