Repurposing Ionophores as novel antimicrobial agents for the treatment of bovine mastitis caused by Gram‐positive pathogens |
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| Authors: | Elizabeth E Hickey Hui San Wong Manouchehr Khazandi Abiodun D Ogunniyi Kiro R Petrovski Sanjay Garg Stephen W Page Ryan O'Handley Darren J Trott |
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| Institution: | 1. Australian Centre for Antimicrobial Resistance Ecology, School of Animal and Veterinary Sciences, The University of Adelaide, Roseworthy, SA, Australia;2. School of Pharmacy and Medical Science, The University of South Australia, Adelaide, SA, Australia;3. Luoda Pharma Pty Ltd, Caringbah, NSW, Australia |
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| Abstract: | Increasing reports of multidrug‐resistant bacterial infections in animals has created a need for novel antimicrobial agents that do not promote cross‐resistance to critically important antimicrobial classes used in human medicine. In response to the recent emergence of antimicrobial resistance in several bovine mastitis pathogens, in vitro antimicrobial susceptibility was determined for four polyether ionophores (lasalocid, monensin, narasin and salinomycin) against Staphylococcus spp. and Streptococcus spp. isolated from clinical cases. In addition, erythrocyte haemolysis and WST ‐1 cell proliferation assays were used to assess in vitro mammalian cell cytotoxicity and biofilm susceptibility testing was performed using the minimum biofilm eradication concentration (MBEC ?) biofilm assay. Lasalocid, monensin, narasin and salinomycin exhibited bacteriostatic antimicrobial activity against all pathogens tested, including methicillin‐resistant staphylococci, with MIC 90 values <16 μg/ml. Narasin and monensin displayed the least toxicity against mammalian cell lines and all compounds significantly reduced viable cell numbers in a Staphylococcus aureus biofilm. Based on in vitro characterization, all four ionophores offer potentially novel treatments against bovine mastitis but in vivo studies will be essential to determine whether acceptable safety and efficacy is present following intramammary administration. |
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| Keywords: | biofilms cytotoxicity Gram‐positive Ionophores mastitis methicillin‐resistant |
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