Steroids as antibacterials

The existence of steroid antibacterials has been studied since the golden age of antibiotics, although the literature on this topic is fragmented. To address this the current review seeks to bring these fragmented lines of enquiry together to assess the utility of steroidal compounds as antibacterials. In doing so this review will document the structural features, biosynthetic/synthetic origins, antibacterial toxicities, potential for fungal biotransformations, and catabolic pathways in the human host. Herein, we identify steroid antibacterials from fungal origins, synthetic steroids, and approved drugs that have the potential for future repurposing as antibacterials. Of particular note are the fusidane steroids of fungal origin, displaying low MIC values and being effective against a variety of Gram-positive and Gram-negative species. At present, fusidic acid is the only steroid that is prescribed as an antibacterial, despite many publications describing antibacterial activity in a range of well-known steroids. The impact of bacterial exposure to steroids naturally differs depending on the nature of the cell membranes, cell wall, and the ability of bacterial to import steroids for use as a carbon source, which is discussed herein. Also, this study explores the biotechnological potential of fungi for the production of antibacterial steroids, and how steroid drugs are metabolised in the human host. Together, this provides an assessment of the potential for steroids as future antibacterial drugs.