Article of Significant Interest in This Issue

Cytochrome bd with the Small Protein CydX Inversely Modulates Salmonella Fitness and Antibiotic Resistance

Cytochrome bd quinol oxidases with high oxygen affinity promote respiration and fitness of facultative anaerobes in less oxic environments. Despite our limited understanding of molecular properties, their presence only in bacteria warrants considering them as potential drug targets in multidrug-resistant pathogens. Duc et al. (e00348-19) report new characteristics of cytochrome bd assembly and function that require the small protein CydX for Salmonella fitness under stress conditions, such as being exposed to antimicrobials or being inside phagocytes. However, they also demonstrate that cytochrome bd inactivation causes increased resistance to bactericidal antibiotics, suggesting that considerable caution should be taken for therapeutic strategies targeting cytochrome bd.