In Vitro Activity of Sodium Bituminosulfonate: Susceptibility Data for the Revival of an Old Antimicrobial.

Revival of old antibiotic compounds is a promising strategy to strengthen the antimicrobial armamentarium in the era of increasing resistance and limited development pipelines. To exploit their full potential, their reinvestigation using current standards is needed. We aimed to investigate the in vitro activity of the old antimicrobial agent sodium bituminosulfonate in accordance with the current recommendations for antimicrobial susceptibility testing (AST) and to generate susceptibility data reflecting the current epidemiological situation. The in vitro activity of sodium bituminosulfonate was tested on consecutive clinical isolates, including 12 methicillin-resistant Staphylococcus aureus (MRSA) and 12 methicillin-susceptible S. aureus (MSSA), 24 coagulase-negative staphylococci (CoNS), 60 streptococci, 12 Enterococcus faecalis, 12 Enterococcus faecium (including two vancomycin-resistant strains), 12 Enterobacterales, 12 nonfermenting Gram-negative bacilli, and 12 Cutibacterium [Propionibacterium] acnes. AST of sodium bituminosulfonate was performed using broth microdilution method for Gram-positive cocci and Gram-negative rods and by agar dilution method for C. acnes. Sodium bituminosulfonate demonstrated activity against Gram-positive pathogens with minimal inhibitory concentration 90 (MIC90) values (g/L) for MRSA 0.25, MSSA 1, CoNS 16, Streptococcus pyogenes 0.03, Streptococcus agalactiae 0.125, Streptococcus dysgalactiae ≤0.015, Streptococcus pneumoniae ≤0.015, viridans streptococci 0.03, E. faecalis 0.25, E. faecium 0.5, and C. acnes 0.03 (without blood supplement). MIC values for Gram-negative bacteria were considerably higher. Blood-supplemented media proved to be unsuitable for activity testing of this agent. Sodium bituminosulfonate may represent an alternative to classical antibiotics for topical use. Although it has been clinically used for many decades, well-designed randomized trials are needed for the effective revival of this old antimicrobial.