The bactericidal mechanism of action of the SK-03-92 antibiotic against Staphylococcus aureus and the eradication of SK-03-92-induced bacterial persistence

Abstract

Infections caused by Staphylococcus aureus kill approximately 52 Americans every day and are particularly lethal when a biofilm has formed. The development of persister cells, and thus a chronic infection, further increases the chances of developing a lethal biofilm-associated infection. The SK-03-92 antibiotic is a promising drug that kills S. aureus, but the killing mechanism has not yet been characterized. Bioinformatic analysis indicated that SK-03-92 kills S. aureus by inducing late-stage competence, a phenomenon characterized by cell-death, increased biofilm production, and the development of persister cells. To test this, the supernatants of S. aureus exposed to SK-03-92 were recaptured and diluted to reduce the residual amount of drug to non-bactericidal levels. This material was named 3HSN (three-hour supernatant). Testing of 3HSN showed results consistent with the late-stage competence model. Namely, 3HSN exposure killed 91% more S. aureus than SK-03-92 alone and increased the output of biofilm produced by S. aureus by 20.7-fold per cell. A scheme to kill persister cells was also developed. We hypothesized that adding concentrated malate (pH ~ 7) to persister-inducing levels of SK-03-92 would force persister cells out of dormancy and allow SK-03-92 to kill 100% of the population. This hypothesis was confirmed experimentally. In sum, in silico and in vitro analysis indicated that SK-03-92 kills S. aureus by causing the cells to release a suicide-inducing pheromone, and the addition of 125 mM of malate to bactericidal levels of SK-03-92 produces a fully effective antibiotic that causes 100% cellular death.