Characterizing the growth patterns of novel S. aureus mutants; both in vitro and ex vivo

Abstract

Staphylococcus aureus (S. aureus) is a ubiquitous commensal of the human anterior nares that is estimated to permanently colonize ~30% of the population. S. aureus is also a predominant infectious pathogen that causes significant morbidity and mortality and bears a considerable burden on the healthcare industry. Options for treating this “superbug” are dwindling at an alarming rate. Although initially being considered a hospital-acquired pathogen, community-associated strains have emerged. These strains have the ability to avoid normal immune cell killing and cause disease in healthy individuals. Mechanisms for how S. aureus can escape the defenses of the body are incompletely defined. Previously published work has demonstrated a role for the two-component gene regulatory system, SaeR/S, in S. aureus and that the SaeR/S system influences the ability for the immune system to perform effectively1–3. Although initially considered a two-component system, SaeR/S is actually composed of four genes: saeP, saeQ, saeR, and saeS and the roles of saeP and saeQ are yet to be fully discovered. It is speculated that SaeR/S inhibits the proper function of attacking innate immune cells that circulate in the blood, although the role of the accessory proteins on the blood are completely unknown. We have begun to characterize the role of these accessory genes by using a clinically relevant strain of S. aureus USA300 and isogenic deletion mutants (deficient in either saeP and saeQ; USA300ΔsaeP and USA300ΔsaeQ, respectively). Experiments first began by quantifying the growth patterns of these mutants during in vitro broth culture, as well as, ex vivo during growth in heparinized human whole blood. These studies will help to fill clinically relevant gaps in our understanding of how S. aureus escapes the host immune system to advance disease during septicemic infection. Defining how this pathogen can survive immune defenses in our circulatory system can help identify new potential targets for the design of therapeutics.