How Well Do Antibiotics Work Against Staphylococcus aureus That Has Been Taken in by Macrophages?

Staphylococcus aureus often causes bloodstream infections, and Kupffer cells (KCs; hepatic macrophages) can clear S. aureus bacteremia (SAB) by engulfing the pathogen. Nonetheless, 10% of S. aureus bacteria survive within such phagocytes, where they are protected from antibiotic exposure. Delayed bloodstream clearance is a well-known risk factor for mortality — and different antibiotics vary in their potency for managing SAB. Researchers assessed the efficacy of various antibiotics using an in vitro assay mimicking the intracellular milieu of phagocytes (e.g., pH 5). In a murine KC line, they also measured the intracellular accumulation of the antibiotics as well as S. aureus time-kill kinetics.

In low-pH medium compared with physiologic con…