Tomatidine Inhibits Replication of Staphylococcus aureus Small-Colony Variants in Cystic Fibrosis Airway Epithelial Cells

Abstract

Small-colony variants (SCVs) often are associated with chronic Staphylococcus aureus infections, such as those encountered by cystic fibrosis (CF) patients. We report here that tomatidine, the aglycon form of the plant secondary metabolite tomatine, has a potent growth inhibitory activity against SCVs (MIC of 0.12 g/ml), whereas the growth of normal S. aureus strains was not significantly altered by tomatidine (MIC, >16 g/ml). The specific action of tomatidine was bacteriostatic for SCVs and was clearly associated with their dysfunctional electron transport system, as the presence of the electron transport inhibitor 4-hydroxy-2-heptylquinoline-N-oxide (HQNO) caused normal S. aureus strains to become susceptible to tomatidine. Inversely, the complementation of SCVs' respiratory deficiency conferred resistance to tomatidine. Tomatidine provoked a general reduction of macromolecular biosynthesis but more specifically affected the incorporation of radiolabeled leucine in proteins of HQNO-treated S. aureus at a concentration corresponding to the MIC against SCVs. Furthermore, tomatidine inhibited the intracellular replication of a clinical SCV in polarized CF-like epithelial cells. Our results suggest that tomatidine eventually will find some use in combination therapy with other traditional antibiotics to eliminate persistent forms of S. aureus.

Outcome and Prevention of Pseudomonas aeruginosa-Staphylococcus aureus Interactions During Pulmonary Infections in Cystic Fibrosis

“…We found that TO has a bacteriostatic activity against SCVs, but not against normal strains. More importantly, we showed that TO has the ability to inhibit the replication of SCVs internalized in CF-like human airway epithelial cells (Mitchell et al, 2011a). The specificity of the action of TO against SCVs was linked to the dysfunctional electron transport chain of these variants.…”

“…In comparison to normal strains, SCVs form pinpoint colonies, are less or nonhemolytic on blood agar plates and have an increased ability to infect non-professional phagocytes and to form biofilms (B). The host-cell infection pictures were prepared as previously described (Mitchell et al, 2011a(Mitchell et al, , 2011b and show Calu-3 cells with actin colored in green and internalized S. aureus bacteria in red. Scale bar is 50 μm.…”

“…Nevertheless, the authors noted that four antibiotics (quinupristin-dalfopristin, moxifloxacin, oritavancin and rifampicin) were more effective in killing intracellular SCVs. In addition, we recently described the first known molecule to specifically target the SCV phenotype of S. aureus (Mitchell et al, 2011a). Tomatidine (TO) is the aglycone form of the plant secondary metabolite tomatine.…”

Infection of Polarized Airway Epithelial Cells by Normal and Small-Colony Variant Strains of Staphylococcus aureus Is Increased in Cells with Abnormal Cystic Fibrosis Transmembrane Conductance Regulator Function and Is Influenced by NF-κB

“…Cell infection assays were performed as previously described with few modifications (35). Briefly, cells were seeded at ϳ1.5 ϫ 10 5 cells/insert on 12-well Transwell plates and cultured for 9 to 10 days in an air-liquid system.…”

The TetR Family of Regulators

“…Given the similarities between BreR and AefR, we predict that the AefR-inducing ligand may be a phytosterol. Phytosterols share structural similarities with bile acids, and some (e.g., tomatidine) are known to have antimicrobial activity (41).…”