Antimicrobial Properties of 8-Hydroxyserrulat-14-en-19-oic Acid for Treatment of Implant-Associated Infections

Abstract

Treatment options are limited for implant-associated infections (IAI) that are mainly caused by biofilm-forming staphylococci. We report here on the activity of the serrulatane compound 8-hydroxyserrulat-14-en-19-oic acid (EN4), a diterpene isolated from the Australian plant Eremophila neglecta. EN4 elicited antimicrobial activity toward various Gram-positive bacteria but not to Gram-negative bacteria. It showed a similar bactericidal effect against logarithmic-phase, stationary-phase, and adherent Staphylococcus epidermidis, as well as against methicillin-susceptible and methicillin-resistant S. aureus with MICs of 25 to 50 g/ml and MBCs of 50 to 100 g/ml. The bactericidal activity of EN4 was similar against S. epidermidis and its ⌬ica mutant, which is unable to produce polysaccharide intercellular adhesin-mediated biofilm. In time-kill studies, EN4 exhibited a rapid and concentration-dependent killing of staphylococci, reducing bacterial counts by >3 log 10 CFU/ml within 5 min at concentrations of >50 g/ml. Investigation of the mode of action of EN4 revealed membranolytic properties and a general inhibition of macromolecular biosynthesis, suggesting a multitarget activity. In vitro-tested cytotoxicity on eukaryotic cells was time and concentration dependent in the range of the MBCs. EN4 was then tested in a mouse tissue cage model, where it showed neither bactericidal nor cytotoxic effects, indicating an inhibition of its activity. Inhibition assays revealed that this was caused by interactions with albumin. Overall, these findings suggest that, upon structural changes, EN4 might be a promising pharmacophore for the development of new antimicrobials to treat IAI.

Preventing Implant-Associated Infections by Silver Coating

“…The strains were stored at Ϫ80°C with the cryovial bead preservation system (Microbank; Pro-Lab Diagnostics, Richmond Hill, Ontario, Canada). The inoculum for in vivo and in vitro studies was prepared as previously published (8,30). Bacterial numbers were determined by plating aliquots from appropriate dilutions on MHA, followed by colony counting after 24 h of incubation at 37°C.…”

“…Due to their ability to rapidly form biofilm on the inert surface, they manage to grow and evade not only the defensive mechanisms of the host but also the bactericidal activity of antibiotics (7). Effective treatment of IAIs therefore involves surgery, often resulting in the removal of the nonsalvageable biomaterial followed by a long course of antibiotic therapy (8,9).…”

Targeting the Bacterial Protective Armour; Challenges and Novel Strategies in the Treatment of Microbial Biofilm

“…The concentration of bactericidal dose is only three to six folds higher than the bactericidal dose [ 120 ]. 8-hydroxyserrulat-14-en-19-oic acid, a plant-derived serrulatane diterpenoid (extracted from the Australian medicinal plant Eremophila neglecta ) showed anti-biofilm formation activity against Gram-positive bacterial but not Gram-negative bacteria by inhibiting the macromolecular biosynthesis of the bacterial membrane [ 121 ]. Table 6 summarises examples of diterpenoids with anti-biofilm activities…”

Foreign Body Infection Models to Study Host-Pathogen Response and Antimicrobial Tolerance of Bacterial Biofilm

“…The MID is an indicator of staphylococcal virulence in this model. For S. aureus it ranges between approximately 5 × 10 2 –5 × 10 3 CFU/cage [ 9 , 30 , 86 ]. In contrast, the MID of S. epidermidis is much higher, namely above 10 6 CFU/cage, and spontaneous clearing occurs, if bacteria are not injected during the perioperative period [ 83 ].…”

“…In vivo however neither bactericidal nor cytotoxic effects were present, indicating an inhibition of its activity. Inhibition assays revealed that this was caused by interaction of EN4 with albumin [ 86 ].…”