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Updated: Oct 19, 2025
Improved Enzyme Protection Assay to Study Staphylococcus aureus Internalization and Intracellular Efficacy of Antimicrobial Compounds
Published on: September 8, 2021
In vitro activity of non-antibiotic drugs against Staphylococcus aureus clinical strains
Natalie K Boyd1, Grace C Lee2, Chengwen Teng3
1College of Pharmacy, The University of Texas at Austin, San Antonio, Texas, USA; Long School of Medicine, University of Texas Health San Antonio, San Antonio, Texas, USA.
Objectives:
We hypothesised that one or more of the non-antibiotic candidates selected for this study would demonstrate antibiotic activity against Staphylococcus aureus.
Methods:
We determined minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) for non-antibiotic drugs (amlodipine, azelastine, ebselen and sertraline) against five clinical S. aureus isolates and one quality control strain using the Microplate Alamar Blue Assay (MABA). Our research group selected clinical isolates obtained from nasal and wound swab cultures of patients with skin and soft-tissue infections who were seen at primary care clinics in the South Texas Ambulatory Research Network (STARNet).
Results:
Three of the non-antibiotic drugs had identical MICs for all isolates: amlodipine, 64 μg/mL; azelastine, 200 μg/mL; and sertraline, 20 μg/mL. MICs for ebselen were 0.25 μg/mL (SA-29213, A1019 and J1019), 0.5 μg/mL (A32 and B60) and 1 μg/mL (B72). MBCs for amlodipine, azelastine and sertraline were within one dilution of their MICs, indicating bactericidal activity for all test isolates. Ebselen MBCs were one to two dilutions higher in most isolates, also indicating bactericidal activity for all test isolates.
Conclusion:
In summary, all four non-antibiotics demonstrated in vitro activity to varying degrees against S. aureus clinical isolates. Ebselen was the most potent of the four non-antibiotics tested.
