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. 2024 Jan 6;14(1):5.
doi: 10.1186/s13568-024-01660-0.

Drug repurposing: insights into the antimicrobial effects of AKBA against MRSA

Yingjia Li  1 , Hongbing Ma  2
Affiliations

Drug repurposing: insights into the antimicrobial effects of AKBA against MRSA

Yingjia Li et al. AMB Express. .

Abstract

Staphylococcus aureus is a major threat in infectious diseases due to its varied infection types and increased resistance. S. aureus could form persister cells under certain condition and could also attach on medical apparatus to form biofilms, which exhibited extremely high resistance to antibiotics. 3-Acetyl-11-keto-beta-boswellic acid (AKBA) is a well-studied anti-tumor and antioxidant drug. This study is aimed to determine the antimicrobial effects of AKBA against S. aureus and its persister cells and biofilms. The in vitro antimicrobial susceptibility of AKBA was assessed by micro-dilution assay, disc diffusion assay and time-killing assay. Drug combination between AKBA and conventional antibiotics was detected by checkerboard assay. And the antibiofilm effects of AKBA against S. aureus were explored by crystal violet staining combined with SYTO/PI probes staining. Next, RBC lysis activity and CCK-8 kit were used to determine the cytotoxicity of AKBA. In addition, murine subcutaneous abscess model was used to assess the antimicrobial effects of AKBA in vivo. Our results revealed that AKBA was found to show effective antimicrobial activity against methicillin-resistant S. aureus (MRSA) with the minimal inhibitory concentration of 4-8 µg/mL with undetectable cytotoxicity. And no resistant mutation was induced by AKBA after 20 days of consecutive passage. Further, we found that AKBA could be synergy with gentamycin or amikacin against S. aureus and its clinical isolates. By crystal violet and SYTO9/PI staining, AKBA exhibited strong biofilm inhibitory and eradication effects at the concentration of 1 ~ 4 µg/mL. In addition, the effective antimicrobial effect was verified in vivo in a mouse model. And no detectable in vivo toxicity was found. These results indicated that AKBA has great potential to development as an alternative treatment for the refractory S. aureus infections.

Keywords: AKBA; Biofilm; Drug repurposing; Persister cells; Staphylococcus aureus.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Fig. 1
Fig. 1
Bactericidal activity of AKBA against MRSA ATCC 43,300. (A) Antimicrobial susceptibility of AKBA determined by K-B test. AKBA: 6 µL. GEN: gentamycin, 10 µg. DMSO (6 µL) was used as a control. (B) Inhibition diameters quantification of the K-B test. (C) Growth inhibition activity by AKBA. (D) Time-killing curve of AKBA against ATCC 43,300. (E) Growth turbidity of ATCC 43,300 after treated with AKBA for 24 h
Fig. 2
Fig. 2
Low antimicrobial resistance inducing ability of AKBA. (A) Resistance inducing ability of AKBA against MRSA ATCC 43,300. (B) MIC determination of AKBA against CIP-induced resistant strains of ATCC 43,300. (C) Resistance inducing ability of AKBA against MSSA ATCC 25,923. (D) MIC determination of AKBA against CIP-induced resistant strains of ATCC 25,923. P1, parallel test (1) P2, parallel test (2) CIP was used as a positive control
Fig. 3
Fig. 3
Drug combination between AKBA and conventional antibiotics determined by checkerboard assay. GEN, gentamycin. AMK, amikacin. VAN, vancomycin. LEV, levofloxacin. AMP, ampicillin. CRO, ceftriaxone sodium. CLA, clarithromycin. AZM, azithromycin. CEF, cefsulodine sodium. PG, penicillin G. TEC, teicoplanin. CHL, chloramphenicol
Fig. 4
Fig. 4
Antibiofilm effects of AKBA. (A) Biofilm inhibition activity of AKBA determined by crystal violet staining. (B) Biofilm eradication activity of AKBA determined by crystal violet staining. (C) Biofilm inhibition visualization by SYTO9/PI staining. (D) Fluorescence intensity quantitation of (C). (E) Biofilm eradication visualization by SYTO9/PI staining. (F) Fluorescence intensity quantitation of (E). The biofilm was stained with SYTO9/PI fluorescent probes. SYTO9 (green) and PI (red) were indicated viable cells and dead cells, respectively. (G) Persister killing activity of AKBA determined by time-killing assay. VAN/CIP/DAP/GEN at the concentration of ten-fold of MIC were used as controls
Fig. 5
Fig. 5
Cytotoxicity of AKBA. (A) Extremely low RBC lysis activity by AKBA. (B-D) Cytotoxicity detection of AKBA against cell lines of LO2 (B), HepG2 (C) and HSF (D) by CCK-8 assay
Fig. 6
Fig. 6
Antimicrobial effects of AKBA in an abscess infection model. Area size quantification (A) and viable cell counting (B) in abscess after treated with AKBA or VAN for 24 h. (C) Inflammatory cells infiltration and cytokines (IL-1β, IL-6, and TNF-α) expression observed by H&E staining and immunohistochemical, respectively
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