Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2024 Jan 26;19(1):e0297493.
doi: 10.1371/journal.pone.0297493. eCollection 2024.

Interactions of plumbagin with five common antibiotics against Staphylococcus aureus in vitro

Songtao Bie  1   2   3 , Qiuyue Mo  1   3 , Chen Shi  1   3 , Hui Yuan  1   3 , Chunshuang Li  1   3 , Tong Wu  1   3 , Wenlong Li  1   2   3 , Heshui Yu  1   2   3
Affiliations

Interactions of plumbagin with five common antibiotics against Staphylococcus aureus in vitro

Songtao Bie et al. PLoS One. .

Abstract

Staphylococcus aureus is the main culprit, causing a variety of severe clinical infections. At the same time, clinics are also facing the severe situation of antibiotic resistance. Therefore, effective strategies to address this problem may include expanding the antimicrobial spectrum by exploring alternative sources of drugs or delaying the development of antibiotic resistance through combination therapy so that existing antibiotics can continue to be used. Plumbagin (PLU) is a phytochemical that exhibits antibacterial activity. In the present study, we investigated the in vitro antibacterial activity of PLU. We selected five antibiotics with different mechanisms and inhibitory activities against S. aureus to explore their interaction with the combination of PLU. The interaction of combinations was evaluated by the Bliss independent model and visualized through response surface analysis. PLU exhibited potent antibacterial activity, with half maximal inhibitory concentration (IC50) and minimum inhibitory concentration (MIC) values against S. aureus of 1.73 μg/mL and 4 μg/mL, respectively. Synergism was observed when PLU was combined with nitrofurantoin (NIT), ciprofloxacin (CPR), mecillinam (MEC), and chloramphenicol (CHL). The indifference of the trimethoprim (TMP)-PLU pairing was demonstrated across the entire dose-response matrix, but significant synergy was observed within a specific dose region. In addition, no antagonistic interactions were indicated. Overall, PLU is not only a promising antimicrobial agent but also has the potential to enhance the growth-inhibitory activity of some antibiotics against S. aureus, and the use of the interaction landscape, along with the dose-response matrix, for analyzing and quantifying combination results represents an improved approach to comprehending antibacterial combinations.

PubMed Disclaimer

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Example of microplate configurations for two-drug dilution assays.
(A) The experimental plate (taking CHL as an example). (B) The control plate. CHL: chloramphenicol; PLU: plumbagin.
Fig 2
Fig 2. Dose-response curves of PLU and antibiotics against S. aureus in vitro using GraphPad Prism 9.0.
PLU: plumbagin, NIT: nitrofurantoin, CPR: ciprofloxacin, MEC: mecillinam, CHL: chloramphenicol, TMP: trimethoprim.
Fig 3
Fig 3. Graphical representation of three metrics generated by the Combenefit software for each of the five antibiotics paired with PLU.
(A) The SUM_SYN_ANT metric was defined as the “sum of synergy and antagonism observed,” representing all values within the dose space. The light blue section showed that the observed synergy was greater than the combination with PLU itself; (B) The SYN_MAX metric is defined as the "maximum observed synergy," which represents the highest value of synergy observed. The ANT_MAX metric was defined as the "maximum antagonism observed," representing the highest value of antagonism recorded. PLU: plumbagin, NIT: nitrofurantoin, CPR: ciprofloxacin, MEC: mecillinam, CHL: chloramphenicol, TMP: trimethoprim.
Fig 4
Fig 4. The interactions of PLU with itself (N = 3) are analyzed by the Bliss independence model to determine the threshold of the metric.
(A) Single-agent dose-response curve for PLU; (B) The interaction landscape of the combinations of PLU with itself, visualizing the efficacy of each of the 49 dual-drug combinations. The plot was colored without regard to statistical significance, according to the Synergism/Antagonism scale located just below the graph; (C) Synergy scores, calculated by the Bliss independence model, were shown in matrix format. The larger numeral in each box was the synergy score. The number below the synergy score was the standard deviation. The boxes, colored according to the synergism/antagonism scale, indicate results that were statistically significant based on the one-sample t-test. The degrees of significance were as follows: *p<0.05; **p<0.001. If the synergy score is not significant, the box is shown in green; significant is shown in blue; and significant antagonism is shown in red. The number of biological replicates (N) is indicated in the top left of the matrix. Raw data of these experiments can be found in (S2 File). PLU: plumbagin.
Fig 5
Fig 5. The interactions of CPR and PLU (N = 3), indicate evident synergy between the two agents.
(A) Single-agent dose-response curve for CPR; (B) Single-agent dose-response curve for PLU. The Bliss independence model generated the reference concentration space from the two single-agent dose-response curves; (C) The interaction landscape of the combinations of CPR and PLU; (D) Synergy scores were calculated by the Bliss independence model and were colored when they are significant. A detailed description of the various plots is given in Fig 4. Raw data of these experiments can be found in (S2 File). CPR: ciprofloxacin, PLU: plumbagin.
Fig 6
Fig 6. The interactions of MEC and PLU (N = 3), indicate evident synergy between the two agents.
(A) Single-agent dose-response curve for MEC; (B) Single-agent dose-response curve for PLU; (C) The interaction landscape of the combinations of MEC and PLU; (D) Synergy scores calculated by the Bliss independence model and colored when significant. A detailed description of the various plots is given in Fig 4. Raw data of these experiments can be found in (S2 File). MEC: mecillinam, PLU: plumbagin.
Fig 7
Fig 7. The interactions of NIT and PLU (N = 3), indicate modest synergy between the two agents.
(A) Single-agent dose-response curve for NIT; (B) Single-agent dose-response curve for PLU; (C) The interaction landscape of the combinations of NIT and PLU; (D) Synergy scores were calculated by the Bliss independence model and were colored when significant. A detailed description of the various plots is given in Fig 4. Raw data of these experiments can be found in (S2 File). NIT: nitrofurantoin, PLU: plumbagin.
Fig 8
Fig 8. The interactions of CHL and PLU (N = 3), indicate indifference between the two agents.
(A) Single-agent dose-response curve for CHL; (B) Single-agent dose-response curve for PLU; (C) The interaction landscape of the combinations of CHL and PLU; (D) Synergy scores were calculated by the Bliss independence model and were colored when significant. A detailed description of the various plots is given in Fig 4. Raw data of these experiments can be found in (S2 File). CHL: chloramphenicol, PLU: plumbagin.
Fig 9
Fig 9. The interactions of TMP and PLU (N = 3), indicate indifference between the two agents.
(A) Single-agent dose-response curve for TMP; (B) Single-agent dose-response curve for PLU; (C) The interaction landscape of the combinations of TMP and PLU; (D) Synergy scores were calculated by the Bliss independence model and were colored when significant. A detailed description of the various plots is given in Fig 4. Raw data of these experiments can be found in (S2 File). TMP: trimethoprim, PLU: plumbagin.
See this image and copyright information in PMC

Similar articles

See all similar articles

References

    1. Cheung GYC, Bae JS, Otto M. Pathogenicity and virulence of Staphylococcus aureus. Virulence. 2021;12: 547–569. doi: 10.1080/21505594.2021.1878688 - DOI - PMC - PubMed
    1. Dayan GH, Mohamed N, Scully IL, Cooper D, Begier E, Eiden J, et al.. Staphylococcus aureus: the current state of disease, pathophysiology and strategies for prevention. Expert Rev Vaccines. 2016;15: 1373–1392. doi: 10.1080/14760584.2016.1179583 - DOI - PubMed
    1. Foster TJ. Antibiotic resistance in Staphylococcus aureus. Current status and future prospects. FEMS Microbiology Reviews. 2017;41: 430–449. doi: 10.1093/femsre/fux007 - DOI - PubMed
    1. Guo Y, Song G, Sun M, Wang J, Wang Y. Prevalence and Therapies of Antibiotic-Resistance in Staphylococcus aureus. Front Cell Infect Microbiol. 2020;10: 107. doi: 10.3389/fcimb.2020.00107 - DOI - PMC - PubMed
    1. Mlynarczyk-Bonikowska B, Kowalewski C, Krolak-Ulinska A, Marusza W. Molecular Mechanisms of Drug Resistance in Staphylococcus aureus. Int J Mol Sci. 2022;23: 8088. doi: 10.3390/ijms23158088 - DOI - PMC - PubMed

Grants and funding

Y W. Science and Technology Program of Tianjin (22ZYJDSS00100). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Y W. Science and Technology Project of Haihe Laboratory of Modern Chinese Medicine (22HHZYSS00003).The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. S B. Innovation Team and Talents Cultivation Program of National Administration of Traditional Chinese Medicine (ZYYCXTD-D202002). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.