Characterization of in vitro antimicrobial activity of gyrophoric acid isolated from Parmotrema indicum on methicillin-resistant Staphylococcus aureus

Aug 21, 2026

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Methicillin-resistant Staphylococcus aureus (MRSA) is linked to severe, hard-to-treat infections that require new antibiotics. This study evaluates the in vitro antimicrobial activity of gyrophoric acid isolated from the lichen Parmotrema indicum against MRSA. Results show activity mainly against Gram-positive bacteria and Candida albicans, with an MRSA MIC of 32 µg/mL and bactericidal effects at 8× MIC after 24 hours, along with low resistance emergence and synergism with ampicillin.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages10

Reading Time25 min

AccessFree to download

Abstract

Introduction

ESKAPE pathogens and MRSA urgency for new antibiotics

Lichens as sources of antimicrobial secondary metabolites

Need for hit validation and declaration stage

Materials and Methods

Results

Minimum inhibitory concentration and bactericidal effect

Resistance frequency and ampicillin synergism

Selective toxicity and biofilm inhibition

Morphological observations by scanning electron microscopy

Conclusion

Journal of Applied Pharmaceutical Science Vol. 14(03), pp 045-054, March, 2024 Available online at [http://www.japsonline.com](http://www.japsonline.com) [DOI: 10.7324/JAPS.2024.163764](DOI: 10.7324/JAPS.2024.163764)[ ](DOI: 10.7324/JAPS.2024.163764)ISSN 2231-3354 Characterization of in vitro antimicrobial activity of gyrophoric acid isolated from Parmotrema indicum on methicillin-resistant Staphylococcus aureus Thang Truong Le1,2, Huy Thuc Duong3, Chuong Hoang Nguyen1* 1Faculty of Biology-Biotechnology, University of Science, VNUHCM, Ho Chi Minh City, Vietnam. 2Center for Research and Application in Bioscience, Ho Chi Minh City, Vietnam. 3Faculty of Chemistry, Ho Chi Minh City University of Education, Ho Chi Minh City, Vietnam. | ARTICLE HISTORY | | --- | | Received on: 04/08/2023
Accepted on: 24/01/2024
Available Online: 05/03/2024 | Key words: Gyrophoric acid, antimicrobial activity, MRSA, Parmotremaindicum, selective bacterial toxicity. ABSTRACT Methicillin-resistant Staphylococcus aureus (MRSA) is a group of pathogenic bacteria associated with hard-to-treat infections in humans, which require new, effective antibiotics for treatment. In the search for new candidates for antibiotics against MRSA, we investigated the in vitro antimicrobial activity of gyrophoric acid isolated from the lichen Parmotrema indicum on MRSA. Gyrophoric acid exerted antimicrobial activity mainly on Gram-positive bacteria and one fungal strain, Candida albicans. The minimum inhibitory concentration (MIC) value for MRSA was 32 µg/ml, and at 8 × MIC, gyrophoric acid showed a bactericidal effect on MRSA after 24 hours of culture. This compound showed a low mutation frequency of 2.4 × 10−9 by a single-step resistance test. Gyrophoric acid expressed a synergistic effect with the antibiotic ampicillin that reduced 16-fold the MIC value of ampicillin on MRSA. Gyrophoric acid showed selective toxicity towards MRSA other than human cell lines, with the selective index ranging from 5.43-fold to 8.78-fold. Biofilm formation of MRSA was inhibited by gyrophoric acid starting from the concentration of 2 × MIC, and the biofilm inhibition was 94% at 16 × MIC of gyrophoric acid. The morphology of MRSA under treatment with gyrophoric acid showed a demolition of the cell envelope of the strain revealed by scanning electron microscope. The results of this study proved that gyrophoric acid is a good compound in the “hit validation and declaration” stage of the development procedure of a new antibiotic candidate for MRSA infection treatment. INTRODUCTION ESKAPE pathogens are virulent bacteria with multidrug resistance characteristics [1] . They are the leading cause of nosocomial infections in the world, which is associated with a high risk of mortality [2]. These pathogens have recently been identified by the World Health Organization in the list of 12 bacteria that urgently need new antibiotics for treatment. The urgency of new antibiotics for these twelve bacteria is classified into critical, high, and medium-priority [3] . Among ESKAPE *Corresponding Author Chuong Hoang Nguyen, Faculty of Biology-Biotechnology, University of Science, VNUHCM, Ho Chi Minh City, Vietnam. E-mail: [nhchuong @ hcmus.edu.vn](nhchuong @ hcmus.edu.vn) pathogens, methicillin-resistant Staphylococcus aureus (MRSA) is on the list of high-priority groups [3] . In association with different virulent characteristics such as toxins, adhesins, enzymes, and immunomodulators [4], the antimicrobial resistance of MRSA has myriad mechanisms to the major antibiotic classes [5] that confer challenges to the treatment decision of this bacterial infection. Therefore, new antimicrobial candidates are currently sought from several sources (i.e., from plants, fungi, bacteria, and synthetic compounds) [6] to meet the crucial requirements. Besides the common sources for new antibiotics searching as mentioned above, lichens become highly interesting because these symbionts

FAQs

What does the study evaluate about gyrophoric acid?

It evaluates the in vitro antimicrobial activity of gyrophoric acid isolated from Parmotrema indicum against MRSA and related microorganisms.

What MIC and bactericidal effect were reported for MRSA?

The MIC value for MRSA was 32 µg/mL, and at 8× MIC gyrophoric acid showed a bactericidal effect after 24 hours of culture.

How did gyrophoric acid affect resistance development and synergy with antibiotics?

Gyrophoric acid showed a low mutation frequency (2.4 × 10−9) in a single-step resistance test and exhibited synergistic effects with ampicillin, reducing ampicillin MIC by 16-fold against MRSA.

Does gyrophoric acid inhibit MRSA biofilm and is toxicity selective?

Biofilm formation was inhibited starting from 2× MIC, reaching 94% inhibition at 16× MIC. Selective toxicity was observed toward MRSA over human cell lines, with a selective index range of 5.43- to 8.78-fold.

Aug 21, 2026

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