Proteome Analyses of Cellular Proteins in Methicillin-Resistant Staphylococcus aureus Treated with Rhodomyrtone, a Novel Antibiotic Candidate

Wipawadee Sianglum,Kanokwan Kittiniyom,Supayang P Voravuthikunchai,Wijit Wonglumsom,Potjanee Srimanote

doi:10.1371/journal.pone.0016628

Abstract

The ethanolic extract from Rhodomyrtus tomentosa leaf exhibited good antibacterial activities against both methicillin-resistant Staphylococcus aureus (MRSA) and S. aureus ATCC 29213. Its minimal inhibitory concentration (MIC) values ranged from 31.25–62.5 µg/ml, and the minimal bactericidal concentration (MBC) was 250 µg/ml. Rhodomyrtone, an acylphloroglucinol derivative, was 62.5–125 times more potent at inhibiting the bacteria than the ethanolic extract, the MIC and MBC values were 0.5 µg/ml and 2 µg/ml, respectively. To provide insights into antibacterial mechanisms involved, the effects of rhodomyrtone on cellular protein expression of MRSA have been investigated using proteomic approaches. Proteome analyses revealed that rhodomyrtone at subinhibitory concentration (0.174 µg/ml) affected the expression of several major functional classes of whole cell proteins in MRSA. The identified proteins involve in cell wall biosynthesis and cell division, protein degradation, stress response and oxidative stress, cell surface antigen and virulence factor, and various metabolic pathways such as amino acid, carbohydrate, energy, lipid, and nucleotide metabolism. Transmission electron micrographs confirmed the effects of rhodomyrtone on morphological and ultrastructural alterations in the treated bacterial cells. Biological processes in cell wall biosynthesis and cell division were interrupted. Prominent changes including alterations in cell wall, abnormal septum formation, cellular disintegration, and cell lysis were observed. Unusual size and shape of staphylococcal cells were obviously noted in the treated MRSA. These pioneer findings on proteomic profiling and phenotypic features of rhodomyrtone-treated MRSA may resolve its antimicrobial mechanisms which could lead to the development of a new effective regimen for the treatment of MRSA infections.

Highlights

Staphylococcus aureus is well-evidenced as a major human pathogen
S. aureus has been a crucial cause of community-acquired infections which may result in morbidity and mortality [2,3]
In order to assess the antibacterial potency of ethanolic extract of R. tomentosa and rhodomyrtone on S. aureus, susceptibility test using broth microdilution was employed

Summary

Introduction

Staphylococcus aureus is well-evidenced as a major human pathogen. The organism commonly involves in skin and soft tissue infections such as pimples, boils, furuncles, cellulites, folliculitis, impetigo, carbuncles, scalded skin syndrome, and abscesses. To provide insights into the antibacterial mechanisms of this potential antibacterial drug, proteomic technologies were used to investigate the effects of rhodomyrtone on protein expression in treated MRSA cells. A total of 380 MRSA protein spots were observed in the cultures after treatment with rhodomyrtone while 301 spots were detected in cells grown in compound-free cultural media.

Results

Conclusion