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

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.

Effect of the Extract of Endophytic fungus, Nigrospora sphaerica CL-OP 30, Against the Growth of Methicillin- Resistant <i>Staphylococcus aureus</i> (MRSA) and <i>Klebsiella pneumonia</i> cells

“…The extract caused formation of pit, irregular shape, deformed septa, cell wall disintegration, and loss of cytoplasm contents. Similar effects of cell wall had been described for oritavancin, rhodomyrtone and marine bacteria derived antibiotic [18][19][20].…”

Time-kill profiles and cell-surface morphological effects of crude Polycephalomyces nipponicus Cod-MK1201 mycelial extract against antibiotic-sensitive and -resistant <i>Staphylococcus aureus</i>

“…Similar cell wall effects have been reported in S. aureus treated with bacteria-derived antibiotics [24,25].…”

Inhibition of staphyloxanthin biosynthesis in Staphylococcus aureus by rhodomyrtone, a novel antibiotic candidate

“…The results indicated that rhodomyrtone inhibited the synthesis of DnaK protein in the treated pathogens (Sianglum et al, 2011). DnaK protein is associated with a wide variety of cellular processes (Hu et al, 2006;Kurt et al, 2006;Singh et al, 2007;Al Refaii & Alix, 2009;René & Alix, 2011), and deletion of dnaK in S. aureus demonstrated an increase in susceptibility to oxidative stress conditions and reduced carotenoid production (Singh et al, 2007).…”

“…The MIC and minimum bactericidal concentration values of rhodomyrtone against MRSA range from 0.39 to 0.78 mg ml 21 , which is very close to those of vancomycin (Limsuwan et al, 2009b). Recently, protein profiling of rhodomyrtone-treated MRSA demonstrated alterations in the expression of several major functional classes of bacterial protein (Sianglum et al, 2011;Visutthi et al, 2011). Therefore, the objective of the present study was to investigate inhibition of pigment synthesis in S. aureus after treatment with rhodomyrtone.…”