Abstract
Purpose: To examine the effect of crude Polycephalomyces nipponicus Cod-MK1201 mycelial extract on the viability and cell surface morphology of methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA). Methods : Time-kill assays were conducted by incubating test bacteria with the extract and sampling at selected time points within a 24 h period. The effects of the extract on MSSA and MRSA ultrastructure were determined using a scanning electron microscope (SEM). Results : Time-kill assay data indicate a bactericidal effect against both strains of staphylococci. The extracts were rapidly bactericidal at concentrations of 1 x MIC and 2 x MIC, achieving complete elimination of the test bacterial strains within 2 h. SEM micrographs of S. aureus taken after treatment with various concentrations of the extract revealed extensive morphological alterations to the cell surface of both MSSA and MRSA. Conclusion : The results confirm the antibacterial activity of P. nipponicus Cod-MK1201 mycelial extract. Further research may allow this to be developed as an alternative therapy to alleviate S. aureus infection. Keywords : Antibacterial activity, Polycephalomyces nipponicus, Staphylococcus aureus, Time-kill assay, Cell surface morphology
Highlights
Staphylococcus aureus is a major human pathogen, causing pyogenic infections such as abscesses, and even fatal septicemia [1]
After 24 h incubation with 0.5 x MIC (1.56 mg/mL) of the extract, a 3 log10 CFU/mL reduction in viability of S. aureus Department of Medical Sciences Thailand (DMST) 2933 occurred (Figure 1A), indicating the extract is bactericidal against this strain of methicillin-susceptible Staphylococcus aureus (MSSA)
Comparable results were not obtained with 0.5 x MIC extract and S. aureus DMST 20651 (Figure 1B), indicating this concentration of extract is bacteriostatic against Methicillin-resistant S. aureus (MRSA)
Summary
Staphylococcus aureus is a major human pathogen, causing pyogenic infections such as abscesses, and even fatal septicemia [1]. Methicillin-resistant S. aureus (MRSA) infections have become an important problem in both the hospital and community requiring vancomycin for effective clinical treatment [2,3]. Cordyceps is a genus of entomopathogenic fungi that are used in traditional Chinese medicine for various health effects including immunomodulatory, anticancer, antioxidant, anti-inflammatory and antimicrobial activities [10,11,12,13]. The methanol extract from Cordyceps militaris has strong antibacterial and antifungal activity too [10]. These findings indicate that many entomopathogenic fungi produce bioactive compounds effective against microbial pathogens. Time-kill data and information on the morphological effects of these extracts on bacterial cells is limited
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