Ann Lab Med.  2016 Mar;36(2):111-116. 10.3343/alm.2016.36.2.111.

Synergistic Anti-bacterial Effects of Phellinus baumii Ethyl Acetate Extracts and beta-Lactam Antimicrobial Agents Against Methicillin-Resistant Staphylococcus aureus

• Hong SB
• Rhee MH
• Yun BS
• Lim YH
• Song HG
• Shin KS

• KMID: 2373509
• DOI: http://doi.org/10.3343/alm.2016.36.2.111

Abstract

BACKGROUND
The development of new drugs or alternative therapies effective against methicillin-resistant Staphylococcus aureus (MRSA) is of great importance, and various natural anti-MRSA products are good candidates for combination therapies. We evaluated the antibacterial activities of a Phellinus baumii ethyl acetate extract (PBEAE) and its synergistic effects with beta-lactams against MRSA.
METHODS
The broth microdilution method was used to determine the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of the PBEAE. The PBEAE synergistic effects were determined by evaluating the MICs of anti-staphylococcal antibiotic mixtures, with or without PBEAE. Anti-MRSA synergistic bactericidal effects of the PBEAE and beta-lactams were assessed by time-killing assay. An ELISA was used to determine the effect of the PBEAE on penicillin binding protein (PBP)2a production.
RESULTS
The MICs and MBCs of PBEAE against MRSA were 256-512 and 1,024-2,048 microg/mL, respectively. The PBEAE significantly reduced MICs of all beta-lactams tested, including oxacillin, cefazolin, cefepime, and penicillin. However, the PBEAE had little or no effect on the activity of non-beta-lactams. Time-killing assays showed that the synergistic effects of two beta-lactams (oxacillin and cefazolin) with the PBEAE were bactericidal in nature (Deltalog10 colony forming unit/mL at 24 hr: 2.34-2.87 and 2.10-3.04, respectively). The PBEAE induced a dose-dependent decrease in PBP2a production by MRSA, suggesting that the inhibition of PBP2a production was a major synergistic mechanism between the beta-lactams and the PBEAE.
CONCLUSIONS
PBEAE can enhance the efficacy of beta-lactams for combined therapy in patients infected with MRSA.

Keyword

Anti-bacterial; beta-lactam; MRSA; Phellinus baumii; Synergy

MeSH Terms

Acetates/chemistry
Agaricales/*chemistry/metabolism
Anti-Infective Agents/chemistry/*pharmacology
Drug Synergism
Enzyme-Linked Immunosorbent Assay
Methicillin-Resistant Staphylococcus aureus/*drug effects/metabolism
Microbial Sensitivity Tests
Penicillin-Binding Proteins/analysis/metabolism
Plant Extracts/chemistry/*pharmacology
beta-Lactams/*pharmacology
Acetates
Anti-Infective Agents
Penicillin-Binding Proteins
Plant Extracts
beta-Lactams

Figure

• 

  Fig. 1 Synergistic effects of 1/2 minimal inhibitory concentration (MIC) the P. baumii ethyl acetate extract alone or combined with oxacillin (A) or cefazolin (B) against a clinical MRSA strain (6432) determined by using the time-killing assay. The results are presented as means±standard deviations from triplicate assays.Abbreviation: CFU, colony-forming unit.

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