Abstract
Methicillin-resistant Staphylococcus aureus (MRSA), along with other antibiotic resistant bacteria, has become a significant social and clinical problem. There is thus an urgent need to develop naturally bioactive compounds as alternatives to the few antibiotics that remain effective. Here we assessed the in vitro activities of bee venom (BV), alone or in combination with ampicillin, penicillin, gentamicin or vancomycin, on growth of MRSA strains. The antimicrobial activity of BV against MRSA strains was investigated using minimum inhibitory concentrations (MIC), minimum bactericidal concentrations (MBC) and a time-kill assay. Expression of atl which encodes murein hydrolase, a peptidoglycan-degrading enzyme involved in cell separation, was measured by reverse transcription-polymerase chain reaction. The MICs of BV were 0.085 µg/mL and 0.11 µg/mL against MRSA CCARM 3366 and MRSA CCARM 3708, respectively. The MBC of BV against MRSA 3366 was 0.106 µg/mL and that against MRSA 3708 was 0.14 µg/mL. The bactericidal activity of BV corresponded to a decrease of at least 3 log CFU/g cells. The combination of BV with ampicillin or penicillin yielded an inhibitory concentration index ranging from 0.631 to 1.002, indicating a partial and indifferent synergistic effect. Compared to ampicillin or penicillin, both MRSA strains were more susceptible to the combination of BV with gentamicin or vancomycin. The expression of atl gene was increased in MRSA 3366 treated with BV. These results suggest that BV exhibited antibacterial activity and antibiotic-enhancing effects against MRSA strains. The atl gene was increased in MRSA exposed to BV, suggesting that cell division was interrupted. BV warrants further investigation as a natural antimicrobial agent and synergist of antibiotic activity.
Highlights
Since 1959 when methicillin was introduced to treat infections caused by penicillin-resistantStaphylococcus aureus, the incidence of methicillin resistance among staphylococcal strains has rapidly increased [1]
Compared to ampicillin or penicillin, both methicillin-resistant Staphylococcus aureus (MRSA) strains were more susceptible to the combination of bee venom (BV) with gentamicin or vancomycin
These results suggest that BV exhibited antibacterial activity and antibiotic-enhancing effects against MRSA strains
Summary
Since 1959 when methicillin was introduced to treat infections caused by penicillin-resistant. It is known that antibiotic-induced killing of Staphylococcus aureus involves a novel regulator of murein hydrolase activity [4]. The most prominent murein hydrolase in the pathogenicity of Staphylococcus aureus is atl gene for its role in cell separation. BV is comprised of a number of bioactive substances such as melittin, apamin, adolapin and mast cell degranulating peptide [7] It contains biologically active amines (histamine, epinephrine) and a few non-peptide components including lipids, carbohydrates and free amino acids [8]. To investigate whether interrupted cell division was due to defective cell separation, the effect of BV on the activity of murein hydrolases was determined based on the expression of atl measured by reverse transcription-polymerase chain reaction (RT-PCR)
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