Objective   To study the in vitro antibacterial activities of the Crataegus pinnatifida (C. p) extracts in combination with 4 kinds of β-lactams antibiotics against methicillin-resistant Staphylococcus aureus (MRSA).    Methods   The dried fruits of C. p were extracted with 75% EtOH followed by being extracted successively with EtOAc and n-BuOH

then the obtained n-BuOH layer was subjected to macroporous D-101 and then to silica gel column chromatography. Finally we obtained the active component of C. p (CP)

and validate the in vitro antibacterial activities of the component CP in combination with 4 kinds of β-lactams antibiotics against MRSA.    Results    The minimal inhibitory concentration (MIC) of Oxacillin

Ampicillin sodium-sulbactam sodium

Ampicillin

Cephazolin and CP component were 256

512

512

128 and 1 024 μg/ml

However

when combined with the C. p component at its sub-MIC (128 μg/ml)

the MIC of the above 4 kinds of β-lactams antibiotics was as lower as 2

32

16 and 2 μg/ml respectively.The fractional inhibitory concentration (FIC) of them were 0.13

0.19

0.16 and 0.14

respectively.    Conclusion   C. p component has synergistic antibacterial effect on MRSA when combined with β-lactams antibiotics.