Objective      To investigate the effects of andrographolide (Andro) against

Staphylococcus aureus

(

S. aureus

) biofilms and its synergistic activity in combination with gentamicin (GEN).       Methods      Turbidimetric method was used to detect the effect of Andro (100 μg/ml

) on

S. aureus

growth curve.

S. aureus

ATCC25923 and 2 clinical strains CY001 and CY002 were used for biofilm formation

in vitro

dividing into a control group

an Andro intervention group

a GEN intervention group and an Andro combined with GEN intervention group. A microplate reader was used to detect the OD600nm values and indirectly observe the biofilm formation ability of each group. Scanning electron microscopy (SEM) was used to directly observe morphology of biofilms treated with different interventions.       Results      Under the action of 100 μg/mL Andro

the growth curve of each strain had no difference as compared to the control group (

P

0.05). Except for CY002 that could not form biofilm

there was no significant difference between the groups (

P

0.05). The biofilms of CY001 and ATCC25923 in each intervention groups were less than those in the control group (

P

0.001). The inhibition effect of 100 μg/mL Andro was stronger than that of 50 μg/ml GEN (

P

=0.001

P

=0.003)

and the inhibitory effect of the combination intervention group was obviously stronger than that of the Andro intervention group and GEN intervention group (

P

0.05). Morphology observation under SEM prompted that each intervention condition had inhibitory effect on

S. aureus

biofilm

while the combination intervention group had the strongest effect.       Conclusion      Andro has no significant effect on the growth of

S. aureus

but has excellent inhibitory effect on the biofilms of S. aureus. Moreover

Andro and GEN have synergistic inhibitory effect.