Bacteriostatic Activity And Mechanism Of Lemon Extract Against Multiresistant Staphylococcus Aureus

Staphylococcus auresus is primary pathogen in hospital. Because of abuse of broad-spectrum antibacterial drugs, staphycoccoccus aureus isolates are mostly multi-drug resistant. So it is important to develop new drugs different from the antibiotics. Recent studies show citrus plants exhibit the bacteriostatic activity due to little environmental pollution and toxic side effects. The aim of our study is to observe the bacteriostatic activity of lemon extract and investigate the relative mechanisms.The spectrum of multi-drug resistant Staphylococcus aureus isolates were determined by Microsdan autoscan-4 automatic instrumment. Firstly, Disc diffusion method and dilution method were conducted to detect the bacteriostatic activity of lemon extract. Lemon extract exhibited inhibitory effect on the clinic multiresistant Staphylococcus. aureus isolate. The diameters of zone of inhibition were larger than 30 mm and the minimal inhibitory concentration (MIC) was 0.16μl/ml respectively. 1/2 MIC was applied to the observation of bacterial cell wall and the following experiments about the bacteriostatic mechanisms. Lemon extracts were added to the prepared biofilm of Staphylococcus aureus, the bacterial colonies were calculated to evaluate the bacteriastatic effect at the different times(60min,120min,180min). the inhibitory effect is the strongest at 180min.Furthermore, the inhibitory mechanisms were investigaed. After the action of 1/2 MIC of lemon extract, electrophoretic patterns of cell protein of Staphylococcus aureu, DNA restriction enzyme map by EcoR I, and gyrA mutation of Staphylococcus aureu on the drug susceptibility to fluoroquinolones were detected by SDS-PAGE, enzyme-restriction method and PCR-RFLP respectively. As a result, apparent shift in the SDS-PAGE map and DNA of the Staphylococcus aureus by EcoR I enzyme appeared. However, no alteration was observed in the gyrA mutation. In addition, the shape of the bacterial cell wall was observed in the hypoosmotic enviromment at different times (5min, 10min and 15min). Bacterial cell wall became swollen and appeared as a baloon at 15 min as compared with the control. The activities of lactate dehydrogenase(LDH), alanine amino-transferase(ALT) and aspartate aminotransferase(AST) were assayed. However, no changes were observed in the activities of the above enzymes.In summary, lemon extract exhibits bacteriostatic activity against multiresistant Staphylococcus aureus and relative biofilm, which indicate good prospect in the treatment of infectious diseases.