Objective: To observe the effects of New Dayuan powder (NDYP) on Methicillin-resistant Staphylococcus aureus (MRSA) biofilms and the embedded bacteria in vitro.
Methods: 2,3-Bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) assays were used to study the effects of NDYP on developing MRSA biofilms: 100 μL of bacterial culture and 100 μL drug solution were added to wells of 96-well plates. After 24 h of incubation, the plates were washed and XTT-phenazine methyl sulfate (PMS) was added to enable counting of the number of live bacteria in biofilms using a microplate reader. XTT assays were also used to explore the effects of NDYP on mature MRSA biofilms: 100 μL of bacterial culture were added to wells of 96-well plates. Bacteria were cultured in the plates for 24 h, and then drug solution was added. The plates were cultured for another 24 h, and then XTT-PMS was added to detect the number of live bacteria in the biofilms. Scanning electron microscopy (SEM) was used to observe the effects of NDYP on mature MRSA biofilms: washed and sterilized glass coverslips were added to 24-well plates. Bacterial culture was added. After 24 h of incubation, drug solution was added. After another 24 h of incubation, the samples were observed by SEM.
Results: XTT assays showed that the number of live bacteria in both developing and mature MRSA biofilms decreased significantly (P < 0.01) after the administration of NDYP. SEM images showed that NDYP could destroy the structure of the bacteria and resulted in uneven thickness of MRSA biofilms.
Conclusion: In vitro, NDYP has obvious inhibitory effects on the formation of MRSA biofilms and on mature biofilms.
Keywords: Biofilms; In vitro techniques; Methicillin-resistant Staphylococcus aureus; New Dayuan powder.