A novel small-molecule compound S-342-3 effectively inhibits the biofilm formation of
Staphylococcus aureus
Authors: Zhang Jiao , Shen Li , Zhou Peiyao , Chen Shuying , Wang Bingjie , Wan Cailin , Han Weihua , Rao Lulin , Zhao Huilin , Wang Xinyi , Wu Chunyang , Shi Junhong , Xiao Yanghua , Song Zengqiang , Yu Fangyou , Lin Chunchan 
Published: October 2023

Staphylococcus aureus
is an important human pathogen in both community and hospital settings that often causes persistent and recurrent infections. The continuous emergence of multidrug-resistant strains and the lag in antibiotic development make the treatment of
S. aureus
more challenging. The biofilm formation of
S. aureus
is an important reason for persistent infection. In this study, we demonstrated that a small-molecule compound S-342-3 can effectively inhibit the biofilm formation of
S. aureus
. The crystal violet semi-quantitative assays revealed that at a sub-minimum inhibitory concentration of 4 µg/mL, S-342-3 reduced
S. aureus
biofilm mass by 57.43%, 52.14%, and 25.49%. Using confocal laser scanning microscopy, we observed that the biofilm was more incompact and less uniform upon the treatment of S-342-3. At a sub-inhibitory concentration (4 µg/mL), the S-342-3 can effectively reduce the production of polysaccharide intercellular adhesin (PIA) and suppress the initial adhesion of cells in the biofilm. Consistently, the results of RT-qPCR revealed that the expression of genes associated with biofilm formation was downregulated by S-342-3 (
P
< 0.05). However, we found that treatment with S-342-3 resulted in a significant decrease in the expression of global regulatory genes
agrA
and
sarA
(
P
< 0.05), which play a key role in promoting cell surface attachment and PIA production in
S. aureus
biofilms. Also importantly, we experimentally proved that the S-342-3 was not toxic to A549 alveolar epithelial cells and the
Galleria mellonella
larvae. Collectively, these results suggest that the S-342-3 may be a promising anti-biofilm drug candidate with excellent biosafety, which can be further explored for its practical application in health care.

IMPORTANCE

Biofilms are an important virulence factor in
Staphylococcus aureus
and are characterized by a structured microbial community consisting of bacterial cells and a secreted extracellular polymeric matrix. Inhibition of biofilm formation is an effective measure to control
S. aureus
infection. Here, we have synthesized a small molecule compound S-342-3, which exhibits potent inhibition of biofilm formation in both MRSA and MSSA. Further investigations revealed that S-342-3 exerts inhibitory effects on biofilm formation by reducing the production of polysaccharide intercellular adhesin and preventing bacterial adhesion. Our study has confirmed that the inhibitory effect of S-342-3 on biofilm is achieved by downregulating the expression of genes responsible for biofilm formation. In addition, S-342-3 is non-toxic to
Galleria mellonella
larvae and A549 cells. Consequently, this study demonstrates the efficacy of a biologically safe compound S-342-3 in inhibiting biofilm formation in
S. aureus,
thereby providing a promising antibiofilm agent for further research.