Sub-Inhibitory Concentrations of Amoxicillin and Tylosin Affect the Biofilm Formation and Virulence of Streptococcus suis

Abstract

Streptococcus suis (S. suis) can form a protective biofilm during infection and lead to prolonged disease. Oral antibiotics are often used for treatment in clinical practice, but sub-inhibitory concentration levels often exist due to low oral absorption rate, resulting in disease deterioration. The purpose of this study was to investigate the effects of Amoxicillin and Tylosin on the biofilm formation and virulence of S. suis HA9801 at sub-inhibitory concentration. We first determined that the test groups (1/4MIC Amoxicillin and Tylosin) could significantly increase the amount of biofilm formation without affecting bacterial growth. The LD50 value of the test groups was significantly higher than that of the control group in the mouse infection model. In the mouse infection model, the LD50 value of the experimental group was significantly increased, but the tissue bacterial load was significantly decreased. Further RT-PCR analysis showed that the expression levels of virulence-related genes in the experimental group were significantly reduced. Our study suggests that both Amoxicillin and Tylosin at sub-inhibitory concentrations could enhance the biofilm formation ability of S. suis HA9801 and reduce its virulence to form persistent infection.

Transcriptome analysis of the biofilm formation mechanism of Vibrio parahaemolyticus under the sub-inhibitory concentrations of copper and carbenicillin

“…Among them, the use of sub-concentration (below MICs, also referred to as sub-lethal levels) antibiotics is a critical reason for promoting the formation of bacterial biofilms (Zhang et al, 2018;Zuo et al, 2022). A study proved that exposure to sub-inhibitory concentrations of amoxicillin and tylosin increased the biofilm formation of S. suis (Zuo et al, 2022). Lactobacillus plantarum also showed similar results after the use of sub-inhibitory concentrations of gentamicin, kanamycin and streptomycin (George and Halami, 2017).…”

“…Therefore, interfering with biofilm formation or stimulating its dissociation is an attractive strategy to combat bacterial infections and prevent their chronic development. Among them, the use of sub-concentration (below MICs, also referred to as sub-lethal levels) antibiotics is a critical reason for promoting the formation of bacterial biofilms (Zhang et al, 2018;Zuo et al, 2022). A study proved that exposure to sub-inhibitory concentrations of amoxicillin and tylosin increased the biofilm formation of S. suis (Zuo et al, 2022).…”