Environmental peracetic acid increases antibiotic resistance in Streptococcus Suis

Disinfectants in the environment have important impacts on the occurrence of antibiotic resistant bacteria, posing a new threat to public health. Streptococcus suis (S. suis) can survive in the environment for three months and carries antibiotic resistance genes. However, it remains unclear whether disinfectants directly induce antibiotic resistance in S. suis. Here, we conducted induction experiments on the S. suis standard strain (CVCC609) with eight disinfectants at different concentrations and investigated their effects on the antibiotic resistance mechanism of S. suis. The results showed that only 64 mg L⁻¹ peracetic acid (PAA) led to an increase (8-fold) in S. suis resistance to tiamulin (TIA) with genetic stability. The treatment also induced significant changes in the morphology and capsule of the mutant strains, as well as triggered an increase in reactive oxygen species and biofilms in bacterial cells, resulting in an emergency response. Moreover, PAA significantly decreased the cell membrane permeability and led to slight changes in the adenosine triphosphate level. The key differentially expressed genes are closely related to these resistance mechanisms. These results reveal the co-selection mechanism of S. suis resistance to PAA and TIA, and highlight the importance of standardized application of disinfectants in livestock and poultry farming.