Uptake of plasmid reduces the adaptation of Shigella flexneri to disinfectants and increases transmission of antibiotic resistance genes

Antibiotic-resistance pathogens pose an increasing threat to humanity. But, whether pathogens can increase their resistance to disinfectants with their antibiotic resistances increasing owing to conjugation. In this study, Shigella flexneri (S. flexneri) was selected as the representative pathogenic recipient. Under the stress treatments of glutaraldehyde solution (GS), didecyldimethylammonium bromide solution (DS), and a combination of these two, the horizontal transfer of RP4 plasmid to S. flexneri resulted in reduced adaptation to these treatments. The abundance of sulfanilamide resistance genes (SRGs), disinfectant resistance genes (DRGs) and intI1 in S. flexneri transconjugant increased by 30.0%–322%, 18.3%–119% and 28.2%–136%, respectively. intI1 may be integrated into the plasmid, leading to an increase of higher gene abundance and significant positive correlations with tetM, tetO, sul1, sul2, qacE, qacΔE1, tetA, tnpR and aphA in transconjugant (p ≤ 0.05). A modest reduction in the conjugation frequency protected the bacteria from the transition invasion of GDS disinfectants and promoted the stable presence of RP4 plasmids in S. flexneri. Specifically, at the concentration of 0.1 mg/L, GDS facilitated plasmid transfer and then promoted the proliferation of intI1 by increasing cell membrane permeability, cellular viability and extracellular polymeric substance (EPS) content in surviving bacteria, resulting in an increased abundance of antibiotic resistance genes (ARGs) and DRGs in transconjugant. Therefore, resistant plasmid effectively improves the response ability of pathogenic bacteria to disinfectants, so that bacterium have the potential to develop multiple antibiotics resistance.