Disruption of the human gut microbiota by antibiotics can lead to Clostridium difficile (CD)-associated diarrhea. CD overgrowth and elevated CD toxins result in gut inflammation. Herein, we report that a gut symbiont, Bacteroides thetaiotaomicron (BT), suppressed CD toxin production. The suppressive components are present in BT culture supernatant and are both heat- and proteinase K-resistant. Transposon-based mutagenesis indicated that the polysaccharide metabolism of BT is involved in the inhibitory effect. Among the genes identified, we focus on the methylerythritol 4-phosphate pathway gene gcpE, which supplies the isoprenoid backbone to produce the undecaprenyl phosphate lipid carrier that transports oligosaccharides across the membrane. Polysaccharide fractions prepared from the BT culture suppressed CD toxin production in vitro; the inhibitory effect of polysaccharide fractions was reduced in the gcpE mutant (ΔgcpE). The inhibitory effect of BT-derived polysaccharide fraction was abrogated by lysozyme treatment, indicating that cellwall-associated glycans are attributable to the inhibitory effect. BT-derived polysaccharide fraction did not affect CD toxin gene expression or intracellular toxin levels. An autolysis assay showed that CD cell autolysis was suppressed by BT-derived polysaccharide fraction, but the effect was reduced with that of ΔgcpE. These results indicate that cell wall-associated glycans of BT suppress CD toxin release by inhibiting cell autolysis.

The global prevalence of pulmonary infections caused by non-tuberculous Mycobacteria (NTM), particularly the Mycobacterium avium complex (MAC), is increasing. Since NTM are ubiquitous in moist environments and resistant to standard disinfectants, this study evaluated the efficacy of chlorous acid water (CAW) against them. CAW demonstrated superior sanitizing effects compared to sodium hypochlorite (NaClO). It efficiently inactivated NTM at free available chlorine concentrations of 25 mg/L without organic matter and 100 mg/L with organic matter. In contrast, NaClO at 1000 mg/L failed to inactivate NTM in the presence of organic matter. MAC showed higher resistance to both agents compared to other NTM species. Mechanistically, the bactericidal effect of CAW did not correlate with DNA degradation. While prolonged exposure induced DNA damage, the primary mode of action was identified as a reduction in membrane potential, ATP production, and reactive oxygen species levels without altering cell morphology. These results indicate that CAW inactivates NTM effectively by damaging membrane components and the respiratory chain, rather than targeting DNA.

The global prevalence of pulmonary infections caused by non-tuberculous Mycobacteria (NTM), particularly the Mycobacterium avium complex (MAC), is increasing. Since NTM are ubiquitous in moist environments and resistant to standard disinfectants, this study evaluated the efficacy of chlorous acid water (CAW) against them. CAW demonstrated superior sanitizing effects compared to sodium hypochlorite (NaClO), efficiently inactivating NTM at 100 mg/L free available chlorine even in the presence of organic matter, where 1000 mg/L NaClO failed. Instead, subcellular fractionation and protein analysis revealed that CAW penetrates the cell to induce extensive aggregation of internal functional proteins, leading to the rapid collapse of membrane potential and ATP production. Furthermore, CAW exhibited significantly lower cytotoxicity toward human lung-derived A549 cells than NaClO. These results indicate that CAW inactivates NTM effectively by targeting internal protein stability and the respiratory chain, offering a potent and safer disinfection strategy for clinical and domestic environments.