Novel hypothesis for infant methemoglobinemia: Survival and metabolism of nitrite-producers from vegetables under gastrointestinal stress and intestinal adhesion.

Infants have digestive environments that are more favorable for microbial proliferation and subsequent endogenous nitrite production than those of adults, but direct evidence of this has been lacking. In this study, we propose a novel epidemiology of infant methemoglobinemia by demonstrating the risk posed by nitrite-producers in the gastrointestinal tract. Nitrite-producers from vegetables (n = 323) were exposed to stress factors of the gastrointestinal environment (gastric pH, intestinal bile salts, anaerobic atmosphere) reflecting 4 different postnatal age periods (Neonate, ≤1 month; Infant A, 1-3 months; Infant B, 3-6 months; Infant C, 6-12 months). "High-risk" strains with a nitrate-to-nitrite conversion rate of ≥1.3 %, the minimum rate corresponding to nitrite overproduction, under the Neonate stress condition were analyzed for intestinal adhesion. Among all the phyla, Pseudomonadota achieved the highest survival (P < 0.05; survival rate of 51.3-71.8 %). Possible cross-protection against bile resistance due to acid shock was observed for all the phyla. All the high-risk strains exhibited moderate autoaggregation (14.0-36.4 %), whereas only a few exhibited satisfactory surface hydrophobicity (>40 %). The Pantoea agglomerans strain strongly adhered to Caco-2 cells (7.4 ± 1.1 %). This study showed the ability of the Pantoea, Enterobacter, and Klebsiella strains to survive under gastrointestinal stress for ≤12 months, to excessively produce nitrite under neonatal stress conditions, and to settle in the human intestine. To our knowledge, this is the first study to reveal the role of the natural flora of vegetables in the epidemiology of infant methemoglobinemia through a multilateral approach.