Shigella flexneri

[NiFe] Hydrogenases—Phagolysosomal Acid Combat#

Possesses H2-uptake hydrogenases Hya and Hyb that combat acid stress during intracellular survival in macrophages.^{[1]Role of Nickel in Microbial PathogenesisRobert J. Maier, Stéphane L. Benoit · 2019Open reference 1 ↓}

Hya activity is three-fold activated within minutes of acid exposure—a rapid-response defense mechanism that provides immediate energy for maintaining cytoplasmic pH homeostasis.

H2 oxidation generates PMF (proton motive force) that powers proton efflux pumps and ATP synthesis under the energy-limiting conditions of the phagolysosome.

This represents a distinct use of hydrogenase compared to Helicobacter pylori (gastric colonization energy) or Campylobacter jejuni (intestinal mucosal competition): Shigella uses H2 metabolism specifically to survive intracellular killing.

Iron Acquisition#

Produces aerobactin and enterobactin siderophores for iron scavenging. Iron acquisition is essential for intracellular replication within epithelial cells and macrophages. Host lactoferrin and transferrin restrict iron availability at the intestinal mucosal surface.

Pathogenesis#

Shigella invades colonic epithelial cells via a Type III secretion system (T3SS), then escapes the phagosome into the cytoplasm. Spreads cell-to-cell using actin-based motility (IcsA/VirG), avoiding extracellular immune surveillance. During initial uptake by macrophages, the bacterium must survive the phagolysosomal acid environment—this is where nickel (Ni)-hydrogenase is critical.

Induces massive inflammatory response with neutrophil infiltration, epithelial destruction, and bloody diarrhea.

Clinical Significance#

Bacillary dysentery: bloody diarrhea with mucus, fever, abdominal cramps. As few as 10 organisms can cause disease (extremely low infectious dose). Children under 5: bear the greatest burden; shigellosis is a leading cause of diarrheal death in this age group.

Antibiotic resistance: multidrug-resistant Shigella is increasingly common; WHO lists fluoroquinolone-resistant Shigella as a priority pathogen. Reactive arthritis: post-infectious joint Metal-Driven Inflammation, similar to Campylobacter jejuni.

Metal exposure in endemic regions (contaminated water sources containing Heavy Metals) may promote Enterobacteriaceae enrichment in the gut, potentially favoring Shigella colonization.^{[2]Toxic and Essential Metals: Metabolic Interactions with the Gut Microbiota and Health ImplicationsQinheng Zhu, Boyan Chen, Fu Zhang et al. · 2024Open reference 2 ↓}