The Real Cause of SIBO — Why Everything You’ve Been Told Is Incomplete — Why the Bacteria Are Far More Sophisticated Than You Have Been Told

The organisms that establish in SIBO are not passive passengers. They are metabolically sophisticated survivors optimized over billions of years to persist in hostile environments. The assumption that a two-week antibiotic course will eliminate them cleanly and permanently is not supported by what we know about their biology. The Enterobacteriaceae dominating SIBO &#8212; E. coli, Klebsiella, Citrobacter &#8212; are the most metabolically flexible organisms in the gut. They are facultative anaerobes with layered electron transport systems: they use oxygen when present, switch to nitrate respiration via NarG when oxygen is limited, switch to fumarate reduction when nitrate is gone, and fall back on fermentation when none of the above is available. They can generate energy under almost any condition the gut can produce. The NarG system specifically allows E. coli to use nitrate &#8212; which becomes abundant in the iNOS-upregulated, inflamed small intestine &#8212; as a terminal electron acceptor with nearly the same energy yield as oxygen. They do not need the environment to be aerobic. They just need the host&#8217;s metabolism to be failing, which provides both the oxygen leak and the nitrate simultaneously. Iron and Bacterial Survival Every pathogenic bacterium establishing in the small intestine requires iron to survive, replicate, and mount biofilm defenses. Pathogenic E. c