Menaquinone production and utilization in germ-free rats after inoculation with specific organisms.

Although menaquinones are biologically active forms of vitamin K, factors that influence their production by bacteria or their absorption from the gut are not well understood. Germ-free rats were inoculated with four different strains of organisms and fecal and tissue menaquinone concentrations were determined. No menaquinones were detected in the tissues or feces of rats colonized with Bifidobacterium longum or Clostridium ramosum, two organisms that have not been reported to produce menaquinones when grown in pure cultures. Rats colonized with Bacteroides vulgatus had high levels of fecal MK-10 with significant amounts of MK-9 and MK-11, whereas rats colonized with Escherichia coli had high levels of fecal MK-8 and small amounts of MK-7. The same menaquinones are produced in pure cultures of these organisms. The predominant fecal menaquinones were also detected in liver and were present in higher concentrations in the liver of those rats not maintained in coprophagy-preventing cages.