Degradation of blood group antigens in human colon ecosystems. II. A gene interaction in man that affects the fecal population density of certain enteric bacteria.

A B S T R A C T The autosomal dominant ABH secretor gene together with the ABO blood type gene control the presence and specificity of A, B, and H blood group antigens in human gut mucin glycoproteins. Certain ob- ligate anaerobes in feces produce extracellular antigenspecific glycosidases that degrade these ABH antigenic determinant glycoside structures. We estimated the pop- ulations of these bacteria in feces of 22 healthy subjects by determining the greatest dilution of feces that yielded A, B. or H blood group-degrading enzyme activity af- ter 24 h incubation in anaerobic cultures. Comparatively small populations of fecal bacteria produce blood group- degrading enzymes; their estimated populations were 100 per g or less in 21 subjects. Fecal populations of B-degrading bacteria were stable over time, and their population density averaged 50,000-fold greater in blood group B secretors than in other subjects. We present evidence that the greater fecal populations of B-degrading bacteria in B secretors is due in part to a competitive nutritional advantage gained by their ability to enzy- matically cleave the B antigenic determinant a-t-galactose from gut mucins of B secretors. Fecal populations of bacteria producing A and H antigen-degrading enzyme activities were comparable in all subjects to the fecal population of B-degrading bacteria in B secretors. The large populations of fecal anaerobes may be an additional source of A antigen substrate for A-degrading bacteria; thus, antigens cross-reacting with A antigen were detected on cell walls of anaerobic bacteria from A portion of this work was published in abstract form in 1973.