0 antigen distribution and sensitivity to the bactericidal effect of normal human serum of Proteus strains from clinical specimens.

9 antigen distribution and sensitivity to the bactericidal effect of normal human serum were determined in 485 Proteus strains isolated from urine, blood, wounds, and feces. Of all strains, 62% could be grouped according to 25 0 antigens. The most frequent one, 0 3, appeared in 13% of all the strains. In blood cultures this antigen was found significantly more often. No other 0 group dominated. Of all strains, 11% were spontaneously agglutinating but such strains were significantly more common in urinary specimens from children with neurogenic bladder disorders. Strains sensitive to the bactericidal effect of normal human serum were significantly more prevalent in urines than in fecal specimens. Most of the sensitive strains were spontaneously agglutinating and were isolated from the urines of children with neurogenic bladder disorders. This may be an example of 'antigenic drift' of the bacteria as a response to host defense mechanisms in the urinary tract.