Asymptomatic bacteriuria in schoolgirls. II. Differences in escherichia coli causing asymptomatic bacteriuria.

Three hundred and forty-three E. coli strains isolated from the urine of patients with asymptomatic bacteriuria (ABU), symptomatic cystitis, or pyelonephritis were analysed with regard to O group distribution and sensitivity to the bactericidal effect of normal serum. Strains of O groups 1, 2, 4, 6, 7, 16, 18 and 75 were found in 31.3% in ABU, in 58.7% in cystitis and in 79.8% in pyelonephritis. Spontaneous agglutination was noted in 45.2% of ABU, 6.5% of cystitis and 1.7% of pyelonephritis strains. The strains from patients with ABU were significantly more sensitive to the bactericidal effect of normal serum than were those from patients with symptomatic urinary tract infection. In some patients with untreated ABU, changes in the characteristics of the urinary strains isolated were noted. The strains tended to become spontaneously agglutinating as well as more sensitive to the bactericidal activity of normal serum. The strains found in patients with ABU probably had an altered cell wall compared with those found in patients with symptomatic infections such that they produce fewer symptoms and possibly be less virulent.