Serotypes, hemagglutinins, siderophore synthesis, and serum resistance of Klebsiella isolates causing human urinary tract infections.

A total of 146 Klebsiella isolates from human asymptomatic bacteriuria (n = 73), cystitis (n = 54), and acute pyelonephritis (n = 19) were examined for the presence of particular virulence factors. Capsular type K2 was the most common serotype observed (13%). This capsule type was prevalent in isolates from asymptomatic bacteriuria and cystitis but not from pyelonephritis. Type 1 fimbriae were found significantly more often in pyelonephritis isolates than among those from asymptomatic and symptomatic lower urinary tract infection (UTI; P < .05), while no marked differences were detected with respect to the distribution of type 3 fimbriae. Serum resistance was more frequent among isolates from symptomatic (26%) than from asymptomatic UTI (18%). Enterochelin was produced by all but 1 of the isolates as determined by a bioassay. In contrast, aerobactin synthesis was rare (3%), with isolates from pyelonephritis showing the highest frequency of aerobactin production (3/19).