A total of 516 strains of Escherichia coli were screened for the presence and expression of the aerobactin iron uptake system. The incidence was markedly higher among clinical isolates from patients with septicemia (68.8%), pyelonephritis (74.6%), and symptomatic (59.8%) and asymptomatic (63.2%) lower urinary tract infections than among normal human fecal isolates (34.3%).

To assess the importance of aerobactin-mediated iron uptake as a bacterial virulence determinant in animal infections, a total of 576 strains of Escherichia coli isolated from cattle, chickens, sheep and pigs were screened by colony hybridization to determine the presence of the aerobactin genetic determinants, and by a bioassay to detect aerobactin secretion in iron-limited conditions. Results obtained by the two complementary methods correlated well. The incidence of the aerobactin system was very high among septicaemia isolates, particularly those from cattle and chickens, an observation that strongly suggests an important role for this mechanism of iron assimilation in pathogenesis. On the other hand, the incidence of the aerobactin system among mastitis strains was not significantly higher than among faecal isolates from healthy animals. No classical enterotoxigenic E. coli strains tested carried the aerobactin genetic determinants. Although most strains that produced aerobactin were also able to make colicin V, the fact that the two characteristics existed separately in a significant minority of isolates suggested that colicin testing alone could not be reliably used to determine the presence of the aerobactin system.

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The distribution of mannose-resistant (MRHA) and mannose-sensitive (MSHA) fimbrial haemagglutinins was examined in 482 strains of Escherichia coli isolated from 390 adult women and 45 pregnant mothers with a variety of urinary tract infections (UTI), and from 47 healthy controls. The proportion of MRHA strains was significantly higher in patients with symptomatic UTI (75%) than in women with non-significant bacteriuria (30%, p less than 0.001), pregnant women with asymptomatic UTI (34%, p less than 0.0001) and healthy controls (0%). The proportion of MSHA strains was significantly lower in patients with symptomatic UTI (22%) than in women with non-significant bacteriuria (46%, p less than 0.001) and pregnant women with asymptomatic UTI (52%, p less than 0.01). Only 17% of the strains from healthy controls had MSHA activity. In pregnant women with UTI, whether this was symptomatic or asymptomatic, there was a significant association between infection with MRHA strains of E. coli and a past history of UTI. Thus, in a pregnant woman with an infection and a past history of UTI there is a seven-fold greater chance that this infection is due to an MRHA-bearing organism than in pregnant women without such a history. There was also a significant association between MRHA organisms and symptomatic infection. The risk of symptomatic patients having an infection with an MRHA strain is six times greater than that for a patient with a covert infection.