Differences in excretion and efficiency of the aerobactin and enterochelin siderophores in a bovine pathogenic strain of Escherichia coli

Abstract

Secretion of aerobactin is thought to play an important part in the virulence of invasive Escherichia coli also capable of synthesizing enterochelin. Why, despite its markedly lower affinity for iron than that of enterochelin, aerobactin proves to be the' predominant active siderophore for bacterial growth in transferrin was investigated. We studied the action of two iron chelators, 2,2'-dipyridyl and transferrin, in expression of the aerobactin and enterochelin genes. Specifically, we describe the sequential localization of the two siderophores in the cell compartments during bacterial growth under different iron limitation conditions. Our results demonstrated that, whatever the exogenous iron-chelating agent used, aerobactin was rapidly excreted, whereas enterochelin accumulated early in periplasm before its very belated release into the external medium. This work also showed that the advantage of aerobactin over enterochelin in competition with transferrin was not due to (i) lack of enterochelin activity, (ii) a cell-bound aerobactin-dependent mechanism, (iii) antagonism between the two siderophores, and probably (iv) genetic preferential induction of aerobactin. We propose that the superiority of aerobactin in competing with transferrin for iron(Ill) was a consequence of its more rapid excretion with respect to enterochelin. In contrast to transferrin, 2,2'-dipyridyl induced a greater efficiency of enterochelin, possibly by a more permanent function as iron-binding compounds in the bacterial envelope. In summary, unlike aerobactin, enterochelin appears to be a weakly secreted high-affinity iron ligand.

Prevalence of CS31A and F165 surface antigens in Escherichia coli isolates from animals in France, Canada and India

“…Bovine E. coli producing the CS31A antigen have been reported in Japan [16] although the fimbriae observed on these strains appear to be different from those described by Girardeau et al [51. Although the role of CS31A and F165 in virulence has not been demonstrated, these surface antigens seem to be mainly associated with E. cob strains from cases of septicemia. Experimental infection of calves with CS31A-positive E. coli produced septicemia [61 and genetic studies have shown that CS31A-positive non-ETEC possess antibiotic resistance plasmids encoding for both CS31A and aerobactin, the latter of which is a virulence factor [17]. Among 0115 E. coli, only those with F165 antigen induced septicemia in piglets [3].…”

Factors and markers of virulence in from human septicemia

“…(6) Cohcin production was measured by the agar overlay method [15] using E. coil K12 D B6433 as the susceptible strain and a mutant of E. coil K12 D B6433 resistant to col V [16] for identifying colicin V. (7) Aerobactin production was identified using the hydroxamate assay of Csaky [17] according to Der Vartanian [18]. (8) Antibiotic resistances were studied using the disk diffusion method [15].…”

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One hundred Escherichia coil isolates from human septicemia were characterized ,~,,ith respect to O serogroups 1,2,4, 6,7,8, 15,18, 75 and 78, a-hemolysin, carboxylesterase B typing, cytotoxic necrotizing factor, F163 and CS31A fimbrial antigens, aerobactin production, colicins, and antibiotic sensitivity. A factorial analysis of correspondence and X-" tests indicated that most of E. coli isolates belonging to the studied O serogroups were positive for the virulence factors or markers a-haemolysin, carboxylesterase B 2 type, cytotoxic necrotizing factor, F165 fimbrial antigen and were antibiotic-sensitive (Group I).

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Escherichia coli K-12 ferrous iron uptake mutants are impaired in their ability to colonize the mouse intestine

“…Although anaerobically grown E. coli cells are able to use enterochelin-Fe 3 + complexes as their iron source [8,17], efficient enterochelin production is accomplished only in extreme iron-poor conditions which are probably never reached in the anaerobic large intestine [18]. In accordance with this, Der Vartanian et al [19] were not able to find enterochelin in the intestinal contents of gnotobiotic lambs challenged with aerobactin-and enterochelin-producing E. coli.…”