Summary. The iron uptake mechanisms of enteropathogenic Escherichia coli (EPEC) were examined and compared with those of control E. coli strains. The incidence of aerobactin production was similar (39% and 37% respectively) in the two groups. The quantities of enterochelin produced by aerobactin-negative EPEC and control strains were similar, as were the quantities of enterochelin produced by aerobactin-positive EPEC and control strains. The ability to use haem or haemoglobin as an iron source in an iron-restricted environment was found in 80.4 % and 60.8 O h of EPEC strains respectively, and in 766 % and 56.6 % of control E. coli strains. The ability of E. coli strains to use these compounds was not related to the production of enterochelin or aerobactin or to the production of haemolysins, and may be an important characteristic of bowel organisms. When growing in an iron-limited environment, the iron contained in haemoglobin was used in preference to ovotransferrin-bound iron. During periods of haemoglobin-stimulated growth, the enterochelin uptake system was shown to be fully expressed and may be involved in transport of haemoglobin-derived iron into the cell. Uptake of ovotransferrin-bound iron took place immediately upon exhaustion of haemoglobin-derived iron. The ability to use iron derived from haem compounds represents an alternative iron uptake mechanism for organisms growing in an iron-limited environment and allows greater flexibility during growth in viuo.

Summary. Enteropathogenic Escherichia coli strains are a common cause of infantile diarrhoea but do not produce recognised enterotoxins. Three strains of proven virulence were examined for toxins which may be missed in conventional tests. Cell lysates and concentrated culture supernates of organisms grown in five different media gave negative results when examined for adenylcyclase stimulating activity. The additions of zinc ions or lincomycin to these media or the use of iron-depleted media also gave negative results. The significance of these findings and the possible role of other toxins in diarrhoea due to enteropathogenic E. coli are discussed.

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ssnploys the staff and operatts the Laboratory in accordance with polides and pmgnms formulated, approved and Wewed by tha Aaociatim.