IRON-REGULATED OUTER-MEMBRANE PROTEINS OF STRAINS OF AVIAN SEPTICEMICESCHERICHIA-COLI

1. Outer-membrane protein patterns of Escherichia coil recovered from the peritoneal cavities of infected guinea pigs and grown in medium M9 containing 2,2'-dipyridyl were studied by polyacrylamide gel electrop horesis (SDS-PAGE) to determine whether in vivo conditions of growth a ffected the expression of these bacterial surface proteins. 2. Eleven strains of septicemic E. coli studied in vitro under conditions of iro n restriction expressed iron-regulated outer-membrane proteins, mainly the protein of approximately 74 kDa, whereas avirulent strains grown under similar conditions did not present the 74-kDa protein. 3. These results show the distribution of iron-regulated outer-membrane protein s among avian E. coli and suggest that the protein of approximately 74 kDa may be important for the virulence of these strains.