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Various Escherichia coli strains differ in the composition of their major outer membrane proteins. However, all E. coli K12 strains tested possess the same major outer membrane proteins a, b, c and d, although quantitative differences were detected. The influence of growth conditions on the composition of the major outer membrane proteins of E. coli was analyzed. It was found that neither the growth phase at which the cells are harvested, nor the fatty acid composition of the phospholipids has a considerable influence on the composition of these proteins. However, the composition of the growth medium, and, to a less extent, the growth temperature, have a pronounced influence. Certain mutants, changed in the composition of their lipopolysaccharide, are deficient in protein b. Also mutants deficient in protein c and d respectively, are described. Proteins b and c of E. coli K12 were found to be associated with peptidoglycan. Protein bands, corresponding with flagellin and pilin respectively, were identified.

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An enzyme-linked immunoassay was used to detect antibodies to the cell wall peptidoglycan of Staphylococcus aureus in human sera. All 170 sera from donors and patients with staphylococcal and nonstaphylococcal infections contained IgG antibodies to peptidoglycan; antibody levels varied with age, and transplacental transfer occurred. IgM antibodies to peptidoglycan were not found in donors and were present in only one patient with serious staphylococcal infection. Significantly elevated levels of IgG antibodies to peptidoglycan were observed in 20 (80%) of 25 patients with deep tissue infection with S. aureus but in only two (9%) of 22 patients with superficial staphylococcal infection. An increase in levels of antibodies to peptidoglycan generally coincided with an increase in level of IgG antibodies to teichoic acid. No cross-reactivity between peptidoglycan and teichoic acid was observed. Thus, staphylococcal peptidoglycan is immunogenic in humans, and testing for IgG antibodies to peptidoglycan may be useful in the diagnosis and follow-up of serious staphylococcal infections.