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In the present study, the hemoglobin (Hb)‐binding activity of Actinobacillus pleuropneumoniaewas examined using fluorescein‐labeled pig Hb and flow cytometry. Comparison of the Hb‐binding activity of A. pleuropneumoniaeserotype 1 strain 4074 grown under iron‐restricted conditions with cells grown under iron‐sufficient conditions indicated that iron‐restriction in A. pleuropneumoniaepromotes the expression of Hb receptors, and that Hb‐binding activity is, at least in part, iron‐repressible. Hb‐binding activity was also observed in representative strains of A. pleuropneumoniaebelonging to serotypes 1 and 2. In addition, A. pleuropneumoniaeserotype 1 LPS or capsule isogenic mutants were tested in flow cytometry in order to understand the influence of surface polysaccharides on Hb‐binding activity. Experiments with an acapsulated mutant indicated that surface molecules with Hb‐binding activity are more exposed at the cell surface in the absence of capsular polysaccharides. However, the Hb‐binding activity of LPS mutants analyzed in this study was unchanged compared to the parent strain. The outer membrane proteins profile of A. pleuropneumoniaeserotype 1 grown under iron‐restricted or iron‐sufficient conditions was also evaluated by polyacrylamide gel electrophoresis. Iron‐regulated outer membrane proteins were observed under iron‐restricted growth conditions which suggests that one or more of these outer membrane proteins may play a role in the Hb‐binding activity detected by flow cytometry.

In the present study, the hemoglobin (Hb)-binding activity of Actinobacillus pleuropneumoniae was examined using fluorescein-labeled pig Hb and flow cytometry. Comparison of the Hb-binding activity of A. pleuropneumoniae serotype 1 strain 4074 grown under iron-restricted conditions with cells grown under iron-sufficient conditions indicated that iron-restriction in A. pleuropneumoniae promotes the expression of Hb receptors, and that Hb-binding activity is, at least in part, iron-repressible. Hb-binding activity was also observed in representative strains of A. pleuropneumoniae belonging to serotypes 1 and 2. In addition, A. pleuropneumoniae serotype 1 LPS or capsule isogenic mutants were tested in flow cytometry in order to understand the influence of surface polysaccharides on Hb-binding activity. Experiments with an acapsulated mutant indicated that surface molecules with Hb-binding activity are more exposed at the cell surface in the absence of capsular polysaccharides. However, the Hb-binding activity of LPS mutants analyzed in this study was unchanged compared to the parent strain. The outer membrane proteins profile of A. pleuropneumoniae serotype 1 grown under iron-restricted or iron-sufficient conditions was also evaluated by polyacrylamide gel electrophoresis. Iron-regulated outer membrane proteins were observed under iron-restricted growth conditions which suggests that one or more of these outer membrane proteins may play a role in the Hb-binding activity detected by flow cytometry.