Flagella and Motility in Actinobacillus pleuropneumoniae

Abstract

Actinobacillus pleuropneumoniae has been considered nonmotile and nonflagellate. In this work, it is demonstrated that A. pleuropneumoniae produces flagella composed of a 65-kDa protein with an N-terminal amino acid sequence that shows 100% identity with those of Escherichia coli, Salmonella, and Shigella flagellins. The DNA sequence obtained through PCR of the fliC gene in A. pleuropneumoniae showed considerable identity (93%) in its 5' and 3' ends with the DNA sequences of corresponding genes in E. coli, Salmonella enterica, and Shigella spp. The motility of A. pleuropneumoniae was observed in tryptic soy or brain heart infusion soft agar media, and it is influenced by temperature. Flagella and motility may be involved in the survival and pathogenesis of A. pleuropneumoniae in pigs.

FIG. 1.

(A and B) Electron micrographs showing flagella on the surfaces of A. pleuropneumoniae cells. Bars, 500 nm. (C) Purified A. pleuropneumoniae flagella. (D) Flagellar preparations electrophoresed in 14% acrylamide gels. Lane 1, flagellin from E. coli; lane 2, flagellin from A. pleuropneumoniae. Molecular mass standards (in kilodaltons) are indicated on the left.

FIG. 2.

(A) Reactivities of flagellar preparations with heterologous antisera as shown by immunoblotting. Flagellin samples were reacted with antiflagellum serum samples from A. pleuropneumoniae (lanes in panel 1), E. coli (lanes in panel 2), Salmonella (lanes in panel 3), and Shigella (lanes in panel 4). Lanes a, E. coli flagellin; lanes b, A. pleuropneumoniae flagellin. (B) A. pleuropneumoniae whole-cell extracts reacted with anti-E. coli flagellin serum. Lanes 1, 2, and 3, serotypes 3, 5b, and 7, respectively. Molecular mass standards (in kilodaltons) are indicated on the left

FIG. 3.

A. pleuropneumoniae motility on soft agar in plates (A and B) and tubes (C). A comparison of cells incubated at 22°C (A) and those incubated at 37°C (B) shows the influence of temperature on motility. (C) Tube 1, E. coli E2348/69 positive control; tube 2, E. coli fliC mutant negative control; tubes 3 and 4, A. pleuropneumoniae serotypes 1 and 5, respectively. Motility in tubes was observed after 48 h of incubation at 37°C.