Pili of Bordetella avium: expression, characterization, and role in in vitro adherence.

Electron microscopy revealed pili on all isolates of Bordetella avium and B. avium-like bacteria examined. Trypticase soy broth (TSB) and 2% peptone agar were the best media for promoting pilus expression. Cultures grown at 37 or 42 C had similar pilus production, whereas cultures grown at 18 C produced few or no pili. Pilus expression of the Art Vax strain was best when that strain was grown in TSB, but the strain yielded fewer pili than B. avium and B. avium-like isolates grown under the same cultural conditions. B. avium pili had a diameter of 2.0 nm, ranged in length from 370 nm to 1500 nm, and had a protein subunit molecular mass of about 13,100 daltons. Purified pili from B. avium did not hemagglutinate guinea pig erythrocytes, and a 1:20 dilution of hyperimmune antisera against B. avium pili did not block the hemagglutinating activity of whole-cell preparations of B. avium. In the indirect immunofluorescence test, B. avium isolates and the Art Vax strain adhered to the tracheal explants of turkeys, but B. avium-like isolates did not. Purified pili from B. avium adhered to the surface of the mucosal lining of the tracheal explants, and hyperimmune antisera against B. avium pili blocked the in vitro adherence of whole-cell preparations of B. avium. It was concluded that pili of B. avium are involved in the in vitro attachment of that bacterium to the mucosal surface of turkey tracheal explants.