Occurrence of pili on and adhesive properties of Haemophilus parainfluenzae.

Of 20 clinical isolates of Haemophilus parainfluenzae, 13 produced a mannose-resistant hemagglutinin that agglutinated erythrocytes from chickens, horses, rabbits, and sheep. Examination with the electron microscope showed that only strain HR-885 was pilate. Grown in static liquid culture, the 12 hemagglutinating, nonpilate isolates formed small, tightly packed clumps, whereas strain HR-885 formed large, loosely packed clumps. However, seven isolates did not produce a hemagglutinin, did not clump, and were nonpilate.