Pasteurella haemolytica in the tracheal air of calves.

Pasteurella haemolytica was shown to be present in the tracheal air of calves and was likely transported in droplet nuclei formed in the nasal passages. The number of colonies of P. haemolytica found in the tracheal air of the calves ranged from 1.9 to 12.5 colonies per cu ft of air. As long as P. haemolytica colonized the nasal passage in numbers detectable in nasal swabs it could be found in the tracheal air but there was no direct correlation between the numbers in the nasal flora and the numbers found in the tracheal air. Of the P. haemolytica which travel via the tracheal air 47.8% were in droplets of the aerodynamic size of from less than one to five microns, the size range which is considered hazardous for lung penetration in man. The technique used demonstrated the presence of P. haemolytica in the tracheal air of calves and provides a useful tool for monitoring and determining the phase in the colonization of the respiratory tract in which the majority of the potential pathogen P. haemolytica pass from the nose to the tracheal air and presumably to the lung.