Quantitative bacterial cultures and cytological examination of bronchoalveolar lavage specimens in dogs

Cytology and quantitative bacterial cultures of lower respiratory tract sec retions are widely used in human medicine to differentiate airway infection from simple bacterial colonization. A retrospective study was conducted to determine the usefulness of quantitative aerobic cultures and Gram stain i ntracellular bacteria counts from bronchoalveolar lavage (BAL) specimens in dogs in diagnosing lower respiratory tract infection (LRTI) and to determi ne whether chronic bronchitis is associated with marked bacterial growth in dogs. The threshold determined to define clinically relevant bacterial gro wth was 1.7 x 10 colony-forming units per milliliter of BAL fluid. We used this threshold and found that diagnostic sensitivity and specificity were 8 6% and 100%, respectively. With a threshold for infection of >2 intracellul ar bacteria observed in any of 50 fields, microscopic examination of Gram s tain BAL preparations had a sensitivity of 71% and a specificity of 97% in establishing LRTI. There was a high correlation between bacterial morpholog y on BAL Gram stain and bacterial cultures. Combining the results of intrac ellular bacteria counts from the BAL Gram stain with those from the quantit ative cultures, the sensitivity in diagnosing LRTI was 87% and the specific ity was 97%. BAL quantitative cultures as well as quantitating intracellula r bacteria on Gram stain BAL cytology were revealed to be useful in Identif ying LRTI in dogs. Chronic bronchitis does not appear to be associated with marked bacterial growth in dogs.