Real-time PCR versus culture of bronchoalveolar lavage fluid for detecting Bordetella bronchiseptica in dogs with persistent lower respiratory signs: a retrospective study of 23 cases

Abstract

Bordetella bronchiseptica (Bb) is a frequent pathogen in dogs and a component of the Canine Infectious Respiratory Disease Complex (CIRDC). However, it can also be detected in the lower respiratory tract of healthy animals, complicating its interpretation in clinical settings. This retrospective study compared the detection of Bb in bronchoalveolar lavage fluid (BALF) samples using real-time PCR versus bacterial culture in dogs referred for persistent lower respiratory tract signs to a referral hospital in Spain between 2018 and 2024. A total of 143 BALF samples were analyzed; 23 dogs tested positive for Bb by at least one method and were included in the clinical analysis. Real-time PCR identified Bb in 16.1% (23/143) of cases (95% CI:10.4-23.1%). Among these, 40% (9/23) had negative culture results. Co-infections with Mycoplasma spp. or Mycoplasma cynos were detected in 30% (7/23) of cases, and 26% (6/23) had positive cultures for other bacteria. Most dogs (91% (21/23)) had received antibiotics prior to BALF collection. The median time to clinical remission was 30 days. While real-time PCR showed a higher detection rate than culture, its results must be interpreted cautiously. PCR may amplify DNA from non-viable organisms or colonizers, and thus does not confirm active infection. Our findings underscore the need to integrate molecular, microbiological, and clinical data to reach an accurate diagnosis and avoid inappropriate antimicrobial use. Combining PCR and culture may enhance diagnostic accuracy, as culture alone would have failed to detect Bb in 40% of PCR positive dogs.