Quantification of Pasteurella multocida in experimentally infected pigs using a real-time PCR assay

- A new qPCR assay was developed to quantify Pasteurella multocida in pigs.
- Validation of the qPCR assay's specificity and sensitivity
- Detection of all P. multocida strains analyzed (isolated from pigs or humans)
- Quantification of P. multocida in specimens from experimentally infected pigs
- A useful tool for controlling pig infections

The aim of the study was to quantify Pasteurella multocida in experimentally infected pigs using a new qPCR assay based on the sodA gene and validated with 35 P. multocida strains, including strains isolated from pigs with pneumonia, clinically healthy pigs (nasal cavities), and human infections. The specificity of the test was verified with a collection of 60 strains of bacterial species other than P. multocida. The estimated detection threshold was 10 genome equivalents per microliter. The amplification efficiency and value of the correlation coefficients were 95.5% (± 3.5%) and 0.995 (± 0.005), respectively. Analysis of P. multocida suspensions in Buffered Peptone Water Broth and of samples prepared from lungs experimentally spiked with P. multocida revealed detection thresholds of 1.4 CFU/μl and 8.4 CFU/μl, respectively. In live pigs, experimentally-infected, approximately 105, 107 and 108 genome equivalents/ml of P. multocida DNA was detected on Day 8 post-infection in the nasal cavities, tonsils and trachea samples, respectively. In dead pigs, approximatively 107 genome equivalents/ml of P. multocida DNA was detected in the lung tissue with pneumonia. The qPCR assay's diagnostic specificity and sensitivity were 100% and 96%, respectively. This new qPCR assay should be a very useful tool for controlling enzootic pneumonia and studying the dynamics of infections in pig herds.