Storage time and temperature affect the isolation rate of Mannheimia haemolytica and Pasteurella multocida from bovine bronchoalveolar lavage samples

A microbiological diagnosis is essential to better target antimicrobial treatment, control and prevention of respiratory tract infections in cattle. Under field conditions, non-endoscopic broncho-alveolar lavage (nBAL) samples are increasingly collected. To what extent the highly variable turnaround time and storage temperatures between sampling and cultivation affect the isolation rate of bacterial pathogens is unknown. Therefore, the objective of this experimental study was to determine the effect of different storage temperatures (0 °C, 8 °C, 23 °C and 36 °C) and times (0,2,4,6,8,24,48 h) on the isolation rate and concentration of Pasteurellaceae in nBAL samples from clinically affected animals. At a storage temperature temperature of 36 °C isolation rates of Mannheimia haemolytica and Pasteurella multocida were significantly reduced 6 h and 48 h after sampling, respectively. At room temperature (23 °C), a decrease in M. haemolytica and P. multocida isolation rate was noticed, starting at 24 and 48 h after sampling, respectively, but only significant for P. multocida at 48 h. The presence of microbial contamination negatively affected the isolation of P. multocida in clinical nBAL samples, but not of M. haemolytica. Optimal M. haemolytica and P. multocida isolation rates from clinical nBAL samples are obtained after storage at 0 °C or 8 °C, provided that the sample is cultivated within 24 h after sampling. The maximum period a sample can be stored without an effect on the M. haemolytica and P. multocida isolation success varies and is dependent on the storage temperature and the degree of microbial contamination.