Abstract
The current production system involves movement of calves combined with mixing animals, favouring the transmission of respiratory pathogens and increasing the risk of using antimicrobials. The aim of the study was to determine the presence and resistant profiles of Pasteurella multocida, Mannheimia haemolytica and Moraxella in the lungs of calves at arrival to the farm and after treatment with tulathromycin and florfenicol. Thoracic ultrasonography was performed in two batches of calves (n = 65 and 120, age=26±11.0, weight=45-55kg) at arrival, to select 27 calves/batch with lesions from low to severe. Bronchoalveolar lavage fluid (BALF) was collected on arrival (D0), D20 and D34, and also on D7 for the second batch. Pasteurella, Mannheimia and Moraxella were identified by VITEK. Detection of Mycoplasma bovis was performed by PCR. Minimal inhibitory concentration (MIC) was determined for 18 antimicrobials. Clinical breakpoints were defined by Clinical Laboratory Standards Institute. ERIC-PCR was performed in all isolates to assess similarities. Time effect was analysed by MIXED Procedure (SAS). At D0, 16 out of 54 BALFs contained P. multocida (n = 11), M. haemolytica (n = 5) and Moraxella (n = 4). The number of calves positive for primary pathogens decreased (P < 0.001) at D7 and D20, whereas by D34 positive animals leapt up to 21. MIC results demonstrated that P. multocida and M. haemolytica obtained at D0 were pansusceptible. Isolates of P. multocida collected after treatment, exhibited resistance to oxytetracycline, tilmicosin, tulathromycin, danofloxacin and enrofloxacin. ERIC-PCR demonstrated similar profiles of P. multocida and Moraxellain the two batches of calves after D7. Primary pathogens were susceptible to the initial treatment, however M. bovis was detected in all animals after D7. Resistant species appeared to recolonize the lungs after D34. ERIC-profile demonstrated that isolates recovered after treatment were different from those colonizing the lungs at arrival, suggesting recirculation of resistant bacteria between batches.
PSVI-25 Antimicrobial resistance profiles of Pasteurella multocida, Mannheimia haemolytica and Moraxella spp. of bovine origin pre- and post- treatment with antimicrobials in calves