Characterization ofMannheimia haemolyticain beef calves via nasopharyngeal culture and pulsed-field gel electrophoresis

Abstract

Abstract. Mannheimia haemolytica is a major bacterial component of bovine respiratory disease (BRD); unfortunately, very little is known about M. haemolytica transmission dynamics among cattle. Identifying potential variation in M. haemolytica populations over time and induction of nasopharyngeal colonization and subsequent shedding are 2 areas where knowledge is lacking. In our study, 2 separate loads of 20 mixed-origin, male calves were purchased through an order buyer on different dates. Deep nasopharyngeal cultures (NPC) were performed on all calves on arrival and, if M. haemolytica-negative, a second screening culture was obtained. Calves that were negative on 2 initial NPCs (NEG; n = 4) were subsequently challenged with a previously isolated field strain of M. haemolytica in both the upper and lower respiratory tract, individually housed, and then monitored for M. haemolytica shedding via NPCs at 0.5, 1, 3, 5, 7, and 9 days postchallenge. Naturally M. haemolyticapositive calves (2 per load) were kept for additional daily cultures (POS; n = 4). Individual calf M. haemolytica status for both the POS and NEG groups was inconsistent between study days. Additionally, pulsed-field gel electrophoresis performed on isolates from the positive cultures showed that the NEG calves did not shed the M. haemolytica challenge strain, but rather 2 distinct clusters of M. haemolytica were shared among POS and NEG calves regardless of their initial status. Although sample sizes were small, these findings illustrate how variable the results of a single nasopharyngeal swab can be and the challenges of using an individual culture to truly represent animal M. haemolytica status.

Bovine Gamma Delta T Cells Contribute to Exacerbated IL-17 Production in Response to Co-Infection with Bovine RSV and Mannheimia haemolytica

“…Four calves were infected via endoscope-guided challenge with 3x10 8 CFU/mL of a field strain of M . haemolytica serotype A1 previously isolated from the lung of a bovine with BRDC [ 31 , 32 ]. Protocols for growing and administering the challenge inoculum have been previously described [ 31 , 32 ].…”

“…haemolytica serotype A1 previously isolated from the lung of a bovine with BRDC [ 31 , 32 ]. Protocols for growing and administering the challenge inoculum have been previously described [ 31 , 32 ]. Four calves served as uninfected controls and received only PBS via endoscope-guided administration.…”

Rapid typing of Mannheimia haemolytica major genotypes 1 and 2 using MALDI-TOF mass spectrometry

“…A test that could rapidly and accurately distinguish genotype 1 and 2 M. haemolytica could be beneficial to diagnostic laboratories and veterinary practitioners that currently identify M. haemolytica at the species level using culture. Within a single animal, M. haemolytica cultured from the nasopharynx may genetically differ from those cultured from the lung, making culture findings from nasal swabs and other antemortem clinical samples challenging to interpret (Capik et al, 2015). A test to rapidly distinguish genotypes would provide an enhanced ability to interpret M. haemolytica culture and subsequent antimicrobial susceptibility testing results from nasal swabs or other samples that contain M. haemolytica of either genotype.…”

Effects ofMannheimia haemolyticachallenge with or without supplementation ofSaccharomyces cerevisiae boulardiistrain CNCM I-1079 on immune upregulation and behavior in beef steers1

“…The results of this study demonstrate that the MH-challenge model successfully initiated immunological signs of disease, despite the fact that there were few observed clinical signs of disease detected following the MH challenge. Gross clinical signs of disease resulting from the challenge model were not expected as previous studies using a similar MH strain with intratracheal delivery reported that MH-challenged animals appeared clinically normal or displayed mild increases in clinical illness scores that were not different from clinically normal (Corrigan et al, 2007;Capik et al, 2015).…”