Location: Animal Health GenomicsTitle: Differentiation of Mannheimia haemolytica genotype 1 and 2 strains by visible phenotypic characteristics on solid media
|Schuller, Genevieve - Gennie|
|LOY, JOHN - University Of Nebraska|
|Clawson, Michael - Mike|
Submitted to: Journal of Microbiological Methods
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/2020
Publication Date: 4/1/2020
Citation: Wynn, E.L., Schuller, G., Loy, J.D., Workman, A.M., McDaneld, T.G., Clawson, M.L. 2020. Differentiation of Mannheimia haemolytica genotype 1 and 2 strains by visible phenotypic characteristics on solid media. Journal of Microbiological Methods. 171. Article 105877. https://doi.org/10.1016/j.mimet.2020.105877.
Interpretive Summary: Mannheimia haemolytica is an opportunistic bacterial pathogen that inhabits the upper respiratory tract of primarily ruminants. When cattle are stressed, M. haemolytica can proliferate, invade their lungs, and cause bovine respiratory disease (BRD). There are two major strains, or genotypes (1 and 2) of M. haemolytica that colonize the upper respiratory tract of cattle, however, genotype 2 is predominantly found in the lungs of cattle with respiratory disease versus genotype 1. A specialized diagnostic test using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is available for genotype 1 and 2 identification. However, this test is typically performed on bacterial colonies in pure culture on solid media, and in the case of M. haemolytica, with little or no prior knowledge of strain genotypes. Consequently, an ability to rapidly distinguish between the genotypes on culture plates would greatly assist in the selection of suspect M. haemolytica cultures for MALDI-TOF MS testing. In this study, we identified color and morphological differences between genotype 1 and 2 strains grown on solid media, and a method to visually distinguish them from each other without specialized equipment. Use of this method can help ensure that both genotypes, if present, are preliminarily detected in BRD case samples, and sent forward for confirmatory identification with MALDI-TOF MS, or other testing procedures. Ultimately, this will help determine the role(s), or lack thereof, of either genotype in BRD cases, and may facilitate better treatment strategies for BRD outbreaks.
Technical Abstract: Genotype 2 Mannheimia haemolytica associate with the lungs of cattle with bovine respiratory disease more frequently than genotype 1 strains. Different colony colors and morphologies were identified between genotype 1 and 2 solid media cultures. Genotype of strains, and frequency differences between them in mixed cultures are discernable by visual inspection.