Bacterial interactions in bovine respiratory and reproductive infections

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Abstract
The ability of the aerobic bacterial flora from the normal bovine respiratory and reproductive tracts to enhance or inhibit the growth of Pasteurella haemolytica, P. multocida and Haemophilus somnus was tested in vitro. Six strains of each of these pathogens were cross streaked with each isolate of bovine normal flora. Flora which enhanced the growth of these pathogenic bacteria outnumbered inhibitors 4 to 1. An intermediate number of isolates produced no effect on pathogen growth. Most enhancers were gram positive (Micrococcus, Staphylococcus, Corynebacterium or Rhodococcus isolates), although several isolates of Moraxella and Actinobacter were also good enhancers. For H. somnus, there were proportionally more organims which produced marked enhancement among the preputial flora than among the nasal flora, which may account for the greater number of genital carriers than nasal carriers. Bacillus isolates were the most significant inhibitors amogn the nasal flora, whereas no genus or species from the reproductive tract was noted to produce appreciable inhibition. Thus, changes in ratios of inhibitors to enhancers may determine, in part, whether a carrier state or disease occurs. Also, suggestions are made for in vitro use of this phenomenon for diagnostic tests.