Well that was not what I had expected! I assumed from the title that the oral bacteria would reveal some preferential defense or resistance to yersinia pestis,

Well that was not what I had expected! I assumed from the title that the oral bacteria would reveal some preferential defense or resistance to yersinia pestis, but instead it was entirely due to the post-epidemic economies of the survivors. This is more like the situation of beriberi crippling the imperial Japanese navy in the 1880s