Different strains of the same bacteria species can produce different immune responses, but if the species is pathogenic to humans, all its strains will also be

Different strains of the same bacteria species can produce different immune responses, but if the species is pathogenic to humans, all its strains will also be considered the same pathogen. The Plague of Justinian and the Black Death were both known to be virulent in that they were both rapid, severe, and destructive, but virulence is not an objectively measurable quality.