The first pathogenic bacterium to be observed under microscope was-

The first pathogenic bacterium to be observed under microscope was Bacillus anthracis. Bacillus anthracis: First pathogenic bacterium to be observed under microscope. First bacterium isolated in pure culture. First communicable disease shown to transmit by inoculation of infected blood. First used for preparation of attenuated vaccine- Pasteur's vaccine-nontoxigenic strain. Recently used for biological warfare as spores enclosed in envelopes.