adenovirus aerobe aerobic bacteria amoeba anaerobe anaerobic bacteria bacillus bacteria bacterium bug coccus disease-producing microorganism echovirus enterovirus filterable virus fungus germ gram-negative bacteria gram-positive bacteria microbe microorganism mold nonfilterable virus pathogen picornavirus protozoa protozoon reovirus rhinovirus rickettsia spirillum spirochete spore streptococcus trypanosome vibrio virus