Key bacterial features

Shapes

• Coccus/Cocci: spheres
• Bacillus/Bacilli: rod shaped
• Vibrio: slightly curved rod, gram-negative
• Spirillum: rigid spiral bacterium
• Spirochaete: flexible spiral bacterium

Defensive structures

• Spore: inert structures, resistant to physical and chemical challenge
• Capsule: outermost layer found in many bacteria, usually made of polysaccharides

Toxin

• Promotes infection and disease by directly damaging host tissues and disabling the immune system

Aerobes and anaerobes

• Aerobic: grow in oxygen
• Obligate aerobes: require oxygen
• Obligate anaerobes: killed by oxygen
• Facultative anaerobes: tolerate oxygen

Identification of bacteria

• Selective media: presence of specific substances permits the growth of one organism over another
• Differential media: incorporation of chemicals produces visible changes in colonies that facilitates identification