Microbiology Overview Quiz

Microbiology

• The study of different organisms including:
  • Archaea
  • Bacteria
  • Protozoa
  • Algae
  • Fungi
  • Acellular entities

Domains of Living Organisms

• Eukarya: Includes all members of the living world except prokaryotes. This domain comprises algae, fungi, and protozoa.

• Bacteria:

  • Unicellular organisms, generally smaller than eukaryotic organisms.
  • Diverse in cell shape, motility, metabolism, and oxygen requirements.
  • Most bacteria are not harmful to humans, but many diseases are caused by bacteria.

• Archaea:

  • Similar in shape, size, and appearance to bacteria.
  • Biochemically distinct from bacteria.
  • Thrive in extreme environments characterized by high heat, cold, pH, or salt concentration.

Medically Significant Entities

• Viruses:

  • Lack many characteristics of living cells.
  • Unable to replicate independently and require host cell biosynthetic processes.

• Prions:

  • Infectious agents composed solely of proteins.

Domain Bacteria

• Organisms are grouped and named based on:
  • Morphologic characteristics
  • Biochemical characteristics
• The binomial Linnaean system is used for naming bacteria with genus and species:
  • Staphylococcus aureus
  • Escherichia coli O157:H7

Morphology

• Study of bacteria's shape and structure.

• Colony morphology: Based on the size, color, shape, and texture of colonies grown on an agar plate.

• Microscopic morphology: Examines bacteria based on cell size, shape, and arrangement.

Colony Characteristics

• Size: Colonies vary from pinpoint (less than 1 mm) to as large as 5-10 mm in diameter.

  • Only well-separated colonies should be measured as crowding can affect size.

• Margin: The periphery of the colonies can exhibit different characteristics:

  • Entire: Rounded projections
  • Notched
  • Threadlike
  • Filamentous
  • Serrated
  • Lobate

• Surface texture: The surface can be:

  • Smooth: Shiny, glistening
  • Rough: Dull, granular
  • Mucoid: Slimmy or gummy
  • Wrinkled
  • Concentric
  • Contoured
  • The surface texture can indicate virulence.

• Elevation:

  • Flat
  • Raised
  • Convex

• Consistency: Determined by touching the colony with a transfer needle

  • Butyrous: Butterlike
  • Viscous
  • Stringy
  • Rubbery
  • Dry
  • Brittle
  • Powdery

• Optical features:

  • Transparent
  • Translucent
  • Opaque

• Pigmentation: Some bacterial species produce pigmented colonies.

  • Examples:
    • Serratia marcescens: Red
    • Staphylococcus aureus: Gold
    • Micrococcus luteus: Yellow
    • Bacteroides melaninogenicus: Black
    • Pseudomonas aeruginosa: Blue green

Bacterial Shape and Arrangement

• Cocci: Spherical cells

  • Chains: Streptococcus species
  • Pairs/Diplococci: Neisseria gonorrhea
  • Clusters: Staphylococcus species

• Bacilli: Cylindrical and rod-shaped organisms

  • Pseudomonads
  • Escherichia

• Coccobacilli: Short, rounded rods

  • Haemophilus

• Spirochetes and Spirilla: Helical, corkscrew-shaped organisms

  • Treponema pallidum

• Vibrios: Comma-shaped rods

  • Vibrio cholerae

• Pleomorphic organisms: Exist in varied forms

  • Legionella
  • Corynebacterium

Examples of Medically Important Bacteria

• BACTERIA | DISEASE |
• Treponema pallidum | Syphilis|
• Neisseria gonorrhea | Gonorrhea|
• Salmonella typhosa | Typhoid fever |
• Vibrio cholerae | Cholera |
• Yersinia pestis | Bubonic plague |
• Staphylococcus aureus | Boils |
• Clostridium tetani | Tetanus |
• Clostridium botulinum | Botulism |
• Legionella pneumophila | Legionnaire's disease |

Stains

• Bacteria are stained to improve visibility under a light microscope due to their small size and transparency.
• Staining characteristics are helpful in classification.
• Main types of staining reactions:
  • Simple stain
  • Gram stain
  • Acid-fast stain
  • Endospore stain
  • Capsule stain

Simple Stain

• Single stain is used to color the cells.
• Examples:
  • Methylene blue
  • Basic fuchsin
  • Crystal violet
  • Safranin