Bacteria vs. Viruses

Kerrigan Krueger


  • Gram staining: used to identify unknown bacteria
  1. Pink color= negative, purple color= positive
  • Shapes
  1. Cocci (spheres): Micrococcus luteus,
  2. Bacilli (rods): Bacillus subtilis, serratia marcescens
  3. Cocobacilli (ovals): Staphylococcus epidermidis
  4. Vibrio (curved rods): Escherichia coli
  5. Spirillia (rigid helices)
  6. Spirochetes (flexible helice)

Bacteria Growth and Nutrition

  • Environmental factors
  1. Solutes
  2. Temperature (incubator)
  3. Radiation: x-rays, ultraviolet
  4. pH
  5. Oxygen concentration
  6. Nutrients (macro and micro)
  • Chemical and physical factors
  1. Chemical: detergents, solvents, alcohols
  2. In lab: Hydrogen peroxide, bleach, lysol, isopropyl alcohol,
  3. Kills/inhibits bacterial growth
  4. Physical: Heat, dry heat, refrigeration
  5. In lab: Bunsen burner


  • Obligate intracellular parasites, sub-microscopic entity consisting of a single nucleic acid surrounded by a protein coat and capable of replication only within the living cells of bacteria, animals, or plants
  • Structures and resistance:
  1. Naked capsid virus: DNA/RNA +capsid protein= Nucleocapsid
  2. Resistant to drying, heat, detergents, and acid
  3. Enveloped virus: Nucleocapsid + lipid membrane and glycoproteins
  4. Sensitive to drying, heat, detergents, and acid
  • Virus replication
  1. Attachment and entry: hijacks healthy receptors for infection process
  2. Uncoating: virion breaks open and releases virus genome nucleic acid
  3. Transcription: virus mRNA provided using cellular enzymes or virus encoded enzymes)
  4. Genome replication: takes place in cytoplasm or nucleus of infected cells
  5. Translation: uses host cell ribosomes, enzymes, etc. and proteins are synthesized
  6. Virion assembly: new proteins and new genomic nucleic acid produce new virus particles
  7. Virion releases: virus buds through cell membrane and pick up envelope or the virus causes lysis of cell, and the host cell dies, releasing progeny virus

Virus transmission and infection

  • Virus transmission
  1. Respiratory: SARS
  2. Fecal/oral
  3. Blood-borne
  4. Sexual: HIV
  5. Animal or insect vectors: Avian influenza
  • Virus infection
  1. Development of viraemia (virus in blood) spreads throughout tissues
  2. Short incubation time, maximal virus production right after
  3. Symptoms appear right after peak
  4. Immune response generated, virus usually killed after 1 to 2 weeks

Compare and Contrast

  • Bacteria: living, reproduces by dividing, exist everywhere
  • Virus: non-living, require living hosts to multiply or they won't survive
  • Bacterial infection: localized to specific parts of the body
  • Viral infection: involve different parts of the body or more than one body system
  • Bacteria: more complex structure than virus, larger than virus
  • Both: contain DNA/RNA and enzymes, both cause illnesses
  • Bacteria: has a cell wall
  • Virus: has a protein coat
  • Bacteria: one chromosome
  • Virus: central core of DNA or RNA