Intro to Microbiology

prokaryotes

• bacteria

• no true nuclei (nucleoid)

• haploid genome

• lack of many cytoplasmic organelles

• possesses cell wall

• simple flagella

• respiration via cytoplasmic membrane

eukaryotes

• algae, fungi, protozoa, plants, animals

• possesses double-membraned nucleus

• diploid genome

• cell wall in fungi

• various cytoplasmic organelles

• complex flagella

• respiration via mitochondria

differences of prokaryotes

• haploid genome vs. diploid genome

  • single mutation will inactivate a function because there is no “backup copy”

• lack of nuclear membrane

  • allows chromosome replication, transcription, and translation to be tied together

• enzymes that synthesize bacterial cell wall structures are unique

  • excellent targets for antibacterial drugs

Koch’s postulates

relates a specific microorganism to a specific disease

gram positive cells

• two layers:

  • inner cytoplasmic membrane

  • outer thick peptidoglycan layer

• low lipid content

• no endotoxin

• no periplasmic space

• no porin channel

• vulnerable to lysozyme and penicillin attack

gram negative cells

• three layers:

  • inner cytoplasmic membrane

  • thin peptidoglycan layer

  • outer membrane with LPS

• high lipid content

• endotoxin (LPS, lipid A)

• periplasmic space

• porin channel

• resistant to lysozyme and penicillin attack

bacterial classification

• microscopic appearance

  • size, shape, and configuration

• ability to retain gram stain

  • gram positive vs. gram negative

• metabolic signature of bacteria

  • anaerobic vs. aerobic environments

• serotyping

  • using antibodies to detect characteristic antigens on bacteria

• analysis of genetic material

  • DNA hybridization, PCR, and DNA sequencing

gram stain

rapid, powerful test that allows clinicians to distinguish between the two major classes of bacteria, develop an initial diagnosis, and initiate therapy based on inherent differences in bacteria

replication

coordinated process in which two equivalent daughter cells are produced

lag time

time to adapt to new environment before bacteria begin dividing

logarithmic (exponential) phase

divide with a doubling time unique to the strain (2n)

stationary phase

bacteria stop growing and enter this phase

death phase

some bacteria stop dividing but remain viable and are often insensitive to antibiotics

doubling time

• the amount of time it takes for a bacterial population to double in size, which can vary depending on the species and conditions

• equation → N_t = N₀ × 2^t/d

flagella

• protein filaments that extend like long tails from cell membranes of certain gram positive and gram negative bacteria

• can have no flagella, single polar flagella, or many peritrichous flagella

pili (fimbriae)

• straight filaments arising from bacterial cell wall

• facilitates bacterial attachment to surfaces and other cells

• transfer genetic material

virulence

• ability of an organism to cause disease

• depends on presence of certain cell structures and on bacterial exotoxins and endotoxins, all of which are virulence factors

• virulence factors help bacteria to…

  • invade host

  • cause disease

  • evade host defenses

spores

dehydrated multi-shelled structure that protects and allows bacteria to exist in “suspended animation”

germination of spores

• mechanical stress, pH, heat, etc.

• swell, shed their coat, and produce one new vegetative cell

endospores

metabolically dormant forms of bacteria that are resistant to heat, cold, drying, and chemical agents

capsules

• enable bacteria to be more virulent because macrophages and neutrophils are unable to phagocytize encapsulated buggers

• functions:

  • influence bacterial adherence

  • interfere with host immune response

  • assist bacterial blood-brain barrier penetration

  • impact on antibiotic resistance

opsonization

the process of antibodies binding to the capsule

biofilm

• extracellular polysaccharide network that forms a mechanical scaffold around bacteria

• protects bacteria from attack by antibiotics and the immune system

• Staphylococcus epidermidis often forms biofilms on intravascular catheters and leaches out to cause bacteremia and catheter related species

facultative intracellular organisms

• many bacteria are phagocytized by macrophages and neutrophils

  • they survive within these cells unharmed

• these bacteria inhibit phagosome-lysosome fusion, thus escaping the host’s deadly H₂O₂ and superoxide radicals

• inside the cells, these bacteria are safe from antibodies and other immune defenses

exotoxins

proteins that are released by both gram positive and gram negative bacteria

neurotoxins

cause paralysis (ex: tetanus and botulinum toxins)

enterotoxins

cause diarrhea

infectious diarrhea

caused by Escherichia coli

food poisoning

caused by Staphylococcus aureus

endotoxins

lipid A component of outer membrane lipopolysaccharide (LPS) of gram negative bacteria

sepsis

bacteremia that causes a systemic inflammatory response to infection

septic shock

inflammation (cytokines) acts on the blood vessels and organs to produce vasodilation, hypotension, and organ system dysfunction and ultimately death