The Microbial World

Question 1

Koch’s Postulates

Answer 1

Koch first demonstrated that a microorganism causes disease (anthrax)

1. The organism is regularly found in the lesions of the disease
2. Isolated in pure culture
3. When inoculated, culture should produce similar disease in experimental animals
4. Organism should be able to be recovered from lesions in these animals

Question 2

Discovery of Antiobiotic

Answer 2

Caused by unkempt lab

Left plates with bacteria on them, came back to find that mold was growing and the area around the mold did not have any bacteria

The mold secreted penicillin which inhibited growth of bacteria

Question 3

Origins of Microbiology

Answer 3

1674: discovered microorganisms
1870: Germ theory
Cause contamination, cause disease
Late 1800s: Agents of diseases discovered; vaccination
Early 1900s: Viruses discovered; antiobiotics discovered
1900s: Threat of ID declines due to sanitation and hygiene, chlorination, antibiotics, vaccines, animal and pest control
Today: Re-emergence of IDs because we were treating patients with antibiotics (comeback diseases) and new diseases

Question 4

Why are some diseases re-emerging?

Answer 4

1. Increased globalization and trade
2. Misuse of antibiotics
3. Evolution of microorganisms
4. Decline in public health (war zones)
5. Inc in IC people (transplants, chemotherapy)

Question 5

Prokaryotic vs. Eukaryotic

Answer 5

Divide by binary fission

Prokaryotic: (Bacteria!)
Small
Rigid peptidoglycan cell wall

Eukaryotic:
Evolved from fusion of prokaryotic cells
Membrane bound organelles
No cell wall in animals
Larger
Nucleus and mito contain DNA

Question 6

Sizes of Microorganisms and How we see them

Answer 6

Viruses < Bacteria < Protozoa and Fungi

Electron microscope < Light microscope < Human eye

Question 7

Taxonomy

Answer 7

Escherichia coli

Genus, species

Question 8

Definition of a species

Answer 8

Eukaryotes: Members can mate and have fertile offspring

Prokaryotes: Look at the 16S rRNA. If it is more than 97% different, they are not in the same species

Question 9

Bacterial Shapes

Answer 9

Bacillus: rod
Coccus: circular
Streptococcus: chain
Staphylococcus: clump
Spirochete: snake-like; predestined to penetrate tissues
Club shaped

Can also have appendages (flagella)
Spores: formed under bad environment as a way for the bacterium to stay alive (dry, nutrient deficient environment)

Capsule: Often anti-phagocytic; leads to more chronic infection that tends to disseminate further than if it were not capsular

Question 10

Gram - membrane

Answer 10

Second outer membrane
Porins allow nutrients in and out of the cell
Thin peptidoglycan layer in periplasmic space
Outer leaflet has lipopolysaccharides linked to membrane by acyl chain
When washed with ethanol, can extract lipids and increase porosity, thus removing the crystal violet-iodine complex

Question 11

Gram + membrane

Answer 11

Thick peptidoglycan layer

Permeability layer; Preventing loss of crystal violet-iodine, appearing purple

Question 12

Gram Stain Test

Answer 12

1. Fresh sample dried on plate
2. Stained with crystal violet, all cells appear purple
3. Add iodine, decreases solubility within cell, cells still appear purple
4. Cells decolonized by washing with ethanol
   * DIFFERENTIAL step*
   Gram+ retain purple
   Gram- do not (colorless)
5. Cells rinsed with counter stain safarin which stains Gram- PINK

Question 13

Virulence

Answer 13

ID and LD (lethal)
ID50: number of microorganisms needed to infect 50% of host population

If you have a 10^5 bacteria and inject into ten mice, half will come infected

Virulence is opposite of ID

Ex. Shigella has a LOW ID, in the 10s. Takes a very small amount of organisms to infect 50% of hosts. Would be considered very virulent

Question 14

Sterile areas in the body

Answer 14

1. Lower respiratory tract
2. Upper genitourinary tract

Intestine is LOADED with bacteria (large)

Skin has no Gram-

Question 15

Lyme disease transmission

Answer 15

Zoonotic
Vector-borne

Reservoir is a mouse, transmitted to humans with the help of a tic

Question 16

Preventive Measures

Answer 16

Standard: Hand hygiene, procedure appropriate

Contact: Gloves, gowns, private room
ex. diarrhea from norovirus or C. diff

Droplet precautions: If pathogens don’t travel more than 3 feet; masks/respirators, closed room
ex. influenza, N. meningitidis

Airborne precautions: Travel more than 3 feet; PARP respirators, airborne infection, All air leaving room going through HEPA filter
ex. Measles, Mycobacterium tuberculosis

Full barrier precautions: airborne + contact plus eye protection
ex. avian/pandemic influenza, SARS

Question 17

Types of pathogens (3)

Answer 17

1. Nonpathogens: present in microbiome; normal flora; occupy niches and prevent pathogens from coming in and causing the disease
2. Opportunistic: present as normal flora; if it gets into the wrong tissues it can cause problems, or if it is given the opportunity of an IC patient
3. Primary pathogens: if you see this in the sample, you know it is causing the disease
   Immunizations common

Question 18

Stages of Bacteria Pathogenesis

Answer 18

1. Transmission
2. Adhesion
3. Colonization
4. Spread
5. Damage (directly- toxins or enzymes by bacterial products; indirectly- inflammation (immune responses))
6. Evasion of host immunity (in host survival)
7. Transmission to a new naive host

Question 19

Virulence factors

Answer 19

Help bacteria invade the host, cause disease, evade host defenses

Some are targeted by vaccines and detected by specific tests

Adhesins: Allow bacteria to adhere to tissues

Invasins: Allow bacteria to get inside a host cell; evade humoral inflammation; now relying on cell-mediated inflammatory response to clear infection; nutrient rich cytoplasm and safe from host defense responses

Exotoxins: (Enterotoxins); secreted from a bacterial cell; bacteria mediated pathogenesis

Endotoxins: Released when cell is lysed; potent toxin that signals immune response; host mediated pathogenesis; GRAM- ONLY

Degradative enzymes: Break down tissues; allow bacteria to spread in tsisues

Question 20

Adhesins

Answer 20

Allow bacteria to adhere to tissues
Pili (fimbriae) on E. coli
Protein adhesins: pull bacteria closer so they stick better to tissues and allow colonization
Biofilms: bacteria stick together and attach to a surface (plaque, catheter causes UTI)

Question 21

Intracellular (bacterium growth)

Answer 21

Obligate: always need a host cell to replicate in
Facultative: can work intracellularly or extracellularly; life to replicate outside of the cell but then go into the cell to escape humoral immune responses and have access to more nutrients

Question 22

Systemic disease (bacterial spread)

Answer 22

Vs. localized

Destruction of tissue barrier by tissue damaging enzymes
Penetration of cell membrane (invasion)

Question 23

Types of Invasion of pathogens

Answer 23

1. Passive uptake: immune cells that uptake bacteria (phagocytosis)
2. Active invasion: Invasins on cell surface induce uptake by non-phagocytic cells; OR make virulence factors that allow them to invade non-phagocytic cells
   Salmonella, Yersinia
3. Transcytosis: Intracellular motility by actin polymerization; go through cells
   Shigella, Listeria

Question 24

Syringe secretion systems

Answer 24

T3SS
Type 3 and 4 are syringe mechanisms
Multi-protein complex expressed by bacteria cell
Can inject effector proteins from bacterium into the cell
1. Mess with actin
2. Cleave rRNA, blocking protein synthesis, killing the cell

Make a complex stretching from bacteria cytosol into the host cell cytosol; effector proteins never encounter extracellular environment

Question 25

Types of exotoxins

Answer 25

1. Enzymes Act on extracellular matrix Collagenase, hyaluronidase ``` 2. AB type toxins Two components (subunits) Cholera, diphtheria, shiga, pertussis, tetanus, anthrax, botulinum, E. coli heat labile toxin ``` 3. Membrane damaging toxins: Phospholipases ex. Perfringens alpha toxin Pore forming toxins ex. Listeriolysin Cause hemolysis 4. Superantigens: Enterotoxins of S. aureus

Question 26

AB toxins

Answer 26

Intracellular acting toxin B: Binds to cell surface receptor; determines host cell specificity of toxin; forms pore A: disulfide bonds are broken and A becomes Active enzymatically and is transported to cell interior; toxic activity Targets of A subunits: 1. ADP ribosylating toxins Diptheria toxin: inactivates elongation factor (translation, protein synthesis) Cholera toxin, pertussis: Activates adenylate cyclase (increasing cAMP levels) 2. Others Shiga, EHEC: cleaves rRNA (translation, protein synthesis) Tetanus, botulinum: Blocks release of neurotransmitter Examples of AB 1. Shiga toxin 2. E coli LT1 3. Petussis toxin Single A subunit with multiple B (A1B5) *B subunit good target because it will affect all things downstream

Question 27

Superantigens

Answer 27

Causes nonspecific binding of T cells Produced by some pathogenic viruses and bacteria most likely as a defense mechanism against the immune system Temporary interaction where the APC will just present the peptides of pathogens to the T lymphocyte VERSUS SUPERANTIGEN which locks the presenting state APC to T lymphocyte

Question 28

Endotoxin: LPS

Answer 28

Released by cell lysis, not secreted Toxicity due to lipid A component (fatty acids, disaccharide, diphosphate) Also has O-antigen component Causes septic shock Binds to LPS binding protein and interacts with host receptor CD14 Signals through toll-like recepor

Question 29

How do pathogens evade host immune responses?

Answer 29

1. Defensive Capsule: protects from being phagocytksed Serum resistance due to modification of LPS preventing C5b-9 complex 2. Offensive Produce toxins which degrade immune components (C5a, IgA proteases) Killing of phagocytes 3. Stealth Antigenic variation

Question 30

Antigenic variation

Answer 30

1. A pathogen expresses an immunodominant surface antigen (largely recognized by immune system) 2. Shut down expression of antigen and start expressing another type of antigen unrecognizable by antibodies 3. Bacteria buys itself time to replicate until host develops a new set of antibodies that will recognize the new coat and try to kill the cells

Question 31

Iron acquisition

Answer 31

Most bacteria need iron for growth -bactin Bacteria produce siderophores which bind to iron and then bind to a receptor on the bacteria to be taken up Main way to acquire iron for growth

Question 32

Virulence factors are encoded on:

Answer 32

1. Chromosome: stable 2. Pathogenicity island: Region of DNA that has all the genes coding for a specific set of virulence genes (ex. all components of T3SS: effector proteins and needle 3. Plasmid: dispensable, can be transferred to another bacteria; extrachromosomal smaller DNA replicon 4. Bacteriophage: spread DNA between bacteria (transduction) - bacterial viruses 5. Transposon: highly motile; can accelerate spread of genetic material

Question 33

Complentation

Answer 33

Reintroduction of a functional gene into mutant bacterium should restore the invasive wild type if the mutant is responsible

Question 34

Type I toxin

Answer 34

Bypass cell membranes by activating signaling molecules on the cell surface

Question 35

Type II

Answer 35

Directly attack the host cell membrane resulting in increased permeability