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Flashcards in Principles of Infectious Disease I Deck (24):
1

What are some factors that may be driving the resurgence in infectious diseases?

-POPULATION MOVEMENTS and intrusion of humans and domestic animals into new habitats
-POPULATION OVERCROWDING, especially coupled with poor public sanitation
-increased long-distance air TRAVEL - contact/transport of arthropod vectors and primary pathogens
-MICROBIAL EVOLUTION, leading to natural selection of multi-resistant agents

2

What are the four major classes of pathogens?

-viruses
-bacteria
-fungi
-parasites
Very Bad Funny Parents? Very Blue Faded Pants?

3

Which of the four agents has a cell wall?

Bacteria (with some exceptions) and Fungi

Parasites do not, with some exceptions
Viruses do not

4

What are the cell plans of the four pathogens?

-viruses: none
-bacteria: prokaryotic
-fungi: eukaryotic
-parasites: eukaryotic

5

Which of the four pathogens are free living?

Bacteria (with some exceptions)
Fungi
Parasites

Not free living: viruses (they are dependent on the host)

6

Which of the four pathogens are intracellular?

Viruses (dependent on the host)

Bacteria, Fungi, and Parasites are not intracellular, with some exceptions.

7

Describe the general features of viruses

-carry genetic information (nucleic acids; DNA or RNA)
-have a protein coat (sometimes with a lipid envelope)
-obligate INTRACELLULAR MICROBES
-use host cell enzymes and machinery to replicate (make copies of genome and proteins)
-most common infectious agents in humans

8

What are the steps of the general replication strategy of viruses?

1 - ATTACHEMENT/adsorption to cell (protein on virus binds to receptor on cell surface)

2 - ENTRY/pentration (often involves escape of virus for endocytic vesicle)

3 - UNCOATING (release of nucleic acid into cytoplasm)

4 - REPLICATION (new copies of the genome are made)

5 - TRANSLATION (the genome is transcribed and translated to make virus proteins that are used in producing new virions and to manipulate the host cell, making it more favorable for replication)

6 - VIRUS ASSEMBLY/packaging (a copy of the genome is incorporated into new virions)

7 - RELEASE (may/may not involve lysis of host cell)

9

Describe the general features of bacteria

- small, single-celled prokaryotic organisms
- no nucleus, no organelles and typically have a single circular chromosome
- bound by rigid cell wall
- divide by binary fission (therefore can multiply rapidly)
- may be free-living, may live inside host cells - or do both!
- full metabolic machinery (do not need host); they can perform protein synthesis and have secretory capacity

-most bacteria are anaerobic, but mostly aerobic bacteria are the ones that infect humans
**cell wall can be target of antibiotic treatement

10

Morphological forms (define)
-cocci
-bacilli
-spiral
-staph
-strep

Morphological forms (define)
-cocci: round
-bacilli: rods
-spiral
-staph: grape/cluster
-strep: chains

11

What are the main features of the bacterial structure?

- LIPID-BASED MEMBRANE around cytoplasm
- CELL WALL (composed of peptidoglycan and other molecules) (a few bacteria do not have cell wall - mycoplasma, ureaplasma)
- with/without CAPSULE/slime layer (thick layer of polysaccharides or proteins surrounding bacteria to protect cell)
- with/without APPENDAGES (pili-attachment to surfaces and host cells, and other functions; flagella-motility)

some bacteria have an outer lipid membrane (additional?)

**Peptidoglycan is found in Gr+ and Gr-, and is unique to bacteria: some innate immune receptors will respond to these; if we develop drugs that block these enzymes, this wouldn't be harmful to us because we don't have peptidoglycan

12

Gram-positive vs. Gram-negative bacteria

Gram-positive:
-thick cell wall lacking an outer membrane
-stains purple (thick cell wall retains dye)

Gram-negative:
-plasma membrane (inner membrane) AND an outer membrane, with a cell wall in between
-outer membrane is rich in lipopolysaccharide (LPS), also called "endotoxin," a potent immune stimulant
-stains light pink

13

Describe the general features of fungi

-eukaryotic organisms, some are pathogenic for humans
-cell wall, otherwise very similar to animal cells
-plasma membrane contains ergosterol (not found in animal cells, it is cholesterol-related, potential therapeutic target for drugs)
-sizes range from small (like bacteria) to macroscopic (mushrooms)
-free-living; full metabolic machinery
-capable of sexual and asexual reproduction
-no photosynthesis

**harder in general to treat because human cells are also eukaryotic
**can cause many different types of infections, including deep and systemic infections

14

Fungal structure

-PLASMA MEMBRANE surrounded by a rigid CELL WALL composed of mannan, chitin, glucan, and other components
-can be found as YEAST (single cells that reproduce by budding) or MOLD (composed of hyphae: tube-like extensions that branch to create a multi-cellular structure) forms
-some are dimorphic- exist in yeast or mold form dependent on environment

15

Describe the general features of parasites

-diverse
-high prevalence in human populations accounting for significant morbidity and mortality, but with considerable geographic variability
-two major taxonomic groups: PROTOZOA (microscopic, single-celled eukaryotes) and HELMINTHS (macroscopic, multicellular worms)

-also, ectoparasites: insects like lice, bedbugs, fleas

16

Protozoa

-eukaryotic
-often have complex life/infection cycles involving multiple hosts and/or unique environmental reservoirs
-usually highly adapted to their host(s) (ex: malarial parasite, two hosts mosquito and human)

17

Helminths

-worms
-often found in digestive and circulatory systems
may produce eggs or live young
-ex: roundworms, tapeworms, flukes

18

What are four types of atypical pathogens?

- MYCOPLASMA (true bacteria but no cell wall)
- CHLAMYDIA (bacteria that only replicate in host cells and that lack peptidoglycan in their cell wall)
- RICKETTSIA (small Gr- bacteria that only replicate in host cells)
-PRIONS (transmittable protein-mediated diseases; ex: Creutzfeldt-Jakob disease and Mad Cow disease which are progressive neurodegenerative diseases)

19

Characteristics of Prions

-cause spongiform encephalopathies in CNS
-diseases have long incubation periods (may be inherited or transmissible)
-prion protein is a cellular protein that can adopt on alternate conformations [the alternate (disease) form catalyzes the conversion of normal forms to the disease form; disease forms of the protein can aggregate in neurons and cause cell death]

20

What is the general immune response to viruses?

-innate immunity includes type-I interferon pathway
-CD8 T cells eliminate virus-infected cells
-antibodies neutralize virus in the blood or at mucosal sites

21

What is the general immune response to fungi?

-innate immunity mediated by phagocytes (neutrophils and macrophages)
-TH1 response key to activating phagocytes so they are better at killing

22

What is the general immune response to bacteria?

-innate mechanisms (complement and phagocytes)
-antibody response facilitates opsonization and complement functions
-intracellular bacteria (such as Listeria) require CD8 T cells

23

What is the general immune response to parasites?

-for some agents, the large size presents a challenge (cannot be ingested by phagocytes and processed)
-TH2 response is critical, mediated by IgE antibodies
-granules released from eosinophils can be toxic to worms and/or cause a strong inflammatory reponse

24

*Note: CD4 T cells are needed to coordinate most of these responses

*Note: CD4 T cells are needed to coordinate most of these responses
(immune responses to viruses, fungi, bacteria, and parasites)