Host-Parasite Interaction Flashcards Preview

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Flashcards in Host-Parasite Interaction Deck (41):
1

commensal

benefit microbe, harmless to the host

2

symbiotic

mutual benefit to both and microbe

3

parasitic

benefit to the microbe, harm to the host

4

pathogenicity factors

- in order for a microbe to be pathogenic, it must enter the host, maintain a population, and cause damage to the host.

5

Type I secretion

- Enterohemorrhagic E. Coli

6

Type II secretion

- Vibrio cholera

7

Type III secretion

- Enteropathogenic E. Coli

8

Type IV secretion

- Agrobacterium tumefacians

9

Adherence

- proteins
- Fimbriae
- Glycocalyx

- sometimes interactions are specific, sometimes not

10

proteins:

- N. gonorrhea
- Opa protein binds receptors in urogenital epithelium

11

Fimbriae

- Salmonella
- fimbriae bind to epithelium of small intestine

12

Glycocalyx

- help streptococcus mutant bind to tooth surfaces

13

Toxins

- exotoxins
- endotoxins

14

endotoxins

- made up of LPS
- the presence of LPS in an animal is always indicative of an infection, and the innate immune system will kick in any time LPS is detected (pyrogenicity)

15

exotoxins

- specifically made by the microbe in response to host invasion
- exported from the cell and have specific targets in or on the host cells.

16

types of exotoxins

- cytotoxins
- neurotoxins
- enterotoxins

17

cytotoxins

- cause damage to host cell structure and activities
- protein synthesis inhibitors - diphtheria toxin
- hemolysins - attack RBC
- leukocidin - attack WBC
- do so by inserting pore forming proteins into target cell membranes

18

neurotoxins

- cause damage to neural tissues and disrupt nerve conduction
- botulism toxin - prevents release of acetyl choline which prevents muscle contraction
- tetanus toxin - blocks release of gaba which prevents muscle relaxation

19

enterotoxins

- mainly act on tissues in intestines
- cholera toxin - massive diarrhea and water loss

20

A-B exotoxins

- A subunit is the toxin
- B subunit binds to the host cell

21

How AB toxin works

- B subunit (bound to A) will recognize a receptor on the host cell surface and bind to it.
- The host cell will be signaled to take up the bound AB toxin via endocytosis.
- upon entry, the A and B will dissociate and the toxin will interact with the target

22

A toxins

- many but not all are enzymes called ADP ribosyltransferases, which transfer the ADP-ribose from a NAD nucleotide to its target protein
- once target protein has been ADP ribosylated, it becomes inactive

23

targets of ADP-ribosylation

- elongation factor 2 - diphtheria toxin
- adenylate cyclase - cholera, pertussis toxin
- G-actin - clostridium toxA

24

Toxin Delivery (Secretion Systems)

- The type I-IV secretion systems are used by Gram-negative bacteria to get virulence factors past both membrane and out of the cell.
- I and II deliver the secreted protein into the environment around the cell, but are not specific for toxin delivery.
- III and IV deliver the toxins directly into the cytoplasm of host cells.

25

Type I secretion system

- consists of an outer membrane channel
- always TolC
- and an inner membrane ABC transporter
- depends on the protein
- each protein requires a unique ABC transporter

26

ABC transporter

- identified by the presence of a protein motif called ATP Binding Casette
- casette binds and hydrolyzes ATP, providing energy to transport the protein.
- the rest of the transporter specific for the protein being transported.

27

E. Coli O157:H7 secretion system

- causes hemolytic uremic syndrome
- the disease is caused by production of hemolysin secreted by type I secretion
- lysed blood cells clog glomerulus in kidneys and waste products accumulate in the blood
- bacteria almost never found in the blood.

28

Hemolysin action

- hemolysin is secreted as a monomer but assembles as an oligomer in the RBC membrane, and then insert as an octomer into and through the membrane.

29

Type II secretion

- method of getting proteins past the outer membrane, but proteins secreted must be in the periplasm to begin with.
- use Sec system to transport proteins into the periplasm
- once in periplasm, push protein past outer membrane by type II
- homology to type IV pilus

30

Cholera toxin secretion system

- when large numbers of it are ingested, they will make and secrete the cholera toxin. Outbreaks correlated to the sea surface temperatures
- since 1817 there have been 7 (or *) major pandemics
- AB toxin that is active against the epithelial cells of the intestines
- once inside cell, A subunit will modify adenylate (through ribosylation) to make it always activated
- increases cAMP levels which triggers massive losses fluid, severe diarrhea, dehydrates, and could result in death (from hypovolemic shock)

31

Type III secretion

- they deliver the toxin directly to the cytoplasm of the host cell.
- The TTSS passes through three membranes.

32

Enteropathogenic E. Coli secretion system (EPEC)

- first attaches to host cell via fimbriae and protein intimin
- once cell close enough the use the TTSS, the Tir proteins are injected
- TSSS will inject toxin identified as EspF

33

Tir proteins

- serve as attachment sites for EPEC as well as nucleation sites for actin polymerization.
- actin pushes the host cell membrane up, creating the pedestal on which EPEC will sit on.
- basically make their own adherence molecule.

34

EspF

- directed to the mitochondria and causes leaks
- mitochondria release cytochrome C which signal signal apoptosis.
- epithelial death causes breakdown of mucosal barrier and diarrhea

35

Type IV secretion

- powered by ATP, also resembles type IV pili (conjugatation pilus)
- directly inject DNA and protein into the cell.
- transport occurs all the way from the cytoplasm of the bacteria to the cytoplasm of the host

36

Agrobacterium tumefaciens secretion system

- a gall (plant cancer) caused by insertion of proteins and oncogenic DNA via a type IV secretion apparatus
- bacteria capable of causing the tumors contain a tumor inducing plasmid (Ti) plasmid
- must enter through a wound

37

Ti plasmid

- contains a small portion of DNA (T-DNA) that is transferred to the plant to cause the tumor, the opine permeate and opine catabolism proteins, and Vir proteins.
- contains genes that encode a type 4 secretion system that will transfer T-DNA and the VirD2.

38

VirD2

- site-specific DNA recombinase that will help transport the T-DNA into the nucleus and insert it directly into the plant chromosome.

39

T-DNA

- contains genes that will make the plant produce auxins (plant hormones) and cytokines, plant steroids that will cause the cell to reproduce rapidly and form the gall.
- also present are the genes that cause the plant to produce opines and nopaline.

40

opines

- rare amino acids that will be excreted by the plant cells to feed the bacteria.
- argenine and lysine residues lined up
- A. tumefaciens use the opines as food, but only if they are carrying the Ti plasmid, as it contains the genes required for opine catabolism.
- bacteria that do not have the plasmid do not have the ability to break down opines.

41

Difference between endotoxin and exotoxin

EXOTOXIN
- protein
- high potency
- high specificity
- enzymatic activity
ENDOTOXIN
- LPS
- low potency
- low specificity
- no enzymatic activity