19 - Bacterial Invasion

Question 1

Use of term “invasiveness”

Answer 1

1. Ability of a microbe to enter a host, grow and reproduce within the host and spread throughout the body
2. Entry and survival within phagocytic cells
3. Ability to enter non-phagocytic host cells, such as epithelial cells

Question 2

Ability of a microbe to enter a host, grow and reproduce within the host and spread throughout the body

Answer 2

Mediated by production of lytic substances or “spreading factors” that may alter or damage host tissue

Question 3

Collagenase

Answer 3

• Breaks down collagen
• E.g. Clostridium

Question 4

Fibrinolysin

Answer 4

• Digests fibrin clots
• e.g. Staphylococcus

Question 5

Hyaluronidase

Answer 5

• Depolymerises hyaluronic acid
• e.g. Streptococcus

Question 6

DNase

Answer 6

• Destroys DNA
• E.g. Clostridium, Staphylococcus, Streptococcus

Question 7

Three niches in phagocyte that intracellular pathogen survive by exploiting

Answer 7

1. Bacteria live in phagolysosome and are resistant to killing
2. Bacteria live in the phagosome and prevent phagosome-lysosome fusion
3. Bacteria escape from phagosome into cell cytoplasm

Question 8

Ability to enter non-phagocytic host cells, such as epithelial cells

Answer 8

• Results in bacterial colonisation within the mucosa,
• or bacterial translocation across the mucosal barrier,
• or bacterial access to deeper or systemic tissues by way blood or lymphatic vesicles

Question 9

How do bacteria force “non professional phagocytes” to take them up

Answer 9

• Bacteria attach to host cell surface
• Cause changes to host cell cytoskeleton, causing actin rearrangements and pseudopod formation

Question 10

Invasins

Answer 10

Bacterial surface proteins that provoke uptake

Question 11

How does invasion benefit the bacterial pathogen

Answer 11

• Provides a safe environment for bacterial growth
• Gain nutrients from host
• No competition for nutrients from other microbes
• Pathogen can evade host immune system and antibiotics

Question 12

Two main mechanisms for invasion of non phagocytic cells

Answer 12

• Zipper mechanism
• Trigger mechanism

Question 13

Zipper mechanism

Answer 13

• Bacterial invasins bind to host cell receptors at a number of points along the cells
• Actin polymerization is triggered and bacteria are surrounded by tight-fitting pseudopodia and engulfed into phagosome

Question 14

Trigger mechanism

Answer 14

• Bacteria inject molecules into host cell via Type III secretion apparatus
• These activate changes to host cell’s actin cytoskeleton causing membrane ruffles or “splash”, leading to uptake of bacterial cell by host cell

Question 15

Examples of bacteria that use zipper mechanism

Answer 15

Listeria and Yersinia

Question 16

Examples of bacteria that use trigger mechanism

Answer 16

Shigella and Salmonella

Question 17

T3SS in trigger mechanism

Answer 17

• Type 3 needle is embedded in bacterial cell envelope
• Close physical contact between bacterial and eukaryotic cell
• Proteins travel from bacterial cell through hollow needle into eukaryotic cell (injection)
• Trigger membrane ruffling

Question 18

Listeria

Answer 18

• Gram positive rods
• Causes serious food-borne infections (listeriosis)
• Facultative intracellular pathogen
• Invades wide variety of cells including phagocytes, liver cells, epithelial cells

Question 19

Pathogenic species of listeria

Answer 19

Listeria monocytogenes

Question 20

Listeria zipper mechanism

Answer 20

• Listeria InLB (internalin, an invasin) binds to the host cell Met receptor
• Binding triggers a signal transduction that activates ARP 2/3 complex
• These promote the recruitment of G actin and assembly of F-actin to result in bacterial uptake by the host cell

Question 21

Cell to cell spread of listeria after invasion by zipper mechanism

Answer 21

• Bacteria contained within vesicle
• Bacteria lyse vacuole membrane and escape into cytoplasm
• Bacteria polymerise actin filaments at one end of cell forming actin tails which propel them through cytoplasm
• Bacteria push into neighbouring cells, forming a protrusion which buds off forming a double membrane vacuole in the new cell
• Bacteria lyse vacuole and enter new cell’s cytoplasm

Question 22

Actin based motility “comet tails”

Answer 22

• Actin is one of the proteins that makes up the eukaryotic cell cytoskeleton
• Listeria cells are able to induce the polymerisation of actin monomers into polymers at one end of the bacterial cell (mediated by Listeria’s ActA protein which activates host cell’s ARP2/3)
• Long actin tails form, where actin is being depolymerised at the end of the tail while being polymerised at the bacterial surface
• This provides a force to push the bacteria through the cell cytoplasm

Question 23

Shigella

Answer 23

• Gram negative rods
• Causes bacillary dysentery (bloody diarrhoea)
• Invades cells of the colon

Question 24

Invasion by trigger mechanism of Shigella

Answer 24

1. Shigella are taken up by M cells in colon
2. Reach the resident macrophages and are endocytosed
3. Escape from the phagosome and induce death of macrophage
4. Shigella are released from macrophage
5. Enter epithelial cell from basolateral surface (underneath) by inducing actin polymerisation and engulfment

Question 25

Cell to cell spread of Shigella

Answer 25

1. Shigella enter cell in vacuole, lyse the vacuole membrane, and escape into cell cytoplasm and multiply
2. Move rapidly within cytoplasm via actin mediated motility (lack flagella)

Question 26

Cell to cell spread of Shigella

Answer 26

• Same as Listeria
• Lack flagella

Question 27

Salmonella

Answer 27

• Gram negative rods
• Invade cells of small intestine via T3SS
• Salmonella enterica serovar Typhi causes typhoid fever
• Other serovars cause enterocolitis/diarrhoea
• Bacteria are ingested from contaminated water or animal products

Question 28

Invasion by trigger mechanism and spread of salmonella

Answer 28

• Invade cells of small intestine via T3SS
• Vacuoles then translocate across cell using two host microtubule proteins
• Bacteria are released to underlying tissues, and then phagocytosed, survive and disseminate systemically

Question 29

Salmonella vs shigella

Answer 29

• Following invasion from the lumen, Salmonella are translocated across intestinal epithelium and gain access to host circulation
• After translocation, Salmonella survive within phagocytes by preventing phagosome-lysosome fusion
• Bacteria disseminate to systemic sites

Question 30

IpaB

Answer 30

• Adhesion
• Binds CD44 receptor
• Located at needle tip, supported by IpaD scaffold proteins

Question 31

IpaC

Answer 31

Travels up needle, interacts with IpaB and inserts into host cell membrane forming a pore

Question 32

IpaA

Answer 32

Actin depolymerisation

Question 33

Invasion mechanism of listeria, shigella and salmonella

Answer 33

• Listeria: Zipper (invasions)
• Shigella: Trigger (T3SS)
• Salmonella: Trigger (T3SS)

Question 34

Internal spread of listeria, shigella and salmonella

Answer 34

• Listeria: Actin based motility
• Shigella: Actin based motility
• Salmonella: Survival and spread in phagocytes

Question 35

IpaC, IpgB1, IpgB2 and lpgD

Answer 35

Actin polymerisation

Question 36

IpaB and D

Answer 36

IpaB located at needle tip, supported by IpaD scaffold proteins, forming needle tip complex