Lecture 12 corynbacterium, Listeria, Bacillus

Question 1

What is Corynebacterium diptheriae?

Answer 1

Koryne=club; small, gram-positive pleomorphic non-sporulating; non-motile.

Question 2

What is the mode of environment/mode of transfer for corynebacterium?

Answer 2

Humans are the only natural reservoir. Spread by respiratory droplets, cutaneous lesions and fomites. Pharyngeal/nasal carriage in some convalescent cases.

Question 3

What are fomites?

Answer 3

Non-living substances, it can distribute pathogens.

Question 4

How can cutaneous lesions spread disease?

Answer 4

When someone bumps into and makes contact with the pathogen.

Question 5

What are convalescent cases?

Answer 5

you get the pathogen, but you don’t die from it and become a carrier

Question 6

What is the principal virulence factor in Corynebacterium diptheria?

Answer 6

Diptheria toxin, a signal toxin can kill a cell. A (catalytic) unit and B (cell binding) unit.

Question 7

How does diptheria toxin work. ?

Answer 7

Toxin is taken up by endocytosis. Acidification of the endosome releases unit A into cytosol. ADP-ribosylation of elongation factor 2 irreversibly halts protein synthesis causing the cell to die.

Question 8

Where is DT encoded?

Answer 8

DT is encoded in lysogenic bacteriophage.

Question 9

What is DtxR?

Answer 9

Iron dependent repressor of the DT. When there are high iron concentrations DT is inhibited because it is a waste of energy.

Question 10

DT is co-regulated with what?

Answer 10

Siderophores (iron binding protein) part of the bacterial iron transport system.

Question 11

What is known about diptheria colonization?

Answer 11

-Generally in the nasopharyngeal region, non-invasive, historically a childhood disease.

Question 12

What are some local toxin effects of C diptheria?

Answer 12

• pharyngitis (sore throat) formation of pseudo membrane.
• Epithelial cell necrosis (cell death)
• Inflammation (IL-1, IL-6, TNF)

Question 13

What are some indicators of pharyngitis?

Answer 13

• Debris, fibrin, formation of pseudomembrane.
• gray/yellow/white membrane with surrounding inflammation.
• mechanical obstruction of airway.

Question 14

What are some systemic toxin effect of C. diptheria?

Answer 14

• myocarditis (muscle hear inflammation); significant cardiomyopathy.
• paralysis of soft palate and select muscle groups, most seriously in the diaphragm.

Question 15

In what scenario can C Diptheria cause skin infections?

Answer 15

Occurs in tropical and hot, arid regions; usually without systemic complications. Different toxins can cause different sx as a result of different distribution and action.

Question 16

What is the Dx of C diptheria?

Answer 16

Isolate form lesions by culture on selective media (Tinsdale agar) for 48 hours containing:

• potassium tellurite: inhibits G - bacteria.
• dark brown/balck colony; H2S production from L-cysteine produces dark halo (CO2 retards halo formation) .

Question 17

Why is it important to have a system to find rare bugs?

Answer 17

Because they rarely occur so you need to be able to identify them.

Question 18

How is diptheria prevented?

Answer 18

• By vaccine DTaP.

- almost completely eliminated (10 cases a year).

Question 19

What is in DTaP vaccine?

Answer 19

• Formalin treated DT- inactivates B while maintaining A structure.
• Ab does not eliminate infection; mild disease, pathogen colonizes but immune system can fight off.

Question 20

What can Corynebacterium jeikeium do?

Answer 20

Is skin microbiota. Can cause bactermia, endocarditis, pneumonia, osteomylitis, meningitis; immunocompromised pts or those with indwelling devices are susceptible. nosocomial infections; multi-drug resistant.

Question 21

What is Listeria monocytogenes?

Answer 21

Gram-positive rod; coccobacilli, catalase +.
Beta-hemolytic on blood agar; grows at low temperatures, low pH, high salt. Intestinal colonization in humans and other animals; widely distributed in environment

Question 22

What are internalins InlA and InlB?

Answer 22

-Allows listeria monocytogenes to bind and invade non-phagocytic cells (intracellular) - involved in crossing critical anatomical membranes

Question 23

What is the the function of IntlA

Answer 23

-binds E-cadherin on intestinal epithelial cells

Question 24

What is the specific function of InlB?

Answer 24

binds HGFR [hepatocyte growth factor receptor]

Question 25

What is Listeriolysin O?

Answer 25

• pore-forming toxin active at pH ~5.5
  
  • Listeria unable to replicate in phagosome; grows well in cytosol
• LLO causes lysis of bacteria-containing phagosome
  
  • LLO-mutant is avirulent
• lytic activity limited by pH optima and proteolytic degradation by proteasome (intracellular protein recycling, MHC I, Peptides)

Question 26

What is phospholipase’s purpose?

Answer 26

In listeria m. releases bacteria from phagosome.

Question 27

What is the purpose of ActA?

Answer 27

surface protein with polar distribution is key for cell-to-cell spread

• promotes actin polymerization: so-called “comet tails” that push bacteria through cytoplasm
• plasma membrane of neighboring cell pinches off forming double-membrane compartment
• LLO/phospholipases allow release into cytosol

Question 28

Listeria is commonly found where?

Answer 28

-Foodborne; incubation period longer than most other food-born illness; outcome depends on host attributes. (soft cheese, mexican).

Question 29

Why is listeria of concern for pregnant women?

Answer 29

• Vertical transmission: feto-placental infections
• early onset: septicemia in utero
• late onset: exposure during birth; meningitis 2-3 wks later

Question 30

What are some concerns of listeria other than pregnant women?

Answer 30

• Elderly; alcoholism; diabetes; corticosteroid use; individuals with compromised cellular immunity
• Meningitis [presents similar to other CNS bacterial infections: fever, headache, stiff neck]
• Septicemia
• If mouse gets it they do not get sick

Question 31

What are some gastrointestinal effects caused by listeria in immune competent people?

Answer 31

• mild flu-like symptoms [low inoculum]
• febrile gastrointestinal infections [high inoculum]
• 20 -30 % mortality when anatomical barrier passed.

Question 32

What is the Dx of Listeria?

Answer 32

Cx CSF, blood, amniotic fluid, placenta, fetal tissue; tumbling motility at RT (non-motile at 37C).

Question 33

Could you engineer listeria vector to combat viral infections or cancer?

Answer 33

-Using listeria to develop antigens, and to induce CD4 T cells against cancer. Firs used dead cells, now using live cell.

Question 34

What is Bacillus cereus?

Answer 34

long-wide GPR [over decolorize to appear GNR]; aerobe; beta-hemolytic; motile; spore former. Widely distributed throughout nature (problem, how to tell whether it is a contaminent).

Question 35

What is the purpose for forming spores?

Answer 35

• heat and dessication resistant
• metabolically inactive
• withstand autoclaving
• germinate into cells after decades of persistence

Question 36

What are the two type of enterotoxins of B. Cereus?

Answer 36

• heat-stable, acid-tolerant, proteolysis-resistant toxin; emetic illness, i.e., vomiting
• heat-labile toxins; associated diarrheal illness

Question 37

How do B. Cereus transmit?

Answer 37

Ocular, catheter and opportunistic infections.

Found in up to 25% of food tested; rice is common vehicle for illness

Question 38

What happens when B. Cereus gastrointestinally infects a host?

Answer 38

• emetic form: N/V, abd cramping, toxin in food, 2-3 hr incubation
• Diarrheal form: intestinal replication, diarrhea, cramp, maybe fever. 6-24 hr incubation.

Question 39

How is B. Cereus identified?

Answer 39

Cx bacteria identified by morphological characteristics.

Question 40

Immunity against Listeria M. depends on?

Answer 40

CD8 T cells