Lecture 12 corynbacterium, Listeria, Bacillus Flashcards
What is Corynebacterium diptheriae?
Koryne=club; small, gram-positive pleomorphic non-sporulating; non-motile.
What is the mode of environment/mode of transfer for corynebacterium?
Humans are the only natural reservoir. Spread by respiratory droplets, cutaneous lesions and fomites. Pharyngeal/nasal carriage in some convalescent cases.
What are fomites?
Non-living substances, it can distribute pathogens.
How can cutaneous lesions spread disease?
When someone bumps into and makes contact with the pathogen.
What are convalescent cases?
you get the pathogen, but you don’t die from it and become a carrier
What is the principal virulence factor in Corynebacterium diptheria?
Diptheria toxin, a signal toxin can kill a cell. A (catalytic) unit and B (cell binding) unit.
How does diptheria toxin work. ?
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.
Where is DT encoded?
DT is encoded in lysogenic bacteriophage.
What is DtxR?
Iron dependent repressor of the DT. When there are high iron concentrations DT is inhibited because it is a waste of energy.
DT is co-regulated with what?
Siderophores (iron binding protein) part of the bacterial iron transport system.
What is known about diptheria colonization?
-Generally in the nasopharyngeal region, non-invasive, historically a childhood disease.
What are some local toxin effects of C diptheria?
- pharyngitis (sore throat) formation of pseudo membrane.
- Epithelial cell necrosis (cell death)
- Inflammation (IL-1, IL-6, TNF)
What are some indicators of pharyngitis?
- Debris, fibrin, formation of pseudomembrane.
- gray/yellow/white membrane with surrounding inflammation.
- mechanical obstruction of airway.
What are some systemic toxin effect of C. diptheria?
- myocarditis (muscle hear inflammation); significant cardiomyopathy.
- paralysis of soft palate and select muscle groups, most seriously in the diaphragm.
In what scenario can C Diptheria cause skin infections?
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.
What is the Dx of C diptheria?
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) .
Why is it important to have a system to find rare bugs?
Because they rarely occur so you need to be able to identify them.
How is diptheria prevented?
- By vaccine DTaP.
- almost completely eliminated (10 cases a year).
What is in DTaP vaccine?
- Formalin treated DT- inactivates B while maintaining A structure.
- Ab does not eliminate infection; mild disease, pathogen colonizes but immune system can fight off.
What can Corynebacterium jeikeium do?
Is skin microbiota. Can cause bactermia, endocarditis, pneumonia, osteomylitis, meningitis; immunocompromised pts or those with indwelling devices are susceptible. nosocomial infections; multi-drug resistant.
What is Listeria monocytogenes?
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
What are internalins InlA and InlB?
-Allows listeria monocytogenes to bind and invade non-phagocytic cells (intracellular) - involved in crossing critical anatomical membranes
What is the the function of IntlA
-binds E-cadherin on intestinal epithelial cells
What is the specific function of InlB?
binds HGFR [hepatocyte growth factor receptor]
What is Listeriolysin O?
- 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)
What is phospholipase’s purpose?
In listeria m. releases bacteria from phagosome.
What is the purpose of ActA?
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
Listeria is commonly found where?
-Foodborne; incubation period longer than most other food-born illness; outcome depends on host attributes. (soft cheese, mexican).
Why is listeria of concern for pregnant women?
- Vertical transmission: feto-placental infections
- early onset: septicemia in utero
- late onset: exposure during birth; meningitis 2-3 wks later
What are some concerns of listeria other than pregnant women?
- 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
What are some gastrointestinal effects caused by listeria in immune competent people?
- mild flu-like symptoms [low inoculum]
- febrile gastrointestinal infections [high inoculum]
- 20 -30 % mortality when anatomical barrier passed.
What is the Dx of Listeria?
Cx CSF, blood, amniotic fluid, placenta, fetal tissue; tumbling motility at RT (non-motile at 37C).
Could you engineer listeria vector to combat viral infections or cancer?
-Using listeria to develop antigens, and to induce CD4 T cells against cancer. Firs used dead cells, now using live cell.
What is Bacillus cereus?
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).
What is the purpose for forming spores?
- heat and dessication resistant
- metabolically inactive
- withstand autoclaving
- germinate into cells after decades of persistence
What are the two type of enterotoxins of B. Cereus?
- heat-stable, acid-tolerant, proteolysis-resistant toxin; emetic illness, i.e., vomiting
- heat-labile toxins; associated diarrheal illness
How do B. Cereus transmit?
Ocular, catheter and opportunistic infections.
Found in up to 25% of food tested; rice is common vehicle for illness
What happens when B. Cereus gastrointestinally infects a host?
- 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.
How is B. Cereus identified?
Cx bacteria identified by morphological characteristics.
Immunity against Listeria M. depends on?
CD8 T cells
