1. Corynebacterium & Listeria
Two aerobic Gram-positive bacilli
L. monocytogenes
C. diphtheriae

2. Features of 2 Aerobic G+ Bacilli
organism capsule spores motility toxins source disease
C. diphtheriae DT Humans Diphtheria
L. monocytogenes LLO Food/animal Meningitis,
Bacteremia

3. Corynebacterium diphtheriae
light microscopy electron microscopy

4. The nasopharyngeal cavity

6. Diphtheria

7. Diphtheria

9. Diphtheria usually presents as pharyngitis or tonsillitis

10. Sometimes as skin lesions

11. Two Lethal Pathologies
Suffocation - edema (i.e., “bull neck”) + pseudomembrane closes airways.
Organ damage due to Diphtheria Toxin (DT). Usually, the heart (i.e., severe myocarditis).

12. Diphtheria toxin acts distally (usually on the heart)

15. Targeted therapeutic delivery of toxins

17. Listeria monocytognes
Gram-positive rods
-hemolytic on blood plates
Can grow at 4o C - in food!
Present in meats, cheese & other dairy products

18. L. monocytogenes Widespread in nature. Causes listeriosis.
Very Rare: 2,500 cases, 500 deaths, 2-30% fatality.
At risk: immunosupressed, pregnant, elderly, newborn, fetuses.

19. Listeria monocytognes

20. Listerosis Asymptomatic, or mild GI, unless disseminated infection.
Bacteremia
Meningitis
Requires cellular immune response to clear. INTRACELLULAR PATHOGEN.
Newborns, pregnant, immunocompromised.
May be transmitted transplacentally.

21. Clinical syndromes associated with Listeria monocytogenes
Febrile gastroenteritis: self-limited disease of healthy hosts. Incubation 6-49h (median 20-25h); symptoms include diarrhea, fever, abdominal pain, chills, headache, myalgias.
Symptoms resolve in 1d (fever) to 2d (diarrhea).
Invasive listeriosis: rare disease, with 896 cases reported to the CDC in 2005 (0.28 cases per 105). However, rates higher in at-risk populations, e.g. pregnant women (12 cases per 105) or patients with AIDS (115 cases per 105). Includes bacteremia and meningitis.

22. At-risk populations for invasive listeriosis
Pregnant women/fetuses
Patients at extremes of age
Patients with AIDS
Patients taking immunosuppressive medications
Patients with immunosuppressing co-morbidities
(cancer, autoimmune disease, alcoholism, diabetes mellitus)

23. Invasive listeriosis in pregnancy
Fever, chills, headache mark period of bacteremia in mother.
Organism can be recovered from amniotic fluid, placenta
Spontaneous abortion or stillbirth in 20% (early in pregnancy)
Preterm delivery
Neonatal infection in up to 2/3 of surviving neonates: pneumonia, bacteremia, meningitis

24. L. monocytogenes Survival is a Multi-Step Process
Internalin = stimulates entry into cells
Listeriolysin O = pore-forming toxin for escape from phagolysosome.
ActA = actin polymerization for intracellular movement.
2 Phospholipase Toxins = entry into 2nd cell.
Antibodies do not work! INTRACELLULAR.

25. Listeria monocytogenes
•L. monocytogenes is a soil organism
•L. monocytogenes has been isolated from, and may transiently colonize, the GI tracts of domestic and wild mammals (42 sp.), domestic and wild birds (17 sp.),
crustaceans, oysters, fish, ticks, flies…and apparently healthy humans.
•Listeria is killed by pasteurization or cooking.
So why does it contaminate things like cold cuts or cantaloupes?

26. L. monocytogenes can grow on surfaces of food & processing equipment as a disinfection-resistant biofilm.

27. L. monocytogenes grows at 4°C

28. 1. Internalin induces uptake
5. LLO + two
PLCs for release
2. LLO to escape
4. Protrusion
3. ActA for actin-based motility

29. Bacteria escape from the phagosome into cytoplasm
from Tilney and Portnoy, 1989 J. Cell Biol. 109:

30. A cholesterol-dependent cytolysin secreted by Listeria monocytogenes
Listeriolysin O (LLO; from hly gene)
A cholesterol-dependent cytolysin secreted by Listeria monocytogenes
Necessary for bacterial transfer from vacuoles (phagosomes) into cytoplasm
Perforates vacuolar membranes; maximal intracellular activity at pH 6

34. Not all bacteria escape from phagosomes

35. Microbicidal activities inside macrophage vacuoles2 1
ROI
lysosome 1
lysosome fusion 2
generation of reactive oxygen intermediates (ROI)

36. Intracellular bacteria have comet-tails of filamentous actin.
Red = L. monocytogenes; Green = filamentous actin

37. The Listeria monocytogenes protein ActA organizes actin polymerization

38. Actin polymers form near bacterial surface

39. EM & fluorescent micrograph of L. monocytogenes
(with actin “comet” tail)

40. Bacteria are propelled into cellular extensions, which are engulfed by neighboring cells

41. Intracellular life history of Listeria monocytogenes
LLO
ActA
LLO
PLC-A, PLC-B

42. Why antibodies are ineffective in the clearance of Listeria monocytogenes
The life cycle of Listeria avoids exposure to the humoral immune system.
Cell A
Cell B

43. IMMUNITY L. monocytogenes lives intracellularly.
Humoral response does not clear.
Requires acquired cellular response.
CD4+ & CD8+ T-cell subsets required.
Neutrophils can assist in early stages.
Those people lacking full T-cell capabilities are at risk.