3. 1. Corynebacteria (Genus Corynebacterium)
Aerobic or facultatively anaerobic
Small, pleomorphic (club-shaped), gram-positive
bacilli that appear in short chains (“V” or “Y”
configurations) or in clumps resembling “Chinese
letters”
Cells contain metachromatic granules (visualize
with methylene blue stain)
Lipid-rich cell wall contains meso-
diaminopimelic acid, arabino-galactan polymers,
and short-chain mycolic acids
Lysogenic bacteriophage encodes for potent
exotoxin in virulent strains
19. 2.Listeria monocytogenes
• Small, Gram +, nonsporing rod
• End-over-end tumbling motility when grown at
20-25°C, not at 37°C
• Facultative anaerobe, ß-hemolytic
• CAMP Test positive (like Group B Streptococcus)
20. Listeriosis
• Humans, domestic animals
described in ≥ 40 species of animals
usually follows ingestion
outbreaks, sporadic cases related to food
asymptomatic fecal carriage common,
especially for those in contact with domestic
animals
Incidence increases in summer, when
outbreaks of food-borne disease are more
common.
21. Listeriosis
Neonates, elderly & immunocompromised
Granulomatosis infantiseptica
• Transmitted to fetus transplacentally
• Early septicemic form: 1-5 days post-partum
• Delayed meningitic form: 10-20 days following birth
Intracellular pathogen
• Cell-mediated and humoral immunity develop
• Only cell-mediated immunity is protective
22. Distribution of Listeria?
Intestinal tract of mammals & birds (especially chickens)
Persists in soil
Soft cheeses & unwashed raw vegetables
Raw or undercooked food of animal origin
Luncheon meats
Hot dogs
Large scale food recalls have become common
23. Epidemiology of Listeria Infections
Natural Common Routes for Population at
Reservoirs Human Exposure Greatest Risk
24. Virulence Factors and Pathogenesis -
Motility
• Actin-mediated motility (ActA)
host cell actin polymerized
growth of tail by actin polymerization at end of
bacterium propels it through cytoplasm
• Uptake: induced phagocytosis
internalin
similar to M protein of S. pyogenes
(antiphagocytic), dissimilar functions
25. Virulence Factors and Pathogenesis
• After entry to epithelial
cells
escapes phagosome,
multiplies in cytoplasm
exocytosis from epithelial
cell followed by
phagocytosis by MØ, PMN
multiplication followed by
death of phagocytes,
secondary phagocytosis
systemic spread
26. Virulence Factors and Pathogenesis -
Listeriolysin
• Major virulence factor: listeriolysin
thiol-activated cytolysin, hemolysin
mediates escape from phagocytic vesicle
• LLO mutants: LD50 5 logs higher than WT,
do not survive in MØ
27. Virulence Factors and Pathogenesis
• Bacteria encountering plasma
membrane continue to move
forward
produce protrusions extending
into adjacent cell: listeriopods
escape listeriopod in double-
membrane vesicle, enter
cytoplasm of adjacent cell
• Mediated by phospholipase
28. Virulence Factors and Pathogenesis -
Actin-based Motility
• Bacteria in cytoplasm
polymerize actin, form
tails
hollow mesh forms on
surface, left behind as
bacterium moves forward
invade adjacent cells
• Actin nucleating factor: ActA
ActA localized at one end of the
bacterium, not found in tail
29.
30. Intracellular Survival & Replication of Listeria
Phagocytosis
Macrophag
e
Listeriolysin O?
Macrophag
e
Intracellula
Actin
r
Filaments
Replication
31. Immune Response
• In infected mice, bacteria first appear in MØ, then
invade hepatocytes
most replication probably occurs in liver
infection of MØ leads to presentation of antigens with
MHC class I, stimulating cytotoxic T cell response
cytotoxic T cells (and NK cells) kill infected hepatocytes
32. bacteria released from lysed host cells killed
bv activated MØ
T cell-deficient mice survive infection:
cytotoxic T-cell response helps clear
hepatocytes, not essential
increased susceptibility in mice unable to
produce IFN-: suggests importance of
activated MØ
33. Erysipelothrix rhusopathiae
Gram-positive non-motile bacillus; forms filaments
Occupational disease of meat and fish handlers,
hunters, veterinarians
Preventable with protective gloves & clothing
Erysipeloid in humans; erysipelas in swine & turkeys
Organisms enter through break in skin
Nonsuppurative, self-limiting skin lesions with erythema
and eruption
Peripheral spread may lead to generalized infection,
septicemia and/or endocarditis
Organisms can be isolated from skin biopsy
39. 3. Erysipelothrix rhusopathiae
Gram-positive non-motile bacillus; forms filaments
Occupational disease of meat and fish handlers,
hunters, veterinarians
Preventable with protective gloves & clothing
Erysipeloid in humans; erysipelas in swine & turkeys
Organisms enter through break in skin
Nonsuppurative, self-limiting skin lesions with erythema
and eruption
Peripheral spread may lead to generalized infection,
septicemia and/or endocarditis
Organisms can be isolated from skin biopsy