The document discusses three pathogenic gram-positive bacilli: Corynebacterium, Listeria monocytogenes, and Erysipelothrix rhusopathiae. Corynebacterium includes the species C. diphtheriae, which causes respiratory diphtheria, and C. urealyticum, which can cause urinary tract infections. L. monocytogenes is an intracellular pathogen that can cause listeriosis, especially in immunocompromised individuals. E. rhusopathiae causes erysipeloid skin lesions in those exposed through meat/fish handling and can potentially spread systemically.

1. Corynebacterium
Erysipelothrix
&
Listeria

2. Pathogenic Anaerobic
Gram-Positive Bacilli

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

4. Distinguishing Features of CMN Group
Corynebacteriu Mycobacterium Nocardia
 m




5. Pathogenic Corynebacterial Species
Corynebacterium diphtheriae
Corynebacterium jeikeium
Corynebacterium urealyticum

6. Corynebacterium urealyticum
Urinary tract infections (UTI’s); rare but
important
Urease hydrolyzes urea; release of NH4+,
increase in pH, alkaline urine, renal stones

7. Corynebacterium diphtheriae
Respiratory diphtheria (pseudomembrane on
pharynx) and cutaneous diphtheria
Prototype A-B exotoxin acts systemically
• Toxoid in DPT and TD vaccines
Diphtheria toxin encoded by tox gene introduced
by lysogenic bacteriophage (prophage)
Selective media: cysteine-tellurite; serum
tellurite; Loeffler’s
Gravis, intermedius, and mitis colonial morphology

8. Epidemiology of
Diphtheria

9. Virulence Factors in Corynebacterium Species

10. Diphtheria tox Gene in
Beta Bacteriophage
and Prophage

11. See Handout on Exotoxins

13. Mechanism of Action of Diphtheria Toxin:
Inhibition of Protein Synthesis

14. Molecular Structure of Diphtheria Toxin
Catalytic Region
A Subunit
B Subunit
Translocation Region
Receptor-Binding Region

15. Heparin-binding epidermal growth
factor on heart & nerve surfaces

16. Diagnostic Schick Skin Test
Immune Status to C. diphtheriae and
Sensitivity to Diphtheria Toxoid
TOXIN TOXOID

17. In vivo Detection
of Diphtheria Exotoxin

18. 2. Genus Listeria

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

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

34. Epidemiology of
Listeriosis

35. Epidemiology of Listeria Infections
Natural Common Routes for Population at
Reservoirs Human Exposure Greatest Risk

36. 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

37. Methods That Circumvent Phagocytic
Killing
See Chpt. 19

38. Intracellular Survival & Replication of Listeria
Phagocytosis
Macrophage
Listeriolysin O?
Macrophage
Intracellular
Actin
Replication
Filaments

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

40. Epidemiology of
Erysipelothrix
Infection