Corynebacterium

Erysipelothrix

&

Listeria

Pathogenic Anaerobic Gram-Positive Bacilli

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

Distinguishing Features of CMN GroupCorynebacteriu

mMycobacterium Nocardia

Pathogenic Corynebacterial Species

Corynebacterium diphtheriae

Corynebacterium jeikeium

Corynebacterium urealyticum

Corynebacterium urealyticum

Urinary tract infections (UTI’s); rare but important

Urease hydrolyzes urea; release of NH4+,

increase in pH, alkaline urine, renal stones

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

Epidemiology of Diphtheria

Virulence Factors in Corynebacterium Species

Diphtheria tox Gene in Beta Bacteriophage

and Prophage

See Handout on Exotoxins

Mechanism of Action of Diphtheria Toxin: Inhibition of Protein Synthesis

Molecular Structure of Diphtheria Toxin

Catalytic Region

Receptor-Binding RegionTranslocation Region

A Subunit

B Subunit

Heparin-binding epidermal growth factor on heart & nerve surfaces

Diagnostic Schick Skin Test

TOXIN TOXOID

Immune Status to C. diphtheriae and Sensitivity to Diphtheria Toxoid

In vivo Detection of Diphtheria Exotoxin

2. Genus Listeria

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)

Listeriosis• Humans, domestic animals

described in ≥ 40 species of animalsusually follows ingestionoutbreaks, sporadic cases related to foodasymptomatic fecal carriage common, especially

for those in contact with domestic animalsIncidence increases in summer, when outbreaks

of food-borne disease are more common.

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

Listeriosis

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

Distribution of Listeria?

Natural Reservoirs

Common Routes for Human Exposure

Population at Greatest Risk

Epidemiology of Listeria Infections

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 phagocytosisinternalinsimilar to M protein of S. pyogenes

(antiphagocytic), dissimilar functions

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

Virulence Factors and Pathogenesis - Listeriolysin

• Major virulence factor: listeriolysinthiol-activated cytolysin, hemolysin

mediates escape from phagocytic vesicle

• LLO mutants: LD50 5 logs higher than WT, do not survive in MØ

Virulence Factors and Pathogenesis

• Bacteria encountering plasma membrane continue to move forwardproduce protrusions extending

into adjacent cell: listeriopodsescape listeriopod in double-

membrane vesicle, enter cytoplasm of adjacent cell

• Mediated by phospholipase

Virulence Factors and Pathogenesis - Actin-based Motility

• Bacteria in cytoplasm polymerize actin, form tailshollow 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

Listeriolysin O?

Macrophage

Macrophage

Phagocytosis

Intracellular Replication Actin

Filaments

Intracellular Survival & Replication of Listeria

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

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

Erysipelothrix rhusopathiaeGram-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

Epidemiology of Listeriosis

Natural Reservoirs

Common Routes for Human Exposure

Population at Greatest Risk

Epidemiology of Listeria Infections

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

Listeriosis

Methods That Circumvent Phagocytic Killing

See Chpt. 19

Listeriolysin O?

Macrophage

Macrophage

Phagocytosis

Intracellular Replication Actin

Filaments

Intracellular Survival & Replication of Listeria

3. Erysipelothrix rhusopathiaeGram-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

Epidemiology of Erysipelothrix

Infection