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 Group

Corynebacteriu

m

Mycobacterium 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 Region

Translocation 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 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.

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 phagocytosis

internalin

similar 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: listeriolysin

thiol-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

forward

produce protrusions extending

into adjacent cell: listeriopods

escape 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

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

Listeriolysin O?

Macrophag

e

Macrophag

e

Phagocytosis

Intracellula

r

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 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

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

ReplicationActin

Filaments

Intracellular Survival & Replication of Listeria

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

Epidemiology of

Erysipelothrix

Infection