Corynebacterium and Other
Non–Spore-forming Gram-Positive Rods
Corynebacterium sp.
Listeria monocytogenes
Erysipelothrix rhusiopathiae
Case Study
 A 76-year-old woman is receiving corticosteroid therapy
 Complained of fever and headache for 7 days
 CBC count showed an elevated white cell count
 CSF analysis showed
 250 WBC/cu mm
 Glucose 30 mg/dL
 Protein 180 mg/dL
 Culture grew beta-hemolytic colonies on sheep blood
agar, gram-positive pleomorphic rods
 Catalase positive, motile at room temperature
 CAMP-factor positive
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Points to Consider
 What type of infection was suspected in this
particular patient?
 What predisposing risk factors were presented by the
patient?
 How are these organisms differentiated from other
groups with similar characteristics?
 What clinical forms of infections are associated with
these groups of organisms?
 Other points to consider
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Corynebacterium Species:
General Characteristics
 Morphology
 Gram-positive, non–sporeforming rods
 Arrange in palisades:
“L-V” shape; “Chinese
characters”
 Pleomorphic: “club-ends”
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Corynebacterium Species
 General characteristics
 Found as free-living saprophytes
 Members of the usual flora of humans and animals
 Corynebacterium diphtheriae is the most significant pathogen
 Other species may cause infections in the
immunocompromised hosts
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Other Corynebacteria
 Significant Corynebacterium species
 C. xerosis
 C. pseudodiphtheriticum
 C. pseudotuberculosis
 C. jekeium
 C. ulcerans
 Rhodococcus equi
 Arcanobacterium haemolyticum
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C. diphtheriae: Agent of Diphtheria
 Toxigenic Corynebacterium diphtheriae
 Worldwide distribution
 rare in places where vaccination programs exist
 Exotoxin as the virulence factor
 Diphtheria toxin
 Toxin is produced by certain strains
 Lysogenized by bacteriophage with toxin gene (tox+)
 Toxin is antigenic
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Toxigenic Corynebacterium diphtheriae
 Toxin consists of two fragments
 A: Active fragment
Inhibits protein synthesis
Catalyzes transfer of ADPR to link with EF2
ADPR.EF (inactive)
Leads to cell/tissue death
 B binds to specific cell membrane receptors
Binds to specific cell membrane receptors
Mediates entry of fragment A
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Clinical Forms of Diphtheria
 Respiratory
 Acquired by droplet spray
 Unimmunized individuals are susceptible
 Nonrespiratory
 Systemic
 Skin and cutaneous forms
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C. diphtheriae:
Causative Agent of Diphtheria
 Respiratory disease–diphtheria
 Incubation period–2 to 5 days
 Symptoms: sore throat, fever, malaise
 Toxin is produced locally, usually in the pharynx or tonsils
 Toxin causes tissue necrosis
 Forms a tough grey to white pseudomembrane
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Clinical Infections:
Non-Respiratory Disease
 Systemic infections
 Toxin is absorbed in the blood stream and carried systemically
 Affects the kidneys, heart, and nervous system
 Death occurs due to cardiac failure
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Clinical Infections:
Non-Respiratory Disease
 Cutaneous form
 More prevalent in the tropics
 Infections occur at the site of minor abrasions
 Maybe superinfected with Streptococcus pyogenes and/or
Streptococcus aureus
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Laboratory Diagnosis
 Microscopic morphology
 Gram-positive, non–sporeforming rods, club-shaped
 Appear in palisades and give
"Chinese letter" arrangement
 Produce metachromatic granules
or “Babes’ Ernst” bodies
Loeffler methylene blue stain
of Corynebacterium sp.
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Laboratory Diagnosis:
Cultural Characteristics
 Loeffler's slant or Pai's slant—
Used to demonstrate
pleomorphism and
metachromatic granules; "Babes’
Ernst bodies"
 Serum Tellurite or modified
Tinsdale- brown or grayish to
black halos around the colonies
Growth of C. diphtheriae
on blood agar
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Laboratory Diagnosis
 Identification
 Confirm identification by
fermentation reactions
 Toxigenicity testing
 Elek test—
Immunodiffusion test
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Differentiating Characteristics of
Corynebacterium Species
Hemolysis
Sucrose
fermentation
Nitrate
reduction
Urease
C. diphtheriae
V
=
+
=
C. xerosis
=
+
+
=
C. pseudophtheriticum
=
=
+
+
C. pseudotuberculosis
+
V
V
+
R. equi
=
=
+
=
Corynebacterium
jekeium
=
=
=
=
Species
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Listeria Monocytogenes:
General Characteristics
 Gram-positive, non–spore-forming rods
 Widespread in nature
 Known to infect a wide variety of animals
 Human exposure is limited; direct or indirect
 Transient colonization occurs without disease
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Listeria monocytogenes:
Clinical Infections
 Adults
 Septicemia/meningitis in the compromised/elderly
 Mild flu-like syndrome in pregnant women could be fatal to fetus
 Neonatal
 Early onset from intrauterine transmission results in sepsis; high
mortality rate
 Late onset manifests as meningitis; lower mortality rate
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Laboratory Diagnosis:
L. monocytogenes
 Identification
 Microscopic morphology
Gram Positive non–sporeforming coccobacillary
 Cultural characteristics
Grows well on blood agar;
colonies produce a narrow
zone of hemolysis similar to
Group B Streptococcus
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Laboratory Diagnosis:
L. monocytogenes
 Identification
 Catalase positive
 Motility:
Motile at 25o C;
"umbrella" type
Tumbling motility in hanging
drop preparations
“Umbrella” motility pattern (Left)
typical for L. monocytogenes
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Laboratory Diagnosis:
L. monocytogenes
 Identification
 CAMP test
Produces a “block” type of
hemolysis in contrast to
“arrow”-shape produced by
Group B Streptococcus
CAMP test with
Listeria monocytogenes
Positive CAMP test for
Group B Streptococcus
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Differentiating Characteristics between
L. monocytogenes and Other Gram Positive Bacteria
Hemolysis
Species
Catalase
Motility
At R. T.
Esculin
Hydrolysis
Growth
6.5% NaCl
L. monocytogenes
+
Beta
+
+
+
Corynebacterium sp.
+
None, alpha
=/+
=
+/=
S. agalactiae
=
Beta
=
=
=/+
Enterococcus sp.
=
None, alpha
beta
=
+
+
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Erysipelothrix rhusiopathiae:
General characteristics
 Gram positive, non–spore-forming, pleomorphic rods
 Distributed in nature
 Can cause disease in animals (swine, turkey, sheep)
 Humans acquire the infection through occupational
exposure
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Erysipelothrix rhusiopathiae:
Clinical Infections
 Erysipeloid
 Self-limiting localized infection at the site of inoculation
 Produces painful swelling, usually on the hands or fingers
 Heals within 3 to 4 weeks
 Endocarditis
 May occur in those who have had valve replacements
 Disseminated infections may occur, but rarely
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Laboratory Diagnosis:
Erysipelothrix rhusiopathiae
 Microscopy
 Pleomorphic, gram-positive thin rods that may form long
filaments, may be arranged singly, in short chains, or in a V
shape
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Laboratory Diagnosis:
Erysipelothrix rhusiopathiae
 Identification
 Catalase negative
 CO2 is required
 Grows on blood or chocolate
agar—colonies may appear gray
or translucent with alpha
hemolysis
 Distinguishing characteristic:
Production of H2S on TSI
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Characteristics of Corynebacterium, Listeria,
and Erysipelothrix
Characteristics
Corynebacterim
spp.
Listeria
monocytogenes
Hemolysis
V
+
=
Discolored/
Catalase
+
+
=
Growth at 4 o
=
+
=
Motility at R.T.
Esculin
hydrolysis
=
+
=
=
+
=
=
+
H2S (TSI butt)
=
Erysipelothrix
rhusiopathiae
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Points to Remember
 Distinguishing characteristics of the genera Listeria,
Corynebacterium, and Erysipelothrix from other gram
positive bacteria
 Clinical infections caused by each of these groups
 Risk factors are associated with these infections
 Biochemical and microscopic features of each of these
species
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