College of Medicine
Microbiology
Bacteriology
Corynebacterium diphtheriae :
Dr.Jawad Kadhim Tarrad
----------------------------------------------------------------------------------------Important properties:
 It is Gram-positive rod.
 It is arranged in Chinese letters and swelling at the ends ( club-shaped).
 It is non-motile .
 It is non-capsulated.
 It is non-spore former.
 Aerobic or facultative.
Virulence factors:
 The major virulence factor is diphtheria toxin(DT). The toxin is consisting of
two fragments; fragment-A (active part) and fragment-B(binding part). Both
fragments are linked together by disulfide bond.
Habitat and transmission:
 Humans are only natural host. The organisms residue in URT (nasopharynx)
of carriers and on skin .
 Transmission of organism by respiratory droplets from person to person or it is
less frequently spread by cutaneous contact with carriers and contaminated
fomites.
Pathogenesis:
 Fragment-B of toxin is binding to specific surface receptor on cell membrane
of host cell, and then is taking into the cell by endocytosis. Because low pH
inside the endosome, the enzymatic fragment-A is separated and released into
cytosol, which stimulate ADP-ribosyl-transferase to cleave NAD(nicotinamide
adenine dinucleotide) and transfer ADP-R(adenosine diphosphate-ribose) to
cellular translation elongation factor-2 (EF-2) lead to formation of ADPR-EF2
complex.
 The ribosylation of EF-2 leads to inactivating it, which resulting in inhibition
of protein synthesis , and death of cell.
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Disease and clinical features:
Diphtheria is mainly a disease caused by this organism , and common in children.
Two main forms of diphtheria are seen:
1. Pharyngeal diphtheria:
 The toxin destroys epithelial cells and polymorphs, and ulcer forms which is
covered with necrotic exudates, cell debris of mucosa and inflammatory
products forming a false-membrane(pseudomembrane) gray , thick, adherent
membrane over the tonsils and throat. These soon become dark and
malodorous.
 Mechanical obstruction of airway by pseudomembrane may cause suffocation
(asphyxia) and death of patient. Intubation or tracheostomy may be required in
severe cases. pharyngitis and tonsillitis are common manifestation.
 Clinical features include fever, croup, sore throat, cervical adenopathy.
Change in phonation (nasal speech), difficult in swallowing (dysphagia), and
in breathing (dyspnea). Cervical lymph nodes (cervical adenitis) may be
enlarging to give bull-neck appearance.
2. Cutaneous diphtheria:
 The organism can colonize small break in skin, especially damage caused by
insect bites or any wound in skin, and the organism produce lesion.
 The lesion may appear as simple pustules or chronic, non-healing necrotic
ulcer. The systemic affects may occur during cutaneous lesion due to
absorption of toxin into the tissues.
Lab. Dx:
 Gram stain showing G+ve bacteria similar Chinese letter.
 Culturing on Loeffler slope and blood Tellurite media.
 ELISA is used to detect antibody against antigen of this organism in serum.
Control and therapy:
 Immunization by antitoxin, which should be given immediately and cannot
wait for laboratory results.
 Mechanical ventilation or respiratory intubation( tracheostomy) or surgical
operation in case with suffocation.
 Antibiotics such as penicillin or erythromycin.
 Diphtheria vaccine usually given for children as combination with Tetanus
and Pertussis vaccine. Triple vaccine abbreviated as DTP
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Listeria monocytogenes:
Important properties:
 Gram-positive rod arranged in V- or L-shape.
 It is non-capsulated.
 It is motile.
 Facultative intracellular.
Virulence factors :
 Endotoxin.
 Intracellular survival.
Habitat and transmission:
 L.monocytogenes primarily found in intestine of domestic animals, mammals
and rodents.
 The infection usually transmitted by ingestion of contaminated food (milk,
cream, cheese, poultry) .
 The bacteria also found in intestine of healthy persons and in vagina of
asymptomatic women. The transmission of organism from mother to fetus
occur across placenta or during delivery.
Pathogenicity and clinical features(listeriosis)
 L.monocytogenes cause neonatal meningitis and neonatal sepsis in newborns
or fetuses.
Neonatal infections acquired either during pregnancy (usually in third
trimester) can cause abortion or still birth, premature delivery, or the infection
acquired during perinatal period and cause sepsis. Perinatal listeriosis causes
two forms of syndrome disease; Early-onset syndrome (infantiseptica); sepsis
is result of infection in uterine, and death may occur before or after delivery.
Late-onset syndrome ; cause development of meningitis between birth and
third week of life. Newborns infected can have acute meningitis 1-4 weeks
later. Listeriosis has significant mortality rate.
 In adults, listeriosis is most common as
meningoencephalitis in
immunocompromised adults, such as elderly, patients receiving
corticosteroids, renal transplant patients or patient with cancer.
 Gastroenteritis (food poisoning) which usually associated with ingestion of
contaminated dairy products. This disease develops after period 6-48 hours.
Lab. Dx:
 Isolation of organism in cultures of blood and CSF.
 Gram-stain display gram-positive rods.
Control:
 Antibiotics including ampicillin and erythromycin.
 Prevention by good food handling and cooking.
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