Aerobic/Facultative Gram Positive Bacilli
• Listeria spp.
• Erysipelothrix spp.
• Lactoacillus spp.
• Corynebacterium spp.
• Arcanobacterium spp.
• Bacillus spp.
• Nocardia spp.
• Rhodococcus spp.
Corynebacterium
• Mycolic acids: Present in cell wall
• Metachromatic granules can be observed in rods stained with
methylene blue
• Metabolism: Fermentative
• “Club”-shaped, non-motile, catalase positive
• Most species grow aerobically on most media
• Lipophilic strains require lipids for good growth
Corynebacterium Species
•Non-Lipophilic
–Corynebacterium diphtheriae
–Corynebacterium amycolatum
–Corynebacterium striatum
–Corynebacterium pseudodiphtheriticum
•Lipophilic
–Corynebacterium jeikeium
–Corynebacterium urealyticum
C. diphtheriae
Pathogenesis and Immunity
C. diphtheriae occurs in the respiratory tract, in wounds, or
on the skin of infected persons or normal carriers. It is
spread by droplets or by direct contact.
Portal of entry: respiratory tract or skin abrasions.
Diphtheria bacilli colonize and grow on mucous membranes,
and start to produce toxin, which is then absorbed into the
mucous membranes, and even spread by the bloodstream.
Local toxigenic effects: elicit inflammatory response and
necrosis of the faucial (咽喉的) mucosa cells-- formation of
"pseudo-membrane“ (composed of bacteria, lymphocytes,
plasma cells, fibrin, and dead cells), causing respiratory
obstruction.
Systemic toxigenic effects: necrosis in heart muscle, liver,
kidneys and adrenals. Also produces neural damage.
Diphtheria toxin is an A-B toxin expressed from a
temperate phage (b-phage) in the presence of low iron
concentrations.
This toxin binds to receptors on the surface of many
eukaryotic cells, particularly heart and nerve cells, and
results in inhibition of polypeptide chain elongation by
ribosylation of the elongation factor EF-2.
It can induce protective antibodies (antitoxin).
Emil von Behring, Shibasaburo Kitasato : Diphtheria
antitoxin serum, 1901 Noble Prize
Emil von Behring discovered that guinea pigs injected
with diphtheria toxin (remnants of diphtheria with the
active bacilli filtered out) can have their tissues
acclimated (適應) to the toxin such that they produce a
substance capable of neutralizing the diptheria toxin
itself. This antitoxin, he mixed with diphtheria toxin and
injected into healthy guinea pigs, yielding no ill effects
after the animals were exposed to diptheria. When this
treatment was applied to humans, the mortality from that
disease was reduced to a negligible level.
Diphtheria Toxin: Structure
• Toxin of 58,342 daltons
molecular weight
• Subunit B
– 21,500 daltons
– receptor-binding domain
and translocation domain
• Subunit A
– catalytic domain
Diphtheria Toxin: Mode of Action
•
•
•
•
•
•
The heparin-binding epidermal
growth factor on the cell surface is
the receptor for the toxin
After attached to the cell, the toxin is
taken up by endocytosis
Acidification of the endocytic vesicle
allows unfolding of the A and B
chains exposing the translocation
domain (T domain) of the toxin
The T domain inserts into the
endosome membrane translocating
the A subunit into the cytoplasm
where it regains its enzymatic
configuration
The enzymatic A subunit inactivates
elongation factor 2 (EF-2) and
terminates host cell protein synthesis
One EF-2 molecule per ribosome in
a cell, so one exotoxin molecule can
completely turn off protein synthesis
C. diphtheriae
Clinical Diseases
Respiratory diphtheria
Incubation period: 2-6 days.
Inflammation begins in the respiratory tract, causing sore throat,
exudative pharyngitis that develops into pseudomembrane, and low
grade fever. Prostration (衰弱) and dyspnea (呼吸困難) soon follow,
which may lead to suffocation if not promptly relieved by intubation
or tracheotomy(氣管切開術).
Damage to the heart causes irregular cardiac rhythm.
Visual disturbance, difficulty in swallowing and paralysis of the
arms and legs also occur but usually resolve spontaneously.
Death may be due to asphyxia(窒息)or heart failure.
Cutaneous diphtheria: mild (papule (丘疹 ) ulcer with grayish
membrane) with little toxigenic effects. Stimulates antitoxin
production.
Diphtheritic “Pseudomembrane”
C. diphtheriae
Laboratory Diagnosis
Specific treatment should be given before the lab reports if the clinical
picture strongly suggests diphtheria.
Specimens: swabs from the nose, throat or suspected lesions.
Gram's stain: beaded rods in typical arrangement (unreliable).
Culture: inoculate specimen onto a cysteine-tellurite blood agar plate.
Identification: biochemical tests (presence of cysteinase).
Toxigenicity test:
1. in vivo test: inject the culture into antitoxin-protected and
unprotected guinea pigs subcutaneously.
2. Tissue culture neutralization assay.
3. in vitro test: immunodiffusion assay (Elek test ).
4. Detection of toxin gene by PCR.
C. diphtheriae on a cysteine-tellurite plate
Elek Test
sterile filter paper with C. diphtheriae antitoxin
Ab-Ag precipitation line
bacteria
C. diphtheriae
Treatment
Treatment of diphtheria rests on prompt
administration of antibiotics (penicillin,
erythromycin) and diphtheria antitoxin.
Maintenance of an open airway.
Treatment of bacteremia or endocarditis
must be guided by antibiotic susceptibility
tests.
C. diphtheriae
Prevention and Control
Humans are the only known reservoir of C. diphtheriae.
Diphtheria was mainly a disease of small children.
This organism is maintained in the oroparynx or skin of
asymptomatic carriers.
The bacteria are spread directly from person to person.
To limit contact with diphtheria bacilli to a minimum,
patients with diphtheria should be isolated.
Prophylactic antibiotic treatment to unimmunized contacts.
C. diphtheriae
Prevention and Control
Active immunization in childhood with diphtheria toxoid yields
antitoxin levels adequate until adulthood. Usually combined
with tetanus toxoid and/or pertussis vaccine (DPT vaccine).
All children must receive an initial course of immunizations
and boosters (5 injections at 2 months, 4 months, 6 months,
15-18 months, and at 4-6 years).
Regular booster (every 10 years) with Td (tetanus and
diphtheria) toxoids are particularly important for adults who
travel to developing countries.
Other Corynebacterium Species
They are ubiquitous in plants and animals. Many are found as
part of human normal flora and may cause opportunistic
infections, such as pneumonia, endocarditis, and soft tissue
and bone infections, in immunocompromised patients.
C. jeikeium: sepsis, endocarditis, wound infections,
foreign body infections.
C. urealyticum causes UT infections. It is a strong urease
producer, infection of UT may lead to formation of stones.
C. ulcerans is closely related to C. diphtheriae. May cause
diphtheria-like disease.
Resistant to many antibiotics. Treatment of bacteremia or
endocarditis must be guided by antibiotic susceptibility tests.
Listeria and Erysipelothrix
L. monocytogenes: meningitis and bacteremia
E. rhusiopathiae: erysipeloid
Structure and Physiology
of Listeria
Small gram-positive coccobacilli;
facultative anaerobe.
Motile at room temperature but
not at 37oC.
Grow on most conventional
media in a wide pH range and
cold temperatures.
L. monocytogenes
Pathogenesis and Immunity
Widely distributed in nature (soil, water, vegetation, and the
intestines of a variety of animals). Fecal (排泄物的) carriage in
healthy people: 1%-5%.
Human disease is rare and is restricted to neonates and the
elderly, pregnant women, and immunocompromised patients
(particularly those with defective cell-mediated immunity, such as
AIDS patients).
Infection may be initiated in the intestine.
Facultative intracellular pathogen. The intracellular survival and
spread of the bacteria are critically important in pathogenesis and,
therefore, cellular immunity is more important than humoral
immunity in host defense against this organism.
Internalins- interaction with
host cell
Listeriolysin Orelease the bacteria
to cytosol
ActA – penetrate to
adjacent cell
L. monocytogenes
Clinical Diseases
Neonates
Early onset disease (acquired
transplacentally in utero):
granulomatosis infantiseptica(敗
血嬰兒肉芽腫 ), with
disseminated abscesses and
granulomas in multiple organs.
Late onset disease (acquired at
or soon after birth): meningitis or
meningoencephalitis with
septicemia, similar to that
caused by group B streptococci.
Adults
Healthy
Asymptomatic or mild
influenza-like illness.
Gastrointestinal symptoms
in some patients.
Immunocompromised
Meningitis (high risk: organ
transplant patients, cancer
patients, pregnant women)
Primary bacteremia: chills
and fever; high fever and
hypotension in severe
cases. Maybe fatal.
L. monocytogenes
Laboratory Diagnosis
Specimen: CSF and blood.
Gram stain: CSF typically show no Listeria because of the
low bacterial concentration.
Culture
Listeria grows on most conventional media.
Selective media and cold enrichment are used for
specimens contaminated with rapidly growing bacteria.
Hemolysis (b-) and motility in liquid or semisolid medium
are useful for preliminary identification.
Identification
Biochemical and serological tests.
L. monocytogenes
Treatment, Prevention, and Control
L. monocytogenes is resistant to multiple antibiotics (e.g.,
cephalosporin and tetracycline). Currently, penicillin or ampicillin,
either alone or with gentamicin, is the treatment of choice.
Outbreaks have been associated with the consumption of
contaminated milk, soft cheese, undercooked meat, unwashed
raw vegetables, and cabbage. Refrigeration of contaminated
food products permits the slow multiplication of the organisms to
an infectious dose.
Because Listeria organisms are ubiquitous and most infections
are sporadic, prevention and control are difficult. High risk
people should avoid eating raw or partially cooked foods.
Food-Borne Listeriosis
• Present in raw milk and
vegetables, fish, poultry,
fresh and processed
meats and fish
• Other implicated foods
have included cabbage,
cole slaw, soft cheeses,
and shrimp
Erysipelothrix (Hair of red disease)
E. rhusiopathiae
Slender gram-positive, microaerophilic, with a tendency to form
filaments. Form small, grayish a-hemolytic colonies after 2 to 3 days
incubation.
Widely distributed in wild and domestic animals. Animal disease
(particularly in swine) is widely recognized, but human disease is
uncommon.
Causes zoonotic infections through an abrasion or wound:
Localized skin infection (erysipeloid): 1-4 day incubation; painful
and pruritic (瘙癢) , slowly spreading inflammatory skin lesions on
the fingers or hands, violaceous with raised edge. Suppuration is
uncommon (distinguishing from Streptococcal erysipeals) .
Generalized (diffuse) cutaneous infection: rare and often associated
with systemic manifestation.
Septicemia: uncommon and frequently associated with endocarditis.
Erysipelothrix
Penicillin is the antibiotic of choice.
Specimen: full-thickness biopsy specimens or deep aspirates
(because the bacteria locate only on deep tissues).
Culture: grow on most conventional media in the presence of
5%-10% CO2.
Identification
Motility- and catalase-negative.
People at occupational risk (butchers, meat processors, farmers,
poultry workers, fish handlers, and veterinarians) are prevented
by use of gloves and other coverings on exposed skin.
Vaccination is used to control disease in swine.