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Corynebacterium
C. diphtheriae: causes diphtheria.
Other corynebacteria (coryneform) may cause opportunistic
infections.
Gram-positive, irregularly-shaped rod. "Club shaped".
In stained smears, individual rods tend to lie parallel or at acute
angles to one another (pallisades). Metachromatic granules
(often near the poles) give the rod a beaded appearance.
Grow aerobically on most media.
Corynebacteria grow on Löffler's
serum medium more readily than
other respiratory pathogens, and
show typical morphology in
smears.
Non-motile; noncapsulate.
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 mucosa cells-- formation of "pseudomembrane“ (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.
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 and dyspnea=‫ اشكال تنفسي‬soon follow, which
may lead to suffocation if not promptly relieved by intubation or
tracheotomy.
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 or heart failure.
Cutaneous diphtheria: mild (papule
ulcer with grayish
membrane) with little toxigenic effects. Stimulates antitoxin
production.
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 blood plate, a Löffler slant,
and a tellurite plate. Identification: biochemical tests.
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
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. All children must
receive an initial course of immunizations and boosters.
Regular booster with Td (tetanus and diphtheria) toxoids are
particularly important for adults who travel to developing
countries.
Schick test can be used to test susceptibility of a person to
diphtheria.
Toxoids for delayed absorption: Fluid toxoid absorbed onto
aluminum hydroxide or aluminum phosphate. Usually combined
with tetanus toxoid and/or pertussis vaccine (DPT vaccine).
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
Small gram-positive coccobacilli,
facultative anaerobic.
Motile at room temperature but
not at 37 oC.
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 carriage in
healthy people: 1%-5%.
Human disease is restricted to neonates and the elderly,
pregnant women, and immunocompromised patients
(particularly those with defective cell-mediated immunity,
such as AIDS patients).
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.
L. monocytogenes
Clinical Diseases
Adults
Neonates
Healthy
Early onset disease (acquired
transplacentally in utero):
granulomatosis infantiseptica,
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.
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.
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, slowly spreading inflammatory skin lesions on the
fingers or hands, violaceous with raised edge. Suppuration is
uncommon.
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.
Biochemical tests.
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.
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).
Back
Bull-neck
appearance
=‫گردن گاو نر‬
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Internalins
Listeriolysin O
ActA
Back
A菌
細菌名稱
B菌
診斷？
型態
生長特性
生化反應
血清學反應
疾病？症狀？
如何造成疾病？（致病機制）
細菌本身：侵襲性（毒力因素？ ）；產毒力（毒素？ ）
宿主因素：抵抗力？ 易感因素？
如何感染：途徑？ 媒介？
治療？
抗生素？ （抗藥性？ ） ；抗毒素？ ；症狀治療？
預防？
環境及個人衛生？ 疫苗？