CorynebacteriumC. 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. diphtheriaePathogenesis 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 "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.

C. diphtheriaeClinical 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 soon 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. diphtheriaeLaboratory 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 as

ymptomatic carriers.

The bacteria are spread directly from person to person.

To limit contact with diphtheria bacilli to a minimum, patien

ts with diphtheria should be isolated.

Prophylactic antibiotic treatment to unimmunized contacts.

Active immunization in childhood with diphtheria toxoid yields

antitoxin levels adequate until adulthood. All children must re

ceive an initial course of immunizations and boosters.

Regular booster with Td (tetanus and diphtheria) toxoids are

particularly important for adults who travel to developing coun

tries.

Schick test can be used to test susceptibility of a person to di

phtheria.

C. diphtheriaePrevention and Control

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 infect

ions, such as pneumonia, endocarditis, and soft tissue and bo

ne 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 end

ocarditis must be guided by antibiotic susceptibility tests.

Listeria and Erysipelothrix

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 t

emperatures.

L. monocytogenes: meningitis and bacteremia

E. rhusiopathiae: erysipeloid

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.

Neonates

Early onset disease (acquired tr

ansplacentally in utero): granulo

matosis infantiseptica, with diss

eminated abscesses and granul

omas in multiple organs.

Late onset disease (acquired at

or soon after birth): meningitis or

meningoencephalitis with septic

emia, similar to that caused by g

roup 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.

Clinical Diseases

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 (-) 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., cepha

losporin and tetracycline). Currently, penicillin or ampicillin, eithe

r alone or with gentamicin, is the treatment of choice.

Outbreaks have been associated with the consumption of conta

minated milk, soft cheese, undercooked meat, unwashed raw v

egetables, and cabbage. Refrigeration of contaminated food pro

ducts permits the slow multiplication of the organisms to an infe

ctious dose.

Because Listeria organisms are ubiquitous and most infections

are sporadic, prevention and control are difficult. High risk peop

le should avoid eating raw or partially cooked foods.

L. monocytogenes

Erysipelothrix (Hair of red disease)E. rhusiopathiae

Slender gram-positive, microaerophilic, with a tendency to form filaments. Form small, grayish -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 te

mperate phage (-phage) in the presence of low iron c

oncentrations.

This toxin binds to receptors on the surface of many e

ukaryotic cells, particularly heart and nerve cells, and r

esults in inhibition of polypeptide chain elongation by ri

bosylation of the elongation factor EF-2.

It can induce protective antibodies (antitoxin).

Back

Back

Bull-neck appearance

Back

Listeriolysin O

Internalins

ActA

Back

細菌名稱

疾病？症狀？

如何造成疾病？（致病機制）

治療？

預防？

診斷？

型態生長特性生化反應血清學反應

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？

抗生素？ （抗藥性？ ） ；抗毒素？ ；症狀治療？

環境及個人衛生？ 疫苗？

A 菌

B 菌