Diphtheria

Diphtheria

Describe the clinical picture of Diphtheria

The answer

Is an acute contagious illness
Diphtheria is the result of local and systemic effects of diphtheria toxin.
It is characterized by membrane formation in throat.
Diphtheria is primarily an illness of children

Describe Corynebacterium diphtheriae, its morphologic, cultural characteristics and their normal habitat and life cycle..

The answer

Source

Humans are the only reservoir of infection
Infection may produce disease or a carrier state

Morphology

Aerobic, club shaped, gram-positive, nonmotile, unencapsulated, pleomorphic bacillus with terminal swellings
When stained it is often found in clusters that form sharp angles with each other and resemble Chinese letters.

Culture

Missed on routine cultures

Who are the susceptible hosts for Corynebacterium diphtheriae

The answer

Children not vaccinated for C. diphtheria.
Poorly immunized adults
Immunocompromised

How does Corynebacterium diphtheriae get exposed to humans?

The answer

Respiratory droplets

Direct contact with cutaneous infection

Fomites

Nasopharyngeal secretions

The organisms can survive in dusts and clothing for up to 6 months.

How does Corynebacterium diphtheriae invade and spread in humans? Describe the pathogenic mechanisms. How do these organisms able to overcome human defenses?

Disease is caused by exotoxin which inhibits protein synthesis of eukaryotic cells

The exotoxin is absorbed into the blood stream and distributed, resulting in systemic complications
- demyelinating neuritis
- myocarditis.
The diphtheria toxin also causes local destruction at the site of membrane formation.
- The toxin contains a toxic A subunit (active toxin) and the receptor binding B subunit.
- Fragment B attaches to cellular receptors and grants fragment A entrance into the cell, where it inhibits protein synthesis.
  - The B subunit (fragment) facilitates translocation of the A subunit from the phagosome to the cytosol, followed by separation, allowing full activity of the A subunit on its target protein elongation factor-2. EF-2 transfers polypeptidyl-transfer RNA from acceptor to donor sites on the ribosome of the host cell.
  - The A subunit catalyzes transfer of adenine ribose phosphate from NAD to EF-2 (ADP ribosylation), inactivating EF-2, and turning off protein synthesis, C. diphtheria toxin is able to inhibit protein synthesis of all eukaryotic cells.
  - Fragment A has the enzymatic activity

Describe the toxin gene of Corynebacterium diphtheriae

The answer

Gene for the diphtheria toxin is carried in genome of a bacteriophage.
C. diphtheria strains must contain a bacteriophage (beta-phage), acquired by transduction from other C. diphtheria strains, in order to express the toxin.
The phage must be Iysogenized following transduction.
The toxin expression (fox gene) is regulated by a chromosomally encoded repressor protein (DtxR) when iron is limited.

What defenses humans have against Corynebacterium diphtheriae?

The answer

We don't seem to have any protection against the toxin.
Protection is ensured only by vaccination.

What are the clinical manifestations of diphtheria? What is the end result of this battle between organisms and humans. Describe the pathological consequences of this battle?

The answer

Incubation period is 2-5 days

Diphtheria is the result of local and systemic effects of diphtheria toxin.

Local
- A "membrane" forms in throat. It is a coagulum of fibrin, leukocytes, cellular debris due to local cytotoxicity by the toxin.
  - The membrane can extend from the oropharynx to larynx and into the trachea.
  - Sore throat, hoarseness and dysphagia follows.
  - Respiratory diphtheria may progress rapidly.
  - Respiratory arrest may occur from airway obstruction with tracheobronchial membrane.
  - Cough, strider wheezing are the result.
Systemic
- Diphtheria toxin can circulate in blood and affect heart and CNS systems.
  - Myocarditis, with cardiac enlargement, circulatory collapse, heart failure, AV blocks and dysrhythmias.
  - Nervous system can also be involved including paralysis of soft palate, oculomotor dysfunction. They resolve with resolution of infection.
- Fever and chills, malaise, cervical adenopathy, nausea and vomiting.

What is the natural history of untreated infection with Corynebacterium diphtheriae?

The answer

Mortality in untreated cases is 10-50%.

How can we diagnose diphtheria?

The answer

Initial diagnosis is clinical
No rapid lab test
Gram stain of throat not helpful
Organism can be cultured to confirm diagnosis.
- Missed on routine cultures.
- Notify the lab of possible diagnosis
Toxin production of cultured strains can be performed by immunodiffusion.
Serum for antibodies to diphtheria toxin

Other useful evaluations

EKG and Cardiac enzymes to detect myocarditis
CXR: Hyperinflation, subglottic narrowing

What will be your therapeutic strategy for diphtheria?

The answer

Strict isolation
C. diphtheriae antitoxin is given promptly to neutralize free toxin.
- Contact CDC for antitoxin and instructions on use.
- Do not wait for culture confirmation.
- Antibodies produced against the toxin in natural infection.
- Treat with toxin to neutralize free toxin before it binds to cells.
The organism itself can be treated with penicillin, cephalosporins, and erythromycin.
Notify the health department
Clinical diphtheria does not confer immunity, hence active immunization with diphtheria toxoid should be provided during convalescence.
Supportive care
- Bronchodilators if needed.
- Watch for respiratory obstruction and take necessary steps.
- Watch for myocarditis and mange appropriately

How can you prevent its occurrence of diphtheria? How can you prevent it from spreading to others? How can you prevent its recurrence?

The answer

Strict isolation of cases
Notify the health department of cases
Surveillance in communities where Diphtheria is endemic
Timely vaccination
- Diphtheria: Immunization with toxoid elicits an antibody response that prevents diphtheria infection.
- Vaccination with toxoid=formalin treated toxin
Booster dose of Tetanus-Diphtheria every 10 years through adulthood
Close contacts
- Should be identified and treated with oral erythromycin for 7-10 days
- Provide active immunization
Clinical diphtheria does not confer immunity, hence active immunization with diphtheria toxoid should be provided during convalescence.

What are the clinical infections of other species of Corynebacterium?

The answer

Corynebacterium ulcerans:

Cutaneous Diphtheria
- Generally caused by tox-strains.
- Produces natural immunity
- Can cause epidemics in poorly immunized populations.

Gas gangrene

Describe the clinical picture of gas gangrene.

The answer

Usually a complication of a crushing injury
Incubation period is fewer than 3 days with rapid onset of symptoms
Infectious disease emergency
Rapid onset of myonecrosis
Gas production
Sepsis
Mortality in traumatic gas gangrene is >25%
Progression of toxemia and shock is rapid.

Describe clostridium welchii, its morphologic, cultural characteristics and their normal habitat and life cycle..

The answer

Source
- Normally found in soil and GI tract and widely distributed in the environment
Morphology
- Large gram positive bacilli, pleomorphic
- Spore forming bacilli
Culture
- Exotoxin producing Clostridial species
- Thrives in the absence of oxygen
- Breed in damaged tissue

Who are the susceptible hosts for gas gangrene?

The answer

Normal host
- Traumatic or post Surgical gas gangrene (Clostridium perfringens)
  - Direct inoculation
  - Contamination may also occur from patient's faecal flora
Immune compromised host
- Spontaneous gas gangrene (Clostridium septicum)
  - Associated with hematological and GI malignancies
  - Drug abuse is a risk factor

How does clostridium welchii gain access to humans?

The answer

Direct inoculation into a open wounds due to trauma, bullet wounds, and multiply along with facultative co infecting or colonizing organisms.
Gas gangrene is usually a mixed infection aerobic and anaerobic.
Condition consisting of low oxidation reduction potential are necessary for C. perfringens sporulation, followed by rapid division.
Presumably, the other facultative organisms assist in reducing the oxidative-reductive potential.

How does clostridium welchii invades and spreads in humans? How do these organisms able to overcome human defenses?

The answer

Exotoxin, not bacterial proliferation, is responsible for rapid spread of infection. Exotoxin causes muscle destruction and creates an anaerobic environment conducive to further bacilli growth.

Primary toxicity
- alpha toxin is produced by the growing C. perfringens, which kill muscle cells and inflammatory cells, alpha toxin's biologic activity is a lecithinase, causing necrosis, and hemolysis.
- Beta and epsilon toxins are also necrotizing, and considered major toxins. Subsequently, new necrotic areas will foster growth and spread of the organisms.
- Carbohydrate fermentation by C. perfringens is responsible for the gas production (crepitus).
Secondary toxicity. Products of tissue breakdown cause secondary toxicity
- CPK
- Myoglobin
- Potassium

What are the human defenses for clostridium welchii infection?

The answer

WBC's try to attack these organisms.
We have no defense against toxins

What is the end result of this battle between organisms and humans. Describe the pathological consequences of this battle? What are the local manifestations of gas gangrene?

The answer

Local findings
- Crepitance
- Brawny edema
- Fowl-smelling serosanguinous discharge
- Skin discoloration
- Cutaneous bullae
- Ischemic appearing muscle tissue
- Gas in soft tissue within fascial planes

What are the systemic manifestations of gas gangrene?

The answer

Death occurs within about two days if the condition is not treated. Often have shock, jaundice, hemolysis and renal failure along with local findings.

Systemic secondary to toxins
- Fever or hypothermia.
  - hypothermia, or just absence of fever can predominate the clinical course.
- Tachycardia
  - frequently out of proportion to elevation of temperature
- Altered level of consciousness
- Hemolytic anemia
- Liver dysfunction
- Hyperkalemia
- Kidney dysfunction
- Metabolic acidosis
- Coagulopathy and thrombocytopenia
- Myoglobinemia and Myoglobinuria

What is the natural history of untreated gas gangrene?

The answer

Death occurs within about two days if the condition is not treated.
Often have shock, jaundice, hemolysis and renal failure along with local findings.

How do we diagnose gas gangrne?

The answer

Rapid diagnosis is by

Clinical presentation
Gram stain of bullae fluid or muscle tissue:
- Paucity of WBC with gram positive bacilli.
- Inflammatory cells are killed along with muscle cells by alpha toxin.
Pathologic demonstration of myonecrosis :
- Myoglobinemia
- Myoglobinuria
Radiographs showing gas within fascial planes
Microbiology culture

Non-specific findings

CBC: Anemia hemolytic secondary to toxins
LFT: Liver dysfunction
Electrolytes: Hyperkalemia
Renal panel: Kidney dysfunction
ABG: Metabolic acidosis
Coagulation panel: Coagulopathy and thrombocytopenia

What is the therapeutic strategy for gas gangrene?

The answer

Emergency Surgical consult.
- Treatment may include fasciotomy, debridement, or amputation.
- Surgical debridement is the definitive treatment:
Oxygen
- Hyperbaric oxygen: may be helpful.
IV fluids:
- Aggressive volume expansion
Antibiotics
- Treat mixed infection with Penicillin Sodium and Amino glycosides or Vancomycin.
Tetanus toxoid
Analgesics

How can you prevent occurrence of gas gangrene? How can you prevent it from spreading to others? How can you prevent its recurrence?

The answer

Appropriate wound care at the time of injury
- removal of dead tissue
- copious irrigation
Prophylactic antibiotics: Benzyl penicillin

The organism is not contagious and does not spread from person to person.

No vaccination
No anti toxin

What are the other body sites where infections of clostridium welchii have been repotted?

The answer

Gall bladder with abdominal wall muscle involvement following surgery,
Uterus (endometrium)

What are the other clinical infections of associated clostridium species?

The answer

Tetanus
Food poisoning: Botulism

Listeria monocytogene

.Describe Listeria monocytogene, its morphologic, cultural characteristics and their normal habitat and life cycle..

The answer

Source
- Listeria monocytogenes is a zoonoses.
- Carried by some animals.
- Contaminated food
Morphology
- Gram positive rod
Culture
- Can grow at refrigerator temperatures
- Beta hemolytic
- Catalase positive
- Motile at 25 degree centigrade (tumbling motility/umbrella motility)
- Non-spore forming rod

Describe succinctly the disease caused by Listeria monocytogene. What are the other clinical infections with these organisms?

The answer

bacteremia
meningitis

What kinds of hosts are susceptible to infection with Listeria monocytogene?

Susceptible hosts

Newborns

Elderly

Immunocompromised

Malignancy
Suppression of cell mediated immunity due to cyclosporine, azathioprine and prednisone.
- Azathioprine, cyclosporine and glucocorticoids suppress the ability of macrophages to ingest and kill intracellular pathogens in this patient.

How does Listeria monocytogene gain access to humans?

Contaminated foods

cabbage
milk products
- soft cheese
  - Mexican style soft cheese has been implicated in a large out break of listeriosis.
- pasteurized milk
sliced dale meats

How does Listeria monocytogene invade and spread in humans?

The answer

Exposure to contaminated food

Invasion of bacteria into intestinal crypt cells, macrophages, M cells mediated by internalin protein.
Bacteria enter cell in a vacuole and escape by producing listerolyisn, a cytolysin similar to streptolysin O
Listeriolysin mediates escape from the membrane bound vacuole into the cytosol.
Hemolysins hydrolyze host cell membranes.
Listeria is able to manipulate host cell action (actin) to propel it into pseudopods that extend to adjacent host cells. Thus, listeria can spread from cell to cell with minimal contact with the host immune system.

Transplacental infection (mother to infant)

What defenses humans have against Listeria monocytogene?

The answer

These are intracellular organisms

Requires cellular immunity with activated macrophages to resolve infection with Listeria

Macrophages ingest and kill these intracellular pathogens.

How does Listeria monocytogene able to overcome human defenses? What is the end result of this battle between organisms and humans. Describe the pathological consequences of this battle?

The answer

Listeria is able to manipulate host cell action (actin) to propel it into pseudopods that extend to adjacent host cells.
Thus, listeria can spread from cell to cell with minimal contact with the host immune system.

How do you diagnose infection with Listeria monocytogene?

Diagnosis

Culture: typical colonies from
- blood
- CSF
- wounds
- stool cultures
CSF findings consistent with meningitis
- mononuclear pleocytosis
- elevated protein
- low sugar

Other useful evaluations

The CT
- Listeria has a propensity for causing encephalitis in an immunosuppressed patient.

What will be your therapeutic strategy for infections due to Listeria monocytogene?

Therapeutic strategy

Ampicillin or penicillin are ideal.

Short courses may be associated with relapse hence at least 4 weeks of treatment is recommended.

The ability of Trimethoprim/Sulfamethoxazole to penetrate intra cellularly may offer an advantage in the treatment of Listeriosis.

How can you prevent its occurrence of Listeria monocytogene infections? How can you prevent it from spreading to others? How can you prevent its recurrence?

The answer

Only by not being exposed to contaminated food?
No vaccination

What are the other clinical infections with Listeria monocytogene?

Neonatal infections
Puerperal infections
Granulomatosis infantiseptica

Neisseria meningitides

Describe the source and morphology of Neisseria meningitides

Source
- either a human carrier or the one with active disease (Nasopharynx)
Morphology
- Gram negative diplococci with flattened sides "kidney bean shaped", polysaccharide capsule present, not readily seen, but serves as the basis for serotyping.
- Capsules and pili

Describe the cultural characteristics Neisseria meningitides

Cultural characteristics

Fastidious species require enriched media (chocolate agar)
Meningococcus grows as a transparent, non-pigmented, non-hemolytic colony under conditions of moisture and 5-10% C02. Mediums include blood agar, trypticase soy agar, supplemented chocolate agar, and Mueller Hinton agar.
Growth enhanced in CO2
Oxidase positive

Describe the structural characteristics Neisseria meningitides

Structural characteristics

Antigenic structure
- Endotoxic lipopolysaccharide complexed with protein in outer membrane
- Polysaccharide capsule
  - 9 serogroups. A,B,C,Y,W-135 most important
  - immunogenic except Group B

Describe the meningitis caused by Neisseria meningitides

The answer

N. meningitides causes acute meningitis and septicemia
Meningitis is an inflammation of the leptomeninges and underlying subarachnoid cerebral spinal fluid.
Signs and symptoms of meningeal inflammation and systemic infection of less than 24 hours

Untreated the patient will die either from systemic complications or from diffuse CNS ischemic injury.

What are the consequences of invasion of meninges by Neisseria meningitides. Describe the pathological consequences?

The answer

This invasion of meninges by this organism results in

Increased permeability of the blood brain barrier
Exudates form extending throughout the CSF, particularly to basal cisterns
- Damaging cranial nerves
- Obliterating CSF pathways (obstructive hydrocephalus)
Impair cerebral blood flow:
- Change of mental status and decreasing alertness.
Intracranial pressure increases
Brain edema progresses
Toxic mediators in CSF

What are the symptoms from meningitis?

Headache
Nuchal rigidity
Fever and chills
Photophobia
Vomiting
Seizures
Altered sensorium

What are the physical findings of meningitis?

Local
- Meningeal irritation
  - Nuchal rigidity
  - Kernig sign (Passive knee extension elicits neck pain and hamstring resistance)
  - Brudzinski sign (Involuntary flexion of hips following passive flexion of neck or single hip)
- Papiledema: Raised intracranial tension
- Isolated cranial nerve abnormalities
- Altered mental status
Systemic
- Arthritis
- Petechiae and cutaneous hemorrhage
- Endotoxic shock

What kinds of hosts are susceptible to infection with Neisseria meningitides?

The answer

normal host
- lack of antibody (prior vaccination)
sporadic cases
local outbreaks
- in young adults
  - college students
  - army recruits

How does Neisseria meningitides gain access to humans?

The answer

Nasopharynx (of a carrier or the one with disease) is a common source
Respiratory droplets requiring close contact and susceptibility (lack of antibody).
The majority of persons exposed do not contract the disease, likely due to the limited time exposure.
The virulence of the strain, host defense and their interactions determine whether the disease is going to follow.

How does Neisseria meningitides invade and spread in humans? What is the end result of this battle between Neisseria meningitides and humans.

The answer

Pathogenicity

Respiratory colonization
- Attachment
  - pilus mediated attachment- microvilli of nonciliated nasopharyngeal cells
  - Transverse cell in vesicle to submucosa
  - Damage ciliated cells
Bacteremia
- Blood stream survival enhanced by antiphagocytic polysaccharide capsule
Meningeal seeding follows bacteremia.
- Bacterial cell wall components initiate a cascade of complement and cytokine mediated events.
- CNS inflammation generated by cell wall peptidoglycan
- LPS, other bacterial products and its mediated by IL-1 and TNF (host response)
- Once in CSF, the paucity of antibodies, complement components, and white blood cells allow the bacterial infection to flourish.
Endotoxin mediated activation of complement leading to shock and hemorrhage

What defenses humans have against Neisseria meningitides?

The answer

Human defenses

Neutrophil pahgocytosis
Complement mediated bactericidal activity
Antibody

How does Neisseria meningitides able to overcome human defenses?

The answer

Polysaccharide capsule resists neutrophil phagocytosis as well as complement mediated bactericidal activity.

How do you diagnose infection with Neisseria meningitides?

The answer

Diagnosis

Spinal tap: CSF
- Chemistry
  - Glucose and protein
- Cell count and differential
- Gram stain
  - demonstrating Gram-negative diplococci is best.
- Bacterial culture
Counter immune electrophoresis or latex agglutination may demonstrate meningococcal polysaccharide antigen detected in CSF, blood, or urine.
- The latter method is good for patients where antibiotics were previously administered, or negative cultures.
CBC with differential
Blood culture

What will be your therapeutic strategy for Neisseria meningitides?

Therapeutic strategy

Initiate antibiotic therapy (Penicillin) within 30 minutes of initial encounter
- Patients decompensate rapidly
Do spinal tap before initiating therapy
Treat systemic complications

How can you prevent its occurrence of Neisseria meningitides? How can you prevent it from spreading to others? How can you prevent its recurrence?

Prevention

Vaccinate all college students and military recruits for N.meningitis
Close contacts (family members or equivalent) are 1000 times more likely to contract disease if not already immune.
- Prophylaxis is appropriate, with Rifampin 600 mg BID for two days.

What are the endotoxin mediated events of Neisseria meningitides?

The answer

Fulminant meningococcal disease, manifested by endotoxin from the N. meningitides cell wall are

DIC (disseminated intravascular coagulation)
Shock
Bilateral hemorrhagic destruction of the adrenal glands (Waterhouse-Friderichsen syndrome) may occur.