Singh's Lecture

Question 1

What’s corynebacterium diphtheria?

Answer 1

• gram +, aerobic, pleomorphic club-shaped rod
• catalase positive
• grows well on rich media enriched with blood or other animal material
• resides mainly in oropharynx, pathogenic
• produces diphtheria toxin which is encoded on a lysogenic bacteriophage
• nonpathogenic commensal corynebacteria are called diphtheroids
• diphtheroids inhabit the pharynx, nasopharynx, and distal urethra and skin

Question 2

What’s the disease, pathogenesis and virulence of corynebacterium diphtheria?

Answer 2

• diphtheria is a disease caused by the local and systemic effects of diphtheria toxin
• the local disease is a sever pharyngitis or tonsillitis typically accompanied by a plaque-like pseudomembrane in the throat and trachea
• toxin in blood circulation can affect multiple organs, but the most important is the heart, where the toxin produces an acute myocarditis

Question 3

What’s the diphtheria toxin?

Answer 3

• an A-B endo toxin
  
  • the A-b toxins are two-component protein complexes secreted by a number of pathogenic bacteria. They can be classified as Type III toxin because they interfere with internal cell function
• toxin binds to cells via B subunit
• internalize by endocytic vacuole
• at low pH of vacuole toxin unfolds and A subunit translocate to cytoplasm
• A subunit ADP-ribosylate elongation factor - 2 (EF-2) which leads to inhibition of protein synthesis

Question 4

What’s the epidemiology and diagnosis and immunology of diphtheria?

Answer 4

Epidemiology
-transmitted by droplet spread, but direct contact with cutaneous infections, and, to a lesser extent, by fomites
-some subjects become convalescent pharyngeal or nasal carriers and continue to harbor the organism for weeks, months, or longer
-rare where immunization is widely practiced
-fewer than 10 cases are reported each year in the USA
Diagnosis
-primary diagnosis is clinical
-culture on selective medium containing potassium tellurite such as Tinsdale medium
Immunology
-diphtheria toxin is antigenic, stimulating the production of neutralizing antitoxin antibodies during natural infection
-formalin inactivated toxin remains antigenic and can stimulate the production of neutralizing antibodies

Question 5

What’s the treatment and prevention of diphtheria?

Answer 5

• early administration of diphtheria antitoxin, an antiserum produced in horses
• penicillins, cephalosporins, erythromycin, and tetracycline can be used to eliminate infection
• immunization with diphtheria toxoid provides protection against toxin by stimulating production of neutralizing antibodies
• immunization done in the first year of life with 3-4 shots
• booster every 10 years maintain immunity

Question 6

What’s listeria monocytogenes?

Answer 6

• aerobic, gram + rod w/ features resembling both corynebacteria and streptococci
• catalase positive, distinguishes from streptococci
• grows well on most rich media
• can grow at temperature a low as O degC
• demonstrate tumbling motility in fluid media at temperatures below 30 degC, distinguishes from corynebacteria

Question 7

Whats the disease, pathogenesis and virulence of listeria monocytogenes?

Answer 7

• out of 6 species, only L. monocytogenes is pathogenic to human
• 12 serotype but most common are 1/2a, 1/2b, 4b
• intracellular pathogen
• listeriosis usually doesn’t present clinically until there is disseminated infection
• in foodborne outbreaks, gastrointestinal manifestations of primary infection such as nausea, abdominal pain, diarrhea, and fever occur
• disseminated infection in adults, usually involves general manifestations, such as fever, malaise, and occasional bacteremia
• can cause encephalitis and meningitis
• listeria monocytogenes may also be transmitted transplacentally to the fetus resulting in still birth or fulminant ( sever or sudden in onset) neonatal sepsis
• internalin and lysteriolylis O are major virulence factors
• infects phagocytes
• internalins (InIA, InIB) mediate attachement to the host cells
• bacterium is internalize by endocytosis
• listeriolysin O (LLO) lyses endocytic vacuole
• bacteria replicate in cytoplasm
• propels its escape from cytoplasm and infect neighboring cells by actin polymerization

Question 8

What’s the epidemiology, diagnosis, and immunology of listeria monocytogenes?

Answer 8

Epidemiology
-ubiquitous in nature can found in soil, water, intestinal tract of animal
-food born pathogen, spread from deli meat, dairy and un-cooked food stored at low temperature
-form biofilms, making the elimination of the bacteria difficult
-may also be transmitted transplacentally to the fetus
-infants under one month of age and elderly over 60 years are more susceptible
Diagnosis
- blood and cerebrospinal fluid culture shows beta-hemolytic gram positive rods
Immunology
-immunity to listeria infection involves both innate and adaptive immune responses
* neutrophil mediated killing of bacteria, innate immunity
* T cell mediated immunity for resolution of infection and long term protection

Question 9

What’s the treatment and prevention of listeria monocytogenes?

Answer 9

• no vaccine
• avoidance of unpasteurized dairy products and thorough cooking of animal products, especially for immunocompromised individuals
• ampicillin and trimethoprim/sulfamethoxazole (TMP/SMX)
• ampicillin combined with gentamicin is considered the treatment of choice for fulminant cases and in patients with severe compromise of T-cell function

Question 10

What’s bacillus anthrasis?

Answer 10

• gram +, aerobic, spore forming long chain rods
• non-motile
• grows well on rich media
• endospores are extremely hardy and have been shown to survive in the environment for decase
• dwells in soil, zoonotic (disease can be transmitted from animal to human)
• produces anthrax A, a potent exotoxin

Question 11

What’s the disease, pathogenesis and virulence of bacillus anthrasis?

Answer 11

• human anthrax is typically an ulcerative sore on an exposed part of the body, which usually resolves w/o complications
• spore germinate of rich environment of human tissue
• antiphagocytic effect of glutamic acid capsule required for virulence
• adenylate cyclase activity of the anthrax toxin causes edema at the site of infection
• in anthrax spores are inhaled, a fulminant pneumonia may lead to respiratory failure and death

Question 12

What’s the diagnosis, immunology, and treatment for bacillus anthrasis?

Answer 12

Diagnosis:
- culture of skin lesions, sputum, blood, and CSF are the primary means of anthrax diagnosis
- smears with large gram positive rod are suggestive
-hemolysis and motility exclude beta anthracis
-sputum and blood culture are positive in pneumonia
Immunology:
-the specific mechanism of immunity against B anthracis are not known
- experimental evidence factors antibody directed against the toxin complex
-the capsular glutamic acid is immunogenic, but antibody against it is not protective
Treatment and prevention:
-ciprofloxacin or doxycycline is used for treatment and prophylaxis
-eradication of animal anthrax is most important
-live and inactivated vaccines are available