Corynebacterium diphtheriae Quiz

Corynebacterium & Mycobacteria

• Lecture 9 covers Microbiology: Corynebacterium & Mycobacteria
• Mycobacterium tuberculosis
  • Key biological characteristics
  • Pathogenesis (including Koch's phenomenon)
  • Diagnosis, treatment, and prevention of M. tuberculosis infection
• Mycobacterium leprae & leprosy
• Corynebacterium diphtheriae and infections

Corynebacterium diphtheriae

• Gram-positive
• Strict aerobe
• Rod-shaped (0.5-1 µm in diameter, several micrometers long)
• Club-shaped swellings at one end
• Granules (metachromatic granules) within the rod, causing a beaded appearance when stained with aniline dyes
• Pleomorphic (occurring in two or more forms in one life cycle)
• Specialized media for diagnosis
  • Tellurite: black colonies, not diagnostically significant, tellurite inhibits many organisms but not C. diphtheriae
  • Loeffler: best colonial morphology, Dextrose horse serum (1887), now Dextrose beef serum
• Culture characteristics on different media
  • Blood agar: colonies are small, granular, gray with irregular edges, may have small zones of hemolysis
  • Potassium tellurite agar: colonies are brown to black with a brown-black halo due to tellurite reduction
• Habitat: skin of infected persons or carriers, upper respiratory tract, GI tract, urogenital tract of humans, wounds
• Spread: by droplets or direct contact to susceptible individuals, then grows on mucous membranes or skin abrasions; toxigenic strains produce toxin.

Diphtheria

• Member of normal pharynx flora
• Overgrowth in upper respiratory tract
• Pseudomembrane
• Choking
• Bacteria do not spread systemically; toxin disseminates
• Disease caused by local and systemic effects of diphtherial toxin (a potent protein synthesis inhibitor)
• Local disease: severe pharyngitis, plaque-like pseudomembrane in throat & trachea
• Life-threatening aspects due to toxin absorption across pharyngeal mucosa and bloodstream circulation.
• Multiple organs affected; most important: heart (acute myocarditis)
• Pathogenesis
  • Diphtheria toxin absorbed into mucous membranes; destroys epithelium; superficial inflammatory response
  • Necrotic epithelium embedded in exuding fibrin & cells, forming grayish pseudomembrane (commonly over tonsils, pharynx, or larynx)
  • Removing pseudomembrane exposes capillaries, leading to bleeding
  • Regional lymph nodes in neck enlarge; marked edema of neck; distortion of airway ("bull neck")
  • Diphtheria bacilli within membrane continue producing toxin.

Corynebacterium: Pathogens

• C. diphtheriae: Diphtheria
• C. pseudotuberculosis: humans, sheep, cattle, suppurative lymphadenitis
• C. ulcerans: humans (pharyngitis), cattle (mastitis)
• C. haemolyticum: pharyngitis, cutaneous infection
• C. pyogenes: cattle, sheep, swine, suppurative infection
• C. pseudodiphtheriticum: endocarditis

Diphtheria - Manifestation

• Thick gray coating over back of throat, expanding down airway; suffocation possible
• Diphtheria throat shows damage to tonsils, uvula, and palate.

Clinical Findings

• Diphtheritic inflammation in respiratory tract causes sore throat & low-grade fever
• Prostration and dyspnea (shortness of breath) follow due to membrane obstruction
• Obstruction can cause suffocation; intubation or tracheostomy needed
• Irregularities in cardiac rhythm indicate heart damage
• Later, vision, speech, swallowing, or limb movement issues may happen
• All manifestations tend to subside spontaneously.
• Symptoms include: pharyngitis, hypoxia, choking ("croup"), fever, and lymphadenitis; all signs/symptoms caused by toxin
• Diphtheria pseudomembrane: No true membrane, few live cells, dead cells + protein deposit; blocks airway

Pharyngeal diphtheria

• Inflammation similar to strep throat
• Leukocytes infiltrated, killed, embedded in fibrin clot
• ToXIN!!!!

Corynobacteria - COVERS and CONTAINS

• Covers: tonsils, uvula, palate, nasopharynx, larynx
• Contains: bacteria, lymphocytes, plasma cells, fibrin, dead cells

Diphtheria Systemic Complications

• Nerves: toxic peripheral neuropathy, paralysis of short nerves (mouth, eye, facial extremities)
• Cardiac: congestive heart failure, high amount of toxin in hours, low amount of toxin in 2-6 weeks

Diphtheria toxin (DT)

• Exogenic toxin spreading; systemic and fatal injury
• DT gene in the lysogenic phage
• DT causes myocarditis; may lead to congestive heart failure

Diphtheria toxin (detailed)

• Heat-labile, single-chain, three-domain polypeptide (62 kDa)
• Lethal dose: 0.1 µg/kg body weight
• If disulfide bonds broken, splits into two fragments
• Fragment B (38 kDa) has no independent activity; functionally divided into receptor & translocation domains
• B unit binds to host cell; A unit inhibits protein synthesis of eukaryotic cells
• Fragment A inhibits polypeptide chain elongation; inactivates elongation factor EF-2 complex (ADP-ribosylation), needing dinucleotide (NAD)

Virulence factors

• Diphtheria toxin (blocks protein synthesis)
• Dermonecrotic toxin (sphingomyelinase—increases vascular permeability)
• Hemolysin
• Cord factor
• Toxic trehalose

Virulence (Diphtheria bacilli)

• Virulence of diphtheria bacilli is due to their ability to establish infection quickly, grow rapidly, and effectively absorb the toxin they produce
• Does not need to be toxigenic to establish localized infection in nasopharynx or skin
• Nontoxigenic strains do not create systemic toxic effects
• Does not typically invade deep tissues, and rarely enters bloodstream
• Invasive infections like endocarditis and septicemia from nontoxigenic C. diphtheriae have increased over last two decades

Wound or skin diphtheria

• Occurs primarily in tropics, occasionally in temperate climates
• Common among alcoholic, homeless, and impoverished groups
• Membrane formation on infected wounds that fail to heal
• Systemic toxin absorption is usually slight and effects are negligible
• Small amount of absorbed toxin develops antitoxin antibodies

Cutaneous diphtheria

• Produces ulcerative lesions

Immunity (Diphtheria)

• Diphtheria resistance depends on neutralizing antitoxin availability in bloodstream and tissues
• Generally occurs only in people lacking antitoxin antibodies (IgG; <0.1 IU/mL)
• Antibodies neutralize toxin
• Formalin-treated toxin (toxoid) retains antigenicity but loses toxicity; used in immunizations

Testing immunity

• Schick skin test for toxin

Prevention (Diphtheria)

• Immunization with 3-4 doses of diphtherial toxoid, starting in first year of life; booster shots at 10-year intervals.
• Fully immunized individuals can still become infected, but the disease is milder.

Treatment (Corynebacterium & Diphtheria)

• Antitoxin for neutralizing free toxin.
• Antibiotic therapy (e.g., erythromycin) for antibacterial action.

Tuberculosis(M. tuberculosis)

• Obligate aerobe, non-motile, acid-fast rods, doesn't form spores.
• Mycobacterial diseases (tuberculosis-like and leprosy-like).
• Laboratory Diagnosis (acid-fast bacteria - sputum).
• Acid-fast: Bright red to intensive purple (B), curved or straight rods, occurring singly or in small groups, may appear beaded. Non-acid fast: Blue color (A).
• Laboratory diagnosis (culture): Grows very slowly (2+ weeks), non-pigmented colonies, niacin production, differentiates from other mycobacteria, polymerase chain amplification (rapid diagnostic).
• Tuberculosis (TB, consumption): major human disease; healthy people infected (1/3 world population), association with AIDS, multiple drug resistance
• Epidemiology (Tuberculosis): Infection in 18th/19th centuries; high attack rates in developing countries; major sociologic components (ignorance, poverty, poor hygiene); globally 1/3 of world population infected.
• Celebrities who died from Tuberculosis: Kamla Nehru, Vivien Leigh, Franz Kafka, Anton Chekhov.
• Transmission (Tuberculosis): Most by respiratory route; repeated coughing generates infectious dose (ID50 < 10 bacilli); poor ventilation increases transmission risk; AIDS and drug resistance enhance spread.
• Pathogenesis (Tuberculosis): MTB multiplies in alveolar macrophages; Blocks acidification of Phagosome: MTB disseminates into lymph nodes and bloodstream; MTB proteins trigger delayed-type hypersensitivity (DTH); resulting in granuloma formation (lymphocytes, macrophages, epithelial cells, fibroblasts, and multinuclear giant cells).
• Granuloma structure: Growth of granuloma leads to necrosis (usually central), called caseous necrosis (cheesy material filling lesion center); due to delayed type hypersensitivity (DTH).
• Latent tuberculosis and reactivation: Primary lesions heal with immunity development, some MTB enter dormant state rather than dying; latent MTB reactivates in aerobic sites leading to destruction that form pulmonary cavities; progressive DTH causes injury.
• Manifestation (Tuberculosis): Mid-lung infiltrates and adenopathy produced, primary infection may progress to reactivation/dissemination; reactivation common in older men, predisposing factors (underlying diseases, life events); Cough is universal symptom; cavities form in lung apexes; Multiple organs can be involved.
• Main symptoms (Pulmonary TB): Central symptoms (appetite loss, fatigue); Lung symptoms (chest pain, coughing up blood, productive and prolonged cough); Skin symptoms (night sweats, pallor).
• Antibiotic treatment: Extensive time periods (e.g., 9 months); organism grows slowly/dormant; two or more antibiotics (e.g., rifampin & isoniazid); minimizes resistance.
• Tuberculosis and drug resistance: Multiple drug resistant (MDR) - resistant to first-line drugs; Extremely drug resistant (XDR) - resistant to some second-line drugs, nearly untreatable

Immunity (Tuberculosis)

• Innate immunity very high, genetically variable
• T_H immunity most important
• CD8 cytotoxic T-lymphocytes may participate

Laboratory Diagnosis (Tuberculosis)

• Skin testing (Mantoux test): Delayed hypersensitivity; tuberculin protein purified derivative (PPD); testing for exposure; does not always indicate active disease

Vaccination (Tuberculosis)

• BCG vaccine (attenuated strain of M. bovis); not effective in US (low incidence).

Mycobacteria and AIDS

• M. avium infections, much less virulent than M. tuberculosis
• M. avium - does not infect healthy people, infects AIDS patients, infection when CD4 count greatly decreased, infects AIDS patients (earlier stage of disease, more systemic)
• M. avium - intracellular complex, non-AIDS infection almost never; AIDS - major bacterial opportunist - multiple drug resistance
• Clinical features with AIDS: systemic disease (versus pulmonary - greater in AIDS), lesions often lepromatous

Other mycobacterial species

• Infect immunocompromised hosts, not transmitted man-to-man, healthy people
• M. avium is common; other species are rare.

Leprosy

• Chronic granulomatous disease of peripheral nerves and superficial tissues, particularly nasal mucosa
• Disease ranges from anesthetic skin lesions to distinctive facial lesions (stigmatizing leprosy)
• M. leprae
• Major disease in the third world; rare in US

Leprosy (Hansen's Disease)

• Causative agent: M. leprae
• Disseminated through nasal droplets
• Chronic disease—disfigurement
• Peripheral nerves demyelinated, rarely seen in US; common in third world
• Effective antibiotic therapy—incidence reduced—infects skin; low temperature.

Manifestation (Leprosy)

• Ulcers, bone resorption
• Worsened nerve damage from careless hand use.

Leprosy (classifications)

• Tuberculoid- ID - few organisms active cell-mediated immunity
• Lepromatous – many organisms; immunosuppression

Production of M. leprae antigens and pathogenesis studies

• In vitro: Non-culturable; low growth
• In vivo: Armadillo (laboratory and native); mouse footpad

Leprosy: Diagnostic

• Lepromin (skin test, similar to tuberculin, positive at 48h, Fernandes test)
• Acid-fast stains (skin biopsies)
• Clinical picture

Treatment (Leprosy)

• Sulfones combined with rifampin for primary treatment
• Dapsone controls/cures when given for 6 months
• Clofazimine for intermediate forms; treatment continued for 2 years

Test your knowledge about Corynebacterium diphtheriae with this quiz. It covers topics such as culture characteristics, isolation media, and the mechanisms of diphtheria toxin. Ideal for microbiology students and enthusiasts looking to deepen their understanding of this bacterium.