Corynaebacterium Diphtheriae Dr. Qurat-Ul-Ain Senior Demonstrator Microbiology, KEMU, Lahore
Corynebacterium diphtheriae
Introduction Klebs--1883 discovered Loefflers--1884 cultured Also known as KLB Emil von Behring- 1890 produced antitoxin Awarded nobel prize Emil Von Behring
Morphology Gram positive bacilli. 3-6 μ x 0.5-0.8 μ. v or k or L shape. Chinese letter pattern, angular arrangement, palisade arrangement Metachromatic granules. volutin granules, polymetaphosphate energy storage depots Alberts stain – green and bluish black Nonmotile noncapsulated, nonsporing pleomorphic
Corynebacterium Biotypes C diphtheriae gravis C diphtheriae intermedius C diphtheriae mitis Helpful for epidemiological tracing Culture identified by biochemical tests.
Transmission and Risk factors solely among humans spread by droplets secretions direct contact Poor nutrition Crowded or unsanitary living conditions Low vaccine coverage among infants and children Immunity gaps in adults
Virulence Factors 1. Diphtheria toxin !!! 2. Dermonecrotic toxin blocks protein synthesis 2. Dermonecrotic toxin sphingomyelinase increases vascular permeability 3. Hemolysin 4. Cord factor -Toxic trehalose corynemycolic acid, corynemyolenic acid
Pathogenesis Part A Part B Bound receptor internalized Endosome Active site N terminal Enzyme Part B Binding site Binds to membrane receptor Bound receptor internalized Endosome Hydrolysed by protease Disulfide broken Part A released
Clinical Features/ Types of Diphtheria Incubation period 2-5 days (range, 1-10 days) May involve any mucous membrane Classified based on site of infection
Pharyngeal and Tonsillar Diphtheria Insidious onset Exudate spreads within 2-3 days and may form adherent membrane Membrane may cause respiratory obstruction Pseudomembrane: fibrin, bacteria, and inflammatory cells, no lipid Fever usually not high but patient appears toxic
Clinical classification i) Malignant (hypertoxic) diphtheria Signs: severe toxemia and adenitis, lymph glands swelling in the neck Complications: death-circulatory failure, paralytic sequelae ii) Septic diphtheria: Signs: ulceration with pseudomembrane formation and cellulites (gangrene around pm) iii) Hemorrhagic diphtheria Signs: local and general bleeding from edge of psudomembrane, conjunctival, epistaxis and purpura
Pseudomembrane COVERS CONTAINS tonsils, bacteria uvula, lymphocytes palate nasopharynx larynx. CONTAINS bacteria lymphocytes plasma cells fibrin dead cells
Cutaneous Diphtheria
Systemic complications Nerves toxic peripheral neuropathy paralysis of short nerves mouth, eye, facial extremities Cardiac Congestive heart failure high amount of toxin 48-72 hours Low amount of toxin 2-6 weeks
Diphtheria Antitoxin Produced in horses First used in the U.S. in 1891 Used only for treatment of diphtheria Neutralizes only unbound toxin Lifetime of Ab: 15 days – 3 weeks, wait 3-4 weeks before giving toxoid. Only given once.
Diphtheria Toxoid Formalin-inactivated diphtheria toxin Schedule Three or four doses + booster Booster every 10 years Efficacy Approximately 95% Duration Approximately 10 years Should be administered with tetanus toxoid as DTaP, DT, Td, or Tdap
i) primary immunization – Schedule i) primary immunization – - infants and children - 3 doses, 4-6 weeks - 4th dose after a year - booster at school entry ii) Booster immunization - adults - Td toxoids used (traveling adults may need more) Shick test-to test sensitivity (allergic reaction)
Diphtheria and Tetanus Toxoids Adverse Reactions Local reactions (erythema, induration) Exaggerated local reactions (Arthus-type) Fever and systemic symptoms not common Severe systemic reactions rare
Schick test Be used to ascertain population risk This test involves the injection of a minute amount of the diphtheria toxin under the skin. The absence of a reaction indicates immunity.
Control Immunization diphtheria toxoid Schick test Passive immunity check for antibodies Passive immunity Antibodies Antibiotics Penicillin & erythromcyin
DIAGNOSIS Clinical: Muscle weakness, edema and a pseudomembranous material in the upper respiratory tract characterizes diphtheria. Laboratory: Tellurite media is the agar of choice for isolation of Corynebacteria, which produce jet black colonies
Diphtheria Laboratory diagnosis Rapid diagnosis required Differentiate from commensals “diphteroids” nose & throat Throat swabs (confirmatory) Blood Tellurite
Specialized media Loeffler serum: best colonial morphology Dextrose horse serum (1887) now Dextrose beef serum Tellurite: black colonies Not diagnosticallly significant .tellurite inhibits many organisms but not C. diphtheriae
Blood tellurite Selective & differential medium Corynebacteria are resistant to tellurite Reduced to tellurium Forms deposit in colonies Colonies appear dark