Sharq Elneil CollegeSchool of Medical Laboratory SciencesDepartment of MicrobiologyMedical Bacteriology courseU.Mahadi Hassan MahmoudBsc, Msc, MIBMS Microbiology
The bacterium that causes diphtheriawas first described by Klebs in 1883,and was cultivated by Loeffler in1884, who applied Kochs postulatesand properly identified Coryneb-bacterium diphtheriae as the agent ofthe disease. In 1884, Loeffler concluded that C.diphtheriae produced a solubletoxin, and thereby provided the firstdescription of a bacterial exotoxin
C. diphtheriae. Cause diphtheria Diphthroides. Opportunisticpathogens that cause infection toimmunocompromized individual. C. ulcerance. Cause Dimphtherialike illness C. pseudotuberculosis. CauseDiphtheria like disease.Species of medical importace:
They are Pleomorpic G+vebacilli found bind to each otherlike Chinese litter or Arrangedin V forms or PalisadesNon motile, Non spore formingNon capsulated, aerobic orfacultative anaerobes.
i. Loefflers Serum Slope. ii. Tellurite BA.- Temp. 37oC,- Aerobic and Facultative AnO2.
They form Polyphosphate(volutin or metachromatic)granules when cultured onhighly enriched media.They are highly resistant todrying.They are fastidious organismthat need Blood, serum or eggfor growth.
Diphtheria is an infection of pharynex thatcharacterized by formation of gray whitepseudomembrane which consist of inflammatorycells, dead tissue and bacilli which may block therespiratory tract leading to Asphexia. This disease occurred due to Exotoxins whichproduced from the bacilli after infection withprophage β which contain tox gene. This toxins spread through the blood causedestruction of cardiac, kidney and nervous tissue byinhibition of Elongation factor 2 leading to inhibitionof protein synthesis. The toxin have 2 fragments A & B. Fragment Benhance entrance of fragment A to the cell, andFragment A inhibit protein synthesis.
Largely controlled now by vaccination However, factors such as poverty and othersocial factors have led to diphtheria being anendemic/epidemic in many regions of theworldEpidemiology
Specimens: Throat swab. Direct examination: Gram stain showing G+ve bacilliarrange in Chinese letter. Inoculation of the specimens onLofflere’s serum media or Dorset eggmedia for 6 hours and stain fixed smearby Albert stain or Neisser stain. Thevolutin granules staind dark green toblack in Albert and dark blue to blackin Neisser stain.
Culture: Blood agar. Selective media is Tellurite Blood agar (contain 0.03%-0.04% K. tellurite) and Modified Tinsdale’s medium(contain cystein). Incubation: At 37 C in aerobic condition. Colonial morphology: B.A Produce small gray or gray white convex colonies. Tellurite blood agar produce black colonies due toformation of K. tellurate, C. garvis, mitis and ulceranceprodue β haemolysis. Modified tinsdale’s media produce brown hallow dueto H2S production.
Biochemical characters: Catalase +ve. Oxidase and Urease –ve. Ferment glucose and maltose withacid production. C. gravis ferment starch andTerialose. C. ulcerance are urease +ve andliquefy gelatin.
Invitrotoxigenicity test (ELEK’S gelprecipitation reaction): Toxigenic strain will secrete toxins that reactwith antitoxin in the filter paper producingprecipitin line. We need: Elek’s plate media with low iron concentration. Tested organism Control strain (Known toxoginic strain). Sterile filter paper impregnated in antitoxin. Procedure. Results (interpretation of results).
Invivotoxigenicity test: Inoculation of toxigenic strain to guineapig will lead to death of animal after 48hours.Schick test Intradermal test used to detectimmunization to diphtheria. 0.2 ml of Highly diluted diphtheriatoxin is injected intradermally in thearm, and heat inactivated toxin isinjected on the other hand. Interpretation:
Sanitary: Reduce carrier rate byuse of vaccine. Immunological: A vaccine (DPT)prepared from an alkalineformaldehyde inactivated toxin(i.e. toxoid) is required. Passiveimmunization with antitoxin canbe used for patients.