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10 Cards in this Set
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- Back
- 3rd side (hint)
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Introduction |
Gram positive. Non acid fast. Non motile. Club shaped swellings. Observed and described by klebs But was first cultivated by loeffler. Known as klebs-loeffler bacillus . ..
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Coryne -club It forms tough, leathery pseudomembrane in the disease. |
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Morphology |
Slender rod with clubbing at one or both ends. Pleomorphic. Non sporing, non capsulated and non motile. Granules situated at poles are called polar bodies. Metachromatic granules (bluish purple by loefflers methylene blue). Also called volutin or babes-ernst granules . Bacilli resembles the letters V or L. Known as chinese letter or cuneiform arrangement. (Due to incomplete separation of daughter cells after binary fission) |
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Cultural characteristics |
Optimum temperature is 37℃ and pH is 7.2. Aerobe and facultative anaerobe. 1. Loeffler's serum slope: colonies are small, circular, white opaque disc but may acquire a distinct yellow tint on continued incubation. 2. Tellurite blood agar: selective media . Diphtheria bacilli reduce tellurite to metallic tellurium, which is Incorporated in colonies, giving them a grey or black color. |
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Classification (McLeod classification) |
1. Gravis (most serious) 2. Intermedius (intermediate severity) 3. Mitis (mildest) |
G I M |
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Biochemical reactions |
Hiss's serum sugars: ferment glucose, galactose, maltose and dextrin. They don't ferment lactose, mannitol or sucrose. Proteolytic activity is absent. |
Non lactose fermenter |
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Toxin |
Produces exotoxin. The standard strain almost universally used for toxin production is the park-williams 8 strain. Toxin consists of two fragments , A and B. When released by the bacterium , the toxin is inactive because the active site on fragment A is masked. Proteases present in culture medium and infected tissue activates the toxin. All the enzymatic activity of toxin is present in fragment A. Fragment B binds the toxin to cells. |
Treatment with 0.2% formalin converts it to toxoid. Toxoid is toxin That has lost its toxicity but not it's antigenicity. |
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Factors affecting toxin production |
1. Corynephages - genetic determinant controlling toxin production. Lysogenic or phage conversion- the conversation of non toxigenic strains into toxigenic by infecting them with beta phage. 2. Concentration of iron in the medium. Mechanism of action : inhibits protein synthesis. Fragment B helps in binding. Fragment A inhibits polypeptide chain elongation in the presence of nicotinamide adenine dinucleotide by inactivating the elongation factor EF-2. |
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Laboratory diagnosis |
Specimen: swabs from lesions using tongue depressor Microscopy: smear examination- neisser's or Albert stain shows metachromatic granules. Albert- green bacilli with purple-blue metachromatic granules. Culture isolation: Loeffler serum slope, tellirite blood agar and blood agar. Tellurite plates important in isolation of diphtheria bacilli from convalescent, contact and carriers. |
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In vitro tests Elek's Gel precipitation test |
● a rectangular strip of filter paper soaked with antitoxin is placed on surface of a 20% normal horse serum agar in a petri dish. ● when agar has set, the surface is dried and narrow streaks of the strains are made at right angles to filter paper strip. ● positive and negative controls should be put up. ● the plate is incubated at 37℃ for 24 to 48 hours. ● toxins produced by the bacterial growth will diffuse in the agar and , where it meets the antitoxin at optimum concentration, will produce a line of precipitation. ● the presence of such arrowhead lines of precipitates indicates that the strain is toxigenic. |
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Prophylaxis |
Immunization. Active, passive and combined. Active immunization provides herd immunity and lead to eradication of the disease. The susceptibility is tested by Schick test. Active immunization : formol and adsorbed toxoid. DPT - Passive - ADS subcutaneously Combined immunization- ADS antidiptherial serum on one hand and adsorbed toxoid on other arm. |
Active Passive Combined |
