Bacteriology- Clostridium | Quick Revision Notes for NEET-PG

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      • Gram-positive spores and toxin-producing anaerobic bacillus
      • Motility present except in
        • C. perfringes(C.welchi)
        • C. tetani type VI
      • Capsule present in
        • C. perfringens
        • C. butyricum

C. perfringens(welchi)

      • Capsulated non-motile organisms which produce oval spores present sub-terminally
      • Stormy fermentation on litmus milk media
        1. Litmus milk media (differential media)contains-
          1. Skimmed milk(W/o Fat) containing sugar(Lactose) & protein (casein-milk protein)
          2. Litmus indicator
          1. C. perfringens show stormy fermentation in litmus milk medium. Lactose in the medium is fermented to organic acid and gas by the organism. Acid changes the color of the indicator litmus from blue to red. Acid coagulates casein (milk protein) in the medium to form a clot. Due to the vigorous production of gas, the clot gets disrupted. The paraffin seal is pushed upwards and shreds of the clot can be seen on the sides of the test tube. This type of fermentation is called stormy fermentation.
      • Shows target/double zone hemolysisθ causes complete/alpha hemolysis and α cause incomplete/beta-hemolysis on blood agar
      • Toxins-

10 02 01 00

      1. Major- α,β, I,ε
      2. Minor-θ
      • There are 5 types of perfringens-A, B, C, D, E
      • Virulence factors
        1. Most important virulence factor is – alpha toxin/phospholipase c/lecithinase- causes intravascular hemolysis
      • Present in the gut as commensals which is indicated by part/remote fecal pollution of water.
      • Diseases caused
        1. Gas gangrene/clostridial myonecrosis-In case of a very severe soiled dirty wound where blood vessels are damaged, spores of the organism can enter our body (spores in soil). These spores give rise to bacteria which releases various toxins(most importantly alpha toxin)into circulation leading to a rapid spread of edematous myonecrosis(gas gangrene). The sample to be collected-necrotic tissue and exudates from the wound
          1. Mainstay- Surgical debridement
        2. Poisoning-by C. perfringens type A
          1. Intakes of food like meat and meat products
          2. Caused due to heat labile enterotoxin
          3. Incubation period-8-16 hrs
        3. Piel/necrotizing enteritis
      • Detected by Nagler’s RXN-

C. Tetani

      • Motile
      • Terminal bulging round spores having Drum stick appearance
      • Culture
        1. On Robertson cooked meat broth, it turns meat particle black with foul odor due to its proteolytic activity
        2. Swarming growth can be seen on Blood agar with polymyxin B plate
      • Virulence factors(2 exotoxins)
        1. Tetanospasmin-It is an exotoxin that acts presynaptically on neuromuscular junction and prevents the release of inhibitory neurotransmitters like GABA and glycine. This causes descending spastic paralysis seen in tetanus.
        2. Tetanolysin-heat and oxygen labile hemolysin which plays no role in the pathogenesis of Tetanus.
      • Causes tetanus/lockjaw characterized by(clinical features)
        1. Opisthotonus
        2. Respiratory paralysis
        3. Convulsions
        4. Diagnosis-Based on clinical symptoms. Culture can be done to support the diagnosis.
        5. Prophylaxis-administration of tetanus toxoid (TT).It is present in 2 forms
          1. Monovalent vaccine-toxoid is prepared by incubating toxin with formalin
          2. Combined vaccine(DPT)

-immunization against Diptheria, Pertussis, and Tetanus. Pertussis component act as adjuvant and inc. antigenicity of DT and TT. Various forms are –

      • DPT -DT+TT+Pertussis(whole cell)
      • DPaT- DT+TT+ Pertussis(acellular)
      • DT-DD+TT
      • dT-It contains TT and adult dose diphtheria toxoid (2Lf) -3 doses(0,1M,1Yr) given to children above 12 yrs.

                 -Schedule-5 doses- Out of 5,3 doses at 6,10,14 weeks after birth and 2 booster dose at 16-24 months and 5yrs

                 -Site-IM at Ant-Lat aspect of the thigh

                 -protective titer-antitoxin titer of 0.01unit/mL

C. botulinum

      • Cause botulism
      • Produces 7 toxins-A,B,C1,CR,D,E,F
      • Botulism toxin is the most toxic to humankind with a minimum lethal dose of -1micro gram
      • Out of 7, six toxins A, B, C1, D, E, F are neurotoxins and cause botulism and CR is cytotoxic(acts by ADP-ribosylation)
      • Most common toxins which cause human disease are A, B & E
      • Botulinum toxin acts pre-synaptically at Neuro-Muscular junction and prevents the release of Acetylcholine leading to descending flaccid paralysis
      • The toxin has parasympathetic activity
      • Clinical features include
        1. Diplopia
        2. Dysphagia
        3. Dry mouth
        4. Constipation
        5. Respiratory paralysis
      • There are 3 types of botulism

Food botulism

Infant botulism

Wound botulism

Most common type



Due to the intake of canned food

Due to the intake of honey contaminated by spores

Due to contamination of the wound with spores of bacteria

During canning, spores enter the food and germinate in the anaerobic environment of the sealed container.

These bacteria then release the toxins

Spores germinate in an alkaline environment of the intestine into bacteria which then produces toxins.


C/F listed above

Baby stops sucking milk and

keeps falling over(k/a Floppy baby syndrome)

C/F listed above except GIT features

Rx-Polyvalent antiserum

C. difficale

      • Present in the gut of 3% of normal people
      • The most common cause of nosocomial diarrhea
      • Cause
        1. Antibiotic-associated colitis /Diarrhea-Intake of antibiotics kill the gut flora except for C. difficult. With no commensals left to inhibit the growth of C. Difficle, these grow rapidly and then produce toxins. Clindamycin has the highest chance to produce this disease
        2. Pseudomembranous enterocolitis-with yellow plaque of size ranging from 1-2mm. Soon, it spreads over the entire colonic surface.

    • Types of toxin
      1. Toxin A-enterotoxin
      2. Toxin B-cytotoxin
      3. Both toxins are needed to cause disease
    • Colonoscopy shows yellowish-white plaque in colon
    • Diagnosis
      1. Culture-not confirmatory
      2. ELISA(to demonstrate toxin)
      3. PCR(to detect genes producing toxins)
    • Treatment
      1. Drug of choice is Metronidazole
      2. Alternate -Vancomycin
      3. New drug-Fidaxomicin
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