The genus Clostridium consists of a group of anaerobic, sporing, G+ve, bacilli. The
diameter of spore of most members is wider than that of the bacterial body giving the
bacillus a swollen appearance resembling a spindle in various spp, the spore is placed
centrally, subterminally, or terminally. Most spp are motile with peritrichous flagella,
produce a zone of haemolysis when inoculated on the blood agar.
Most spp are saprophytic organisms which grow normally in the soil, Cl.welchii and
Cl.sporogenes are commensals of the intestinal tract of animals and man. A few spp
of Clostridium are opportunistic pathogens and cause three major diseases of man
which are tetanus, gas gangrene and food-poisoning. Clostridial pathogenecity is due
to powerful exotoxin produced by the organisms.
Classification
The Clostridia may be classified on the basis of diseases produced by them.
A)Tetanus ………..Cl.tetani
B)Gas gangrene
1-Established pathogens …….Cl.welchii (60%), Cl.novyi (30-40%), Cl.septicum
(10-20%)
2-Less pathogenic………..Cl.histolyticum, Cl.fallax
3-Doubtful pathogens……… Cl.bifermentans, Cl.sporogenes
C)Food poisoning
1-Gastroentritis……. Cl.welchii (a sub group of type A)
2-Botulism…………Cl.botulinum
D-Acute colitis……Cl.difficile
Biochemical reactions
Clostridia are biochemically active and most ferment a variety of sugars and
hydrolyse protein. Based on biochemical property, they may be classified as
predominantly saccharolytic, predominantly proteolytic and slightly proteolytic
Toxin
Most clostridia produce one or a variety of poisonous protein toxins which are
responsible for pathogenic effects on the host. Toxins produced by Cl.tetani and
Cl.botulinum attack nervous pathways and are called neurotoxin. The gas gangrene
clostridia attack soft tissues by toxins are known as histotoxic.
Culture
Clostridia grow fairly well on ordinary media only under anaerobic conditions,
which can be achieved by the following methods:
1- After inoculation of nutrient agar or blood agar plate or tube, it is placed in an
air-tight jar from which air is removed and placed by nitrogen with 10% CO2.
The jar with culture media is then kept inside an incubator at 37C˚ for 2-3
days. Most clostridia produce haemolytic colony on blood agar.
2- Liquid media like Robertson’s cooked meat media (contains chopped cooked
meat) or thioglycolate media are used for clostridial culture. The inoculated
culture tubes are incubated for 2-4 days in ordinary laboratory conditions and
bacterial growth occurs at the bottom.
Cl.welchii
It is the most important causative agents of gas gangrene, this bacteria is G+ve,
capsulated non motile bacillus with subterminal spore.
The different strains of Cl.welchii produce at least 12 distinct in addition to several
enzymes and biologically active soluble substances, such as alpha, beta, epsilon and
iota toxins and enzymes like DNA-ase, hyaluronidase, collagenase …etc. On the basis
of production of the 4 major toxins ( alpha, beta, epsilon and iota) Cl.welchii are
differentiated into 5 types A,B,C,D and E.
Alpha (α)toxins
It is produced by all strains of Cl.welchii but more abundantly by Cl.welchii type A of
gas gangrene. Chemically it is phospholipase (Lecithinase) and most lethal of all
clostridial toxins and is responsible for profound toxaemia in gas gangrene patients. It
is relatively heat stable, necrotising, cytotoxic or membranolytic. The toxin splits
lecithin which is an important constituent of mammalian cell membrane.
Pathogenesis
Cl.welchii type A is the predominant bacterial agent causing gas gangrene in man. A
subgroup(some strains) of type A of Cl.welchii also cause food-poisoning.
I-Gas Gangrene: Cl.welchii is normal commensals of intestinal tract of man and
animals and its spores are widely distributed in nature e.g., soil, dust, faeces, and
human skin. When awound gets contaminated by soil or faecal matter, there may
be 3 types of anaerobic wound infection.
a) Simple contamination of wound
* There are only small numbers of clostridia of low virulence
* The organisms do not invade tissue
b) Anaerobic cellulites
*This type of lesion is caused by clostridia of low invasive power & poor
toxigenecity.
* There is gas production but little toxaemia and it tends to be a self-limiting lesion.
c) Anaerobic myositis (gas gangrene)
This is a serious condition and is associated with formation of abundant amount of
exotoxin. Cl.welchii type A is the predominant agent causing anaerobic myositis ( gas
gangrene).
The incubation period varies from 6 hours to 6 weeks. In the wound, the spores
germinate and thrive in dead tissue where oxygen tension is low. Hence their infection
may complicate wound with extensive destruction of tissue (accidental injury), pelvic
infection in women, wounds with lack of free drainage, pyogenic infections, tissues
with some interference with circulation (ischaemia), intestinal operation and septic
abortion. Along with multiplication, the organisms ferment carbohydrates present in
the tissue producing gas which causes distension of sarcolemmal sheath of muscle
cells and ischaemia. Moreover, the alphatoxin of Cl.welchii destroys cell membrane
of muscle fiber and alters vascular permeability. All these together lead to necrosis of
muscle tissue which provides further opportunity for increased bacterial growth.
Meanwhile, other toxins and enzymes, such as hyaluronidase, collagenase,
leucocidim, fibrinolysin and haemolytic toxins enhance their effect and favour spread
of infection. Anaemia develops rapidly and in terminal stages bacterial dissemination
may lead to bacteraemia, shock and death.
Clinically, it is a spreading gangrene of the muscles with profound toxaemia and
shock. There is increasing pain, tenderness, oedema with blackening of tissues and
foul smelling serous exudates. Crepitus due to accumulation of gas babbles is often
detected under the skin.
Cl.welchii food poisoning usually follows the ingestion of large numbers of clostridia
that have grown in warmed meat dishes. The toxin forms when the organisms
sporulate in the gut, with the onset of diarrhea-usually without vomiting or fever-in 618 hours. The illness lasts only 1-2 days.
Treatment
 Treatment with early surgery (amputation) and antitoxin administration.
 Gas gangrene clostridia are susceptible to penicillin, sulphonamide, and
metronidazole.