Clostridium:  A genus of rod-shaped, spore-forming, chiefly anaerobic bacteria including the nitrogen-fixing bacteria
found in soil and those causing botulism and tetanus.
Clostridium bifermen´tans  a species common in feces, sewage, and soil and associated with gas gangrene.
Clostridium botuli´num  the causative agent of botulism, divided into six types (A through F) which elaborate
                      immunologically distinct toxins.
Clostridium diffi´cile  a species often occurring transiently in the gut of infants, but whose toxin causes
                      pseudomembranous enterocolitis in those receiving prolonged antibiotic therapy.
Clostridium histoly´ticum  a species found in feces and soil.
Clostridium kluy´veri  a species used in the study of both microbial synthesis and microbial oxidation of fatty acids.
Clostridium no´vyi  an important cause of gas gangrene.
Clostridium oedema´tiens  C. novyi.
Clostridium perfringens:  the most common etiologic agent of gas gangrene, distinguishable as several
different types;  type A causes human gas gangrene (necrotizing --  flesh eating), colitis, and food poisoning
and type C causes enteritis.
Clostridium ramo´sum  a species found in human and animal infections and feces and commonly isolated from clinical
                      specimens.
Clostridium sporo´genes  a species widespread in nature, reportedly associated with pathogenic anaerobes in
                      gangrenous infections.
Clostridium ter´tium  a species found in feces, sewage, and soil and present in some gangrenous infections.
Clostridium te´tani  a common inhabitant of soil and human and horse intestines, and the cause of tetanus in humans
                      and domestic animals.
Clostridium wel´chii  British name for C. perfringens.
http://medical-dictionary.thefreedictionary.com/Clostridium

When the environment becomes stressed,  the bacteria produce spores that tolerate the extreme
conditions that the active bacteria cannot. In their active form, these bacteria secrete powerful exotoxins that are
responsible for such diseases as tetanus, botulism, and gas gangrene.  This non-motile bacterium is an invasive
pathogen that can be contracted from dirt via large cuts are wounds. C. perfringens cells proliferate after spore
germination occurs and they release their exotoxin. The toxin causes necrosis [death] of the surrounding tissue
(Clostridial myonecrosis destroys muscular tissus). The bacteria themselves produce gas which leads to a bubbly
deformation of the infected tissues. C. perfringens is capable of necrotizing intestinal tissues and can release an
enterotoxin that may lead to severe diarrhea.  Clostridium difficile is a motile bacterium that can be part of the natural
intestinal flora. Infection can occur through the use of broad-spectrum antibiotics which lower the relative amount of
other normal gut flora. When this situation occurs, C. difficile proliferates and infects the large intestine. The bacterium
then releases two enterotoxins that destroy the intestinal lining and cause diarrhea.