Clostridium perfringens
Clostridium perfringens (formerly known as C. welchii, or Bacillus welchii) is a Gram-positive, rod-shaped, anaerobic, spore-forming bacterium of the genus Clostridium. C. perfringens is everpresent in nature and can be found as a normal component of decaying vegetation, marine sediment, the intestinal tract of humans and other vertebrates, insects, and soil.  It has the shortest reported generation time of any organism at 6.3 minutes in thioglycollate medium.
C. perfringens is the third most common cause of food poisoning in the United Kingdom and the United States though it can sometimes be ingested and cause no harm.
Infections due to C. perfringens show evidence of tissue necrosis, bacteremia, emphysematous cholecystitis, and gas gangrene, which is also known as clostridial myonecrosis. The toxin involved in gas gangrene is known as -toxin, which inserts into the plasma membrane of cells, producing gaps in the membrane that disrupt normal cellular function. C. perfringens can participate in polymicrobial anaerobic infections.  Clostridium perfringens is commonly encountered in infections as a component of the normal flora. In this case, its role in disease is minor.
The action of C. perfringens on dead bodies is known to mortuary workers as tissue gas and can be halted only by embalming.

# Food poisoning
In the United Kingdom and United States, C. perfringens bacteria are the third most common cause of foodborne illness, with poorly prepared meat and poultry, or food properly prepared but left to stand too long, the main culprits in harboring the bacterium. The clostridium perfringens enterotoxin (CPE) mediating the disease is heat-labile (inactivated at 74 C (165.2 F)). It can be detected in contaminated food (if not heated properly), and feces. Incubation time is between six and 24 (commonly 10-12) hours after ingestion of contaminated food.
Since C. perfringens forms spores that can withstand cooking temperatures, if cooked food is let stand for long enough, germination can ensue and infective bacterial colonies develop. Symptoms typically include abdominal cramping, diarrhea; vomiting and fever are usual. The whole course usually resolves within 24 hours. Very rare, fatal cases of clostridial necrotizing enteritis (also known as pigbel) have been known to involve "Type C" strains of the organism, which produce a potently ulcerative -toxin. This strain is most frequently encountered in Papua New Guinea.
Many cases of C. perfringens food poisoning likely remain subclinical, as antibodies to the toxin are common among the population. This has led to the conclusion that most of the population has experienced food poisoning due to C. perfringens.
Despite its potential dangers, C. perfringens is used as the leavening agent in salt rising bread. The baking process is thought to reduce the bacterial contamination, precluding negative effects.

# Infection
Clostridium perfringens is the most common bacterial agent for gas gangrene, which is necrosis, putrefaction of tissues, and gas production. It is caused primarily by Clostridium perfringens alpha toxin.  The gases form bubbles in muscle (crepitus) and the characteristic smell in decomposing tissue.  After rapid and destructive local spread (which can take only hours), systemic spread of bacteria and bacterial toxins may cause death. This is a problem in major trauma and in military contexts. C. perfringens grows readily on blood agar plate in anaerobic conditions, and often produces a double zone of beta hemolysis.
Research published in 2014 suggested that a strain of C. perfringens might be implicated in multiple sclerosis (MS). Tests in mice found that a toxin made by a rare strain of C. perfringens caused MS-like damage in the brain, and earlier work had identified this strain of C. perfringens in a human with MS. MS patients were found to be ten times more immune-reactive to the epsilon toxin than healthy people.

# Diagnosis
C. perfringens can be diagnosed by Nagler's reaction where the suspect organism is cultured on an egg yolk media plate. One side of the plate contains anti-alpha-toxin, while the other side does not. A streak of suspect organism is placed through both sides. An area of turbidity will form around the side that does not have the anti-alpha-toxin, indicating uninhibited lecithinase activity.
Other tests/reactions: Catalase: Negative, Spot indole: Positive, Lecithinase: Positive, Lipase: Negative, Litmus Milk: Stormy Fermentation, Reverse CAMP plate: Positive, Gas Liquid Chromatography products: (Acetic, Butyric and Lactic Acids).

# Differential diagnosis
Clostridium perfringens infection must be differentiated from other causes of viral, bacterial, and parasitic gastroentritis.
8Small bowel diarrhea: watery, voluminous with less than 5 WBC/high power field
Large bowel diarrhea: Mucousy and/or bloody with less volume and more than 10 WBC/high power field
 It could be as high as 1000 based on patient's immunity system.
The table below summarizes the findings that differentiate inflammatory causes of chronic diarrhea

# Food poisoning incidents
On May 7, 2010, 42 residents and 12 staff members at a Louisiana state psychiatric hospital experienced vomiting, abdominal cramps, and diarrhea. Within 24 hours, three patients had died.   The outbreak was linked to chicken which was cooked a day prior to being served and was not cooled down according to hospital guidelines.  The outbreak affected 31% of the residents of the hospital and 69% of the staff who ate the chicken.  It is unknown how many of the affected residents ate the chicken.
In May 2011, a man died after allegedly eating food contaminated with the bacteria on a transatlantic American Airlines flight. The man's wife and daughter are suing American and LSG Sky Chefs, the German company that prepared the inflight food.
In December 2012, a 46-year-old woman died two days after eating a Christmas Day meal at a pub in Hornchurch, Essex, England. She was among about 30 people to fall ill after eating the meal. Samples taken from the victims contained C.perfringens. The hotel manager and the cook were jailed for offences arising from the incident.
In December 2014, 87 year old Bessie Scott died three days after eating a church potluck supper in Nackawic, New Brunswick, Canada. Over 30 other people reported signs of gastrointestinal illness, diarrhea and abdominal pain. The province's acting chief medical officer says Clostridium perfringens is the bacteria that most likely caused the womans death.