Clostridium perfringens: Characteristics and Types

Clostridium perfringens

• Originally known as Clostridium welchii in the 1890s.
• F.W. Andrewes and E. Klein associated it with foodborne outbreaks.
• Identified in a variety of diseases in 1892.
• Gram-positive, anaerobic, spore-forming bacterium.
• Non-motile, mesophilic, encapsulated rod-shaped microorganism with square ends.
• Found ubiquitously in nature, except the Sahara desert sand, due to its spore-forming ability.
• Common in soil, decaying vegetation, the intestinal tract of humans and animals, insects, and marine sediment.
• Produces various compounds including acetone, butanol, ethanol, butyric acid, acetic acid, propionic acid, lactic acid, carbon dioxide, and hydrogen.
• Ferments sugars, starch, and pectin.
• The most common cause of clostridial gas gangrene, accounting for 80-90% of human cases.
• Classified into 5 types (A-E) based on the production of 4 major exotoxins (a, b, e, i) and 8 minor ones.
• Type A is linked to gas gangrene and foodborne illness (perfringens food poisoning).
• Type A produces only the a major toxin, but the foodborne illness is caused by an enterotoxin from sporulating cells.
• Type C produces a and b toxins, potentially causing enteritis necroticans (pig-bel), a rare but serious illness that can be fatal due to intestinal necrosis and resulting septicemia; low levels of intestinal proteases are a predisposing factor.

Clostridium perfringens Food Poisoning

• Incubation period: 8 to 24 hours
• Illness occurs when contaminated food is ingested, leading to bacterial multiplication and toxin production in the intestines.
• Requires a large infective dose (108 vegetative cells) to cause infection and illness.
• Symptoms include a sudden onset of acute abdominal cramps, followed by diarrhea; nausea may occur, but vomiting is rare.
• It is generally a mild disease of short duration (1 day).
• Treatment is usually not necessary except for fluid replacement.
• Commonly associated with reheated meats, such as stews and gravies.
• Often linked to food served in institutions where large quantities are not chilled or heated properly, or are held at warm temperatures.
• Prevention involves thoroughly cooking foods containing meat or poultry, rapidly cooling foods after cooking (dividing large quantities into smaller portions to speed up cooling), and holding hot foods above 64°C.

Bacillus cereus

• Gram-positive, large, rod-shaped, facultatively anaerobic spore-former.
• First suspected as a causative agent of food poisoning in 1906.
• Conclusively established in 1950 after outbreaks in Norway associated with vanilla sauce.
• Colonies were originally isolated from an agar plate exposed to air in a cow shed.
• One of the most common contaminants in pharmaceutical manufacturing facilities.
• Widely distributed in the environment, found in soil, water, and vegetation.
• Causes two types of foodborne intoxications/infections: diarrheal type and vomiting (emetic) type.

Bacillus cereus Food Poisoning - Diarrhoeal Type

• Similar symptoms to Clostridium perfringens, including abdominal pain and profuse watery diarrhea.
• Incubation period is 8 to 16 hours (relatively long onset).
• Caused by a heat-labile enterotoxin.
• Frequently associated with cooked meat or vegetable-containing foods.

Bacillus cereus Food Poisoning - Vomiting (Emetic) Type

• Similar to Staphylococcus aureus poisoning, with symptoms like nausea, vomiting, and cramps.
• Incubation period of 1 to 6 hours (relatively rapid onset).
• Caused by a heat-stable enterotoxin.
• Most often associated with fried rice that has been cooked and held at warm temperatures for several hours.
• Both types are short-lived illnesses (1 day).
• Mild food poisoning.

Staphylococcus aureus

• First identified in 1880 in Aberdeen, Scotland, by surgeon Sir Alexander Ogston in pus from a surgical abscess.
• Name later amended by Friedrich Julius Rosenbach.
• An estimated 20% to 30% of the human population are long-term carriers.
• Found as part of the normal skin flora, in the nostrils, and as a normal inhabitant of the lower reproductive tract of women.
• One of the five most common causes of hospital-acquired infections and often the cause of wound infections following surgery.
• Facultative anaerobic, gram-positive coccal bacterium.
• Non-motile and does not form spores.
• Appears as staphylococci (grape-like clusters) under a microscope.
• Forms large, round, golden-yellow colonies, often with hemolysis, when grown on blood agar plates.
• Reproduces asexually by binary fission; complete separation of daughter cells is mediated by S. aureus autolysin.
• Easily killed with heat treatment.
• Able to grow in a wide range of temperatures (7°C to 48.5°C), pH (4.2 to 9.3), and NaCl concentrations (up to 15%).
• These characteristics allow it to grow in a wide range of foods.
• Catalase-positive, meaning it can produce the enzyme catalase.
• Catalase converts hydrogen peroxide (H2O2) to water and oxygen.

Staphylococcus aureus Food Poisoning

• Some strains produce a heat-stable enterotoxin that can cause food poisoning (intoxication).
• There are 14 types of enterotoxin produced, with toxins A and D being most associated with food illness.
• Also produces other toxins not associated with food poisoning, such as Toxic Shock Syndrome Toxin (TSST).
• Rapid incubation period: about six hours (can range from 30 minutes to 8 hours).
• Small infective dose: less than 1mg of toxin will produce symptoms (toxin level is reached when S. aureus populations exceed 100,000/g).
• Symptoms include abdominal cramps, nausea, vomiting, and sometimes diarrhea.
• Recovery is usually spontaneous after 24 hours.
• Main foods implicated vary by country, but animal foods are more commonly associated.
• Humans are the primary reservoir, so contaminated skin, hands, nasal passages, and fingernails are the main sources during food handling and preparation.
• Bacteria are destroyed by heat, but not necessarily the toxin.
• Large numbers (10^6/g) are required for the production of enough toxin to cause food poisoning.
• Tests for the presence of viable S. aureus in food can be performed using Baird Parker agar.
• Enterotoxin detection is a more useful indication of hazard.
• Prevention involves refrigerating foods and using good hygienic practices.