USMLE® Step 1 style questions USMLE
A 30-year-old man is brought to the emergency department with pain and discoloration of the right thigh. A week ago the patient was involved in a motor vehicle accident and suffered deep lacerations over the same region. The patient was evaluated at an urgent care facility afterward and a piece of scrap metal was removed from the right thigh. Currently, temperature is 38.9°C (102.0°F), pulse is 108/min, respirations are 14/min, blood pressure is 70/44 mmHg and SpO2 is 93% of room air. The appearance of the right thigh is shown below. On palpation of the right thigh, there is tenderness and crepitus. Which of the following toxins is most likely responsible for this patient’s presentation?
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Clostridium perfringens exam links
Content Reviewers:Rishi Desai, MD, MPH, Yifan Xiao, MD
Contributors:Justin Ling, MD, MS, Evan Debevec-McKenney
Clostridium perfringens is from the family of Clostridia, and as a family, they’re obligate anaerobes, meaning they don’t require oxygen to thrive, in fact, they’re better off without it.
Anaerobes, clostridia included, tend to lack the enzymes catalase or superoxide dismutase, so oxygen is actually toxic to them.
In nature, they thrive in deep, compact soil, and when they feel the stress of fresh oxygenated air, they often produce spores, which are extremely resilient to the environment, and can even survive cooking.
When conditions improve, for example, when food is slowly cooled or stored, the spores can sprout into full-fledged Clostridia.
In fact, at an optimum temperature, Clostridium perfringens has one of the fastest growing rates of any bacterium! In the lab, when doing a gram stain, Clostridium perfringens is Gram-positive, or purple when Gram stained, and look like big cylinders or rods, also called bacilli.
Clostridium perfringens is a common cause of food poisoning, in fact, it’s sometimes called “the cafeteria germ”.
That’s because it typically infects food that’s prepared in large quantities, and then kept warm for prolonged periods, such as in cafeterias or buffets.
Clostridium perfringens are found in the environment and they can accidentally contaminate food when it’s been left out for a while.
If a person eats food contaminated with C. perfringens, the bacteria will soon colonize the gut.
Within 24 hours, the bacteria starts to make clostridium perfringens enterotoxin, or CPE.
The CPE specifically targets the tight junctions that connect epithelial cells lining the intestines to one another.
When the tight junctions get destroyed, it causes inflammation and compromises the structural integrity of the intestinal wall.
Fortunately, CPE is heat labile, so prolonged cooking at 72°C or above will inactivate it.
And that’s one reason why freshly cooked food is best to eat - the other reason is that it’s simply tastier that way!
But uncooked food - like salads, or reheated food - like leftovers, can be a good home to Clostridium perfringens.
The symptoms of Clostridium perfringens enteritis include abdominal cramping, watery diarrhea, and vomiting.
Fortunately, most of these improve over the course of a day, as the bacteria makes its way through the intestines.
In terms of treatment, antibiotics aren’t needed, and instead the goal is to keep the individual well hydrated.
Now, instead of getting into food, Clostridium perfringens can also sometimes get into a wound.
This can happen when wounds are made by dirty, sharp objects, that come into contact with soil that’s rich with Clostridium perfringens and other anaerobes, like gardening or farming equipment.
And if there’s a deep wound, it can cause clostridial myonecrosis.
Clostridium perfringens is a spore-forming, gram-positive obligate anaerobe bacterium that can cause food poisoning. The most common symptoms of Clostridium perfringens food poisoning are abdominal cramps and diarrhea, and vomiting. Clostridium perfringens also causes myonecrosis or gas gangrene once it gets into a wound. It can be deadly unless urgent surgical debridement and antibiotic therapy are initiated rapidly.