Back To CourseMicrobiology 101: Intro to Microbiology
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Angela has taught college Microbiology and has a doctoral degree in Microbiology.
In August 1988, almost 6,500 women gathered in Michigan for a five-day outdoor music festival. The annual festival, informally known as Women's Woodstock, is staffed, entertained and attended by only women, a celebration of the sex. Except for a brief bout of diarrhea that affected a few staff members leading up to the start of the festival, the event went off without a hitch - until about two days after the festival ended.
Attendees, now back home, spread across the United States, started getting sick. All across the country, the women were experiencing fevers, abdominal pain and diarrhea, similar to the staffers who had been sick. All told, about 3,200 of the 6,500 attendees developed some variation of the same symptoms; 117 had to be hospitalized. Another 182 people who didn't attend the festival caught the illness from someone who did.
During the investigation into the outbreak, officials determined that the sick staffers contaminated the food served during the large, communal meals. Specifically, a tofu salad, served uncooked, was transmitting the disease. Alone, this foodborne source would have been bad enough, but it was compounded by the lack of access to soap and running water needed for appropriate sanitation and personal hygiene. Not only were people exposed to the disease by the tofu, they were also directly passing it from person to person.
The causative organism responsible for making the festival women sick was Shigella sonnei, one of the more virulent, yet rarely life-threatening, bacterial pathogens. In this lesson, we will examine Shigella and see what, if anything, these women could have done to reduce their chances of infection.
Shigella is a genus of Gram-negative, rod-shaped bacteria that only infects humans and other primates. 'Gram-negative' refers to Shigella having a cell wall with a thin peptidoglycan layer and an outer membrane, making these cells appear red in the classic Gram stain.
There are several species of Shigella that cause disease in humans, but there are two that are of particular importance in the United States. The first is Shigella sonnei. This is the species responsible for the festival outbreak. Infections from S. sonnei are not generally considered life-threatening and are responsible for the majority of cases in the United States. S. dysenteriae is the deadliest species, responsible for causing more severe illness. Fortunately, infections by S. dysenteriae are not very common in the United States, but more frequent outbreaks occur in the developing world and can be deadly.
People catch Shigella by the fecal-oral route. Anywhere that is crowded and difficult to keep clean can be a source of infection. Not surprisingly, cases of Shigella pop up most frequently in daycare centers. Young children are not the easiest to keep clean, and they're too young to be good at maintaining appropriate personal hygiene themselves.
Adults come into contact with Shigella through water contaminated with feces or through food contaminated by infected preparers or handlers. The festival attendees ran into a little of both. The food preparers initially infected some people, but then these people, by not having the ability to thoroughly and frequently wash after using the bathroom, exposed even more people through direct contact.
Regardless of how it happens, consuming Shigella usually leads to the development of illness. Shigellosis is a food infection caused by bacteria of the genus Shigella. Remember, in a food infection, the symptoms are a result of actively growing bacteria in the host's body. Shigella is noteworthy here because a person only needs to consume a few cells, as few as 10 to 200, for the infection to develop. As a comparison, E. coli and Salmonella, two other common causes of foodborne illness, require several thousand to tens of thousands of cells for symptoms to develop. This allows Shigella to spread very rapidly and infect many people.
So, once infected, what can you expect? The bacteria attack the cells that line the large intestine, triggering the cells to engulf the bacteria. For the next two to four days, the bacteria reproduce inside the cells and release an exotoxin, called a Shiga toxin. The toxin damages the blood vessels and intestinal lining, causing inflammation. Eventually, the reproducing bacteria lyse the intestinal cells, spill out into the large intestine, and reinfect neighboring cells. The lysis and toxin release cause the symptoms of the disease.
Some healthy adults will not show any symptoms, as the immune system quickly handles the infection. Others will only experience mild, watery diarrhea from the intestinal damage and inflammation. But most patients who develop shigellosis will have a fever, abdominal pain and diarrhea containing blood and mucus. Shigellosis usually clears up on its own in about a week.
People infected with S. dysenteriae can develop a more severe illness. Bacterial dysentery is a disease characterized by severe inflammation of the large intestine caused by bacterial pathogen. Dysentery sufferers can expect profuse, prolonged diarrhea with large amounts of blood and mucus as well as fever and abdominal pain. The rapid fluid loss can quickly become life-threatening, and treatment is required. Children who get dysentery can also develop convulsions as a result of the high fever.
Many foodborne illnesses cause diarrhea, so how do you know you have Shigella? Usually, the presence of fresh, bright red blood in the feces, combined with a probable source of infection, is enough for a positive diagnosis. Your doctor can also culture the bacteria from a sample of your feces. There are several different growth media that are used that will differentiate Shigella from the other potential causes.
In the case of uncomplicated shigellosis, treatment is frequently not needed. In more severe cases or if dysentery has developed, the patient can be given one of several common antibiotics to reduce the duration of symptoms and the amount of bacteria shed in the feces. Antibiotic resistance has become more common recently, so the antibiotic of choice keeps changing to stay ahead of the bacteria. In addition, dysentery patients often require intravenous fluids and salt supplements to replace losses from the diarrhea. Despite treatment, most people will become carriers for up to a month, shedding infectious bacteria in their feces.
There is no vaccine for Shigella, but there are a few things you can do to prevent getting or spreading the disease. The number one thing you can do is practice good personal hygiene. Thoroughly washing your hands after using the bathroom will go a long way towards prevention. This might have been the biggest problem for the women at the festival. Better access to soap and water might have prevented many of those infections.
Also, thoroughly cooking foods will eliminate bacterial contamination from food handlers. It was the uncooked tofu that led to the initial infections in Michigan. Worldwide, Shigella dysenteriae kills about a million people a year. Half of those deaths are children under five years. Most infections in the United States, about 14,000 a year, result from Shigella sonnei, not S. dysenteriae, so fatalities are much rarer.
Let's review. Shigella is a genus of Gram-negative, rod-shaped bacteria that only infects humans and other primates. People acquire Shigella by fecal-oral contamination, usually resulting from water exposed to sewage or food handled by infected people.
Once consumed, the bacteria invade the cells that line the large intestine. The bacteria release the exotoxin, Shiga toxin, and rupture the host cells, causing disease symptoms. Since the symptoms are a result of the actively growing bacteria, shigellosis is considered a food infection. Symptoms can range from a mild, watery diarrhea to a combination of bloody, mucoid diarrhea, fever and abdominal pain. Some cases result in bacterial dysentery, a severe and profuse diarrhea accompanied by fresh blood and mucus.
Most shigellosis cases resolve without treatment in a week or so. Severe cases and dysentery require antibiotics and fluid replacement. Even with treatment, patients will continue to shed infectious bacteria for up to a month. The best way to prevent shigellosis is to remember to always wash your hands after using the bathroom and to thoroughly cook your food.
After seeing this video lesson, students should now know what Shigella is, how people catch it and what can be done to prevent spreading the bacteria. They should be familiar with the two species of Shigella that are significant in the United States. Students may also understand how the bacteria could potentially lead to dysentery.
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Back To CourseMicrobiology 101: Intro to Microbiology
20 chapters | 207 lessons