Question

Salmonella, Shigella and Escherichia coli are important pathogens of the gastrointestinal tract. Provide a detailed description of these pathogens, including diagnostic methods used, their role in asymptomatic carriage and disease, pathogenesis, treatment, and potential complications that may occur in other organs of the body following on from gastrointestinal infection.

Answer 1

Salmonella

Salmonella is gram-negative, flagellated, facultatively anaerobic bacilli with over 2,300 subtypes, including species of enterititis and typhimurium.

• Pathogenesis: Pathogenic salmonellae pass through the gastric acid barrier and produce toxins upon invading the mucosa layer of the intestines. They result in the release of cytokines which induce an inflammatory reaction which may lead to diarrhea, mucosa destruction or ulceration.
• Epidemiology: salmonellosis is a common disease of humans and animals where the disease is usually food-borne. Some infections are spread via the fecal-oral route and asymptomatic human carriers may also spread the infection.
• Symptoms: Nausea, Vomiting, Abdominal cramps, Diarrhea, Fever, Headache, Stool blood
• Causes: Most salmonella infections are caused by eating infected animals or foods that have been contaminated by feces. Generally, the consumption of raw meat, poultry, eggs, raw fruits, and vegetables lead to higher exposure.
• Diagnosis: Diarrhea and vomiting are generally an indication of gastroenteritis. Further tests of blood and stool can help to determine the infection and stage.
• Treatment: Intake of plenty of fluid to prevent dehydration is the first stage of treatment besides antibiotics and anti-motility drugs. Moreover, vaccines are there for typhoid caused by salmonella.

Shigella

Shigellae are nonmotile, gram-negative, non-spore forming, facultatively anaerobic bacilli with 4 main serogroups having different serotypes.

• Pathogenesis: Diarrhea may occur as the organisms pass through the small intestine mucosa due to toxins. Bacterial invasion of the colonic epithelium occurs in shigellosis and local release of cytokines causes inflammatory colitis. That can result in bacillary dysentery symptoms.
• Epidemiology: Typically 10-20% percent of enteric disease, and most of the blood and mucus associated diarrhea or dysentery can be characterized as shigellosis. Transmissions can occur via contaminated food and water or person-to-person. Humans are the natural carriers for the infection.
• Symptoms: Stomach pain, Diarrhea, Fever, Stool blood.
• Causes: Most shigellae infections are caused by handling objects or foods that have been contaminated by feces. These infections can also be caused by swallowing stool contaminated river or lake water or anal sexual activities.
• Diagnosis: Fresh blood in the stool is a sign of shigellosis. Moreover, stool tests that find neutrophils in stool smears also strongly suggest infection.
• Treatment: The most effective first-hand treatment is the prevention of fecal-oral transmission. Severe dysentery can be treated with ampicillin or ciprofloxacin.

E. coli

E. coli are gram-negative, facultatively anaerobic, bacilli that are commonly found in the lower gut of organisms. Most strains are harmless, but some serotypes are responsible for food contamination.

• Pathogenesis: E. coli colonize the ileal mucosa layer and enterotoxins induce diarrhea. These may induce inflammatory reactions and lead to dysentery.
• Epidemiology: E. coli infection prevails more in places of poor sanitation and is transmitted through the oral-fecal route.
• Symptoms: Bloody diarrhea, Stomach cramps, Nausea, vomiting.
• Causes: E. coli infection is generally caused by contact with the feces of humans or animals via raw fruits or vegetables or contaminated water.
• Diagnosis: The diagnosis is mainly by stool tests and tests to determine virulence factors.
• Treatment: The primary step for treatment is the prevention of fecal-oral transmission. Good sanitary practices, Water chlorination, and sewage treatment are good measures to prevent infection. Furthermore, excess water intake and broad-spectrum antibiotics are used for treatment.