Enterobacteriaceae

Be aware that we will not include all pathogenic members, and that details can be found elsewhere.

• They are ubiquitous in the environment, and some are commensals.
• They are a significant cause of disease, particularly urinary tract and gastrointestinal infections.

The following characteristics are helpful in identification:

• The bacteria in this family share a common surface antigen.
• They are facultative anaerobes.
• The ferment glucose and reduce nitrate
• They are catalase positive and oxidase negative
• They have common virulence factors, including endotoxin, antibiotic resistance, and others.

Now, we'll organize our diagram according to their ability to ferment lactose. Ferments lactose: Escherichia coli

• When grown in MacConkey's agar, lactose-fermenters, including most strains of E. coli, produce bright pinkish-purple colonies; in Eosin methylene blue agar, lactose-fermenters produce colonies with a bright green sheen.

Escherichia coli produce extra-intestinal and gastrointestinal infections, depending on the bacterial strain.

• Extra-intestinal infections are typically caused by opportunistic pathogens, such as commensals that migrate to new anatomical niches.

– Primary cause of urinary tract infections. – Significant cause of neonatal meningitis.

• Gastrointestinal infections are caused by pathogenic strains in the GI tract; they are usually introduced via contaminated food or water.
• Pathogenesis and symptoms vary by pathotype
• Infants and children are most likely to suffer long-term consequences of dehydration due to severe diarrhea and/or vomiting.
• Pathotypes that tend to produce their effects in the small intestine and cause watery diarrhea and vomiting (illness is often referred to as "traveler's diarrhea):

– Enteropathogenic, Enterotoxigenic, and Enteroaggregative; Enteroaggregative E. coli also affects the large intestine.

• Pathotypes that primarily affect the large intestine and produce watery, then bloody diarrhea:

– *Shiga toxin-producing Escherichia coli***, as its name suggests, produces Shiga-like toxin.

• Enterohemorrhagic Escherichia coli (EHEC) is usually considered a subset of Shiga toxin-producing Escherichia coli*.

In severe infection, a condition called hemolytic uremic syndrome (HUS) can develop when red blood cells and platelets are destroyed; the damaged cells can obstruct the renal filtration system and cause renal failure. Antibiotics increase the risk of HUS in patients with Shiga toxin-producing Escherichia coli infection. – Enteroinvasive Escherichia coli is similar to Shigella, which produces inflammatory lesions and ulcers in the colon. Enterobacteriaceae that do not ferment lactose (or do so very slowly) They produce colorless colonies on MacConkey's agar, as opposed to the bright pink colonies of E. coli*. Salmonella

• Transmitted via the fecal-oral route, usually via contaminated foods.
• Causes typhoid and paratyphoid fevers, which are characterized by flu-like, nonspecific and gastrointestinal symptoms.

– More specific signs of typhoid and paratyphoid fever include *gallbladder infection due to bacterial replication, liver and spleen enlargement, and the development of so-called rose spots over the skin of the torso.

• Also causes gastroenteritis without typhoid fever; this is the most common form of infection in the United States.

Can cause extra-intestinal problems, such as osteomyelitis and septicemia; recurrent septicemia is an AIDS-defining condition.* Shigella

• Transmitted via the fecal-oral route, and show that it is an intracellular pathogen.
• Shigellosis is most common in children, and is easily transmitted due to its low infectious dose.
• Associated with watery, then bloody diarrhea.

Shigella strains that produce the Shiga toxin can cause Hemolytic uremia syndrome (HUS)*, often in children. Yersinia

• Zoonotic infections.

Fleas transmit the strain of Yersinia that causes the plague, which is characterized by fever, chills, and weakness.* Three key forms of the plague: bubonic, system, and pneumonic. Bubonic plague* is characterized by infection of the lymphatic system, and that bacterial replication in the lymph nodes produces buboes. – Localized lymph node destruction produces these inflamed, raised areas that are tender or even painful. Septicemic plague* occurs when the bacteria enter the bloodstream. Patients experience extreme weakness, as well as pain in the abdominal area. – Disseminated intravascular coagulation occurs, producing necrosis and even organ failure without treatment. Pneumonic plague* can occur if bubonic plague spreads to the lungs, or, in other cases, as the result of human-human transmission via respiratory droplets. – Inflammation and necrosis in the lungs can rapidly lead to respiratory failure. Entercolitis is caused by other strains of Yersinia*

• Transmitted via consumption of infected animals, especially pork products.

– Whereas younger children are likely to have bloody diarrhea, older children tend to experience pain the right abdomen that may be mistaken for appendicitis.