Unit 6 Enterobacteriaceae Organisms

What are the main pathogens associated with gastrointestinal illness in the Enterobacteriaceae family?

Escherichia coli (hemorrhagic), Salmonella, Shigella, Yersinia, Plesiomonas shigelloides.

What is the most common species of Escherichia isolated from human specimens?

E. coli.

What are the common infections caused by E. coli?

Urinary tract infections, bacteremia, and neonatal meningitis.

What is Shiga toxin-producing E. coli (STEC) also known as?

Enterohemorrhagic E. coli (EHEC).

What are the symptoms of infection with E. coli O157:H7?

Bloody diarrhea, severe abdominal cramps, and can lead to Hemolytic uremic syndrome (HUS).

What types of foods are commonly associated with E. coli O157:H7 infections?

Ground beef, raw milk, unchlorinated municipal water, apple cider, raw vegetables, and sprouts.

What differentiates E. coli O157:H7 from normal E. coli flora on MacConkey with Sorbitol media?

E. coli O157:H7 does not ferment sorbitol and appears clear, while normal flora E. coli appears pink.

What are the two types of enterotoxins produced by Enterotoxigenic E. coli (ETEC)?

Heat-labile E. coli enterotoxin (LT) and heat-stable E. coli enterotoxin (ST).

What are the symptoms of Enteropathogenic E. coli (EPEC) infection?

Severe, prolonged, non-bloody diarrhea, vomiting, and fever, especially in infants.

What is the pathogenic mechanism of Enteroinvasive E. coli (EIEC)?

Strains invade colon cells and produce watery but occasionally bloody diarrhea, similar to Shigella.

How is Salmonella typically transmitted to humans?

Through contamination of food or water with animal feces, particularly from poultry and eggs.

What are the four disease states caused by Salmonella in humans?

Typhoid fever, carrier state, sepsis, and gastroenteritis.

What is the clinical presentation of typhoid fever caused by Salmonella typhi?

Sustained high fever, headache, and abdominal pain, often without diarrhea.

What laboratory methods are used to identify Salmonella species?

Culture, biochemical tests, and serotyping based on O, Vi, and H antigens.

What is the role of the O antigen in Salmonella?

It is a somatic antigen that provides antigenic variation and is an endotoxin.

What is the significance of E. coli as part of normal bowel flora?

It is part of the healthy bowel flora but certain strains can cause infections in both healthy and immunocompromised individuals.

What is the most common cause of urinary tract infections?

E. coli.

What are the clinical consequences of Hemolytic uremic syndrome (HUS)?

Anemia, thrombocytopenia, and renal failure.

What is the primary cause of traveler's diarrhea in developing countries?

Enterotoxigenic E. coli (ETEC).

What are the common symptoms associated with Salmonella infections?

Diarrhea, fever, and abdominal cramps lasting a week or longer.

What is the role of the H antigen in bacteria?

It is a flagellar antigen that provides antigenic variation and motility through gene rearrangement.

What does the Vi-antigen signify in S. Typhi?

It is a capsular antigen that protects the bacteria from antibody attacks on the O antigen, aiding in resistance.

How does S. Typhi appear on MacConkey Agar?

It grows as a non-lactose fermenter.

What does a black center on HE agar indicate for Salmonella?

It indicates H2S production.

What are the four subgroups of Shigella?

Shigella dysenteriae, Shigella flexneri, Shigella boydii, Shigella sonnei.

What are the symptoms of Shigella infection?

Watery diarrhea that may progress to dysentery with blood, mucus, and pus.

What is the primary transmission method for Shigella?

Person-to-person via ingestion of contaminated food and water.

Who first isolated Yersinia pestis and when?

Alexandre Yersin in 1894.

What are the three clinical forms of plague caused by Yersinia pestis?

Bubonic, pneumonic, and septicemic.

What is yersiniosis and what causes it?

A foodborne illness caused by Yersinia enterocolitica and Yersinia pseudotuberculosis.

What is the primary reservoir for Yersinia pestis?

Rodents, with transmission occurring mainly via their fleas.

What are the characteristics of Klebsiella pneumoniae?

Non-motile, can cause sepsis, and is often hospital-acquired.

What infections can K. oxytoca cause?

UTIs, wound infections, and pneumonia-like symptoms.

What distinguishes Proteus mirabilis in culture?

It is very motile and does not form round colonies, appearing smeared.

What is a notable feature of Proteus vulgaris?

It can form biofilms around medical devices, complicating catheter-associated UTIs.

What is the significance of Citrobacter in clinical settings?

It can cause urinary and respiratory tract infections in hospitalized patients.

What does Serratia marcescens produce and what infections can it cause?

It produces a bright red pigment and can cause UTIs, wound infections, or pneumonia.

What is the transmission route for Yersinia enterocolitica?

Ingestion of contaminated food, especially undercooked pork, unpasteurized milk, or untreated water.

What is the role of Enterobacter in the intestinal tract?

It is part of the normal flora but can occasionally cause hospital-acquired infections.

What is the clinical significance of Plesiomonas shigelloides?

It can cause outbreaks of gastroenteritis, particularly in Japan.

What are the symptoms of gastrointestinal infections caused by Yersinia?

Abdominal pain, fever, and sometimes bloody diarrhea.