Escherichia coli & Kebsiella Flashcards
(20 cards)
What are the common features of Enterobacteriaceae?
They are all Gram-negative rods, facultative anaerobes, ferment glucose, are oxidase-negative, and reduce nitrates to nitrites.
What are the cultural characteristics of E. coli on MacConkey agar?
E. coli forms circular, convex, smooth colonies with distinct edges and is a lactose fermenter, producing pink colonies on MacConkey agar.
What are the three major antigens involved in the antigenic structure of Enterobacteriaceae?
The three major antigens are:
1. O antigens (somatic antigens)
2. H antigens (flagellar antigens)
3. K antigens (capsular antigens).
What are the virulence factors of E. coli?
The virulence factors of E. coli include:
1. Surface antigens (H, O, and K antigens)
2. Toxins:
a) Endotoxins
b) Exotoxins:
- Hemolysins
- Enterotoxins (Heat labile toxin (LT), Heat stable toxin (ST), and Verotoxin (VT) also known as Shiga-like toxin (SLT)).
What is the role of the heat-labile toxin (LT) produced by E. coli?
The heat-labile toxin (LT) activates adenylate cyclase in the enterocytes, increasing the level of cyclic adenosine 5’ monophosphate (cAMP), which leads to increased outflow of water and electrolytes into the gut lumen, causing diarrhea.
What diseases are caused by Enterohemorrhagic E. coli (EHEC)?
Enterohemorrhagic E. coli (EHEC) is associated with hemorrhagic colitis (a severe form of diarrhea) and Hemolytic Uremic Syndrome (HUS).
What is the significance of the O157:H7 serotype of E. coli?
The O157:H7 serotype of E. coli is a Shiga toxin-producing strain that causes hemorrhagic colitis and Hemolytic Uremic Syndrome (HUS).
What is the function of the K antigen in Enterobacteriaceae?
The K antigen is a capsular polysaccharide antigen, particularly prominent in heavily encapsulated organisms like Klebsiella. It is identified by the quelling (capsular swelling) reaction and is used to serotype E. coli and Salmonella typhi for epidemiologic purposes.
What are the characteristics of Klebsiella colonies on culture media?
Klebsiella colonies are large and very mucoid on culture media.
What is the role of the Shiga-like toxin (SLT) in E. coli pathogenesis?
The Shiga-like toxin (SLT) penetrates cells, disrupts protein synthesis, and destroys intestinal villi, leading to decreased absorption and increased fluid secretion, resulting in diarrhea.
What are the major diseases caused by Klebsiella?
Klebsiella causes pneumonia and urinary tract infections.
What is the significance of the Vi antigen in Salmonella typhi?
The Vi antigen is a capsular antigen in Salmonella typhi, the cause of typhoid fever, and is used for serotyping and epidemiologic purposes.
What is the difference between lactose fermenters and non-lactose fermenters on MacConkey agar?
Lactose fermenters, such as E. coli and Klebsiella, produce pink colonies on MacConkey agar, while non-lactose fermenters, such as Salmonella and Shigella, produce pale or colorless colonies.
What is the role of the O antigen in Enterobacteriaceae?
The O antigen is the outer polysaccharide portion of the lipopolysaccharide in the cell wall. It is the basis for serologic typing of many enteric rods, and antibodies to O antigens are predominantly IgM.
What is the significance of the H antigen in Enterobacteriaceae?
The H antigen is found on the flagellar protein of motile organisms like Escherichia and Salmonella. Non-motile organisms, such as Klebsiella and Shigella, do not have H antigens.
What are the characteristics of Enterotoxigenic E. coli (ETEC)?
Enterotoxigenic E. coli (ETEC) is the common cause of ‘traveler’s diarrhea’ and produces heat-stable enterotoxin (ST) or heat-labile enterotoxin (LT), or both, leading to watery diarrhea.
What is the role of the heat-stable toxin (ST) in E. coli?
The heat-stable toxin (ST) binds to and activates guanylate cyclase in the enterocytes, increasing the level of cyclic guanosine monophosphate (cGMP), leading to hypersecretion of fluid and diarrhea.
What is the significance of the K1 antigen in E. coli?
E. coli strains producing the K1 antigen are prominent in neonatal meningitis.
What are the characteristics of Enteroinvasive E. coli (EIEC)?
Enteroinvasive E. coli (EIEC) invades epithelial cells of the large intestine, causing tissue destruction, inflammation, and symptoms of bacillary dysentery.
What is the role of the capsule in Klebsiella pneumoniae?
The large polysaccharide capsule of Klebsiella pneumoniae is antiphagocytic, making it a primary pathogen and contributing to its virulence.
