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42 Cards in this Set

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What are enteric bacteria?
Gram-negative bacteria that are associated with gastrointestinal flora or disease.
What are six families of enteric bacteria?
1) Enterobacteriaceae
2) Vibrionaceae
3) Pseudomonadeceae
4) Bacteroidaceae
5) Campylobacteraceae
6) Helicobacteraceae
What are eight genera that are part of the Enterobacteriaceae family?
1)Escherichia
2) Salmonella
3) Shigella
4) Klebsiella
5) Proteus
6) Enterobacter
7) Serratia
8) Yersinia
What are the oxygen requirements of most G- rods?
Facultative anaerobes
What are three exceptions of G- rods that are NOT facultative anaerobes?
Pseudomonas and Bacteroides are obligate anaerobes
Campylobacter is microaerophilic
What are three common metabolic characteristics of most G- rods?
1) Ferment glucose to produce acid and gas
2) Reduce nitrates to nitrites
3) Oxidase negative
What is the one exception to the three common metabolic characteristics of most G- rods?
Pseudomonas does not ferment glucose and is oxidase positive.
What biochemical properties can be used to differentiate enteric bacteria?
1) Ability to ferment lactose
2) Ability to produce urease
3) Ability to produce hydrogen sulfide (H2S)
Which three intestinal pathogens cannot ferment lactose?
1) Shigella
2) Salmonella
3) Pseudomonas
Which three intestinal pathogens can ferment lactose?
1) Escherichia
2) Enterobacter
3) Klebsiella
EEK! a mouse eats cheese (lactose)
Which five enteric bacteria produce urease?
1) Helicobacter
2) Klebsiella
3) Proteus
4) Providencia
5) Morganella
What is the function of urease?
Metabolizes urea to form carbon dioxide ammonia, and water, producing a habitable alkaline environment.
What differential media can be used to isolate enteric bacteria from G+ bacteria?
Eosin-methylene blue (EMB) agar
MacConkey agar,
Hektoen enteric agar
What characteristic do Eosin-methylene blue (EMB) agar, MacConkey agar, &Hektoen enteric agar select for?
G- bacteria
How does EMB inhibit growth of G+ bacteria?
Aniline dyes
How does MacConkey agar inhibit growth of G+ bacteria?
Bile salts and crystal violet
How does Hektoen enteric agar inhibit growth of G+ bacteria
Bile salts
What characteristic do Eosin-methylene blue (EMB) agar, MacConkey agar, &Hektoen enteric agar screen for?
Lactose-fermenting versus
Lactose-NONfermenting bacteria
How do lactose-fermenting bacteria appear on EMB?
Metallic-green colonies
How do lactose-fermenting bacteria appear on MacConkey agar?
Pink colonies
How do lactose-fermenting bacteria appear on Hektoen enteric agar?
Yellow or orange
How do nonlactose-fermentig bacteria appear on EMB?
Translucent
How do nonlactose-fermenting bacteria appear on macConkey agar?
Translucent
How do nonlactose-fermenting bacteria appear on Hektoen enteric agar?
Blue-green
What other media selects against G+ organisms?
Salmonella-Shigella agar
Which four surface antigens are used to differentiate among enteric bacteria?
O antigen
H antigen
K antigen
and pili
What is the O antigen?
Heat-stable cell wall antigen located on the most external surface of LPS (remember "O" for outer)
What part of the O antigen confers unique characteristics to different O antigens?
Sugars, e.g., the O157 subtype, which is differentiated by its sugar moiety.
What is the H antigen?
Antigen located on teh flagella
Only those bacteria with "flagHella" will have an H antigen.
What is the K antigen?
Antigen associated with the capsule of fimbriae
What are pili?
Antigenic fimbriae responsible for attachment and colonization of an organism.
What three characteristics make enteric bacteria pathogenic?
1) Enterotixins
2) Endotoxins
3) Capsule
How are enterotoxins pathogenic?
They cause transduction of fluid into the ileum.
How are endotoxins different from enterotoxins?
Enterotoxins are released from bacteria.
Endotoxins are found in the LPS complex of the bacterial outer membrane.
What endotoxin do almost all G- rods contain?
LPS
What is a common component in most endotoxins?
Toxid Lipid A
Why are endotoxins pathogenic?
1) Stimulate release of tumor necrosis factor, interleukin-1, and IL-6 leading to hypotension.
2) Stimulate release of IL-1 and IL-6 leading to fever.
3) Hemorrhage in the intestine, adrenal glands, heart, and kidneys.
How is the capsule pathogenic?
It suppreses phagocytosis
Where do G- rods usually cause disease?
Intraintestinal, extraintestinal, or both, depending on genera.
Which G- rods cause disease primarily inside the enteric tract?
Shigella
Vibrio
Helicobacter
Which G- rods cause disease outside of the enteric tract?
Klebsiella, Enterobacter, Serratia, Proteus, Providencia, Morganella, Pseudomonas, and Bacteroides
Which G- rods cause disease both inside and outside of the enteric tract?
Escherichia
Salmonella
Yersinia
Campylobacter