Gram Negative: Enteric Bacteria Flashcards
1
Q
Some enterics can ferment lactose - how do we culture for these organisms?
A
- can use an EMB agar or a MacConkey agar
- EMB: eosin and methylene blue; MB kills Gram positive organisms, lactose fermenters will become deep purple/black*
- MacConkey: bile salts kills Gram positive organisms, lactose fermenters will become pink/purple
- *on EMB agar, E. coli (a lactose fermenter) will actually become a metallic green rather than the classic deep purple/black
2
Q
What are the major varying surface antigens of the enterics?
A
- O antigen: the external component of the lipopolysaccharide (LPS) layer
- K antigen: the capsule of the O antigen
- H antigen: the subunit of the flagella (so it’s only found in flagellated enterics)
3
Q
What are the different levels of pathogenic invasion these organisms can cause? Give examples of organisms for each.
A
- no cell invasion: pathogen adheres, but does not enter the cell; exotoxin (enterotoxin) release causes osmotic diarrhea (ETEC, Vibrio cholera)
- cell invasion: adherence and invasion into the cell; cell death and immune response cause dysentery and fever (EIEC, Shigella, Salmonella enteritidis)
- invasion of lymph nodes and bloodstream: dysentery, fever, headache, raised WBC, lymphadenopathy, sepsis (Salmonella typhi, Yersinia enterocolitica, Campylobacter jejuni)
4
Q
Other than enteritis, what other diseases can these organisms cause? Which populations are particularly at risk?
A
- can cause many other diseases such as urinary tract infections (UTIs), pneumonia, sepsis, etc.
- main at risk population is hospitalized patients
5
Q
What are the major characteristics of Escherichia coli? Which diseases it is commonly associated with?
A
- E. coli is part of the normal gut flora; disease occurs when it acquires a virulence factor
- Gram negative bacillus, catalase positive, oxidase negative, facultative anaerobe, ferments lactose, multiple flagella
- the most common cause of UTI
- the most common cause of Gram negative sepsis (nosocomial)
- common cause of diarrhea, nosocomial pneumonia and neonatal meningitis
6
Q
Which organisms are the major causes of neonatal meningitis?
A
- Escherichia coli
- Listeria mnocytogenes
- Group B streptococci (Strep. agalactiae)
7
Q
ETEC
A
- ETEC (entero-toxic E. coli)
- causes traveler’s diarrhea (AKA Montezuma’s revenge); non-invasive; adheres via pili, secretes heat labile toxin (LT) and heat stable toxin (ST)
- these enterotoxins inhibit NaCl reabsorption and stimulate Cl- excretion to cause rice-water stool (very similar to cholera)
- no fever (because non-invasive)
8
Q
EHEC
A
- EHEC (entero-hemorrhagic E. coli)
- non-invasive; adheres via pili, secretes shiga-like toxin that inhibits protein synthesis
- this exotoxin kills the epithelial cells, causing bloody diarrhea and severe cramps (“hemorrhagic colitis”)
- strain O157:H7’s toxin can cause hemolytic-uremic syndrome (HUS): anemia, thrombocytopenia (decreased platelets), and renal failure (uremia)
9
Q
EIEC
A
- EIEC (entero-invasive E. coli)
- invades epithelial cells to cause dysentery and fever (very similar to shigellosis)
- EIEC also secretes some shiga-like toxin
10
Q
What are the major characteristics of Klebsiella pneumoniae? Which diseases is it commonly associated with?
A
- Gram negative bacillus, catalase positive, oxidase negative, facultative anaerobe, ferments lactose, non-motile (lacks flagella and therefore the H antigen)
- Klebsiella penumoniae is associated with hospitals and nosocomial infections; it is the 2nd most common cause of nosocomial Gram negative sepsis (1st is E. coli), and also causes UTIs and pneumonia in hospitalized patients
11
Q
What type of pneumonia is cause by Klebsiella pneumoniae?
A
- a very violent pneumonia with thick, bloody, red-currant jelly sputum
12
Q
What are the major characteristics of Shigella dysenteriae? Which diseases is it commonly associated with?
A
- Gram negative bacillus, catalase positive, oxidase negative, facultative anaerobe, does not ferment lactose, non-motile (lacks flagella and therefore the H antigen)
- its only reservoir is humans, but it is NOT part of the normal gut flroa
- Shigella mainly causes invasive enterocolitis in very young and elderly patients; it secretes the very potent shiga toxin, which inhibits protein synthesis of intestinal epithelial cells (by inhibiting the 60S ribosome) to cause cell death (fever, dysentery, abdominal pain)
13
Q
What are the major characteristics of Salmonella? Which diseases is it commonly associated with?
A
- Gram negative bacillus, catalase positive, oxidase negative, facultative anerobe, does not ferment lactose, flagellated
- Salmonella species are all zoonotic (found in the GITs of animals), except for S. typhi (only found in humans)
- 4 disease states: typhoid fever, carrier state, sepsis, and diarrhea
14
Q
What is typhoid fever? Which organism causes it? How do we treat it?
A
- Salmonella typhi; it is AKA enteric fever
- S. typhi invades the intestinal epithelial cells AS WELL AS the lymph nodes and bloodstream to seed into multiple organs
- patients develop fever, rose spots, headache, and abdominal pain (usually of the terminal ileum)
- treat with ceftriaxone or ciprofloxacin
- survivors may become chronic carriers
15
Q
Where does Salmonella tyhpi reside in the survivors of tyhpoid fever who become carriers?
A
- the bug stays in the gallbladder and is constantly excreted with bile
