S1B5 - Enterobacteriaceae Flashcards
(133 cards)
What does infection from Proteus spp. usually cause?
Proteus spp. are responsible for nosocomial urinary tract infections (UTIs), such as pyelonephritis, and can lead to sepsis.
What organism is the most common cause of urinary tract infections in women?
E. coli is the most common cause of urinary tract infections in women.
Why are the other species of Shigella (not. S. dysenteriae) not as virulent?
Other species include S. flexneri, S. boydii (India), and S. sonnei, which have decreased virulence because of the lack of toxin production.
What is another bacterial species that can lead to hemolytic-uremic syndrome besides E. coli?
Some strains of S. dysenteriae produce a Shiga toxin that can lead to Hemolytic-Uremic Syndrome (HUS).
What method is used to diagnose Escherichia coli infection?
Diagnosis of E. Coli is made by stool culture on blood agar plate and differential media.
MacConkey’s agar is a differential media on which E. Coli grows pink colonies because it ferments lactose.
Eosin methylene blue (EMB) agar is a differential media on which E. Coli appears to have a dark metallic green sheen because it ferments lactose. Salmonella and Shigella do not ferment lactose and are colorless on EMB agar.
Urinalysis, urine culture, and urine microscopy are used to diagnose urinary tract infection.
Is S. dysenteriae motile or non-motile?
S. dysenteriae is non-motile (vs. motile Salmonella), however note that S. dysenteriae polymerizes actin to travel from enterocyte to enterocyte.
What is the morphology, gram staining, urease positive/negative and oxygen requirement of Klebsiella pneumoniae?
Klebsiella pneumoniae is an encapsulated, urease-positive, gram-negative, facultative anaerobic bacillus.
How is secondary pneumonic plague acquired?
Secondary pneumonic plague is a complication of Y. pestis infection, acquired by hematogenous spread of Y. pestis from a bubo to the lungs.
Serologic testing in Yersinia pestis infection might find elevated antibody titers to what Y. pestis antigen?
Serological testing may demonstrate a rise in antibody titers to the F-1 antigen of Y. pestis. Rapid antibody tests are available in endemic areas.
How will Yersinia pestis infection appear with Wayson staining?
Wayson stain demonstrates a typical “safety pin” appearance (bipolar staining).

What lung findings would you find on physical exam and lab testing in Klebsiella pneumoniae pneumonia?
Physical exam and laboratory testing of K. pneumoniae pneumonia are consistent with single lung consolidation, known as lobar pneumonia in cases of community-acquired pneumonia. Patients may also present with a patchy or diffuse infiltrate, known as bronchopneumonia in cases of nosocomial pneumonia.
A 29-year-old woman presents with diarrhea several hours after eating a chicken sandwich that she thinks may have been undercooked. Which of the following suggests Salmonella gastroenteritis?
A) Gram negative rods producing Shiga-like toxin
B) Comma-shaped organisms expressing oxidase
C) Gram negative lactose fermenters that produce hydrogen sulfide
D) Gram negative, motile, lactose nonfermenters
E) Gram positive obligate anaerobes
Gram negative, motile, lactose nonfermenters
Answer Explanation
Salmonella are gram-negative, lactose nonfermenters who produce hydrogen sulfide (H2S) and possess flagellar motility.
Comma-shaped organisms causing diarrhea that produce oxidase are suggestive of either Vibrio spp. or Campylobacter spp. GNR producing Shiga-like toxin is enterohemorrhagic E. coli (O157:H7). Gram-positive obligate anaerobes that cause diarrhea are C. difficile.
How would Klebsiella pneumoniae appear on MacConkey’s agar?
K. pneumoniae is lactose-fermenting, growing pink colonies on MacConkey’s agar. It is a non-motile enteric like Shigella. Lactose-fermenting enterics (“KEE”) include Klebsiella, E. coli, and Enterobacter, while enteric non-lactose fermenters (“SSP”) include Salmonella, Shigella, and Proteus.
What is the morphology, gram staining, lactose fermenting/non-fermenting, and oxygen requirement of Escherichia coli?
Escherichia coli is a lactose fermenting, gram-negative, facultative anaerobic bacillus.
How does the disease caused by Salmonella paratyphi differ from the disease caused by Salmonella typhi?
Salmonella paratyphi causes paratyphoid fever, and like typhoid fever it is also referred to as enteric fever. The course of paratyphoid fever resembles typhoid fever, but presents with a more abrupt onset, milder symptoms, and a shorter course.
What distinguishes Uropathogenic E. Coli (UPEC) from other serotypes of E. Coli? .
Uropathogenic E. Coli (UPEC) adheres with type I fimbriae and P pili, contains hemolysin and other toxins, and is the major cause of urinary tract infections (UTIs).
What diseases does Klebsiella pneumoniae cause?
K. pneumoniae causes
- Nosocomial and community-acquired pneumonia
- Nosocomial urinary tract infections
- Liver abscesses
What are some of the characteristics of Yersinia pestis - Morphology? - Gram-stain? - Motile/non-motile? - Sporulating/nonsporulating? - Intracellular/extracellular?
Yersinia pestis is a nonmotile, pleomorphic, nonsporulating, facultative intracellular, gram-negative bipolar staining bacillus (coccobacillus) that belongs to the Enterobacteriaceae family.
Describe the pathogenesis behind the formation of staghorn calculi in Proteus spp. urinary tract infection.
The urease that Proteus spp. possesses functions to split urea in the urinary tract to form ammonium hydroxide, ultimately resulting in an increased pH. The increase in pH precipitates ammonium magnesium phosphate, leading to struvite calculi that often form large staghorn calculi.

Does S. dysenteriae produce H2S?
S. dysenteriae does not produce H2S (vs. Salmonella, which produces H2S).
What type of diarrhea does S. dysenteriae cause? What are the initial manifestations?
Patients present early with non-bloody, voluminous diarrhea caused by enterotoxin in the small intestine. Dysentery occurs within hours to days and involves frequent, small, bloody, mucoid stools with abdominal cramps and tenesmus.
What distinguishes Enteroaggregative E. coli (EAEC) from other serotypes of E. Coli (toxins and GI symptoms)?
Enteroaggregative E. Coli (EAEC) uses aggregative adherence fimbriae (AAF) to make a biofilm of bacterial clusters on the intestinal wall. It causes diarrhea with mucus.
summarize this picmonic
What groups of individuals have a higher susceptibility to Salmonella infection?
Sufficiently large amounts of bacteria are needed to cause Salmonella infection (high ID50), since many bacteria are destroyed in the stomach upon ingestion. For this reason, individuals that are at high risk of infection include
- Individuals with impaired gastric acid secretion (bypassing destruction of bacteria by gastric acid)
- Individuals with sickle-cell due to autosplenectomy
- Young children
- The elderly
- Immunosuppressed individuals




