Exam 2: Microbiology of UTI II DSA

Question 1

DSA checkpoints:

1. How can you distinguish between E. coli, K. pneumoniae, Enterobacter, Citrobacter, Serratia?

Assume Serratia produces prodigiosin.

Answer 1

• One way to distinguish Serratia and Citrobacter from other Gram-negative rods like E. coli and K. pneumoniae and Enterobacter
  
  • Serratia and Citrobacter are slow lactose fermenters.
    
    • On MacConkey and EMB agar, the colonies do not change color as quickly as fast lactose-fermenting bacteria do
• Some, but not all, species of Serratia produce a red pigment** called **prodigiosin.
  
  • Pigment production by Serratia can distinguish it from Citrobacter
• Citrobacter gets its name because it can use citrate as its carbon source.
  
  • This can further assist in distinguishing it from E. coli which typically can’t use citrate as an energy source.
  • However, other members of Enterobacteriaceae can use citrate as an energy source so the citrate test is of little use in distinguishing them from Citrobacter.

Question 2

DSA checkpoints:

1. How can you distinguish between E. coli, K. pneumoniae, Enterobacter, Citrobacter, Serratia?

Answer 2

• Like all members of Enterobacteriaceae, Enterobacter are Gram-negative rods.
• In addition, Enterobacter also are fast lactose fermenters like E. coli and K. pneumoniae.
• However, Enterobacter are indole negative
  
  • distinguishing them from E. coli.
• While some strains of Enterobacter can produce mucoid colonies, they are never as “slimy” as Klebsiella.

Question 3

DSA checkpoints:

2. Which traits possessed by Staphylococcus aureus distinguish it from other staphylococcus?

Answer 3

• Staphylococci are catalase positive
  
  • while the streptococci are catalase negative.
• S. aureus is β-hemolytic, produces coagulase and ferments mannitol.
  
  • S. epidermidis and S. saprophyticus are γ-hemolytic (non-hemolytic) and do not produce coagulase.
• S. aureus colonies have a gold color in culture.

Question 4

DSA checkpoints:

3. Both S. epidermidis and S. saprophyticus are γ-hemolytic, how can you distinguish between the two?

Answer 4

• S. epidermidis and S. saprophyticus are
  
  • γ-hemolytic (non-hemolytic)
  • and do not produce coagulase.
• Distinguishing between S. epidermidis and S. saprophyticus requires the use of novobiocin.
  
  • S. epidermidis is novobiosin sensitive
  • S. saprophyticus is novobiocin resistant

Question 5

DSA checkpoints:

4. What are the 3 leading causes of sexually-transmitted, bacterial urethritis**?

Answer 5

1. Chlamydia trachomatis is the leading cause of sexually transmitted urethritis.
2. Neisseria gonorrhoeae
3. Ureaplasma urealyticum

• Urethritis** is a bacterial or viral infection that causes swelling and irritation of the urethra.
  
  • It’s commonly caused by a sexually transmitted infection.
  • Symptoms include painful, burning, or frequent urination, or a discharge from the urethra.

Question 6

DSA checkpoints:

5. Which trait of N. gonorrhoeae’s pili facilitates repeated infections?

Answer 6

• N. gonorrhoeae possesses a pili that is highly variable in its amino acid composition.
• The pili is the common antigen that the immune system generates antibodies against
  
  • but since the bacteria can vary its composition so easily, infection does not provided protection from sequential infections.
  • In addition, the variable structure of the pili makes it difficult to generate an effective vaccine against N. gonorrhoeae.

Question 7

DSA checkpoints:

6. How does N. gonorrhoeae infect cells and evade the immune response?

Answer 7

• The pili
  
  • assists in the attachment of N. gonorrhoeae to the walls of the urethra and protects the bacteria from phagocytosis by holding the bacteria extremely close to host cells.
    
    • This tight interaction inhibits phagocytosis from macrophage and neutrophils.
• In addition, other virulence factors promote the invasion of N. gonorrhoeae into cells:
  
  • Outer membrane protein porin and Opa proteins.
• Replication of gonococci begins with the adherence to non-ciliated cells.
  
  • Once ciliated cells are exposed to N. gonorrhoeae LPS, they are destroyed.
  • the bacteria then cannot be cleared from the mucosal membrane.
• The gonococci undergo parasite-directed endocytosis where they are taken up by the microvilli of the non-ciliated cells acting like phagocytes.
  
  • Inside the cell, the gonococci replicate within vacuoles which then combine into larger vacuoles.
    
    • Here they can avoid phagocytosis, antibodies, and anti-microbial agents.
    • These larger vacuoles transport the gonococci to the base of the non-ciliated cells where they escape into subepithelial tissue, creating inflammation or disseminating into the bloodstream.
• Neutrophils are frequently infected by N. gonorrhoeae.

Question 8

DSA checkpoints:

7. What type of environment does N. gonorrhoeae grow well in?

Answer 8

• One trait of N. gonorrhoeae that is of interest is that it only grows well in environments with high CO₂.
• Because of this, N. gonorrhoeae usually only infects the urethra, cervix, rectum, and throat.

Question 9

DSA checkpoints:

8. N. gonorrhoeae and C. trachomatis commonly cause asymptomatic infections in women.

Why is this problematic for women and their sexual partners?

Answer 9

• Spreading to sexual partners may be the only indication that a woman is infected.
• In addition to the urethra, N. gonorrhoeae infects the cervix in women and can infect deeper into the reproductive tract
  
  • leading to pelvic inflammatory disease (PID).

Question 10

DSA checkpoints:

9. What are some of the consequences of pelvic inflammatory disease?

Answer 10

• In PID, the N. gonorrhoeae infection spreads to the uterus, fallopian tubes, and/or ovaries.
• Patients with PID commonly present with fever, lower abdominal pain, abnormal menstrual cycle, and cervical tenderness.
• There are several serious consequences associated with the scarring and damage caused by PID. Complications of PID include:
  
  • sterility
  • ectopic pregnancy
  • abscesses
  • peritonitis
  • peri-hepatitis (Fitz-Hugh-Curtis syndrome).
    
    • Fitz-Hugh-Curtis syndrome is an infection in the capsule that surrounds the liver.

Question 11

DSA checkpoints:

10. In addition to PID, what rare complication of a N. gonorrhoeae infection can potentially lead to life-threatening illness?

Answer 11

• In both men and women, there is a small risk of disseminated infections by N. gonorrhoeae (1-3%)
  
  • the consequences are substantial:
    
    • septicemia
    • meningitis
    • pericarditis
    • infectious endocarditis
    • dermatitis
    • septic arthritis
      
      • in the U.S., N. gonorrhoeae is the number one cause of septic arthritis in sexual active, young adults
• Oral sex can also result in pharyngitis as well.
• Can also cause ophthalmia neonatorum in newborns
  
  • transmitted from an infected mother
  • and usually manifests within the first 5 days after birth.
• Rarely, conjunctivitis can also occur in adults.

Question 12

DSA checkpoints:

11. What is the agar used for N. gonorrhoeae?

Why is this agar used?

Answer 12

• Laboratory diagnosis of N. gonorrhoeae involves a Gram stain and a culture.
• Gram staining of the purulent discharge will reveal a Gram-_negative_ diplococci, sometimes inside neutrophils (Figure 5).
• The agar used to culture N. gonorrhoeae is a modified version of chocolate agar containing antibiotics and an antifungal to select for N. gonorrhoeae growth:
  
  • Thayer-Martin VCN agar.
    
    • Vancomycin (V), colistin (C), nystatin (N), and trimethoprim are added to inhibit the growth of other bacteria and fungi.
    • The inhibitors added to Thayer-Martin agar are not important for the exam, just know that Thayer-Martin agar selects for N. gonorrhoeae.
• The agar is placed in a high CO₂ environment to further select for N. gonorrhoeae.
• The reason all these additional inhibitors must be added is that the areas Neisseria frequently causes disease (rectum, throat, urogenital tract) have abundant normal flora.
  
  • Without these selectors, the plate would be overrun with other microbes! In addition, the agar is placed in a high CO₂ environment to further select for N. gonorrhoeae.

Question 13

DSA checkpoints:

12. How can you tell the difference between N. gonorrhoeae and N. meningitidis?

Answer 13

• N. gonorrhoeae can be distinguished from N. meningitis by carbohydrate fermentation.
  
  • N. gonorrhoeae ferments only glucose,
  • N. meningitis ferments both glucose and maltose.
• An easy pneumonic
  
  • “meningitis” contains both a g & m, representative of Glucose and Galtose (N. _mening_itis)
  • N. _g_onorrhoeae only contains a g for glucose.

Question 14

DSA checkpoints:

13. Which diseases are caused by the A, B, and C serotypes of Chlamydia trachomatis?

How are they transmitted?

Answer 14

• Serotypes A, B, and C cause trachoma
  
  • a disease characterized by scarification of the inner eyelid.
  • Leads to corrosion of the cornea and eventually, blindness.
  • The damage of the inner eyelid can cause the eye lashes to point inwards, causing them to constantly scrape against the eye.
  • Blindness occurs slowly over the course of 10-15 years typically.
  • Blindness caused by C. trachomatis is the most preventable form of blindness in the world.
  • Hand-to-hand transmission of infected eye secretions, or sharing towels or rags, is a common way the pathogen is spread.
  • Flies are also a possible mode of transmission.

Question 15

DSA checkpoints:

13. Which diseases are caused by the D, E, F, G, H, I, J and K serotypes of Chlamydia trachomatis?

How are they transmitted?

Answer 15

• C. trachomatis serotypes D, E, F, G, H, I, J and K
  
  • can cause urethritis
  • frequently causes asymptomatic disease in women
    
    • incredibly detrimental to long-term reproductive health and a risk factor during birth.
    • Without significant symptoms, pelvic inflammatory disease (PID) may progress and do permanent damage to the reproductive tract!
      
      • Roughly 8% of women are sterile after one bout of PID, roughly 20% after the second infection, and 40% after the third.
    • Even if they are not rendered sterile, pregnancy complications (ectopic birth) rise substantially after PID.
  • C. trachomatis infections in pregnant women can have dire consequences on newborns.
    
    • C. trachomatis causes both inclusion conjunctivitis and pneumonia in newborns when it is transmitted from mother to child during birth.

Question 16

DSA checkpoints:

13. Which diseases are caused by the L₁, L₂, and L₃ serotypes of Chlamydia trachomatis?

How are they transmitted?

Answer 16

• C. trachomatis serotypes L₁, L₂, and L₃
  
  • cause lymphogranuloma venereum (LGV).
    
    • LGV typically starts as a painless bump or ulceration on the genitals that heals spontaneously.
    • In most patients, it goes unnoticed.
    • However, over the next two months, swelling of the local lymph nodes will occur and may rupture and drain pus if left unattended.
    • Remember, the L serotypes cause lymphogranuloma!

Question 17

Chlamydia trachomatis Lab Diagnosis

Answer 17

• Giemsa stain (DNA) or iodine (starch) can be used to visualize Chlamydia
  
  • however, even these stains can be inconsistent since Chlamydia has such an odd life cycle. A negative stain does not rule out Chlamydia.
• Antibodies specific for Chlamydia species and serotypes have been conjugated to fluorochromes to visualize the bacteria.
• ELISA and serology can also be used to detect bacterial antigens and host antibody titers.
• However, the current gold standard for laboratory diagnosis of Chlamydia is nucleic acid amplification test like PCR. This works for all species of Chlamydia.

Question 18

DSA checkpoints:

14. Which other genus of bacteria does Ureaplasma closely resemble?

Answer 18

• Ureaplasma urealyticum.
  
  • common causes of urethritis
  • U. urealyticum is part of the normal flora of the urogenital tract in roughly 60% of sexually active adults.
• Ureaplasma urealyticum is closely related to Mycoplasma pneumoniae.
  
  • Both belong to the same family.
  • Like Mycoplasma pneumoniae, U. urealyticum is smaller than most viruses, is pleomorphic, contains no cell wall, and is a _facultative intra_cellular pathogen.
    
    • As such, antibiotics that target cell wall construction (penicillins) will have no effect on U. urealyticum. Just like Mycoplasma,
  • U. urealyticum requires sterols in the growth media as well.

Question 19

DSA checkpoints:

15. Why do penicillins not work on U. urealyticum?

Answer 19

• Like Mycoplasma pneumoniae, U. urealyticum is
  
  • smaller than most viruses
  • pleomorphic
  • contains no cell wall
  • and is a facultative intracellular pathogen.
• As such, antibiotics that target cell wall construction (penicillins) will have no effect on U. urealyticum.

Question 20

DSA checkpoints:

16. Where do the various species of Schistosoma colonize when they infect a host?

Where are they commonly found geographically?

Answer 20

• The parasitic worms that cause schistosomiasis live in certain species of freshwater snails
• People become infected when they swim or come into contact with water containing the infectious form of the parasite, cercariae.

Question 21

DSA checkpoints:

17. Which form of Schistosoma is contagious?

Be able to describe the life cycle of Schistosoma.

Answer 21

• The parasitic worms that cause schistosomiasis live in certain species of freshwater snails
  
  • people become infected when they swim or come into contact with water containing the infectious form of the parasite, cercariae.
• After the cercariae are released from snails
  
  • they infect humans
    
    • Dermatitis along with an intense itch occurs at the site of contact as the worm penetrates the host’s skin
  • lose their tail
  • and become schistosomulae
  • migrate to blood vessels surrounding either the gastrointestinal tract or the urinary tract.
    
    • S. japonicum and S. mansoni infect the vessels around the intestines
    • S. haematobium infects the vessels around the bladder.
• They reproduce and the eggs are shed
  
  • S. japonicum and S. mansonices in feces
  • S. haematobium in urine
• The eggs hatch, releasing miracidia which infect snails
  
  • starting the process all over again.

Question 22

DSA checkpoints:

18. Even though Schistosoma stays localized in either the bladder or gastrointestinal tract, the symptoms can be systemic. Why?

Answer 22

• As the worm begins to produce eggs
  
  • a strong immune response is evoked.
• Some of the eggs enter the bloodstream and are deposited in distal areas
  
  • activating the immune response and leading to tissue damage.
• Katayama fever (aka bilharzia or snail fever)
  
  • follows roughly 4-8 weeks after the initial exposure
  • includes a wide range of symptoms including:
    
    • fever, hives, weight loss, cough, lymph node enlargement, liver enlargement, and spleen enlargement with eosinophilia.
• Schistosomiasis can persist for years.
  
  • Patients may also develop hematuria, chronic abdominal pain, diarrhea, and rarely, brain or spinal cord injury.
  • Permanent damage to the liver, intestines, spleen, lungs, and bladder are frequent complications of chronic schistosomiasis.
• With S. haematobium, blood in the urine and/or difficulty passing urine may be present.
  
  • Also, there is a strong link between a chronic S. haematobium infection and bladder cancer.

Question 23

DSA checkpoints:

19. How does the appearance of the eggs of Schistosoma species differ?

Identify the species associated with the following egg morphologies:

Answer 23

• egg morphologies Dx
  
  • S. mansoni
    
    • large lateral spine
    • detected in the stool
  • S. haematobium
    
    • prominent terminal spine
    • detected in the urine
  • S. japonicum
    
    • vestigial, nubby lateral spine
    • detected in the stool
• However, the eggs are sporadically shed
  
  • so a blood test for antibodies against Schistosoma or antigens from Schistosoma may also be helpful in a diagnosis.
  • It typically takes 6-12 week after exposure to the parasite to detect antibodies against it.
  • In addition, like most parasitic infections, elevated eosinophils are commonly present in blood samples.