Urinary Tract Infections - Pathogenesis / Microbes

Question 1

What is pyelonephritis?

Answer 1

Bacterial infection of the kidney, causing inflammation

Question 2

Why do UTI-causing pathogens need pili / adhesins to “reach out” to host epithelial cells?

Answer 2

The bacterial cell and epithelial cells are both negatively charged, so the repulsive forces would push them apart

Gram positive will often adhere via polysaccharides

Question 3

What are the two leading pathogens of uncomplicated UTI?

Answer 3

1. E. coli

2. Staphylococcus saprophyticus

Question 4

What strain of E. coli is often implicated in UTIs? Where does it come from and how is it identified in the lab?

Answer 4

UPEC - Uropathogenic E. coli

Comes from own or sexual partner’s intestinal microflora

Identified as beta-hemolytic, lac + gram negative rod.

It is oxidase negative

Question 5

How is a UTI quantitatively determined in the lab?

Answer 5

A 10 microliter calibrated loop of urine is plated onto a blood agar plate. Each colony represents 100 CFU/mL.

> 100,000 CFU / mL = bacterial infection. 10,000-100,000 is ambiguous. <10,000 is normal contamination.

Question 6

What are the three main types of Pili on UPEC and what is their mannose-sensitivity (unable to work when a plate it covered in it)

Which ones agglutinate RBC in the lab?

Answer 6

1. P-pili - mannose insensitive
2. Type 1 Pili - mannose sensitive (bind mannose)
3. Type S fimbriae - mannose insensitive

They all agglutinate RBCs in the lab

Question 7

What does P-pili bind and what does the name mean?

Answer 7

P-pili = pyelonephritis pili - found in 80% of pyelonephritis isolates

These pili bind globobiose, a glycosphingolipid

Question 8

What are the functions of the P-pili?

Answer 8

Make the organism hard to phagocytose

Induce inflammation and PMN infiltration into the bladder (inducing IL-8 production, as well as IL-6 (pyrogenic))

Question 9

What do Type 1 Pili bind? When is it expressed?

Answer 9

Mannose

Has an invertible promoter so that it is “on” in the bladder but “off” in the kidney -> expressed early in infection

Question 10

What do Type S fimbriae bind? What are they associated with?

Answer 10

S = Sialic acid on glycoproteins

Associated with both cystitis and pyelonephritis, as well as neonatal meningitis + bactermia

Question 11

What is the purpose of the afimbrial adhesins?

Answer 11

They recognize the Dr blood group antigen, and adhere to urepithelial surface for internalization of UPEC (evade immune response)

Question 12

What is the purpose of the UPEC hemolysin?

Answer 12

Primarily exists for iron acquisition. It is a the mediator of kidney damage in pyelonephritis by lysing tubular cells and RBCs

Question 13

What is the second toxin produced by UPEC?

Answer 13

Cytotoxic necrotizing factor type 1 (cnf1)

Found in about half of strains, serves to kill human bladder epithelium in apoptosis

Question 14

What else about E. coli works synergistically with the P-pili’s inflammatory properties?

Answer 14

LPS -> induces proinflammatory cytokines like IL-8

Question 15

What is the purpose of K antigen?

Answer 15

Capsule composed of polysaccharides - antiphagocytic

Question 16

What is the morphology of S. saprophyticus, and who does it disproportionately cause UTI’s in?

Answer 16

Gram + cocci, disproportionately affects females (above normal UTI rates)

Question 17

What does S. saprophyticus usually cause?

Answer 17

Urethritis and cystitis, but not pyelonephritis

Question 18

What do women with UTI’s tend to have more of?

Answer 18

More mannose receptors, for binding of Type 1 pili, as well as globobiose for binding of P-pili

Question 19

Does S. saprophyticus have a hemolysin?

Answer 19

Yes, but it is not found in all strains. Goes along with the hemagglutinin virulence factors

Question 20

What is the protein on the outside of S. saprophyticus?

Answer 20

Ssp = Saprophyticus surface-associated protein

Question 21

What are kidney stones and how does S. saprophyticus promote their formation?

Answer 21

Struvite stones - magnesium ammonium phosphate

They have a urease which hydrolyzes urea to give ammonium ions, alkalizing the urine and promoting stone formation

Question 22

What is the most common way to get S. saprophyticus?

Answer 22

Autoinfection from colon

Question 23

How is S. saprophyticus identified in the lab?

Answer 23

Grows on CNA agar (Gram positive), is catalase + (it’s Staph), catalase negative (not aureus), and novobiocin-resistant

Question 24

What is the morphology of K. pneumoniae and how can it be told apart from E. coli? How does this relate to its pathogenesis?

Answer 24

Gram negative rods forming mucoid colonies. Also lac+

It is non-hemolytic -> it is more often seen in patients with underlying disease

Question 25

What two fimbriae does K. pneumoniae have?

Answer 25

Type 1 fimbriae -> mannose-sensitive like E. coli | Type 3 fimbriae -> mannose-resistant

Question 26

What other virulence factors does K. pneumoniae have?

Answer 26

1. Capsule - bilayered and antiphagocytic 2. LPS 3. Urease - induces stone formation

Question 27

Where is K. pneumoniae normally found?

Answer 27

The colon

Question 28

How is Proteus mirabilis told apart from K. pneumoniae or E. coli?

Answer 28

It is a gram negative rod, beta-hemolytic like E. coli. Big difference: LAC negative (-)

Question 29

Why is Proteus mirabilis of particular concern?

Answer 29

It is highly urease positive - to the point that you can smell it. Forms kidney stones very well

Question 30

Where is P. mirabilis most often found and who does it infect?

Answer 30

Found in the colon, often infects patients with underlying disease (like K. pneumoniae)

Question 31

Why is Proteus really good at causing pyelonephritis?

Answer 31

Has adhesions like MR/P (mannose-resistant, proteus-like) and displays "swarming" motility - it is highly motile and easily ascends via flagella through ureters to kidney

Question 32

What is PMF? Why is it different than other fimbriae?

Answer 32

Proteus Mirabilis Fimbriae Not a hemagglutinin Important in bladder but NOT kidney colonization

Question 33

How can Enterococcus species be told apart from S. saprophyticus?

Answer 33

It will grow in high salt conditions (6.5% NaCl) as well as Bile Esculin agar. Also, it is catalase negative (Staphylococci are catalase positive)

Question 34

What patient population is Enterococcus commonly found in?

Answer 34

It comes from the colon, but it is seen in patients with indwelling catheters

Question 35

What is Asa1?

Answer 35

Aggregation substance, a virulence factor of Enterococcus which fascilitates conjugal plasmid exchange for antibiotic resistance, and is also involved in adherence via integrins

Question 36

What are two other virulence factors of enterococci?

Answer 36

1. Cytolysin - lyses RBC for iron | 2. Sex pheromones - function in plasmid acquisition but also trigger neutrophil attraction and immune damage

Question 37

What is on the tip of Type 1 fimbriae?

Answer 37

FimH tip - important in bladder adhesion

Question 38

What is on the tip of P-pili which infect kidney and how does it contribute to pathogenesis?

Answer 38

PapG tip - involved in antigen switching to evade immune response