1. Urinary Tract Infections
MLAB 2534 –Microbiology
Keri Brophy-Martinez

2. Definitions UTI = Urinary Tract Infection
Spectrum of diseases caused by microbial invasion of the genitourinary tract
Upper UT includes renal parenchyma (pyelonephritis) and ureters (ureteritis)
Symptoms include: fever, flank pain & tenderness
Lower UT includes bladder (cystitis), urethra (urethritis), and, in males, the prostrate (prostatitis)
Symptoms include: pain on urination, increased frequency, urgency, suprapubic tenderness
Bacteriuria = presence of bacteria in urine; may be symptomatic or asymptomatic

3. Anatomy of the Urinary Tract

4. Urinary System Hyperosmolarity Low pH
Resistant to colonization and infection
Characteristics of urine
Hyperosmolarity
Low pH
Very dilute urine fails to grow most bacteria
Men have prostatic fluid that is inhibitory
Flow has a washing effect

5. Risk Factors: Age Infants
Boys have higher incidence rates due to uncircumcision
Pre-school age
Girls infected more than boys
Most renal damage due to UTI at this age
School-age children
Girls more prone to develop UTI upon sexual activity

6. Risk Factors: Age Adults to 65
Low incidence unless genital-urinary abnormalities

7. Risk Factors: Age Over age 65
UTIs increase dramatically in both genders
Atypical presentation
Fever, delirium, failure to thrive
Males
Prostate changes & increased catherization
Neuromuscular changes
Females
Fecal soiling & increased catherization
Bladder prolapse

8. Risk Factors: Other Institutionalized care Pregnancy Renal transplant
Increase in UTIs
Instrumentation/catherization
Genital-urinary tract abnormalities
Pregnancy
Renal transplant

9. Risk Factors: Other Urinary conditions High ammonia concentration
Lowered pH
Decreased blood flow in renal medulla
Results in:
Reduced chemotaxis of WBCs
Reduced bactericidal activity of WBCs

10. Clinical Signs and Symptoms
Infants and children < 2 years age
Nonspecific symptoms: failure to thrive, vomiting, lethargy, fever
Children > 2 years
Likely to have localized symptoms:
Dysuria, frequency, abdominal or flank pain
Adults with lower UT infections
Dysuria, frequency, urgency, and sometimes suprapubic tenderness

11. Clinical Signs and Symptoms (cont’d)
Adults with Upper UTIs
Especially those acute pyelonephritis, include LUTI symptoms along with flank pain and tenderness and fever
AGN (Acute Glomerulonephritis)
Results from immune response to S. pyogenes (Group A) infections, either respiratory or pyodermal
Edema around eyes
Hematuria
RBC and WBC casts

12. Pathogenesis of UTIs Three access routes Ascending (most significant)
Usually seen in females since ureter is shorter
Descending
Also referred to as Hematogenous/Blood-borne
Occurs as a result of bacteremia
Less than 5% of UTI’s
Lymphatic
Increased pressure on bladder causes a redirect of lymph fluid to kidney
Infection dependent on size of the bacteria, strength of the bacteria present, and how strong the body's defense mechanisms are at the time.
Very rare

13. Flora of Normal Voided Urine
Staphylococcus epidermidis
Predominant
Streptococci
Alpha
Nonhemolytic
Lactobacillus species
Diphtheroids
Yeast

14. Microbial Agents of UTIs

15. Specimen Collection
Need to collect specimen to prevent normal vaginal, perianal, and urethral flora
Mid-stream clean catch – if self collected, patient needs GOOD instructions
Catheterized- sample must come from port NOT bag
Suprapubic aspiration ( only for anaerobic culture)

16. Specimen Collection (cont’d)
Additives – even with additive, time from collection to processing should not exceed 24 hours
Grey top culture tubes( sodium borate) keep sample integrity for up to 48 hours
Transport
If not processed or preserved, urine should be cultured within 2 hours
If refrigerated, urine can be held for 24 hours

17. Preculture Screening Manual screening: Routine Urinalysis
Chemical screening
Leukocyte Esterase and Nitrate on urine dipstick
Urine microscopic
5 to 10 WBC/hpf is upper limit of normal
Presence of bacteria
Automated methods – expensive, except in large volume labs
Gram stains generally not performed on urines

18. Causes for Rejection Inadequate method of collection or transport
Labeling incomplete
name, source, acc # etc.
Insufficient volume
Fecal contamination
24 hour urines, pooled urines, and Foley catheter tips must be rejected for culture

19. Setup of Urine Culture Setup 1 Selective agar: MacConkey
1 Nonselective agar: Blood
OR Bi-Plate

20. Urine Culture Procedure
Inoculation using either a 0.001ml(x1000) OR a 0.01 ml (x100) loop onto selective/nonselective media, such as BAP and MAC
Dip calibrated loop into well-mixed urine. Quickly make a single streak down the middle of the BAP with the loop containing urine
Streak back and forth across the plate perpendicular to the original inoculum, this creates a “lawn”
With the same calibrated loop, do the same with the MAC plate
Incubate at 35oC for hours

21. Urine Streaking Technique

22. Interpretation of Urine Cultures
Is there growth?
If no growth:
At 24 hours:
Preliminary report: no growth at 24 hours
Reincubate plates
At 48 hours:
Final report: no growth at 48 hours
Discard plates

23. Interpretation of Urine Cultures
If there is growth, what media has it grown on?
BAP only: rules out the enteric GNR’s, colonies may be GPC, GPR, GNDC
BAP and MAC: most likely an enteric GNR or Pseudomonas. If multiple colony types, a gram stain must be done.

24. Interpretation of Urine Cultures
How many colony types are growing?
Specimen with ≥ three organisms is probably contamination and should not be identified unless specifically requested by physician
One or two pathogens ≥ 100,000 CFU/ml should be identified and sensitivities done
One or two pathogens ≥ 100 CFU/ml should be identified only if clinical situation warrants or specimen is catheterized or suprapubic aspiration

25. Determining the CFU Count the numbers of colonies of the plate
Multiply that number by the dilution factor of the loop

26. Test YOUR Understanding
A clean catch urine is collected from a pregnant patient with symptoms of urinary tract infection. The urine is inoculated onto blood and MacConkey agar with a loop. After 24 hour incubation, 72 colonies grew on the blood plate.
What is the colony count?

27. Interpretation of Urine Cultures
Things to consider in UTI’s
Colony count of pure or predominant organism
Measurement of pyuria
Presence or absence of symptoms

28. References
Engelkirk, P., & Duben-Engelkirk, J. (2008). Laboratory Diagnosis of Infectious Diseases: Essentials of Diagnostic Microbiology . Baltimore, MD: Lippincott Williams and Wilkins.
Mahon, C. R., Lehman, D. C., & Manuselis, G. (2011). Textbook of Diagnostic Microbiology (4th ed.). Maryland Heights, MO: Saunders.