Urinary Tract Infections

1. Urinary Tract Infections MLAB 2434 –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 • 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 • Neuromuscular changes • Bladder prolapse

8. Risk Factors:Other • Institutionalized care • 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 • Lactobillus 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 24-48 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 0.001 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. • https://catalog.hardydiagnostics.com/cp_prod/CatNav.aspx?oid=7405&prodoid=J116 • Mahon, C. R., Lehman, D. C., & Manuselis, G. (2011). Textbook of Diagnostic Microbiology (4th ed.). Maryland Heights, MO: Saunders.