2 Definitions UTI = Urinary Tract Infection Spectrum of diseases caused by microbial invasion of the genitourinary tractUpper UT includes renal parenchyma (pyelonephritis) and ureters (ureteritis)Symptoms include: fever, flank pain & tendernessLower UT includes bladder (cystitis), urethra (urethritis), and, in males, the prostrate (prostatitis)Symptoms include: pain on urination, increased frequency, urgency, suprapubic tendernessBacteriuria = presence of bacteria in urine; may be symptomatic or asymptomatic
4 Urinary System Hyperosmolarity Low pH Resistant to colonization and infectionCharacteristics of urineHyperosmolarityLow pHVery dilute urine fails to grow most bacteriaMen have prostatic fluid that is inhibitoryFlow has a washing effect
5 Risk Factors: Age Infants Boys have higher incidence rates due to uncircumcisionPre-school ageGirls infected more than boysMost renal damage due to UTI at this ageSchool-age childrenGirls 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 gendersAtypical presentationFever, delirium, failure to thriveMalesProstate changes & increased catherizationNeuromuscular changesFemalesFecal soiling & increased catherizationBladder prolapse
8 Risk Factors: Other Institutionalized care Pregnancy Renal transplant Increase in UTIsInstrumentation/catherizationGenital-urinary tract abnormalitiesPregnancyRenal transplant
9 Risk Factors: Other Urinary conditions High ammonia concentration Lowered pHDecreased blood flow in renal medullaResults in:Reduced chemotaxis of WBCsReduced bactericidal activity of WBCs
10 Clinical Signs and Symptoms Infants and children < 2 years ageNonspecific symptoms: failure to thrive, vomiting, lethargy, feverChildren > 2 yearsLikely to have localized symptoms:Dysuria, frequency, abdominal or flank painAdults with lower UT infectionsDysuria, frequency, urgency, and sometimes suprapubic tenderness
11 Clinical Signs and Symptoms (cont’d) Adults with Upper UTIsEspecially those acute pyelonephritis, include LUTI symptoms along with flank pain and tenderness and feverAGN (Acute Glomerulonephritis)Results from immune response to S. pyogenes (Group A) infections, either respiratory or pyodermalEdema around eyesHematuriaRBC and WBC casts
12 Pathogenesis of UTIs Three access routes Ascending (most significant) Usually seen in females since ureter is shorterDescendingAlso referred to as Hematogenous/Blood-borneOccurs as a result of bacteremiaLess than 5% of UTI’sLymphaticIncreased pressure on bladder causes a redirect of lymph fluid to kidneyInfection 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 epidermidisPredominantStreptococciAlphaNonhemolyticLactobillus speciesDiphtheroidsYeast
15 Specimen CollectionNeed to collect specimen to prevent normal vaginal, perianal, and urethral floraMid-stream clean catch – if self collected, patient needs GOOD instructionsCatheterized- sample must come from port NOT bagSuprapubic aspiration ( only for anaerobic culture)
16 Specimen Collection (cont’d) Additives – even with additive, time from collection to processing should not exceed 24 hoursGrey top culture tubes( sodium borate) keep sample integrity for up to 48 hoursTransportIf not processed or preserved, urine should be cultured within 2 hoursIf refrigerated, urine can be held for 24 hours
17 Preculture Screening Manual screening: Routine Urinalysis Chemical screeningLeukocyte Esterase and Nitrate on urine dipstickUrine microscopic5 to 10 WBC/hpf is upper limit of normalPresence of bacteriaAutomated methods – expensive, except in large volume labsGram stains generally not performed on urines
18 Causes for Rejection Inadequate method of collection or transport Labeling incompletename, source, acc # etc.Insufficient volumeFecal contamination24 hour urines, pooled urines, and Foley catheter tips must be rejected for culture
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 MACDip calibrated loop into well-mixed urine. Quickly make a single streak down the middle of the BAP with the loop containing urineStreak 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 plateIncubate at 35oC for hours
22 Interpretation of Urine Cultures Is there growth?If no growth:At 24 hours:Preliminary report: no growth at 24 hoursReincubate platesAt 48 hours:Final report: no growth at 48 hoursDiscard 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, GNDCBAP 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 physicianOne or two pathogens ≥ 100,000 CFU/ml should be identified and sensitivities doneOne 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’sColony count of pure or predominant organismMeasurement of pyuriaPresence or absence of symptoms
28 ReferencesEngelkirk, 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=J116Mahon, C. R., Lehman, D. C., & Manuselis, G. (2011). Textbook of Diagnostic Microbiology (4th ed.). Maryland Heights, MO: Saunders.