Urinary Tract Infections
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Transcript of Urinary Tract Infections
Urinary Tract Infections
MLAB 2434 –Microbiology Keri Brophy-Martinez
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
Anatomy of the Urinary Tract
Urinary System Resistant to colonization and infection Characteristics of urine
HyperosmolarityLow pHVery dilute urine fails to grow most
bacteriaMen have prostatic fluid that is
inhibitoryFlow has a washing effect
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
Adults to 65Low incidence unless genital-
urinary abnormalities
Risk Factors:Age
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
Risk Factors:Other Institutionalized care
Increase in UTIs• Instrumentation/catherization• Genital-urinary tract abnormalities
Pregnancy Renal transplant
Risk Factors:Other Urinary conditions
High ammonia concentrationLowered pHDecreased blood flow in renal
medulla
Results in:• Reduced chemotaxis of WBCs• Reduced bactericidal activity of WBCs
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
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
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
Flora of Normal Voided Urine
Staphylococcus epidermidisPredominant
StreptococciAlphaNonhemolytic
Lactobillus species Diphtheroids Yeast
Microbial Agents of UTIs
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)
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
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
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
Setup of Urine Culture Setup
1 Selective agar: MacConkey1 Nonselective agar: BloodOR Bi-Plate
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
Urine Streaking Technique
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
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.
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
Determining the CFU Count the numbers of colonies of
the plate Multiply that number by the
dilution factor of the loop
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?
Interpretation of Urine Cultures Things to consider in UTI’s
Colony count of pure or predominant organism
Measurement of pyuriaPresence or absence of
symptoms
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.