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interpretation of urine cultures cumitech guidelines incorporated

Interpretation of urine culturesCumitech Guidelines incorporated

Dr.T.V.Rao MD

Dr.T.V.Rao MD

pathophysiology of urinary tract infection
Pathophysiology of urinary tract infection
  • Uncomplicated urinary tract infection: Bacterial or yeast infection in a structurally and neurologically normal urinary tract
  • Complicated urinary tract infection: Bacterial or yeast infection in a urinary tract with functional or structural abnormalities
risk factors in complicated urinary tract infection
Indwelling catheters

Urinary calculi

Neurogenic bladder

Prostatic enlargement

Uterine prolapse

Urologic instrumentation or surgery

Renal transplantation

Diabetes mellitus

Risk factors in complicated urinary tract infection
urinary tract specimens
First-voided morning urine optimal (generally bacteria have been proliferating in bladder urine for several hours)

Midstream urine specimens (initially voided urine contains urethral commensals)

Indwelling catheters (freshly placed, urine aspirated by needle inserted into catheter) (Foley catheter tips not acceptable)

Straight catheter specimens

Suprapubic aspirates (infants or children, recovery of anaerobes)Cystoscopiccollection of urine

Contamination-free specimen

Urinary Tract Specimens

Dr.T.V.Rao MD

collection of urine specimens
Collection of Urine Specimens
  • Urine collected in sterile specimen container must be processed within 2 hours, or refrigerated and processed within 24 hours
  • Urine collected in sterile specimen container with borate preservative should be processed within 24 hours (no refrigeration required)

Dr.T.V.Rao MD

prompt transpiration needed
Prompt transpiration needed
  • Transport to lab as soon as possible
  • Urine should be cultured within 2 hours or be refrigerated for up to 24 hours
  • Microorganisms grow very rapidly in urine at room temperature
  • This could give a false positive culture result

Dr.T.V.Rao MD

specimen inoculations
Specimen Inoculations
  • All cultures processed by Semiquantitative method a loop of standard dimension of approximately known volume is inoculated into selected culture plate
  • In general a loop of SWG – 28 with a diameter of 3.26 mm internal diameter which can hold a drop of water or urine 0.004 ml.
  • After inoculation the culture plates are incubated at 370c extending to > 18 hours are read
  • The colony counts are made, as each colony corropsdes to number of viable bacteria per ml of urine

Dr.T.V.Rao MD

inoculation of urine
Inoculation of urine for quantitative culture (colony forming units→cfu’s) performed with a calibrated 0.001 mL and 0.01 mL plastic or wire loop

Sheep blood agar (SBA) utilized for quantitative urine culture

With 0.001 ml loop, 1 colony on SBA equivalent to 1,000 cfu’s per mL of urine

With 0.01 ml loop, 1 colony on SBA equivalent to 100 cfu’s per mL of urine

MacConkey agar utilized as selective differential agar for gram-negative bacteria, Colistin nalidixic acid agar as selective agar for gram-positive bacteria, and chocolate agar for fastidious gram-negative bacteria (Haemophilus)

Inoculation of Urine

Dr.T.V.Rao MD

common uropathogens
Common Uropathogens
  • Escherichia coli
  • Other Enterobacteriaceae (Klebsiella, Enterobacter, Proteus, Citrobacter)
  • Pseudomonas aeruginosa
  • Enterococcus
  • Staphylococcus saprophyticus
  • Staphylococcus aureus
  • Streptococcus agalactiae (group B)
  • Candida

Dr.T.V.Rao MD

uncommon uropathogens
Uncommon Uropathogens
  • Corynebacterium urealyticum
  • Hemophilus influenzae and H. parainfluenzae
  • Blastomyces dermatitidis
  • Neisseria gonorrhaeae
  • Mycobacterium tuberculosis

Dr.T.V.Rao MD

counting the colonies
Counting the colonies

Dr.T.V.Rao MD

With 0.001 ml loop, 1 colony on SBA equivalent to 1,000 cfu’s per mL of urine

With 0.01 ml loop, 1 colony on SBA equivalent to 100 cfu’s per mL of urine

interpretation of urine cultures general guidelines
Interpretation of Urine Cultures: General Guidelines
  • A single species of Enterobacteriaceae recovered at >105 cfu’s/mL urine: with patients symptomatic for urinary tract infection, 95% probability of true bacteriuria

Dr.T.V.Rao MD

what is significant bacteriuria
What is Significant bacteriuria

Dr.T.V.Rao MD

Significant bacteriuria in an asymptomatic patient is 100,000 or more colonies per milliliter of urine from a midstream, clean-catch specimen; yet, a colony count of 200 Escherichia coli per ml may be significant in a midstream male void or catheterized female. About 95% of all positive UTI cultures will produce essentially pure cultures if urine is collected carefully and the media inoculated promptly.

what can be a significant count
What can be a significant count

Dr.T.V.Rao MD

A single species of Enterobacteriaceae recovered at 104-105 cfu’s/mL urine: with patients symptomatic for urinary tract infection, 33% probability of true bacteriuria

urine cultures
Organisms/ml --- very important!

<10,000 (Rare)

May indicate contamination

Lab usually does not identify the organisms

Generally not treated unless there is a single organism and patient has S&S

Urine Cultures

Dr.T.V.Rao MD

urine cultures16
Urine Cultures…

>100,000 organisms/ml (Many)

  • Usually indicates an infection
  • Patient most likely will have S&S
  • Most often will be treated with antibiotic appropriate for that organism

Dr.T.V.Rao MD

cumitech guidelines for interpretation of routine urine cultures
Cumitech Guidelinesfor Interpretation of Routine Urine Cultures

Dr.T.V.Rao MD

One isolate at >104: Full ID and Susceptibility

One or two gram-negative isolates at >105 and other isolates at least 10X less: Full ID and Susceptibility of gram-negative isolates

cumitech guidelines for interpretation of routine urine cultures 1
One isolate at >104: Full ID and Susceptibility

One or two gram-negative isolates at >105 and other isolates at least 10X less: Full ID and Susceptibility of gram-negative isolates

Other patterns of isolates at >104: Presumptive ID only

Ignore mixed urethral flora at <104

1Clarridge, Johnson, Pezzlo, and Weissfeld, ASM Cumitech 2B, November 1998.

Cumitech Guidelines for Interpretation of Routine Urine Cultures1

Dr.T.V.Rao MD

how to report urine cultures cumitech recommendations
HOW TO REPORT URINE CULTURES: Cumitech Recommendations
  • Negative urines (no growth)0.01 ml inoculum Sterile or < 100 CFU/ml OR
  • No growth of > 100 CFU/ml
  • 0.001 ml inoculum Sterileor < 1000 CFU/ml OR
  • No growth of > 1000 CFU/ml

Dr.T.V.Rao MD

reading the culture plates
Reading the Culture Plates

A true infection in the absence of prior antibiotic therapy the number of bacteria is likely to be at least 105or more.

Contaminated specimens present with colony counts <104, however even less than 103

On several occasions the colonies are diverse species

Several studies prove counts >104 to be considered as presence of Urinary tract infection with the supporting clinical history

On some occasions more than one pathogen is isolated but should be processed for all practical purposes

eg E.coli along with Streptococcus fecalis

On few occasions even counts 103 are proved significant

Dr.T.V.Rao MD

interpretation of enterobacteriaceae
Interpretation of Enterobacteriaceae

Dr.T.V.Rao MD

A single species of Enterobacteriaceaerecovered at >105 cfu’s/mL urine: with patients symptomatic for urinary tract infection, 95% probability of true bacteriuria

A single species of Enterobacteriaceae recovered at 104-105 cfu’s/mL urine: with patients symptomatic for urinary tract infection, 33% probability of true bacteriuria

interpretation of enterobacteriaceae22
Interpretation of Enterobacteriaceae

Dr.T.V.Rao MD

A single species of Enterobacteriaceaerecovered at >105 cfu’s/mL urine: with patients symptomatic for urinary tract infection, 95% probability of true bacteriuria

A single species of Enterobacteriaceae recovered at 104-105 cfu’s/mL urine: with patients symptomatic for urinary tract infection, 33% probability of true bacteriuria

gram positives and fungi the counts may be 10 5
Gram positives and fungi the counts may be <105
  • Gram-positive, fungal, and fastidious uropathogens often present in lower numbers (104-105 cfu’s/mL urine)
  • Urethral commensals recovered at <104 cfu’s/mL urine

Dr.T.V.Rao MD

cumitech guidelines for interpretation of routine urine cultures 124
Cumitech Guidelines for Interpretation of Routine Urine Cultures1

Dr.T.V.Rao MD

Other patterns of isolates at >104: Presumptive ID only

Ignore mixed urethral flora at <104

1Clarridge, Johnson, Pezzlo, and Weissfeld, ASM Cumitech 2B, November 1998.

slide25

Cumitech Guidelines for Interpretation of Special or uncommon Urine Cultures1

Dr.T.V.Rao MD

One or two isolates at >102 to 105: Full ID and Susceptibility is essential before confirmed as uncommon isolates

1Clarridge, Johnson, Pezzlo, and Weissfeld, ASM Cumitech 2B, November 1998.

reporting of negative urine cultures
Reporting of negative urine cultures

Dr.T.V.Rao MD

Negative culture results showing no bacterial growth are available after 24 hours. Positive results require 24-72 hours to complete identification of the number and type of bacteria found

asymptomatic bacteriuria
Asymptomatic Bacteriuria
  • Presence of uropathogens by culture without signs or symptoms of urinary tract infection
  • Clinically significant (should be treated) with preschool children (? vesicoureteral reflux, congenital urinary tract anomaly), pregnant women, and adults with obstructive uropathy
  • Without clinical significance (should not be treated) for adults in absence of urinary tract obstruction

Dr.T.V.Rao MD

when to do an antibiotic sensitivity testing on urine isolate
When to do an antibiotic sensitivity testing on Urine Isolate?
  • Follow laboratory guidelines for susceptibility testing of isolates in which a definitive ID and AST is recommended, according to Cumitech, CMPH, MCM, IDSA, other guidelines. That would include “significant CFU/ml” of :Enterobacteriaceae
  • P. aeruginosa
  • Enterococcus sp.
  • S. aureus
  • Significant CoNS, except S. saprophyticus
  • Others, including yeast, upon request or if SOP’s have been set up in accordance with CLSI Guidelines of Best practices

Dr.T.V.Rao MD

slide29

Created by Dr.T.V.Rao MD for ‘e’Learning” resources for Microbiologists in the Developing World

  • Email
  • doctortvrao@gmail.com

Dr.T.V.Rao MD