17-laboratory evaluation of urinary tr act infection v1- 3

8/8/2019 17-Laboratory Evaluation of Urinary Tr Act Infection v1- 3

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Laboratory Evaluation of

Urinary Tract InfectionDr. John R. Warren

Department of Pathology

Northwestern UniversityFeinberg School of Medicine

June 2007


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Essential Elements of Urine

Cultures Pathophysiology of urinary tract

infection

Microbiology of urinary tract infection

Clinical signs and symptoms of urinarytract infection


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Essential Elements of Urine

Cultures Technical variables in specimen

collection and transport

Interpretation of urine cultures

Quality management


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Pathophysiology of urinary tract

infection Ascending route of infection most common Colonization of urethra and periurethral tissue by

uropathogens the initial event in urinary tract infection

Urinary tract infection more common in women than men dueto short female urethra with distention and turbulent flow that

washes urethral organisms into the bladder during micturitionand in close proximity to perianal areas

Hospital infection associated with lower urinary tractinstrumentation (catheterization, cystoscopy)

Once in the bladder uropathogens multiply, then pass up theureters (especially if vesicoureteral reflux present) to the renal

pelvis and parenchyma Source of uropathogens: enteric bacteria


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infection Cystitis: localized infection of the bladder with superficialneutrophilic inflammation of the mucosa (lower urinary tractinfection)

Pyelonephritis: infection of the kidney with acute suppurativeinflammation of the pelvis, medullary and cortical tubules, and

corticomedullary intersititum (upper urinary tract infection) Urosepsis: bacteremia due to pyelonephritis

Papillary necrosis: complication of pyelonephritis in diabetesand urinary tract obstruction with coagulative necrosis of renalpyramids and an intense inflammatory response betweenpreserved and necrotic tissue

Sloughing of necrotic pyr

amids: complication of papillarynecrosis that can cause urinary tract obstruction (in some

instances sloughed portions voided and recovered in urine)

Perinephricabscess: associated with obstruction of an infectedkidney with abscess formation in the pernephric space due toextension of bacterial infection across the renal capsule


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infection Uncomplicated urinary tract infection:

Bacterial or yeast infection in a

structurally and neurologically normalurinary tract

Complicated urinary tract infection:

Bacterial or yeast infection in a urinary

tract with functional or structuralabnormalities


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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


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Bacterial virulence factors in

urinary tract infection Escherichia colistrains expressing O-antigens O1,

O2, O4, O6, O7, O8, O75, O150, and O18ab causehigh proportion of infections

Capsular K1, K5, and K12 antigens ofE. coli

associated with clinical severity (antiphagocytic) P-fimbriae enhance mannose-resistant attachment ofE. colito globoseries glycosphingolipid receptors(gal-gal) of uroepithelial cells (P-fimbriated E. colidominant as cause of pyelonephritis and urosepsis)

Type 1 fimbriae enhance mannose-susceptibleadherence ofE. colito uroepithelial cells (virtually allcystitis-producing E. colistrains express type 1fimbriae)

Motile bacteria ascend the ureter against urine flow


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Bacterial virulence factors in

urinary tract infection Bacterial urease (Proteus, Corynebacterium

urealyticum) splits urinary urea with generation ofammonium ion that alkalinizes urine with loss of acidpH as natural defense barrier against infection, stoneformation with ureteral obstruction and survivial ofbacteria deep within stones resisting eradication byantibiotic, and alkaline-encrusted cystitis

Gram-negative endotoxin decreases ureteralperistalsis

Hemolysin produced by many uropathogens

damages renal tubular epithelium and promotesinvasive infection

Aerobactin (a siderophore) present at increasedfrequency in uropathogenic strains ofE. colipromoting intracellular iron accumulation for

bacterial replication


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Host protective factors in urinary

tract infection Flushing mechanism of micturition a major

protective factor

Low vaginal pH (3.5-4.5) (due to lactic acid producedby action ofLactobacillion glycogen of sloughed

vaginal epithelial cells) suppresses colonization byuropathogens

Normal acid pH of urine (4.6-6) anti-bacterial

Urinary Tamm-Horsefall protein (secreted byascending loop of Henle) binds to mannose-sensitive fimbriae and blocks E. coliattachment touroepithelial cells

Chemotactic interleukin-8 released upon bacterialattachment to uroepithelial cells with recruitment ofphagocytic neutrophils and eradication of bacteriuria


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Immune responses in urinary

tract infection Large numbers of submucosal IgA-

producing plasma cells in bacterial cystitis

IgM and/or IgG antibodies produced against

O-antigen, K antigen, type 1 and P fimbriae,and lipid A

Protective role of antibodies unclear, may

limit damage within the kidney and preventpersistent colonization and thus recurrence

of infection


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infection Hematogenous seeding of renal cortex less

frequent than ascending infection

Kidney a common site of abscess formationin Staphylococcus aureus bacteremia, lessoften in candidemia, rarely with gram-negative bacteremia

Hematogenous seeding of kidney alsooccurs with Salmonella(typhoid) and

Mycobacterium tuberculosis Evidence for a role of periureteral and renal

lymphatics in urinary infection lacking


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Common Uropathogens

Escherichia coli

OtherEnterobacteriaceae (Klebsiella, Enterobacter,Proteus, Citrobacter)

Pseudomonas aeruginosa

Enterococcus

Staphylococcus saprophyticus

Staphylococcus aureus1

Streptococcus agalactiae (group B)2

Candida1Associated with staphylococcemia2Denotes vaginal colonization in pregnant women


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Uncommon Uropathogens

Corynebacterium urealyticum1

Haemophilus influenzae and H. parainfluenzae2

Blastomyces dermatitidis3

Neisseria gonorrhaeae4

Mycobacterium tuberculosis51Colistin nalidixic acid (CNA) agar2Chocolate agar3Brain heart infusion, inhibitory mold, or Sabourad

dextrose agar4Enhanced recovery with chocolate agar5Lowenstein-Jensen medium, Middlebrook broth or

agar


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Commensal Microflora of the

Urethra Coagulase-negative staphylococci

(except S. saprophyticus)

Viridans and non-hemolyticstreptococci

Lactobacilli

Diphtheroids (Corynebacteriumexcept

C. urealyticum) Saprophytic Neisseria

Anaerobic bacteria


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Common Risk Factors for

Urinary Tract Infection: Women Urinary tract obstruction (including calculi)

Catheterization (straight, indwelling)

Pregnancy


Neurogenic bladder


Sexual intercourse Estrogen deficiency (loss of vaginal

lactobacilli)


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Common Risk Factors for

Urinary Tract Infection: Men Urinary tract obstruction (including calculi)

Catheterization (straight, indwelling)

Prostatic enlargement


Neurogenic bladder


Insertive rectal intercourse Lack of circumcision (children and young

adults)


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Signs and Symptoms of Lower

Urinary Tract Infection Inflammatory irritation of urethral and

bladder mucosa

Frequent and painful urination of smallvolumes of turbid urine

Occasional suprapubic pain or

sensation of heaviness

Fever generally absent


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Signs and Symptoms of Upper

Urinary Tract Infection Fever and chills (systemic reaction)

Flank pain

Lower urinary tract signs andsymptoms (frequency, urgency, and

dysuria)


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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


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Urinary Tract Specimens

First-voided morning urine optimal (generallybacteria have been proliferating in bladder urine forseveral hours)

Midstream urine specimens (initially voided urine

contains urethral commensals) Indwelling catheters (freshly placed, urine aspirated

by needle inserted into catheter) (Foley catheter tipsnot acceptable)

Straight catheter specimens

Suprapubic aspirates (infants or children, recoveryof anaerobes)1

Cystoscopic collection of urine1Contamination-free specimen


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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)


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Inoculation of Urine

Inoculation of urine for quantitative culture (colonyforming unitscfus) performed with a calibrated0.001 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 cfus per mL of urine

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

MacConkey agar utilized as selective differentialagar for gram-negative bacteria, colistin nalidixicacid agar as selective agar for gram-positivebacteria, and chocolate agar for fastidious gram-negative bacteria (Haemophilus)


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Interpretation of Urine Cultures:

General Guidelines A single species ofEnterobacteriaceae recovered at

>105 cfus/mL urine: with patients symptomatic forurinary tract infection, 95% probability of truebacteriuria

A single species ofE

nteroba

cteriaceae recovered at104-105 cfus/mL urine: with patients symptomatic for

urinary tract infection, 33% probability of truebacteriuira

Gram-positive, fungal, and fastidious uropathogensoften present in lower numbers (104-105 cfus/mL

urine) Urethral commensals recovered at


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Cumitech Guidelines for

Inoculation of Urine Cultures1

Routine: uncomplicated urinary tract infection inambulatory outpatients (0.001 mL loop, SBA, MAC;24 hr incubation)

Surveillance: neurogenic bladder, indwelling

catheter, geriatric patents (0.001 mL loop, SBA,MAC, CNA; 24 hr incubation)

Special: suprapubic aspirates or straight catheterspecimens where previous cultures negative,unresponsive to therapy, or possibility of unusualurinary tract pathogen (0.001 and 0.01 mL loop, BA,

MAC, CHOC; minimum 48 hr incubation)1Clarridge, Johnson, Pezzlo, and Weissfeld, ASM

Cumitech 2B, November 1998.


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Interpretation of Routine Urine

Cultures1

One isolate at >104: Full ID and Susceptibility

One or two gram-negative isolates at >105

and other isolates at least 10X less: Full IDand Susceptibility of gram-negative isolates

Other patterns of isolates at >104:Presumptive ID only

Ignore mixed urethral flora at


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Interpretation of Surveillance

Urine Cultures1

One isolate at >104: Full ID and Susceptibility

One gram-negative isolate at >105 with others

at least 10X less: Full ID and Susceptibility Other patterns of isolates at >104:

Presumptive ID only

Ignore mixed urethral flora at


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Interpretation of Special Urine

Cultures1

One or two isolates at >102 to 105: Full

ID and Susceptibility

1Clarridge, Johnson, Pezzlo, and

Weissfeld, Cumitech 2B, November1998


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ASM Manual Guidelines for Urine

Culture Results Likely to Be

Significant1 Midstream, female with cystitis, >102 with positive urine

leukocyte esterase

Midstream, female with pyelonephritis, >105 with positive urineleukocyte esterase

Midstream, asymptomatic, >105 with negative urine leukocyteesterase (usually)

Midstream, male with UTI: >103 with leukocyte with urineleukocyte esterase positive

Straight catheter: >102 with urine leukocyte esterase positive

Indwelling catheter: >103 with urine leukocyte esterase positiveor negative

1Manual of Clinical Microbiology, 8th Edition, ASM, 2003


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NMH Guidelines for

Interpretation of Urine Cultures1

Urine leukocyte esterase positive

One or two organisms at >103: FullID and Susceptibility

One organism at >104

with others (2 ormore) at least 10X less: Full ID andsusceptibility of predominantorganism

Report all group B -hemolytic

streptococci for women < 50 years1Modified from ASM Cumitech, ASM Manual,

and CDC MMWR 2002;51 (RR-11):1-22


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NMH Guidelines for

Interpretation of Urine Cultures1

Urine leukocyte esterase negative

One or two organisms at >105: Fulland Susceptibility

One gram-negative organism (pure culture) at

>10

4

: Full ID and SusceptibilityYeast in pure culture: ID as Candida

albicans or not C.albicans

Report all group B -hemolytic streptococci forwomen


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Quality Monitor for Urine

Cultures

104/mL


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References

Sobel and Kaye. Urinary Tract Infections. InMandell, Douglas, and Bennetts Principles andPractice of Infectious Diseases, 6th edition, Elsevier,2005, pp. 975-905.

Clarride, Johnson, Pezzlo, and Weissfeld.Laboratory Diagnosis of Urinary Tract Infections.Cumitech 2B, ASM Press, 1998, pp. 2-19.

Thomson, Jr. and Miller. Specimen Collection,Transport, and Processing: Bacteriology. In Manualof Clinical Microbiology, 8th edition, ASM Press,

2003, pp. 286-330. Chapter 60. Infections of the Urinary Tract. In Bailey

& Scotts Diagnostic Microbiology, 11th edition,Mosby, pp. 927-938,

17-laboratory evaluation of urinary tr act infection v1- 3

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