The document discusses the role of microbiology laboratories in diagnosing and treating urinary tract infections caused by Escherichia coli. It states that a mid-stream clean catch urine specimen is required for testing. The laboratory will culture the urine on selective agar plates and perform biochemical tests to identify E. coli based on morphological and biochemical characteristics. E. coli appears as a Gram-negative bacillus that is catalase-positive and oxidase-negative with specific reactions on additional test media. Once identified, appropriate antibiotics effective against E. coli can be prescribed to the patient.

1. The Role of Microbiology in the Diagnosis and Treatment of
Urinary Tract Infections (UTIs) Caused by the Bacteria
Escherichia coli
Katie McDowall, Kim Campbell, Bri McKenna| Tiffany Gill | MLT-1080 Clinical Microbiology
Abstract
Acceptable Culture Specimen
Laboratory Results Diagnostic of E. Coli
Additional Testing
Interfering Substances
• Mid-stream, clean catch urine specimen
• Patient education on proper cleansing of external
genitalia is required to prevent normal flora
contamination
• Catheterized urine collection or suprapubic bladder
aspiration may be required depending on the patient
• Random urine specimens must be delivered within 2
hours of collection unless on ice or refrigerated
Treatment
• E. coli is normal flora of human GI tract, also found at the anus
• Improper hygiene, (wiping back to front after using the toilet), or
sexual intercourse can introduce E. coli into the urethra
• E. coli have virulence factors such as: fimbriae, hemolysins, &
capsules which enhance adhesion & colonization in the urinary
tract causing an urgent need to urinate accompanied by
pain/burning sensation
• Pregnant women and immune-compromised are especially at
risk for UTIs
Works Cited
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Staphylococcus Saphrophticus. Retrieved from
https://www.ncbi.nlm.nih.gov/books/NBK482367/
Gill, T. (2019). E. coli biochemical test. Retrieved from
https://mylearning.csmd.edu/d2l/le/content/60416/viewContent/888117/View
Gram stain of Escherichia coli. (2019). Retrieved from
http://faculty.ccbcmd.edu/courses/bio141/labmanua/lab1/gnrod.html
Tille, P. M. (2017). Bailey & Scott’s Diagnostic Microbiology
(14th ed.). St. Louis, MO: Elsevier.
Urinary Tract Infections- Lab diagnosis (e.coli, klebsiella,
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tract-infectionslab-diagnosis-ecoli-klebsiella-proteus-pseudomonas
Urinary Tract Infection (UTI). (2019, Jan 30). Retrieved
March14, 2019, from https://www.mayoclinic.org/disease-conditions/urinary-
tract-infection/diagnosis-treatment/drc-20353453
Pathophysiology
The Microbiology lab plays an important role in the
diagnosis and treatment of UTIs. Most UTI’s are caused
by the bacteria E. coli. Typically urine and the areas of the
urinary tract above the urethra are sterile. However,
improper hygiene or sexual intercourse can
introduce E.coli into the urinary tract, causing a UTI. When
a patient exhibits symptoms of a UTI, such as pain and
frequent or urgent need to urinate, he or she will likely go
to a doctor's office or clinic where the physician will ask
the patient to provide a mid-steam clean catch urine
specimen. The micro lab will then inoculate the urine onto
selective and differential agar plates and run various
biochemical tests to identify the bacteria. E. coli will
appear as a Gram-negative bacilli on the Gram stain, gray,
smooth and beta-hemolytic on Blood Agar, pink on
MacConkey agar, and yellow or orange on Hektoen agar.
Other diagnostic lab results of E.coli include: Catalase +,
Oxidase negative, Citrate & Urease negative, & Nitrate
Reduction +. Once the pathogen has been identified as E.
coli an appropriate antibiotic that is effective against E.
coli, such as Nitrofurantoin, can be prescribed.
Primary set-up for a urine specimen
• Blood Agar Plate
• MacConkey agar plate
• Plates are streak with a calibrated loop
• Incubated for 24 hours at 35℃ in a CO2 incubator
Interpretation of primary plates
• Gray, smooth, and often
beta-hemolytic on BAP
• Lactose fermenters
and will appear pink on MAC
• Gram stain is done if there is
if there is abundant growth
(≥ 105 CFU/mL)
Gram stain
• Gram-negative bacilli
Biochemical and secondary media
• Catalase: positive
• Oxidase: negative
• HE agar: yellow/orange colonies
• TSI: A/AG or K/AG
• MIO: V+, +, V+
• Citrate: negative
• Urease: negative
• Nitrate reduction: positive
Contamination:
• If the specimen provided was not a clean catch, there
could be growth of the normal flora from the urethra or
genitals. The normal flora includes CNS, Lactobacilli,
Viridans Streptococci, Corynebacteria, and
Enterobacteriaceae.
• If the cup or plate was touched, there could be
contamination from the skin.
There may be no growth if there was bleach or a
preservative that inhibits bacteria growth present in the
specimen cup.
• Phenazopyridine hydrochloride can be used to treat
symptoms but will not treat the infection.
• Common brands include Uristat and AZO.
• Infection must be treated with antibiotics-untreated can lead
to more serious problems such as kidney infection and
damage.
• Most effective antibiotics are sulfamethoxazole, fosfomycin,
nitrofurantoin, cephalexin, and ceftriaxone.
• Antibiotic Susceptibility Testing
• Urine dipstick analysis
• Microscopic analysis