The Cyto-Bacteriological Urine Examination

The Cyto-Bacteriological Urine Examination (CBUE) is requested in the event of symptoms of urinary tract infection.
1/Macroscopic examination :
*Color: yellow (normal), pink to red (hematuria >1,000 red blood cells/mL), mahogany-orange (jaundice)

*Appearance: Clear or cloudy (presence of leukocytes, bacteria).
*pH: acid (normal), alkaline (urinary tract infection).
2/Microscopic examination:
2.1/Fresh state: Detection of bacteria (E. coli, klebsiella, enterococci, staphylococci, streptococci), yeasts (Candida), red blood cells, leukocytes, epithelial cells, cylinders, crystals.

2.2/Gram staining for bacteria
2.3/Ziehl’s stain: for mycobacteria
3/Bacterial count (bacteriuria) :
Normally sterile urine (< 10³ bacteria/mL)
Selective media:
*CLED: Yellow (fermenting) and blue/colorless (non-fermenting) colonies.
*MacConkey: Selective for Gram- bacteria
*Blood agar: Hemolysis alpha (partial), beta (total), gamma (none)
4/Identification/Antibiogram
Only significant colonies are identified, others are contaminants.
*Identification: Macroscopic examination, Gram stain, enzymatic (oxidase, catalase) and biochemical tests.
*Antibiogram: Performed if the count indicates a urinary tract infection.
5/Interpretation of results :
Interpretation of the ECBU is based on five criteria:
1-Leukocyturia
< 10⁴ leukocytes/mL: No inflammation, therefore often no urinary tract infection, with some exceptions (neutropenia, early infection).
≥ 10⁴ leuko/mL: Inflammation, sign of urinary tract infection.
Caution: Patients with urinary catheters may present leukocyturia without infection
2-Bacteriuria:
< 10³ CFU/mL: No infection (if no antibiotic treatment, no hyperhydration, urinary abstinence > 3 h).
≥ 10⁵ CFU/mL: Frequent indication of urinary tract infection in a symptomatic subject.
3-Uropathogenicity groups:
Group I (E. coli, Staphylococcus saprophyticus): Infection from 10³ CFU/mL.
Group II (other enterobacteria, Pseudomonas aeruginosa, etc.): Infection from 10⁴ CFU/mL for women and 10³ CFU/mL for men.
Group III (Streptococcus agalactiae, Candida spp, etc.): Infection from 10⁵ CFU/mL and other criteria (double positive sample, inflammation).
Group IV (Streptococcus alpha hemolyticus, Lactobacillus spp., etc.): Generally considered contaminants, except in the case of suprapubic puncture.
4-Number of species isolated
Urinary tract infections are generally monomicrobial
Bimicrobial infections are rare, especially in nosocomial infections
More than two germs indicate contamination; repeat the ECBU
If one germ is in the majority, the other is probably a contaminant.
5-Clinical context
Symptoms and risk factors (urinary catheterization, surgery)
Current antibiotic treatment
Pregnancy
The presence of symptoms helps differentiate between urinary tract infection and colonization (presence of germs without symptoms).