What is the significance of finding gram-positive bacilli surrounding epithelial cells in a urine sample?

Gram-Positive Bacilli Surrounding Epithelial Cells in Urine: Clinical Significance

The presence of gram-positive bacilli surrounding epithelial cells in a urine sample most commonly represents contamination from periurethral or perineal flora, particularly Lactobacillus species, rather than true urinary tract infection.

Primary Interpretation: Contamination vs. Infection

The finding of gram-positive bacilli adherent to squamous epithelial cells strongly suggests specimen contamination rather than bladder infection 1. This occurs because:

• Squamous epithelial cells originate from the distal urethra, vagina, or perineal skin, not from the bladder mucosa 1
• Gram-positive bacilli (especially Lactobacillus) are normal flora of the vaginal and periurethral areas in women 2
• True bladder infections typically show bacteria free-floating in urine or adherent to white blood cells, not clustered around epithelial cells 1

Differential Diagnosis of Gram-Positive Bacilli in Urine

Most Likely: Contamination

• Lactobacillus species are the most common gram-positive bacilli found as contaminants, appearing as long rods surrounding epithelial cells 2
• Collection technique issues: Inadequate cleansing before midstream collection or bag specimens increase contamination risk 1

Less Common: True Uropathogens

If clinical symptoms are present and proper collection technique was used, consider these gram-positive bacilli as potential pathogens 2:

• Enterococcus faecalis: Appears as gram-positive cocci in chains, not bacilli 2
• Corynebacterium urealyticum: Gram-positive bacillus, causes alkaline-encrusted cystitis in patients with urologic abnormalities 2
• Aerococcus urinae: Gram-positive coccus (not bacillus), causes UTI in elderly males with prostatic disease 3, 2
• Gardnerella vaginalis: Small gram-variable coccobacillus, typically a vaginal contaminant 2

Important Caveat

Gram-positive bacilli are NOT typical uropathogens in most clinical scenarios 1. The guidelines emphasize that urinary tract infections are predominantly caused by gram-negative bacilli (E. coli and other Enterobacteriaceae) and gram-positive cocci (Enterococcus), not gram-positive bacilli 1.

Clinical Decision Algorithm

Step 1: Assess Specimen Quality

• Presence of squamous epithelial cells indicates contamination 1
• Multiple organisms on Gram stain suggests contamination rather than infection 1
• Proper collection method: Catheterized or suprapubic aspiration specimens have higher specificity than midstream catch 1, 4

Step 2: Correlate with Clinical Presentation

• Symptomatic patient (dysuria, frequency, urgency, fever): Consider repeat specimen with proper collection technique 1
• Asymptomatic patient: Do not treat; this represents asymptomatic bacteriuria or contamination 1

Step 3: Review Urinalysis Results

• Pyuria (>5-10 WBC/HPF) supports infection if present 1
• Absence of pyuria in 20% of true pyelonephritis cases, so cannot rule out infection entirely 1
• Positive leukocyte esterase or nitrite increases likelihood of true infection 1

Step 4: Interpret Culture Results

• Single organism with ≥50,000 CFU/mL in children or ≥100,000 CFU/mL in adults suggests true infection 4
• Multiple organisms or low colony counts with gram-positive bacilli on epithelial cells confirms contamination 1
• Lactobacillus growth should be reported as "normal flora/contamination" in most cases 2

Common Pitfalls to Avoid

1. Treating contaminated specimens as infections: This leads to unnecessary antibiotic exposure and contributes to resistance 1, 5

2. Failing to obtain proper specimen: Bag specimens in infants have high contamination rates; catheterization or suprapubic aspiration is preferred for definitive diagnosis 1

3. Ignoring specimen transport time: Urine held at room temperature >1 hour allows bacterial multiplication, falsely elevating colony counts 1

4. Misidentifying gram-positive bacilli: Most true uropathogens are gram-negative bacilli or gram-positive cocci, not gram-positive bacilli 1, 2

5. Treating asymptomatic bacteriuria: Even with positive cultures, treatment is not indicated except in pregnancy or before urologic procedures 1

Recommended Action

For your specific finding of gram-positive bacilli surrounding epithelial cells:

• Report as "contamination with normal flora" if multiple epithelial cells are present 1
• Recommend repeat specimen with proper collection technique if clinical suspicion for UTI remains high 1
• Do not initiate empiric antibiotics based on this finding alone, as it does not represent bladder infection 1
• If culture grows Lactobacillus or mixed flora, report as contaminated specimen requiring recollection 1, 2

The key distinction is that bacteria adherent to squamous epithelial cells originate from outside the bladder, whereas true bladder infections show bacteria free in urine or associated with inflammatory cells from the bladder mucosa 1, 6.