Is Staphylococcus hemolyticus in urine significant?

Is Staphylococcus hemolyticus Significant in Urine?

Staphylococcus hemolyticus in urine should be considered a potential pathogen rather than automatically dismissed as a contaminant, particularly when isolated as a single organism at ≥50,000 CFU/mL in patients with urinary symptoms and pyuria.

Clinical Significance Assessment

The significance of S. hemolyticus depends on several critical factors that must be evaluated systematically:

Colony Count Thresholds

• ≥50,000 CFU/mL of a single organism meets the diagnostic threshold for significant bacteriuria when accompanied by urinary symptoms and pyuria 1
• For catheterized specimens, colony counts as low as 10,000 CFU/mL may be clinically significant 2
• The presence of a single organism rather than mixed flora strongly supports true infection over contamination 2, 1

Supporting Laboratory Findings

• Pyuria (elevated white blood cells in urine) is essential for confirming UTI—bacteriuria without pyuria may indicate contamination or asymptomatic bacteriuria 1
• Urinalysis showing ≥2+ leukocyte esterase, 20-40 WBCs/HPF, and bacteria supports active infection 2
• Both positive urinalysis AND adequate colony counts are required for UTI diagnosis 1

Clinical Context Matters

S. hemolyticus is recognized as an opportunistic pathogen that primarily affects immunocompromised or elderly patients 3. Consider it significant when:

• Patient has urinary symptoms (dysuria, frequency, urgency, suprapubic pain)
• Patient is elderly (>66 years), diabetic, has cancer, or other immunocompromising conditions 3
• Patient has recent or current urinary catheterization 4
• Patient has persistent or recurrent urinary symptoms 5

Evidence Supporting S. hemolyticus as a Uropathogen

Recent molecular evidence demonstrates that S. hemolyticus harbors virulence genes associated with UTI, particularly icaC and icaA genes involved in biofilm formation 6. In a 2023 study, S. hemolyticus was the most common coagulase-negative Staphylococcus species causing UTI (41.5% of cases), with 90.8% of isolates possessing UTI-associated virulence genes 6.

The study concluded that laboratories should carefully interpret significant bacteriuria due to coagulase-negative Staphylococci in relation to UTI symptoms and pyuria before labeling them as contaminants 6.

Treatment Considerations

When S. hemolyticus is deemed significant:

• All S. hemolyticus isolates in published cases were susceptible to vancomycin, nitrofurantoin, and trimethoprim-sulfamethoxazole 3
• Trimethoprim-sulfamethoxazole successfully resolved persistent S. hemolyticus UTI in documented cases 5
• However, 92.3% of recent isolates carried antimicrobial resistance genes, most commonly dfrG (trimethoprim resistance), blaZ (penicillin resistance), and mecA (methicillin resistance) 6
• Treatment should be guided by antimicrobial susceptibility testing given high resistance rates 6

When to Treat vs. Observe

Treat when:

• Single organism ≥50,000 CFU/mL with urinary symptoms AND pyuria 1
• Catheterized patient with ≥10,000 CFU/mL, symptoms, and pyuria 2
• Immunocompromised host with any significant growth and symptoms 3

Do NOT treat:

• Asymptomatic bacteriuria should not be treated except in pregnant women or patients undergoing urological procedures with anticipated mucosal bleeding 7
• Mixed growth suggesting contamination 7
• Absence of pyuria despite bacteriuria 1

Common Pitfalls to Avoid

• Do not automatically dismiss coagulase-negative Staphylococci as contaminants—perform more in-depth characterization, especially in persistent or recurrent cases 3
• Do not rely solely on colony count—always correlate with clinical symptoms and urinalysis findings 1
• Do not ignore the collection method—bag-collected specimens have high contamination rates and should not be used for definitive diagnosis 1
• Do not treat asymptomatic bacteriuria as this promotes antimicrobial resistance without patient benefit 7