How does Staphylococcus saprophyticus respond to Augmentin (amoxicillin-clavulanate) in a young adult with a urinary tract infection?

Staphylococcus saprophyticus Response to Augmentin

Staphylococcus saprophyticus is generally susceptible to amoxicillin-clavulanate (Augmentin), making it an appropriate first-line treatment option for uncomplicated urinary tract infections caused by this organism in young adults. 1, 2

Microbiological Susceptibility

• All S. saprophyticus strains tested in a 10-year Spanish study showed 100% susceptibility to amoxicillin-clavulanic acid, demonstrating reliable in vitro activity against this pathogen 2
• S. saprophyticus maintains consistent susceptibility to amoxicillin-clavulanate across multiple studies, unlike its high resistance rates to other commonly used empiric UTI antibiotics 3, 2

Clinical Context and Treatment Appropriateness

Amoxicillin-clavulanate is recommended as a first-line option for uncomplicated lower UTI when local E. coli resistance is <20%, and this recommendation extends to S. saprophyticus infections 1

Key Clinical Considerations:

• S. saprophyticus causes UTIs predominantly in young women aged 15-44 years (83.9% of cases), with peak incidence during spring and autumn months 2
• The organism accounts for approximately 10-20% of community-acquired UTIs in this demographic, making it the second most common cause after E. coli 2
• 60% of S. saprophyticus cystitis cases and 25% of pyelonephritis cases receive inappropriate empiric therapy when clinicians fail to consider this pathogen 3

Important Resistance Patterns to Avoid

Antibiotics with Poor Activity:

• Ceftriaxone shows high MICs (4 to >32 μg/ml) against S. saprophyticus, making third-generation cephalosporins unreliable for this organism 3
• Approximately 45-55% resistance to penicillin alone exists, necessitating the beta-lactamase inhibitor component 2
• Erythromycin resistance is high (37.7%) and increasing over time 2
• Trimethoprim-sulfamethoxazole resistance occurs in approximately 6% of isolates 2

Reliable Alternative Options:

• Fluoroquinolones maintain excellent activity with only 0.9% resistance, making ciprofloxacin or levofloxacin suitable alternatives 4, 2
• Nitrofurantoin remains highly effective for uncomplicated lower UTI 1
• All strains show 100% susceptibility to vancomycin, rifampin, and gentamicin, though these are reserved for complicated cases 2

Critical Pitfalls to Avoid

Do not use third-generation cephalosporins (ceftriaxone, cefotaxime) for empiric treatment when S. saprophyticus is suspected, as MIC values frequently exceed therapeutic thresholds despite the organism being methicillin-susceptible 3

• The oxacillin disk diffusion test may incorrectly classify 45% of S. saprophyticus as "resistant" using standard CLSI breakpoints, but this does not predict amoxicillin-clavulanate failure 2
• Pregnant women with S. saprophyticus UTI benefit particularly from amoxicillin-clavulanate, as it avoids the FDA pregnancy concerns associated with fluoroquinolones and trimethoprim-sulfamethoxazole 2

Dosing and Duration

• Standard dosing of amoxicillin-clavulanate 500/125 mg three times daily or 875/125 mg twice daily for 5-7 days is appropriate for uncomplicated cystitis 1
• Short-course therapy (3-7 days) achieves similar cure rates to longer courses while minimizing adverse events and resistance development 1

Emerging Resistance Concerns

• Multidrug resistance occurs in approximately 58% of S. saprophyticus isolates in some regions, with 21% harboring the mecA gene 5
• Biofilm formation capability exists in 65% of isolates, potentially complicating treatment in catheter-associated infections 5
• Local resistance patterns should guide empiric therapy selection, though amoxicillin-clavulanate maintains superior activity compared to most alternatives 1, 2