Antibiotic of Choice for Staphylococcus hominis subsp. hominis Infections
Vancomycin is the empiric antibiotic of choice for Staphylococcus hominis subsp. hominis infections because the vast majority of clinical isolates are methicillin-resistant and multidrug-resistant. 1, 2, 3
Initial Empiric Therapy
- Start vancomycin 30-60 mg/kg/day IV in 2-4 divided doses targeting trough levels of 10-15 mg/L for most infections 4, 1
- Vancomycin is recommended as first-line empiric therapy because most S. hominis isolates from clinical infections are methicillin-resistant, particularly in healthcare-associated settings 1, 2
- Over 80% of clinical S. hominis strains demonstrate multidrug resistance, with many resistant to 7 or more antibiotics 3
De-escalation Strategy Based on Susceptibility Testing
- If susceptibility testing confirms methicillin susceptibility (rare), switch to nafcillin, oxacillin, or flucloxacillin because beta-lactams are superior to vancomycin for susceptible organisms 1
- First-generation cephalosporins like cefazolin are acceptable alternatives for patients with non-immediate penicillin allergies 1
- However, be aware that methicillin-susceptible S. hominis is uncommon in clinical practice 2, 3
Alternative Agents for Resistant Strains
- Daptomycin is an excellent alternative if vancomycin fails or the patient cannot tolerate it, as clinical isolates have shown consistent susceptibility 2, 5
- Tigecycline remains active against multidrug-resistant S. hominis strains 2
- Linezolid should be avoided as resistance has been documented in S. hominis with glycopeptide-intermediate susceptibility 2
Critical Pitfalls and Resistance Patterns
- Beware of heterogeneous vancomycin resistance: approximately 18% of S. hominis strains show reduced vancomycin susceptibility (MIC 4-8 mg/L) or heterogeneous resistance profiles 3, 6
- Vancomycin MICs can increase from 4 mg/L to 16-32 mg/L after prolonged exposure, associated with cell wall thickening 6
- Most strains harbor the mecA gene and carry SCCmec elements, often with novel or nontypeable configurations 3, 7
- Common resistance genes include tetK, acc(6')-Ie aph(2''), ant(4')-I, and erm(C) 3
Refractory Infections Requiring Combination Therapy
- For persistent bacteremia despite appropriate monotherapy, consider triple combination therapy: vancomycin + meropenem + clindamycin for at least 3 weeks 5
- This approach was successful in a documented case of refractory S. hominis bacteremia in an immunocompromised patient 5
- Combination therapy should be reserved for severe infections with persistent positive blood cultures after 72 hours of appropriate antibiotics 1, 5
Duration of Therapy by Clinical Scenario
- Uncomplicated catheter-related bloodstream infection: 5-7 days if catheter removed, or 10-14 days with antibiotic lock therapy if catheter retained 1
- Prosthetic valve endocarditis: minimum 6 weeks with vancomycin plus rifampin, adding gentamicin for first 2 weeks 1
- Native valve endocarditis: 6 weeks with vancomycin 1
- Persistent or complicated infections: extend duration based on clinical response, potentially requiring several weeks 5