Does Keflex Cover Staphylococcus lugdunensis?
Yes, Keflex (cephalexin) provides excellent coverage for methicillin-susceptible Staphylococcus lugdunensis, as this organism is uniformly susceptible to first-generation cephalosporins and behaves clinically like methicillin-susceptible S. aureus (MSSA). 1, 2
Microbiological Activity
- S. lugdunensis is a coagulase-negative staphylococcus that is typically methicillin-susceptible and acts similarly to S. aureus in terms of virulence and antibiotic susceptibility 1
- First-generation cephalosporins like cephalexin demonstrate good activity against methicillin-susceptible staphylococcal species, including S. lugdunensis 2, 3
- Unlike other coagulase-negative staphylococci, S. lugdunensis remains susceptible to most antibiotics, with methicillin resistance still rare 4
- Penicillinase-resistant penicillins (flucloxacillin, dicloxacillin) and first-generation cephalosporins (cefazolin, cephalexin) are appropriate therapeutic options for methicillin-susceptible staphylococcal infections 5
Clinical Application
- For mild-to-moderate skin and soft tissue infections caused by S. lugdunensis, cephalexin 500 mg orally every 6 hours for 5 days is appropriate 2, 6
- The WHO Essential Medicines guidelines list cephalexin as a first-choice agent for mild skin and soft tissue infections commonly caused by staphylococcal species 2
- Cephalexin achieves cure rates of 90% or higher for staphylococcal skin infections and remains effective after decades of clinical use 7
Critical Caveat: Methicillin Resistance
- This recommendation applies ONLY to methicillin-susceptible S. lugdunensis—if methicillin resistance is suspected or confirmed, alternative agents such as vancomycin, linezolid, or daptomycin must be used 2
- Although methicillin-resistant strains carrying the mecA gene are rare in S. lugdunensis, they do occur and would render cephalexin ineffective 4
- Despite in vitro susceptibility results, methicillin-resistant coagulase-negative staphylococci exhibit cross-resistance to cephalosporins, making these agents clinically ineffective 1
Special Considerations for Severe Infections
- S. lugdunensis causes a substantially more virulent form of infective endocarditis with high rates of perivalvular extension and metastatic infection 1
- For severe or invasive S. lugdunensis infections (such as endocarditis), intravenous therapy with cefazolin or an anti-staphylococcal penicillin (nafcillin, oxacillin) is recommended rather than oral cephalexin 2
- The standard regimen for methicillin-susceptible staphylococcal endocarditis includes a semisynthetic β-lactamase-resistant penicillin (nafcillin or oxacillin) intravenously for 4-6 weeks, with cefazolin as an alternative 1
- S. lugdunensis is always methicillin-susceptible and can be treated with cloxacillin according to European guidelines 1
Common Pitfalls to Avoid
- Do not assume all coagulase-negative staphylococci are low-virulence organisms—S. lugdunensis requires the same aggressive treatment approach as S. aureus 1
- Do not use cephalexin for catheter-related bloodstream infections caused by S. lugdunensis, as these infections manifest with prominent symptomatology similar to S. aureus-associated CLABSI and require parenteral therapy 1
- Microbiological differentiation of S. lugdunensis requires specific biochemical assays; initial screening can be done with pyrrolidonyl aminopeptidase hydrolysis testing 1