Prevalence of a cefazolin inoculum effect associated with blaZ gene types, and clinical outcomes among methicillin-susceptible Staphylococcus aureus blood isolates of patients with infective endocarditis - 28/10/22
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Highlights |
• | Cefazolin inoculum effect was present in 18% of S. aureus strains from endocarditis. |
• | Cefazolin minimum inhibitory concentrations remained generally low at high inoculum. |
• | Type A beta-lactamase was the most frequently detected. |
• | No association between cefazolin inoculum effect and clinical failure was found. |
Abstract |
Objectives |
A proportion of blaZ gene-positive methicillin-susceptible Staphylococcus aureus (MSSA) strains exhibits the cefazolin inoculum effect (CInE). Its clinical impact remains uncertain but could compromise the use of cefazolin in high-burden infections. To date, no study has been conducted in France or in Europe. We aimed to assess the prevalence of CInE and its association with blaZ beta-lactamase and S. aureus protein A (spa) types, and to assess the clinical outcomes in cefazolin-treated patients for infective endocarditis whose strain exhibited a CInE.
Methods |
This was a French single-center retrospective study of 51 MSSA strains from patients of the Nantes endocarditis prospective cohort, conducted between 2013 and 2018.
Results |
Cefazolin MIC50 at high inoculum was 2 mg/L (IQR 1–2). CInE was found in 17.6 % of tested strains. Among blaZ-positive strains (n = 44), type A beta-lactamase was predominant (n = 25, 57 %). Thirty-seven S. aureus protein A (spa) types were found. No statistical association was shown between blaZ or spa types and CInE. CInE was neither associated with a higher rate of persistent bacteremia (25 % vs 56.3 %, p = 0.58) nor with clinical failure in patients treated with cefazolin, in comparison to patients with no CInE strain (25 % vs 56.3 %, p = 0.58).
Conclusion |
The cefazolin inoculum effect was found in a substantial number of Staphylococcus aureus strains; however, minimum inhibitory concentrations remained globally low. CInE was not associated with a higher proportion of clinical failure on treatment.
Le texte complet de cet article est disponible en PDF.Keywords : Staphylococcus aureus, Cefazolin, Infective endocarditis, Inoculum effect, Minimum inhibitory concentration
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