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Implications of acquired oxacillin resistance in the management and control of Staphylococcus aureus infections
R M Massanari1, M A Pfaller, D S Wakefield
1Department of Internal Medicine, University of Iowa College of Medicine.
Abstract:
Refinements in testing for resistance to penicillinase-resistant penicillins (PRP) in Staphylococcus aureus have resulted in confusion in classifying isolates as PRP susceptible or resistant. Specifically, a group of organisms has been identified that produce large amounts of beta-lactamase and appear borderline resistant. These organisms have been called "occult resistant" or "acquired oxacillin-resistant" S. aureus (AORSA). A retrospective study was conducted to evaluate the implication of this in vitro phenomenon in managing patients with AORSA infections. Among 134 patients with S. aureus infections, 89 were infected with oxacillin-susceptible S. aureus (OSSA), 26 with AORSA, and 19 with oxacillin-resistant S. aureus (ORSA). There were no significant differences in outcomes when OSSA and AORSA infections were treated with PRP (chi 2MH = .990; P = .32). These results do not suppor the contention that AORSA infections should be managed differently from OSSA infections. Identifying AORSA may not be helpful in guiding antimicrobial therapy or predicting the outcome of infections with AORSA.
Insights
Newly identified "occult resistant" Staphylococcus aureus (AORSA) strains do not require different treatment than susceptible strains. Penicillinase-resistant penicillin treatment outcomes were similar for both acquired oxacillin-resistant S. aureus and oxacillin-susceptible S. aureus infections.
Area of Science:
- Microbiology
- Infectious Diseases
- Clinical Medicine
Background:
- Refined testing for penicillinase-resistant penicillins (PRP) in Staphylococcus aureus has led to classification challenges.
- A subset of S. aureus isolates, termed "occult resistant" or acquired oxacillin-resistant S. aureus (AORSA), produce high levels of beta-lactamase and exhibit borderline resistance.
Purpose of the Study:
- To retrospectively evaluate the clinical implications of AORSA in patient management.
- To determine if AORSA infections necessitate different therapeutic strategies compared to oxacillin-susceptible S. aureus (OSSA) infections.
Main Methods:
- Retrospective analysis of 134 patients with S. aureus infections.
- Categorization of isolates into OSSA (n=89), AORSA (n=26), and oxacillin-resistant S. aureus (ORSA) (n=19).
- Comparison of patient outcomes based on infection classification and PRP treatment.
Main Results:
- No statistically significant difference in clinical outcomes was observed between patients with OSSA and AORSA infections treated with PRP (P = .32).
- The study identified no significant variations in treatment efficacy or patient outcomes when comparing OSSA and AORSA infections.
Conclusions:
- The findings do not support the management of AORSA infections differently from OSSA infections.
- Identifying AORSA may not be clinically beneficial for guiding antimicrobial therapy or predicting infection outcomes.