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Isolation of Staphylococcus aureus from sputum in cystic fibrosis
Abstract:
The success in the isolation of Staphylococcus aureus of different methods of sputum processing was investigated in 60 specimens collected from 14 patients with cystic fibrosis during a seven-month period. Fifty specimens (83%) from 11 patients yielded Staph. aureus by one or more methods. Direct plating of purulent portions of sputum on to media designed for general use in respiratory infections gave unsatisfactory results (35% yield of Staph. aureus). Some increase in isolations was obtained with preliminary liquefaction of sputum; but the best results were given by the addition of a medium selective for staphylococci (mannitol salt agar, BBL) or by initial sonication of sputum (each 83% yield). Seven of the 11 strains of Staph. aureus were thymidine-dependent and otherwise atypical in laboratory characteristics; these were isolated from patients who had received co-trimoxazole.
Insights
Detecting Staphylococcus aureus in cystic fibrosis patients is crucial. Sputum sonication or mannitol salt agar significantly improved Staphylococcus aureus isolation rates compared to direct plating.
Area of Science:
- Microbiology
- Clinical Diagnostics
- Infectious Diseases
Background:
- Staphylococcus aureus is a common pathogen in cystic fibrosis patients.
- Accurate isolation of Staphylococcus aureus from sputum is essential for effective treatment.
- Current sputum processing methods may not be optimal for Staphylococcus aureus detection.
Purpose of the Study:
- To evaluate the efficacy of different sputum processing methods for isolating Staphylococcus aureus.
- To compare direct plating, liquefaction, selective media, and sonication techniques.
Main Methods:
- Sixty sputum specimens from 14 cystic fibrosis patients were analyzed.
- Methods included direct plating, preliminary liquefaction, addition of mannitol salt agar, and initial sonication.
- Isolation rates of Staphylococcus aureus were compared across methods.
Main Results:
- Overall, 83% of specimens yielded Staphylococcus aureus using optimized methods.
- Direct plating showed a low yield (35%).
- Mannitol salt agar and sonication achieved the highest isolation rates (83% each).
- Atypical, thymidine-dependent Staphylococcus aureus strains were isolated from patients treated with co-trimoxazole.
Conclusions:
- Sonication or mannitol salt agar are superior methods for Staphylococcus aureus isolation from cystic fibrosis sputum.
- Atypical Staphylococcus aureus strains may be associated with co-trimoxazole treatment.
- Optimized diagnostic methods are vital for managing Staphylococcus aureus infections in cystic fibrosis.