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Recognition of coagulase-negative Staphylococcus aureus strains by primary polymyxin susceptibility testing
Abstract:
A prospective study evaluating the usefulness of polymyxin susceptibility testing in unveiling coagulase-negative S. aureus strains was undertaken. During a six months study period, 14 staphylococcal isolates from four patients were initially found to lack coagulase activity and to be polymyxin resistant; in comparison, approximately 1500 ordinary, coagulase-positive, polymyxin resistant S. aureus isolates were found during the same period. One isolate from each of the four patients together with a previously isolated coagulase-negative S. aureus strain from our own collection were further characterized. Two of the strains turned out to show delayed coagulase activity on retesting, while the other three strains failed to produce clotting in any coagulase assay. Judged by thermostable nuclease activity, phage typing and biochemical profiles these three coagulase-negative strains are bona fide S. aureus strains. The polymyxin test thus appears to be useful in disclosing S. aureus variants not identified as S. aureus by routinely performed coagulase assays.
Insights
Polymyxin susceptibility testing can identify certain strains of Staphylococcus aureus that standard coagulase tests miss. This method aids in detecting S. aureus variants that might otherwise go unrecognized.
Area of Science:
- Microbiology
- Clinical Diagnostics
- Infectious Diseases
Background:
- Coagulase-negative Staphylococcus aureus (S. aureus) strains can be challenging to identify using standard laboratory methods.
- Accurate identification of S. aureus is crucial for effective patient treatment and infection control.
Purpose of the Study:
- To evaluate the utility of polymyxin susceptibility testing in identifying coagulase-negative S. aureus strains.
- To determine if polymyxin resistance can serve as a marker for S. aureus variants missed by coagulase assays.
Main Methods:
- Prospective study over six months analyzing staphylococcal isolates.
- Isolates initially tested for coagulase activity and polymyxin resistance.
- Selected coagulase-negative, polymyxin-resistant strains further characterized using thermostable nuclease activity, phage typing, and biochemical profiling.
Main Results:
- Fourteen staphylococcal isolates were found to be coagulase-negative and polymyxin-resistant.
- Three of these isolates, confirmed as S. aureus by advanced methods, showed no coagulase activity.
- Polymyxin resistance identified S. aureus variants not detected by routine coagulase testing.
Conclusions:
- Polymyxin susceptibility testing is a valuable tool for detecting S. aureus strains that exhibit atypical coagulase activity.
- This method enhances the identification of S. aureus variants, improving diagnostic accuracy in clinical microbiology.