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Lack of mecA transcription in slime-negative phase variants of methicillin-resistant Staphylococcus epidermidis
M Mempel1, H Feucht, W Ziebuhr
1Institute for Medical Microbiology and Immunology, University Hospital Eppendorf, Hamburg, Federal Republic of Germany.
Abstract:
Five phase variants (PV1 to PV5) of the well-characterized, slime-producing, methicillin-resistant, pathogenic strain of Staphylococcus epidermidis sensu strictu RP62A (ATCC 35984) were isolated by the Congo red agar method. In comparison with the parent strain, the phase variants showed a different colonial morphology on Congo red agar, a strongly reduced adherence capacity, and decreased levels of resistance to methicillin, oxacillin, and penicillin. All phase variants yielded biochemical reaction patterns and profiles in pulsed-field gel electrophoresis identical to those of parent strain RP62A, indicating a common origin. All phase variants proved to have the capacity to shift back to the original phenotype of parent strain RP62A. A search for the resistance mechanisms of strain RP62A revealed beta-lactamase production and the presence of mecA in PV1 to PV5 as well as parent strain RP62A. In Northern blots of total staphylococcal RNA, the phase variants showed no detectable mecA-specific transcription product, whereas parent strain RP62A revealed a strong signal, indicating that mecA transcription is not the mechanism responsible for the decreased methicillin resistance phenotype of phase variants PV1 to PV5.
Insights
Phase variants of Staphylococcus epidermidis RP62A exhibit reduced antibiotic resistance and adherence. These variants, while sharing genetic profiles with the parent strain, do not show mecA transcription, suggesting alternative resistance mechanisms.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Antimicrobial Resistance
Background:
- Staphylococcus epidermidis RP62A is a well-characterized, slime-producing, pathogenic strain.
- Methicillin resistance is a significant concern in Staphylococcus epidermidis infections.
Purpose of the Study:
- To investigate the characteristics of phase variants of Staphylococcus epidermidis RP62A.
- To understand the mechanisms behind altered phenotypes in these variants, particularly concerning antibiotic resistance.
Main Methods:
- Isolation of phase variants using the Congo red agar method.
- Phenotypic characterization including colonial morphology, adherence capacity, and antibiotic resistance profiling.
- Genotypic analysis using pulsed-field gel electrophoresis and biochemical reactions.
- Investigation of resistance gene transcription via Northern blot analysis.
Main Results:
- Five phase variants (PV1-PV5) were isolated, displaying altered colonial morphology, reduced adherence, and decreased resistance to methicillin, oxacillin, and penicillin compared to the parent strain.
- All variants shared identical biochemical and pulsed-field gel electrophoresis profiles with the parent strain, indicating a common origin and the ability to revert to the parent phenotype.
- Both parent and phase variants possessed beta-lactamase production and the mecA gene, but only the parent strain showed detectable mecA transcription.
Conclusions:
- Phase variants of Staphylococcus epidermidis RP62A exhibit a distinct phenotype with reduced antibiotic resistance and adherence.
- The decreased methicillin resistance in phase variants is not due to the absence of the mecA gene but rather a lack of its transcription.
- Further investigation is needed to elucidate the precise mechanisms underlying the reduced antibiotic resistance in these Staphylococcus epidermidis phase variants.