Related Experiment Videos
[Methicillin-resistant Staphylococcus aureus forming the fried egg appearance colonies isolated from a patient with
A Tanimoto1, Y Kitagaki, M Hiura
1Department of Clinical Laboratory, Tottori University Hospital, Yonago.
Abstract:
Slower growing and peculiar colonies, "fried egg" appearance, of different sizes were temporally grown on a sheep blood agar plate from a clinical blood sample obtained from a patient with mediastinitis due to infection by methicillin-resistant Staphylococcus aureus (MRSA) following the graft replacement of thoracic aorta. The organisms revealed morphologically characteristic "fried egg" appearance, mainly Gram-positive cocci including some Gram-negative cells and cell-debris, catalase test positive and coagulase test positive as well as having the identical profiles for S. aureus on biochemical examination with VITEK Systems. The rough surfaced cell walls with unequal thickness of the organisms were observed in an electronmicroscope. According to these bacteriological studies, the organisms were identified as a mutant of S. aureus which had many similarities to staphylococcal L-form. Being resistant to oxacillin, instead of methicillin susceptibility test, and possessing a mecA gene, the organisms were confirmed to belong to MRSA. It is likely that this mutant of S. aureus was induced by a long term medication of sulfamethoxazole-trimetoprim, since the patient had been receiving the drug during 5 weeks when the colonies were first detected.
Insights
This study identified a unique mutant of methicillin-resistant Staphylococcus aureus (MRSA) exhibiting L-form characteristics. This MRSA strain, found in a patient with mediastinitis, may have been induced by prolonged sulfamethoxazole-trimethoprim treatment.
Area of Science:
- Microbiology
- Infectious Diseases
- Bacterial Genetics
Background:
- A patient with mediastinitis post-aortic graft replacement developed an unusual infection.
- The infection was caused by methicillin-resistant Staphylococcus aureus (MRSA).
Observation:
- Slower-growing colonies with a characteristic "fried egg" appearance were cultured from blood samples.
- Microscopic examination revealed Gram-positive cocci, some Gram-negative cells, and cell debris.
- Electron microscopy showed rough cell walls of unequal thickness.
Findings:
- Biochemical tests and VITEK Systems confirmed the organism as Staphylococcus aureus.
- The isolate exhibited characteristics similar to staphylococcal L-forms.
- Genetic analysis confirmed the presence of the mecA gene, identifying it as MRSA.
- Resistance to oxacillin was noted, differentiating it from standard methicillin susceptibility testing.
Implications:
- This case highlights a potential drug-induced mutation in MRSA, possibly linked to sulfamethoxazole-trimethoprim.
- Understanding such bacterial adaptations is crucial for managing persistent infections.
- The findings suggest a need for vigilance regarding antimicrobial-induced resistance mechanisms.