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Scanning electronmicroscopy of Staphylococcus aureus and Enterococcus faecalis exposed to daptomycin
L J Wale1, A P Shelton, D Greenwood
1Department of Microbiology, University Hospital, Queen's Medical Centre, Nottingham.
Abstract:
The novel lipopeptide antibiotic, daptomycin, at a concentration of 8 mg/L, caused gross morphological changes in both a methicillin-sensitive and a methicillin-resistant strain of Staphylococcus aureus and in a strain of Enterococcus faecalis. The earliest (after 1 h) surface lesion observed was the appearance of boss-like processes randomly distributed on the cell surface. Later, grossly deformed bacteria were seen and in two of the three bacteria prolonged exposure led to degeneration of the cells into an amorphous syncytial mass. Omission of calcium (which is known to potentiate the activity of daptomycin) from the culture medium did not affect the morphological response to an inhibitory concentration of the antibiotic.
Insights
The antibiotic daptomycin causes significant cell damage in Staphylococcus aureus and Enterococcus faecalis. This novel lipopeptide antibiotic induces early surface lesions and later cell degeneration, impacting bacterial morphology.
Area of Science:
- Microbiology
- Antibiotic Research
- Cell Biology
Background:
- Daptomycin is a novel lipopeptide antibiotic with potent activity against Gram-positive bacteria.
- Understanding the morphological effects of daptomycin is crucial for its clinical application.
- Staphylococcus aureus (including MRSA) and Enterococcus faecalis are significant human pathogens.
Purpose of the Study:
- To investigate the gross morphological changes induced by daptomycin in key bacterial pathogens.
- To characterize the timeline and nature of daptomycin-induced cellular alterations.
Main Methods:
- Exposure of methicillin-sensitive Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, and Enterococcus faecalis to daptomycin (8 mg/L).
- Microscopic observation of bacterial cell surface and overall morphology over time.
- Assessment of calcium's role in daptomycin's morphological effects.
Main Results:
- Daptomycin induced rapid (1-hour) boss-like surface lesions on bacterial cells.
- Prolonged exposure resulted in grossly deformed bacteria and, in some cases, amorphous syncytial masses.
- The absence of calcium in the culture medium did not alter the observed morphological response.
Conclusions:
- Daptomycin elicits distinct and progressive morphological changes in S. aureus and E. faecalis.
- The antibiotic's mechanism of action involves significant disruption of bacterial cell integrity.
- Calcium potentiation does not appear to be a prerequisite for daptomycin's observed morphological effects.