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In vitro resistance to platelet microbicidal protein correlates with endocarditis source among bacteremic
1Department of Microbiology, California State University, Long Beach 90840.
Abstract:
Traditionally, platelets have been thought to contribute to the induction and propagation of infective endocarditis (IE). However, recent studies suggest that platelets may potentially mitigate IE via secretion of alpha-granule-derived platelet microbicidal protein (PMP). In this study, we compared the PMP susceptibility of bacteremic isolates from patients with and without IE. Isolates of Staphylococcus aureus (n = 17), coagulase-negative staphylococci (CNS; n = 28), viridans streptococci (VS; n = 54), and Enterococcus faecalis (n = 20), each at a final inoculum of 2 x 10(3) CFU/ml, were exposed to PMP [100 U/ml, (5 micrograms/ml)] for 2 h, and the percent survival was determined. For S. aureus, CNS, and VS isolates, there was a significant correlation between an IE source and increased percent survival post-PMP exposure; the mean percent survivals of S. aureus, CNS, and VS were significantly greater for IE versus non-IE isolates (P < 0.005 for each organism). No significant correlation was observed between the source of bacteremic E. faecalis isolates and PMP susceptibility. These data suggest that staphylococcal and VS (but not enterococcal) resistance to PMP may facilitate either the induction or progression of IE.
Insights
Platelet microbicidal protein (PMP) resistance in Staphylococcus aureus and viridans streptococci may drive infective endocarditis (IE). Enterococcus faecalis resistance did not correlate with IE, suggesting varied roles in this infection.
Area of Science:
- Microbiology
- Immunology
- Cardiovascular Medicine
Background:
- Platelets were traditionally implicated in infective endocarditis (IE) development.
- Emerging evidence suggests platelets may protect against IE through platelet microbicidal protein (PMP).
Purpose of the Study:
- To investigate the susceptibility of bacterial isolates from IE and non-IE patients to PMP.
- To determine if PMP resistance correlates with infective endocarditis.
Main Methods:
- Bacteremic isolates of Staphylococcus aureus, coagulase-negative staphylococci (CNS), viridans streptococci (VS), and Enterococcus faecalis were exposed to PMP.
- Percent survival of bacterial isolates post-PMP exposure was quantified.
Main Results:
- Staphylococcus aureus, CNS, and VS isolates from IE patients showed significantly higher survival rates post-PMP exposure compared to non-IE isolates.
- Enterococcus faecalis isolates did not exhibit a significant correlation between IE source and PMP susceptibility.
- Increased resistance to PMP was observed in Staphylococcus aureus, CNS, and VS isolates from IE patients.
Conclusions:
- Bacterial resistance to PMP may play a role in the induction or progression of infective endocarditis.
- Staphylococcal and viridans streptococci resistance to PMP could facilitate IE.
- Enterococcal PMP resistance does not appear to be a significant factor in IE.