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Evolutionary and ecological significance of colonization with multiple strains of Staphylococcus aureus in healthy carriers

English title Evolutionary and ecological significance of colonization with multiple strains of Staphylococcus aureus in healthy carriers
Applicant Sakwinska Olga
Number 118814
Funding scheme Marie Heim-Voegtlin grants
Research institution Département de Microbiologie Fondamentale Faculté de Biologie et de Médecine Université de Lausanne
Institution of higher education University of Lausanne - LA
Main discipline Ecology
Start/End 01.09.2007 - 31.08.2009
Approved amount 172'405.00
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All Disciplines (2)

Discipline
Ecology
Infectious Diseases

Keywords (4)

co-infection; co-colonization; virulence; mixed infections

Lay Summary (English)

Lead
Lay summary
Staphylococcus aureus is a major human pathogen causing a variety of infections. It can also be carried asymptomatically by healthy people. Although methicillin resistant Staphylococcus aureus (MRSA), a dangerous nosocomial pathogen, has been known since the sixties, the existence of SCCmecA (staphylococcal cassette chromosome containing mecA gene) was discovered only recently.The extent, frequency and consequences of SCCmecA acquisition by S. aureus remain poorly understood. SCCmecA is a dynamic structure with parts of phylogenetically distant and/or unknown origin, where recombination, deletions and insertions happen much more frequently than in other parts of the genome. The contribution of mobility of SCCmecA and its fitness burden to appearance and success of MRSA will be investigated. The comparison of S. aureus collected from healthy carriers with the hospital-associated strains suggests that loss and acquisition SCCmecA in S. aureus happens much more frequently than previously thought. The magnitude of fitness costs associated with the presence of different types of SCCmecA will be investigated by comparing fitness of pairs of closely related strains which differ in the presence of SCCmecA as well as strains with laboratory-excised SCCmecA. Combining the phylogenetic analysis of SCCmecA acquisition and loss and laboratory experiments on bacterial fitness will allow identifying which factors are the most important for the success of MRSA. It might also help to decide where to focus the efforts to limit this dangerous pathogen.The diversity and availability of SCCmecA which are not (yet) part of the gene pool of S. aureus are very likely to play a crucial role in the ongoing and future evolution of MRSA. S. epidermidis, a part of a normal skin flora, nearly always co-occurs with S. aureus. Very likely, it is a major source of SCCmecA for S. aureus. Preliminary determination of the presence of SCCmecA in S. epidermidis confirmed isolated observations that around 25% of S. epidermidis strains carried by healthy humans are mecA positive. It means that around 5% of healthy humans carry S. aureus together with S. epidermidis harbouring SCCmecA. Moreover, SCCmecA in S. epidermidis shows considerable mobility and diversity, also even in a single carrier. More precise analysis of the composition of SCCmecA will be carried out and followed by comparison with SCCmecA from MRSA.
Direct link to Lay Summary Last update: 21.02.2013

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Associated projects

Number Title Start Funding scheme
106195 Evolutionary and ecological significance of colonization with multiple strains of Staphylococcus aureus in healthy carriers 01.09.2005 Marie Heim-Voegtlin grants

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