Download staphylococcus epidermidis as the founder species of sccmec iv?

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STAPHYLOCOCCUS EPIDERMIDIS AS THE FOUNDER SPECIES OF SCCMEC IV?
J. Rolo1, M. Miragaia1, H. de Lencastre1,2
1
Laboratory of Molecular Genetics, Instituto de Tecnologia Química e Biológica (ITQB) / Universidade Nova de Lisboa, Oeiras,
2
Portugal, Laboratory of Microbiology, The Rockefeller University, New York, NY, USA
Background: Methicillin-resistant Staphylococcus epidermidis (MRSE) is one of the main nosocomial human pathogens.
Resistance to methicillin is conferred by the mecA gene, which is carried by a mobile genetic element called the staphylococcal
chromosomal cassette mec (SCCmec). Mobility of SCCmec is achieved through site-specific recombinases that promote the
transfer of SCCmec between different staphylococcal strains and species. SCCmec type IV is the most frequent type both in
MRSE and in community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA).
Objective: In this study our aim was to evaluate if S. epidermidis was the founder species of SCCmec IV.
Methods: In order to achieve this aim, a well characterized and genetically diverse collection of 99 methicillin-susceptible S.
epidermidis (MSSE) and six MRSE isolated from 822 draftees as well as 22 hospital-associated MSSE (HA-MSSE) were tested
for the presence of ccr genes by PCR and Southern hybridization. SCCmec typing and subtyping was carried out by multiplex
PCR. Allelic variation of ccrB was evaluated by ccrB typing. Long-range PCR was used to verify the pro ximity of structural
regions inside SCC.
Results: Five out of six MRSE strains carried several different SCCmec IV subtypes. Interestingly, we found that 20% of the
MSSE carried ccrAB2. The ccrB2 allotypes carried by MSSE strains have very high homology (96-100%) with ccrB from S.
aureus SCCmec IV. In addition, we found five HA-MSSE strains with the J1 region typical of SCCmec IVh linked to ccrB2.
Conclusions: Our results suggest that ccrAB2 is a native gene of S. epidermidis that in HA-MSSE is linked to a structural
region typical of SCCmec IV. Moreover, we confirmed that SCCmec IV is common among CA- and HA-MRSE. Altogether,
these data strongly support the hypothesis that SCCmec IV was first assembled in HA-MSSE and later transferred to other
staphylococcal species.