Dissemination among staphylococci of DNA sequences associated with methicillin resistance

Abstract

DNA probes consisting of pUC19 containing cloned Staphylococcus aureus chromosomal fragments were constructed from two methicillin-resistant S. aureus strains with diferent DNA sequences 5' to mecA, the gene that mediates methicillin resistance. The probe from one strain, BMS1, contained a portion of the regulatory sequences (the terminal 641 bp of mecRI and all of mecI) associated with the induction and repression of mecA transcription (pGO195). The second probe, from strain COL (pGO198), contained DNA not found in strain BMS1. This DNA was within the sequences added at the site of a mecRI deletion. epidermidis and all 20 S. haemolyticus isolates had from 5 to more than 20 additional chromosomal bands that hybridized with pGO198; none of 21 S. aureus isolates had additional hybridizing bands. These data suggest that the additional DNA responsible for the mecRi deletion was part of a repetitive, and possibly mobile, element resident in coagulase-negative staphylococci but not in S. aureus. These data also support a hypothesis that the deletion event occurred in a coagulase-negative staphylococcus with subsequent acquisition of the interrupted sequences by S. aureus.

Epidemiology of Emerging Methicillin-Resistant Staphylococcus aureus (MRSA) in Denmark: a Nationwide Study in a Country with Low Prevalence of MRSA Infection

“…CA-MRSA clones may have emerged as the result of successive genetic events that involve the acquisition of PVL genes and the type IV SCCmec (or other small SCCmec cassettes, such as the recently described SCCmec type V [20]), most likely from coagulasenegative staphylococci indigenous to the skin flora, as previously proposed by others (6,22).…”

The evolutionary history of methicillin-resistant Staphylococcus aureus (MRSA)

“…The ccr and mec genes that are the basis of SCCmec typing are thought to have first been introduced into coagulase-negative staphylococci (4,26,27) from an unknown source, where deletion of the mec regulatory genes occurred, and then into S. aureus. It is unclear which staphylococcal species donated the four SCCmec types found among MRSAs, but the presence of four types suggests multiple introductions into S. aureus, and their presence in the same ST indicates that horizontal transfer of mec genes is relatively frequent within S. aureus.…”

“…For isolates outside the box not all SLVs are shown. ST250 -MSSA isolates were not present in our collection but have been described (26).…”

One ring to rule them all: Current trends in combating bacterial resistance to the β‐lactams

“…Expression of mecA is induced in the presence of blactams by the mec pathway (or in its absence by the analogous bla pathway 48,49 ), which consists of a transmembrane sensor/transducer protein located in the cytoplasmic membrane (MecR1) that binds blactam, resulting in de-repression of the mecA gene by cleavage of the mecI repressor (reviewed in Ref. 50).…”