Molecular Characterization

Methicillin resistance in S. aureus and other staphylococci is caused by the production of penicillin-binding protein 2a (PBP2a, also known as PBP2'), a novel 78-kilo Dalton penicillin-binding protein encoded by the mecA gene.[10] PBP2a, along with PBPs normally produced by S. aureus, are enzymes that catalyze peptidoglycan cross-linking reactions in the bacterial cell wall, resulting in a rigid structure that protects the bacterium against osmotic cell lysis and death.[10] However, PBP2a is distinct from putative S. aureus PBPs in that it has a low binding affinity for ß-lactam antibiotics, resulting in continued cell wall synthesis, albeit not as efficiently, at ß-lactam concen trations that would otherwise be lethal.[10] Nevertheless, mecA expression—and hence PBP2a production—is variable, being regulated by at least 20 additional genes of known or unknown function.[10,17,18] Two particularly important regulatory genes are located adjacent to the mecA locus, namely, mecRl (encoding a membrane-bound signal transducer/inducer protein triggered by the presence of p-lactam antibiotic) and mecl (encoding a mecA transcription repressor protein), which make up the mec regulatory gene system, and, together with mecA, form the mec gene complex (of which there are two configurations in MRSA, designated type A or B).[18] These complexes, in turn, are located on a recently described large (21-67 kb) mobile genetic element, termed the staphylococcal cassette chromosome mec (SCCmec), which, via its cassette chromosome recombinase A and B (ccrA and ccrB) genes, integrates into the S. aureus chromosome at a specific location near the origin of replication.[7,18] These two ccr genes form part of a ccr gene complex, of which there are three types.[7,18] There are five types of SCCmec element, based on their overall genetic composition, including the type of mec and ccr gene complex they carry.[7,18] These elements function as antibiotic resistance islands and are responsible for the horizontal transmission of resistance to methicillin and other non-p-lactam anti

Table 2 Oligonucleotides used for molecular beacon probe-based real-time multiplex PCR

Target gene

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

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