For full resistance to the streptogramine combination quinupristin-dalfopristin, strains need to carry additional resistance to streptogramin A compounds, which may be mediated by acetylation INCB024360 manufacturer (acetyl transferase genes vat(A), vat(B) and vat(C), or by putative efflux pumps encoded by vga(A) and vga(B)[5, 6]. Tetracycline resistance in staphylococci is either based on the expression of a ribosomal protection factor encoded by the widely disseminated tet(M) gene or mediated by tet(K)
mediated efflux of the antibiotics [7]. For aminoglycoside resistance, the presence of aminoglycoside – modifying enzyme genes aac(6′)-aph (2″), aph(3′)-IIIa and ant(4′)-Ia has been analysed. The most frequently encountered gene in staphylococci
is the aac(6′)-aph(2″) which codes for a bifunctional enzyme and confers resistance to gentamicin, tobramycin, kanamycin and when over-expressed to amikacin but not to streptomycin [8]. For the quinolones such as ciprofloxacin and pefloxacin, a main mechanism of resistance is the spontaneous accumulation of mutations in the genes encoding subunits of the DNA gyrase (gyrA and parC) [9]. Other important antimicrobials include chloramphenicol and co-trimoxazole (trimethoprim + sulphamethoxazole). Resistance to chloramphenicol is mainly mediated by the catA gene which is responsible for the chloramphenicol acetyl Acalabrutinib transferase while co-trimoxazole resistance is due to mutations of the enzyme dihydrofolate reductase encoded by the dhfr gene [10]. Methicillin resistance in staphylococci is mainly due to the expression of the mecA gene, which specifies penicillin binding protein 2a (PBP2a), a transpeptidase with a low affinity for β-lactams
[11]. mecA is located on a 21-to 67-kb mobile genetic element (MGE) called Staphylococcal Chromosome Cassette mec (SCCmec) [11, 12]. Different SCCmec elements in staphylococci have been classified and characterized according to the combination of two parts: the ccr complex and the mec complex. Cassette chromosome recombinase (ccr) genes (ccrC or the pair of ccrA and ccrB) encode recombinases that mediate integration and excision of SCCmec into and from the chromosome [12–14]. The ccr gene(s) form the ccr gene complex. The mec gene complex on the other hand, consists of mecA, mecR1 and mecI regulatory Carnitine palmitoyltransferase II genes and associated insertion sequences and has been classified into six different classes: A, B, C1, C2, D and E [13, 14]. The regions located between these complexes are called J (joining) regions. In every SCCmec elements there are three of these regions (J1-J3) and polymorphisms in the regions are used for the definition of SCCmec type IV subtypes [15]. In addition to ccr and mec gene complexes and J regions, SCCmec contains a few other genes or pseudogenes that does not appear to be essential to the bacterial cell with exceptions including various other MGE, e.g.
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