In this work, a fully antibiotic-susceptible S. aureus EPs, including the proton motive force uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP), the alkaloid reserpine, as well as different members of the phenothiazines, among others. In order to find specific inhibitors of these pumps or simply to demonstrate the presence of efflux activity, different compounds have been tested for their ability to hinder the activity of S. 9–11 Although these pumps show different substrate specificity, most of them are capable of extruding compounds of different chemical classes, thus providing the cell with the means to develop a multidrug resistance (MDR) phenotype or to survive in a hostile environment. aureus such as MepA, a member of the multidrug and toxic compound extrusion family, as well as Smr, which belongs to the small multidrug resistance (SMR) family, and SepA. 3–8 Other types of pumps have also been described for S. 2 Most of these pumps belong to the major facilitator superfamily, namely the chromosomally encoded NorA, NorB, NorC, MdeA and SdrM as well as the plasmid-encoded QacA/B pumps. To date, more than 10 efflux pumps (EPs) have been described for S. 1 On the other hand, antibiotic resistance based on efflux systems capable of extruding the drug or other noxious agents from the cell is less well characterized for these bacteria. Several of these mechanisms are well known, and have been characterized: resistance to β-lactam antibiotics mediated by PBP2a, encoded by the mecA gene, or resistance to fluoroquinolones resulting from mutations in either topoisomerase IV or gyrase genes. Besides its pathogenic potential, this bacterium also shows many different mechanisms of resistance towards antibiotics. Staphylococcus aureus is one of the most common human pathogens, being responsible for a wide variety of infections, many of which can be life-threatening. Staphylococci, efflux pumps, NorA, overexpression Introduction
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