Glycopeptides and Lipoglycopeptides

The glycopeptide and lipoglycopeptide antibiotics are natural antibiotics obtained from cultures of certain microorganisms. These antibiotics inhibit bacterial cell wall peptidoglycan synthesis but cannot cross the cell wall of gram-negative bacteria. Their antibacterial spectrum includes aerobic and anaerobic gram-positive bacteria. The glycopeptides may be divided into at least five groups on the basis of their chemical structures. Due to their large mass, glycopeptides cannot cross the lipoprotein cell wall of gram-negative bacteria and are therefore totally inactive against them. The molecules belonging to group II (Avoparcin Type) are mainly actinodin, avoparcin, chloropolysporin, galacardin, helvecardin, and synmonicin. Resistance to vancomycin and teicoplanin is due to synthesis of modified precursors that display decreased affinity for both compounds. Six types of resistance have been reported to date: VanA, VanB, VanC, VanD, VanE, and VanG. The combination of a glycopeptide with an aminoglycoside is synergistic against the majority of strains of staphylococci and enterococci. The in vitro activity of dalbavancin was investigated by following NCCLS-recommended methods and comparatively with vancomycin, linezolid, and quinuprisitin-dalfoprisitin (Q-D).