Zbigniew Ochocki, Andrzej Stańczak
Peptide antibiotics. Over the past decade, levels of bacterial resistance to antibiotics have risen dramatically and "superbugs" resistant to most or all available agents have appeared in the clinic. One potential source of novel antibiotics are the antimicrobial peptides, which have been isolated from most living entities as components of their non-specific defenses against infectious organisms. Peptide antibiotics are complexes of heterocyclic molecules consisting of a peptide backbone to which are attached various substituted sugars. Glycopeptides are too bulky to penetrate the external membrane of Gram-negative bacteria, so the spectrum of activity is generally restricted to Gram-positive organisms. Acquired resistance used to be uncommon, but resistant strains of enterococci are now widely prevalent and staphylococci exhibiting reduced susceptibility are causing concern. For example Vancomycin is the compound widely used for the treatment of infections caused by staphylococci that are resistant to methicillin and other b-lactam antibiotics, and for serious infections with Gram-positive organisms in patients who are hypersensitive to penicillin. Polymyxins are cationic detergent antibiotics, with a general structure of a cyclic peptide with a long hydrophobic tail. Some of them as bacitracin and polymyxins are toxic to humans and are used externally only. At present there are two structurally novel classes of antibiotics entering the clinic ? the lipopeptide daptomycin and the streptogramins.