ABSTRACT
Introduction ........................................................................................................ 255 Resistance to Antibiotics Active on the Cell Wall or Cell Membrane .............. 256
β-Lactam Antibiotics .............................................................................. 256 Target-Based Resistance: Low-Af nity Penicillin-Binding
Proteins ........................................................................... 256 Resistance in Enterococcus faecium ........................................... 257 β-Lactamase Production .............................................................. 259
Glycopeptides ......................................................................................... 259 Phenotypic Descriptions of Glycopeptide Resistance Classes .... 260 Genotypic Classi cation of Glycopeptide Resistance ................. 261
Resistance to Lipopeptide Antibiotics .................................................... 264 Resistance to Agents Acting on the Bacterial Ribosome .................................. 265
Aminoglycosides .................................................................................... 265 Resistance to Synergistic Killing ................................................. 265
Macrolides, Lincosamides, and Streptogramins .................................... 268 Macrolides .................................................................................... 268 Lincosamides ............................................................................... 269 Streptogramins ............................................................................. 270
Chloramphenicol .................................................................................... 271 Tetracyclines ........................................................................................... 271 Oxazolidinones ....................................................................................... 272
Resistance to Fluoroquinolones ......................................................................... 273 Conclusions ........................................................................................................ 273 References .......................................................................................................... 274
Enterococcal infections can be among the most challenging problems encountered in the practice of clinical infectious diseases. The Enterococcus is the third most common pathogen causing left-sided, native valve infective endocarditis, after streptococci and Staphylococcus aureus [1]. Because enterococci are typically resistant to killing by penicillins or glycopeptides alone [2], successful treatment has usually
required combinations of cell wall-active agents with aminoglycosides that achieve synergistic bactericidal activity in vitro [3]. Such regimens, when they can be employed, may be associated with signi cant toxicities. However, in some cases, resistance to either the cell wall antibiotic or to the aminoglycoside, or to both components, can preclude the possibility of even attaining bactericidal synergism with such combination regimens [4].