For Personal Use. Only Reproduce with Permission from the Lancet Publishing Group. Vancomycin-resistant Staphylococcus Aureus: a New Model of Antibiotic Resistance
For Personal Use. Only Reproduce with Permission from the Lancet Publishing Group. Vancomycin-resistant Staphylococcus Aureus: a New Model of Antibiotic Resistance
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K. Hiramatsu
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K. Hiramatsu
Vancomycin has been the most reliable therapeutic agent against infections caused by meticillin-resistant Staphylococcus aureus (MRSA). However, in 1996 the first MRSA to acquire resistance to vancomycin, was isolated from a Japanese patient. The patient had contracted a post-operative wound infection that was refractory to long-term vancomycin therapy. Subsequent isolation of several vancomycin resistant S aureus (VRSA) strains from USA, France, Korea, South Africa, and Brazil has confirmed that emergence of vancomycin resistance in S aureus is a global issue. A certain group of S aureus, designated hetero-VRSA, frequently generate VRSA upon exposure to vancomycin, and are associated with infections that are potentially refractory to vancomycin therapy. Presence of hetero-VRSA may be an important indicator of the insidious decline of the clinical effectiveness of vancomycin in the hospitals. Vancomycin resistance is acquired by mutation and thickening of cell wall due to accumulation of excess amounts of peptidoglycan. This seems to be a common resistance mechanism for all VRSA strains isolated in the world so far. Meticillin-resistant Staphylococcus aureus (MRSA) has occurred in many countries since its discovery in 1961. 1 However, in recent years, clinicians have been concerned by the increased frequency of MRSA infections. 2 This resurging MRSA problem seems to be based on the lack of potent therapeutic agents having an unequivocal cell-killing effect, and thus capable of eliminating MRSA from the patient's body. Increased use of vancomycin—a drug with rather weak cell-killing potency against prevailing MRSA—seems to have set a basis for the selection of vancomycin resistance in MRSA. In 1997, we reported the first MRSA strains with reduced susceptibility to vancomycin, which were isolated from patients in whom vancomycin therapy was ineffective. 3,4 We reported two classes of vancomycin-resistant strains: vancomycin-resistant S aureus (VRSA) that has a vancomycin minimum inhibitory concentration (MIC) of 8 mg/L, and hetero-VRSA that spontaneously generates VRSA within the cell population. The nomenclature is based on the MIC breakpoints of the British Society for Antimicrobial Chemotherapy who define the MIC of 8 mg/L as " resistant. " However according to the National Committee for Clinical Laboratory Standards (NCCLS) breakpoint, these strains are called vancomycin-intermediate S aureus (VISA) or glycopeptide-intermediate S aureus (GISA) in the USA. 5 Although hetero-VRSA is categorised as " susceptible " to vancomycin based on current MIC breakpoints, it generates VRSA cells at a high frequency within its cell population. To date, as well as Japan, VRSA strains have …
