Our fax numbers: 617-739-9864 and 617-734-4457Our e-mail address: letters@nejm.orgWe cannot acknowledge receipt of your letter, but we will notify you when we have made a decision about publication. We are unable to provide prepublication proofs. Financial associations or other possible conflicts of interest must be disclosed. Submission of a letter constitutes permission for the Massachusetts Medical Society, its licensees, and its assignees to use it in the Journal' s various print and electronic publications and in collections, revisions, and any other form or medium. 1 report that adjuvant chemotherapy with fluorouracil is as effective in older patients with resected colon cancer as it is in younger patients. Their conclusion is based on the absence of a statistically significant interaction between age and treatment effect for both overall and disease-free survival. However, the survival curves for treated and untreated patients who were more than 70 years old seem closer than the curves for treated and untreated younger patients. In our opinion, the absolute gain in survival is the measure that should be discussed with patients when deciding whether to use an adjuvant treatment. We suspect that the absolute differences in the study by Sargent et al. were small, and we would like to know what the absolute gain in survival was at each year of follow-up. 1. Nauta R, Stablein DM, Holyoke ED. Survival of patients with stage B2 colon carcinoma: the Gastrointestinal Tumor Study Group experience. Arch Surg 1989;124:180-2. 2. Gastrointestinal Tumor Study Group. Adjuvant therapy for colon cancerresults of a prospectively randomized trial. N Engl J Med 1984;310:737-43.To the Editor: Sargent et al. state that elderly persons receive adjuvant chemotherapy less frequently than younger patients, citing rates of chemotherapy use from a study that linked 1992 data from the Surveillance, Epidemiology, and End Results (SEER) Program with Medicare data for 1992. 1 However, two more recent studies of SEER-Medicare data report rates of use of adjuvant chemotherapy among elderly persons with stage III colon cancer that are considerably higher than the rates reported by Sargent et al. 2,3 With the use of data from 1992 to 1996, these studies showed that the rate of adjuvant-chemotherapy use wasThe New England Journal of Medicine Downloaded from nejm.org at STOCKHOLMS UNIVERSTITETSBIBL on August 10, 2015. For personal use only. No other uses without permission.

Two main mechanisms of macrolide resistance have been described in erythromycin-resistant Streptococcus pneumoniae (ERSP): a ribosomal methylase, ErmAM, and a macrolide efflux pump, MefE. In this study, we examined the prevalence of these mechanisms in 114 clinical isolates of ERSP from a 30-center study conducted in the United States between November 1994 and April 1995. The isolates were screened by polymerase chain reaction for the presence of known macrolide resistance genes. Seventy (61%) ERSP contained the macrolide efflux gene (mefE), whereas 36 isolates (32%) contained the biosomal methylase gene (ermAM). Isolates that were ermAM-positive had constitutive macrolide resistance. The minimum inhibitory concentrations (for which 90% of isolates were susceptible) of clarithromycin for the efflux-positive strains were much lower than those for the ermAM-positive strains (4 microg/mL vs. >128 microg/mL, respectively). The efflux mechanism is the predominant form of macrolide resistance in the United States.

An international multilaboratory collaborative study was conducted to develop standard media and consensus methods for the performance and quality control of antimicrobial susceptibility testing of Mycoplasma pneumoniae, Mycoplasma hominis, and Ureaplasma urealyticum using broth microdilution and agar dilution techniques. A reference strain from the American Type Culture Collection was designated for each species, which was to be used for quality control purposes. Repeat testing of replicate samples of each reference strain by participating laboratories utilizing both methods and different lots of media enabled a 3-to 4-dilution MIC range to be established for drugs in several different classes, including tetracyclines, macrolides, ketolides, lincosamides, and fluoroquinolones. This represents the first multilaboratory collaboration to standardize susceptibility testing methods and to designate quality control parameters to ensure accurate and reliable assay results for mycoplasmas and ureaplasmas that infect humans. Methods for in vitro antimicrobial susceptibility testing of mycoplasmas were first described in the 1960s (6). Despite numerous publications during the ensuing years that have reported the activities of antimicrobial agents against these organisms, there have been no universally accepted or standardized broth dilution-or agar-based methods designating the optimum testing conditions, pH, media, length of incubation, quality control (QC) MIC reference ranges, or reference strains. The lack of a consensus method for MIC determination, coupled with complex cultivation requirements, has resulted in considerable confusion regarding the antimicrobial activities of various drugs against these fastidious organisms.To address the need for a standard method for performing and validating in vitro susceptibility tests for human mycoplasmas and ureaplasmas, the Clinical and Laboratory Standards (CLSI) Subcommittee on Antimicrobial Susceptibility Testing of Human Mycoplasmas devised a series of studies involving a total of 10 laboratories from 3 different countries representing academia, industry, and government. Sequential evaluations of both brothand agar-based methods were done with Mycoplasma hominis, Mycoplasma pneumoniae, and Ureaplasma species. The methods included commercial and individual laboratory-produced media and the testing of multiple reference strains for evaluation as QC strains. The QC strains and their respective MIC reference ranges were designated for several drug classes, including macrolides, ketolides, lincosamides, tetracyclines, and fluoroquinolones for each organism. MATERIALS AND METHODSThe CLSI mandates specific protocols and numbers of participating laboratories for determining MIC reference ranges for QC purposes and for the actual measurement of MICs. These requirements have evolved over the years and have now become quite stringent (2). However, the fastidious nature, complex media and incubation requirements, and relatively slow growth for some mycoplasmal species necessitated s...

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Macrolide resistance in Streptococcus pneumoniae has been associated with two main mechanisms: target modification by Erm methyltransferases and efflux by macrolide pumps. The ketolide ABT-773, which has a 3-keto group and no L-cladinose sugar, represents a new class of drugs with in vitro activity against a variety of resistant bacteria. Several approaches were undertaken to understand how ABT-773 was able to defeat resistance mechanisms. We demonstrated tighter ribosome binding of ABT-773 than erythromycin. We also showed that ABT-773 (i) accumulated in macrolide-sensitive S. pneumoniae at a higher rate than erythromycin, (ii) was able to bind with methylated ribosomes, though at lower affinities than with wild-type ribosomes, and (iii) accumulated in S. pneumoniae strains with the efflux-resistant phenotype.Macrolide resistance in Streptococcus pneumoniae has been associated with two main mechanisms. The first resistant strains described were of the macrolide-lincosamide-streptogramin B (MLS) phenotype (18). These strains have a posttranslational modification of 23S rRNA due to the methylation of A2058 (Escherichia coli numbering system) by Erm methyltransferase, resulting in a conformational change in the ribosomes. Resistance to macrolides may be constitutively expressed or induced by sub-MICs of the macrolide (18,20). The second mechanism of resistance recently found in S. pneumoniae, and referred to as the M phenotype, results from the active efflux of 14-and 15-membered macrolides (16). The macrolide efflux pump protein in S. pneumoniae is encoded by the gene mefE (17). The prevalence of M phenotype resistance in clinical isolates of S. pneumoniae has been reported to be a significant portion (60 to 75%) of the resistance population in the United States (8, 14,15,16).The ketolide ABT-773, which has a 3-keto group and no L-cladinose sugar, represents a new class of drugs with in vitro activity against a variety of resistant phenotypes (1). The purpose of this study was to understand how ABT-773 is able to defeat these resistance mechanisms. Several approaches were undertaken, including the measurement of drug-ribosome binding kinetics, drug uptake and efflux rates, and drug effect on cell-free protein translation. MATERIALS AND METHODSChemicals and radioisotopes. Todd-Hewitt broth and yeast extract were obtained from Difco Laboratories (Detroit, Mich.) Miller's M9 medium was prepared with M9 salts purchased from Life Technologies LTD (Paisley, Scotland) but without vitamins or amino acids, as described elsewhere (10). Luciferin reagents (GenLux kit) were purchased from Wallac (Turku, Finland). All other chemicals, including carbonyl cyanide m-chlorophenylhydrazone (CCCP), were purchased from Sigma Chemical Co. (St. Louis, Mo.). [N-methyl-14 C]erythromycin (55 mCi/mmol) was obtained from NEN Life Science Products (Boston, Mass.), and unlabeled erythromycin was made in-house. [N-methyl-14 C]ABT-773 (27 mCi/mmol) was prepared in-house by coupling 6-0-allyl ketolide and 3-[U-14 C]bromoquinoline according to a...