Eighty-five strains of vancomycin-resistant gram-positive bacteria from three genera, Leuconostoc, Pediococcus, and Lactobacilus, were tested to determine susceptibility to 24 antimicrobial agents by broth microdilution and to 10 agents by disk diffusion. The MICs of vancomycin and teicoplanin ranged from 64 to >512 ,ug/ml; however, the MICs of daptomycin, a new lipopeptide, were all .0.25 ,ug/ml. None of the organisms were resistant to imipenem, minocycline, chloramphenicol, gentamicin, or daptomycin. The MICs of penicillin were in the moderately susceptible range for all but three strains. Susceptibility to the other agents varied by genus and, in some cases, by species. When disk diffusion results were compared with MICs for drugs recommended for streptococci by the National Committee for Clinical Laboratory Standards, Vilanova, Pa., few very major or major errors were obtained, but the number of minor errors was 19.3%. Therefore, we recommend that MIC testing be used instead of disk diffusion testing for these organisms.Because of the increase in nosocomial infections caused by gram-positive cocci, especially staphylococci (both Staphylococcus aureus and coagulase-negative staphylococci) (T. Horan, D. Culver, W. Jarvis, G. Emori, S. Banerjee, W. Martone, and C. Thornsberry, Antimicrob. Newsl. 5:65-67, 1988), and because of the growing prevalence of methicillin resistance in staphylococci (9), vancomycin has been used more often for treating patients who have or who are suspected of having infections caused by gram-positive organisms. Reports of clinical infections caused by vancomycin-resistant organisms have been more frequent in recent years, with resistance in staphylococci (22), enterococci (14-16, 26), and lactobacilli (1, 8, 11) described. Clinically significant vancomycin resistance in Leuconostoc and Pediococcus spp. was rarely reported before 1985 (19). The first case of a clinically significant infection caused by a Leuconostoc sp. was reported as being caused by a Streptococcus sanguis II strain in 1984 (24). The identity of the strain reported was later questioned (C. Thornsberry and R. Facklam, Antimicrob. Newsl. 1:63-64, 1984) and reidentified as Leuconostoc sp. by one of us (R.R.F.).Since then, a number of clinically significant infections caused by Leuconostoc spp. have been reported (2,3,5,10,12,13,(19)(20)(21)27), including a case of meningitis in a previously healthy 16-year-old girl (4). There has been only one report of infections caused by Pediococcus sp. (3), although many such strains from clinical sources have been submitted to the Centers for Disease Control for identification or antimicrobial susceptibility studies (7). Vancomycin resistance in lactobacilli has also been reported (1, 8, 11), but resistance of and clinical infection caused by Lactobacillus confusus, an organism that may often be confused with these gram-positive cocci, have not been documented.Because of the possibility that these organisms may be pathogens, we tested a number of them to determine pat-* Correspon...

In vitro studies were performed comparing ciprofloxacin (Bay o 9867) and norfloxacin with three related organic acids. Ciprofloxacin was two to eight times more active than norfloxacin against 658 bacterial isolates representing 30 species. For all species tested, ciprofloxacin MICs for 90% inhibition were c 2.0 pL-g/ ml. Additional tests with 5,994 isolates detected only 37 (0.6%) strains resistant to 2.0 pLg of ciprofloxacin per ml and 106 (1.8%) resistant to 1.0 F.g/ml. Only 6 (0.1%) of the 5,994 strains were resistant to 16 j±g of norfloxacin per ml, and 129 (2.1%) were resistant to 4.0 ,ug/ml. The majority of resistant strains were streptococci or Pseudomonas spp. Resistance among the Enterobacteriaceae was extremely rare (i.e., > 99.8% susceptible to both drugs).Ciprofloxacin (Bay o 9867) is a new quinolone carboxylic acid derivative that is being developed for oral and parenteral use in treatment of systemic infections as well as urinary tract infections (1,3,5,7,9). Structurally, ciprofloxacin closely resembles norfloxacin, except that ciprofloxacin has a cyclopropyl group in the 1 position, whereas norfloxacin has an ethyl group in that position. In this report, we compare the in vitro activity of ciprofloxacin with that of norfloxacin and three related organic acids currently being used for treatment of urinary tract infections. Broth microdilution tests were first performed with 658 isolates representative of common bacterial species. To further document the incidence of resistance among isolates currently being encountered, all isolates selected for susceptibility testing in four different clinical laboratories were tested against ciprofloxacin and norfloxacin for 30 to 45 days.MATERIALS AND METHODS Antimicrobial agents. Ciprofloxin was supplied as laboratory standard powder by Miles Pharmaceuticals (West Haven, Conn.). Norfloxacin was provided by Merck Institute for Therapeutic Research, Rahway, N.J. Nalidixic acid was obtained from Sterling Winthrop Research Institute, Rensselaer, N.Y. Eli Lilly Research Laboratories, Indianapolis, Ind., provided cinoxacin and oxolinic acid. Ciprofloxacin was dissolved and diluted in sterile water, and the other drugs were dissolved in 0.1 N NaOH and diluted in sterile water.Bacterial isolates. The 658 aerobic or facultatively anaerobic bacterial isolates used in the first phase of this study were collected from six geographically separate medical centers, and additional isolates were contributed by the Centers for Disease Control, Atlanta, Ga. The contributing laboratories include The Cleveland Clinic Foundation,

The effect of calcium and magnesium on the susceptibility of 13 species of Pseudomonas to tetracycline, gentamicin, polymyxin B, and carbenicillin was measured. The majority of the minimum inhibitory concentrations (MICs) of these antibiotics was increased if these cations were added to the test media. The increases in MICs caused by calcium or magnesium were similar, but the combination of both -ions generally caused a greater change than either alone. Although the MIC of polymyxin B was most affected by calcium and magnesium, its interpretive susceptibilities (i.e., whether susceptible or resistant) were least changed. Susceptibility tests on Pseudomonas species probably should be done with Muller-Hinton broth supplemented with physiological concentrations of calcium and magnesium to better approximate the in vivo activity of these antibiotics. When the susceptibility tests were performed with Mueller-Hinton agar, the MICs were slightly less than those obtained with Mueller-Hinton broth supplemented with both cations but greater than those obtained with MuellerHinton broth supplemented with individual cations.

A multilaboratory in vitro study was carried out to determine disk diffusion susceptibility testing quality control limits for two new semisynthetic penicillins, mezlocillin and piperacillin. Existing limits for carbenicillin and ampicillin were reevaluated. Multiple tests (which followed standards set by the National Committee for Clinical Laboratory Standards, ASM-2 revised) were performed in nine laboratories by different technologists using disks and Mueller-Hinton agar from different manufacturers. Clinically significant differences between disks produced by different manufacturers were not noted. Inhibitory zone diameter measurements from all laboratories were analyzed, and upper and lower control limits were established by using the overall median +0.5 the median range of the individual laboratory measurements as determining parameters. Close agreement of the data in this study with the results of national proficiency testing and quality control programs for ampicillin and carbenicilhin supports the validity of our approach to making initial recommendations for quality control guidelines for new antimicrobial agents.

The in vitro activity of BMY-28142, a new cephalosporin, was tested by a broth microdilution system and compared with those of cefotaxime, ceftazidime, cefoperazone, moxalactam, and HR 810 against 747 bacterial isolates, one-third of which were resistant to one or more third-generation cephalosporins. BMY-28142 was the most active drug tested against 326 Enterobacteriaceae with an MIC for 90% of the organisms tested (MIC90) of 1.0 ,Ig/ml. Against these Enterobacteriaceae the relative activities were: BMY-28142 > HR 810 > moxalactam and ceftazidime > cefotaxime > cefoperazone. For cefotaxime-and cefoperazone-resistant strains, the MIC90 of BMY-28142 was 4.0 ,ug/ml (compared with 0.13 ,ug/ml for susceptible strains 577, 1983).In this study, we compared the in vitro activity of BMY-28142 in a broth microdilution system with those of four third-generation cephalosporins: cefotaxime, ceftazidime, cefoperazone, and moxalactam, as well as with HR 810, a structurally similar and potent new cephalosporin (4). The ,-lactamase stability of BMY-28142 and ,-lactamase inhibition by this drug are also reported. Susceptibility testing. For most organisms, MICs were determined by broth microdilution methods as described by the National Committee for Clinical Laboratory Standards (7) and in previous studies (2-4). For testing nonenterococcal streptococci and Neisseria gonorrhoeae, an agar dilution method was used, which has been described previously in more detail (1). A sample of 106 nonfastidious organisms were also tested simultaneously by both agar dilution and broth microdilution methods to assess the comparability of the results of the two methods (7). The drug concentrations tested were serial twofold increments ranging from 0.008 to 256 ,ug/ml for BMY-28142 and HR 810 and from 0.06 to 32 ,ug/ml for cefotaxime, cefoperazone, moxalactam, and ceftazidime. The lowest concentration inhibiting the growth of an inoculum containing about 5 x 105 CFU/ml after 16 to 20 h of aerobic incubation at 35°C was considered the MIC in broth microdilution tests. For agar dilution, the inoculum contained about 104 CFU per spot. MATERIALS AND METHODS13-Lactamase studies. The 1-lactamase stability of BMY-28142 as well as its inhibiting effect on various Plactamases were determined by previously described methods (3,5