The in vitro activities of the new agents linezolid, quinupristin-dalfopristin, moxifloxacin, and trovafloxacin were determined and compared with those of penicillin, clindamycin, and four macrolides against 53 erythromycin-resistant Streptococcus pneumoniae, 117 S. pyogenes (64 erythromycin-susceptible and 53 -resistant), and 101 S. agalactiae (53 erythromycin-susceptible and 48 -resistant) isolates. Differentiation of macrolide resistance phenotypes was performed by the double-disk method. The genetic basis for macrolide resistance in 52 strains was also determined. The M phenotype was found in 84.9, 6.3, and 1.9% of S. pyogenes, S. agalactiae, and S. pneumoniae isolates, respectively. These strains were susceptible to miocamycin and clindamycin. Strains with the inducible phenotype accounted for 27.1% of S. agalactiae isolates and 9.4% each of S. pyogenes and S. pneumoniae isolates. All erythromycin-resistant isolates were also resistant to the 14-and 15-membered macrolides tested. Strains with all three phenotypes were susceptible to <2 g of linezolid per ml. Quinupristin-dalfopristin exhibited good in vitro activity against all strains, irrespective of their resistance to erythromycin (MICs at which 90% of the isolates tested were inhibited [MIC 90 s], 0.2 to 1 g/ml). Against the erythromycin-resistant S. pyogenes and S. agalactiae strains, moxifloxacin and trovafloxacin were the most active agents (MIC 90 s, 0

No abstract

No abstract

The antimicrobial activities of trovafloxacin, moxifloxacin, sanfetrinem, quinupristin-dalfopristin, and 14 other antimicrobial agents against 218 Bacteroides fragilis group strains were determined. A group of 10 imipenem-resistant strains were also tested. Imipenem, meropenem, and sanfetrinem had the lowest MICs of all of the β-lactams. Quinupristin-dalfopristin inhibited all of the strains at 2 μg/ml. Overall, the MICs of trovafloxacin and moxifloxacin for 90% of the strains tested were 1 and 2 μg/ml, respectively.

The activity of MK-0826, a new carbapenem, against 309 Bacteroides fragilis group strains was investigated and compared with that of 11 other ␤-lactam and 5 non-␤-lactam agents. MK-0826 showed excellent activity (MICs ranged from <0.06 to 4 g/ml). The new carbapenem may be useful in the treatment of mixed anaerobic infections involving B. fragilis group strains.Bacteroides fragilis group organisms are the anaerobic bacteria most frequently isolated in clinical infections and among the most resistant of all anaerobes to antibiotics. During the last few decades, different surveys have noted increased resistance of this group to several ␤-lactam and other antianaerobic agents (1-4, 10, 12). 345) is a new 1-␤-methyl injectable carbapenem that is highly resistant to inactivation by many extended-and broad-spectrum ␤-lactamases. It has a broad and potent spectrum of activity against both aerobic and anaerobic bacteria (6-9, 14). MK-0826 possesses pharmacokinetic advantages over currently available carbapenems. It is stable in the presence of human dehydropeptidase and therefore does not require the addition of cilastatin. Moreover, MK-0826 has a significantly longer half-life than imipenem and meropenem, which allows single daily dosing.The present study was undertaken to determine the in vitro activity of MK-0826 against 309 recently isolated B. fragilis group strains. This activity was compared with those of 11 other ␤-lactam agents and 5 non-␤-lactam agents.( Susceptibility testing was performed by the agar dilution method according to the National Committee for Clinical Laboratory Standards (NCCLS) (11) with brucella blood agar. Approximately 10 5 CFU/spot was inoculated using a Steers multipoint replicator. The plates were incubated at 35°C for 48 h in an anaerobic chamber. MICs were defined as the lowest concentration of antimicrobial agent that yielded either no growth or a marked change in the appearance of growth compared to that of the growth on the control plate. MICs were determined for the group as a whole and for individual species as well. Reference strains B. fragilis ATCC 25285 and B. thetaiotaomicron ATCC 29741 were used as controls.Analysis of the species distribution showed higher proportions of B. uniformis and B. fragilis than reported by other studies (2,10,12). The comparative activities of MK-0826 and the other agents tested are summarized in Table 1. The activity of MK-0826 against B. fragilis group strains was similar to that of imipenem and meropenem (MICs ranged from Յ0.06 to 4 g/ml). The majority (84.5%) of strains tested were inhibited by MK-0826 at Յ1 g/ml; for 11.3 and 4.2% of isolates, MK-0826 MICs were 2 and 4 g/ml, respectively. For B. fragilis strains, the MICs at which 50 and 90% of the isolates were inhibited (MIC 50 s and MIC 90 s, respectively) of both MK-0826 and imipenem were slightly lower than those for B. thetaiotaomicron, B. uniformis, and B. distasonis isolates.According to the majority of published studies (1-3, 7, 12), metronidazole and chloramphenicol were active agai...