Determining incidence of extended spectrum beta-lactamase producing Enterobacteriaceae, vancomycin-resistant Enterococcus faecium and methicillin-resistant Staphylococcus aureus in 38 centres from 17 countries: the PEARLS study 2001-2002.

The PEARLS study prospectively monitored selected nosocomial pathogens from 38 centres in 13 European, three Middle Eastern countries and South Africa during 2001-2002. Extended spectrum beta-lactamase (ESBL) production rates among Escherichia coli, Klebsiella pneumoniae, and Enterobacter spp. were 5.4% (142/2609), 18.2% (401/2,206) and 8.8% (204/2,328), respectively, for all study sites. The overall ESBL production rate for the combined Enterobacteriaceae was 10.5% (747/7,143), highest in Egypt, 38.5%, and Greece, 27.4%, and lowest in The Netherlands, 2.0%, and Germany, 2.6%. IEF, PCR and DNA sequencing determined 10.7% false positives among Enterobacter spp. when using NCCLS guidelines to screen for ESBL production. The prevalence of nosocomial methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium was 32.4% (294/908) and 8.7% (83/949), respectively. PEARLS provides baseline data against which prospective changes in resistant determinants and outcomes can be measured in this ongoing study.

Activities of three quinolones, alone and in combination with extended-spectrum cephalosporins or gentamicin, against Stenotrophomonas maltophilia.

The present study examined the activities of trovafloxacin, levofloxacin, and ciprofloxacin, alone and in combination with cefoperazone, ceftazidime, cefpirome, and gentamicin, against 100 strains of Stenotrophomonas maltophilia by the MIC determination method and by synergy testing of the combinations by the time-kill and checkerboard titration methods for 20 strains. The respective MICs at which 50% and 90% of isolates were inhibited for the drugs used alone were as follows: trovafloxacin, 0.5 and 2.0 microg/ml; levofloxacin, 2.0 and 4.0 microg/ml; ciprofloxacin, 4.0 and 16.0 microg/ml; cefoperazone, >128.0 and >128.0 microg/ml; ceftazidime, 32.0 and >128.0 microg/ml; cefpirome, >128.0 and >128.0 microg/ml; and gentamicin, 128.0 and >128.0 microg/ml. Synergistic fractional inhibitory concentration indices (/=50% of strains for trovafloxacin-cefoperazone, trovafloxacin-ceftazidime, levofloxacin-cefoperazone, levofloxacin-ceftazidime, ciprofloxacin-cefoperazone, and ciprofloxacin-ceftazidime, with other combinations affecting fewer strains. For 20 strains tested by the checkerboard titration and time-kill methods, synergy (>/=100-fold drop in count compared to the count achieved with the more active compound) was more pronounced after 12 h due to regrowth after 24 h. At 12 h, trovafloxacin at 0.004 to 0.5 microg/ml showed synergy with cefoperazone for 90% of strains, with ceftazidime for 95% of strains with cefpirome for 95% of strains, and with gentamicin for 65% of strains. Levofloxacin at 0.03 to 0.5 microg/ml and ciprofloxacin at 0.5 to 2.0 microg/ml showed synergy with cefoperazone for 80% of strains, with ceftazidime for 90 and 85% of strains, respectively, with cefpirome for 85 and 75% of strains, respectively, and with gentamicin for 65 and 75% of strains, respectively. Time-kill assays were more discriminatory than checkerboard titration assays in demonstrating synergy for all combinations.

Activities and time-kill studies of selected penicillins, beta-lactamase inhibitor combinations, and glycopeptides against Enterococcus faecalis.

The activities of piperacillin, piperacillin-tazobactam, ticarcillin, ticarcillin-clavulanate, ampicillin, ampicillin-sulbactam, vancomycin, and teicoplanin were tested against 212 Enterococcus faecalis strains (9 beta-lactamase producers) by standard agar dilution MIC testing (10[4] CFU/spot). The MICs at which 50 and 90% of the isolates were inhibited (MIC50s and MIC90s, respectively) were as follows (microg/ml): piperacillin, 4 and 8; piperacillin-tazobactam, 4 and 8; ticarcillin, 64 and 128; ticarcillin-clavulanate, 64 and 128; ampicillin, 2 and 2; ampicillin-sulbactam, 1 and 2; vancomycin, 1 and 4; and teicoplanin, 0.5 and 1. Agar dilution MIC testing of the nine beta-lactamase-positive strains with an inoculum of 10(6) CFU/spot revealed higher beta-lactam MICs (piperacillin, 64 to >256 microg/ml; ticarcillin, 128 to >256 microg/ml; and ampicillin, 16 to 128 microg/ml); however, MICs with the addition of inhibitors were similar to those obtained with the lower inoculum. Time-kill studies of 15 strains showed that piperacillin-tazobactam was bactericidal (99.9% killing) for 14 strains after 24 h at four times the MIC, with 90% killing of all 15 strains at two times the MIC. After 12 and 6 h, 90% killing of 14 and 13 strains, respectively, was found at two times the MIC. Ampicillin gave 99.9% killing of 14 beta-lactamase-negative strains after 24 h at eight times the MIC, with 90% killing of all 15 strains at two times the MIC. After 12 and 6 h, 90% killing of 14 and 13 strains, respectively, was found at two times the MIC. Killing by ticarcillin-clavulanate was slower than that observed for piperacillin-tazobactam, relative to the MIC. For the one beta-lactamase-producing strain tested by time-kill analysis with a higher inoculum, addition of the three inhibitors (including sulbactam) to each of the beta-lactams resulted in bactericidal activity at 24 h at two times the MIC. For an enzyme-negative strain, addition of inhibitors did not influence kinetics. Kinetics of vancomycin and teicoplanin were significantly slower than those of the beta-lactams, with bactericidal activity against 6 strains after 24 h at eight times the MIC, with 90% killing of 12 and 14 strains, respectively, at four times the MIC. Slower-kill kinetics by both glycopeptides were observed at earlier periods.

Determination of activities of levofloxacin, alone and combined with gentamicin, ceftazidime, cefpirome, and meropenem, against 124 strains of Pseudomonas aeruginosa by checkerboard and time-kill methodology.

A total of 124 Pseudomonas aeruginosa strains were tested for synergy between levofloxacin and cefpirome, ceftazidime, gentamicin, and meropenem. Checkerboards yielded synergistic fractional inhibitory concentration (FIC) indices (< or =0.5) with 25 of 496 possible combinations. All other FIC indices were >0.5 to 2 (additive or indifferent), with no antagonism. Time-kill studies with 12 strains showed that levofloxacin (0.06 to 0.5 microg/ml) was synergistic with cefpirome, ceftazidime, gentamicin, and meropenem in 10, 9, 4, and 11 strains, respectively.

Synergistic activity of trovafloxacin with other agents against gram-positive and -negative organisms.

The synergistic activity of trovafloxacin with other agents against 55 Gram-positive and -negative bacteria was determined by checkerboard titration. Synergistic fractional inhibitory concentration (FIC) indices (< or = 0.5) were seen in two methicillin-susceptible and one methicillin-resistant Staphyloccocus aureus with teicoplanin, one of each of the latter two with vancomycin; one methicillin-resistant coagulase-negative Staphylococcus with rifampin and one with fusidic acid; five Stenotrophomonas maltophilia with cefoperazone; three Pseudomonas aeruginosa with ticarcillin/clavulanate, four with aztreonam, two with ceftazidime, one with tobramycin, one with cefoperazone, and one with ceftriaxone; one pneumococcus with ceftriaxone; one Enterococcus faecalis with ceftriaxone, and one with vancomycin; two Bacteroides fragilis with metronidazole, two with clindamycin, and one with cefoxitin; and one Clostridium perfringens with metronidazole and one with clindamycin. All other FIC indices were additive/indifferent (0.51-2.0), and no antagonistic FIC indices (> 4.0) were observed.

Susceptibilities of penicillin- and erythromycin-susceptible and -resistant pneumococci to HMR 3647 (RU 66647), a new ketolide, compared with susceptibilities to 17 other agents.

Susceptibility of 230 penicillin- and erythromycin-susceptible and -resistant pneumococci to HMR 3647 (RU 66647), a new ketolide, was tested by agar dilution, and results were compared with those of erythromycin, azithromycin, clarithromycin, roxithromycin, rokitamycin, clindamycin, pristinamycin, ciprofloxacin, sparfloxacin, trimethoprim-sulfamethoxazole, doxycycline, chloramphenicol, cefuroxime, ceftriaxone, imipenem, and vancomycin. HMR 3647 was very active against all strains tested, with MICs at which 90% of the strains were inhibited (MIC90s) of 0.03 microg/ml for erythromycin-susceptible strains (MICs, < or =0.25 microg/ml) and 0.25 microg/ml for erythromycin-resistant strains (MICs, > or =1.0 microg/ml). All other macrolides yielded MIC90s of 0.03 to 0.25 and >64.0 microg/ml for erythromycin-susceptible and -resistant strains, respectively. The MICs of clindamycin for 51 of 100 (51%) erythromycin-resistant strains were < or =0.125 microg/ml. The MICs of pristinamycin for all strains were < or =1.0 microg/ml. The MIC90s of ciprofloxacin and sparfloxacin were 4.0 and 0.5 microg/ml, respectively, and were unaffected by penicillin or erythromycin susceptibility. Vancomycin and imipenem inhibited all strains at < or =1.0 microg/ml. The MICs of cefuroxime and cefotaxime rose with those of penicillin G. The MICs of trimethoprim-sulfamethoxazole, doxycycline, and chloramphenicol were variable but were generally higher in penicillin- and erythromycin-resistant strains. HMR 3647 had the best kill kinetics of all macrolides tested against 11 erythromycin-susceptible and -resistant strains, with uniform bactericidal activity (99.9% killing) after 24 h at two times the MIC and 99% killing of all strains at two times the MIC after 12 h for all strains. Pristinamycin showed more rapid killing at 2 to 6 h, with 99.9% killing of 10 of 11 strains after 24 h at two times the MIC. Other macrolides showed significant activity, relative to the MIC, against erythromycin-susceptible strains only.

Susceptibility of penicillin-susceptible and -resistant pneumococci to dirithromycin compared with susceptibilities to erythromycin, azithromycin, clarithromycin, roxithromycin, and clindamycin.

Agar dilution with incubation in air and CO2 was used to determine the MICs of erythromycin, dirithromycin, azithromycin, clarithromycin, roxithromycin, and clindamycin for 79 penicillin-susceptible, 72 penicillin-intermediate, and 74 penicillin-resistant pneumococci (158 erythromycin-susceptible and 67 erythromycin-resistant pneumococci). MICs obtained in air were usually 1 to 3 dilutions lower than those obtained in CO2. In air, the respective MICs at which 50% (MIC50s) and 90% (MIC90s) of penicillin-susceptible, -intermediate, and -resistant strains are inhibited were as follows: erythromycin, 0.016 and 0.5, 0.03 and > 64, and 2 and > 64 microg/ml; dirithromycin, 0.03 and 0.5, 0.06 and > 64, and 8 and > 64 microg/ml; azithromycin, 0.03 and 0.5, 0.06 and > 64, and 2 and > 64 microg/ml; clarithromycin, 0.016 and 0.06, 0.03 and > 64, and 2 and > 64 microg/ml; roxithromycin, 0.06 and 2, 0.06 and > 64, and 2 and > 64 microg/ml; and clindamycin, 0.03 and 0.06, 0.06 and > 64, and 0.06 and > 64 microg/ml. The MICs of erythromycin, azithromycin, and dirithromycin were very similar; however, clarithromycin MICs were generally 1 to 2 dilutions lower and roxithromycin MICs were 1 to 2 dilutions higher than those of the other compounds tested. Strains resistant to one macrolide were resistant to all macrolides; however, not all macrolide-resistant strains were resistant to clindamycin, and 32 macrolide-resistant (MICs, > or = 28 microg/ml), clindamycin-susceptible (MICs, < or = 0.25 microg/ml) strains were encountered. Time-kill testing of six strains showed similar killing kinetics for all compounds, with 99.9% killing of all strains observed with the compounds only at or above the MIC after 24 h.

Comparative activity of trovafloxacin, alone and in combination with other agents, against gram-negative nonfermentative rods.

In the first part of this study, agar dilution MICs were used to test the activities of trovafloxacin, ciprofloxacin, ofloxacin, levofloxacin, sparfloxacin, clinafloxacin, ceftazidime, and imipenem against 458 gram-negative nonfermenters. The overall respective MICs at which 50% of isolates are inhibited (MIC50s) and MIC90s were as follows: trovafloxacin, 1.0 and 16.0 microg/ml; ciprofloxacin, 2.0 and 16.0 microg/ml; ofloxacin, 2.0 and 32.0 microg/ml; levofloxacin, 1.0 and 16.0 microg/ml; sparfloxacin, 1.0 and 16.0 microg/ml; clinafloxacin, 0.5 and 4.0 microg/ml; ceftazidime, 8.0 and 128.0 microg/ml; imipenem, 2.0 and 256.0 microg/ml. Clinafloxacin was the most active of all the quinolones tested. The MIC90s of trovafloxacin were < or = 4.0 microg/ml for Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Flavobacterium odoratum, and Chryseobacterium meningosepticum; trovafloxacin MIC90s were < or = 2.0 microg/ml for Moraxella spp., Pseudomonas stutzeri, and Chryseobacterium indologenes-C. gleum. Of the other quinolones tested, the MICs of sparfloxacin and levofloxacin were lower than those of ciprofloxacin and ofloxacin. High ceftazidime MICs (> or = 32.0 microg/ml) were observed for all nonfermentative species tested. Although for the majority of strains tested imipenem MICs were < or = 8.0 microg/ml, high imipenem MICs were observed for many species, especially S. maltophilia, Burkholderia cepacia, F. odoratum, and Chryseobacterium meningosepticum. For Alcaligenes xylosoxidans strains, the MICs of all compounds were generally a few dilutions lower than those for Alcaligenes faecalis-A. odorans. Time-kill studies with five strains revealed that trovafloxacin and all quinolones yielded more rapid time-kill kinetics than ceftazidime and imipenem. Synergy testing by checkerboard titrations of 286 strains with trovafloxacin combined with ceftazidime, amikacin, and imipenem revealed fractional inhibitory concentration (FIC) indices in the range indicating synergism (< or = 0.5) for 81, 41, and 40 strains, respectively, and FIC indices indicating additivity or indifference (> 0.5 to 4.0) for 205, 245, and 246 strains, respectively. No FIC indices indicating antagonism (> 4.0) were observed. Synergy between trovafloxacin and ceftazidime was found for 32 of 36 S. maltophilia strains. Time-kill studies with 20 strains showed that for most strains for which FIC indices were in the range indicating additivity or indifference, FIC indices indicated synergy by the time-kill method. Synergy was particularly noticeable for S. maltophilia strains with combinations of ceftazidime and trovafloxacin.

Susceptibility of twenty penicillin-susceptible and -resistant pneumococci to levofloxacin, ciprofloxacin, ofloxacin, erythromycin, azithromycin, and clarithromycin by MIC and time-kill.

This study uses MIC and time-kill methodology to examine the antipneumococcal activity of levofloxacin, ciprofloxacin, ofloxacin, erythromycin, azithromycin, and clarithromycin against 20 pneumococci. Ten strains had levofloxacin MICs of 1.0 microgram/ml, and ten levofloxacin MICs of 2.0 micrograms/ml. Five strains in each group were macrolide susceptible, and five were macrolide resistant. MICs for ciprofloxacin and ofloxacin ranged from 0.5 to 4.0 micrograms/ml and 1.0 to 8.0 micrograms/ml, respectively. MICs of erythromycin, azithromycin, and clarithromycin were similar for macrolide susceptible strains, ranging between 0.004 to 0.06 microgram/ml, and were > or = 128.0 micrograms/ml for macrolide resistant strains. The three quinolones were bactericidal (99.9% killing) for all macrolide-susceptible strains at 2 x MIC at 24 h. The three quinolones yielded 99% killing of all strains after 12 h at 2 x MIC, and 90% killing of all strains after 6 h at the MIC of levofloxacin and ciprofloxacin and 2 x MIC for ofloxacin. Levofloxacin yielded 90% killing of all strains after 4 h at 2 x MIC and ofloxacin at 4 x MIC. For macrolide-susceptible strains, erythromycin and clarithromycin were bactericidal for 9 of 10 strains after 24 h at 4 x and 2 x MIC, respectively, and azithromycin was bactericidal after 24 h at 2 x MIC for 8 of 10 strains. All three macrolides were bactericidal after 12 h only, while 90% killing occurred in 9 of 10 strains at 8 x MIC after 6 h. Quinolone kill kinetics were similar for the 10 macrolide-resistant strains. For macrolide-resistant strains, at 64 to 128.0 micrograms/ml, virtually no decrease in count was seen, with no bactericidal effect.

Activities of levofloxacin, ofloxacin, and ciprofloxacin, alone and in combination with amikacin, against acinetobacters as determined by checkerboard and time-kill studies.

A total of 101 Acinetobacter genospecies (77 Acinetobacter baumannii strains and 24 non-A. baumannii strains) were tested for their susceptibilities to levofloxacin, ofloxacin, and ciprofloxacin and for synergy between the quinolones and amikacin by checkerboard titration and time-kill analyses. The MICs at which 50% of the isolates are inhibited (MIC50)/MIC90s for the 101 strains were as follows (in micrograms per milliliter): levofloxacin, 0.25/16.0; ofloxacin, 0.5/32.0; ciprofloxacin, 0.25/> 64.0; and amikacin, 1.0/> 32.0. At empiric breakpoints of < or = 2.0 microg/ml, 61% of the strains were susceptible to all three quinolones. At a breakpoint of < or = 16.0 microg/ml, 84% of the strains were susceptible to amikacin. Checkerboard titrations yielded synergistic fractional inhibitory concentration (FIC) indices (< or = 0.5) for one strain with levofloxacin and amikacin and for two strains with ofloxacin and amikacin. Indices of > 0.5 to 1.0 were seen for 57, 54, and 55 strains with levofloxacin plus amikacin, ofloxacin plus amikacin, and ciprofloxacin plus amikacin, respectively, and indices of > 1.0 in 43, 45, and 46 strains, respectively, were found with the above three combinations. No strains yielded antagonistic FIC indices (> 4.0). Most FIC results of > 1.0 occurred in strains for which the quinolone MICs were > 2.0 microg/ml and for which the amikacin MICs were > or = 32.0 microg/ml. By contrast, synergy (defined as > or = 2 log10 decrease compared to the more active compound alone by time-kill analysis) was found in all seven strains tested for which the quinolone MICs were < or = 2.0 microg/ml. For eight other strains for which the quinolone MICs were > 2.0 microg/ml as determined by time-kill analysis, quinolone and amikacin concentrations in combination were usually too high to permit clinical use. Time-kill analysis was found to be more sensitive in detecting synergy than was the checkerboard method.

Activities of beta-lactams against Acinetobacter genospecies as determined by agar dilution and E-test MIC methods.

The agar dilution MIC method was used to test activities of ticarcillin, ticarcillin-clavulanate, amoxicillin, amoxicillin-clavulanate, ampicillin, ampicillin-sulbactam, piperacillin, piperacillin-tazobactam, inhibitors alone, ceftazidime, and imipenem against 237 Acinetobacter genospecies. A total of 93.2% of strains were beta-lactamase positive by the chromogenic cephalosporin method. Overall, ampicillin-sulbactam was the most active combination against all strains (MIC at which 50% of the isolates are inhibited [MIC50] and MIC90, 4.0 and 32.0 microg/ml; 86.9% susceptible at < or = 16 microg/ml), followed by ticarcillin-clavulanate (16.0 and 128.0 microg/ml; 85.7% susceptible at < or = 64 microg/ml), piperacillin-tazobactam (16.0 and 128.0 microg/ml; 84.8% susceptible at < or = 64 microg/ml), and amoxicillin-clavulanate (16.0 and 64.0 microg/ml; 54.4% susceptible at < or =16 microg/ml). Ceftazidime and imipenem yielded MIC50s and MIC90s of 8.0 and 64.0 microg/ml (ceftazidime) and 0.5 and 1.0 microg/ml (imipenem), respectively; 71.3% of strains were susceptible to ceftazidime at < or = 16 microg/ml, and 99.2% were susceptible to imipenem at < or = 8 microg/ml. Sulbactam was the most active beta-lactamase inhibitor alone (MIC50 and MIC90, 2.0 and 16.0 microg/ml); clavulanate and tazobactam were less active (16.0 and 32.0 microg/ml for both compounds). Enhancement of beta-lactams by beta-lactamase inhibitors was not always seen in beta-lactamase-positive strains, and activity of combinations such as ampicillin-sulbactam was due to the inhibitor alone. Acinetobacter baumannii was the most resistant genospecies. By contrast, Acinetobacter haemolyticus, Acinetobacter calcoaceticus, Acinetobacter johnsonii, Acinetobacter junii, Acinetobacter radioresistens, and other non-Acinetobacter baumannii strains were more susceptible to all compounds tested. E-test MICs were within 1 dilution of agar dilution MICs in 38.4 to 89.6% of cases and within 2 dilutions in 61.6 to 98.6% of cases.

Antipneumococcal activity of BAY 12-8039, a new quinolone, compared with activities of three other quinolones and four oral beta-lactams.

Activities of BAY 12-8039 against 205 pneumococci were tested by agar dilution. MICs (in micrograms per milliliter) at which 50 and 90% of the isolates are inhibited (MIC50s and MIC90s, respectively) were 0.125 and 0.25 (BAY 12-8039), 2.0 and 4.0 (ciprofloxacin and ofloxacin), and 0.25 and 0.5 (sparfloxacin). Beta-lactam MIC50s and MIC90s for penicillin-susceptible, -intermediate, and -resistant strains, in that order, were 0.016 and 0.03, 0.25 and 2.0, and 2.0 and 4.0 (amoxicillin); 0.03 and 0.06, 0.25 and 4.0, and 4.0 and 8.0 (ampicillin); 0.03 and 0.06, 0.5 and 4.0, and 4.0 and 8.0 (cefuroxime); and 0.03 and 0.125, 0.25 and 2.0, and 4.0 and 8.0 (cefpodoxime). At two times their MICs after 24 h, BAY 12-8039, ciprofloxacin, ampicillin, and cefuroxime were uniformly bactericidal (99.9% killing) against 12 strains; other compounds were bactericidal at four times their MICs.

Antipneumococcal activities of cefpirome and cefotaxime, alone and in combination with vancomycin and teicoplanin, determined by checkerboard and time-kill methods.

The checkerboard titration method was used to test the synergy of cefpirome and cefotaxime with teicoplanin or vancomycin against 35 penicillin-susceptible, 34 penicillin-intermediate, and 31 penicillin-resistant pneumococci. The MICs at which 50 and 90% of isolates are inhibited (MIC50s and MIC90s, respectively) of both cefpirome and cefotaxime were 0.016 and 0.06 microgram/ml, respectively, for penicillin-susceptible strains and 0.125 and 0.5 microgram/ml, respectively, for penicillin-intermediate strains. The MIC50s and MIC90s of cefotaxime for penicillin-resistant strains were 1.0 and 2.0 micrograms/ml, respectively, and those of cefpirome were 0.5 and 1.0 microgram/ml, respectively. All pneumococci were inhibited by cefpirome at MICs of < or = 1.0 microgram/ml. The MIC50s and MIC90s of vancomycin and teicoplanin (0.25 and 0.25 microgram/ml and 0.03 and 0.03 microgram/ml, respectively) did not differ for the three groups. Checkerboard synergy studies showed that cefpirome and vancomycin showed synergy for 31 strains (fractional inhibitory concentration [FIC] indices, < or = 0.5) cefpirome and teicoplanin showed synergy for 18 strains, cefotaxime and vancomycin showed synergy for 51 strains, and cefotaxime and teicoplanin showed synergy for 27 strains. Cefpirome and vancomycin had FIC indices indicating indifference (2.0) for two strains, and cefotaxime and vancomycin had FIC indices indicating indifference for one strain. All other FIC indices indicating indifference or additivity were > 0.5 to 1.0. No FIC indices indicating antagonism (> 4.0) were found. Synergy between beta-lactams and glycopeptides for three susceptible, three intermediate, and three resistant strains were tested by the time-kill assay, and all combinations were synergistic by this method. Synergy between cephalosporins and glycopeptides can be demonstrated and may be useful for the treatment of pneumococcal infections, especially meningitis.

Comparative activities of clarithromycin, erythromycin, and azithromycin against penicillin-susceptible and penicillin-resistant pneumococci.

Activities of clarithromycin, erythromycin, and azithromycin against 120 pneumococci from the United States were tested by agar dilution MIC. All three compounds yielded MICs at which 90% of the isolates were inhibited (MIC90S) of < or = 0.125 micrograms/ml against penicillin-susceptible and -intermediate strains, but MIC90S against resistant strains were > 128.0 micrograms/ml. All erythromycin-resistant strains were also resistant to clarithromycin and azithromycin. Clarithromycin yielded MICs which were generally one or two dilutions lower than those of the other two compounds for all strains. The respective bacteriostatic and bactericidal values (micrograms per milliliter) for two susceptible, two intermediate, and two resistant strains were 0.004 to 0.03 and 0.016 to 0.03 (0.004 to 0.03/0.016 to 0.03) (clarithromycin), 0.008 to 0.06/0.016/0.016 to 0.125 (erythromycin), and 0.016 to 0.06/0.03 to 0.125 (azithromycin); clarithromycin yielded the lowest values. All compounds were uniformly bactericidal after 24 h only; erythromycin was bactericidal at eight times the MIC, and azithromycin and clarithromycin were both bactericidal at two time the MIC. The relevance of these in vitro differences requires clarification by clinical trials.

Susceptibilities of non-Pseudomonas aeruginosa gram-negative nonfermentative rods to ciprofloxacin, ofloxacin, levofloxacin, D-ofloxacin, sparfloxacin, ceftazidime, piperacillin, piperacillin-tazobactam, trimethoprim-sulfamethoxazole, and imipenem.

Agar dilution MICs of 10 agents against 410 non-Pseudomonas aeruginosa gram-negative nonfermentative rods were determined. MICs at which 50 and 90% of the isolates were inhibited, respectively, were as follows (in micrograms per milliliter): sparfloxacin, 0.5 and 8.0; levofloxacin, 1.0 and 8.0; ciprofloxacin, 2.0 and 32.0; ofloxacin, 2.0 and 32.0; D-ofloxacin, 32.0 and > 64.0; ceftazidime, 8.0 and 64.0; piperacillin with or without tazobactam, 16.0 and > 64.0; trimethoprim-sulfamethoxazole, 0.5 and > 64.0; imipenem, 2.0 and > 64.0. With the exception of those for Stenotrophomonas maltophilia, Burkholderia cepacia, and Alcaligenes faecalis-A. odorans, agar dilution MICs for all strains tested were within 1 dilution of inhibitory (bacteriostatic) levels as determined by time-kill methodology.

MIC and time-kill study of activities of DU-6859a, ciprofloxacin, levofloxacin, sparfloxacin, cefotaxime, imipenem, and vancomycin against nine penicillin-susceptible and -resistant pneumococci.

MIC and time-kill methods were used to test the activities of DU-6859a, ciprofloxacin, levofloxacin, sparfloxacin, cefotaxime, imipenem, and vancomycin against nine penicillin-susceptible, -intermediate, and -resistant pneumococci. The MIC of penicillin for penicillin-susceptible strains was 0.016 micrograms/ml, those for intermediate strains were 0.25 to 1.0 microgram/ml, and those for resistant strains were 2.0 to 4.0 micrograms/ml. Of the four quinolones tested, DU-6859a had the lowest MIC (0.064 micrograms/ml), followed by sparfloxacin (0.25 to 0.5 micrograms/ml) and levofloxacin and ciprofloxacin (both 1.0 to 4.0 micrograms/ml). Vancomycin inhibited all strains at MICs of 0.25 to 0.5 micrograms/ml. The MICs of imipenem and cefotaxime for penicillin-susceptible, -intermediate, and -resistant strains were 0.004 to 0.008, 0.008 to 0.032, and 0.25 micrograms/ml and 0.016, 0.125 to 0.5, and 2.0 micrograms/ml, respectively. DU-6859a was bactericidal at eight times the MICs (0.5 micrograms/ml) for seven of the nine strains after 4 h and bactericidal for all nine strains after 6 h at eight times the MICs and after 12 h at two times the MICs. By comparison, sparfloxacin, the next most active quinolone, was uniformly bactericidal at two times the MICs only after 24 h, with little activity after 2 h. Levofloxacin and ciprofloxacin were bactericidal against all strains after 12 h at eight times the MICs and against all strains at 24 h at four times the MICs. Imipenem was bactericidal against all strains, at concentrations exceeding the MICs, after 24 h. Cefotaxime was also uniformly bactericidal only after 24 h of incubation at two times the MICs. Vancomycin, despite having uniformly low MICs for all strains irrespective of their penicillin susceptibility, was uniformly bactericidal only at two times the MICs after 24 h.

Activity of CP 99,219 (trovafloxacin) compared with ciprofloxacin, sparfloxacin, clinafloxacin, lomefloxacin and cefuroxime against ten penicillin-susceptible and penicillin-resistant pneumococci by time-kill methodology.

Activity of CP 99,219 (trovafloxacin), clinafloxacin, ciprofloxacin, sparfloxacin, lomefloxacin and cefuroxime against 4 penicillin-susceptible, 2 penicillin-intermediate and 4 penicillin-resistant pneumococci was tested by MIC and time-kill methodology. Bacteriostatic values for all three groups did not differ significantly with all compounds tested except cefuroxime, and were lowest for trovafloxacin and clinafloxacin, followed by sparfloxacin, ciprofloxacin and lomefloxacin; cefuroxime yielded values which increased in line with those of penicillin G. The test compounds were bactericidal (i.e. they reduced original counts by > or = 3 log10 cfu/mL at one dilution above bacteriostatic levels) in most cases, though some strains showed slightly greater discrepancies between bacteriostatic and bactericidal levels of all compounds tested. Trovafloxacin, clinafloxacin and sparfloxacin yielded MIC and time-kill results which point to possible efficacy in treatment of penicillin-susceptible and -resistant pneumococcal infections.

Activities of oral and parenteral agents against penicillin-susceptible and -resistant pneumococci.

This study examined bacteriostatic and bactericidal activities of oral and parenteral antibiotics for penicillin-susceptible and intermediately and fully penicillin-resistant pneumococci. beta-Lactamase inhibitors did not affect beta-lactam results. The activities of ampicillin, amoxicillin +/- clavulanate, WY-49605, cefuroxime, cefpodoxime, cefdinir, cefixime, and cefaclor against two penicillin-susceptible, two intermediately penicillin-resistant, and two fully penicillin-resistant pneumococcal strains were tested. For all three groups, bacteriostatic values of amoxicillin and WY-49605 were lower than were those of other beta-lactams tested. Of the cephalosporins, cefdinir, cefuroxime, and cefpodoxime yielded the lowest bacteriostatic values. All beta-lactams were bactericidal (reduced original counts by > or = 3 log10 CFU/ml) at 1 dilution above bacteriostatic values, except for cefpodoxime (bactericidal at 2 dilutions above bacteriostatic values for one susceptible strain and one intermediately resistant strain), cefuroxime (bactericidal at 2 dilutions above bacteriostatic values for one intermediately resistant strain), and ampicillin (bactericidal at 2 dilutions above bacteriostatic values for one intermediately resistant strain). The activities of piperacillin, piperacillin-tazobactam, ticarcillin, ticarcillin-clavulanate, ampicillin, ampicillin-sulbactam, ceftriaxone, ceftazidime, and ciprofloxacin against four penicillin-susceptible, two intermediately penicillin-resistant, and four fully penicillin-resistant pneumococcal strains were evaluated. Bacteriostatic values of piperacillin, ampicillin, and ceftriaxone for all groups were lower than were those of ticarcillin and ceftazidime. Bacteriostatic values of ciprofloxacin were unaffected by penicillin susceptibility. All beta-lactams were bactericidal at 1 dilution above the bacteriostatic value, except for piperacillin (bactericidal at 2 dilutions above the bacteriostatic value for one intermediately resistant strain), ticarcillin (bactericidal at 2 dilutions above the bacteriostatic value for one susceptible strain and one resistant strain), ampicillin (bactericidal at 2 dilutions above the bacteriostatic value for two resistant strains), ceftriaxone (bactericidal at 2 dilutions above the bacteriostatic value for one resistant strain), and ceftazidime (bactericidal at 2 dilutions above the bacteriostatic value for one susceptible strain).