Linda M. Kelly

Susceptibilities to telithromycin and six other agents and prevalence of macrolide resistance due to L4 ribosomal protein mutation among 992 Pneumococci from 10 central and Eastern European countries.

ABSTRACT The macrolide and levofloxacin susceptibilities of 992 isolates of Streptococcus pneumoniae from clinical specimens collected in 1999 and 2000 were determined in 10 centers in Central and Eastern European countries. The prevalences of penicillin G-intermediate (MICs, 0.125 to 1 μg/ml) and penicillin-resistant (MICs, ≤2 μg/ml) Streptococcus pneumoniae isolates were 14.3 and 16.6%, respectively. The MICs at which 50% of isolates are inhibited (MIC50s) and the MIC90s of telithromycin were 0.016 and 0.06 μg/ml, respectively; those of erythromycin were 0.06 and >64 μg/ml, respectively; those of azithromycin were 0.125 and >64 μg/ml, respectively; those of clarithromycin were 0.03 and >64 μg/ml, respectively; and those of clindamycin were 0.06 and >64 μg/ml, respectively. Erythromycin resistance was found in 180 S. pneumoniae isolates (18.1%); the highest prevalence of erythromycin-resistant S. pneumoniae was observed in Hungary (35.5%). Among erythromycin-resistant S. pneumoniae isolates, strains harboring erm(B) genes (125 strains [69.4%]) were found to be predominant over strains with mef(E) genes (25 strains [13.4%]), L4 protein mutations (28 strains [15.6%]), and erm(A) genes (2 strains [1.1%]). Similar pulsed-field gel electrophoresis patterns suggested that some strains containing L4 mutations from the Slovak Republic, Bulgaria, and Latvia were clonally related. Of nine strains highly resistant to levofloxacin (MICs, >8 μg/ml) six were isolated from Zagreb, Croatia. Telithromycin at ≤0.5 μg/ml was active against 99.8% of S. pneumoniae isolates tested and may be useful for the treatment of respiratory tract infections caused by macrolide-resistant S. pneumoniae isolates.

Antipneumococcal Activities of Gemifloxacin Compared to Those of Nine Other Agents

ABSTRACT The activities of gemifloxacin compared to those of nine other agents was tested against a range of penicillin-susceptible and -resistant pneumococci by agar dilution, microdilution, time-kill, and post-antibiotic effect (PAE) methods. Against 64 penicillin-susceptible, 68 penicillin-intermediate, and 75 penicillin-resistant pneumococci (all quinolone susceptible), agar dilution MIC50s (MICs at which 50% of isolates are inhibited)/MIC90s (in micrograms per milliliter) were as follows: gemifloxacin, 0.03/0.06; ciprofloxacin, 1.0/4.0; levofloxacin, 1.0/2.0; sparfloxacin, 0.5/1.0; grepafloxacin, 0.125/0.5; trovafloxacin, 0.125/0.25; amoxicillin, 0.016/0.06 (penicillin-susceptible isolates), 0.125/1.0 (penicillin-intermediate isolates), and 2.0/4.0 (penicillin-resistant isolates); cefuroxime, 0.03/0.25 (penicillin-susceptible isolates), 0.5/2.0 (penicillin-intermediate isolates), and 8.0/16.0 (penicillin-resistant isolates); azithromycin, 0.125/0.5 (penicillin-susceptible isolates), 0.125/>128.0 (penicillin-intermediate isolates), and 4.0/>128.0 (penicillin-resistant isolates); and clarithromycin, 0.03/0.06 (penicillin-susceptible isolates), 0.03/32.0 (penicillin-intermediate isolates), and 2.0/>128.0 (penicillin-resistant isolates). Against 28 strains with ciprofloxacin MICs of ≥8 μg/ml, gemifloxacin had the lowest MICs (0.03 to 1.0 μg/ml; MIC90, 0.5 μg/ml), compared with MICs ranging between 0.25 and >32.0 μg/ml (MIC90s of 4.0 to >32.0 μg/ml) for other quinolones. Resistance in these 28 strains was associated with mutations in parC, gyrA,parE, and/or gyrB or efflux, with some strains having multiple resistance mechanisms. For 12 penicillin-susceptible and -resistant pneumococcal strains (2 quinolone resistant), time-kill results showed that levofloxacin at the MIC, gemifloxacin and sparfloxacin at two times the MIC, and ciprofloxacin, grepafloxacin, and trovafloxacin at four times the MIC were bactericidal for all strains after 24 h. Gemifloxacin was uniformly bactericidal after 24 h at ≤0.5 μg/ml. Various degrees of 90 and 99% killing by all quinolones were detected after 3 h. Gemifloxacin and trovafloxacin were both bactericidal at two times the MIC for the two quinolone-resistant pneumococci. Amoxicillin at two times the MIC and cefuroxime at four times the MIC were uniformly bactericidal after 24 h, with some degree of killing at earlier time points. Macrolides gave slower killing against the seven susceptible strains tested, with 99.9% killing of all strains at two to four times the MIC after 24 h. PAEs for five quinolone-susceptible strains were similar (0.3 to 3.0 h) for all quinolones, and significant quinolone PAEs were found for the quinolone-resistant strain.

Comparative antianaerobic activity of BMS 284756

ABSTRACT Agar dilution MIC methodology was used to compare the activity of BMS 284756 with those of ciprofloxacin, levofloxacin, moxifloxacin, trovafloxacin, amoxicillin-clavulanate, piperacillin-tazobactam, imipenem, clindamycin, and metronidazole against 357 anaerobes. Overall, the respective MICs at which 50% of the isolates tested were inhibited (MIC50s) and MIC90s (in micrograms per milliliter) were as follows: BMS 284756, 0.5 and 2.0; ciprofloxacin, 2.0 and 16.0; levofloxacin, 1.0 and 8.0; moxifloxacin, 0.5 and 4.0; trovafloxacin, 0.5 and 2.0; amoxicillin-clavulanate, 0.5 and 2.0; piperacillin-tazobactam, 0.25 and 8.0; imipenem, 0.06 and 1.0; clindamycin, 0.25 and 8.0; and metronidazole, 1.0 and >16.0. BMS 284756 is a promising new quinolone with excellent antianaerobic activity.

Susceptibility to Telithromycin in 1,011 Streptococcus pyogenes Isolates from 10 Central and Eastern European Countries

ABSTRACT Among 1,011 recently isolated Streptococcus pyogenes isolates from 10 Central and Eastern European centers, the MICs at which 50% of isolates are inhibited (MIC50s) and the MIC90s were as follows: for telithromycin, 0.03 and 0.06 μg/ml, respectively; for erythromycin, azithromycin, and clarithromycin, 0.06 to 0.125 and 1 to 8 μg/ml, respectively; and for clindamycin, 0.125 and 0.125 μg/ml, respectively. Erythromycin resistance occurred in 12.3% of strains. Erm(A) [subclass erm(TR)] was most commonly encountered (60.5%), followed by mef(A) (23.4%) and erm(B) (14.5%). At <0.5 μg/ml, telithromycin was active against 98.5% of the strains tested.

Activities and Postantibiotic Effects of Gemifloxacin Compared to Those of 11 Other Agents against Haemophilus influenzae and Moraxella catarrhalis

ABSTRACT The activity of gemifloxacin against Haemophilus influenzae and Moraxella catarrhalis was compared to those of 11 other agents. All quinolones were very active (MICs, ≤0.125 μg/ml) against 248 quinolone-susceptible H. influenzae isolates (40.7% of which were β-lactamase positive); cefixime (MICs, ≤0.125 μg/ml) and amoxicillin-clavulanate (MICs ≤4.0 μg/ml) were active, followed by cefuroxime (MICs, ≤16.0 μg/ml); azithromycin MICs were ≤4.0 μg/ml. For nine H. influenzae isolates with reduced quinolone susceptibilities, the MICs at which 50% of isolates are inhibited (MIC50s) were 0.25 μg/ml for gemifloxacin and 1.0 μg/ml for the other quinolones tested. All strains had mutations in GyrA (Ser84, Asp88); most also had mutations in ParC (Asp83, Ser84, Glu88) and ParE (Asp420, Ser458), and only one had a mutation in GyrB (Gln468). All quinolones tested were equally active (MICs, ≤0.06 μg/ml) against 50 M. catarrhalis strains; amoxicillin-clavulanate, cefixime, cefuroxime, and azithromycin were very active. Against 10 H. influenzae strains gemifloxacin, levofloxacin, sparfloxacin, and trovafloxacin at 2× the MIC and ciprofloxacin at 4× the MIC were uniformly bactericidal after 24 h, and against 9 of 10 strains grepafloxacin at 2× the MIC was bactericidal after 24 h. After 24 h bactericidal activity was seen with amoxicillin-clavulanate at 2× the MIC for all strains, cefixime at 2× the MIC for 9 of 10 strains, cefuroxime at 4× the MIC for all strains, and azithromycin at 2× the MIC for all strains. All quinolones except grepafloxacin (which was bactericidal against four of five strains) and all ß-lactams at 2× to 4× the MIC were bactericidal against five M. catarrhalis strains after 24 h; azithromycin at the MIC was bactericidal against all strains after 24 h. The postantibiotic effects (PAEs) against four quinolone-susceptible H. influenzae strains were as follows: gemifloxacin, 0.3 to 2.3 h; ciprofloxacin, 1.3 to 4.2 h; levofloxacin, 2.8 to 6.2 h; sparfloxacin, 0.6 to 3.0 h; grepafloxacin, 0 to 2.1 h; trovafloxacin, 0.8 to 2.8 h. At 10× the MIC, no quinolone PAEs were found against the strain for which quinolone MICs were increased. Azithromycin PAEs were 3.7 to 7.3 h.

In Vitro Antianaerobic Activity of Ertapenem (MK-0826) Compared to Seven Other Compounds

ABSTRACT Ertapenem, imipenem, meropenem, ceftriaxone, piperacillin, piperacillin-tazobactam, clindamycin, and metronidazole were agar dilution MIC tested against 431 anaerobes. Imipenem, meropenem, and ertapenem were the most active β-lactams (MICs at which 50% of the strains are inhibited [MIC50s], 0.125 to 0.25 μg/ml; MIC90s, 1.0 to 2.0 μg/ml). Time-kill studies revealed that ertapenem at two times the MIC was bactericidal for 9 of 10 strains after 48 h. The kinetics for other β-lactams were similar to those of ertapenem.

Antistaphylococcal Activity of DX-619, a New Des-F(6)-Quinolone, Compared to Those of Other Agents

ABSTRACT The in vitro activity of DX-619, a new des-F(6)-quinolone, was tested against staphylococci and compared to those of other antimicrobials. DX-619 had the lowest MIC ranges/MIC50s/MIC90s (μg/ml) against 131 Staphylococcus aureus strains (≤0.002 to 2.0/0.06/0.5) and 128 coagulase-negative staphylococci (0.004 to 0.25/0.016/0.125). Among strains tested, 76 S. aureus strains and 51 coagulase-negative staphylococci were resistant to ciprofloxacin. DX-619 had the lowest MIC50/MIC90 values against 127 quinolone-resistant staphylococci (0.125/0.5), followed by sitafloxacin (0.5/4), moxifloxacin (2/8), gatifloxacin (4/16), levofloxacin (16/>32), and ciprofloxacin (>32/>32). Raised quinolone MICs were associated with mutations in GyrA (S84L) and single or double mutations in GrlA (S80F or Y; E84K, G, or V) in all S. aureus strains tested. A recent vancomycin-resistant S. aureus (VRSA) strain (Hershey) was resistant to available quinolones and was inhibited by DX-619 at 0.25 μg/ml and sitafloxacin at 1.0 μg/ml. Vancomycin (except VRSA), linezolid, ranbezolid, tigecycline, and quinupristin-dalfopristin were active against all strains, and teicoplanin was active against S. aureus but less active against coagulase-negative staphylococci. DX-619 produced resistant mutants with MICs of 1 to >32μ g/ml after <50 days of selection compared to 16 to> 32 μg/ml for ciprofloxacin, sitafloxacin, moxifloxacin, and gatifloxacin. DX-619 and sitafloxacin were also more active than other tested drugs against selected mutants and had the lowest mutation frequencies in single-step resistance selection. DX-619 and sitafloxacin were bactericidal against six quinolone-resistant (including the VRSA) and seven quinolone-susceptible strains tested, whereas gatifloxacin, moxifloxacin, levofloxacin, and ciprofloxacin were bactericidal against 11, 10, 7, and 5 strains at 4× MIC after 24 h, respectively. DX-619 was also bactericidal against one other VRSA strain, five vancomycin-intermediate S. aureus strains, and four vancomycin-intermediate coagulase-negative staphylococci. Linezolid, ranbezolid, and tigecycline were bacteriostatic and quinupristin-dalfopristin, teicoplanin, and vancomycin were bactericidal against two, eight, and nine strains, and daptomycin and oritavancin were rapidly bactericidal against all strains, including the VRSA. DX-619 has potent in vitro activity against staphylococci, including methicillin-, ciprofloxacin-, and vancomycin-resistant strains.

Activities of a New Oral Streptogramin, XRP 2868, Compared to Those of Other Agents against Streptococcus pneumoniae and Haemophilus Species

ABSTRACT MIC methodology was used to test the antibacterial activity of XRP 2868, a new oral combination of two semisynthetic streptogramins, RPR 132552A and RPR 202868, compared to activities of other antibacterial agents against pneumococci, Haemophilus influenzae, and Haemophilus parainfluenzae. For 261 pneumococci, XRP 2868 and pristinamycin MICs were similar, irrespective of penicillin G and erythromycin A susceptibilities (MIC at which 50% of isolates were inhibited [MIC50], 0.25 μg/ml; MIC90, 0.5 μg/ml), while quinupristin/dalfopristin had MICs which were 1 to 2 dilutions higher. Single components of both XRP 2868 and quinupristin/dalfopristin had higher MICs. Erythromycin A, azithromycin, clarithromycin, and clindamycin MICs were higher for penicillin G-intermediate and -resistant than -susceptible pneumococci. Against 150 H. influenzae strains, all compounds tested had unimodal MIC distributions. XRP 2868 had an overall MIC50 of 0.25 μg/ml and an MIC90 of 1.0 μg/ml, with no differences between β-lactamase-positive, β-lactamase-negative, and β-lactamase-negative ampicillin-resistant strains. Of note was the similarly low activity of one of its components, RPR 132552A. Pristinamycin and quinupristin/dalfopristin had MICs of 0.125 to 8.0 μg/ml; quinupristin alone had MICs of 8.0 to >64.0 μg/ml, and dalfopristin had MICs of 1.0 to >64.0 μg/ml. Erythromycin A, azithromycin, and clarithromycin had modal MICs of 4.0, 1.0, and 8.0 μg/ml, respectively. MICs of all compounds against H. parainfluenzae were 1 to 2 dilutions higher than against H. influenzae. XRP 2868 showed potent activity against pneumococci and Haemophilus strains irrespective of their susceptibility to other agents.

Antipneumococcal Activity of DK-507k, a New Quinolone, Compared with the Activities of 10 Other Agents

ABSTRACT Agar dilution MIC determination was used to compare the activity of DK-507k with those of ciprofloxacin, levofloxacin, gatifloxacin, moxifloxacin, sitafloxacin, amoxicillin, cefuroxime, erythromycin, azithromycin, and clarithromycin against 113 penicillin-susceptible, 81 penicillin-intermediate, and 67 penicillin-resistant pneumococci (all quinolone susceptible). DK-507k and sitafloxacin had the lowest MICs of all quinolones against quinolone-susceptible strains (MIC at which 50% of isolates were inhibited [MIC50] and MIC90 of both, 0.06 and 0.125 μg/ml, respectively), followed by moxifloxacin, gatifloxacin, levofloxacin, and ciprofloxacin. MICs of β-lactams and macrolides rose with those of penicillin G. Against 26 quinolone-resistant pneumococci with known resistance mechanisms, DK-507k and sitafloxacin were also the most active quinolones (MICs, 0.125 to 1.0 μg/ml), followed by moxifloxacin, gatifloxacin, levofloxacin, and ciprofloxacin. Mutations in quinolone resistance-determining regions of quinolone-resistant strains were in the usual regions of the parC and gyrA genes. Time-kill testing showed that both DK-507k and sitafloxacin were bactericidal against all 12 quinolone-susceptible and -resistant strains tested at twice the MIC at 24 h. Serial broth passages in subinhibitory concentrations of 10 strains for a minimum of 14 days showed that development of resistant mutants (fourfold or greater increase in the original MIC) occurred most rapidly for ciprofloxacin, followed by moxifloxacin, DK-507k, gatifloxacin, sitafloxacin, and levofloxacin. All parent strains demonstrated a fourfold or greater increase in initial MIC in<50 days. MICs of DK-507k against resistant mutants were lowest, followed by those of sitafloxacin, moxifloxacin, gatifloxacin, ciprofloxacin, and levofloxacin. Four strains were subcultured in subinhibitory concentrations of each drug for 50 days: MICs of DK-507k against resistant mutants were lowest, followed by those of sitafloxacin, moxifloxacin, gatifloxacin, levofloxacin, and ciprofloxacin. Exposure to DK-507k and sitafloxacin resulted in mutations, mostly in gyrA.

Antipneumococcal Activities of Two Novel Macrolides, GW 773546 and GW 708408, Compared with Those of Erythromycin, Azithromycin, Clarithromycin, Clindamycin, and Telithromycin

ABSTRACT The MICs of GW 773546, GW 708408, and telithromycin for 164 macrolide-susceptible and 161 macrolide-resistant pneumococci were low. The MICs of GW 773546, GW 708408, and telithromycin for macrolide-resistant strains were similar, irrespective of the resistance genotypes of the strains. Clindamycin was active against all macrolide-resistant strains except those with erm(B) and one strain with a 23S rRNA mutation. GW 773546, GW 708408, and telithromycin at two times their MICs were bactericidal after 24 h for 7 to 8 of 12 strains. Serial passages of 12 strains in the presence of sub-MICs yielded 54 mutants, 29 of which had changes in the L4 or L22 protein or the 23S rRNA sequence. Among the macrolide-susceptible strains, resistant mutants developed most rapidly after passage in the presence of clindamycin, GW 773546, erythromycin, azithromycin, and clarithromycin and slowest after passage in the presence of GW 708408 and telithromycin. Selection of strains for which MICs were ≥0.5 μg/ml from susceptible parents occurred only with erythromycin, azithromycin, clarithromycin, and clindamycin; 36 resistant clones from susceptible parent strains had changes in the sequences of the L4 or L22 protein or 23S rRNA. No mef(E) strains yielded resistant clones after passage in the presence of erythromycin and azithromycin. Selection with GW 773546, GW 708408, telithromycin, and clindamycin in two mef(E) strains did not raise the erythromycin, azithromycin, and clarithromycin MICs more than twofold. There were no change in the ribosomal protein (L4 or L22) or 23S rRNA sequences for 15 of 18 mutants selected for macrolide resistance; 3 mutants had changes in the L22-protein sequence. GW 773546, GW 708408, and telithromycin selected clones for which MICs were 0.03 to >2.0 μg/ml. Single-step studies showed mutation frequencies <5.0 × 10−10 to 3.5 × 10−7 for GW 773546, GW 708408, and telithromycin for macrolide-susceptible strains and 1.1 × 10−7 to >4.3 × 10−3 for resistant strains. The postantibiotic effects of GW 773546, GW 708408, and telithromycin were 2.4 to 9.8 h.