C L Clark

Penn State Hershey Medical Center and Penn State College of Medicine, Hershey, Pennsylvania, United States

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Publications (5)21.38 Total impact

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    ABSTRACT: Single- and Multi-step selection studies were used to test the ability of BMS-284756, ciprofloxacin, levofloxacin, trovafloxacin and moxifloxacin to yield resistant clones from 12 quinolone-susceptible and -resistant Streptococcus pneumoniae strains. Although all quinolones selected, to a greater or lesser degree, for resistant clones with mutations usually in parC or gyrA, BMS-284756 tended to select for resistant clones at a lower rate than other quinolones studied.
    Clinical Microbiology and Infection 07/2002; 8(6):373-80. DOI:10.1046/j.1469-0691.2002.00405.x · 5.77 Impact Factor
  • C L Clark · L M Kelly · M R Jacobs · P C Appelbaum
    European Journal of Clinical Microbiology 08/2000; 19(7):565-7. DOI:10.1007/s100960000314 · 2.67 Impact Factor
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    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 microgram/ml) against 248 quinolone-susceptible H. influenzae isolates (40.7% of which were beta-lactamase positive); cefixime (MICs, </=0.125 microgram/ml) and amoxicillin-clavulanate (MICs </=4.0 microgram/ml) were active, followed by cefuroxime (MICs, </=16.0 microgram/ml); azithromycin MICs were </=4.0 microg/ml. For nine H. influenzae isolates with reduced quinolone susceptibilities, the MICs at which 50% of isolates are inhibited (MIC(50)s) were 0.25 microgram/ml for gemifloxacin and 1.0 microgram/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 microgram/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 2x the MIC and ciprofloxacin at 4x the MIC were uniformly bactericidal after 24 h, and against 9 of 10 strains grepafloxacin at 2x the MIC was bactericidal after 24 h. After 24 h bactericidal activity was seen with amoxicillin-clavulanate at 2x the MIC for all strains, cefixime at 2x the MIC for 9 of 10 strains, cefuroxime at 4x the MIC for all strains, and azithromycin at 2x the MIC for all strains. All quinolones except grepafloxacin (which was bactericidal against four of five strains) and all ss-lactams at 2x to 4x 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 10x 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.
    Antimicrobial Agents and Chemotherapy 04/2000; 44(3):633-9. DOI:10.1128/AAC.44.3.633-639.2000 · 4.48 Impact Factor
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    C L Clark · M R Jacobs · P C Appelbaum
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    ABSTRACT: Time-kill studies indicated that clinafloxacin showed synergy after 24 h with ceftazidime, amikacin, and imipenem against 12, 8, and 10 of 33 gram-negative rods, respectively; with vancomycin, teicoplanin, cefotaxime, and amikacin against 3, 3, 1, and 1 of 9 staphylococci and enterococci, respectively; and with vancomycin, penicillin, and cefotaxime against 0, 2, and 2 of 3 pneumococci, respectively. The MICs of clinafloxacin alone for most strains were >/=1 microg/ml.
    Antimicrobial Agents and Chemotherapy 09/1999; 43(9):2295-8. · 4.48 Impact Factor
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    C L Clark · M R Jacobs · P C Appelbaum
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    ABSTRACT: The activities of levofloxacin and clarithromycin against 199 penicillin- and macrolide-susceptible and -resistant pneumococci were tested by agar and microdilution methods in air and by disk diffusion and E-test methods in air and CO2. For levofloxacin, >/=99. 0% of strains were susceptible at </=2.0 microgram/ml with zone diameters of >/=17 mm, regardless of incubation in air or CO2. Although zone sizes were smaller and E-test MICs were higher for clarithromycin in CO2 than those in air, category differences were minor, and susceptibility rates for clarithromycin were similar to those obtained by agar and microdilution in air (range, 76.9 to 80.9% by all methods). For clarithromycin, adjustment of breakpoints based upon distribution of results resulted in susceptibility rates which were similar by all methods (75.8 to 76.9% susceptible, 0 to 1.5% intermediate, 22.6 to 23.1% resistant). Minor discrepancies were obtained with levofloxacin for one strain (0.5%) by microdilution and two strains (1.0%) by disk diffusion in CO2. For clarithromycin, minor discrepancies were found in three strains (1.5%) by microdilution, seven strains (3.5%) by agar dilution, four strains (2.0%) by E-test in air, six strains (3.0%) by disk diffusion in air, and five strains (2.5%) by disk diffusion in CO2. Major discrepancies occurred with levofloxacin in one strain (0.5%) by microdilution but were not found with clarithromycin. Very major discrepancies were not seen with levofloxacin, but occurred with clarithromycin in five strains (2.5%) by microdilution, three strains (1.5%) by agar dilution, two strains (1.0%) by E-test in air, eight strains (4.0%) by disk diffusion in air, and one strain (0.5%) by disk diffusion in CO2.
    Journal of Clinical Microbiology 01/1999; 36(12):3579-84. · 3.99 Impact Factor

Publication Stats

69 Citations
21.38 Total Impact Points


  • 1999–2002
    • Penn State Hershey Medical Center and Penn State College of Medicine
      • Department of Pathology
      Hershey, Pennsylvania, United States
  • 2000
    • Case Western Reserve University
      • Department of Oral Pathology
      Cleveland, Ohio, United States