Journal of Antimicrobial Chemotherapy (1999) 44, 621-627
© 1999 The British Society for Antimicrobial Chemotherapy
Activity of moxifloxacin against pathogens with decreased susceptibility to ciprofloxacin
a Department of Paediatrics b Centre for Research in Anti-Infectives and Biotechnology, Department of Medical Microbiology and Immunology, Creighton University School of Medicine, Omaha, NE 68178 c Childrens Hospital, San Diego, CA 92123, USA
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Abstract |
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A panel of 279 clinical isolates of Gram-positive cocci and Gram-negative bacilli with varying levels of resistance to ciprofloxacin were analysed for susceptibility to moxifloxacin, ciprofloxacin, ofloxacin and nalidixic acid. Moxifloxacin was eight- to 32-fold more potent than ciprofloxacin and ofloxacin against staphylococci and Streptococcus pneumoniae, and equivalent to eight-fold more potent against enterococci. Although ciprofloxacin was intrinsically more potent than the other quinolones against highly susceptible Gram-negative isolates, the percentages of Gram-negative isolates susceptible to 1 mg/L of moxifloxacin or ciprofloxacin, or 2 mg/L of ofloxacin were 78%, 80% and 76%, indicating in-vitro equivalence of the agents against a collection that included isolates with diminished quinolone susceptibility. Staphylococci were analysed according to their ciprofloxacin susceptibility status. As ciprofloxacin resistance increased to high levels, all quinolone MICs increased, but moxifloxacin and ofloxacin MICs increased less than ciprofloxacin MICs. In mutational studies moxifloxacin inhibited more mutants (69%) at a concentration of 1 mg/L than did ciprofloxacin (63%) at 1 mg/L or ofloxacin at 2 mg/L (31%). The study indicated that moxifloxacin is more potent than ciprofloxacin and ofloxacin against Gram-positive pathogens, may be comparable in activity against less quinolone-susceptible Gram-negative isolates (other than Pseudomonas aeruginosa), and is less affected than ciprofloxacin by mechanisms responsible for increasing quinolone resistance in staphylococci.
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Introduction |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
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Quinolones are a class of antibiotics widely used in clinical medicine. Development of resistance is a limiting factor in treatment especially with certain bacterial pathogens.1,2 While cross resistance between older quinolones can occur, certain newer quinolones are more potent and may maintain activity against less susceptible mutants of pathogens such as pneumococci, staphylococci, and non-fermentative Gram-negative bacilli such as Stenotrophomonas maltophilia, Acinetobacter spp., etc.3,4,5 These agents may prove to be of better clinical value because of their increased activity and decreased potential for selecting resistant mutants.
Moxifloxacin (BAY 12-8039) is an 8-methoxyquinolone with increased activity against Gram-positive bacteria.6,7,8,9,10,11,12 The purpose of this study was to determine (i) the in-vitro activity of moxifloxacin against bacteria with varying levels of resistance to ciprofloxacin; (ii) the potential of moxifloxacin to select mutational resistance; (iii) the degree of cross resistance of mutants selected with various fluoroquinolones; and (iv) the bactericidal activity of moxifloxacin, ciprofloxacin and ofloxacin against selected isolates of Staphylococcus aureus and Streptococcus pneumoniae.
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Materials and methods |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
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Bacterial strains
A total of 279 clinical isolates with varying susceptibility to ciprofloxacin, ß-lactams and aminoglycosides were tested. The isolates were recovered from patients throughout Australia, Czechoslovakia, Hungary, Spain, Sweden, the UK and the USA. Some isolates were obtained from patients treated unsuccessfully with currently available antibiotics. They were not random clinical isolates.
Susceptibility testing
Antimicrobial agents tested were moxifloxacin, ciprofloxacin (Bayer, Inc., West haven, CT, USA), ofloxacin (R.W. Johnson Pharmaceutical Research Institute, Raritan, NJ, USA), imipenem (Merck Sharp & Dohme, West Point, PA, USA), piperacillin–tazobactam (Wyeth-Ayerst, Pearl River, NY, USA), nalidixic acid, tetracycline, oxacillin, penicillin (Sigma Chemical Co., St Louis, MO, USA), ceftazidime (Glaxo Pharmaceuticals, Research Triangle Park, NC, USA), gentamicin (Schering Corporation, Bloomfield, NJ, USA) and vancomycin (Eli Lilly, Indianapolis, IN, USA), The quinolones were tested against all clinical isolates and mutants. Non-quinolone agents were tested only against parent and mutant strains to determine whether mutational cross resistance emerged to other classes of agents following exposure to quinolones.
Antibiotic susceptibilities were determined by agar dilution methodology using a multipoint inoculator (manufactured by the Physics Machine Shop at Creighton University, Omaha, NE, USA) and an inoculum of 104 cfu/spot on Mueller–Hinton agar (CM337, Oxoid Ltd., Basingstoke, UK).13 The Mueller–Hinton agar was supplemented with 4% NaCl for tests of staphylococci with ß-lactams, 5% sheep blood for S. pneumoniae, and Haemophilus Test medium supplementation for Haemophilus influenzae. Cultures were incubated for 18–24 h in air, except for S. pneumoniae and H. influenzae which were incubated in 5% CO2. Quality control strains were Escherichia coli ATCC 25922, E. coli ATCC 35218, Enterococcus faecalis ATCC 29212, Pseudomonas aeruginosa ATCC 27853, H. influenzae ATCC 49247 and S. pneumoniae ATCC 49619.
The staphylococci were separated into three phenotypic groups on the basis of their
susceptibility to ciprofloxacin in agar dilution tests: susceptible (MIC 
0.5 mg/L),
moderately
resistant (1–4 mg/L) and highly resistant (
8 mg/L).
Mutational frequencies
Mutants were selected from eight representative strains of S. pneumoniae, E. faecalis, Enterococcus faecium, S. aureus, Staphylococcus epidermidis, E. coli, Klebsiella pneumoniae and Moraxella catarrhalis. Parent strains were grown in Mueller–Hinton broth until mid-logarithmic phase. S. pneumoniae was grown on blood agar overnight and suspended in sterile physiological saline. Inocula of 107–109 cfu were added to Mueller–Hinton agar or Mueller–Hinton agar with 5% sheep blood (S. pneumoniae) containing quinolones at superinhibitory concentrations of two, four and eight times the MIC. The actual inoculum used was determined by serial dilution plate counts. Plates were incubated for 48–72 h at 35°C in air (5% CO2 for S. pneumoniae) and colony counts were performed. Mutational frequencies were calculated from the results obtained for plates containing the highest drug concentration on which colonies were obtained. The procedure was repeated with first step mutants to select second and subsequent step mutants in tests with staphylococci. Antimicrobial susceptibilities of parents and mutants were determined as described above with the non-quinolone agents included to evaluate the development of resistance to other drug classes.
Bactericidal activity
Investigations into bactericidal activity were performed with S. aureus strain 41 (oxacillin susceptible), S. aureus strain 27 (oxacillin resistant) and S. pneumoniae strain 212. Stationary-phase cultures were exposed to each fluoroquinolone at multiples of 0.5 x, 1 x, and 4 x MIC and incubated at 37°C in air or 5% CO2 (S. pneumoniae). Samples were subcultured at intervals of 0, 2, 4, 6 and 24 h for viable counts on Mueller–Hinton or sheep blood (S. pneumoniae only) agar containing 5 mM FeCl3 to overcome drug carryover.14 Agar dilution MICs were determined for organisms that showed an increase in numbers after initial killing. Viable counts were compared with drug free control cultures. The lowest countable number obtainable with this procedure was 300 cfu/mL.
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Results |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
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Antibiotic susceptibilities
Moxifloxacin was eight- to 32-fold more potent than ciprofloxacin and ofloxacin against staphylococci and S. pneumoniae, and up to eight-fold more potent against enterococci (Table I). Moxifloxacin was two- to eight-fold more potent against oxacillin-susceptible S. aureus than against oxacillin-resistant S. aureus. Against Enterobacteriaceae, M. catarrhalis and H. influenzae, moxifloxacin was generally up to four-fold less potent than ciprofloxacin, and up to two-fold more potent than ofloxacin. The percentages of isolates susceptible to ciprofloxacin, ofloxacin, nalidixic acid or to 1 mg/L of moxifloxacin are shown in Table I. For all Gram-positive isolates these percentages were 77, 48 and 62% for moxifloxacin, ciprofloxacin and ofloxacin, respectively, while the comparable respective percentages for all Gram-negative isolates were 78, 80 and 76%. Resistance to 2 mg/L of moxifloxacin occurred in S. aureus (nine isolates), coagulase-negative staphylococci (eight isolates), enterococci (four isolates), Serratia marcescens (five isolates), Citrobacter freundii (four isolates), Klebsiella spp. (three isolates), E. coli (two isolates), Enterobacter aerogenes (two isolates) and E. cloacae (one isolate). All S. pneumoniae isolates were inhibited by 0.25 mg/L of moxifloxacin.
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Susceptibilities to moxifloxacin of S. aureus strains with varying resistance to ciprofloxacin are shown in Table II. Moxifloxacin was approximately eight-fold more potent than ciprofloxacin against ciprofloxacin-susceptible strains (MIC of ciprofloxacin
0.5
mg/L), and was approximately 32-fold more potent against moderately ciprofloxacin resistant
(MIC 1–4 mg/L) and highly ciprofloxacin-resistant (MIC > 8 mg/L) strains. A
comparable increase in relative potency was also seen in tests with coagulase-negative
staphylococci (data not shown). Moxifloxacin was two- to four-fold more potent than
ciprofloxacin against ciprofloxacin-susceptible coagulase-negative strains, approximately
eight-fold more potent against moderately ciprofloxacin-resistant strains and approximately
32-fold more potent against highly ciprofloxacin-resistant strains. Moxifloxacin was consistently
eight- to 16-fold more potent than ofloxacin against staphylococci, with no significant change in
the relative potencies of the two agents as quinolone resistance increased.
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Mutant studies
The ability of the quinolones to select less susceptible single-step mutants was determined by exposing eightisolates to superinhibitory concentrations of each agent. Mutants were selected from all eight strains exposed to ciprofloxacin, and from six and five strains exposed to moxifloxacin and ofloxacin, respectively. A total of 32 mutants were selected. Of these, 69% and 63% were susceptible to 1 mg/L of moxifloxacin and ciprofloxacin, respectively, and 31% were susceptible to 2 mg/L of ofloxacin. When only mutants selected at the highest concentration of each quinolone were considered, mutational frequencies ranging from 10-6 to 10-8 were obtained for 17 of the 20 (85%) single-step mutants recovered.
Concurrent decreases in susceptibility to non-quinolone agents were detected in mutants selected from two Gram-negative organisms. Two of five mutants selected from K. pneumoniae strain 130 exhibited 16-fold increases in MIC of imipenem (from 0.12 to 2 mg/L). These mutants were selected with moxifloxacin and ciprofloxacin. Two out of eight mutants selected with ofloxacin from M. catarrhalis BT84 exhibited four-fold increases in the MIC of tetracycline (from 1 to 4 mg/L).
Effect of de-novo quinolone resistance on subsequent development of quinolone resistance
Attempts were made to select successive single-step mutants from a single strain each of S.
aureus and S. epidermidis. Using moxifloxacin and ciprofloxacin as selecting
agents it was not possible to select less susceptible mutants of S. aureus strain 255 with
moxifloxacin. First-, second- and third-step mutants however, were selected with ciprofloxacin,
each at a frequency of 10-7. After three mutational steps, the MICs of
ciprofloxacin and ofloxacin were 128 mg/L, whereas the MIC of moxifloxacin was only 4
mg/L (Table III).
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In tests with S. epidermidis strain 1, first- and second-step mutants were selected after exposure to moxifloxacin at a mutational frequency of 10-9, but no subsequent-step mutants were selected with this agent (Table III). Greater mutational frequencies (10-5–10-7) were detected when first-, second- and third-step mutants were selected with ciprofloxacin. the third-step mutant selected with ciprofloxacin exhibited MICs of 1, 64 and 16 mg/L for moxifloxacin, ciprofloxacin and ofloxacin, respectively.
A first-step mutant of S. pneumoniae strain 212 was selected only with exposure to ciprofloxacin. No subsequent-step mutants were selected with either ofloxacin, moxifloxacin or ciprofloxacin.
Bactericidal activity against S. aureus and S. pneumoniae
Initial inocula were 4.4 x 105 cfu/mL, 5.5 x 104
cfu/mL and 5.6 x 105 cfu/mL for S. aureus strain 41
(oxacillin-susceptible), S. aureus strain 27 (oxacillin-resistant) and S. pneumoniae
strain 212, respectively. All quinolones tested were bactericidal ( 3 log10
decrease in viable count) against each strain at concentrations four-fold above the MIC, as shown
in Figures 1, 2 and 3.
Ofloxacin was also bactericidal at its MIC against S. aureus strain
41. Less susceptible mutants of S. aureus strain 41 were selected at the MIC and half the
MIC of ciprofloxacin, and at half the MIC of moxifloxacin. Less susceptible mutants of S.
aureus strain 27 were selected at the MIC of each agent. The concentrations of each drug to
inhibit all staphylococcal mutants were 0.25 mg/L of moxifloxacin and 2 mg/L of ciprofloxacin
and ofloxacin. No mutational decreases in susceptibility were detected in tests with S.
pneumoniae strain 212.
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; Mox 0.5, 
;
Mox1x, •; Mox 4x,
; Oflox 0.5x, 
; Oflox
1x, 
; Oflox 4x, 
; Cipro 0.5x, 
; Cipro 1x,
; Cipro 4x, 
.
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Discussion |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
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High potency and low potential for mutational selection are desired features of an antimicrobial agent. The current study confirmed the greater potency of moxifloxacin compared with ciprofloxacin and ofloxacin against Gram-positive organisms including oxacillin-resistant S. aureus. Moreover, in contrast to many studies of predominantly highly-susceptible isolates,6,7,8,9 moxifloxacin and ofloxacin were found to have comparable activity to ciprofloxacin against this collection of Gram-negative isolates which included many isolates with reduced susceptibility to ciprofloxacin. This finding should be interpreted against the perspective that the study did not include P. aeruginosa (an organism against which ciprofloxacin is highly active),1,5,6,12,14 and also the presumption of a susceptible moxifloxacin breakpoint of 1 mg/L.
The reason for moxifloxacin being less affected than ciprofloxacin by mechanisms responsible for increasing quinolone resistance in staphylococci were not investigated. However, this finding was consistent with other reports in which ciprofloxacin was noted to be more affected than some other quinolones by quinolone resistance mechanisms in staphylococci and in other types of bacteria.5,14,1516 This feature of moxifloxacin, coupled with its enhanced potency against a variety of Gram-positive pathogens, suggests that it should be a suitable candidate for clinical evaluation.
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Acknowledgments |
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The results of this study were presented in part at the Thirty-Seventh Interscience Conference on Antimicrobial Agents and Chemotherapy, Toronto, Canada, 1997. Abstract C-85. We thank the many colleagues who provided the isolates included in the study, S. S. Morrow for excellent technical assistance, K. Wise for typing the manuscript and B. Painter for making the study possible. This work was supported by a grant from Bayer Inc.
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Notes |
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* Corresponding author. Tel +1-402-208-1881; Fax: +1-402-280-1225; E-mail: kstaac{at}creighton.edu
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References |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
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1 . Dalhoff, A. (1994). Quinolone resistance in Pseudomonas aeruginosa and Staphylococcus aureus. Development during therapy and clinical significance. Infection 22, Suppl 2, S111–21.
2 . Wiedemann, B. & Heisig, P. (1994). Mechanisms of quinolone resistance. Infection 22, Suppl. 2, S73–9.
3
.
Akaniro, J. C., Stutman, H. R., Arguedas, A. G. & Vargas, O. M. (1992). In-vitro activity of sparfloxacin (AT-4140), a new quinolone agent, against invasive
isolates from pediatric patients. Antimicrobial Agents and Chemotherapy
36,255
–61.
4 . Aldridge, K. E., Jones, R. N., Barry, A. L. & Gelfand, M. S. (1992). In-vitro activity of various antimicrobial agents against Staphylococcus aureus isolates including fluoroquinolone- and oxacillin-resistant strains. Diagnostic Microbiology and Infectious Disease 15,517 –21.[Web of Science][Medline]
5
.
Thomson, K. S., Sanders, C. C. & Hayden, M. E. (1991). In-vitro
studies with five quinolones: evidence for changes in relative potency as quinolone resistance
rises. Antimicrobial Agents and Chemotherapy
35,2329
–34.
6
.
Bauernfeind, A. (1997). Comparison of the
antibacterial activities of the quinolones BAY 12-8039, gatifloxacin (AM 1155), trovafloxacin,
clinafloxacin, levofloxacin and ciprofloxacin. Journal of Antimicrobial Chemotherapy
40,639
–51 (Erratum 41, 672).
7 . Brueggemann, A. B., Kugler, K. C. & Doern, G. V. (1997). In-vitro activity of BAY 12-8039, a novel 8-methoxyquinolone, compared to activities of six fluoroquinolones against Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis. Antimicrobial Agents and Chemotherapy 41,1594 –7.[Abstract]
8 . Dalhoff, A., Petersen, U. & Endermann, R. (1996). In-vitro activity of BAY 12-8039, a new 8-methoxyquinolone. Chemotherapy 42, 410–25.[Web of Science][Medline]
9 . Fass, R. J. (1997). In-vitro activity of BAY 12-8039, a new 8-methoxyquinolone. Antimicrobial Agents and Chemotherapy 41,1818 –24.[Abstract]
10 . Souli, M., Wennersten, C. B. & Eliopoulos, G. M. (1998). In-vitro activity of BAY 12-8039, a new fluoroquinolone, against species representative of respiratory tract pathogens. International Journal of Antimicrobial Agents 10, 23–30.[Web of Science][Medline]
11 . Visalli, M. A., Jacobs, M. R. & Applebaum, P. C. (1997). Antipneumococcal activity of BAY 12-8039, a new quinolone, compared with activities of three other quinolones and four oral ß-lactams. Antimicrobial Agents and Chemotherapy 41,2786 –9[Abstract]
12 . Woodcock, J. M., Andrews, J. M., Boswell, F. J., Brenwald, N. P. & Wise, R. (1997). In-vitro activity of BAY 12-8039, a new fluoroquinolone. Antimicrobial Agents and Chemotherapy 41,101 –6.[Abstract]
13 . National Committee for Clinical Laboratory Standards. (1997). Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow Aerobically—Fourth Edition: Approved Standard M7-A4. NCCLS, Villanova, PA.
14
.
Thomson, K. S. & Sanders, C. C. (1998). The effects of
increasing
levels of quinolone resistance on in-vitro activity of four quinolones. Journal of Antimicrobial Chemotherapy
42,179
–87.
15
.
Thomson, K. S. & Sanders, C. C. (1994). Dissociated resistance
among
fluoroquinolones. Antimicrobial Agents and Chemotherapy
38, 2095–100.
16 . Thomson, K. S., Moland, E. S. & Sanders, C. C. (1999). Activity of trovafloxacin against antibiotic-resistant pathogens. Infectious Diseases in Clinical Practice 8, Suppl. 1, S7–16.
Received 5 February 1999; returned 21 April 1999; revised 28 May 1999; accepted 28 June 1999
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