Minimal inhibitory concentrations and time-kill determination of moxifloxacin against aerobic and anaerobic isolates

International Journal of Antimicrobial Agents 19 (2002) 111– 118 www.ischemo.org

Original article

Minimal inhibitory concentrations and time-kill determination of moxifloxacin against aerobic and anaerobic isolates A. Speciale *, R. Musumeci, G. Blandino, I. Milazzo, F. Caccamo, G. Nicoletti Department of Microbiological and Gynaecological Sciences, Uni6ersity of Catania, Via Androne, 81 -95124 Catania, Italy Received 24 August 2001; accepted 11 October 2001

Abstract Moxifloxacin is a new oral 8-methoxy-quinolone with a wide spectrum of activity against Gram-negative and anaerobic bacteria, atypical micro-organisms and multi-resistant Gram-positive bacteria. This study was designed to assess the in vitro activity of moxifloxacin against Gram-positive bacteria with different resistance patterns, anaerobes and atypical micro-organisms such as Chlamydia and Mycoplasma. Moxifloxacin had good activity against Streptococcus pneumoniae with all strains inhibited by 00.12 mg/l. The minimal inhibitory concentrations (MICs) of moxifloxacin for Streptococcus pyogenes and Streptococcus agalactiae ranged from 0.03 to 0.5 mg/l while those of ciprofloxacin were about two- to four-fold higher (MICs = 0.12–1 mg/l). Moxifloxacin was poorly active against enterococci but its activity against Clostridium and Bacteroides spp. was in the same range as that of metronidazole and superior to that of clindamycin. Moxifloxacin was substantially more active than both ciprofloxacin and sparfloxacin against Chlamydia. © 2002 Elsevier Science B.V. and the International Society of Chemotherapy. All rights reserved. Keywords: Moxifloxacin; Aerobes; Anaerobes; Time-kill

1. Introduction Fluoroquinolones came into clinical use in the 1980s with the release of norfloxacin and ciprofloxacin [1]. Since then, many additional fluoroquinolones have been developed. Fluoroquinolones are effective in the management of Gram-negative bacterial infections [2,3], but the usefulness of currently available agents against Gram-positive micro-organisms is not well defined [4]. Treatment of Gram-positive infections is becoming more difficult with increasing resistance developing to commonly used antibiotics and so there is a need for newly developed antimicrobial agents. Several fluoroquinolones used to treat Gram-negative bacterial infections have shown good antibacterial activity against Gram-positive bacteria [5]. Moxifloxacin is a new oral 8-methoxy-quinolone with a wide spectrum of * Corresponding author. Tel.: + 39-095-312386; fax: +39-095325032. E-mail address: [email protected] (A. Speciale).

activity; it is active against Gram-negative and anaerobic bacteria, atypical bacteria and multi-resistant Gram-positive bacteria [6–8]. This study assessed the in vitro activity of moxifloxacin against Gram-positive bacteria with different resistance patterns, anaerobes and atypical micro-organisms such as Chlamydia and Mycoplasma.

2. Methods

2.1. Bacterial strains Bacteria studied included methicillin-resistant/ ciprofloxacin-sensitive Staphylococcus aureus (n=20), methicillin-resistant/ciprofloxacin-resistant S. aureus (10), methicillin-sensitive Streptococcus epidermidis (18), methicillin-resistant S. epidermidis (10), Streptococcus pneumoniae (43), Streptococcus pyogenes (16), Streptococcus agalactiae (18), Enterococcus faecalis (12), Enterococcus faecium (15, Van A= 6 of 15), Clostridium

0924-8579/02/$ - $20 © 2002 Elsevier Science B.V. and the International Society of Chemotherapy. All rights reserved. PII: S 0 9 2 4 - 8 5 7 9 ( 0 1 ) 0 0 4 8 6 - 1

112

A. Speciale et al. / International Journal of Antimicrobial Agents 19 (2002) 111–118

perfrigens (10), Clostridium difficile (1), Bacteroides fragilis (14), Mycoplasma pneumoniae (12), Mycoplasma hominis (8), Ureaplasma urealyticum (11), Chlamydia trachomatis (10) and Chlamydia pneumoniae (7).

2.2. Antibiotics The following drugs (provided as laboratory powders) were evaluated: moxifloxacin and ciprofloxacin (Bayer AG), sparfloxacin (Rhoˆ ne-Poulenc Rorer), ceftriaxone (Roche), imipenem and cefoxitin (Merck, Sharp & Doˆ hme), teicoplanin (Hoechst, Marion-Roussel), vancomycin (Eli-Lilly), erythromycin and clarithromycin (Abbott), clindamycin (Upjohn), penicillin, ampicillin and amoxycillin (Pharmacia), cefixime (Menarini), meropenem (Zeneca), tazobactam/ piperacillin (Lederle), cefotetan (Zeneca), metronidazole (Bristol-Myers Squibb), doxycycline (Liferpharma).

2.3. Minimal inhibitory concentration determination Minimal inhibitory concentration (MIC) values for Gram-positive cocci were determined by a broth microdilution procedure (Mueller-Hinton broth for staphylococci and enterococci) as recommended by the National Committee for Clinical Laboratory Standards [9] and by the Manual of Clinical Microbiology [10]. Cation-adjusted Mueller-Hinton broth with 5% lysed sheep blood was used for streptococci. Fresh cultures of each strain were used to inoculate each well of a microtitre plate, giving a final inoculum of : 5 ×105 colony-forming units (CFU/ml) derived from an 18-h broth culture. Serial two-fold dilutions of antimicrobial agents were made. After 24 h incubation at 37 °C, the presence or absence of growth was observed for each well. The MIC was defined as the lowest concentration of an agent that yielded no growth or a marked change in the appearance of growth compared with the growth control plate. Agar dilution MICs for anaerobes were determined as recommended by the National Committee for Clinical Laboratory Standards [11] on Wilkins Chalgren Agar supplemented with 1% heat-inactivated horse serum and 0.5 mg of vitamin K1 per ml. The antibiotics were incorporated into the media in a log 2 series from 0.008 to 128 mg/l. An inoculum of 104 CFU/spot was achieved by preparing a saline suspension equivalent to McFarland 0.5 standard for each strain and making a further one in 10 dilution in sterile saline. The plates were incubated at 37 °C for 40 h in a Wise Anaerobic Workstation (Don Whitley Scientific, Shipley, UK) and read by eye in comparison with an antibiotic-free control plate. MICs for mycoplasma and ureaplasma used a microbroth incorporation technique in mycoplasma culture

medium supplemented with gamma-globulin-free horse serum (final concentration 20% v/v) and containing glucose (final concentration 0.1% w/v) for M. pneumoniae, arginine (final concentration 0.1% w/v) for M. hominis and urea (final concentration (0.1% w/v) for U. urealyticum. The inoculum used for each isolate was :105 CFU. MICs were determined after incubation at 37 °C, as the lowest concentration of the antimicrobial tested which prevented growth of the inoculum as shown by a lack of pH colour change when compared with an inoculum growth control in antimicrobial-free medium. Strains of C. trachomatis and C. pneumoniae were grown in LCC-MK2 cells. Antimicrobial testing was performed on cell monolayers in 24-well plates. Each well was infected with an inoculum of 5× 103 IFU (Infecting Forming Unit)/ml and centrifuged at 1700 g for 1 h. After incubation at 35 °C for 72 h, cultures were fixed and stained for inclusion with the monoclonal antibody to the lipopolysaccharide genus antigen. The MIC was the lowest antibiotic concentration at which no inclusion was seen.

2.4. Time-kill determination Killing curves were obtained by adding moxifloxacin, at concentrations corresponding to 1× MIC and 4× MIC, to diluted log-phase bacterial cultures adjusted with a McFarland standard, at about 1× 106 CFU/ml and grown in 30 ml flasks at 37 °C. Colony counts were determined at 0, 2, 4, 6, 12 and 24 h by removing samples (100 ml) at each time-point and, following serial ten-fold dilutions in sterile 0.85% NaCl, plating on Mueller-Hinton agar plates (blood agar base for streptococci). Colonies were counted and averaged after 48 h of incubation at 37 °C. Results were charted graphically by plotting log10 CFU against time. The killing rate over time was determined to be bactericidal if a reduction of three log10 CFU/ml could be achieved by the antimicrobial test levels at 24 h incubation (T24) or a two log10 CFU/ml decrease at 6 h. Time-kill kinetic studies for different concentrations were carried out twice for each microorganism.

3. Results

3.1. Minimal inhibitory concentrations The in vitro antimicrobial activity of moxifloxacin and comparators against staphylococci is shown in Table 1. Moxifloxacin was the most active agent tested against methicillin-susceptible and ciprofloxacin-susceptible S. aureus: it was four-fold more active than sparfloxacin and six-fold more active than ciprofloxacin against these organisms. All strains of methicillin-sus-

A. Speciale et al. / International Journal of Antimicrobial Agents 19 (2002) 111–118

ceptible and ciprofloxacin-susceptible S. aureus were inhibited by 0.015 to 0.25 mg/l of moxifloxacin. Moxifloxacin also showed potent activity against methicillinresistant and ciprofloxacin-resistant isolates of S. aureus (MIC50 =1 mg/l; MIC90 =2 mg/l) compared with ciprofloxacin (MIC50 =16 mg/l; MIC90 =32 mg/l). Moxifloxacin was four-fold more active against methicillin-sensitive S. epidermidis than sparfloxacin and ciprofloxacin with a MIC90 of 0.25 mg/l. The MIC90 of moxifloxacin against methicillin-resistant S. epidermidis was 0.12 mg/l, which was five-fold lower than MIC90 of both sparfloxacin and ciprofloxacin. All erythromycinor clindamycin-resistant S. aureus and S. epidermidis strains were susceptible to moxifloxacin. Table 2 shows the comparative in vitro activity of moxifloxacin against streptococci, enterococci and anaerobes. All 43 isolates of S. pneumoniae were inhibited by moxifloxacin at 00.12 mg/l. In addition, with a

113

MIC90 of 0.12 mg/l, moxifloxacin was four- and five-fold more active than sparfloxacin and ciprofloxacin, respectively, against our isolates of S. pneumoniae. Moxifloxacin also showed an improved activity compared with sparfloxacin and ciprofloxacin against S. pyogenes and S. agalactiae. Moxifloxacin was the most active antibiotic against E. faecalis: all isolates were inhibited by 0 0.5 mg/l, two- to four-fold higher than ciprofloxacin and sparfloxacin. Moxifloxacin also showed antibacterial activity against vancomycin-susceptible and ciprofloxacin-resistant E. faecium (MIC50 = 2 mg/l; MIC90 = 16 mg/l). Disappointingly, the MIC90 of the six vancomycin resistant E. faecium was 32 mg/l. C. perfrigens strains had MIC values for moxifloxacin ranging from 0.12 to 0.5 mg/l, while C. difficile strain tested was less susceptible with a MIC of 1 mg/l. Generally moxifloxacin was also two- to five-fold more active than both sparfloxacin and ciprofloxacin against

Table 1 In vitro activity of moxifloxacin (mg/l) and other antimicrobial agents against S. aureus and S. epidermidis Bacteria (no.) and antibiotics tested

Range

MIC50

MIC90

Mode MIC

%S

S. aureus Met-S Cip-S (n= 20) Moxifloxacin Sparfloxacin Ciprofloxacin Ceftriaxone Imipenem Teicoplanin Vancomycin Erythromycin Clindamycin

0.015–0.25 0.12–1 0.5–1 4–8 0.06–4 0.25–2 0.5–4 0.5 to \64 0.25 to \64

0.06 0.5 1 4 0.12 1 1 1 1

0.12 0.5 1 8 4 2 2 \64 \64

0.03 0.5 1 4 0.12 1 1 4 1

ND ND 100 100 100 100 100 55 90

S. aureus Met-R Cip-R (n=10) Moxifloxacin Sparfloxacin Ciprofloxacin Teicoplanin Vancomycin Erythromycin Clindamycin

1–2 1–32 8–32 0.25–2 0.25–2 0.25 to \64 0.25 to \64

1 8 16 0.5 1 64 32

2 32 32 2 2 \64 \64

1 8 16 1 1 64 32

ND ND 0 100 100 10 33

S. epidermidis Met-S (n =18) Moxifloxacin Sparfloxacin Ciprofloxacin Ceftriaxone Imipenem Teicoplanin Vancomycin Erythromycin Clindamycin

0.015–0.5 0.06–1 0.25–1 0.5 to \64 0.06–4 0.5–2 0.25–2 0.25 to \64 0.12 to \64

0.06 0.5 1 8 0.25 0.5 1 1 1

0.25 1 1 32 1 1 2 \64 \64

0.03 1 1 8 0.25 0.5 1 2 1

ND ND 100 33 100 100 100 44 44

S. epidermidis Met-R (n= 10) Moxifloxacin Sparfloxacin Ciprofloxacin Teicoplanin Vancomycin Erythromycin Clindamycin

0.03–0.5 0.12–1 0.5–2 0.5–2 0.5–4 0.5 to \64 0.25 to \64

0.06 0.25 0.5 0.5 1 \64 \64

0.12 1 1 1 2 \64 \64

0.06 0.25 0.5 0.5 1 \64 \64

ND ND 60 100 100 10 10

114

A. Speciale et al. / International Journal of Antimicrobial Agents 19 (2002) 111–118

Table 2 In vitro activity of moxifloxacin (mg/l) and other antimicrobial agents against S. pneumoniae, S. pyogenes, S. agalactiae, E. faecalis, E. faecium, Clostridium spp. and B. fragilis Bacteria (no.) and antibiotics tested

Range

MIC50

MIC90

Mode MIC

%S

S. pneumoniae (n= 43) Moxifloxacin Sparfloxacin Ciprofloxacin Vancomycin Penicillin Ampicillin Ceftriaxone Meropenem Clindamycin Erythromycin Clarithromycin

0.03–0.12 0.03–4 0.06–4 0.06–0.5 0.03–1 0.06–2 0.03–0.25 0.03–0.25 0.03 to \64 0.03 to \64 0.015 to \64

0.03 0.5 1 0.12 0.03 0.06 0.06 0.06 0.06 0.06 0.06

0.12 1 2 0.5 0.12 0.12 0.25 0.12 0.5 \64 \64

0.03 0.5 1 0.12 0.03 0.06 0.06 0.06 0.06 0.06 0.06

– 77 – 100 88 ND 100 100 86 70 70

S. pyogenes (n =16) Moxifloxacin Sparfloxacin Ciprofloxacin Penicillin Ampicillin Cefixime Ceftriaxone Erythromycin

0.03–0.25 0.03–1 0.12–1 00.015–0.06 00.015–0.12 00.015–0.5 00.015–0.12 00.015 to \64

0.06 0.06 0.25 00.015 00.015 0.015 0.015 00:06

0.25 0.25 1 0.06 0.015 0.03 0.06 \64

0.03 0.06 0.25 00.015 00.015 0.015 0.015 0.03

– – – 100 100 ND 100 87

S. agalactiae (n = 18) Moxifloxacin Sparfloxacin Ciprofloxacin Penicillin Amoxycillin Cefixime Ceftriaxone Erythromycin

0.06–0.5 0.12–0.5 0.25–1 00.015–0.12 00.015–0.06 0.03–0.25 0.03–0.12 0.06–64

0.12 0.25 0.25 00.015 0.03 0.06 0.06 0.06

0.25 0.5 1 0.015 0.06 0.12 0.12 64

0.12 0.25 0.25 00.015 0.03 0.06 0.03 0.06

– – – 100 100 ND 100 83

E. faecalis (n = 12) Moxifloxacin Sparfloxacin Ciprofloxacin Ampicillin Meropenem Piperacillin/Tazobactam Teicoplanin Vancomycin Erythromycin

0.12–0.5 0.25–1 0.5–1 1–16 0.5 to \128 1–16 0.06–8 0.25–4 0.5–128

0.12 0.5 0.5 2 4 4 0.5 2 2

0.25 0.5 1 16 8 16 8 4 128

0.012 0.5 0.5 1 8 4 0.5 2 2

– – 100 83 ND 83 100 100 8

E. faecium (n= 15) (Van A =6) Moxifloxacin Sparfloxacin Ciprofloxacin Ampicillin Meropenem Piperacillin/Tazobactam Teicoplanin Vancomycin Erythromycin

2–32 4–\128 8 to \128 1–128 8 to \128 2 to\128 0.125 to \128 1 to \128 4 to \128

32 \128 \128 64 \128 64 64 \128 \128

32 \128 \128 128 \128 \128 128 \128 \128

32 \128 \128 64 \128 \128 64 \128 \128

– – 0 27 – 27 33 40 0

Clostridium spp.a (n =11) Moxifloxacin Sparfloxacin Ciprofloxacin Clindamycin Metronidazole Cefoxitin

0.12–1 0.5–32 0.25–16 0.015–8 0.06–2 0.25 to \64

0.25 4 0.5 0.5 0.25 0.5

0.5 4 4 2 1 1

0.25 4 0.5 0.5 0.25 1

– – – 91 100 91

A. Speciale et al. / International Journal of Antimicrobial Agents 19 (2002) 111–118

115

Table 2 (Continued ) Bacteria (no.) and antibiotics tested

Range

MIC50

MIC90

Mode MIC

%S

Cefotetan Imipenem Meropenem

0.12 to \64 0.03–2 B0.015–0.25

0.25 0.12 0.015

2 0.5 0.03

0.25 0.12 0.015

91 100 100

B. fragilis (n = 14) Moxifloxacin Sparfloxacin Ciprofloxacin Clindamycin Metronidazole Cefoxitin Cefotetan Imipenem Meropenem

0.12–2 0.5–8 2–16 0.015 to \64 0.06–2 1–32 1–32 0.06–1 0.06–2

0.25 1 4 0.5 0.5 8 8 0.12 0.06

0.5 2 16 4 1 16 32 0.5 0.25

0.25 2 4 0.25 0.5 8 8 0.12 0.06

– – – 86 100 93 86 100 100

a

C. perfrigens (n =10), C. difficile (n= 1).

clostridium strains. B. fragilis strains were all inhibited by moxifloxacin: MIC50 and MIC90 were 0.25 mg/l and 0.5 mg/l, respectively. Ciprofloxacin showed the lowest activity of the quinolones tested (MIC50 =4 mg/l; MIC90 =16 mg/l). The activity of moxifloxacin against Clostridium spp. and Bacteroides spp. was overall comparable with that of metronidazole. Moxifloxacin was the most active quinolone tested. The MIC90 for both clostridial and bacteroides isolates was 0.5 mg/l while the MIC90 values of sparfloxacin and ciprofloxacin were four- to 32-fold higher than those of moxifloxacin. The activities of the non-quinolone antibiotics were comparable with that of moxifloxacin, except for cefotetan and cefoxitin that showed poor activity particularly against B. fragilis strains. Moxifloxacin showed excellent in vitro activity against mycoplasma (Table 3). The overall MIC range was 0.03 –0.12 mg/l this is well within the range of expected clinical susceptibility. Ciprofloxacin was slightly less active than moxifloxacin (overall MIC range 0.5– 2 mg/l). U. urealyticum was substantially less susceptible to both

moxifloxacin and ciprofloxacin with MIC values of 0.06–1 and 0.5–2 mg/l, respectively. Erythromycin showed good activity against M. pneumoniae but was less active against U. urealyticum. Doxycycline was active against both M. pneumoniae and U. urealyticum. The susceptibility of Chlamydia spp. to moxifloxacin and other compounds is shown in Table 4. All C. trachomatis isolates had MIC values for moxifloxacin of 0.03– 0.06 mg/l, whereas those of ciprofloxacin ranged between 1 and 2 mg/l. The MIC values of erythromycin and doxycycline were well within achievable serum concentrations. Both standards and clinical isolates of C. pneumoniae were susceptible to moxifloxacin (MIC range 0.06–0.5 mg/l) and the other compounds.

3.2. Time-killing Time-kill results (Fig. 1a–e) show that moxifloxacin at 4× MIC concentration had a bactericidal activity

Table 3 In vitro activity of moxifloxacin (mg/l) and other antimicrobial agents against M. pneumoniae, M. hominis and U. urealyticum Bacteria (no.) and antibiotics tested

Range

MIC50

MIC90

Mode MIC

M. pneumoniae (12) Moxifloxacin Ciprofloxacin Erythromycin Doxycycline

0.03–0.06 0.5–2 B0.015–0.015 0.015–0.5

0.06 1 B0.015 0.06

0.06 2 0.015 0.25

0.06 1 0.015 0.06

M. hominis (8) Moxifloxacin Ciprofloxacin

0.06–0.12 0.5–1

0.06 1

U. urealyticum (11) Moxifloxacin Ciprofloxacin Erythromycin Doxycycline

0.06–1 0.5–2 0.12–8 0.06–0.12

0.12 2 1 0.06

0.06 1 0.5 2 1 0.12

0.12 2 1 0.06

A. Speciale et al. / International Journal of Antimicrobial Agents 19 (2002) 111–118

116

Table 4 In vitro activity of moxifloxacin (mg/l) and other antimicrobial agents against Chlamydia spp

Table 5 Time to 3 log reduction at 1×MIC and at 4×MIC for all the tested species

Bacteria (no.) and antibiotics tested

Micro-organism

1×MIC (h)

4×MIC (h)

S. S. S. S. E.

12 5 6 \12 –

4 1.5 3 10 7

Range

MIC50

C. trachomatis (10) Moxifloxacin Ciprofloxacin Erythromycin Doxycycline

0.03–0.06 1–2 0.06–0.25 0.03–0.12

0.06 2 0.12 0.06

C. pneumoniae (7)a Moxifloxacin Ciprofloxacin Erythromycin Doxycycline

0.06–0.5 0.5–2 0.06–0.5 0.12–0.25

0.06 0.5 0.06 0.12

a

MIC90

0.06 2 0.25 0.12

Two nosocomial isolates and five collection strains.

against methicillin-resistant S. aureus in about 4 h with a reduction of 3 log. S. pneumoniae both penicillin-susceptible (PenS) and penicillin-resistant (PenR) strains were reduced more rapidly than S. aureus. There was a 6 log reduction in 4 and 6 h for PenS and PenR strains, respectively, at 4× MIC concentration of moxifloxacin. The slowest killing activity was against S. pyogenes at both 1× MIC and 4 × MIC concentrations. Moxifloxacin also showed killing activity against E. faecalis that was not concentration-dependent. A 2–3 log reduction of viable counts occurred within 12 h at 1 ×MIC and 4× MIC concentrations. There was no regrowth after 24 h at either concentration. Table 5 shows the time to 3 log reduction at 4× MIC and at 1× MIC for all the tested species.

4. Discussion The results of this study indicate that moxifloxacin has an extended antibacterial spectrum that includes important Gram-positive and atypical pathogens of the lower respiratory tract such as S. pneumoniae, M. pneumoniae and C. pneumoniae [12– 17]. Our results showed that moxifloxacin was more active in vitro than ciprofloxacin against staphylococci and streptococci, as noted by others [5,13,15]. These authors found moxifloxacin to be from four- to ten-fold more active than ciprofloxacin against both the coagulase-positive and coagulase-negative staphylococci. Our methicillin-resistant S. aureus isolates were inhibited by moxifloxacin at 1– 2 mg/l and methicillin-resistant S. epidermidis by 0.03 – 0.5 mg/l while the MIC range of ciprofloxacin was 8– 32 mg/l for

aureus pneumoniae PenS pneumoniae PenR pyogenes faecalis

methicillin-resistant S. aureus and 0.5–2 mg/l for methicillin-resistant S. epidermidis. Moxifloxacin had greatly enhanced activity against staphylococci compared with sparfloxacin. We found moxifloxacin to have good activity against S. pneumoniae with all strains being inhibited by antibiotic concentrations of B 0.12 mg/l. Based on the MIC range sparfloxacin and ciprofloxacin were less active with MIC values ranging from 0.03 to 4 mg/l and from 0.06 to 4 mg/l, respectively. Our results on the susceptibility to fluoroquinolones of S. pneumoniae strains with a different pattern of resistance to penicillin agree with those of Buxbaum et al. [13] but not with those of Barry et al. [18]. In fact, we found that moxifloxacin activity is unaffected by penicillin susceptibility or resistance of the strains while ciprofloxacin and sparfloxacin show less activity against resistant strains (low or high levels of resistance). Moxifloxacin has been shown to have improved activity over ciprofloxacin against S. pyogenes and S. agalactiae. In fact the MICs of moxifloxacin ranged from 0.03 to 0.5 mg/l while those of ciprofloxacin were about two- to four-fold higher (MIC=0.12–1 mg/l). Moxifloxacin also showed improved activity against streptococci when compared with sparfloxacin [19,20]. In common with other fluoroquinolones moxifloxacin is poorly active against enterococci [6]. Our results showed that moxifloxacin is as active as sparfloxacin and more active than ciprofloxacin against E. faecalis, while E. faecium had MIC90 of 32 mg/l, probably because of the greater degree of antibiotic resistance in this species. Our six isolates of E. faecium resistant to vancomycin and teicoplanin were also resistant to moxifloxacin (MIC= 32 mg/l). Our results indicate that moxifloxacin has a good antibacterial activity against anaerobes as previously reported by others [5–7,21]. The in vitro activity of moxifloxacin against our isolates of clostridia and bacteroides is similr to that of metronidazole and superior to that of clindamycin.

Fig. 1. (a) In vitro activity of moxifloxacin at MIC (2 mg/l) and 4 ×MIC against an isolate of methicillin-resistant S. aureus. (b) In vitro activity of moxifloxacin at MIC (0.03 mg/l) and 4 × MIC against an isolate of penicillin-susceptible S. pneumoniae. (c) In vitro activity of moxifloxacin at MIC (0.06 mg/l) and 4 × MIC against an isolate of penicillin-resistant S. pneumoniae. (d) In vitro activity of moxifloxacin at MIC (0.06 mg/l) and 4 ×MIC against an isolate of S. pyogenes. (e) In vitro activity of moxifloxacin at MIC (0.25 mg/l) and 4 ×MIC against an isolate of E. faecalis.

117

Fig. 1.

A. Speciale et al. / International Journal of Antimicrobial Agents 19 (2002) 111–118

118

A. Speciale et al. / International Journal of Antimicrobial Agents 19 (2002) 111–118

In addition, moxifloxacin had excellent broad-spectrum antimycoplasma activity against human Mycoplasma species that was better than that of ciprofloxacin [22]. Several of the newer quinolones have been reported to have a greater activity against chlamydia [23]. Our results indicate that moxifloxacin is substantially more active than both ciprofloxacin and sparfloxacin against chlamydia. Because of the broad spectrum, moxifloxacin may be useful for the treatment of infections in which aerobes, anaerobes and atypical micro-organisms play a part. Clinical studies will be necessary in order to test this hypothesis.

References [1] Hooper DC, Wolfson JS. Fluoroquinolone antimicrobial agents. N Engl J Med 1991:324 –84. [2] Andriole VT. The future of the quinolones. Drugs 1993;45(Suppl 3):1– 7. [3] Wolfson JS, Hooper DC. Fluoroquinolone antimicrobial agents. Clin Microbiol Rev 1989;2:378 –424. [4] Piddock LJV. New quinolones and Gram-positive bacteria. Antimicrob Agents Chemother 1994;30:163 –9. [5] Dalhoff A, Petersen U, Endermann R. In vitro activity of BAY 12 – 8039, a new 8-methoxyquinolone. Chemotherapy 1996;42:410 – 25. [6] Fass RJ. In vitro activity of BAY 12-8039, a new 8-methoxyquinolone. Antimicrob Agents Chemother 1997;41:1818 –24. [7] Aldridge KE, Ashcraft DS. Comparison of the in vitro activities of BAY 12-8039, a new quinolone, and other antimicrobials against clinically important anaerobes. Antimicrob Agents Chemother 1997;41:709 –11. [8] Felmingham D, Robbins MJ, Leakey A, et al. In vitro activity of BAY 12-8039 against bacterial respiratory tract pathogens, mycoplasmas and obligate anaerobic bacteria. In: Program and abstracts of the 36th Interscience Conference on Antimicrobial Agents and Chemotherapy. Washington, DC: American Society for Microbiology, 1996:101 Abstr. F-8. [9] National Committee for Clinical Laboratory Standards (NCCLS): methods for dilution and antimicrobial susceptibility test for bacteria that grow aerobically. 5th ed. Approved Standard, 2000. [10] Murray PR, Baron EJ, et al. Manual of clinical microbiology, 6th ed. Washington: ASM Press, 1995.

[11] National Committee for Clinical Laboratory Standards (NCCLS): methods for dilution and antimicrobial susceptibility test for bacteria that grow anaerobically, vol. 41. 4th ed. Approved Standard, 1997. p. 1818 – 24. [12] Blondeau JM. A review of the comparative in vitro activities of 12 antimicrobial agents, with a focus on five new ‘‘respiratory quinolones’’. J Antimicrob Chemother 1993;43(Suppl B):1 –11. [13] Austrian Bacterial Surveillance Network, Buxbaum A, Straschil U, Moser C, Graninger W, Georgopoulos A. Comparative susceptibility to penicillin and quinolones of 1385 Streptococcus pneumoniae isolates. J Antimicrob Chemother 1999;43(Suppl B):13 – 8. [14] Felmingham D, Robbins MJ, Keakey A, et al. In vitro activity of Bay 12 – 8039 against bacterial respiratory tract pathogens, mycoplasmas and obligate anaerobic bacteria. In: Abstracts of the 36th ICAAC, New Orleans, vol. F8, 1996:101. [15] Thomson KS, Backes SS, Sanders CC. Susceptibility to Bay 12-8039 of pneumococci and staphylococci with varying levels of ciprofloxacin resistance. In: Abstracts of the 36th ICAAC, New Orleans, vol. F16, 1996:102. [16] Reinert RR, Dalhoff A, Schlaeger JJ, Lemperle M, Lutticken R. In vitro activity of Bay 12-8039, a new 8-methoxy-quinolone against S. pneumoniae. In: Abstracts of the 37th ICAAC, Toronto, vol. F129, 1997:168. [17] Donati M, Rumpianesi F, Pavan G, Sambri V, Cevenni R. In vitro activity of Bay 12-8039 against Chlamydia. In: Abstracts of the 37th ICAAC, Toronto, vol. F142, 1997:171. [18] Barry AL, Fuchs PC, Brown SD. In vitro activities of five fluoroquinolone compounds against strains of Streptococcus pneumoniae with resistance to other antimicrobial agents. Antimicrob Agents Chemother 1996;40:2431 – 3. [19] Child J, Adres J, Boswell F, Breuwald N, Wise R. The in vitro activity of CP99.219, a new caphthyridone antimicrobial agent: a comparison with fluoroquinolone agents. J Antimicrob Chemother 1995;35:869 – 76. [20] Eliopoulos GM, Klimm K, Eliopoulos GT, Ferraro MJ, Moellering RC. In vitro activity of CP 99.219 a new fluoroquinolone, against clinical islates of Gram-positive bacteria. Antimicrob Agents Chemother 1993;37:366 – 70. [21] Goldstein EJC, Citron DM, Hudspeth M, Gerardo SH, Merriam CV. In vitro activity of Bay 12-8039, a new 8-methoxyquinolone, compared to the activities of 11 other oral antimicrobial agents against 390 aerobic and anaerobic bacteria isolated from human and animal bite wound skin and soft tissue infections in humans. Antimicrob Agents Chemother 1997;41:1522 – 7. [22] Kenny GE, Cartwright FD. Susceptibilities of human Mycoplasmas to BAY 12-8039. In: Abstract of the 37th ICAAC, Toronto, vol. F-143, 1997. [23] Jones RB, Van Der Pol B, Johnson RB. Susceptibility of Chlamydia trachomatis to trovafloxacin. J Antimicrob Chemother 1997;39(Suppl. B):63 – 5.