Approved standard M7-A2. National Committee for Clinical Laboratory Standards, Villano- va, Pa. 4. Schadow, K. H., W. A. Simpson, and G. D. Christensen.
ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, Sept. 1990, p. 1843-1845 0066-4804/90/091843-03$02.00/0 Copyright C 1990, American Society for Microbiology
Vol. 34, No. 9
Antistaphylococcal Activities of Sparfloxacin (CI-978; AT-4140), Ofloxacin, and Ciprofloxacin ARIF Z. CHAUDHRY, CYNTHIA C. KNAPP, JUAN SIERRA-MADERO, AND JOHN A. WASHINGTON* The Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, Ohio 44195-5140 Received 27 March 1990/Accepted 19 June 1990
The activity of sparfloxacin (CI-978; AT-4140) was compared with those of ofloxacin and ciprofloxacin against clinical isolates of Staphylococcus aureus and Staphylococcus epidermidis. Al 10 ciprofloxacin-resistant staphylococci had reduced susceptibility to sparfloxacin and ofloxacin. Against 105 ciprofloxacin-susceptible strains of S. aureus, the sparfloxacin MIC for 90% of strains tested was at least fourfold lower than those of ciprofloxacin and ofloxacin, while against 104 ciprofloxacin-susceptible strains of S. epidermidis, the MIC of sparfloxacin for 90% of strains tested was twofold lower than that of ciprofloxacin and fourfold lower than that of ofloxacin. MBCs of sparfloxacin were 4 ,ug/ml) staphylococci are shown in Table 1 and were >4
Sparfloxacin (CI-978; AT-4140) is a new fluoroquinolone with increased activity in vitro against gram-positive bacteria (1, 2; K. Nakata, H. Maeda, A. Fuji, and S. Kamidono, Program Abstr. 29th Intersci. Conf. Antimicrob. Agents Chemother., abstr. no. 1200, 1989; N. X. Chin, J. W. Gu, K. W. Yu, Y. X. Zhang, and H. C. Neu, 29th ICAAC, abstr. no. 1239, 1989). The purpose of this study was to compare the in vitro activities of sparfloxacin, ciprofloxacin, and ofloxacin against oxacillin-susceptible and -resistant staphylococci and to assess the effects of inoculum size, pH, and serum on in vitro antistaphylococcal activity, as well as to determine the effects of subinhibitory concentrations of the three quinolones on the adherence of staphylococci to plastic surfaces. All strains tested were either fresh or stored (-70°C) clinical isolates of oxacillin-susceptible and -resistant Staphylococcus aureus and Staphylococcus epidermidis. Also tested were 11 fresh clinical isolates of S. aureus (5 isolates) and S. epidermidis (6 isolates) that were resistant to ciprofloxacin. Frozen strains were thawed, subcultured on blood agar, and transferred on blood agar prior to testing. MICs were determined by micro- and macrodilution according to standard procedures published by the National Committee for Clinical Laboratory Standards (3) with an inoculum prepared from early to mid-logarithmic-phase growth and adjusted to provide a final inoculum of approximately 5 x 10' CFU/ml. Inoculum effects on the MICs of each quinolone were determined by adjusting the inocula of early to mid-logarithmic-phase growth of four strains each of S. aureus and S. epidermidis to 5 x 103 and 5 x 107 CFU/ml, respectively. MBCs were determined with each ciprofloxacin-susceptible strain according to procedures described by Shanholtzer et al. (5) by subculturing 100 ,ul from each well without visible growth onto blood agar which was incubated at 350C for 48 h. The MBC was the lowest concentration of each quinolone which exhibited .99.9% bactericidal activity. The effects of pH on MICs were determined by broth macrodilution using cation-adjusted Mueller-Hinton broth adjusted to pHs 6.5, 7.3, and 8.5 and inoculated with early to mid-logarithmic-phase growth which was adjusted to ap*
TABLE 1. Activities of ofloxacin and ciprofloxacin against
ciprofloxacin-resistant staphylococcia Organism (isolate no.)
MIC (pg/ml)
Ciprofloxacin
S. aureus, oxacillin sus-
Ofloxacin
Sparfloxacin
32
16
8
32 16 64 16
8 8 32 8
4 8 16
8 64 16 8 128 64
8 16 16 8 64 16
4 4
ceptible (1) S. aureus, oxacillin resistant 1 2 3
4
8
S. epidermidis, oxacillin resistant
1 2 3 4 5 6
Corresponding author.
aResults obtained by broth macrodilution.
1843
8 4 8 4
1844
ANTIMICROB. AGENTS CHEMOTHER.
NOTES
TABLE 2. Activities of sparfloxacin, ciprofloxacin, and ofloxacin against ciprofloxacin-susceptible staphylococcia
MIC (,ug/ml)
Organism
Drug
(no. of isolates)
50tlo
90to
0.06 0.25 0.25
0.06 0.5 0.5
S. aureus, oxacillin susceptible (49)
Sparfloxacin Ciprofloxacin Ofloxacin
Range s0.03-0.12 0.06-1 0.12-1
S. aureus, oxacillin resistant (56)
Sparfloxacin Ciprofloxacin Ofloxacin
s0.03-0.12 0.12-1 0.12-0.5
s0.03 0.25 0.25
0.12 0.5 0.5
S. epidermidis, oxacillin susceptible (50)
Sparfloxacin Ciprofloxacin Ofloxacin
s0.03-0.12 0.12-0.5 0.25-1
0.12 0.25 0.5
0.12 0.25 0.5
S. epidermidis, oxacillin resistant (54)
Sparfloxacin Ciprofloxacin Ofloxacin
s0.03-0.25 0.12-0.5
0.06 0.12 0.25
0.12 0.25 0.5
a
0.25-0.5
Results obtained by broth microdilution.
,ug/ml for sparfloxacin and ofloxacin. Sparfloxacin MICs were generally twofold lower than those of ofloxacin, which, in turn, were generally at least twofold lower than those of ciprofloxacin. MIC ranges and MICs for 50% and 90o (MIC50s and MIC90s, respectively) of ciprofloxacin-susceptible, oxacillin-susceptible, and oxacillin-resistant isolates are shown in Table 2. Against S. aureus, the MIC50s and MIC90s of ciprofloxacin and ofloxacin were identical, while the respective values for sparfloxacin were at least fourfold lower. Against ciprofloxacin-susceptible isolates of S. epidermidis, the sparfloxacin MIC90 was twofold lower than that of ciprofloxacin and fourfold lower than that of ofloxacin (Table 2). MICs with inocula of 5 x 103 CFU/ml were usually the same as those with inocula of 5 x 105 CFU/ml, while MICs with inocula of 5 x 107 CFU/ml were up to fourfold higher than those with inocula of 5 x 105 CFU/ml, with two exceptions that were eightfold higher (Table 3). MBCs, with a single exception, were s4x, and usually 1 to 2x, the respective MICs of sparfloxacin, ciprofloxacin, and ofloxacin. MICs of each quinolone tested against four isolates of S. epidermidis in Mueller-Hinton broth adjusted to pHs 6.5, 7.3, and 8.5 were the same. MICs of each quinolone tested against the same four isolates of S. epidermidis in Mueller-
Hinton broth containing 25% serum remained unchanged from those in serum-free broth. The adherence of S. epidermidis ATCC 35984 and CCF 104 was reduced at least 95% by 1/2 and 1/8 of the MIC, respectively, of each quinolone (Table 4). These results differ from those of Schadow et al. (4) in which norfloxacin had no effect on adherence of S. epidermidis ATCC 35984. This difference may be time related in that Schadow et al. (4) measured adherence for up to 6 h, whereas we measured adherence for up to 24 h. Our MIC and MBC results were consistent with those of Kojima et al. (1) and Nakamura et al. (2). Kojima et al. (1) observed higher MICs of sparfloxacin among methicillinresistant isolates of S. aureus which did reflect resistance of at least 10% of their isolates to existing quinolones but not necessarily to sparfloxacin. Among their clinical isolates of S. aureus, Kojima et al. (1) noted the following six groupings as regards quinolone activity: (i) methicillin-susceptible S. aureus susceptible to sparfloxacin, ciprofloxacin, ofloxacin, and norfloxacin; (ii) methicillin-resistant S. aureus susceptible to all four quinolones; (iii) methicillin-resistant S. aureus susceptible to sparfloxacin but resistant to the other three quinolones; (iv) methicillin-resistant S. aureus resistant to all
TABLE 3. Inoculum effects on quinolone activities MIC (,ug/ml) at increasing CFU/ml
Organism (isolate no.)
Sparfloxacin
Ciprofloxacin
Ofloxacin 107
103
105
107
103
105
107
0.12 0.06
0.25 0.25
0.25 0.25
0.5 0.25
1 0.5
0.25 0.12
0.25 0.12
1 0.25
0.06 '0.03
0.06 0.06
0.25 0.5
0.25 0.25
0.25 0.25
1 0.5
0.12 0.12
0.12 0.12
1 0.5
c0.03 '0.03
s0.03 0.06
0.12 0.12
0.12 0.25
0.25 0.5
0.25 0.5
0.12 0.25
0.25 0.5
1 0.5
c0.03 s0.03
s0.03 c0.03
0.06 0.12
0.25 0.12
0.25 0.25
0.5 0.25
0.25 0.12
0.25 0.25
0.5 1
103
105
0.06 0.06
S. epidermidis, oxacillin resistant 1 2 S. aureus, oxacillin susceptible 1 2
S. epidermidis, oxacillin susceptible 1 2
S. aureus, oxacillin resistant 1 2
NOTES
VOL. 34, 1990 TABLE 4. Effects of ciprofloxacin, ofloxacin, and sparfloxacin on staphylococcal adherence Antimicrobial agent
S. epidermidis strain
Minimum concn (pug/ml) that inhibited: Growth
90TO Adherence'
Ciprofloxacin
104 35984
0.12 0.12
0.02 0.06
Ofloxacin
104 35984
0.25 0.25
0.06 0.12
Sparfloxacin
104 35984
0.03 0.03
0.004 0.02
a Adherence values read at 24 h.
four quinolones; (v) methicillin-susceptible S. aureus resistant to norfloxacin but susceptible to the other three quinolones; and (vi) methicillin-susceptible S. aureus resistant to all four quinolones. Our ciprofloxacin-resistant (MIC range, 8 to 128 ,ug/ml) isolates had lower sparfloxacin and ofloxacin MICs (relative to those of ciprofloxacin); however, all ofloxacin MICs were .8 ,ug/ml (range, 8 to 32 ,ug/ml) and all sparfloxacin MICs were .4 ,ug/ml (range, 4 to 16 ,ug/ml). In conclusion, sparfloxacin was more active than ciprofloxacin and ofloxacin against ciprofloxacin-resistant and -susceptible staphylococci. Depending on the pharmacokinetics of sparfloxacin, its increased activities against ciprofloxacin-resistant (versus ciprofloxacin-susceptible) staph-
1845
ylococci may or may not be clinically important in the management of patients with ciprofloxacin-resistant staphylococcal infections. We gratefully acknowledge Lynne Atkinson for technical assistance and Estella Stovall for manuscript preparation. We gratefully acknowledge the Parke-Davis Pharmaceutical Division for a grant in support of this project. LITERATURE CITED 1. Kojima, T., M. Inoue, and S. Mitsuhashi. 1989. In vitro activity of AT-4140 against clinical bacterial isolates. Antimicrob. Agents
Chemother. 33:1980-1988. 2. Nakamura, S., A. Minami, K. Nakata, N. Kurobe, K. Kouno, Y. Sakaguchi, S. Kashimoto, H. Yoshida, T. Kojima, T. Ohue, K. Fujimoto, M. Nakamura, M. Hashimoto, and M. Shimizu. 1989. In vitro and in vivo antibacterial activities at AT-4140, a new broad-spectrum quinolone. Antimicrob. Agents Chemother. 33: 1167-1173. 3. National Committee for Clinical Laboratory Standards. 1990. Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically (2nd ed.). Approved standard M7-A2. National Committee for Clinical Laboratory Standards, Villanova, Pa. 4. Schadow, K. H., W. A. Simpson, and G. D. Christensen. 1988. Characteristics of adherence of coagulase-negative staphylococci exposed to subinhibitory concentrations of antibiotics. J. Infect. Dis. 157:71-77. 5. Shanholtzer, C. J., L. R. Peterson, M. L. Mohn, J. A. Moody, and D. N. Gerding. 1984. MBCs for Staphylococcus aureus as determined by macrodilution and microdilution techniques. Antimicrob. Agents Chemother. 26:214-219.
