Activities of ABT-773 against Listeria monocytogenes and coryneform bacteria of clinical interest

ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, Apr. 2003, p. 1403–1406 Vol. 47, No. 4 0066-4804/03/$08.00⫹0 DOI: 10.1128/AAC.47.4.1403–1406.2003 Copyright © 2003, American Society for Microbiology. All Rights Reserved. Activities of ABT-773 against Listeria monocytogenes and Coryneform Bacteria of Clinical Interest María del Carmen Conejo, 1 Luis Martínez-Martínez, 1,2 *A ´lvaro Pascual, 1,2 Ana Isabel Sua´rez, 2 and Evelio J. Perea 1,2 Department of Microbiology, School of Medicine, 1 and University Hospital Virgen Macarena, 2 University of Seville, Seville, Spain Received 29 July 2002/Returned for modification 9 October 2002/Accepted 31 December 2002 The in vitro activities of ABT-773 were evaluated against 15 Listeria monocytogenes strains and 196 coryneform bacteria isolated from clinical samples. One hundred percent of the L.monocytogenes strains were inhibited by <0.015 ␮g of ABT-773/ml. MICs of ABT-773 (␮g/ml) at which 50% of the isolates tested were inhibited (MIC 50 s) and MIC 90 s for other organisms were 0.125 and 0.5 (Corynebacterium amycolatum), 1 and >32 (Corynebacterium jeikeium), 0.03 and >32 (Corynebacterium minutissimum), >32 and >32 (Corynebacterium pseudodiphtheriticum and Corynebacterium urealyticum), 0.125 and >32 (Corynebacterium striatum), and 0.03 and 0.5 (Rhodococcus equi), respectively. Two relevant aspects related to coryneform bacteria have become significant during the last decade: the recognition of the medical importance of some species, including Corynebacterium jeikeium,Corynebacterium urealyticum,Corynebacterium striatum,Corynebacterium amycolatum, and Corynebacterium minutissimum, and the changes in the taxonomy of these organisms leading to the recognition of a large number of new species and the redefinition of already known organisms (1, 2, 4, 6, 8). It is critical that studies of the activities of antimicrobial agents be based on testing microorganisms identified according to the new taxonomic criteria, in order to really obtain clinically significant information and to allow the comparison of data obtained from different laboratories (3, 5, 13, 19, 24). Unfortunately, there is yet no standardized methodology for susceptibility testing of coryneform bacteria. The NCCLS has not defined breakpoints for clinical categories of antimicrobial agents against coryneform bacteria, and in the case of Listeria spp. only the category of susceptibility to ampicillin and penicillin has been suggested (16). There is scant information on the activities of antimicrobial agents against coryneform bacteria (4–6, 9). C.jeikeium,C.urealyticum, and C.amycolatum are usually multiresistant organisms, and only glycopeptides remain universally active against these species (4–6, 18, 19, 22, 23). Some reports suggest that other species may be susceptible to commonly used antimicrobial agents, but we lack reliable clinical evidence supporting these in vitro observations. It is necessary to evaluate the activities of new antimicrobial agents against coryneform bacteria of clinical importance (3, 7, 10–12, 19). It has been shown previously that ketolides show a broader spectrum of activity than do reference macrolides, being active against macrolide-susceptible gram-positive cocci and against gram-positive organisms in which macrolide resistance is caused by active efflux or inducible production of methylase (21). In a previous study we showed that the new ketolide telithromycin was more active than were 14and 16-membered macrolides, azithromycin, or clindamycin against many coryneform bacteria and had high in vitro activity against Listeria monocytogenes (10). The objective of this study was to evaluate the in vitro activities of ABT-773 in comparison with other compounds against L.monocytogenes and different species of coryneform bacteria isolated from clinical samples. Two hundred eleven organisms isolated from clinical samples at the Department of Clinical Microbiology, University Hospital Virgen Macarena, Seville, Spain, were evaluated, including the following species (number of strains): L.monocytogenes (15), C.amycolatum (40), C.jeikeium (40), C.minutissimum (14), Corynebacterium pseudodiphtheriticum (12), C. striatum (40), C.urealyticum (40), and Rhodococcus equi (10). Microorganisms were identified according to the method of Funke et al. (4), by using API-CORYNE strips and additional phenotypic tests when necessary. After identification, organisms were maintained in tryptic soy broth–10% glycerol at ⫺80°C. The following reference strains were also tested: C. jeikeium ATCC 43734, C.striatum ATCC 6940, and C.urealyticum ATCC 43042. Staphylococcus aureus ATCC 29213 and Enterococcus faecalis ATCC 29212 were used as control strains for susceptibility testing assays. The following compounds were studied: ABT-773 (Abbott), cefuroxime (Sigma), clindamycin (Sigma), co-trimoxazole (Gayoso, Madrid, Spain), erythromycin (Sigma), and vancomycin (Sigma). Solutions of antimicrobial agents were prepared on the same day as testing, according to the manufacturer’s instructions. The MICs of the above-indicated antimicrobial agents were determined, as previously described, by in-house microdilution according to NCCLS guidelines (15, 16), with the exception that, when C. jeikeium and C.urealyticum (lipophilic organisms) were tested, the broth was supplemented with 0.5% Tween 80 (Difco, Detroit, Mich.). Plates were inoculated with a suspension (approximately 5 ⫻10 5 CFU/ml) in Mueller-Hinton broth (plus 0.5% Tween 80 in the case of C.jeikeium and C.urealyticum) prepared from bacteria grown on Columbia agar with 5% sheep blood for 24 to 48 h. Plates were incubated, after inoc- * Corresponding author. Mailing address: Department of Microbiology, School of Medicine, University of Seville, Apdo. 914, 41080 Seville, Spain. Phone: 34 95 500 8287. Fax: 34 95 437 7413. E-mail: [email protected]. 1403 on July 31, 2017 by USE/BCTA.GEN UNIVERSITARIAhttp://aac.asm.org/Downloaded from ulation, at 35°C for 20 to 24 h, or (in the case of C.jeikeium and C.urealyticum) for up to 48 h, to allow bacterial growth in control (antibiotic-free) wells of the microtiter plate. The activities of the agents herein tested have been considered in terms of MIC 50 s (MICs at which 50% of the isolates tested are inhibited), MIC 90 s, and MIC ranges (Table 1). Additionally, the numbers and percentages of strains inhibited at each concentration of ABT-773 and the related drugs erythromycin and clindamycin have also been determined (Table 2). All strains of L.monocytogenes were inhibited by ⱕ0.015 ␮gof ABT-773/ml. MIC 90 s of ABT-773 were ⱖ32and ⱖ128-fold lower than those of erythromycin and clindamycin, respectively. Interestingly, this value is also much lower than that recently obtained in our laboratory for telithromycin, for which the MIC 50 and MIC 90 were 0.125 and 0.25 ␮g/ml, respectively. Our results are similar to those obtained in a previous study (17), in which all 24 strains of L.monocytogenes were inhibited at 0.03 ␮g/ml. This good in vitro activity of ABT-773 against L. monocytogenes contrasts with its relatively high effective dose (100.1 mg/kg of body weight/day) in an animal model of sepsis caused by L.monocytogenes (14). Vancomycin and co-trimoxazole also showed good in vitro activities against L.monocytogenes. ABT-773 inhibited higher percentages of strains of all Corynebacterium species and of R.equi evaluated than did erythromycin. At a concentration of 0.5 ␮g/ml (the breakpoint of susceptibility for erythromycin against Staphylococcus spp.) the percentages of inhibition by ABT-773 and erythromycin were 92.5 and 15.0% for C.amycolatum, 90.0 and 60.0% for R. equi, 62.5 and 20.0% for C.striatum, 50.0 and 37.5% for C. minutissimum, 47.5 and 2.5% for C.jeikeium, 33.3 and 25.0% for C.pseudodiphtheriticum, and 7.5 and 5.0% for C.urealyticum, respectively. Clindamycin was even less active than erythromycin against the tested strains. We have previously evaluated the activities of telithromycin against coryneform bacteria, with the same methodology used in this study (10). ABT-773 showed an activity similar to that of telithromycin against coryneform bacteria, except in the case of C.striatum, for which the MIC 50 and MIC 90 of telithromycin (0.03 and 0.06 ␮g/ml, respectively) were lower than those of ABT-773 (0.125 and ⬎32 ␮g/ml, respectively). The actual reasons for the difference in the activities of the two ketolides against C.striatum are presently unknown. It could well be that ABT-773 is intrinsically less active than telithromycin is against this organism, but since the isolates evaluated in this study were more recent than those in the study with telithromycin, the observed lower susceptibility of C.striatum to ABT-773 could be due to a recent increase in the level of resistance of C.striatum to ketolides, a situation already described for fluoroquinolones (11). The differences in susceptibilities to ABT-773 and to erythromycin in the tested strains indicate that macrolide-resistant coryneform bacteria are still inhibited by ketolides. The mechanisms underlying this observation remain undefined, since the mechanisms of resistance to both macrolides and ketolides in coryneform bacteria are poorly known. The ermC gene has been reported to be present in most C.striatum strains resistant to erythromycin (20). The existence of bimodal populations among C.minutissimum,C.pseudodiphtheriticum,C.striatum, and C.urealyticum suggests that these species may TABLE 1. Ranges, MIC 50 s, and MIC 90 s of antimicrobial agents for L. monocytogenes and coryneform bacteria Bacterium (no. of isolates) and antimicrobial agent MIC (␮g/ml) Range MIC 50 MIC 90 Listeria monocytogenes (15) a ABT-773 ⱕ0.015 ⱕ0.015 ⱕ0.015 Erythromycin 0.125–0.5 0.25 0.5 Clindamycin 0.5–222 Co-trimoxazole 0.015–0.03 0.015 0.03 Vancomycin 0.5–111 C. amycolatum (40) ABT-773 ⱕ0.015–2 0.125 0.5 Erythromycin ⱕ0.06–⬎128 16 128 Clindamycin 0.25–⬎64 ⬎64 ⬎64 Cefuroxime ⱕ0.03–⬎128 0.25 0.5 Co-trimoxazole 0.25–⬎16 ⬎16 ⬎16 Vancomycin 0.25–1 0.5 0.5 C. jeikeium (40) ABT-773 ⱕ0.015–⬎32 1 ⬎32 Erythromycin ⱕ0.06–⬎128 ⬎128 ⬎128 Clindamycin 0.25–⬎64 ⬎64 ⬎64 Cefuroxime 0.06–⬎64 ⬎64 ⬎64 Co-trimoxazole 0.125–⬎16 ⬎16 ⬎16 Vancomycin 0.5–1 0.5 1 C. minutissimum (14) ABT-773 ⱕ0.015–⬎32 0.03 ⬎32 Erythromycin ⱕ0.06–⬎128 32 ⬎128 Clindamycin 0.06–⬎64 ⬎64 ⬎64 Cefuroxime 0.06–⬎64 0.5 32 Co-trimoxazole 0.06–⬎16 2 ⬎16 Vancomycin 0.125–1 0.25 0.5 C. pseudodiphtheriticum (12) ABT-773 ⱕ0.015–⬎32 ⬎32 ⬎32 Erythromycin ⱕ0.06–⬎128 ⬎128 ⬎128 Clindamycin ⱕ0.03–⬎64 ⬎64 ⬎64 Cefuroxime ⱕ0.03–1 0.125 0.5 Co-trimoxazole 0.5–⬎16 4 ⬎16 Vancomycin 0.25–0.5 0.25 0.25 C. striatum (40) ABT-773 ⱕ0.015–⬎32 0.125 ⬎32 Erythromycin ⱕ0.06–⬎128 8 ⬎128 Clindamycin 1–⬎64 ⬎64 ⬎64 Cefuroxime 0.5–⬎64 2 4 Co-trimoxazole 0.5–16 4 8 Vancomycin 0.125–0.5 0.25 0.25 C. urealyticum (40) ABT-773 ⱕ0.015–⬎32 ⬎32 ⬎32 Erythromycin ⱕ0.06–⬎128 ⬎128 ⬎128 Clindamycin 0.125–⬎64 ⬎64 ⬎64 Cefuroxime ⬎64 ⬎64 ⬎64 Co-trimoxazole ⬎16 ⬎16 ⬎16 Vancomycin 0.125–1 0.5 0.5 Rhodococcus equi (10) ABT-773 ⱕ0.015–4 0.03 0.5 Erythromycin ⱕ0.06–⬎128 0.5 ⬎128 Clindamycin 0.125–⬎64 4 ⬎64 Cefuroxime 0.5–⬎64 8 ⬎64 Co-trimoxazole 0.25–⬎16 16 ⬎16 Vancomycin 0.5 0.5 0.5 a Following the NCCLS suggestion (16), MICs of cefuroxime against L. monocytogenes are not detailed. 1404 NOTES ANTIMICROB.AGENTS CHEMOTHER. on July 31, 2017 by USE/BCTA.GEN UNIVERSITARIAhttp://aac.asm.org/Downloaded from express a similar determinant of resistance, but further studies are obviously needed in this area. All coryneform bacteria evaluated were inhibited by 1 ␮gof vancomycin/ml, in agreement with previous studies (10, 19, 23). On the other hand, co-trimoxazole was poorly active against coryneform bacteria, and for this agent all MIC 50 s against C. amycolatum,C.jeikeium, and C.urealyticum were ⬎16 ␮g/ml. MIC 50 s of co-trimoxazole were higher than 2/38 ␮g/ml (the breakpoint for staphylococci that may be considered as a reference indicator) for C.pseudodiphtheriticum,C.striatum, and R.equi. Cefuroxime was also poorly active in vitro against most coryneform bacteria. Cefuroxime showed good in vitro activities against C.amycolatum (MIC 90 , 0.5 ␮g/ml), C.pseudodiphtheriticum (MIC 90 , 0.5 ␮g/ml), and to a lesser extent C.striatum (MIC 90 ,4␮g/ml). 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Percentages of strains of L. monocytogenes and coryneform bacteria inhibited at the indicated concentrations of ABT-773, erythromycin, and clindamycin Bacterium (no. of isolates) Antimicrobial agent % of strains inhibited at concn (␮g/ml): ⱕ0.015 0.03 0.06 0.125 0.25 0.5 1248163264⬎64 C. amycolatum (40) ABT-773 30.0 35.0 45.0 75.0 85.0 92.5 95.0 100 Erythromycin 15.0 30.0 35.5 55.0 80.0 87.5 100 Clindamycin 10 15.0 17.5 100 C. jeikeium (40) ABT-773 7.5 12.5 30 42.5 45.0 47.5 60.0 62.5 65.0 100 Erythromycin 2.5 5.0 7.5 15.0 20.0 100 Clindamycin 2.5 100 C. minutissimum (14) ABT-773 42.9 57.2 64.3 100 Erythromycin 28.6 35.7 42.9 50.0 57.2 100 Clindamycin 7.2 14.3 28.6 42.9 100 C. pseudodiphtheriticum (12) ABT-773 33.3 41.7 100 Erythromycin 16.7 25.0 100 Clindamycin 8.3 25.0 100 C. striatum (40) ABT-773 27.5 30 47.5 57.5 60.0 62.5 100 Erythromycin 20 25.0 47.5 55.0 60.0 62.5 100 Clindamycin 2.5 12.5 20.0 100 C. urealyticum (40) ABT-773 5.0 7.5 10.0 100 Erythromycin 50 100 Clindamycin 5.0 100 L. monocytogenes (15) ABT-773 100 Erythromycin 6.7 73.3 100 Clindamycin 6.7 40.0 100 R. equi (10) ABT-773 40.0 60.0 70.0 80.0 90.0 100 Erythromycin 20.0 30.0 60.0 70.0 100 Clindamycin 20.0 30.0 40.0 70.0 100 VOL. 47, 2003 NOTES 1405 on July 31, 2017 by USE/BCTA.GEN UNIVERSITARIAhttp://aac.asm.org/Downloaded from 11. 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