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Antimicrobial Agents and Chemotherapy, June 1998, p. 1509-1511, Vol. 42, No. 6
National Reference Center for Streptococci,
Institute of Medical Microbiology, University Hospital (RWTH)
Aachen, Aachen, Germany1 and
Hoechst
Marion Roussel, Romainville, France2
Received 12 January 1998/Returned for modification 4 March
1998/Accepted 8 April 1998
The comparative in vitro activity of HMR 3004 and HMR 3647, new
ketolide antibiotics, was tested by a standard agar dilution technique
against 221 pneumococcal strains, including isolates with intermediate
levels of resistance to penicillin and erythromycin-resistant isolates.
The ketolides were more active than other macrolides and showed
excellent activity against erythromycin-resistant strains. All the
strains were inhibited by The worldwide incidence of
infections caused by pneumococci resistant to penicillin G and other
antimicrobials has increased at an alarming rate during the past two
decades (1, 12, 17). In Europe, Spain, France, and Hungary
have recorded the highest incidences of resistance to penicillin G as
well as to other antibiotics among clinical isolates of
Streptococcus pneumoniae (6, 13). In contrast,
studies in Germany carried out between 1979 and 1995 revealed only a
low rate of intermediate resistance to penicillin G (10, 14, 20,
21). Nevertheless, S. pneumoniae isolates with
reduced susceptibility to penicillin G, including strains for which the
MICs were The increased erythromycin A resistance has become a worldwide problem.
A recent 30-center national surveillance study by Doern and coworkers
has documented erythromycin A resistance rates of 19 to 20% with
isolates with an intermediate level of resistance to penicillin and of
49% with penicillin-resistant isolates recovered from outpatients in
the United States (4). In France resistance to erythromycin
A, which was first detected in 1976, increased to 20% in 1984 and
reached 29% in 1990 (7). In Germany the rate of
pneumococcal resistance to erythromycin A is low (3.2% [21]) and more often seen in children (18).
HMR 3004 and HMR 3647 are new ketolides. The ketolides are
semisynthetic 14-membered-ring macrolides, characterized by a 3-keto group instead of the L-cladinose sugar of the erythronolide
A ring. Previous studies have documented the antipneumococcal activity of this group of antibiotics (2, 3, 5, 8, 9, 16, 22).
In the present investigation 221 representative isolates, including 86 consecutive pneumococcal strains isolated between October 1996 and
March 1997, were randomly selected from a collection of strains
obtained from blood cultures or cerebrospinal fluid or other normally
sterile body sites as part of the 1992-to-1997 national surveillance
study of the antimicrobial resistance of S. pneumoniae
in Germany (17).
The MICs of HMR 3004 (Hoechst Marion Roussel,
Romainville, France), HMR 3647 (Hoechst Marion Roussel),
penicillin G (Grünenthal, Stolberg, Germany), amoxicillin
(SmithKline Beecham Pharmaceuticals, Munich, Germany),
erythromycin A (Hoechst Marion Roussel), azithromycin (Pfizer,
Karlsruhe, Germany), roxithromycin (Hoechst Marion Roussel), clarithromycin (Abbott, Wiesbaden, Germany), josamycin
(Hoechst Marion Roussel), ofloxacin (Hoechst Marion Roussel), and
tetracycline (Sigma Chemicals, Munich, Germany) were determined by a
standard agar dilution technique with Mueller-Hinton agar (Oxoid,
Basingstoke, Hampshire, United Kingdom) supplemented with 5% sheep
blood (Oxoid), following the recommendation of the National Committee
for Clinical Laboratory Standards (15).
Suspensions with a turbidity equivalent to that of a 0.5 McFarland
standard were prepared by growth from blood agar plates in 2 ml of
Mueller-Hinton broth (Difco, Detroit, Mich.). The suspensions were diluted 1:10 to obtain a final inoculum of
104 CFU per spot. Plates were inoculated with a 19-prong
replicating device and incubated overnight in ambient air at 37°C.
The effects of the incubation atmosphere on HMR 3004 and HMR 3647 agar dilution MICs for 19 pneumococcal strains were determined by
incubation of agar plates in both ambient air and in a 5 to 7%
CO2 atmosphere. The standard quality control strain
S. pneumoniae ATCC 49619 was included in each run. The
activity of clindamycin (Upjohn, Heppenheim, Germany) was determined
for the erythromycin-resistant strains. The erythromycin-resistant
strains were further screened for the type of
macrolide-lincosamide-streptogramin B (MLS) resistance (constitutive
versus inducible) by disk diffusion on Mueller-Hinton agar (BBL,
Heidelberg, Germany) supplemented with 5% sheep blood with disks
(Oxoid, Wesel, Germany) containing erythromycin A (15 µg) and
clindamycin (2 µg). Inducible resistance was characterized by
blunting of the clindamycin inhibition zone when the clindamycin disk
was placed at a distance of 12 mm from the erythromycin A disk.
The MICs at which 50% of the isolates are inhibited
(MIC50s), MIC90s, and MIC ranges for the
four groups of pneumococcal strains investigated are shown in
Table 1. HMR 3004 and HMR 3647 were highly active, with MIC90s of
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Copyright © 1998, American Society for Microbiology. All rights reserved.
In Vitro Activities of the New Ketolide Antibiotics HMR 3004 and HMR 3647 against Streptococcus pneumoniae in
Germany
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ABSTRACT
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Abstract
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2 µg of HMR 3004/ml or by
0.5 µg of
HMR 3647/ml.
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TEXT
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Abstract
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2 µg/ml and which caused therapeutic problems in a few
cases, have been reported (19). Pneumococci with reduced
sensitivity to penicillin G are often found to also be resistant to
erythromycin A and other 14-membered-ring macrolides, such as
clarithromycin and roxithromycin, and to azithromycin.
0.03 to 2 µg/ml.
There was no significant difference between the activities of the two
ketolides. Ofloxacin activity was independent of penicillin G
susceptibility (MIC90, 4 µg/ml). Thirteen of the 28 erythromycin-resistant strains were found to be clindamycin susceptible
(MIC
0.25 µg/ml [presumptive M phenotypes]). The MICs of
the ketolides (HMR 3004 MIC90, 0.06 µg/ml; HMR 3647 MIC90, 0.125 µg/ml) and all other macrolides
(erythromycin A MIC90, 16 µg/ml; roxithromycin
MIC90,
32 µg/ml; azithromycin MIC90,
16 µg/ml; clarithromycin MIC90, 8 µg/ml) for
these strains were lower than those for the 15 strains belonging to the
constitutive MLS phenotype of erythromycin A resistance, for all of
which the macrolide MICs were
32 µg/ml. The MICs of the ketolides
for these strains were slightly elevated (HMR 3004 MIC90,
0.5 µg/ml; HMR 3647 MIC90, 0.25 µg/ml). Inducible MLS
resistance was not detected. Josamycin was active against
clindamycin-susceptible strains (MIC90, 0.5 µg/ml). Among
86 consecutive pneumococcal strains isolated between October 1996 and
March 1997, resistance to penicillin G or amoxicillin was not detected.
Only 95.4% of the strains were found to be erythromycin
susceptible. The highest rate of resistance was recorded for
tetracycline, with 4.7% of the strains resistant. The effect of the
incubation atmosphere on ketolide MICs versus S. pneumoniae was investigated by simultaneously determining MICs in
CO2 and ambient air. These experiments showed that the MICs of both ketolides were higher when strains were incubated in a CO2 atmosphere. For HMR 3647, a twofold increase of
MIC90 was observed; the MIC90 of HMR 3004 was
four dilution steps higher when plates were incubated in a
CO2 atmosphere.
TABLE 1.
In vitro activity of the new ketolides HMR 3004 and HMR
3647 compared with those of other macrolides, ofloxacin,
tetracycline, amoxicillin, penicillin G, and tetracycline
in Germany
The results of this study reflect the excellent activity of both ketolides (HMR 3004 and HMR 3647) against German S. pneumoniae isolates and confirm previous findings of American study groups (2, 3, 5, 8, 9, 16, 22).
As expected, erythromycin-resistant strains showed cross-resistance to the other macrolides and to azithromycin. The absence of erythromycin A cross-resistance may prove to be the major advantage of HMR 3004 and HMR 3647, particularly since erythromycin resistance has gradually increased in many parts of the world, including Germany. Ketolide MICs in our study were found to be a few dilutions higher for erythromycin-resistant strains than for erythromycin-susceptible strains, but the values were still lower than those for the other macrolides.
The results of the current study are also notable for the influence of a CO2 incubation atmosphere on ketolide MICs. The MICs of HMR 3004 and HMR 3647 were consistently two to four times higher when plates were incubated in a CO2 atmosphere. The CO2 incubation may lead to a marked decrease of pH in test media or perhaps alter the growth characteristics of test strains, in turn leading to a decrease of ketolide activity. As far as we know, the prevalence of pneumococcal isolates from systemic infections showing reduced susceptibility to penicillin G in Germany is one of the lowest published to date worldwide (12). In contrast to the situation in Germany, studies from Spain (resistance rate, 44.3%), Hungary (57.8%), and France (>40%) report very high incidences of strains exhibiting reduced susceptibility to penicillin G (6, 11, 13). In the present study no penicillin G resistance was detected in the group of consecutive strains isolated between October 1996 and March 1997, which confirms previous findings by our working group of a very low level of penicillin G resistance in Germany (1.8% of strains with an intermediate level of resistance to penicillin in 1992 to 1994) (21).
In summary, HMR 3004 and HMR 3647 show great potential for the treatment of pneumococcal infections. Clinical studies are warranted to test this hypothesis.
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ACKNOWLEDGMENTS |
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We thank M. Lemperle and I. Wolf-Leistner for excellent technical assistance.
This study was supported by a grant from Hoechst Marion Roussel, Romainville, France.
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FOOTNOTES |
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* Corresponding author. Mailing address: Institute of Medical Microbiology, University Hospital (RWTH) Aachen, National Reference Center for Streptococci, Pauwelsstr. 30, D-52057 Aachen, Germany. Phone: 49 241 8089787. Fax: 49 241 8888 483. E-mail: Reinert{at}RWTH-Aachen.de.
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