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Antimicrobial Agents and Chemotherapy, November 2006, p. 3897-3900, Vol. 50, No. 11
0066-4804/06/$08.00+0 doi:10.1128/AAC.00057-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Telithromycin-Nonsusceptible Clinical Isolates of Streptococcus pneumoniae from Europe
Adnan Al-Lahham,1,
Peter C. Appelbaum,2
Mark van der Linden,1 and
Ralf René Reinert1*
Institute of Medical Microbiology, National Reference Center for Streptococci, University Hospital, Aachen, Germany,1
Hershey Medical Center, Hershey, Pennsylvania2
Received 13 January 2006/
Returned for modification 13 March 2006/
Accepted 30 July 2006

ABSTRACT
Telithromycin-nonsusceptible pneumococcal clinical isolates
(
n = 17) were analyzed for their antimicrobial susceptibility,
macrolide resistance mechanisms, and genetic relatedness. All
strains showed the
erm(B) genotype and showed a wide range of
combinations of macrolide resistance mechanisms. The predominant
clone (
n = 7) was serotype 14, sequence type 143.

TEXT
Streptococcus pneumoniae continues to be a significant cause
of morbidity and mortality in humans (
14). The worldwide increase
in antibiotic resistance in this species has become a serious
problem within the last 20 years (
2). Macrolide resistance in
S. pneumoniae is usually caused by methylation of A2058 of the
23S rRNA mediated by the
erm(B) gene or by an efflux mechanism
mediated by the
mef gene (
13). In addition, other mechanisms
of macrolide resistance have been described (
4,
20,
21). Ketolides
form a new class of semisynthetic agents derived from erythromycin
A designed to overcome erythromycin A resistance in
S. pneumoniae.
Ketolide compounds inhibit bacterial protein synthesis by interacting
with the peptidyltransferase site of the 50S ribosomal subunit
and interact closely with domains II, at A752, and V, at A2058
and A2059, of the 23S rRNA (
1). Ketolides show good activity
against gram-positive bacteria responsible for respiratory tract
infections, including penicillin G- and erythromycin A-resistant
S. pneumoniae (
11). The ketolide-resistant pneumococci described
usually show the
erm(B) genotype, and some, but not all, strains
show additional alterations in the L4 ribosomal protein (
1,
16). The scope of the present paper was to investigate the occurrence
of these mechanisms of resistance in a collection of 17 telithromycin-nonsusceptible
pneumococcal isolates from Europe.
(This work was presented in part at the 45th Interscience Conference on Antimicrobial Agents and Chemotherapy, 16 to 19 December 2005, Washington, D.C. [1a]).
MIC testing was performed using the broth microdilution method recommended by the Clinical Laboratory Standards Institute (formerly the National Committee for Clinical Laboratory Standards) (5). PCR of macrolide resistance genes was performed as described previously (17). Sequencing of the 23S rRNA and the genes encoding the ribosomal proteins L4 (rplD) and L22 (rplV) was performed as reported earlier by Tait-Kamradt et al. (4, 21) and Walsh et al. (22). The erm(B) gene and the erm(B) promoter region were amplified by PCR using the primers published by Walsh et al. (22). Pneumococcal strains were serotyped by Neufeld's Quellung reaction using type and factor sera provided by the Statens Serum Institut, Copenhagen, Denmark. Multilocus sequence typing (MLST) was carried out as described by Enright and Spratt (8). Phylogenetic analysis was performed as described before (18). Nucleotide sequences of the upstream regions of the erm gene were aligned using the program ClustalW. Sequence types (STs) of the telithromycin-nonsusceptible isolates were compared with those of all isolates available in the MLST database.
Demographic data and data on antibiotic resistance are presented in Table 1. Isolates were collected between 2001 and 2005 from patients with invasive and noninvasive pneumococcal disease, mostly in France (10 out of 17 strains). Telithromycin MICs ranged between 2 and 8 µg/ml. All strains were multiply resistant and besides being telithromycin nonsusceptible showed reduced susceptibility to ß-lactams and resistance to macrolides, lincosamides, and tetracycline. One strain additionally showed high-level fluoroquinolone resistance.
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TABLE 1. Characteristics, MICs, and resistance phenotypes of 17 telithromycin-nonsusceptible S. pneumoniae strains from Europe
|
Genotypic and phenotypic characteristics and results from MLST
are presented in Table
2. The predominant serotype was type
14 (10 of 17 isolates). The predominant clone was ST 143 (7
of 17 isolates), which was found in France (
n = 6) and Germany
(
n = 1). Telithromycin resistance has also spread to the Spain
23F-1
clone (ST 81;
n = 1) and its 19A variant. All strains showed
the
erm(B) genotype and the cMLS
B phenotype and were negative
for the
mef gene. The isolates had multiple alterations in 23S
rRNA. Analysis of the genes encoding ribosomal protein L22 showed
a wild type for all isolates. Of note, in nine isolates an S20N
alteration in ribosomal protein L4 was observed. Isolates belonging
to one clone showed identical or quite similar resistance mechanisms.
Of note, three clones were described for the first time in the
present investigation (strain PW 778, ST 1569; PW 735, ST 1558;
and PW 868, ST 2010) (Table
3).
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TABLE 2. Genotypic and phenotypic characterization and macrolide resistance mechanisms of 17 telithromycin-nonsusceptible S. pneumoniae strains from Europe
|
The DNA sequences of the
erm(B) upstream region of the telithromycin-nonsusceptible
clinical isolates were compared to the upstream sequence region
of
erm(B) found in Tn
1545 (accession no. X52632) (
15),
erm(B)
(accession no. AJ972605) (
7), pAM77 (accession no. K00551) (
12),
and Tn
917-like LP-1 (accession no. AB111455) (
15) (Fig.
1).
In the region upstream of the
erm(B) start codon, mutations
were found at positions 5, 6, 7, 28,
33, and 90 [upstream of the ATG start codon of
erm(B)]. These mutations were homologous to mutations found
at positions 320, 319, 318, 297, and 292 in Tn
1545, respectively.
In the open reading frame of
erm(B), the mutation E58A was observed
in 1 isolate, I75T was observed in 9 isolates, N100S was observed
in 13 isolates, H118R was observed in 9 isolates, and V171A
was observed in 2 isolates. However, some of the mutations described
in the present study are likely not involved in resistance and
are outside of regions that are known to interact with the ribosome.
Therefore, these mutations may simply represent heterogeneity
in the
erm(B) gene and its promoter region.
To our knowledge, the present report describes the largest collection
of telithromycin-nonsusceptible clinical isolates characterized
for their resistance mechanisms and their epidemiological background
to date. The global surveillance project PROTEKT (Prospective
Resistant Organism Tracking and Epidemiology for the Ketolide
Telithromycin) reported that only 0.2% of
S. pneumoniae isolates
collected between 1999 and 2003 were resistant to telithromycin
and that all showed the cMLS
B phenotype (
10). Concordantly,
the present study and other studies on telithromycin resistance
in
S. pneumoniae report on resistance mainly in
erm(B)-positive
strains. In addition, a recent study showed that telithromycin
can be removed from
Streptococcus pyogenes by efflux, related
to the presence of the
mef gene (
3). Faccone and coworkers have
reported on a high-level telithromycin-resistant isolate from
Argentina. The isolate was
mef(E) positive, but
erm(B) and
erm(A)
negative (
9). In addition, substantial levels of telithromycin
resistance were recently detected in a collection of soil isolates,
possibly due to inactivation of the compound (
6). Analysis of
the clonal relatedness of the present collection of strains
showed that telithromycin resistance was predominantly found
among two clones, ST 81 and ST 143. ST 81 (Spain
23F-1 clone
and its serotype 19A variant) is known to be responsible for
the worldwide spread of resistance among pneumococci (
19).
In summary, the present study demonstrates that mutations in the erm(B) gene, its promoter region, ribosomal protein L4, and 23S rRNA may be associated with resistance to telithromycin in clinical isolates of S. pneumoniae. Although the incidence of telithromycin resistance in pneumococci remains rare worldwide, the spread of telithromycin resistance to multidrug resistance clones with worldwide distribution is a worrisome finding of the present study.
Nucleotide sequence accession numbers.
The GenBank accession numbers of the ermB (upstream region and open reading frame) sequences of this study are DQ855638 (PW1791 and PW1420), DQ855639 (PW899, PW1765, PW1976, and PW521), DQ855640 (PW1840), DQ855641 (PW712 and PW715), DQ855642 (PW1760), DQ855643 (PW735), DQ855644 (PW788), DQ855645 (PW868), DQ855646 (Pn302), DQ855647 (PW1981), DQ855648 (PS5646), and DQ855649 (PW1996).

ACKNOWLEDGMENTS
The authors thank Sandra Barbosa for excellent technical assistance.
We thank the PneumoWorld Study Group for cooperation and for
providing the isolates.
This study was supported in part by grant RKI-415/1369235 from the German Ministry of Health (Bundesminister für Gesundheit) and by the German Ministry for Science and Technology (BMFT) (CAP net).

FOOTNOTES
* Corresponding author. Mailing address: Institute for Medical Microbiology, National Reference Center for Streptococci, University Hospital (RWTH), Pauwelsstr. 30, Aachen, Germany. Phone: 49 241 8089946. Fax: 49 241 8082483. E-mail:
Reinert{at}rwth-aachen.de.

Present address: German Jordanian University, School of Applied Medical Sciences, Amman, Jordan. 

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Antimicrobial Agents and Chemotherapy, November 2006, p. 3897-3900, Vol. 50, No. 11
0066-4804/06/$08.00+0 doi:10.1128/AAC.00057-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
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