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Journal of Clinical Microbiology, January 1999, p. 221-224, Vol. 37, No. 1
0095-1137/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Dissemination of High-Level Penicillin-, Extended-Spectrum
Cephalosporin-, and Erythromycin-Resistant Streptococcus
pneumoniae Clones in Taiwan
Po-Ren
Hsueh,1,2
Lee-Jene
Teng,3
Li-Na
Lee,1,2
Pan-Chyr
Yang,2
Shen-Wu
Ho,3 and
Kwen-Tay
Luh1,2,*
Departments of Laboratory
Medicine1 and
Internal
Medicine,2 National Taiwan University
Hospital, and
School of Medical Technology, National Taiwan
University College of Medicine,3 Taipei, Taiwan
Received 17 August 1998/Returned for modification 16 September
1998/Accepted 15 October 1998
 |
ABSTRACT |
Sixty-seven clinical isolates of Streptococcus
pneumoniae (40 of serotype 23F, 19 of serotype 19F, and 8 of
serotype 6B) with decreased susceptibilities to penicillin and
erythromycin were characterized by antimicrobial susceptibility
patterns; DNA restriction endonuclease cleavage profiles of the
penicillin-binding protein genes pbp1a,
pbp2b, and pbp2x; random amplified polymorphic
DNA (RAPD) patterns generated by arbitrarily primed PCR; and
chromosomal macrorestriction profiles based on pulsed-field gel
electrophoresis. A total of 22 clones (identical or closely related
pulsotypes and identical RAPD patterns) were identified; 14 clones of
23F, 6 of 19F, and 2 of 6B. Three 23F clones (26 isolates) and one 19F
clone (9 isolates) expressed high-level resistance to penicillin, cefotaxime, and erythromycin (MICs
256 µg/ml). These data
strongly suggest that multiple high-level penicillin-,
extended-spectrum cephalosporin-, and macrolide-resistant clones of
S. pneumoniae have been disseminated in Taiwan.
 |
TEXT |
The emergence of strains of
Streptococcus pneumoniae resistant to penicillin,
extended-spectrum cephalosporins, and macrolides has become a
considerable concern in many parts of the world, including Taiwan, as
it limits the options available for the treatment of serious
pneumococcal infections (1, 8, 10, 11, 14, 17, 25). Previous
observations provide strong evidence that the spread of
penicillin-resistant S. pneumoniae in a geographic area may
be due to transfer of mosaic pbp genes from resistant isolates into susceptible isolates (horizontal spread) or to
dissemination of a pneumococcal clone (clonal spread) (2, 3, 6, 7, 13, 26). In addition, dissemination of a multidrug-resistant S. pneumoniae (MDRSP) phenotype to additional
serotypes due to in vivo capsular transformation may occur
(3, 13, 16). Dissemination of serotype 23F MDRSP or other
serotype clones of S. pneumoniae has been documented in
several countries; however, no reported clones possessed
extremely high resistance to erythromycin (MICs
256 µg/ml)
(5, 12, 18, 20-22, 24, 27).
Bacterial isolates.
A total of 67 isolates (40 of serotype
23F, 19 of serotype 19F, and 8 of serotype 6B) of S. pneumoniae with reduced susceptibilities to penicillin and
erythromycin recovered from various clinical specimens from patients
who were treated at National Taiwan University Hospital, a tertiary
referring center with 2,000 beds in northern Taiwan, from January
1996 to December 1997 were studied. These isolates were recovered from
67 patients, 30 adults and 37 children, who resided in the
northern part of Taiwan. Sources of the isolates included sputum or
bronchial secretion (34 isolates), blood (14 isolates),
ear-nose-throat-sinus (10 isolates), wound and pus (6 isolates),
cerebrospinal fluid (2 isolates), and bile (1 isolate). All isolates
were identified by conventional methods (25).
Antimicrobial susceptibility testing.
MICs of seven
antimicrobial agents for the 67 isolates, determined by the agar
dilution method with Mueller-Hinton agar containing 5% sheep blood
(BBL Microbiology Systems), were adopted from our previous study
(10). MIC breakpoints for defining susceptibility and
resistance were in accordance with the 1998 guidelines of the National
Committee for Clinical Laboratory Standards, except for gentamicin and
cefpirome, for which no criteria were provided (23). MDRSP
was defined as showing intermediate or high-level resistance to
penicillin and resistance to one or more classes of the other
antibiotics tested. Antibiotypes of the isolates were considered to be
different if the MIC of at least one of the antimicrobial agents tested
was a
2-dilution discrepancy.
DNA fingerprinting of genes encoding pbp1a,
pbp2b, and pbp2x.
Segments of the
pbp1a, pbp2b, and pbp2x genes of the
isolates were amplified from chromosomal DNA by PCR with the previously described oligonucleotide primers (21). Gene fingerprinting of the segments of the pbp1a, pbp2b, and
pbp2x genes was performed with the restriction enzymes
HinfI and AluI (Gibco BRL, Gaithersburg, Md.)
(18, 26).
RAPD analysis.
The preparation of isolates for random
amplified polymorphic DNA (RAPD) analysis, generated by arbitrarily
primed PCR, and extraction of genomic DNA were as described
previously (9). Three primers were used: M13
(5'-GAGGGTGGCGGTTCT-3'), ERIC1
(5'-GTGAATCCCCAGGAGCTTACAT-3'), and OPA-7
(5'-GAAACGGGTG-3'). Patterns differing by more than one band
were considered to be different.
PFGE analysis.
DNA fingerprinting of the isolates by
pulsed-field gel electrophoresis (PFGE) analysis was
performed in accordance with previous descriptions (15,
19). The DNA was digested by SmaI, and the fragments
were resolved by PFGE in 1% agarose (SeaKem GTC agarose; FMC
Bioproducts, Rockland, Maine) in 0.5× Tris-borate-EDTA buffer for
20 h at 14°C and 6 V/cm with a CHEF-DRIII apparatus (Bio-Rad Laboratories, Richmond, Calif.). Interpretation of PFGE
profiles (pulsotypes) was in accordance with the criteria
described by Tenover et al. (28).
Phenotypic and genotypic characteristics of the isolates are presented
in Tables 1 and
2. Among the isolates, 22 different clones were identified, including 22 RAPD patterns (patterns A to V)
and 22 different pulsotypes (profiles a to v) (Fig.
1 and Table 1). Figure
2 shows the pulsotypes of the nine clones
(clones 1 to 9) of serotype 23F with high-level resistance to
penicillin. Isolates having the same pulsotypes and RAPD patterns all
belonged to different serotypes. Among the 22 clones, 17 antibiotypes
were identified (Table 2) and all isolates were MDRSP. Forty-four (66%) isolates belonging to 11 clones had erythromycin MICs of
256
µg/ml.

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FIG. 1.
RAPD patterns generated by arbitrarily primed PCR of the
22 clones of S. pneumoniae with two primers, M13 and ERIC1.
Molecular sizes (lane M) are indicated in kilobases (Gibco BRL).
|
|

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FIG. 2.
PFGE profiles of SmaI-digested chromosomal
DNA of nine clones of serotype 23F S. pneumoniae isolates.
Lane M is a molecular size standard for a bacteriophage ladder
(Gibco BRL); lanes 1 to 9 show clones 1 to 9, respectively.
|
|
Of the 14 clones (clones 1 to 14) of isolates belonging to serotype
23F, two major clones (clones 1 and 9) comprised 55% (22 isolates) of
the isolates; these isolates all had high-level resistance to
penicillin and erythromycin, with MICs of
256 µg/ml. Clone 1 isolates were also highly resistant to cefotaxime (MICs of 8 µg/ml)
and cefpirome (MICs of 4 µg/ml). Among the 31 isolates belonging to
the five clones (clones 1, 2, 3, 9, and 10) resulting in dissemination
(more than one isolate included in a single clone), the majority were
recovered from sputum or bronchial secretion (52%), followed by blood
(29%), and 26 isolates (84%) were recovered from children.
Among the 19 isolates of serotype 19F, six distinct clones were
identified, with one principal clone (clone 19) comprising
nine closely
related isolates which had intermediate resistance
to penicillin but
had erythromycin MICs of

256 µg/ml. Clonal
dissemination was found
in four clones (clones 15 and 17 to 19).
Seven (88%) of the serotype
6B isolates belonged to one clone
(clone 21), and all had intermediate
resistance to penicillin
(MICs of 0.5 µg/ml). Among these seven
isolates, four were recovered
from
children.
Among the 67 isolates, seven fingerprint profiles of
pbp1a,
five of
pbp2b, and five of
pbp2x were identified
(Table
1). All
isolates of the same clones had identical
pbp1a,
pbp2b, and
pbp2x fingerprint
profiles, confirming their clonal origin. Isolates
of clone 1 had
unique
pbp1a,
pbp2b, and
pbp2x gene
fingerprint
profiles, which were different from those obtained from
other
clones. Twenty-two of the 24 serotype 23F isolates, other than
clone 1, had the same
pbp2x fingerprint profile (profile II)
as
the 16 isolates of serotype 19F. The same
pbp2b
fingerprint profile
(profile IV) was obtained from 9 isolates (clones
4, 5, 9, and
11) of serotype 23F and 16 isolates (clones 15, 17, 19, and 20)
of serotype 19F. Twenty-seven isolates including nine different
clones (clones 4, 5, 8, 9, 15, 17, 19, 20, and 22) had identical
pbp2x (profile II) and
pbp2b (profile IV)
fingerprint profiles.
The
pbp2x (profile II) and
pbp2b (profile III) fingerprint profiles
were found in eight
serotype 23F isolates of five different clones
(clones 3, 6, 10, 12, and 14). Two clones (clones 5 and 9), comprising
seven isolates of
serotype 23F, had identical
pbp1a,
pbp2b, and
pbp2x fingerprint profiles and identical antibiotypes for

-lactam
antibiotics. Identical susceptibilities to

-lactam
antibiotics
and restriction profiles of
pbp1a,
pbp2b, and
pbp2x were also
found in two serotype
6B isolates (clones 20 and
22).
In our previous survey we noted a marked increase in erythromycin
resistance in clinical isolates of
S. pneumoniae, from 9.1%
in 1984 to 85.8% in 1997, in Taiwan (
10). In addition, the
resistance
rate of penicillin increased from 1.6% in 1992 to 66.2% in
1997,
of which 60% of the isolates had high-level resistance and the
majority belonged to serotypes 23F, 19F, or 6B (
10). Our
prior
study also showed that a surprisingly large fraction of the
isolates
belonged to serotype 23F (from 8.8% during 1984 to 1986 to
32.5%
during 1996 to 1997), and the majority of the isolates had less
susceptibility to penicillin and high-level resistance to erythromycin
(MICs

256 µg/ml) (
8,
10). This suggests that
epidemic spread
of a few bacterial clones occurred in this
area.
In the present study, three important points regarding the molecular
epidemiology of the most frequently encountered serotypes
of clinical
isolates of
S. pneumoniae with reduced susceptibility
to
penicillin and erythromycin were clarified. First, four major
clones
(clones 1, 9, 19, and 21) involving serotypes 23F, 19F,
and 6B have
obviously been disseminated in Taiwan. The majority
of these isolates
were highly resistant to penicillin, extended-spectrum
cephalosporins,
and erythromycin (MICs

256 µg/ml). Second, several
isolates
expressing serotype 23F or 19F and having identical altered
pbp genes and

-lactam susceptibilities had
different RAPD patterns
and PFGE profiles (different clones),
suggesting that the occurrence
of horizontal transfer of
pbp
genes between strains is likely.
Third, none of the isolates
originating from a common ancestor
(a single clone) expressed different
serotypes, indicating that
serotype (capsular) transformation in vivo
did not occur in these
strains.
Although resistant pneumococci may be selected due to antibiotic
pressure in a given geographic area, it is suggested that
the spread of
individual highly resistant clones has contributed
to the emergence of
worldwide resistance (
20). In the present
study, one of the
principal clones (clone 1, serotype 23F) comprises
16 isolates
recovered from different patients, showing that this
clone has been
widely spread in northern Taiwan. A similar scenario
might be seen with
serotypes 19F (clone 19) and 6B (clone 21)
in the near future in
Taiwan.
In this study, we did not simultaneously compare the
pbp
gene fingerprint profiles or PFGE profiles of our serotype 23 clones
with the South African or Spanish erythromycin-resistant serotype
23F
clone. However, dissemination of the Spanish or South African
23F clone
to Taiwan is not likely, for three reasons. First, the
origins of
serotype 23F isolates in northern Taiwan appeared to
be heterogeneous,
since 14 distinct clones were clearly identified.
Multiplication of a
single imported clone is not the only process
used to explain the
recent upsurge in the proportion of penicillin-
and
erythromycin-resistant serotype 23F isolates. Second, our
principal
clone of serotype 23F (clone 1) had an antibiotype,
i.e., high MICs
(

256 µg/ml) of erythromycin as well as high penicillin
and
cefotaxime MICs (4 and 8 µg/ml, respectively), which was different
from that of the Spanish or South African clone. Third, we compared
the
PFGE profiles of our disseminated serotype 23 clones with
those of the
Spanish clone published in the literature, and no
identical or closely
related profiles were found (
4,
19).
In conclusion, our data strongly suggest that multiple high-level
penicillin-, extended-spectrum cephalosporin-, and macrolide-resistant
clones of
S. pneumoniae have become disseminated in Taiwan.
This
might explain the extremely high rates of resistance to these
drugs in clinical isolates of
S. pneumoniae recovered in
Taiwan.
Clinicians in Taiwan should be alerted to the possible spread
of these multiresistant strains, which may pose serious dilemmas
for
the treatment of patients with infections caused by these
organisms.
 |
ACKNOWLEDGMENTS |
This work was partly supported by a grant (NSC86-2314-B-002-053)
from the National Science Council, Republic of China.
 |
FOOTNOTES |
*
Corresponding author. Mailing address: Department of
Laboratory Medicine, National Taiwan University Hospital, No. 7 Chung-Shan South Rd., Taipei, Taiwan. Phone: 886-2-23562149. Fax:
886-2-23224263. E-mail: luhkt{at}ha.mc.ntu.edu.tw.
 |
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Journal of Clinical Microbiology, January 1999, p. 221-224, Vol. 37, No. 1
0095-1137/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
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