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Group B Streptococcal Disease in Nonpregnant Patients: Emergence of Highly Resistant Strains of Serotype Ib in Taiwan in 2006 to 2008

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DOI: 10.1128/JCM.00810-10 · Source: PubMed
Abstract
Among the 228 group B Streptococcus (GBS) isolates recovered in 2006 to 2008, higher resistance to erythromycin (58.3%) and clindamycin (57.9%) was found in isolates with certain resistance phenotypes. Serotype Ib isolates (24.6%) were the second most prevalent serotype, next to serotype V (29.4%), and showed the highest resistance rates to erythromycin (91.0%) and clindamycin (82.1%).
JOURNAL OF CLINICAL MICROBIOLOGY, July 2010, p. 2571–2574 Vol. 48, No. 7
0095-1137/10/$12.00 doi:10.1128/JCM.00810-10
Copyright © 2010, American Society for Microbiology. All Rights Reserved.
Group B Streptococcal Disease in Nonpregnant Patients: Emergence
of Highly Resistant Strains of Serotype Ib
in Taiwan in 2006 to 2008
Ying-Hsiang Wang,
1,3
Lin-Hui Su,
3,5
Jiun-Nun Hou,
4
Tsung-Han Yang,
2
Tzou-Yien Lin,
6
Chishih Chu,
4
* and Cheng-Hsun Chiu
3,6
*
Departments of Pediatrics
1
and Laboratory Medicine,
2
Chang Gung Memorial Hospital, Chiayi, Taiwan; Graduate Institute of
Clinical Medical Sciences, Chang Gung University College of Medicine, Taoyuan, Taiwan
3
; Department of
Microbiology and Immunology, National Chiayi University, Chiayi, Taiwan
4
; and Department of
Laboratory Medicine, Chang Gung Memorial Hospital,
5
and Division of Pediatric Infectious Diseases,
Chang Gung Children’s Hospital,
6
Taoyuan, Taiwan
Received 23 April 2010/Accepted 26 April 2010
Among the 228 group B Streptococcus (GBS) isolates recovered in 2006 to 2008, higher resistance to
erythromycin (58.3%) and clindamycin (57.9%) was found in isolates with certain resistance phenotypes.
Serotype Ib isolates (24.6%) were the second most prevalent serotype, next to serotype V (29.4%), and showed
the highest resistance rates to erythromycin (91.0%) and clindamycin (82.1%).
Application of a perinatal disease prevention strategy based
on intrapartum antibiotic prophylaxis in 1996 resulted in a
substantial decline in early-onset group B Streptococcus (GBS;
Streptococcus agalactiae) infections in the United States (19).
The incidence of invasive GBS infections in nonpregnant pa-
tients, however, has increased over the past decades (17), par-
ticularly in elderly patients and those with underlying medical
conditions (21). Diabetes mellitus, cirrhosis, and renal failure
are common risk factors associated with invasive GBS disease
in nonpregnant adults (11). Whereas clinical GBS isolates usu-
ally remain susceptible to penicillin, dramatic increases in re-
sistance to erythromycin and clindamycin have raised concerns
about their use as alternative agents in many countries (8, 10).
The present study was undertaken to investigate the clinical
characteristics of invasive GBS infection and the resistance
phenotypes, capsular serotypes, and pulsed-field gel electro-
phoresis (PFGE) genotypes among the associated clinical iso-
lates.
From October 2006 to June 2008, all hospitalized nonpreg-
nant patients who were admitted to Chang Gung Memorial
Hospital (CGMH) in Chiayi and had a culture-proved GBS
infection were included for study. For each patient, only the
first GBS isolate was subjected to laboratory investigation and
analyzed. Community-acquired GBS (CA-GBS) is defined as
isolates from specimens obtained within 48 h of admission, and
hospital-acquired GBS (HA-GBS) as those recovered thereaf-
ter (9). The isolation of GBS from a normally sterile site
suggests an invasive infection in the patient.
Double disc diffusion tests were used to determine suscep-
tibility to erythromycin and clindamycin. Phenotypes of mac-
rolide-lincosamide-streptogramin B (MLS
B
) resistance were
determined in accordance with previous reports (20). After
incubation at 35.8°C for 24 h, blunting of the clindamycin
inhibition zone proximal to the erythromycin disc indicated an
inducible (iMLS
B
) resistance. Clindamycin resistance with no
blunting inhibition zones suggested a constitutive (cMLS
B
)
resistance. Macrolide phenotypes (M) were characterized by
clindamycin susceptibility with no blunting inhibition zones
around the clindamycin disc. In addition, the MICs of dalfo-
pristin were used to identify the lincosamide-streptogramin A
(LSA) phenotype in isolates with erythromycin susceptibility
and clindamycin resistance. Resistance to erythromycin, clin-
damycin, and dalfopristin was determined by an agar dilution
method according to the criteria suggested by the Clinical and
Laboratory Standards Institute (7).
Capsular serotypes of the isolates were determined by a
previously described multiplex PCR assay (18). SmaI (New
England BioLabs, Frankfurt, Germany)-digested macrofrag-
ments of genomic DNA from serotype Ib isolates were ana-
lyzed by PFGE as previously described (25). Genotypes and
subtypes were determined according to the criteria of Tenover
(23).
The
2
, Fisher exact
2
, or Student ttest was used to analyze
the categorical data. Univariate and multivariate logistic re-
gression analyses were used to discriminate independent risk
factors of comorbidity. A Pvalue of 0.05 indicates statistical
significance.
A total of 228 GBS patients were included in this study
(Table 1). The majority of the patients were from the age
groups of 40 to 59 years (34.7%) and 60 to 79 years (35.1%).
Few cases were detected in patients younger than 19 years of
age (7.4%), including 11 (4.8%) infants younger than 3 months
old. The female gender was predominant (64%), and most
GBS diseases were noninvasive infections (all urinary tract
infections) (76.8%). In contrast, invasive infections were more
* Corresponding author. Mailing address for C.-H. Chiu: Division of
Pediatric Infectious Diseases, Chang Gung Children’s Hospital, 5 Fu-
Hsin Street, Kweishan, Taoyuan 333, Taiwan. Phone: 886-3-3281200,
ext. 8896. Fax: 886-3-3288957. E-mail: chchiu@adm.cgmh.org.tw.
Mailing address for C. Chu: Department of Microbiology and
Immunology, National Chiayi University, 300 Syuefu Road, Chiayi
600, Taiwan. Phone: 886-5-2717898. Fax: 886-5-2717831. E-mail: cschu
@mail.ncyu.edu.tw.
Published ahead of print on 5 May 2010.
2571
common in males (66.0% in males versus 26.9% in females;
P0.01) and those over 40 years of age (26.6% among those
over 40 years old compared to 11.8% among those younger).
The most common comorbidity condition was diabetes
(27.6%). Multivariate analysis identified that diabetes, moder-
ate to severe renal disease, any prior tumor, and moderate to
severe liver disease were independent risk factors for invasive
diseases (P0.01). The Charlson Comorbidity Index (CCI) is
a weighted score based on the relative risk of 19 conditions
significantly influencing outcomes (6). Patients were consid-
ered to have a comorbidity condition if they showed a listed
disorder in the records or were treated for the disorder. The
combination of the weighted scores of all comorbidity condi-
tions present in patients was then scaled to establish the CCI.
There was no significant difference in the mean CCI between
genders, serotypes, and erythromycin resistance. The mean
CCI of invasive diseases was significantly higher than that of
noninvasive diseases (2.0 versus 0.62, respectively; P0.01),
suggesting that the CCI is a better predictive factor for invasive
GBS diseases than are individual comorbidity conditions.
The majority (94.3%) of the 228 nonrepeat GBS isolates
were associated with CA-GBS, while erythromycin resistance
was significantly higher in HA-GBS than in CA-GBS isolates
(92.3% versus 56.3%; P0.01) (Table 1). Among the 12
erythromycin-resistant HA-GBS isolates, 7 showed cMLS
B
re-
sistance, and the remaining 5 showed iMLS
B
resistance. Com-
pared to CA-GBS, HA-GBS tended to cause invasive diseases
(61.5% versus 20.9%; P0.01) and to infect elder patients
(mean age, 65.1 years for HA-GBS versus 52.8 years for CA-
GBS; P0.05). Serotype Ib was the most prevalent serotype
among the HA-GBS isolates.
Serotype distribution of the 228 isolates is shown in Table 2.
Resistance to erythromycin and clindamycin was found in 133
(58.3%) and 132 (57.9%) isolates, respectively. Invasiveness of
the infection types was not correlated with any specific sero-
types or resistance phenotypes. Compared to isolates of the
other serotypes, serotype Ib isolates showed a significantly
higher resistance to erythromycin (91.0% versus 47.7%; P
0.01) and clindamycin (82.1% versus 50.0%; P0.01). The
iMLS
B
resistance type was also more frequently found in se-
rotype Ib isolates than the others (48.1% versus 12.1%; P
0.01).
Among the 56 serotype Ib isolates, PFGE analysis revealed
six major genotypes that included a total of 17 subtypes (Fig.
1). Genotype A was the most prevalent (47 isolates [83.9%])
and contained 11 subtypes, with genotype A1 being the most
prevalent (35 isolates [62.5%]). The other non-genotype A
isolates were relatively more diverse, with five belonging to
genotype B (2 subtypes) and one each found in genotypes C
to F (Table 3). The only four isolates that were susceptible to
both erythromycin and clindamycin demonstrated distinct
PFGE patterns (A3, B1, D, and F). The prevalence levels of
isolates that were associated with invasive diseases were similar
among serotype Ib isolates of genotype A1 and those of the
other PFGE patterns (17.1% versus 19.0%; P1.00).
Similar to previous studies from the United States (5), we
observed that the majority of the GBS infections in nonpreg-
nant patients in Taiwan occurred in adults, with an adult-to-
child ratio of 12.4:1. We also found that invasive diseases were
more common in male patients, usually involving subjects over
40 years of age. In the present study, risk factors for invasive
GBS infection were also similar to those reported previously
(11). To predict outcomes of the patients, the CCI is probably
the most widely used comorbidity index to date (22), with
TABLE 1. Comparison of clinical features and erythromycin susceptibility between HA- and CA-GBS infections
a
Clinical
feature
No. (%) of patients
Total With HA-GBS infection With CA-GBS infection
S R Subtotal S R Subtotal S R Subtotal
UTI 72 (41.1) 103 (58.9) 175 1 4 5 71 99 170
SSTI 12 (44.4) 15 (55.6) 27 0 3 3 12 12 24
Sepsis 10 (45.5) 12 (55.5) 22 0 4 4 10 8 18
Peritonitis 1 (50.0) 1 (50.0) 2 0 0 0 1 1 2
Endocarditis 0 (0) 1 (100) 1 0 0 0 0 1 1
Meningitis 0 (0) 1 (100) 1 0 1 1 0 0 0
Total 95 (41.7) 133 (58.3) 228 1 12 13 94 121 215
a
S, erythromycin susceptible; R, erythromycin resistant; UTI, urinary tract infection; SSTI, skin and soft tissue infection.
TABLE 2. Frequency of resistance phenotypes among various serotypes of GBS isolates
a
Erythromycin/clindamycin
phenotype (resistance
phenotype)
No. of isolates (% of resistant isolates) of indicated serotype Total no. of
isolates (%
of resistant
isolates)
Ia Ib II III IV V VI VII Nontypeable
R/R (cMLS
B
)0 (0) 20 (38.5) 3 (60.0) 13 (72.2) 7 (77.8) 34 (77.3) 5 (50.0) 0 (0) 4 (100) 86 (60.1)
R/R (iMLS
B
)1 (100) 25 (48.1) 1 (20.0) 2 (11.1) 0 (0) 4 (9.1) 3 (30.0) 0 (0) 0 (0) 36 (25.2)
R/S (M) 0 (0) 6 (11.5) 0 (0) 2 (11.1) 1 (11.1) 1 (2.3) 1 (10.0) 0 (0) 0 (0) 11 (7.7)
S/R (LSA) 0 (0) 1 (1.9) 1 (20.0) 1 (5.6) 1 (11.1) 5 (11.4) 1 (10.0) 0 (0) 0 (0) 10 (7.0)
S/S 2 441414231437 85
a
R, resistance; S, susceptibility.
2572 NOTES J. CLIN.MICROBIOL.
standard clinical variables as the factors for the CCI assess-
ment. In this study, we found that the CCI appeared useful for
clinical care and risk adjustment of invasive GBS disease in
nonpregnant patients.
Since the 1990s, an increase in resistance to erythromycin
and clindamycin in GBS has been reported in Taiwan, from
30% and 24% in 1997 (27) to 46% and 43% in 2001 (10), and
up to 58.3 and 57.9% in the present study. With a steady
increase in resistance, our study also represents the first report
on the significantly high incidence of erythromycin resistance
(92.3% [12/13]) among HA-GBS isolates from the nonpreg-
nant patients admitted in our hospital. Despite the small num-
ber of isolates, the results suggest that GBS is not only an
established community pathogen but also could cause HA in-
fections under high antibiotic pressure.
The MLS
B
phenotype was not only prevalent among HA-
GBS isolates, but it was also the most predominant resistance
phenotype among the resistant GBS isolates during the study
period. These data highlight the fact that target site modifica-
tion by rRNA methylases, encoded by erm genes, might play a
major role in the geographical and temporal variability in mac-
rolide resistance among GBS in Taiwan. The observation is
different from those reported in England, Wales, and the
United States, where the macrolide phenotype is more fre-
quent and usually involves mef genes (2, 26). Furthermore, a
previous report from New Zealand indicated that the LSA
phenotype was mainly found in serotype III and I isolates (14).
In the present study, however, the LSA phenotype was pre-
dominant in serotype V and rarely found in serotypes Ib, II,
III, IV, and VI. The presence of the LSA phenotype in differ-
ent serotypes also suggested a horizontal transfer of the resis-
tance (1).
The prevalent serotypes of GBS isolates from nonpregnant
patients may vary, usually depending on the time and geo-
graphical location (3, 16). Since it was first reported in 1985,
serotype V has been the most common serotype among non-
pregnant adults in North America, Taiwan, and Zimbabwe (4,
12, 16). Whereas serotype Ib was an infrequent serotype else-
where (15, 24), we found an increased isolation of serotype Ib,
the second most common serotype found in this study. Our
study also disclosed the high incidence of erythromycin and
clindamycin resistance in isolates of this serotype (12, 13, 27).
FIG. 1. Pulsed-field gel electrophoresis patterns of serotype Ib GBS isolates. Genotype A (11 subtypes, A1 to A11) was identified in 47 isolates.
Genotype B (2 subtypes, B1 and B2) was identified in five isolates. Genotypes C, D, E, and F were identified in one isolate each.
TABLE 3. Distribution of PFGE genotypes and resistance phenotypes among 56 serotype Ib isolates
a
Erythromycin/clindamycin
phenotype (resistance
phenotype)
Total no. of
isolates
No. of isolates with PFGE genotype:
AB
CDEF
A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 B1 B2
R/R (cMLS
B
)20 1120010000 1 1 210010
R/R (iMLS
B
)25 1901100111 0 0 010000
R/S(M) 6 400001000 0 0 001000
S/R (LSA) 1 1 00000000 0 0 000000
S/S 4 001000000 0 0 100101
a
R, resistance; S, susceptibility.
VOL. 48, 2010 NOTES 2573
This remarkable elevation correlated with the emergence of
high rates of antimicrobial resistance. The situation may be
due to the clonal expansion of genotype A1 isolates in the
serotype Ib population, as revealed by the conserved PFGE
analysis in the present study. To our knowledge, no recent
studies have examined the genetic variation of serotype Ib
GBS isolates. This observation is of significant epidemiological
implication. The emergence of a new genetic lineage that car-
ries resistance to antimicrobial agents widely used in the region
may represent a result of selection phenomena, as well as a
therapeutic challenge. The major limitation of this study is that
the isolates examined are not population based and, therefore,
may not reflect the collective bias. Further surveillance of the
clonal heterogeneity of GBS isolates by different measures is
necessary.
This work was supported by grants CMRPG660061 and CM-
RPG660091 from Chang Gung Memorial Hospital, Chiayi, Taiwan.
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