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Journal of Clinical Microbiology, October 2002, p. 3835-3837, Vol. 40, No. 10
0095-1137/02/$04.00+0 DOI: 10.1128/JCM.40.10.3835-3837.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Association of the prtF1 Gene (Encoding Fibronectin-Binding Protein F1) and the sic Gene (Encoding the Streptococcal Inhibitor of Complement) with emm Types of Group A Streptococci Isolated from Japanese Children with Pharyngitis
Xiaoming Ma,1 Hideaki Kikuta,1* Nobuhisa Ishiguro,1 Mikio Yoshioka,1 Takashi Ebihara,1 Teiko Murai,2 Intetu Kobayashi,3 and Kunihiko Kobayashi1
Department of Pediatrics, Hokkaido University School of Medicine, Sapporo,1
School of Nursing, Faculty of Medicine, Toho University,2
Department of Infectious Diseases, Mitsubishi Kagaku Bio-Clinical Laboratory, Tokyo, Japan3
Received 3 May 2002/
Returned for modification 18 June 2002/
Accepted 17 July 2002

ABSTRACT
A total of 66 clinical isolates of group A streptococci (GAS)
were obtained from 66 Japanese children with pharyngitis. The
prtF1 gene (encoding fibronectin-binding protein F1) and the
sic gene (encoding the streptococcal inhibitor of complement)
were present in 51 (77.3%) and 48 (72.7%) of the 66 isolates,
respectively. These results indicated that a high prevalence
of two virulence genes,
prtF1 and
sic, is characteristic of
GAS in Japan.

TEXT
Group A streptococci (GAS; also referred to as S
treptococcus pyogenes) are major etiological agents causing a wide variety
of human diseases, ranging from pharyngitis to severe invasive
diseases (
3). The N-terminal region of the M protein is located
distally to the surface of the bacterium and displays antigenic
diversity. This heterogeneity provides the basis for identifying
more than 100 different GAS serotypes (
6). However, many GAS
isolates are often nontypeable because of the lack of appropriate
type-specific antisera or because of a loss of antigen expression
under cultivation conditions. T typing has also been used as
an alternative or supplement to M typing. The T antigen is a
trypsin-resistant cell surface protein that exhibits extensive
antigenic diversity but is not defined as a virulence factor
(
3). Recently, a genomic typing method based on the variable
5'
emm gene has become widely used, and more than 150 different
types of the
emm gene, encoding the N-terminal region of the
M protein, have been characterized (
13) (
http://www.cdc.gov/ncidod/biotech/strep/strains.html).
This methodology has enabled the recognition of several previously
unknown GAS M types in different geographic areas. Additionally,
emm typing has been shown to be useful for detecting genetic
diversity among GAS isolates.
GAS cell surface proteins have been identified as virulence factors. More than 40 putative virulence-associated genes have also been identified (5). Some of these GAS cell surface proteins, such as fibronectin-binding proteins, function as adhesins. Adherence of GAS to pharyngeal or dermal epithelial cells is the first step in colonization of the host and development of infectious disease. Other GAS cell surface proteins, such as the streptococcal inhibitor of complement, are protective against the host defense system or trigger a severe nonspecific immunological response in the human host (3). The M protein, an important GAS virulence factor, has a dual role: it is a major antiphagocytic factor of GAS, and it is also an adhesin that binds fibronectin, fibrinogen, and albumin. Fibronectin-binding protein F1, encoded by the prtF1 gene, is one of the adhesins; it has been shown to be important for binding of the bacterium to the extracellular matrix of respiratory epithelial cells and for promoting entry into these cells (8). Intracellular localization of GAS has been suggested as an explanation for the failure of penicillin treatment of GAS infections (4). However, the relationship between the presence of the prtF1 gene and the failure of eradication is still controversial (2, 4, 11). The protein encoded by the sic gene is expressed extracellularly and inhibits in vitro the normal cytolytic function of the complement C5b-C9 membrane attack complex, which is responsible for target killing (1). The presence of the sic gene in GAS strains of 55 different M serotypes has been investigated; the genes have been reported to be present in M1- and M57-type strains but absent from other GAS strains (1). The purpose of this study was to determine the phenotypic (M and T types and azithromycin [AZM] sensitivity) and genotypic (emm type and the presence or absence of the prtF1 and sic genes) characteristics of 66 GAS isolates from 66 pediatric patients (2 to 12 years old) with pharyngitis treated at eight hospitals in Hokkaido, the northernmost island of Japan, during the period from August 2000 to March 2001.
All 66 isolates were examined for M and T types by standard M protein precipitation in gel agar and by the T agglutination method, respectively (9). M-type-specific antisera were available for types 1, 2, 3, 4, 5, 6, 8, 9, 11, 12, 13, 14, 18, 19, 22, 23, 27, 28, 29, 39, 41, 49, 53, 56, and Matsuyama 2166 (a provisional type). The variable 5' emm type was examined by sequence analysis of emm gene-specific PCR products (13). The primer sequences used were 5'-TATT(C/G)GCTTAGAAAATTAA-3' and 5'-GCAAGTTCTTCAGCTTGTTT-3'. The PCR-amplified products were sequenced directly by using a BigDye dye terminator cycle sequencing ready-reaction kit (Perkin-Elmer Applied Biosystems, Tokyo, Japan) with an ABI PRISM 310 genetic analyzer (Perkin-Elmer Applied Biosystems). Primer seq2, 5'-TATTCGCTTAGAAAATTAAAAACAGG-3', was used for sequencing. Nucleotide sequences of at least 160 bases were subjected to homology searches in the GenBank (http://www.ncbi.nlm.nih.gov/BLAST) and the Centers for Disease Control and Prevention (http://www.cdc.gov/ncidod/biotech/infotech_hp.html) databases. Table 1 summarizes the association of emm type with T type, M type, and the presence or absence of the prtF1 and sic genes. The 66 isolates were of 10 T types and 6 M types, including one provisional T B3264 type and one provisional M Matsuyama 2166 type. Although all of the isolates were T typeable, six exhibited complex forms of T antigens. T types of most GAS isolates were associated with specific M and emm types. Commonly isolated strains among the 66 isolates were M4 and M12 types. Ten emm types were found among the 66 isolates. The prevalent emm types were emm12 (18 isolates) and emm4 (16 isolates). No new emm type was detected. M Matsuyama 2166-type GAS has been found in Japan, Thailand, and Malaysia, but the emm type(s) and its worldwide prevalence are not known (9). The M Matsuyama 2166-type strain was type T2 and type emm75. The T B3264 type was correlated with either emm89 or emm94. The MIC of AZM was determined by the agar dilution method according to the National Committee for Clinical Laboratory Standard guidelines. AZM-resistant strains were defined as those for which the MIC of AZM was more than 2 µg/ml. Only 3 (4.5%) of the 66 isolates were resistant to AZM.
The presence of two virulence genes,
prtF1 and
sic, was determined
by PCR. The primer sequences used to amplify the
prtF1 gene
and sequence the PCR-amplified products were 5'-TTTTCAGGAAATATGGTTGAGACA-3'
and 5'-TCGCCGTTTCACTGAAACCACTCA-3'. PCR-amplified products were
subjected to electrophoresis through a 2.0% agarose gel. The
prtF1 gene was present in 51 (77.3%) of the 66 isolates, which
were of various
emm types, a somewhat higher percentage than
previously reported for that gene (
2,
7,
10). The
prtF1 gene
was not detected in
emm94-,
emm2-, and
emm1-type isolates. The
association between the presence of the
prtF1 gene and the
emm type of the isolates in this study is in agreement with results
of previous studies of the distribution of the
prtF1 gene in
GAS isolates of various
emm types (
2,
10). Gel electrophoresis
revealed that the PCR-amplified products were of five different
molecular sizes, ranging from approximately 100 to 750 bp. Repeat
domain type 2 (RD2) is composed of 37 amino acid residues repeated
fully four times and partially a fifth time (
12). PCR-amplified
products of 126, 237, 348, 459, and 745 bp corresponded to RD2
repeat numbers of 1, 2, 3, 4, and 6, respectively. The number
of RD2 repeats was confirmed by direct sequencing of several
representative PCR-amplified products and was constant among
individual
emm-type isolates except for those of type
emm4 or
emm75. The primer sequences used to amplify the
sic gene and
sequence the PCR-amplified products were 5'-GATGAGACAGAAGATAAAC-3'
and 5'-TTACGTTGCTGATGGTGTAT-3'. The presence of the
sic gene
was confirmed by Southern blot hybridization and direct sequencing
of two representative PCR-amplified products. The
sic gene was
detected in GAS of various
emm types, and 48 (72.7%) of the
66 isolates were
sic gene positive.
In the present study, we have determined the phenotypic and genotypic characteristics of GAS isolates from patients with pharyngitis in Japan. Unexpectedly, the majority of GAS isolates possessed two virulence genes, the prtF1 and sic genes. The high prevalence of these genes may be due to horizontal gene transfer and recombination. The results of this study should contribute to a better understanding of the pathogenesis of GAS as well as the epidemiology of GAS-associated disease and to the establishment of methods for prevention of diseases caused by GAS in Japan.

ACKNOWLEDGMENTS
We thank Nobuyoshi Ishikawa, Yachio Ota, Hiroyuki Sawada, Naofumi
Kajii, Mutsuo Sibata, Masanori Nakanishi, Yoshihiro Matsuzono,
and Keisaku Imamura for providing samples and Stewart Chisholm
for proofreading the manuscript.

FOOTNOTES
* Corresponding author. Mailing address: Department of Pediatrics, Hokkaido University School of Medicine, N-15, W-7, Kita-ku, Sapporo 060-8638, Japan. Phone: 81-11-716-1161, ext. 5954. Fax: 81-11-706-7898. E-mail:
hide-ki{at}med.hokudai.ac.jp.


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Journal of Clinical Microbiology, October 2002, p. 3835-3837, Vol. 40, No. 10
0095-1137/02/$04.00+0 DOI: 10.1128/JCM.40.10.3835-3837.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
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