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Journal of Clinical Microbiology, May 2002, p. 1851-1853, Vol. 40, No. 5
0095-1137/02/$04.00+0 DOI: 10.1128/JCM.40.5.1851-1853.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Household Transmission of Streptococcus pneumoniae among Siblings with Acute Otitis Media
Jun Shimada,1* Noboru Yamanaka,1 Muneki Hotomi,1 Masaki Suzumoto,1 Akihiro Sakai,1 Kimiko Ubukata,2 Toshihiro Mitsuda,3 Shumpei Yokota,4 and Howard Faden5
Department of Otolaryngology-Head and Neck Surgery, Wakayama Medical University, Wakayama,1
Institute of Microbial Chemistry, Tokyo,2
Division of Clinical Laboratory Medicine,3
Department of Pediatrics, School of Medicine, Yokohama City University, Kanagawa, Japan,4
Department of Pediatrics, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, and Division of Infectious Disease, Children's Hospital of Buffalo, Buffalo, New York5
Received 24 September 2001/
Returned for modification 26 November 2001/
Accepted 22 January 2002

ABSTRACT
Nasopharyngeal transmission of
Streptococcus pneumoniae was
evaluated among 23 siblings with acute otitis media (AOM). Restriction
fragment length polymorphism revealed that the nasopharyngeal
strains were identical between siblings in 12 of 13 clusters
of AOM experienced in 11 families. This study demonstrated person-to-person
transmission of
S. pneumoniae, especially drug-resistant strains,
among siblings with AOM.

TEXT
Acute otitis media (AOM) is the most common infectious disease
during childhood. Approximately one-third of children experience
three or more episodes in the first 3 years of life (
2). Nasopharyngeal
colonization with potential middle ear pathogens is an important
first step in the development of AOM. Especially heavy growth
of a particular pathogen in nasopharyngeal specimens may correlate
well with the organism causing otitis media (
6).
Streptococcus pneumoniae,
Haemophilus influenzae, and
Moraxella catarrhalis are considered normal flora of the nasopharynx in children;
however, these microbes are very likely to be causative pathogens
of AOM. Moreover, there has been an alarming increase in the
antimicrobial resistance of
S. pneumoniae that may be responsible
for treatment failures. The standard method for differentiating
strains of
S. pneumoniae is serotyping based on capsular antigens.
However, this approach is limited because of the potential for
horizontal transfer of capsular genes (
1). Pulsed-field gel
electrophoresis (PFGE) is currently considered the most reliable
and practical tool for epidemiological analysis of bacterial
infections. The present study was designed to investigate household
transmission of
S. pneumoniae among siblings with AOM utilizing
restriction fragment length polymorphism analysis by PFGE.
Twenty-three siblings in 11 families (A through K) with concurrent or closely related episodes of AOM were enrolled in this study (Table 1). Nasopharyngeal isolates were obtained with a transnasal swab (Carry Mate calcium alginate swab; Osaka Seiyaku, Osaka, Japan) inserted into the nasopharynx through the nose. Specimens were cultured on sheep blood agar (Nippon Becton Dickinson, Tokyo, Japan) at 37°C with CO2 for 24 to 48 h. S. pneumoniae was identified by standard methods (8). Potential middle ear pathogens were identified in the nasopharyngeal culture. The growth of pathogens in culture was recorded semiquantitatively from 0 to 3+, and growth at 2+ or 3+ was considered significant. MICs of antibiotics for S. pneumoniae isolates were determined by the NCCLS-recommended broth microdilution method (10). The antibiotics employed in this study were penicillin G, ampicillin (Meiji Seika Kaisha., Ltd., Tokyo, Japan), cefotaxime (Nippon Hoechst Marion Roussel, Tokyo, Japan), clindamycin (Pharmacia Co., Ltd., Tokyo, Japan), cefaclor, erythromycin (Shionogi & Co., Ltd., Osaka, Japan), and levofloxacin (Daiichi Pharmaceutical Co., Ltd., Tokyo, Japan). The definition of the susceptibility of S. pneumoniae to penicillin G was based on the criteria established by the NCCLS (10). Capsular serotypes of S. pneumoniae were determined by the Quellung reaction with Danish typing sera (Statens Seruminstitut, Copenhagen, Denmark) (9). Genomic DNA was prepared by modification of the procedure described by Mitsuda et al. (7). The isolate was grown at 37°C for 6 h in Todd-Hewitt broth under 10% CO2. The cells were harvested and resuspended in washing buffer (50 mM Tris-HCl [pH 7.5]). Fifty microliters of each cell suspension was used for plug preparation. An equal volume of melted 2% agarose was added to this suspension. Sample plug molds were incubated with lysis buffer (0.25 M EDTA, 1% sodium dodecyl sulfate, 10 mM Tris-HCl [pH 9.5], proteinase K at 0.5 mg/ml) overnight at 50°C and then rinsed with washing buffer. Restriction of genomic DNA was carried out with 20 U of SmaI for 20 h at 30°C or ApaI at 37°C for 20 h. Electrophoresis was performed on a GenePath PFGE apparatus (Bio-Rad Laboratories, Hercules, Calif.) with program 12 (18.5 h at 6 V/cm and 14°C in 0.5x TBE buffer [1x TBE buffer is 0.1 M Tris-HCl + 0.1 M boric acid + 2 mM EDTA {pH 8.0}]). After gel electrophoresis, the gels were stained with ethidium bromide and photographed under UV light. Isolates were assigned a major pattern designation (S1 or A1) when they showed the same PFGE pattern.
Thirteen clusters of AOM in siblings were observed in 11 families.
Two clusters of AOM among siblings occurred in families A and
G. (Table
1). PFGE analysis with
SmaI revealed 13 different
patterns. The strain polymorphism found by
ApaI testing was
similar to that found by
SmaI testing (Fig.
1). Comparison of
the PFGE patterns of pneumococcal isolates with 13 clusters
in 11 families revealed 100% homology between the siblings in
12 clusters (92%). One common PFGE pattern (S9, A9) was seen
in siblings of three different families (families G, H, and
J). Although these three families lived in different districts
of the same town and the children attended different day care
centers (families H and J), they might have had some contacts
or there might be endemic dissemination of the specific pathogen
in such a small town. Four different serotypes were detected.
Serotype 19 was the most prevalent, and serotypes 23 and 19
accounted for the majority of the isolates. Antimicrobial susceptibility
tests showed that 10 (37%) strains were penicillin-susceptible
S. pneumoniae. Seventeen strains (63%) displayed reduced susceptibility
to penicillin (penicillin-intermediately resistant
S. pneumoniae).
Resistance to two or more antibiotics was observed among 20
strains (74%).
Typing by PFGE, capsular serotype determination, and antibiotic
susceptibility testing were equally able to demonstrate homology
between pairs of organisms from siblings; however, only PFGE
was able to distinguish pairs in the population of 27 organisms
since there were 12 PFGE types, four capsular serotypes, and
overlapping antibiotic susceptibility patterns. Our study provides
evidence for the household transmission of genetically similar
strains of
S. pneumoniae between siblings. Hendley et al. (
4)
first described intrafamily spread of
S. pneumoniae more than
25 years ago by simply documenting pharyngeal colonization among
family members. This crude technique demonstrated the high rate
of colonization in families with young children as opposed to
families without children. Subsequent studies used capsular
typing to demonstrate the epidemiology of colonization within
individuals over time (
3,
5). More recent studies have utilized
DNA fingerprinting to study the spread of resistant strains
in a day care setting (
11). Sluijter et al. (
12) compared restriction
fragment end labeling, capsular typing, and penicillin binding
protein genotyping for effectiveness in the characterization
of
S. pneumoniae colonization in children from birth to 2 years
of age. They concluded that restrictions fragment end labeling
was superior to capsular typing in distinguishing strains, and
they observed horizontal transfer of capsular genes between
strains. Chromosomal analysis by PFGE in the present study allowed
the identification of one endemic multi-drug-resistant strain
(S9, A9) in three unrelated families, which were otherwise indistinguishable
by serotyping or antibiogram. In conclusion, the PFGE analysis
clearly demonstrated person-to-person transmission of
S. pneumoniae among siblings with AOM and clinicians should take account of
the likelihood of a single pathogen causing AOM among siblings.

FOOTNOTES
* Corresponding author. Mailing address: Department of Otolaryngology-Head and Neck Surgery, Wakayama Medical University, 811-1 Kimiidera, Wakayama City, Wakayama 641-0012, Japan. Phone: 81-73-441-0651. Fax: 81-73-446-3846. E-mail:
junpe{at}wakayama-med.ac.jp.


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Journal of Clinical Microbiology, May 2002, p. 1851-1853, Vol. 40, No. 5
0095-1137/02/$04.00+0 DOI: 10.1128/JCM.40.5.1851-1853.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
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