Jpn. J. Infect. Dis., 55, 2002

Laboratory and Epidemiology Communications

Molecular Epidemiological Surveillance of Methicillin-Resistant
Staphylococcus aureus in a Hiroshima Community Hospital in 2002
Rie Sasaki, Tomoko Fujino1, Katsutoshi Saruta1, Junko Kawasaki,
Norikazu Shigeto and Teruo Kirikae1*
Hiroshima City Medical Association-Administered Aki City Hospital(former National Hataka Hospital),
Hataka 2-14-1, Aki, Hiroshima 736-0088 and1
International Medical Center of Japan,
Toyama 1-21-1, Shinjuku-ku, Tokyo 162-8655
Communicated by Hiroshi Yoshikura(Accepted July 10, 2002)
Methicillin-resistant Staphylococcus aureus (MRSA) is amajor hospital-acquired pathogen in institutions including
community hospitals with relatively small numbers of beds
(1,2). Molecular epidemiological surveillance using restriction fragment-length polymorphisms of genomic DNA
employing pulsed-field gel electrophoresis (PFGE) is essential
for assessment of hospital infection controls (3).
The present surveillance was conducted in a hospital in
Hiroshima. The hospital had two wards totaling 120 beds.
The subjects included 100 inpatients and 111 medical staff
members present in the hospital in February 2002. A total of39 MRSA isolates were obtained from five patients’ sputa,
one patient’s bedsore, and nasal swabs of ten patients andthree nurses in ward I; five patients’ sputa, two patient’s urine,
nasal swabs of eight patients and three nursing staff members
including one nurse and two assistant nurses in ward II; andnasal swabs of one doctor and one nurse in charge of outpatients. Carriage rates of MRSA were 31% for inpatientsand 9% for medical staff members. The isolates were testedfor chromosomal DNA typing by using a contour-clamped
homogeneous electric field system (CHEF MapperTM: BioRad Laboratories, Hercules, Calif., USA), enterotoxin
serotyping (SET-RPLA: Denka Seiken Co., Tokyo), toxic
shock syndrome toxin-1 (TSST-1) production (TST-RPLA:Denka Seiken), and coagulase serotyping (Denka Seiken).
Twenty-two different PFGE patterns of SmaI DNA digests
were detected (Fig. 1). A band-based cluster analysis (Molecular AnalystTM: Bio-Rad), in which PFGE-band similarity
exceeding 70% was used as the criterion of cluster formation, revealed 7 cluster patterns: A, G, H, C, I, E, and J (Fig.
2A). The frequency distribution of MRSA of these different
PFGE patterns is shown in Fig. 2B. The most frequent pattern(A11) and the second-most frequent one (A1) represented
29% and 19% of the total isolates, respectively. Distribution ofMRSA isolates in the wards is shown in Table 1. The isolates
belonging to PFGE patterns A11 and A1 were the mostFig. 1. Pulsed-field gel electrophoresis of SmaI-digested genomic DNA from MRSA isolates. M: low range PFG Marker.
Lanes 1 to 22: MRSA isolates with different PFGE patterns A1 to J shown in Fig. 2.

*Corresponding author: Fax: +81-3-3202-7181, E-mail: tkirikae@ri.imcj.go.jp
93Jpn. J. Infect. Dis., 55, 2002
(A)

Table 1. Distribution and PFGE pattern of MRSA isolates in a hospital
PFGEpattern
A1A7A11A13
A14A15A16A17A18
A19A20C5C6C7E3E4G1G2G3HIJ(B)

WardIII1●●● *●●○ *2●●●●○●●●●●●○●●●○ *3○ *4●
●
●
●
●
●
●
●
●
●
○
○

●

●
○
●

*1 Closed symbols represent MRSA isolates from inpatients.
*2 Open symbols represent MRSA isolates from medical staffs.
*3 represents a MRSA isolate from a doctor.
*4 represents a MRSA isolate from a nurse in charge of outpatients.

Fig. 2. Cluster analysis of MRSA isolates based on PFGE patterns.

common and were spread over wards I and II. Three isolates
having PFGE pattern A14 were obtained from patients in bothwards I and II as well as from a doctor. PFGE patterns A16and G3 were detected in both wards I and II. The remaining
17 PFGE patterns were detected from a single patient or
medical staff member.
Among the 39 MRSA isolates, 37 isolates produced
coagulase type II, and the remaining two produced coagulase
type I or III. Twenty-five isolates produced enterotoxin typeC, two isolates enterotoxin type B, nine isolates enterotoxin
types B and C, one isolate enterotoxin A, and one isolate
enterotoxin other than types A, B, C, or D. Thirty-four isolates
produced TSST-1, while the other five did not. Collectively,
among 39 MRSA isolates, 25 isolates produced coagulase
type II, enterotoxin type C, and TSST-1. Nine isolates withPFGE pattern A11 produced coagulase type II, enterotoxin
types B and C, and TSST-1.
The PFGE patterns of these MRSA isolates were comparedwith those of MRSA isolates obtained in the same hospital inAugust and December 2000 (1), and in September 2001 (2).

Fig. 3. Cluster analysis of MRSA isolates obtained at different periods.

94Jpn. J. Infect. Dis., 55, 2002
From a total of 70 isolates, 39 different PFGE patterns weredetected (data not shown). Band-based cluster analysis ofthese patterns revealed 10 clusters A to J (Fig. 3). Four ofseven PFGE patterns in August 2000, five of nine in December
2000, five of seven in September 2001, and 11 of 22 inFebruary 2002 were of cluster type A. PFGE pattern A1 wasdetected during all the investigated periods. Pattern A2 wasdetected in August 2000 and September 2001, pattern A7 wasdetected in September 2001 and February 2002, and pattern
A11 was detected in December 2000 and February 2002.
Collectively, the above observations indicate the spread of
two MRSA strains with patterns A11 and A1 in the hospitalin February 2002. Pattern A1 strain had settled in the hospital
before December 2000 and continued to circulate. Anotherstrain with pattern A11 which appeared in December 2000 wasa newcomer to the hospital. Other MRSAs whose infections
were sporadic were considered to be introduced from outside.

REFERENCES
1. Kawasaki, J., Fujio, T., Naiki, Y., Mori, N., Sasaki, R.,
Shigeto, N. and Kirikae, T. (2001): Molecular epidemiology of methicillin-resistant Staphylococcus aureus in acommunity hospital in Hiroshima. Jpn. J. Infect. Dis.,54, 117-118.
2. Sasaki, R., Fujino, T., Kawasaki, J., Furukawa, T., Mori,N., Shigeto, N. and Kirikae, T. (2001): Epidemiologicalanalysis of methicillin-resistant Staphylococcus aureus
in a community hospital in Hiroshima. Jpn. J. Infect. Dis.,54, 191-193.
3. Fujino, T., Mori, N., Kawana, A., Naiki, Y., Kawahata,
H., Kuratsuji, T., Kudo, K., Kobori, O., Yazaki, Y. andKirikae, T. (2001): Molecular epidemiology of methicillinresistant Staphylococcus aureus in a Tokyo hospital in
2001. Jpn. J. Infect. Dis., 54, 240-242.

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