Jpn. J. Infect. Dis., 52, 1999

Laboratory and Epidemiology Communications●Selection of Methicillin‑Resistant Staphylococcus aweus followlng●Increased Use of Vancomycln despite Restricted Use of
Third Generation Cephem
Kozue Iwakawa, Naho Tsusaka, JunkoKizul and Kenji Yamamoto*
Division of Clinical Bacteriology and LDivision of Pharmacology, Bun 'in Hospital of Universityof Tokyo,
Mejirodai 3‑28‑6, Bunkyo‑ku, To桓O

CommunicatedbyHiroshi

Yoshikuraa‑d(Accepted November 25, 1999)
l I

Continued use of the same antibiotic in a hosp血l or ward

results in the increased isolation of bacteria resistant to theantibiotic. Suspension of the administration of the antibiotic

4. 30 LO‑.L r L JTLoo0000

420864

results in a decreased presence of the bacteria resistant to theantibiotic. This is the reason why proper use of antibiotics is(joq∈nu)<stJ三3221〇 5 0 5でoq∈nu)<ssM

required.

The amount of prescribed antibiotics and the rate of isola‑tion of methicillin‑resistant Staphylococcus aureus (MRSA)
were followed from 1989 to 1998 in a teaching hospital inTokyo (1).
Figure 1 shows the use of all the antibiotics and that ofthird generation cephems in 1989‑ 1998. The total amount of

the prescribed antibiotics decreased to 60% from 1 989 to I 994.
1990

The prescription of third generation cephem was decreased toless than30% during thisperiod. From 1994 to 1998, the total

1991

1992

1993

1994

1905

1996

1997

1998

yOar

Fig･ 2･ Number of MSSA and MRSA isolates in 1990‑1998･amount of prescribed antibiotics, both for all the antibiotics●: MSSA O:MRSA

and the third generation antibiotics, remained unchanged.

Figure 2 shows the isolation of methicillin‑sensitive

Staphylococcus aureus (MSSA) and MRSA in 199011998.
The isolation of MRSA decreased by halffrom 1990 to 1993.

9 8 7 6 5 4 3〇 〇2 〇 〇 〇 〇 〇 〇q)

thND^○lU 三PaSt?OL9UJ.tJ ‑^誘虻三000

0●

However, it began to increase in 1994 and regalned its 1990

peq!JoSBJd王3^

level in 1998. Meanwhile, MSSA gradually increased from●●32 0 0 0 0 0 0●1990 to 1997, but in 1998 it decreased to its orlglnal 1990

level. The decrease of MRSA from 1990 to 1993 is well
explained by the decreased use of third generation cephem

and antibiotics in general (Fig. I). However, the increase in45000

10000

40000

9000
1989

1991

1992

1993

1994

1995

1996

1997

1998

year
∈oLJdou o!teJaU36pJ!LJト

Fig･ 3･ Use ofVCM associated with increased isolation of MRSA with

30000
SU!30!q!tut!こく1990

8 7 60 0 00 0 00 0 035000

higher resistance to VCM･+ :amount of VCM prescribed (expressed by the standard doses for25000
th 4 3 2adults)

0 0 0 00 020000

0 : incidence of MRSA whose MIC to VCM was I.015000
0 00 00 0MRSA since 1994 cannot be explained by the data in Figure I ･All the MRSA isolates since 1993 have been stocked in10000
5000

skim milk conservation medium. They were examined fわr01989

the minimal inhibitory concentration (MIC) of vancomycin
1990 1991 19921993

1994

1995

1996

1997

1998

(VCM). The MIC value was determined as either O･5 or l･0year(LLg/ml). The assays were highly reproducible･ It should beFig･ 1 ･ Amount ofalltheantibioticsand third generation cephems pre‑noted that the MIC value of 1.0 is not diagnostic fわr VRSA

scribed in 1989‑1998･ The prescribed amount is expressed by the(Vancomycin‑resi stant Staphylococcus aureus) ･stan血rd doses f♭r adults.

Figure 3 shows the proportion (%) of isolates with MIC

0 :all the antibiotics + : third generation cephems

values of Ilo for each year･ The curve of the incidence of*Corresponding author: E‑mail:bacteria@ims･u‑tokyo･acJPMRSA with the higher MIC runs in parallel with that of the221

Jpn. J. Infect. Dis., 52, 1999

amount of prescribed VCM but with a delay of one year. Thisappears to suggest that the increased use of VCM, Without
increased use of third generation cephem, endowed MRSA
with a selective advantage and increased resistance to VCM.
Though the action points ofVCM and third generation cephem

REFERENCES
1. Kizu, ∫., Arano, K., Minowa, H., Yamamoto, K. andKawana, S. ( 1 995): Trend in MRSA‑infected patients anduse of antibiotics. Nihon‑Kankyo‑Kansen, 10, 1 5‑22 (inare different, the both affect cell wall synthesis. Some muta‑Japanese).

tions responsible for methicillin resistance may favor thepersistence of the bacteria in the presence of VCM.

222