Jpn. J. Infect. Dis., 53, 164‑165, 2000

Short Communication

An Increase in Multi‑Drug‑Resistant Isolates of Salmonella Typhimurium
from Healthy Carriers in Aichi, Japan
Masakado Matsumoto* , Masahiro Suzuki, Reij i Hiramatsu, Mitsugu Yamazaki,
Hironori Matsui, Kenji Sakae, Yasumoto Suzuki and Yutaka Miyazaki
Department of Microbiology, A ich i Pflefectural Institute of Public Health
7‑6 Nagare Tsuji‑machi, Kita‑ku, Nagoya 462‑8576, A ichi, Japan(Received September 5, 2000. Accepted September 14, 2000)

SUMMARY: To investlgate the prevalence of drug‑resistant isolates of Salmonella Typhimurium in Aichi,

Japan, we performed antimicrobial susceptibilitytests for 148 isolates from healthy carriers, and from sporadic
and outbreak cases of salmonellosis from 1980 to 1999. We found an increase in drug‑resistant isolates from56% (37/66) in the 1980s to 74% (61/82) in the 1990s due to increasing examples offour‑, five‑, and six‑drugresistances. Of 98 resistant iso)atesin1980 A 1999, 12 were identified as ampicilhn (A)‑, chloramphenicol (C)‑,streptomycin (S)‑, sulfonamide (Su)‑, and tetracycline (T)‑resistant S. Typhimurium (4 in the 1980S, 8 in the1 990S), whose pattem was identical to that of multi‑drug‑resistant S. Typhimurium definitive phage type 104(DTIO4) which has been recently detected in various developed countries. Six‑drug‑resistance ACSSuTP(piperacillin), in which P was added to the core pattem of the ACSSuT, was also found in four isolates in the1 980s and seven in the 1 990S･ Another six‑drug‑resIStant Pattem, ACSSuTN (nalidixic acid), app?ared in rlVe
isolates in the 1 990S･ These multi‑drug‑resistant isolates were predominately found in healthy carriers (2 1/28),

suggesting that in Aichi the multi‑ (five‑ or six‑) drug‑resistant isolates of S. Typhimurium have existed inhealthy carriers as well as in diarrhea patients in 1980 to 1999.

In various developed countries, a marked increase in仇ewith sporadic illness, and 22 from 1 1 outbreak cases (one tonumber of multi‑drug‑resistant Salmonella Typhimurium

three isolates per one ou他reak). All isolates were obtained inisolates belonging to definitive phage type 1 04 (DTI 04) fromour laboratory, laboratories or reglOnal health centers, andsporadic and ou他reak cases of gastroenteritis has beenclimical laboratories of general hospitalsinAichi.Antimicrobial

reported starting around 1990. The organism has a coresusceptibility tests were performed uslng the agar dilution

pattem of resistance to ampicillin (A), chloramphenicol (C),method (5). Antibiotics used in this study and their minimum

streptomycin (S), sulfonamide (Su), and tetracycline (T) ( 1 ,2).

inhibitory concentrations interpreted as resistance were as

Japanese researchers demonstrated the involvement of multi‑

follows: A (16 LLg/ml), C (8 LLg/ml), S (16 LLg/ml),
sulfamethoxazole (SX) (256 LLg/ml), T (8 LLg/ml), gentamycin

drug‑resistant S. Typhimurium DTI 04 in sporadic cases ofillness in the past 20 years. Four DT104‑related outbreaks(G) (4 LLg/ml), nalidixic acid (N) (16 LLg/ml), piperacillin(P) (64 LLg/ml), trimethoprim (Tp) (8 LLg/ml) (2,6). All anti‑biotics were purchased &om Sigma Chemical, St. Louis, Mo.,
USA.

were recognized between 1997 and 1998 in Tokyo (3,4). The
multi‑drug‑resistant isolate ofS. Typhimurium DT 1 04 is thus
an enteric pathogen which causes serious public healthproblems. Despite wide investigation of the bacteria, theThe Table summarizes the number of antibiotics to which

reasons for the prevalence of the pathogen with multi‑drug‑

the isolates were resistant and the pattems of drug resistance.

resistance among healthy carriers in Japan are not fully
understood. In the current study, we tested the drug‑resistanceAmong 66 isolates in 1980 ‑ 1989, 37 (56%) were resistant
to?ne to six antibiotics tested, but the majority(73%) Wereof 148 S. Typhimurium isolates from healthy carriers as wellresistant tO less than three antibiotics. In contrast, 61 (74%) ofas sporadicand outbreak cases of salmonellosis in Aichi from82 isolates in 1990 ‑ 1999 were found to be resistant. More‑1980 to 1999, although we could not perform phage typing

over, most were resistant to four or more antibiotics and thus

for S. Typhimurium.

the ratio of the isolates, which showed one to three drug‑

Among the 148 isolates examined, 90 were from healthy

resistances, was significantly less than that in 1980 ‑ 1989

carriers whose occupation was food handler, 36 kom patients(36% versus 73%). Of98 resistant isolates &om 1980 to 1999,

Table･ Rate of drug‑resistant strains and their resistance patterns ofS. Typhimurium

periodofNo.

ofNo.

of

Five

Three or less FourSixisolation isolates tested drug‑resistant isolates ACSSXT Others ACSSXTP ACSSXTN
1980‑

1990‑11989

99966
82

37(56%)
61(74%)

27(73%)
22(36%)

11448

154075Resistance symbols: A, ampicillin; C, chloramphemicol; S, streptomycin; SX, sulfamethoxazole; T, tetracycline; P, piperacillin; N, nalidixic acid

*Corresponding author: Tel: +81152‑91 1‑31 ll ext. 261, Fax: +81‑
52‑9 1 3‑364 1 , E‑mail: masakado｣¶atsumoto@pretaichijp164

12 were identirled as ACSSuT‑resistant S･ Typhimuri.um (4ACKNOWLEDGMENTS

in the 1980S, 8 in the 1990S), whose pattern was identlCal tothat of the multi‑drug‑resistant S. Typhimurium DT 1 04, which

We thank the staff members of the laboratories ofreglonalhas been recently detected in various advanced nations. Thesehealth centers, and of the clinical laboratories orgeneral hos‑were from 1 0 healthy carriers, followed by two sporadic cases.

pitals in Aichi for providing S. Typhimurium isolates.

Six‑drug‑resistance (ACSSuTP), in which P waヲ added to thecore patternofthe ACSSuT, was found in four lSOlates in theREFERENCES

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