Jpn. J. Infect. Dis., 60, 2007

Laboratory and Epidemiology Communications

Food Poisoning Caused by Mannitol Nonfermenting
Staphylococcus aureus: Case Report
Setuko Haga*, Ikumi Hishinuma, Iwao Itoh, Nanako Kumagai1, Hisako Eguchi2 and Mariko Tanaka2
Aizu Branch of Fukushima Institute of Public Health, Fukushima 965-0873; 1Fukushima Institute ofPublic Health, Fukushima 960-8560; and 2Niigata City Institute of Public Health, Niigata 950-2023, Japan
Communicated by Haruo Watanabe(Accepted January 31, 2007)

On August 4, 2005, 20 people who participated in the closing ceremonies of a community festival experienced nausea,vomiting, diarrhea and abdominal pain. The community wherethe festival took place was under the jurisdiction of the Aizu
Health Center of Fukushima Prefecture. The foods that allof these patients had consumed were rice balls prepared bycaterer A. Another 8 people, who did not participate in thefestival but who had ingested the rice balls, also became ill.
The Aizu Branch of the Fukushima Institute of Public
Health examined 3 specimens of the remaining rice balls,
6 finger swab specimens from the cooks, 6 kitchen utensil
swab specimens, 6 stool specimens from the patients withsymptoms and 5 stool specimens from the cooks. Additionally, the Niigata City Institute of Public Health and the Niigata
Prefectural Instiute of Public Health and Environmental Sciences examined one stool specimen from each of the otherpatients. The Aizu Branch isolated 7 Staphylococcus aureus
strains and the Niigata City Institute of Public Health isolated 2 strains. The characteristics of the 9 isolates are summarized in Table 1. Bacterial identification was conductedusing an ID test SP-18 (Nissui Pharmaceutical Co., Ltd.,Tokyo, Japan), a coagulase test for Staphylocoagulase antisera (Denka Seiken, Co., Ltd., Tokyo, Japan) and the detection and typing of staphylococcal enterotoxin by reversed
passive latex agglutination (RPLA) for types A - D (DenkaFig. 1. Pulsed-field gel electrophoresis of SmaI digests of the chromosomal
DNAs of S. aureus isolates. Lane 1, rice ball (pickled plum); 2, riceball (seaweed); 3, fried food; 4, swab specimen from an employee(caterer A shop B); 5, swab specimen from an employee (caterer A shopB); 6, swab specimen from the handle of the refrigerator (caterer Ashop B); 7, swab specimen from a cook (caterer A); 8-9, patient’s
stool specimen (Niigata City Institute of Public Health); the same
patient. M, molecular size marker (Salmonella Braenderup strain
H9812, XbaI digest).

Table 1. Characteristics of S. aureus isolated

12
3
4
5
6
7
8*
9*

rice ball (pickled plum)
rice ball (seaweed)
fried foodswab specimen from an employee(caterer A shop B)
swab specimen from an employee(caterer A shop B)
swab specimen from the handle ofthe refrigerator (caterer A shop B)
swab specimen from a cook (caterer A)
patient’s stool specimen (Niigata CityInstitute of Public Health)ditto

Colony characters on egg yolk plates
egg yolk reaction mannitol fermentation

Enterotoxin

Coagulase

A
A––IVIV
III
III++++––++–

UT++–

III++AA

IVIV++––

DII++*: 8,9, the same patient. UT, untypable.

*Corresponding author: Mailing address: Aizu Branch of Fukushima Institute of Public Health, 7-40 Oute-machi, Aizuwakamatsu,
Fukushima 965-0873, Japan. E-mail: haga_setsuko_01@pref.
fukushima.jp145Seiken) and by polymerase chain reaction (PCR) for types
A - E (Takara Bio, Otsu, Japan).
Samples that were positive for S. aureus for type IV
coagulase and enterotoxin A were isolated from pickled plumand seaweed rice balls, a finger swab specimen from a cook
and a stool specimen examined at the Niigata City Instituteof Public Health. The strain grew as a nearly pure culture on
egg yolk isolation plates. The colonies were not typical for S.
aureus in that, though positive for the egg yolk reaction, they
were only faintly yellow and negative for mannitol fermentation.
The 9 isolates listed in Table 1 were submitted to pulsedfield gel electrophoresis (PFGE) of SmaI digests of chromosomal DNAs (Fig. 1). The conditions for electrophoresis were
the following: pulse time, 5.3 - 34.9 sec; voltage, 6V/cm; andduration, 19 h. Two isolates from the rice balls (lanes 1 and2), one isolate from a finger swab from the cook and one
isolate from a patient’s stool specimen examined at the Niigata

City Institute of Public Health showed the same pattern. We
therefore assume that the rice balls were responsible for thefood poisoning.
Mannitol nonfermenting colonies are often discarded as
non-staphylococcal colonies. In the present case, the nearlypure culture of the colonies led us to suspect them as thecausative agent. It is important to keep in mind that biochemical markers should not be relied upon too heavily inthe laboratory identification of S. aureus, especially whereatypical phenotypes are involved. Massive growth as a pureculture such as that in the present case should be taken as anindication for further investigation.
We thank Dr Hiroshi Yoshikura, Emeritus Researcher of
the National Institute of Infectious Diseases, for advice on
preparing the manuscript.
This article appeared in the Infectious Agents Surveillance
Report (IASR), vol. 27, p. 72-73, 2006 in Japanese.

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