Snow Brand Milk Products Co. said Thursday it will consider closing its Osaka plant following the recent outbreak of food poisoning caused by milk products shipped from the plant.

Tetsuro Ishikawa, president of Snow Brand, also announced that he will resign in September to take responsibility for the mass poisoning, in which more than 11,000 people in western Japan have been sickened.

“It will be extremely difficult to keep up operations (at the Osaka plant), and we will consider various options, including closure,” the firm said in a statement.

The case is having a serious impact on Snow Brand’s business, the nation’s largest manufacturer of dairy products, as supermarkets and convenience stores nationwide remove its products from their shelves.

The outbreak hit last week as people began falling ill after consuming low-fat and calcium-enriched milk produced at the Osaka plant.

The milk was found to be contaminated by a toxin-producing bacteria known as staphylococcus aureus.

On Wednesday, the Tokyo Metropolitan Government ordered Snow Brand to shut down a holding tank at its processing plant in Hino, western Tokyo, after health inspectors found there were no cleaning records kept at the facility.

The metropolitan government took the measure after health officials conducted simultaneous inspections of Snow Brand factories around the country following the outbreak of food-poisoning.

Tokyo health officials said they have found nothing unhygienic in the Hino milk tank but ordered the company to stop using it because officials of the factory could not produce cleaning records.

Hino factory officials said the tank, which can hold up to 2 tons of milk, was added to the plant last summer as a backup facility.

Snow Brand officials claimed that workers at the Hino factory clean the milk tank manually every day.

Tokyo health officials have taken milk samples from the Hino plant and plan to conduct a chemical analysis to determine if it has been contaminated. There have been no reports of food poisoning from milk products made at the Hino plant.

The metropolitan government added that health inspectors have completed inspections at four of the eight Snow Brand production facilities in the Tokyo metropolitan area.

It has ordered municipalities to stop using products from Snow Brand’s Hino plant for school lunches. The products had been used at 174 schools in western Tokyo.

Some municipalities — including Yao, Ikeda and Toyonaka, all in Osaka Prefecture — have decided to stop using Snow Brand products at city-run schools, nurseries and hospitals.

By noon Thursday, the number of people sickened by the company’s low-fat and calcium-enriched milk in the past week had risen to 11,376 in Osaka, Wakayama, Nara, Hyogo, Kyoto, Hiroshima, Shiga and Okayama prefectures.

Investigative sources said workers at the Osaka plant that produced the tainted milk operated and cleaned the production machinery based strictly on their own initiative, and supervisors rarely checked their work.

Operations at the plant, in Osaka’s Miyakojima Ward, were suspended indefinitely by the city public health center.

Meanwhile, the regional office of Snow Brand in Nagoya has retrieved about 11,000 cartons of low-fat milk and a yogurt drink following the food poisoning outbreak. The milk products were shipped to seven prefectures in central Japan. The seven prefectures are Gifu, Mie, Fukui, Ishikawa, Toyama, Shizuoka and Aichi.

The company said that so far there have been no reports from consumers of illness or food poisoning in these prefectures, although it had received a number of complaints and questions about the safety of Snow Brand products.