Photo/Illutration Carbapenem-resistant Enterobacteriaceae (CRE) (Provided by the U.S. Centers for Disease Control and Prevention)

Health experts are alarmed by the sharp rise in Japan of cases involving colon bacilli and other bacteria originating overseas that have a strong resistance to most antibacterial drugs.

The National Institute of Infectious Diseases (NIID) said such drug-resistant bacteria were discovered in 13 cases in 2017, the year when the institute launched a study.

The figure surged to 42 in 2018.

Prior to 2018, the presence of "superbugs" was confirmed in Tokyo and five prefectures. The drug-resistant bacteria were discovered in Tokyo, Hokkaido and 14 prefectures over the past year.

“It is not known how such bacteria found their way into patients, but it seems that we are seeing a new phase of the proliferation of drug-resistant bacteria,” said Motoyuki Sugai, director of NIID’s Antimicrobial Resistance Research Center.

The bacteria in question belong to the strain Enterobacteriaceae that is resistant to carbapenem antibiotics, last-line agents used to treat seriously ill patients with infections.

It is a type of bacteria that has a resistance gene originating from overseas that creates an enzyme that destroys pharmaceutical ingredients.

Most of the anti-bacterial drugs available in Japan are not effective in treating patients harboring this type of bacteria, according to researchers.

Of the total of 55 cases discovered so far, 41 involved patients who have never visited other countries or it is unclear whether they have been abroad.

Researchers with the NIID say it is also possible that patients were infected with bacteria resistant to carbapenem antibiotics via healthy people harboring them.

The strains belonging to Enterobacteriaceae, such as colon bacilli and pneumobacilli, are expected to cause little harm to healthy people under normal conditions as long as they remain in the stomach.

But people are likely to develop a serious infection when their immune systems are weakened.

Carbapenem antibiotics have been used to treat gravely ill patients with infections. However, the proliferation of bacteria resistant to carbapenem antibiotics has emerged as a global challenge.

According to a report on risk assessment released in 2018 by the European Center for Disease Prevention and Control, the rate of fatality among patients with serious infection caused by carbapenem-resistant Enterobacteriaceae (CRE) ranged from 30 percent to 75 percent.

More than half of patients are likely to die when they have bacteremia, an infection referring to the presence of bacteria in the blood.

The U.S. Centers for Disease Control and Prevention recognizes CRE as the most life-threatening drug-resistant bacteria, calling it the “nightmare bacteria.”

Of the CRE, a type creating an enzyme that destroys pharmaceutical ingredients is particularly worrisome, according to experts.

In March 2017, the Japanese Ministry of Health, Labor and Welfare introduced a checkup system to determine the presence of a resistance gene and its type when patients are infected with CRE.

The study of the 2017 and 2018 cases by the NIID showed that there is a risk of becoming infected with a type of bacteria deriving from overseas even if people remained in Japan.

But little progress has been made in the world in the development of new antibacterial drugs.

The World Health Organization said drugs to fight CRE and two other bacteria should be given the highest priority in the development of antibacterial agents.