'Last-resort' antibiotics failing as drug-resistant Salmonella found in Chinese infants

This image is not directly related to the article. [Getty Images Bank]

A strain of Salmonella resistant even to the antibiotics doctors call their "last resort" has infected six infants aged 8 to 12 months in southern China, a new study has found. The research team said the findings raise concern that the bacteria may already be circulating in the community, given that none of the babies had been hospitalized or received antibiotics before falling ill.

The findings were published in the 2026 issue of the Journal of Infection by a joint research team led by Dr. Xu Xuebin of the Shanghai Municipal Center for Disease Control and Prevention and Professor Wang Yanan of Henan Agricultural University.

The team isolated Salmonella from six infants admitted to a hospital in the Guangxi Zhuang Autonomous Region of China between 2024 and 2025 with acute diarrhea. Analysis confirmed that all six strains carried genes encoding carbapenem-degrading enzymes.

Last-resort antibiotics rendered ineffective

Salmonella is commonly known as a foodborne pathogen. In healthy adults, the infection typically resolves on its own within days or can be treated with standard antibiotics. In infants whose immune systems are not yet fully developed, however, the bacteria can spread into the bloodstream and cause sepsis, making antibiotic treatment essential.

Antibiotics are tiered by potency.

When first-line drugs fail, doctors escalate to stronger options — and when those also fail, the final option they reach for is the carbapenem class of antibiotics.

The chart shows antibiotic susceptibility results for the six isolated strains (vertical axis): red indicates resistance, blue indicates susceptibility. All six strains were resistant to ertapenem (ETP), a carbapenem-class last-resort antibiotic, but responses to meropenem (MEM) and others varied — raising the risk that standard single-drug testing could miss resistant strains. [Journal of Infection, 2026]

The strains identified in this study carried genes that render even those last-resort antibiotics ineffective. The WHO classifies carbapenem-resistant bacteria among the most dangerous pathogens in clinical settings.

When the research team tested the six strains against a range of antibiotics, all showed resistance to commonly used drugs including penicillin and cephalosporins. Resistance or intermediate resistance to carbapenem-class antibiotics was also confirmed.

Infants infected outside the hospital

The transmission pattern was also unusual. None of the six infants had been previously hospitalized, and none had a history of antibiotic use. They had not traveled to areas known for the emergence of highly resistant bacteria, and no epidemiological link was found among the six cases.

Highly drug-resistant bacteria typically emerge in patients who have been hospitalized for extended periods or are undergoing immunosuppressive treatment.

That infants with none of these risk factors became infected in ordinary daily life suggests the bacteria may already be present in environments outside hospitals.

Genomic analysis further underscores the severity of the situation. The four strains identified in 2024 were nearly genetically identical, suggesting they spread from a single source. The two strains from 2025, however, were distinct — indicating the bacteria are continuing to spread.

The research team also found that the resistance gene structure of the 2024 strains matched those of E. coli isolated in other parts of China by more than 99.9 percent, suggesting the resistance genes likely transferred from E. coli to Salmonella.

Because resistance genes can be passed between bacteria as transferable genetic material — not only through the bacteria themselves — they become extremely difficult to control once they enter the environment.

Inconsistent drug responses make detection difficult

The research team also issued a separate warning in the paper: current hospital testing methods may fail to identify these strains as resistant.

Standard hospital practice involves testing one or two carbapenem drugs to check for resistance. But four of the six strains in this study showed strong resistance to ertapenem while appearing fully susceptible to meropenem and imipenem.

Had clinicians tested only the more commonly used drugs, they could have misdiagnosed four of the strains as ordinary Salmonella. Prescribing the wrong antibiotic and missing the window for proper treatment could prove fatal for infants.

"The limitations of testing methods that rely on a single drug have been exposed," the research team said, calling for more comprehensive testing strategies.

The research team concluded that the bacteria are actively spreading. Salmonella transmits through contaminated food or water and contact with animals, and the pace of spread could accelerate further given that resistance genes can transfer to other bacterial species.

Reference

DOI: 10.1016/j.jinf.2026.106786

Why Europeans won't eat silkworm soup — the answer lies in genes from 9,000 years ago [Huam-dong Research Lab]

"You can just toss it all in one bag and it still gets recycled" — a tenfold difference in lead levels rebuffed that assumption [Huam-dong Research Lab]

A clock that measures your body's 'real age' — not the one on your ID [Huam-dong Research Lab]