The capsule of Klebsiella pneumoniae is more than a protective coat. It is a major virulence factor, a useful epidemiological marker, and an important clue for selecting future vaccines, antimicrobial strategies, and phage therapies. However, capsule typing can be difficult to perform rapidly. Serological methods depend on costly antisera and can suffer from cross-reactivity, while PCR or sequencing methods cannot distinguish between live and dead bacteria.
A new study describes a modular reporter phage platform that turns capsule recognition into a measurable light signal. The researchers first engineered the K2-targeting bacteriophage RCIP0109 by inserting the NanoLuc luciferase reporter gene, creating ΦRCIP0109:: nluc . When the reporter phage infects its matching K. pneumoniae hosts, it produces bioluminescence that can be measured in a standard microplate reader.
The key innovation is modularity. Because receptor-binding proteins (RBPs) help determine which capsule a Klebsiella phage recognizes, the team used RBP swapping to redirect the host range of the reporter phage chassis. This strategy generated reporter phages targeting K1, K47, K57, and K64 strains, adding to the K2-specific chassis and covering several clinically important capsular types associated with hypervirulence or carbapenem resistance.
“By swapping receptor-binding proteins, we can turn the natural specificity of phages into an adaptable diagnostic signal,” said Jie Feng, corresponding author of the study. “This work suggests a path toward rapid, scalable capsule typing that could be expanded as more phage-host recognition modules become available.”
The platform showed strong performance in multiple testing settings. For K2 detection, high bacterial concentrations were detected within 0.5 hours, and the limit of detection reached 10 CFU/mL after 2.5 hours. The RBP-swapped reporter phages selectively identified their corresponding capsular types with no detectable cross-reactivity. In synthetic urine, reporter phages detected K1, K2, K47, K57, and K64 K. pneumoniae strains at clinically relevant bacterial loads, with signals appearing within 0.5 hours at ≥10 5 CFU/mL while consistent luminescence kinetics were also observed at 10 3 -10 4 CFU/mL. In polymicrobial urine-like samples containing other common uropathogens, the reporter phage panel still identified target strains within about 3 hours.
The researchers also demonstrated that directed evolution can tune reporter phage performance. An evolved K2 reporter phage produced 10- to 100-fold higher luminescence than its ancestral strain and shortened detection times at several bacterial concentrations. A separately evolved K57 reporter phage showed improved adsorption, higher titer, and a broader linear detection range, supporting the idea that phage evolution can be used to improve assay sensitivity.
Together, the findings present a scalable route for rapid K. pneumoniae capsular typing in near-clinical matrices. Because the assay can be read on standard microplate instruments and may also support visual inspection, it offers practical flexibility for future point-of-care development. Future integration with machine-learning prediction of phage-host interactions, AI-assisted protein design, and targeted mutagenesis could extend the approach to additional capsular types and other priority pathogens. This work was conducted by researchers at Shandong First Medical University and Shandong Academy of Medical Sciences; the Institute of Microbiology, Chinese Academy of Sciences; the University of Chinese Academy of Sciences; Yunnan University; and Peking University Third Hospital. Support was provided by the National Key Research and Development Program of China under Grant/Award 2024YFA0919400.
D OI Link:
https://doi.org/10.1016/j.hlife.2026.06.001
About Author
Jie Feng is affiliated with the State Key Laboratory of Microbial Diversity and Innovative Utilization, Institute of Microbiology, Chinese Academy of Sciences. Her research focuses on the mechanisms of antimicrobial resistance in pathogenic bacteria and strategies for their prevention and control, with particular emphasis on bacteriophage-bacterium interactions, phage resource and functional element libraries, engineered phages, and the development of phage-based therapeutic technologies. She has published more than 50 papers in journals including Genome Medicine , Advanced Science , and Gut Microbes . The work represented here centers on bacteriophage host specificity, receptor-binding protein engineering, and rapid microbial detection.
hLife
A phage-based luminescent reporter platform for rapid typing of multiple capsular types of Klebsiella pneumoniae
26-Jun-2026