Hypervirulent Carbapenem-Susceptible Klebsiella pneumoniae ST412/K57 with Strong Biofilm Formation: association with gas gangrene and sepsis.

Hypervirulent Klebsiella pneumoniae (hvKp) poses a serious public health threat. Gas gangrene caused by hvKp was rarely reported, potentially resulting in a poor prognosis. In this study, we described the case of a hospitalized patient with gas gangrene and sepsis by hvKP. The carbapenem-susceptible hypervirulent Klebsiella pneumoniae (CS-hvKp) strains KPLSN and KPLSX were isolated from the knee joint pus and blood specimens of the patient for further investigations. Whole genome sequencing revealed that KPLSN and KPLSX were highly homologous (SNPs<10) and belonging to ST412/K57. The minimum inhibitory concentration and minimum bactericidal concentration under biofilm values of meropenem in KPLSN and KPLSX were significantly higher than planktonic state (>128 mg/L versus 0.25 mg/L, P<0.0001). These two strains had high biofilm formation ability, and fluorescence staining experiments results showed that they were not easily killed by meropenem in the biofilm state. KPLSN and KPLSX showed high capsular production and were confirmed with high virulence through experiments with the Galleria mellonella and BALB/c mice abdominal infection model. The persistent symptoms may be due to enhanced biofilm and capsule formation. Global ST412 strains phylogenetic analysis showed their evolution towards higher virulence and resistance. It emphasizes the critical need for judicious antibiotic use and novel therapeutic approaches to combat special infections caused by these pathogens.