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 is rarely reported and potentially results in a poor prognosis. This study describes the case of a hospitalised patient with gas gangrene and sepsis caused by hvKP. 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 (single nucleotide polymorphisms [SNPs]<10) and belonged to ST412/K57. The minimum inhibitory concentration and minimum bactericidal concentration under biofilm values of meropenem in KPLSN and KPLSX were significantly higher than in the planktonic state (>128 mg/L vs. 0.25 mg/L, P<0.0001). These two strains had high biofilm formation ability, and the results from fluorescence staining experiments showed that they were not easily killed by meropenem in the biofilm state. KPLSN and KPLSX showed high capsule production and were confirmed to have high virulence through experiments with the Galleria mellonella infection model and the BALB/c mice abdominal infection model. The persistent symptoms may be due to enhanced biofilm and capsule formation. Phylogenetic analysis of global ST412 strains showed their evolution towards higher virulence and resistance. These results emphasise the critical need for judicious antibiotic use and novel therapeutic approaches to combat special infections caused by these pathogens.