High Prevalence and Fitness of IncFrepB Carrying qnrS1 in Hypervirulent Klebsiella pneumoniae Isolates.

This study aimed to reveal the prevalence and fitness of -carrying plasmids in hypervirulent (hvKP) isolates. Two hundred ninety-nine hvKP strains carrying qnrS1 were collected and screened for resistance genes using PCR and sequencing. The location of and was identified by Southern blotting. The transferability and fitness of -carrying plasmids were analyzed by conjugation experiments and plasmid stability assay. In 299 hvKP isolates, the most frequently detected capsular serotype was K64 (81.9%, 245/299), followed by K1 (4.7%, 14/299) and K2 (3.7%, 11/299). All K64-hvKP were sequence type (ST) 11. The and gene mainly was located on the ∼70-210 kb IncFrepB and ∼170-220 kb IncFIB plasmid, respectively. QnrS1-carrying plasmids could be transferred into J53. However, the plasmid was transferred at a low rate of 13.4% (40/299). The 40 donor isolates belong to 4 STs-ST11, ST700, ST592, and ST86, and none contains the CRISPR-Cas loci. CRISPR-Cas loci were mainly found in ST23 . The relative fitness (RF) of -carrying plasmids in ST86 and ST11 (cotransfer with genes) was more than one and enhanced during cultivation, especially in ST86. However, the RF of -carrying plasmids in ST592 and ST700 showed a high fitness cost. Whole-genome sequencing showed that the -carrying plasmids in ST86 harbored more maintenance modules (SOS inhibitor protein , , and partition systems) and insertion sequence (IS) elements (IS91, IS481-like, IS1380), indicating that the -carrying plasmid in ST86 is more stable than the other types of -carrying plasmids. -carrying IncFrepB plasmids were highly prevalent and show polymorphism in hvKP strains. The -carrying IncFrepB plasmid in ST86 hvKP should be highlighted due to its remarkable adaptability advantages.