Microbiological and Clinical Characteristics ofKlebsiella pneumoniaeIsolates of K57 Capsular Serotype in China

Background:K57Klebsiella pneumoniae(K57-KP) is associated with hypervirulence, but the basis and systematic data of K57-KP are limited. Materials and Methods:A retrospective study was conducted in 156 patients between January 2013 and January 2016. The clinical and molecular data, including antimicrobial susceptibility testing, multilocus sequence typing, antimicrobial resistance genes, and virulence determinants were assessed. Results:Among the 39 K57-KP isolates, 14 isolates (35.9%) were associated with various types of invasive infections. Diabetes, drainage, use of carbapenems and quinolone antibiotics were dependent risk factors for K57-KP infections. Sequence type (ST)412 was the most prevalent among K57-KP isolates. K57-KP isolates were more resistant to clinically often used antimicrobial agents than hvKP (K1/K2) strains, and 12.8% (5/39) of the strains were resistant to carbapenems, which all harboredbla(KPC-2). The prevalence of hypermucoviscosity phenotype,aerobactin,rmpA,rmpA2, andybtsrevealed 66.7%, 100%, 89.7%, 89.7%, and 30.8%, whereaswcaG,allS,magAandkfurevealed 0%, 0%, 0%, and 5.1%, which were significantly lower than that of hvKP (K1/K2). The serum sensitivity, neutrophil phagocytic rate, and biofilm formation capacity of K57-KP strains were higher than that of K1/K2. Conclusion:There were no significant differences in the prevalence of hypermucoviscosity phenotype, carriage ofrmpAand aerobactin genes between K57 and K1/K2 isolates, but the composition and production of capsule polysaccharide of K57-KP may be different from that of K1/K2 strains. K57-KP isolates exhibited distinctive virulence-associated traits, most of which belonged to ST412. Physicians should enhance the management of K57-KP infections because of the emergence of more and more carbapenem-resistant K57-KP isolates.