AUTHOR=Lin Zhi-wei , Zheng Jin-xin , Bai Bing , Xu Guang-jian , Lin Fo-jun , Chen Zhong , Sun Xiang , Qu Di , Yu Zhi-jian , Deng Qi-wen 

TITLE=Characteristics of Hypervirulent Klebsiella pneumoniae: Does Low Expression of rmpA Contribute to the Absence of Hypervirulence?

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.00436

DOI=10.3389/fmicb.2020.00436

ISSN=1664-302X

ABSTRACT=<p>Multidrug-resistant hypervirulent <italic>Klebsiella pneumoniae</italic> (MDR-hvKP) has been increasingly reported and is now recognized as a significant threat to public health; however, characterization of MDR-hvKP has not been systematically investigated. In the present study, 124 of 428 (28.92%) <italic>K. pneumoniae</italic> clinical isolates collected from January 2010 to December 2016 were identified with aerobactin and defined as hvKP; these included 94 non-MDR-KP, 20 extended-spectrum β-lactamase-producing <italic>K. pneumoniae</italic> (ESBL-KP), and 10 carbapenem-resistant <italic>K. pneumoniae</italic> (CR-KP) isolates. The remaining 304 isolates without presence of virulence factor aerobactin were defined as classic <italic>K. pneumoniae</italic> (cKP). The antimicrobial resistance rate of cKP was significantly higher than that of the hvKP isolates in the non-MDR-KP group, but showed no significant differences in the ESBL-KP and CR-KP groups. The detection frequencies of capsular serotype K1 (<italic>magA</italic>), hypermucoviscosity, sequence type 23 (ST23), and the virulence gene <italic>rmpA</italic> were significantly higher in the hvKP than cKP isolates in all three groups (<italic>P</italic> &lt; 0.05). Most of the hypervirulent ESBL-KP and CR-KP isolates were K non-typeable (16/30) and harbored at least one gene for virulence (26/30). The hypervirulent ESBL-KP isolates primarily carried <italic>bla</italic><sub><italic>CTX–M</italic></sub> (12/20, 60%) genes, and the hypervirulent CR-KP isolates mainly carried <italic>bla</italic><sub><italic>NDM–</italic></sub><sub>1</sub> (8/10, 80%) genes. Moreover, three hypervirulent ESBL-KP and two hypervirulent CR-KP isolates showed resistance to tigecycline but were sensitive to colistin. The transcriptional levels of <italic>rmpA</italic> in cKP were much lower than that in hvKP isolates in all three groups. Furthermore, overexpression of <italic>rmpA</italic> in the <italic>rmpA</italic>-low-expression cKP isolates could enhance bacterial virulence in the mouse infection experiment. In conclusion, our data suggest that the capsular serotype K1 (<italic>magA</italic>), <italic>rmpA</italic>, hypermucoviscosity, and ST23 were strongly associated with hvKP in non-MDR-KP, ESBL-KP, and CR-KP groups, and low <italic>rmpA</italic> expression levels contributed to the absence of hypervirulent phenotype.</p>