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Ou Hongyu's Group Discovers Mobilization Modes of Virulence Plasmids from Klebsiella Pneumoniae

August 02, 2021      Author:

Recently, Genome Medicine, a leading journal in biology, published a paper by the State Key Laboratory of Microbial Metabolism (Ministry of Science and Technology), School of Life Sciences and Biotechnology of Shanghai Jiao Tong University and Ruijin Hospital affiliated to Shanghai Jiao Tong University School of Medicine. The paper reports the non-autonomous mobilization of the nonconjugative virulence plasmids from Klebsiella pneumoniae with the assistance of conjugative plasmids. PhD student Xu Yanping from Ruijin Hospital and PhD student Zhang Jianfeng from SJTU School of Life Sciences and Biotechnology are the co-first authors of the paper, while Professor Qu Jieming from the Department of Respiratory and Critical Care Medicine of Ruijin Hospital, Professor Ou Hongyu from SJTU School of Life Sciences and Biotechnology and Deputy Chief Technologist Sun Jingyong from the Department of Clinical Microbiology, Ruijin Hospital, are the co-corresponding authors.

Klebsiella pneumoniae, a conditionally pathogenic bacterium of the Enterobacteriaceae family, is one of the most common clinically isolated Gram-negative drug-resistant bacteria in China.

In an effort to elucidate the mobilization mechanism of nonconjugative virulence plasmid from Klebsiella pneumoniae, several teams from the School of Life Sciences and Biotechnology and Ruijin Hospital have conducted in-depth collaborative studies. It was shown that transfer interactions exist between the conjugative plasmid and virulence plasmid of Klebsiella pneumoniae, which may greatly contribute to the co-dissemination of two important traits, drug-resistance and virulence, in the pathogenic bacteria.

The research group of Ou Hongyu of the School of Life Sciences and Biotechnology has long been involved in the study of bacterial drug-resistant mobile elements. The above collaborative paper is another important development following a series of research results.

 

Source: School of Life Sciences and Biotechnology

Translated by Chen Chen

  

ABSTRACT:

Background

Klebsiella pneumoniae, as a global priority pathogen, is well known for its capability of acquiring mobile genetic elements that carry resistance and/or virulence genes. Its virulence plasmid, previously deemed nonconjugative and restricted within hypervirulent K. pneumoniae (hvKP), has disseminated into classic K. pneumoniae (cKP), particularly carbapenem-resistant K. pneumoniae (CRKP), which poses alarming challenges to public health. However, the mechanism underlying its transfer from hvKP to CRKP is unclear.

Methods

A total of 28 sequence type (ST) 11 bloodstream infection-causing CRKP strains were collected from Ruijin Hospital in Shanghai, China, and used as recipients in conjugation assays. Transconjugants obtained from conjugation assays were confirmed by XbaI and S1 nuclease pulsed-field gel electrophoresis, PCR detection and/or whole-genome sequencing. The plasmid stability of the transconjugants was evaluated by serial culture. Genetically modified strains and constructed mimic virulence plasmids were employed to investigate the mechanisms underlying mobilization. The level of extracellular polysaccharides was measured by mucoviscosity assays and uronic acid quantification. An in silico analysis of 2608 plasmids derived from 814 completely sequenced K. pneumoniae strains available in GenBank was performed to investigate the distribution of putative helper plasmids and mobilizable virulence plasmids.

Results

A nonconjugative virulence plasmid was mobilized by the conjugative plasmid belonging to incompatibility group F (IncF) from the hvKP strain into ST11 CRKP strains under low extracellular polysaccharide-producing conditions or by employing intermediate E. coli strains. The virulence plasmid was mobilized via four modes: transfer alone, cotransfer with the conjugative IncF plasmid, hybrid plasmid formation due to two rounds of single-strand exchanges at specific 28-bp fusion sites or homologous recombination. According to the in silico analysis, 31.8% (242) of the putative helper plasmids and 98.8% (84/85) of the virulence plasmids carry the 28-bp fusion site. All virulence plasmids carry the origin of the transfer site.

Conclusions

The nonconjugative virulence plasmid in ST11 CRKP strains is putatively mobilized from hvKP or E. coli intermediates with the help of conjugative IncF plasmids. Our findings emphasize the importance of raising public awareness of the rapid dissemination of virulence plasmids and the consistent emergence of hypervirulent carbapenem-resistant K. pneumoniae (hv-CRKP) strains.