AUTHOR=Liu Zhou , Hang Xiubing , Xiao Xiao , Chu Wenwen , Li Xin , Liu Yangyang , Li Xi , Zhou Qiang , Li Jiabin 

TITLE=Co-occurrence of blaNDM–1 and mcr-9 in a Conjugative IncHI2/HI2A Plasmid From a Bloodstream Infection-Causing Carbapenem-Resistant Klebsiella pneumoniae

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.756201

DOI=10.3389/fmicb.2021.756201

ISSN=1664-302X

ABSTRACT=<p>Spread of the carbapenemase-encoding and mobilized colistin resistance (<italic>mcr</italic>) genes among Enterobacteriales poses a great threat to global public health, especially when the both genes are transferred by a single plasmid. Here, we identified a <italic>bla</italic><sub><italic>NDM–</italic>1</sub>- and <italic>mcr-9</italic>-co-encoding plasmid harbored by a clinical isolate of <italic>Klebsiella pneumoniae</italic> (KPN710429). KPN710429 was recovered from a blood sample from an inpatient in a tertiary hospital in China, and antimicrobial susceptibility testing showed that it was multidrug-resistant and only susceptible to aztreonam, colistin, and tigecycline. KPN710429 belongs to sequence type (ST) 1308 and capsular serotype KL144. The string test of KPN710429 was negative, and this strain didn’t exhibit a hypervirulent phenotype according to serum-killing and <italic>Galleria mellonella</italic> lethality assessments. Whole-genome sequencing revealed the KPN710429 genome comprises a single chromosome and three plasmids. All virulence associated genes were harbored by chromosome. Most of its antimicrobial resistance genes, including <italic>bla</italic><sub><italic>NDM–</italic>1</sub> and <italic>mcr-9</italic> were carried by plasmid pK701429_2, belonging to the incompatibility (Inc) HI2/HI2A group and ST1. Comparative genomics assays indicates that pK710429_2 could be a hybrid plasmid, formed by a Tn<italic>6696</italic>-like <italic>bla</italic><sub><italic>NDM–</italic>1</sub> region inserting into a <italic>mcr-9</italic>-positive-IncHI2/HI2A plasmid. pK710429_2 contained the conjugative transfer gene regions, Tra1 and Tra2, with some structural variations, and conjugation assays revealed that pK710429_2 was transferable. Although pK710429_2 lacked the <italic>qseB</italic>-<italic>qseC</italic> regulatory genes, <italic>mcr-9</italic> expression was upregulated after pretreatment with colistin for 6 h, leading to colistin resistance in KPN710429. To our knowledge, this is the first report of a <italic>bla</italic><sub><italic>NDM–</italic>1</sub>- and <italic>mcr-9</italic>-co-encoding transferable plasmid harbored by a bloodstream-infection-causing <italic>K. pneumoniae</italic> strain in China. Effective surveillance should be implemented to assess the prevalence of the plasmid co-harboring carbapenemase-encoding gene and <italic>mcr-9</italic>.</p>