AUTHOR=Liu Yanling , Lin Yiqing , Wang Ziwen , Hu Niya , Liu Qiong , Zhou Wenkai , Li Xiuzhen , Hu Longhua , Guo Jian , Huang Xiaotian , Zeng Lingbing 

TITLE=Molecular Mechanisms of Colistin Resistance in Klebsiella pneumoniae in a Tertiary Care Teaching Hospital

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=11

YEAR=2021

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2021.673503

DOI=10.3389/fcimb.2021.673503

ISSN=2235-2988

ABSTRACT=<sec><title>Background</title><p>Over the last two decades, the prevalence of colistin resistance among the members of <italic>Enterobacteriaceae</italic> has been increasing, particularly among <italic>Klebsiella pneumoniae</italic> isolates; this limits the potential use of colistin and leads to worsened clinical outcomes.</p></sec><sec><title>Methods</title><p>We investigated the prevalence and genetic characteristics of colistin-resistant <italic>K. pneumoniae</italic> (COLR-KP) in clinical isolates using genomic sequencing.</p></sec><sec><title>Results</title><p>In total, 53 K<italic>. pneumoniae</italic> isolates (4.5%, 53/1,171) were confirmed as COLR-KP, of which eight isolates carried mobile colistin-resistant (<italic>mcr</italic>) gene. Although the overall prevalence rate (0.7%, 8/1,171) of <italic>mcr</italic>-like genes in clinical <italic>K. pneumoniae</italic> remained relatively low, the presence of <italic>mcr</italic> (15.1%, 8/53) among the COLR-KP isolates indicated that the mobile resistance gene was already widespread among <italic>K. pneumoniae</italic> isolates in hospital setting. We randomly selected 13 COLR-KP isolates (four <italic>mcr</italic>-bearing and nine non-<italic>mcr</italic>-bearing isolates) for whole-genome sequencing, including two pandrug-resistant and four sequence type 11 (ST11) isolates. Phylogenetic analysis revealed that all COLR-KP isolates were genetically diverse. Among the four <italic>mcr</italic>-bearing isolates, three (KP4, KP18, and KP30) were positive for <italic>mcr-1</italic> and one (KP23) for <italic>mcr-8</italic>; none of the other <italic>mcr</italic> genes were detected. The <italic>mcr-1</italic> in the KP4 and KP30 isolates were located in an <italic>IncX4</italic> plasmid (approximately 33 kb) and could be successfully transferred to <italic>Escherichia coli</italic> J53AZ<sup>R</sup>. In contrast, for the <italic>mcr-8</italic>-bearing plasmid in KP23 (<italic>IncFII</italic>), colistin resistance could not be transferred by conjugation. The mcr-1-producing isolate KP18 coexists a novel plasmid-carried tigecycline resistance gene tmexCD1-toprJ1. The most common chromosomal mutation associated with colistin resistance was a T246A amino acid substitution in PmrB, which was identified in most COLR-KP isolates (11/13, 84.6%). All ST11 isolates additionally had an R256G amino acid substitution. Critical virulence factors associated with hypervirulent <italic>K. pneumoniae</italic> were detected in four COLR-KP isolates; these virulence factors included aerobactin, salmochelin, and yersiniabactin.</p></sec><sec><title>Conclusion</title><p>We found that <italic>mcr</italic>-bearing COLR-KP emerged in our hospital and was growing at an increasing rate. Simultaneous emergence of hypervirulence and colistin–tigecycline–carbapenem resistance in the epidemic clone ST11 <italic>K. pneumoniae</italic> was also observed; this highlights the significance of active and continuous surveillance.</p></sec>