Temperatures above 37°C increase virulence of a convergentKlebsiella pneumoniaesequence type 307 strain
Authors: Müller Justus U. , Schwabe Michael , Swiatek Lena-Sophie , Heiden Stefan E. , Schlüter Rabea , Sittner Max , Bohnert Jürgen A. , Becker Karsten , Idelevich Evgeny A. , Guenther Sebastian , Eger Elias , Schaufler Katharina 
Published: February 2024

Hypermucoviscosity inKlebsiella pneumoniaeis often related to the overexpression of capsular polysaccharides, regulated by complex biosynthetic mechanisms in response to external cues. However, little is known about the processes involved in hypermucoviscosity in convergentK. pneumoniae, which combine extensive drug resistance with high bacterial virulence, under pathophysiological conditions. This study aimed to fill this gap by investigating the temperature dependence of hypermucoviscosity and overall virulence in a convergentK. pneumoniaestrain isolated during a clonal outbreak belonging to the high-risk sequence type (ST)307.

Hypermucoviscosity, biofilm formation, and mortality rates inGalleria mellonellalarvae were examined at different temperatures (room temperature, 28°C, 37°C, 40°C and 42°C) and with various phenotypic experiments including electron microscopy. The underlying mechanisms of the phenotypic changes were explored via qPCR analysis to evaluate plasmid copy numbers, and transcriptomics.

Our results indicate a temperature-dependent “switch” above 37°C to a hypermucoviscous phenotype, correlating with increased biofilm formation capacity andin vivomortality, which might be due to a bacterial response to pathophysiological conditions, i.e., fever. In addition, we detected upregulation of a hybrid plasmid encoding both carbapenemase and the mucoid regulatorrmpAgenes. Surprisingly,rmpAdid not exhibit temperature-dependent differential gene expression, suggesting other drivers. Apparent co-regulation of hypermucoviscosity and fimbrial expression was also identified.

This study not only revealed the impact that increased temperatures above 37°C have on hypermucoviscosity and virulence in a convergentK. pneumoniaestrain but contributes to the understanding of previously unrecognized dimension ofK. pneumoniaésbehavior, emphasizing its adaptability to changing environments.

Abstract importance

Understanding the temperature-dependent dynamics of hypermucoviscosity inKlebsiella pneumoniaeis crucial for unraveling the intricacies of its hypervirulence. This study investigates a convergentK. pneumoniaestrain, ST307, revealing a temperature-dependent switch to hypermucoviscosity above 37 °C. The findings showcase a correlation between increased temperature, hypermucoviscosity, enhanced attachment, and heightenedin vivomortality. Notably, a hybrid plasmid encoding carbapenemase and mucoid regulator genes was upregulated at elevated temperatures. The study sheds light on previously unexplored aspects ofK. pneumoniaebehavior, emphasizing its adaptability in response to changing environments. The identified temperature-associated regulatory mechanisms offer insights into the pathogen’s response to fever, contributing to our broader understanding of bacterial adaptation. This research contributes to addressing the global challenge of hypervirulent, drug-resistantK. pneumoniaestrains, providing valuable implications for future treatment strategies.