Diversity of mucoid to non-mucoid switch among carbapenemase-producing Klebsiella pneumoniae

Abstract

Background Klebsiella pneumoniae is a leading cause of intractable hospital-acquired multidrug-resistant infections and carbapenemase-producing K. pneumoniae (CPKp) are particularly feared. Most of the clinical isolates produce capsule as a major virulence factor. Recombination events at the capsule locus are frequent and responsible for capsule diversity within Klebsiella spp. Capsule diversity may also occur within clonal bacterial populations generating differences in colony aspect. However, little is known about this phenomenon of phenotypic variation in CPKp and its consequences. Results Here, we explored the genetic causes of in vitro switching from capsulated, mucoid to non-mucoid, non-capsulated phenotype in eight clinical CPKp isolates. We compared capsulated, mucoid colony variants with one of their non-capsulated, non-mucoid isogenic variant. The two colony variants were distinguished by their appearance on solid medium. Whole genome comparison was used to infer mutations causing phenotypic differences. The frequency of phenotypic switch was strain-dependent and increased along with colony development on plate. We observed, for 72 non-capsulated variants that the loss of the mucoid phenotype correlates with capsule deficiency and diverse genetic events, including transposition of insertion sequences or point mutations, affecting genes belonging to the capsule operon. Reduced or loss of capsular production was associated with various in vitro phenotypic changes, affecting susceptibility to carbapenem but not to colistin, in vitro biofilm formation and autoaggregation. Conclusions The different impact of the phenotypic variation among the eight isolates in terms of capsule content, biofilm production and carbapenem susceptibility suggested heterogeneous selective advantage for capsular loss according to the strain and the mutation. Based on our results, we believe that attention should be paid in the phenotypic characterization of CPKp clinical isolates, particularly of traits related to virulence and carbapenem resistance.

A European multicenter evaluation study to investigate the performance on commercially available selective agar plates for the detection of carbapenemase producing Enterobacteriaceae

“…This sample resulted in growth of mucoid and non-mucoid colonies of Klebsiella with different meropenem MICs. This phenomenon is well described by Chiarelli et al (2020). As this strain was detected in all seven laboratories on all except one agar plate (Table 5), it is therefore very unlikely that this has influenced the interpretation of the growth on these plates.…”

In-Human Multiyear Evolution of Carbapenem-Resistant Klebsiella pneumoniae Causing Chronic Colonization and Intermittent Urinary Tract Infections: A Case Study

“…These findings highlight the genetic and phenotypic flexibility of K. pneumoniae and its ability to adapt to the dynamic ecosystem within the human body to support prolonged colonization and recurring infections. Studies have shown how K. pneumoniae can evolve in vivo and in vitro within biofilms and exhibit increased antibiotic resistance, as well as the ability for CRKP strains to alter their capsule phenotypes over time, impacting biofilm production ( 51 – 53 ). Further study into which metabolic pathways and transcriptional changes influenced by carbapenems to significantly induce biofilm production and acquire resistance mutations could shed light on how repeated courses of carbapenem therapy potentially drive long-term persistence of CRKP in the bladder.…”

The Emergence of Novel Sequence Type Strains Reveals an Evolutionary Process of Intraspecies Clone Shifting in ICU-Spreading Carbapenem-Resistant Klebsiella pneumoniae

“…More than 77 capsular types (K-types) have been reported in clinical isolates of K. pneumoniae , and recombination events involving the capsule biosynthesis (cps) region are frequently observed within several dominant sequence type (ST) clones, such as CG258 (ST258, ST512, ST11, etc.) isolates ( Wyres et al, 2015 ; Chiarelli et al, 2020 ). In China, ST11 is believed to be the most dominant CRKP clone, with a prevalence greater than 60% ( Zhang et al, 2017 ; Wang et al, 2018 ).…”