A Siderophore-Encoding Plasmid Encodes High-Level Virulence in Escherichia coli

Coexistence of virulent and multidrug-resistant plasmids in an uropathogenic Escherichia coli

OBJECTIVES

The emergence of pathogens co-harbouring multiple mobile resistance and virulence elements is of great concern in clinical settings. Herein, we report an O101: H10-ST167 Escherichia coli Hu106 strain isolated from the urinary tract of a female in China.

METHODS

Antibiotic susceptibility testing was used to present the antimicrobial resistance spectrum. Whole-genome sequencing (WGS) and bioinformatic analysis were used to clarify the virulent and resistance mechanisms. Furthermore, the virulence of this strain was tested by the Greater wax moth larvae and siderophore production experiment.

RESULTS

The strain E. coli Hu106 was resistant to almost all antimicrobials tested, and only susceptible to aztreonam, amikacin, and tigecycline. WGS analysis revealed that the strain Hu106 co-harboured blaNDM-9 and mcr-1 on p2-Hu106, belonging to IncHI2/IncHI2A (256,000 bp). The co-existence of both resistance genes, blaNDM-9 and mcr-1, on the plasmid p2-Hu106 was mainly acquired by transposition recombination of mobile antibiotic elements mediated by IS26 and/or IS1 on IncHI2/IncHI2A type plasmid. In addition, the virulence clusters aerobactin (iutA-iucABCD) and salmochelin (iroBCDEN) were identified on an IncFIB/IncFIC(IncFII) type plasmid p1-Hu106, flanked by small mobile elements such as IS1A, ISkpn28, and IS3, respectively. After performing genomic comparison of p1-Hu106 with the WGS in NCBI, we identified that the virulent plasmid p1-Hu106-like could spread in different clones of E. coli and Klebsiella pneumoniae, revealing its underlying dissemination mechanism between Enterobacterales. Furthermore, the strain caused a decreased survival rate of larvae and produced high siderophore units (62.33%), similar to hypervirulent K. pneumoniae NTUH-K2044.

CONCLUSIONS

The strains co-carrying the multidrug-resistant plasmid p2-Hu106 and virulent plasmid p1-Hu106 should be closely monitored to prevent its further spreading.

Emergence of an ST1934:KL121 hypervirulent Klebsiella pneumoniae carrying a novel virulence-resistance hybrid plasmid with chromosomal integration of ICEKp1

To identify the phenotypic and genomic characteristics of K. pneumoniae KP43 from bloodstream infection. KP43 was resistant to ticarcillin and tetracycline and was hypervirulent in the Galleria mellonella larvae infection model, positive for string test, and possessed high-level macrophage killing resistance. The hypervirulence phenotype was associated with the chromosome integration of ICEKp1 carrying iroBCDN-iroP, rmpADC, and peg-344, and a novel plasmid pKP43_vir_amr harboring iutAiucABCD. pKP43_vir_amr was an IncFIBκ/FII virulence-resistance hybrid conjugative plasmid which also carried antibiotic resistance genes. The emergence of such a strain and the spread of the novel virulence-resistance plasmid might pose a potential threat to public health.

Characterization of an ST38 carbapenem-resistant and highly virulent Escherichia coli carrying conjugatively transferable ColV virulence-resistance and blaNDM-5-positive resistance plasmids

OBJECTIVES

To characterize an Escherichia coli strain causing bloodstream infection encoding both high-virulence and carbapenem-resistance phenotypes.

METHODS

Antimicrobial susceptibility testing, WGS and bioinformatics analysis were performed to characterize strain E1. The function of the ColV plasmid was investigated by the Galleria mellonella infection model, serum killing and macrophage killing assays. The fitness effect of the ColV plasmid was tested by growth curve, plasmid stability tests and the in vitro competition assay. The conjugation assay was performed to test the transferability of the ColV and blaNDM-5-carrying plasmids.

RESULTS

E. coli E1 from bloodstream infection was MDR and highly virulent in the G. mellonella infection model. It belonged to phylogroup D, ST38 and serotype O7:H8. E1 carried a conjugatively transferable IncI1-type blaNDM-5-positive plasmid, which conferred carbapenem resistance, a conjugative IncFIB/FII-type ColV plasmid encoding an array of virulence-associated genes and antibiotic resistance genes blaTEM-1B, strAB and sul2, and seven other plasmids. Co-transfer of the ColV plasmid and the blaNDM-5-positive plasmid was observed. The ColV virulence-resistance hybrid plasmid contributed to the virulence, resistance to serum killing, and macrophage phagocytosis in E. coli E1. The carriage of this ColV plasmid did not constitute an in vitro fitness burden to strain E1 but caused fitness costs to E. coli strain EC600.

CONCLUSIONS

The emergence of such a highly virulent and resistant strain with conjugative blaNDM-5-positive and ColV plasmids posed a significant threat to public health. Implementation of control measures is needed to prevent such strains from further disseminating in hospital settings and the community.

Acquisition of regulator on virulence plasmid of hypervirulent Klebsiella allows bacterial lifestyle switch in response to iron

Hypervirulent Klebsiella pneumoniae causes liver abscess and potentially devastating metastatic complications. The majority of Klebsiella-induced liver abscess are caused by the CG23-I sublineage of hypervirulent Klebsiella pneumoniae. This and some other lineages possess a >200-kb virulence plasmid. We discovered a novel protein IroP nestled in the virulence plasmid-encoded salmochelin operon that cross-regulates and suppresses the promoter activity of chromosomal type 3 fimbriae (T3F) gene transcription. IroP is itself repressed by iron through the ferric uptake regulator. Iron-rich conditions increase T3F and suppress capsule mucoviscosity, leading to biofilm formation and cell adhesion. Conversely, iron-poor conditions cause a transcriptional switch to hypermucoid capsule production and T3F repression. The likely acquisition of iroP on mobile genetic elements and successful adaptive integration into the genetic circuitry of a major lineage of hypervirulent K. pneumoniae reveal a powerful example of plasmid chromosomal cross talk that confers an evolutionary advantage. Our discovery also addresses the conundrum of how the hypermucoid capsule that impedes adhesion could be regulated to facilitate biofilm formation and colonization. The acquired ability of the bacteria to alternate between a state favoring dissemination and one that favors colonization in response to iron availability through transcriptional regulation offers novel insights into the evolutionary success of this pathogen. IMPORTANCE Hypervirulent Klebsiella pneumoniae contributes to the majority of monomicrobial-induced liver abscess infections that can lead to several other metastatic complications. The large virulence plasmid is highly stable in major lineages, suggesting that it provides survival benefits. We discovered a protein IroP encoded on the virulence plasmid that suppresses expression of the type 3 fimbriae. IroP itself is regulated by iron, and we showed that iron regulates hypermucoid capsule production while inversely regulating type 3 fimbriae expression through IroP. The acquisition and integration of this inverse transcriptional switch between fimbriae and capsule mucoviscosity shows an evolved sophisticated plasmid-chromosomal cross talk that changes the behavior of hypervirulent K. pneumoniae in response to a key nutrient that could contribute to the evolutionary success of this pathogen.