ORF-based binarized structure network analysis of plasmids (OSNAp), a novel approach to core gene-independent plasmid phylogeny

Novel insights into genetic characteristics of blaGES-encoding plasmids from hospital sewage

Introduction

The prevalence of Guiana extended-spectrum (GES)-type carbapenemase producers is increasing worldwide, and hospital water environments are considered as potential reservoirs. However, the genetic features underlying this resistance are not yet fully understood. This study aimed to characterize blaGES-encoding plasmids from a single-hospital sewage sample in Japan.

Methods

Carbapenemase producers were screened using carbapenemase-selective agar and polymerase chain reaction. Whole-genome sequencing analyzes were performed on the carbapenemase-producing isolates.

Results

Eleven gram-negative bacteria (four Enterobacter spp., three Klebsiella spp., three Aeromonas spp., and one Serratia spp.) with blaGES-24 (n = 6), blaGES-6 (n = 4), and blaGES-5 (n = 1) were isolated from the sewage sample. Five blaGES-24 and a blaGES-5 were localized in IncP-6 plasmids, whereas three blaGES-6 plasmids were localized in IncC plasmids with IncF-like regions. The remaining blaGES-6 and blaGES-24 were, respectively, localized on IncFIB-containing plasmids with IncF-like regions and a plasmid with an IncW-like replication protein. The IncP-6 and IncW-like plasmids had a close genetic relationship with plasmids from Japan, whereas the IncC/IncF-like and IncFIB/IncF-like plasmids were closely related to those from the United States and Europe. All blaGES genes were located on the class 1 integron cassette of the Tn3 transposon-related region, and the IncC/IncF-like plasmid carried two copies of the integron cassette. Eight of the eleven blaGES-encoding plasmids contained toxin-antitoxin system genes.

Discussion

The findings on the plasmids and the novel genetic content from a single wastewater sample extend our understanding regarding the diversity of resistance and the associated spread of blaGES, suggesting their high adaptability to hospital effluents. These findings highlight the need for the continuous monitoring of environmental GES-type carbapenemase producers to control their dissemination.

Genetic basis of I-complex plasmid stability and conjugation

Plasmids are major drivers of increasing antibiotic resistance, necessitating an urgent need to understand their biology. Here we describe a detailed dissection of the molecular components controlling the genetics of I-complex plasmids, a group of antibiotic resistance plasmids found frequently in pathogenic Escherichia coli and other Enterobacteriaceae that cause significant human disease. We show these plasmids cluster into four distinct subgroups, with the prototype IncI1 plasmid R64 subgroup displaying low nucleotide sequence conservation to other I-complex plasmids. Using pMS7163B, an I-complex plasmid distantly related to R64, we performed a high-resolution transposon-based genetic screen and defined genes involved in replication, stability, and conjugative transfer. We identified the replicon and a partitioning system as essential for replication/stability. Genes required for conjugation included the type IV secretion system, relaxosome, and several uncharacterised genes located in the pMS7163B leading transfer region that exhibited an upstream strand-specific transposon insertion bias. The overexpression of these genes severely impacted host cell growth or reduced fitness during mixed competitive growth, demonstrating that their expression must be controlled to avoid deleterious impacts. These genes were present in >80% of all I-complex plasmids and broadly conserved across multiple plasmid incompatibility groups, implicating an important role in plasmid dissemination.

Assessment of plasmids for relating the 2020 Salmonella enterica serovar Newport onion outbreak to farms implicated by the outbreak investigation

BACKGROUND

The Salmonella enterica serovar Newport red onion outbreak of 2020 was the largest foodborne outbreak of Salmonella in over a decade. The epidemiological investigation suggested two farms as the likely source of contamination. However, single nucleotide polymorphism (SNP) analysis of the whole genome sequencing data showed that none of the Salmonella isolates collected from the farm regions were linked to the clinical isolates-preventing the use of phylogenetics in source identification. Here, we explored an alternative method for analyzing the whole genome sequencing data driven by the hypothesis that if the outbreak strain had come from the farm regions, then the clinical isolates would disproportionately contain plasmids found in isolates from the farm regions due to horizontal transfer.

RESULTS

SNP analysis confirmed that the clinical isolates formed a single, nearly-clonal clade with evidence for ancestry in California going back a decade. The clinical clade had a large core genome (4,399 genes) and a large and sparsely distributed accessory genome (2,577 genes, at least 64% on plasmids). At least 20 plasmid types occurred in the clinical clade, more than were found in the literature for Salmonella Newport. A small number of plasmids, 14 from 13 clinical isolates and 17 from 8 farm isolates, were found to be highly similar (> 95% identical)-indicating they might be related by horizontal transfer. Phylogenetic analysis was unable to determine the geographic origin, isolation source, or time of transfer of the plasmids, likely due to their promiscuous and transient nature. However, our resampling analysis suggested that observing a similar number and combination of highly similar plasmids in random samples of environmental Salmonella enterica within the NCBI Pathogen Detection database was unlikely, supporting a connection between the outbreak strain and the farms implicated by the epidemiological investigation.

CONCLUSION

Horizontally transferred plasmids provided evidence for a connection between clinical isolates and the farms implicated as the source of the outbreak. Our case study suggests that such analyses might add a new dimension to source tracking investigations, but highlights the need for detailed and accurate metadata, more extensive environmental sampling, and a better understanding of plasmid molecular evolution.

Bird's-eye MApping of plasmids (BeMAp) for visualization and comparison of genomic structures of different plasmids by mapping antimicrobial resistance genes on spreadsheets

Effective classification and visualization of multiple antimicrobial resistance plasmids can be challenging, and few tools to analyze similarities among plasmids depending on the location of genes are available. We created a new plasmid mapping program called Bird's-eye MApping of plasmids (BeMAp) to map antimicrobial resistance genes across multiple plasmids onto a spreadsheet and visualize their similarities based on gene types, locations, alignments, and organization. We analyzed plasmids containing various antimicrobial resistance genes, together with genes coding for IMP-type metallo-β-lactamases. Moreover, the mapping of plasmids with antimicrobial resistance genes and Incompatibility (Inc) groups showed that clustered plasmids with a similar organization of antimicrobial resistance genes were not always classified into the same Inc groups, indicating that the program displays multiple plasmids regardless of the Inc group classification. Our results showed that this calculation protocol and mapping strategy could provide a valuable tool for the practical and convenient visualization and comparison of the genomic structure of multiple plasmids in parallel.

Rapid phylogenetic analysis using open reading frame content patterns acquired by Oxford Nanopore sequencing

AIMS

Phylogenetic analysis based on core genome single nucleotide polymorphisms (cgSNPs) using whole-genome sequencing (WGS) is increasingly used in epidemiological investigations of bacteria. The approach, however, is both resource intensive and time-consuming. Oxford Nanopore Technologies (ONT) sequencing is capable of real-time data analysis but the high error rate hampers its application in cgSNP-based phylogenetic analysis. Here, we developed a cgSNP-independent phylogenetic analysis method using ONT read assemblies by focusing on open reading frame (ORF) content patterns.

METHODS AND RESULTS

WGS data of 66 Enterobacter hormaechei strains acquired by both ONT and Illumina sequencing and 162 strains obtained from NCBI database were converted to binary sequences based on the presence or absence of ORFs using BLASTn. Phylogenetic trees calculated from binary sequences (ORF trees) were compared with cgSNP trees derived from Illumina sequences. Clusters of closely related strains in the cgSNP trees formed comparable clusters in the ORF trees built with binary sequences, and the tree topologies between them were similar based on Fowlkes-Mallows index.

CONCLUSIONS

The ORF-based phylogenetic analysis using ONT sequencing may be useful in epidemiological investigations and offer advantages over the cgSNP-based approach.

SIGNIFICANCE AND IMPACT OF THE STUDY

Conversion of assembled WGS data to binary sequences based on the presence or absence of ORFs circumvents read error concerns with ONT sequencing. Since ONT sequencing generates data in real-time and does not require major investment, this ORF-based phylogenetic analysis method has the potential to enable phylogenetic and epidemiological analysis at the point of care.

PCR-based ORF typing of Klebsiella pneumoniae for rapid identification of global clones and transmission events

AIMS

Klebsiella pneumoniae is a major cause of healthcare-associated infections. In this study, we aimed to develop a rapid and simple genotyping method that can characterize strains causing nosocomial infections.

METHODS AND RESULTS

The PCR-based open reading frame (ORF) typing (POT) method consists of two multiplex PCR reactions which were designed to detect 25 ORFs specific to bacterial genetic lineages, species, antimicrobial resistant genes (bla_{CTX-M group-1} , bla_{CTX-M group-9} , bla_IMP and bla_KPC ), a capsular K1-specific gene, and a virulence factor gene (rmpA/A2). The electrophoresis results are then digitized. A total of 192 strains (136 clinical and 8 reference strains of K. pneumoniae, 33 clinical and 1 reference strains of K. variicola, and 14 clinical strains of K. quasipneumoniae) were classified into 95, 26, and 11 POT values, respectively. The distribution patterns of ORFs among K. pneumoniae correlated well with multilocus sequence typing (MLST). Furthermore, closely related species could be distinguished and key antimicrobial resistance and hypervirulence genes were identified as part of POT.

CONCLUSIONS

The POT method was developed and validated for K. pneumoniae. In comparison to MLST, the POT method is a rapid and easy genotyping method for monitoring transmission events by K. pneumoniae in clinical microbiology laboratories.

SIGNIFICANCE AND IMPACT OF THE STUDY

The POT method supplies clear and informative molecular typing results for K. pneumoniae. The method would facilitate molecular epidemiological analysis in infection control and hospital epidemiology investigations.

Dissecting the clonality of I1 plasmids using ORF-based binarized structure network analysis of plasmids (OSNAp)

OBJECTIVES

We aimed to elucidate the relationship among bla_CTX-M-carrying plasmids and their transmission between humans and domestic animals.

METHODS

Phylogenetic relationship of 90 I1 plasmids harboring bla_CTX-M genes encoding extended-spectrum β-lactamase (ESBL) was analyzed using the ORF-based binarized structure network analysis of plasmids (OSNAp).

RESULTS

The majority of plasmids carrying bla_CTX-M-1 or bla_CTX-M-8 belonged to a single lineage, respectively, and were primarily associated with domestic animals especially chickens. On the other hand, plasmids carrying bla_CTX-M-14 or bla_CTX-M-15, identified from both humans and domestic animals, were distributed in two or more lineages.

CONCLUSION

OSNAp has revealed the phylogenetic relationships and diversity of plasmids carrying bla_CTX-M more distinctly than pMLST. The findings suggest that circulation of I1 plasmids between humans and animals may contribute to their diversity.

Characterization of bla CTX-M-27/F1:A2:B20 Plasmids Harbored by Escherichia coli Sequence Type 131 Sublineage C1/H30R Isolates Spreading among Elderly Japanese in Nonacute-Care Settings

We characterized 29 bla _CTX-M-27-harboring plasmids of Escherichia coli sequence type 131 (ST131) sublineage C1/H30R isolates from healthy individuals and long-term-care facility (LTCF) residents. Most (27/29) plasmids were of the FIA, FIB, and FII multireplicon type with the same plasmid multilocus sequence typing (pMLST). Several plasmids (7/23) from LTCF residents harbored only bla _CTX-M-27 as the resistance gene; however, their fundamental structures were very similar to those of previously isolated bla _CTX-M-27/F1:A2:B20 plasmids, suggesting their prevalence as a newly arising public health concern.