Tackling Drug Resistant Infection Outbreaks of Global Pandemic Escherichia coli ST131 Using Evolutionary and Epidemiological Genomics

Comprehensive Assessment of Initial Adaptation of ESBL Positive ST131 Escherichia coli to Carbapenem Exposure

Background

It remains unclear how high-risk Escherichia coli lineages, like sequence type (ST) 131, initially adapt to carbapenem exposure in their progression to becoming carbapenem resistant.

Methods

Carbapenem mutation frequency was measured in multiple subclades of extended-spectrum β-lactamase (ESBL) positive ST131 clinical isolates using a fluctuation assay followed by whole genome sequencing (WGS) characterization. Genomic, transcriptomic, and porin analyses of ST131 C2/ H 30Rx isolate, MB1860, under prolonged, increasing carbapenem exposure was performed using two distinct experimental evolutionary platforms to measure fast vs. slow adaptation.

Results

All thirteen ESBL positive ST131 strains selected from a diverse (n=184) ST131 bacteremia cohort had detectable ertapenem (ETP) mutational frequencies with a statistically positive correlation between initial ESBL gene copy number and mutation frequency (r = 0.87, P -value <1e-5). WGS analysis of mutants showed initial response to ETP exposure resulted in significant increases in ESBL gene copy numbers or mutations in outer membrane porin (Omp) encoding genes in the absence of ESBL gene amplification with subclade specific associations. In both experimental evolutionary platforms, MB1860 responded to initial ETP exposure by increasing bla CTX-M-15 copy numbers via modular, insertion sequence 26 (IS 26 ) mediated pseudocompound transposons (PCTns). Transposase activity driven by PCTn upregulation was a conserved expression signal in both experimental evolutionary platforms. Stable mutations in Omp encoding genes were detected only after prolonged increasing carbapenem exposure consistent with clinical observations.

Conclusions

ESBL gene amplification is a conserved response to initial carbapenem exposure, especially within the high-risk ST131 C2/ H 30Rx subclade. Targeting such amplification could assist with mitigating carbapenem resistance development.

DNA supercoiling and regulation of intrinsic β-lactamase in pathogenic Escherichia coli

This review addresses the involvement of DNA supercoiling in the development of virulence and antibiotic profiles for uropathogenic Escherichia coli and the emergence of new pathotypes such as strain ST131 (serotype O25:H4). The mechanism suggests a role for topoisomerase enzymes and associated mutations in altering the chromosomal supercoiling state and introducing the required DNA twists for expression of intrinsic β-lactamase by ampC and certain virulence factors. In Escherichia coli, constitutive hyperexpression of intrinsic ampC is associated with specific mutations in the promoter and attenuator regions. However, many reports have documented the involvement of slow growth interventions in the expression of intrinsic resistance determinants. There is evidence that a stationary phase transcriptional switch protein, "BolA," is involved in the expression of the intrinsic ampC gene under starvation conditions. The process involves changes in the activity of the enzyme "gyrase," which leads to a change in the chromosomal DNA topology. Consequently, the DNA is relaxed, and the expression of the bolA gene is upregulated. The evolution of the extraintestinal pathogenic E. coli strain ST131 has demonstrated successful adaptability to various stress conditions and conferred compensatory mutations that endowed the microbe with resistance to fluoroquinolones and β-lactams. The results of this study provided new insights into the evidence for the influence of DNA topology in the expression of virulence genes and various determinants of antibiotic resistance (e.g., the intrinsic ampC gene) in Escherichia coli pathotypes.

Occurrence of Major Human Extraintestinal Pathogenic Escherichia coli Sequence Types Among Diarrheic Pet Animals: A Potential Public Health Threat

Background: Extraintestinal pathogenic Escherichia coli (ExPEC) has become a mounting public health concern. The present study was conducted to address the role of diarrheic pet animals as potential reservoirs for major human ExPEC sequence types (STs). Materials and Methods: Rectal swabs were collected from 145 diarrheic pet animals (75 dogs and 70 cats). Samples were processed for isolation and identification of E. coli by culture methods. Afterward, ExPEC isolates were identified on a molecular basis through detection of ExPEC phylogroups (B2 and D) coupled with carriage of two or more of the virulence genes associated with ExPEC (papAH, papC, sfa/focDE, afa/draBC, iutA, and kpsMT II). ExPEC STs 131, 73, 69, and 95 were identified among ExPEC isolates by quadruplex PCR and tested for their antimicrobial susceptibility. Eventually, two isolates underwent gene sequencing for the phylogenetic analysis. Results: Of 145 pet animals, 16 (11%) E. coli strains were identified as ExPEC, in which 15 (10.3%) isolates belonged to phylogroup B2 and 1 (0.69%) strain belonged to phylogroup D. The major human ExPEC STs were detected in 13 (9%) isolates, whereas the prevalence rates were 5.3% and 12.9% for dogs and cats, respectively. The isolation rates of ExPEC STs were 4.8%, 2.8%, 0.69%, and 0.69% for ST73, ST131, ST95, and ST69, respectively. Regarding the prevalence of virulence genes among ExPEC STs, the most prevalent ones were papC and sfa/focDE (92.3%), followed by papAH (76.9%), iutA (53.8%), afa/draBC (30.8%), and kpsMT II (30.8%). Moreover, 38.5% of the obtained human ExPEC STs were multidrug resistant. The phylogenetic analysis of two ExPEC ST73 gene sequences showed high genetic relatedness to those isolated from humans in different countries. Conclusions: The fecal carriage of major human ExPEC STs among diarrheic dogs and cats poses a potential zoonotic hazard with serious public health implications.

Bacterial plasmid-associated and chromosomal proteins have fundamentally different properties in protein interaction networks

Plasmids facilitate horizontal gene transfer, which enables the diversification of pathogens into new anatomical and environmental niches, implying that plasmid-encoded genes can cooperate well with chromosomal genes. We hypothesise that such mobile genes are functionally different to chromosomal ones due to this ability to encode proteins performing non-essential functions like antimicrobial resistance and traverse distinct host cells. The effect of plasmid-driven gene gain on protein-protein interaction network topology is an important question in this area. Moreover, the extent to which these chromosomally- and plasmid-encoded proteins interact with proteins from their own groups compared to the levels with the other group remains unclear. Here, we examined the incidence and protein-protein interactions of all known plasmid-encoded proteins across representative specimens from most bacteria using all available plasmids. We found that plasmid-encoded genes constitute ~ 0.65% of the total number of genes per bacterial sample, and that plasmid genes are preferentially associated with different species but had limited taxonomical power beyond this. Surprisingly, plasmid-encoded proteins had both more protein-protein interactions compared to chromosomal proteins, countering the hypothesis that genes with higher mobility rates should have fewer protein-level interactions. Nonetheless, topological analysis and investigation of the protein-protein interaction networks' connectivity and change in the number of independent components demonstrated that the plasmid-encoded proteins had limited overall impact in > 96% of samples. This paper assembled extensive data on plasmid-encoded proteins, their interactions and associations with diverse bacterial specimens that is available for the community to investigate in more detail.

Informing plasmid compatibility with bacterial hosts using protein-protein interaction data

The compatibility of plasmids with new host cells is significant given their role in spreading antimicrobial resistance (AMR) and virulence factor genes. Evaluating this using in vitro screening is laborious and can be informed by computational analyses of plasmid-host compatibility through rates of protein-protein interactions (PPIs) between plasmid and host cell proteins. We identified large excesses of such PPIs in eight important plasmids, including pOXA-48, using most known bacteria (n = 4363). 23 species had high rates of interactions with four blaOXA-48-positive plasmids. We also identified 48 species with high interaction rates with plasmids common in Escherichia coli. We found a strong association between one plasmid and the fimbrial adhesin operon pil, which could enhance host cell adhesion in aqueous environments. An excess rate of PPIs could be a sign of host-plasmid compatibility, which is important for AMR control given that plasmids like pOXA-48 move between species with ease.

Changes in the characteristics of community-onset fluoroquinolone-resistant Escherichia coli isolates causing community-acquired acute pyelonephritis in South Korea

PURPOSE

This study aimed to examine the changes in the characteristics of community-onset fluoroquinolone-resistant (FQ-R) Escherichia coli isolates causing community-acquired acute pyelonephritis (APN) in South Korea.

METHODS

Blood or urine samples were prospectively collected from patients aged ≥15 years with community-acquired APN who were admitted to one of the eight Korean hospitals included in this study between September 2017 and August 2018. Phylogenetic typing, multilocus sequence typing, and molecular characterization of β-lactamase resistance and plasmid-mediated quinolone resistance (PMQR) determinants were performed. The data were compared with those from a previous study with the same design conducted in 2010-2011.

RESULTS

A total of 300 and 346 isolates were identified in 2010-2011 and 2017-2018, respectively. Among them, 76 (22.0%) and 77 (25.7%) FQ-R isolates were identified in 2010-2011 and 2017-2018, respectively. A significantly higher antimicrobial resistance against third-to fourth-generation cephalosporins, including cefotaxime (23.9% vs. 77.9%, P < 0.001), were observed among FQ-R isolates in 2017-2018 than among those in 2010-2011. A higher proportion of ST131 isolates (27.6% vs. 66.2%, P < 0.001), as well as isolates that had extended-spectrum β-lactamase (ESBL)/plasmid-mediated AmpC β-lactamase (PABL) (23.7% vs. 79.2%, P < 0.001), was observed in 2017-2018 than in 2010-2011. Further, more PMQR determinants (11.8% vs. 40.8%, P < 0.001) were observed in 2017-2018 than in 2010-2011.

CONCLUSIONS

Among uropathogenic FQ-R E. coli isolates in South Korea, the prevalence of ST131 and the proportion of isolates containing ESBL and/or PMQR determinants have increased.

Genomic comparisons of Escherichia coli ST131 from Australia

Escherichia coli ST131 is a globally dispersed extraintestinal pathogenic E. coli lineage contributing significantly to hospital and community acquired urinary tract and bloodstream infections. Here we describe a detailed phylogenetic analysis of the whole genome sequences of 284 Australian ST131 E. coli isolates from diverse sources, including clinical, food and companion animals, wildlife and the environment. Our phylogeny and the results of single nucleotide polymorphism (SNP) analysis show the typical ST131 clade distribution with clades A, B and C clearly displayed, but no niche associations were observed. Indeed, interspecies relatedness was a feature of this study. Thirty-five isolates (29 of human and six of wild bird origin) from clade A (32 fimH41, 2 fimH89, 1 fimH141) were observed to differ by an average of 76 SNPs. Forty-five isolates from clade C1 from four sources formed a cluster with an average of 46 SNPs. Within this cluster, human sourced isolates differed by approximately 37 SNPs from isolates sourced from canines, approximately 50 SNPs from isolates from wild birds, and approximately 52 SNPs from isolates from wastewater. Many ST131 carried resistance genes to multiple antibiotic classes and while 41 (14 %) contained the complete class one integron-integrase intI1, 128 (45 %) isolates harboured a truncated intI1 (462-1014 bp), highlighting the ongoing evolution of this element. The module intI1-dfrA17-aadA5-qacEΔ1-sul1-ORF-chrA-padR-IS1600-mphR-mrx-mphA, conferring resistance to trimethoprim, aminoglycosides, quaternary ammonium compounds, sulphonamides, chromate and macrolides, was the most common structure. Most (73 %) Australian ST131 isolates carry at least one extended spectrum β-lactamase gene, typically bla_CTX-M-15 and bla_CTX-M-27. Notably, dual parC-1aAB and gyrA-1AB fluoroquinolone resistant mutations, a unique feature of clade C ST131 isolates, were identified in some clade A isolates. The results of this study indicate that the the ST131 population in Australia carries diverse antimicrobial resistance genes and plasmid replicons and indicate cross-species movement of ST131 strains across diverse reservoirs.

Protein over-expression in Escherichia coli triggers adaptation analogous to antimicrobial resistance

BACKGROUND

The E. coli pET system is the most widely used protein over-expression system worldwide. It relies on the assumption that all cells produce target protein and it is generally believed that integral membrane protein (IMP) over-expression is more toxic than their soluble counterparts.

RESULTS

Using GFP-tagged proteins, high level over-expression of either soluble or IMP targets results in > 99.9% cell loss with survival rate of only < 0.03%. Selective pressure generates three phenotypes: large green, large white and small colony variants. As a result, in overnight cultures, ~ 50% of the overall cell mass produces no protein. Genome sequencing of the phenotypes revealed genomic mutations that causes either the loss of T7 RNAP activity or its transcriptional downregulation. The over-expression process is bactericidal and is observed for both soluble and membrane proteins.

CONCLUSIONS

We demonstrate that it is the act of high-level over-expression of exogenous proteins in E. coli that sets in motion a chain of events leading to > 99.9% cell death. These results redefine our understanding of protein over-production and link it to the adaptive survival response seen in the development of antimicrobial resistance.

Plasmids shape the diverse accessory resistomes of Escherichia coli ST131

The human gut microbiome includes beneficial, commensal and pathogenic bacteria that possess antimicrobial resistance (AMR) genes and exchange these predominantly through conjugative plasmids. Escherichia coli is a significant component of the gastrointestinal microbiome and is typically non-pathogenic in this niche. In contrast, extra-intestinal pathogenic E. coli (ExPEC) including ST131 may occupy other environments like the urinary tract or bloodstream where they express genes enabling AMR and host cell adhesion like type 1 fimbriae. The extent to which commensal E. coli and uropathogenic ExPEC ST131 share AMR genes remains understudied at a genomic level, and we examined this here using a preterm infant resistome. We found that individual ST131 had small differences in AMR gene content relative to a larger shared resistome. Comparisons with a range of plasmids common in ST131 showed that AMR gene composition was driven by conjugation, recombination and mobile genetic elements. Plasmid pEK499 had extended regions in most ST131 Clade C isolates, and it had evidence of a co-evolutionary signal based on protein-level interactions with chromosomal gene products, as did pEK204 that had a type IV fimbrial pil operon. ST131 possessed extensive diversity of selective type 1, type IV, P and F17-like fimbriae genes that was highest in subclade C2. The structure and composition of AMR genes, plasmids and fimbriae vary widely in ST131 Clade C and this may mediate pathogenicity and infection outcomes.

Virulence and resistance properties of E. coli isolated from urine samples of hospitalized patients in Rio de Janeiro, Brazil - The role of mobile genetic elements

Extraintestinal pathogenic E. coli (ExPEC) is the most frequent etiological agent of urinary tract infections (UTIs). Particular evolutionary successful lineages are associated with severe UTIs and higher incidences of multidrug resistance. Most of the resistance genes are acquired by horizontal transfer of plasmids and other mobile genetic elements (MGEs), and this process has been associated with the successful dissemination of particular lineages. Here, we identified the presence of MGEs and their role in virulence and resistance profiles of isolates obtained from the urine of hospitalized patients in Brazil. Isolates belonging to the successful evolutionary lineages of sequence type (ST) 131, ST405, and ST648 were found to be multidrug-resistant, while those belonging to ST69 and ST73 were often not. Among the ST131, ST405, and ST648 isolates with a resistant phenotype, a high number of mainly IncFII plasmids was identified. The plasmids contained resistance cassettes, and these were also found within phage-related sequences and the chromosome of the isolates. The resistance cassettes were found to harbor several resistance genes, including bla_CTX-M-15. In addition, in ST131 isolates, diverse pathogenicity islands similar to those found in highly virulent ST73 isolates were detected. Also, a new genomic island associated with several virulence genes was identified in ST69 and ST131 isolates. In addition, several other MGEs present in the ST131 reference strain EC958 were identified in our isolates, most of them exclusively in ST131 isolates. In contrast, genomic islands present in this reference strain were only partially present or completely absent in our ST131 isolates. Of all isolates studied, ST73 and ST131 isolates had the most similar virulence profile. Overall, no clear association was found between the presence of specific MGEs and virulence profiles. Furthermore, the interplay between virulence and resistance by acquiring MGEs seemed to be lineage dependent. Although the acquisition of IncF plasmids, specific PAIs, GIs, and other MGEs seemed to be involved in the success of some lineages, it cannot explain the success of different lineages, also indicating other (host) factors are involved in this process. Nevertheless, the detection, identification, and surveillance of lineage-specific MGEs may be useful to monitor (new) emerging clones.

Antibiotic-Resistant Escherichia coli and Sequence Type 131 in Fecal Colonization in Dogs in Taiwan

Background: Most drug-resistant Escherichia coli isolates in dogs come from diseased dogs. Prior to this study, the prevalence and risk factors of fecal carriage drug-resistant E. coli and epidemic clone sequence type (ST) 131 (including subtypes) isolates in dogs were unknown. Methods: Rectal swabs were used for E. coli isolation from 299 non-infectious dogs in a veterinary teaching hospital in Taiwan. Antibiotic resistance and multiplex PCR analyses of E. coli for major STs were performed. Result: There were 43.1% cefazolin-resistant, 22.1% fluoroquinolone-resistant, and 9.4% extended-spectrum beta-lactamase-producing E. coli in our cohort. In the phylogenetic study, B2 was the predominant group (30.1%). The cefazolin-resistant group and ciprofloxacin-resistant group had greater antibiotic exposure in the last 14 days (p < 0.05). The age, sex, and dietary habits of the antibiotic-resistant and -susceptible groups were similar. In the seven isolates of ST131 in fecal colonization, the most predominant subtypes were FimH41 and FimH22. Conclusion: Recent antibiotic exposure was related to the fecal carriage of antibiotic-resistant E. coli isolates. Three major subtypes (FimH41, H22, and H30) of ST131 can thus be found in fecal carriage in dogs in Taiwan.

Characterization of fosfomycin heteroresistance among multidrug-resistant Escherichia coli isolates from hospitalized patients in Rio de Janeiro, Brazil

OBJECTIVES

Urinary tract infections (UTIs) caused by multidrug-resistant Escherichia coli have become a major medical concern. Old antibiotics such as fosfomycin have become an alternative therapeutic option due to their effectiveness and, as a result, fosfomycin is now used as a first-line drug for the treatment of UTIs in many countries. Despite low resistance rates, fosfomycin heteroresistance, defined as a phenomenon where subpopulations of bacteria are resistant to high antibiotic concentrations whereas most of the bacteria are susceptible, is an underestimated problem.

METHODS

The frequency of heteroresistance in E. coli isolated from hospitalized patients in Brazil and its effect on susceptibility of E. coli in biofilms was studied and the isolates were molecularly characterized to reveal the mechanisms behind their fosfomycin heteroresistance using whole-genome sequencing.

RESULTS

A higher frequency of fosfomycin heteroresistance compared with other studies was found. In biofilms, most heteroresistant isolates were less sensitive to fosfomycin than control isolates and showed overexpression of metabolic genes thereby increasing their survival rate. Molecular characterization showed that some resistant subpopulations derived from heteroresistant isolates had a defect in their fosfomycin uptake system caused by mutations in transporter and regulatory genes, whereas others overexpressed the murA gene. None to minor effects on bacterial fitness were observed. Oxidative stress protection, virulence and metabolic genes were differentially expressed in resistant subpopulations and heteroresistant isolates.

CONCLUSION

Frequent detection of heteroresistance in UTIs may play a role in the failure of antibiotic treatments and should therefore be more carefully diagnosed.

An Escherichia coli ST131 pangenome atlas reveals population structure and evolution across 4,071 isolates

Escherichia coli ST131 is a major cause of infection with extensive antimicrobial resistance (AMR) facilitated by widespread beta-lactam antibiotic use. This drug pressure has driven extended-spectrum beta-lactamase (ESBL) gene acquisition and evolution in pathogens, so a clearer resolution of ST131's origin, adaptation and spread is essential. E. coli ST131's ESBL genes are typically embedded in mobile genetic elements (MGEs) that aid transfer to new plasmid or chromosomal locations, which are mobilised further by plasmid conjugation and recombination, resulting in a flexible ESBL, MGE and plasmid composition with a conserved core genome. We used population genomics to trace the evolution of AMR in ST131 more precisely by extracting all available high-quality Illumina HiSeq read libraries to investigate 4,071 globally-sourced genomes, the largest ST131 collection examined so far. We applied rigorous quality-control, genome de novo assembly and ESBL gene screening to resolve ST131's population structure across three genetically distinct Clades (A, B, C) and abundant subclades from the dominant Clade C. We reconstructed their evolutionary relationships across the core and accessory genomes using published reference genomes, long read assemblies and k-mer-based methods to contextualise pangenome diversity. The three main C subclades have co-circulated globally at relatively stable frequencies over time, suggesting attaining an equilibrium after their origin and initial rapid spread. This contrasted with their ESBL genes, which had stronger patterns across time, geography and subclade, and were located at distinct locations across the chromosomes and plasmids between isolates. Within the three C subclades, the core and accessory genome diversity levels were not correlated due to plasmid and MGE activity, unlike patterns between the three main clades, A, B and C. This population genomic study highlights the dynamic nature of the accessory genomes in ST131, suggesting that surveillance should anticipate genetically variable outbreaks with broader antibiotic resistance levels. Our findings emphasise the potential of evolutionary pangenomics to improve our understanding of AMR gene transfer, adaptation and transmission to discover accessory genome changes linked to novel subtypes.

Determining the Virulence Properties of Escherichia coli ST131 Containing Bacteriocin-Encoding Plasmids Using Short- and Long-Read Sequencing and Comparing Them with Those of Other E. coli Lineages

Escherichia coli ST131 is a clinical challenge due to its multidrug resistant profile and successful global spread. They are often associated with complicated infections, particularly urinary tract infections (UTIs). Bacteriocins play an important role to outcompete other microorganisms present in the human gut. Here, we characterized bacteriocin-encoding plasmids found in ST131 isolates of patients suffering from a UTI using both short- and long-read sequencing. Colicins Ia, Ib and E1, and microcin V, were identified among plasmids that also contained resistance and virulence genes. To investigate if the potential transmission range of the colicin E1 plasmid is influenced by the presence of a resistance gene, we constructed a strain containing a plasmid which had both the colicin E1 and blaCMY-2 genes. No difference in transmission range was found between transformant and wild-type strains. However, a statistically significantly difference was found in adhesion and invasion ability. Bacteriocin-producing isolates from both ST131 and non-ST131 lineages were able to inhibit the growth of other E. coli isolates, including other ST131. In summary, plasmids harboring bacteriocins give additional advantages for highly virulent and resistant ST131 isolates, improving the ability of these isolates to compete with other microbiota for a niche and thereby increasing the risk of infection.

Genome and plasmid diversity of Extended-Spectrum β-Lactamase-producing Escherichia coli ST131 - tracking phylogenetic trajectories with Bayesian inference

Clonal lineages of ESBL (Extended-Spectrum β-Lactamase)-producing E. coli belonging to sequence type 131 (ST131) have disseminated globally during the last 30 years, leading to an increased prevalence of resistance to fluoroquinolones and extended-spectrum cephalosporins in clinical isolates of E. coli. We aimed to study if Swedish ESBL-producing ST131 isolates originated from single or multiple introductions to the population by assessing the amount of genetic variation, on chromosomal and plasmid level, between Swedish and international E. coli ST131. Bayesian inference of Swedish E. coli ST131 isolates (n = 29), sequenced using PacBio RSII, together with an international ST131 dataset showed that the Swedish isolates were part of the international ST131 A, C1 and C2 clades. Highly conserved plasmids were identified in three clusters although they were separated by several years, which indicates a strong co-evolution between some ST131 lineages and specific plasmids. In conclusion, the tight clonal relationship observed within the ST131 clades, together with highly conserved plasmids, challenges investigation of strain transmission events. A combination of few SNPs on a genome-wide scale and an epidemiological temporospatial link, are needed to track the spread of the ST131 subclones.