Diversity of P1 phage-like elements in multidrug resistant Escherichia coli

Characterization of Salmonella Phage P1-CTX and the Potential Mechanism Underlying the Acquisition of the blaCTX-M-27 Gene

The P1 phage has garnered attention as a carrier of antibiotic resistance genes (ARGs) in Enterobacteriaceae. However, the transferability of ARGs by P1-like phages carrying ARGs, in addition to the mechanism underlying ARG acquisition, remain largely unknown. In this study, we elucidated the biological characteristics, the induction and transmission abilities, and the acquisition mechanism of the blaCTX-M-27 gene in the P1 phage. The P1-CTX phage exhibited distinct lytic plaques and possessed a complete head and tail structure. Additionally, the P1-CTX phage was induced successfully under various conditions, including UV exposure, heat treatment at 42 °C, and subinhibitory concentrations (sub-MICs) of antibiotics. Moreover, the P1-CTX phage could mobilize the blaCTX-M-27 gene into three strains of Escherichia coli (E. coli) and the following seven different serotypes of Salmonella: Rissen, Derby, Kentucky, Typhimurium, Cerro, Senftenberg, and Muenster. The mechanism underlying ARG acquisition by the P1-CTX phage involved Tn1721 transposition-mediated movement of blaCTX-M-27 into the ref and mat genes within its genome. To our knowledge, this is the first report documenting the dynamic processes of ARG acquisition by a phage. Furthermore, this study enriches the research on the mechanism underlying the phage acquisition of drug resistance genes and provides a basis for determining the risk of drug resistance during phage transmission.

Presence of phage-plasmids in multiple serovars of Salmonella enterica

Evidence is accumulating in the literature that the horizontal spread of antimicrobial resistance (AMR) genes mediated by bacteriophages and bacteriophage-like plasmid (phage-plasmid) elements is much more common than previously envisioned. For instance, we recently identified and characterized a circular P1-like phage-plasmid harbouring a bla CTX-M-15 gene conferring extended-spectrum beta-lactamase (ESBL) resistance in Salmonella enterica serovar Typhi. As the prevalence and epidemiological relevance of such mechanisms has never been systematically assessed in Enterobacterales, in this study we carried out a follow-up retrospective analysis of UK Salmonella isolates previously sequenced as part of routine surveillance protocols between 2016 and 2021. Using a high-throughput bioinformatics pipeline we screened 47 784 isolates for the presence of the P1 lytic replication gene repL, identifying 226 positive isolates from 25 serovars and demonstrating that phage-plasmid elements are more frequent than previously thought. The affinity for phage-plasmids appears highly serovar-dependent, with several serovars being more likely hosts than others; most of the positive isolates (170/226) belonged to S. Typhimurium ST34 and ST19. The phage-plasmids ranged between 85.8 and 98.2 kb in size, with an average length of 92.1 kb; detailed analysis indicated a high amount of diversity in gene content and genomic architecture. In total, 132 phage-plasmids had the p0111 plasmid replication type, and 94 the IncY type; phylogenetic analysis indicated that both horizontal and vertical gene transmission mechanisms are likely to be involved in phage-plasmid propagation. Finally, phage-plasmids were present in isolates that were resistant and non-resistant to antimicrobials. In addition to providing a first comprehensive view of the presence of phage-plasmids in Salmonella, our work highlights the need for a better surveillance and understanding of phage-plasmids as AMR carriers, especially through their characterization with long-read sequencing.

The faecal microbiome of the Australian silver gull contains phylogenetically diverse ExPEC, aEPEC and Escherichia coli carrying the transmissible locus of stress tolerance

Wildlife are implicated in the dissemination of antimicrobial resistance, but their roles as hosts for Escherichia coli that pose a threat to human and animal health is limited. Gulls (family Laridae) in particular, are known to carry diverse lineages of multiple-antibiotic resistant E. coli, including extra-intestinal pathogenic E. coli (ExPEC). Whole genome sequencing of 431 E. coli isolates from 69 healthy Australian silver gulls (Chroicocephalus novaehollandiae) sampled during the 2019 breeding season, and without antibiotic selection, was undertaken to assess carriage in an urban wildlife population. Phylogenetic analysis and genotyping resolved 123 sequence types (STs) representing most phylogroups, and identified diverse ExPEC, including an expansive phylogroup B2 cluster comprising 103 isolates (24 %; 31 STs). Analysis of the mobilome identified: i) widespread carriage of the Yersinia High Pathogenicity Island (HPI), a key ExPEC virulence determinant; ii) broad distribution of two novel phage elements, each carrying sitABCD and iii) carriage of the transmissible locus of stress tolerance (tLST), an element linked to sanitation resistance. Of the 169 HPI carrying isolates, 49 (48 %) represented diverse B2 isolates hosting FII-64 ColV-like plasmids that lacked iutABC and sitABC operons typical of ColV plasmids, but carried the serine protease autotransporter gene, sha. Diverse E. coli also carried archetypal ColV plasmids (52 isolates; 12 %). Clusters of closely related E. coli (<50 SNVs) from ST58, ST457 and ST746, sourced from healthy gulls, humans, and companion animals, were frequently identified. In summary, anthropogenically impacted gulls host an expansive E. coli population, including: i) putative ExPEC that carry ColV virulence gene cargo (101 isolates; 23.4 %) and HPI (169 isolates; 39 %); ii) atypical enteropathogenic E. coli (EPEC) (17 isolates; 3.9 %), and iii) E. coli that carry the tLST (20 isolates; 4.6 %). Gulls play an important role in the evolution and transmission of E. coli that impact human health.

Interaction with a phage gene underlie costs of a β-lactamase

The fitness cost of an antibiotic resistance gene (ARG) can differ across host strains, creating refuges that allow the maintenance of an ARG in the absence of direct selection for its resistance phenotype. Despite the importance of such ARG-host interactions for predicting ARG dynamics, the basis of ARG fitness costs and their variability between hosts are not well understood. We determined the genetic basis of a host-dependent cost of a β-lactamase, blaTEM-116*, that conferred a significant cost in one Escherichia coli strain but was close to neutral in 11 other Escherichia spp. strains. Selection of a blaTEM-116*-encoding plasmid in the strain in which it initially had a high cost resulted in rapid and parallel compensation for that cost through mutations in a P1-like phage gene, relAP1. When the wild-type relAP1 gene was added to a strain in which it was not present and in which blaTEM-116* was neutral, it caused the ARG to become costly. Thus, relAP1 is both necessary and sufficient to explain blaTEM-116* costs in at least some host backgrounds. To our knowledge, these findings represent the first demonstrated case of the cost of an ARG being influenced by a genetic interaction with a phage gene. The interaction between a phage gene and a plasmid-borne ARG highlights the complexity of selective forces determining the maintenance and spread of ARGs and, by extension, encoding phage and plasmids in natural bacterial communities.IMPORTANCEAntibiotic resistance genes (ARGs) play a major role in the increasing problem of antibiotic resistance in clinically relevant bacteria. Selection of these genes occurs in the presence of antibiotics, but their eventual success also depends on the sometimes substantial costs they impose on host bacteria in antibiotic-free environments. We evolved an ARG that confers resistance to penicillin-type antibiotics in one host in which it did confer a cost and in one host in which it did not. We found that costs were rapidly and consistently reduced through parallel genetic changes in a gene encoded by a phage that was infecting the costly host. The unmutated version of this gene was sufficient to cause the ARG to confer a cost in a host in which it was originally neutral, demonstrating an antagonism between the two genetic elements and underlining the range and complexity of pressures determining ARG dynamics in natural populations.

Urinary Plasmids Reduce Permissivity to Coliphage Infection

The microbial community of the urinary tract (urinary microbiota or urobiota) has been associated with human health. Bacteriophages (phages) and plasmids present in the urinary tract, like in other niches, may shape urinary bacterial dynamics. While urinary Escherichia coli strains associated with urinary tract infection (UTI) and their phages have been catalogued for the urobiome, bacterium-plasmid-phage interactions have yet to be explored. In this study, we characterized urinary E. coli plasmids and their ability to decrease permissivity to E. coli phage (coliphage) infection. Putative F plasmids were predicted in 47 of 67 urinary E. coli isolates, and most of these plasmids carried genes that encode toxin-antitoxin (TA) modules, antibiotic resistance, and/or virulence. Urinary E. coli plasmids, from urinary microbiota strains UMB0928 and UMB1284, were conjugated into E. coli K-12 strains. These transconjugants included genes for antibiotic resistance and virulence, and they decreased permissivity to coliphage infection by the laboratory phage P1vir and the urinary phages Greed and Lust. Plasmids in one transconjugant were maintained in E. coli K-12 for up to 10 days in the absence of antibiotic resistance selection; this included the maintenance of the antibiotic resistance phenotype and decreased permissivity to phage. Finally, we discuss how F plasmids present in urinary E. coli strains could play a role in coliphage dynamics and the maintenance of antibiotic resistance in urinary E. coli. IMPORTANCE The urinary tract contains a resident microbial community called the urinary microbiota or urobiota. Evidence exists that it is associated with human health. Bacteriophages (phages) and plasmids present in the urinary tract, like in other niches, may shape urinary bacterial dynamics. Bacterium-plasmid-phage interactions have been studied primarily in laboratory settings and are yet to be thoroughly tested in complex communities. This is especially true of the urinary tract, where the bacterial genetic determinants of phage infection are not well understood. In this study, we characterized urinary E. coli plasmids and their ability to decrease permissivity to E. coli phage (coliphage) infection. Urinary E. coli plasmids, encoding antibiotic resistance and transferred by conjugation into naive laboratory E. coli K-12 strains, decreased permissivity to coliphage infection. We propose a model by which urinary plasmids present in urinary E. coli strains could help to decrease phage infection susceptibility and maintain the antibiotic resistance of urinary E. coli. This has consequences for phage therapy, which could inadvertently select for plasmids that encode antibiotic resistance.

Dominance of Escherichia coli sequence types ST73, ST95, ST127 and ST131 in Australian urine isolates: a genomic analysis of antimicrobial resistance and virulence linked to F plasmids

Extraintestinal pathogenic Escherichia coli (ExPEC) are the most frequent cause of urinary tract infections (UTIs) globally. Most studies of clinical E. coli isolates are selected based on their antimicrobial resistance (AMR) phenotypes; however, this selection bias may not provide an accurate portrayal of which sequence types (STs) cause the most disease. Here, whole genome sequencing (WGS) was performed on 320 E. coli isolates from urine samples sourced from a regional hospital in Australia in 2006. Most isolates (91%) were sourced from patients with UTIs and were not selected based on any AMR phenotypes. No significant differences were observed in AMR and virulence genes profiles across age sex, and uro-clinical syndromes. While 88 STs were identified, ST73, ST95, ST127 and ST131 dominated. F virulence plasmids carrying senB-cjrABC (126/231; 55%) virulence genes were a feature of this collection. These senB-cjrABC+ plasmids were split into two categories: pUTI89-like (F29:A-:B10 and/or >95 % identity to pUTI89) (n=73) and non-pUTI89-like (n=53). Compared to all other plasmid replicons, isolates with pUTI89-like plasmids carried fewer antibiotic resistance genes (ARGs), whilst isolates with senB-cjrABC+/non-pUTI89 plasmids had a significantly higher load of ARGs and class 1 integrons. F plasmids were not detected in 89 genomes, predominantly ST73. Our phylogenomic analyses identified closely related isolates from the same patient associated with different pathologies and evidence of strain-sharing events involving isolates sourced from companion and wild animals.

Enterobacteriaceae genome-wide analysis reveals roles for P1-like phage-plasmids in transmission of mcr-1, tetX4 and other antibiotic resistance genes

P1 -like phage-plasmids (PPs) are important gene vehicles in isolated pathogens. In this study, we conducted genome-wide and cross-species analysis of antimicrobial resistance genes (ARGs) from 35 ARG-positive P1-like PPs. LS-BSR analysis reveal that P1-like PPs had in common 7 highly variable regions and carried 48 different ARG subtypes. The most prevalent gene groups were the colistin resistance gene mcr-1 and a class 1 integron. Analysis of the flanking sequences of mcr-1 indicated an "IS30-mcr-1-ORF-IS30" as the core cluster. In particular, we found an mcr-1- and bla_CTX-M-55-coharboring large fusion P1-like PP. Also, tet(X4) was detected and flanking sequences indicated tet(X4)-bearing cluster can formed a larger size fusion plasmid mediated a wider spread via IS26 hotspots. Overall, this study demonstrated that P1-like PPs can not only mobilize a large number of ARGs in variable regions but also form larger hybrid P1-like PPs that would increase their ability to spread antimicrobial resistance.

The Role of Temperate Phages in Bacterial Pathogenicity

Bacteriophages are viruses that infect bacteria and archaea and are classified as virulent or temperate phages based on their life cycles. A temperate phage, also known as a lysogenic phage, integrates its genomes into host bacterial chromosomes as a prophage. Previous studies have indicated that temperate phages are beneficial to their susceptible bacterial hosts by introducing additional genes to bacterial chromosomes, creating a mutually beneficial relationship. This article reviewed three primary ways temperate phages contribute to the bacterial pathogenicity of foodborne pathogens, including phage-mediated virulence gene transfer, antibiotic resistance gene mobilization, and biofilm formation. This study provides insights into mechanisms of phage–bacterium interactions in the context of foodborne pathogens and provokes new considerations for further research to avoid the potential of phage-mediated harmful gene transfer in agricultural environments.

Similarities of P1-Like Phage Plasmids and Their Role in the Dissemination of blaCTX-M-55

The P1-like phage plasmid (PP) has been widely used as a molecular biology tool, but its role as an active accessory cargo element is not fully understood. In this study, we provide insights into the structural features and gene content similarities of 77 P1-like PPs in the RefSeq database. We also describe a P1-like PP carrying a blaCTX-M-55 gene, JL22, which was isolated from a clinical strain of Escherichia coli from a duck farm. P1-like PPs were very similar and conserved based on gene content similarities, with only eight highly variable regions. Importantly, two kinds of replicon types, namely, IncY and p0111, were identified and can be used to specifically identify the P1-like phage. JL22 is similar to P1, acquiring an important foreign DNA fragment with two obvious features, namely, the plasmid replication gene repA' (p0111) replacing the gene repA (IncY) and a 4,200-bp fragment mobilized by IS1380 and IS5 and containing a blaCTX-M-55 gene and a trpB gene encoding tryptophan synthase (indole salvaging). The JL22 phage could be induced but had no lytic capacities. However, a lysogenic recipient and intact structure of JL22 virions were observed, showing that the extended-spectrum β-lactamase blaCTX-M-55 gene was successfully transferred. Overall, conserved genes can be a good complement to improve the identification efficiency and accuracy in future screening for P1-like PPs. Moreover, the highly conserved structures may be important for their prevalence and dissemination. IMPORTANCE As a PP, P1 DNA exists as a low-copy-number plasmid and replicates autonomously with a lysogenization style. This unique mode of P1-like elements probably indicates a stable contribution to antibiotic resistance. After analyzing these elements, we show that P1-like PPs are very similar and conserved, with only eight highly variable regions. Moreover, we observed the occurrence of replicon IncY and p0111 only in the P1-like PP community, implying that these conserved regions, coupled with IncY and p0111, can be an important complement in future screening of P1-like PPs. Identification and characterization of JL22 confirmed our findings that major changes were located in variable regions, including the first detection of blaCTX-M-55 in such a mobile genetic element. This suggests that these variable regions may facilitate foreign DNA mobilization. This study features a comprehensive genetic analysis of P1-like PPs, providing new insights into the dissemination mechanisms of antibiotic resistance through P1 PPs.

Phage-Plasmids Spread Antibiotic Resistance Genes through Infection and Lysogenic Conversion

Antibiotic resistance is rapidly spreading via the horizontal transfer of resistance genes in mobile genetic elements. While plasmids are key drivers of this process, few integrative phages encode antibiotic resistance genes. Here, we find that phage-plasmids, elements that are both phages and plasmids, often carry antibiotic resistance genes. We found 60 phage-plasmids with 184 antibiotic resistance genes, providing resistance for broad-spectrum-cephalosporins, carbapenems, aminoglycosides, fluoroquinolones, and colistin. These genes are in a few hot spots, seem to have been cotranslocated with transposable elements, and are often in class I integrons, which had not been previously found in phages. We tried to induce six phage-plasmids with resistance genes (including four with resistance integrons) and succeeded in five cases. Other phage-plasmids and integrative prophages were coinduced in these experiments. As a proof of concept, we focused on a P1-like element encoding an extended spectrum β-lactamase, bla_CTX-M-55. After induction, we confirmed that it is capable of infecting and converting four other E. coli strains. Its reinduction led to the further conversion of a sensitive strain, confirming that it is a fully functional phage. This study shows that phage-plasmids carry a large diversity of clinically relevant antibiotic resistance genes that they can transfer across bacteria. As plasmids, these elements seem plastic and capable of acquiring genes from other plasmids. As phages, they may provide novel paths of transfer for resistance genes because they can infect bacteria that are distant in time and space from the original host. As a matter of alarm, they may also mediate transfer to other types of phages.

Molecular Characterization of pBOq-IncQ and pBOq-95LK Plasmids of Escherichia coli BOq 01, a New Isolated Strain from Poultry Farming, Involved in Antibiotic Resistance

The increase in antimicrobial resistance has raised questions about how to use these drugs safely, especially in veterinary medicine, animal nutrition, and agriculture. Escherichia coli is an important human and animal pathogen that frequently contains plasmids carrying antibiotic resistance genes. Extra chromosomal elements are required for various functions or conditions in microorganisms. Several phage-like plasmids have been identified, which are important in antibiotic resistance. In this work, the molecular characterization of the pBOq-IncQ (4.5 kb) and pBOq-95LK (95 kb) plasmids found in the E. coli strain BOq 01, a multidrug resistant bacteria isolated from a poultry farm, are considered. Plasmid pBOq-IncQ belongs to the incQ incompatibility plasmid family and is involved in sulfonamide resistance. Plasmid pBOq-95LK is a lytic phage-like plasmid that is involved in the lysis of the E. coli BOq 01 strain and carries a bleomycin resistance gene and a strain cured of this plasmid shows bleomycin sensitivity. Induction of the lytic cycle indicates that this phage-like plasmid is an active phage. This type of plasmid has been reported to acquire genes such as mcr-1, which codes for colistin resistance and bacterial persistence and is a significant public health threat. A genome comparison, a pangenomic and phylogenomic analysis with other phage-like plasmids reported in the literature were performed to understand better the evolution of this kind of plasmid in bacteria and its potential importance in antibiotic resistance.

Evolution of horizontal transmission in antimicrobial resistance plasmids

Mobile genetic elements (MGEs) are one of the main vectors for the spread of antimicrobial resistance (AMR) across bacteria, due to their ability to move horizontally between bacterial lineages. Horizontal transmission of AMR can increase AMR prevalence at multiple scales, from increasing the prevalence of infections by resistant bacteria to pathogen epidemics and worldwide spread of AMR across species. Among MGEs, conjugative plasmids are the main contributors to the spread of AMR. This review discusses the selective pressures acting on MGEs and their hosts to promote or limit the horizontal transmission of MGEs, the mechanisms by which transmission rates can evolve, and their implications for limiting the spread of AMR, with a focus on AMR plasmids.

Biological foundations of successful bacteriophage therapy

Bacteriophages (phages) are selective viral predators of bacteria. Abundant and ubiquitous in nature, phages can be used to treat bacterial infections (phage therapy), including refractory infections and those resistant to antibiotics. However, despite an abundance of anecdotal evidence of efficacy, significant hurdles remain before routine implementation of phage therapy into medical practice, including a dearth of robust clinical trial data. Phage-bacterium interactions are complex and diverse, characterized by co-evolution trajectories that are significantly influenced by the environments in which they occur (mammalian body sites, water, soil, etc.). An understanding of the molecular mechanisms underpinning these dynamics is essential for successful clinical translation. This review aims to cover key aspects of bacterium-phage interactions that affect bacterial killing by describing the most relevant published literature and detailing the current knowledge gaps most likely to influence therapeutic success.

Mobility of antimicrobial resistance across serovars and disease presentations in non-typhoidal Salmonella from animals and humans in Vietnam

Non-typhoidal Salmonella (NTS) is a major cause of bacterial enterocolitis globally but also causes invasive bloodstream infections. Antimicrobial resistance (AMR) hampers the treatment of these infections and understanding how AMR spreads between NTS may help in developing effective strategies. We investigated NTS isolates associated with invasive disease, diarrhoeal disease and asymptomatic carriage in animals and humans from Vietnam. Isolates included multiple serovars and both common and rare phenotypic AMR profiles; long- and short-read sequencing was used to investigate the genetic mechanisms and genomic backgrounds associated with phenotypic AMR profiles. We demonstrate concordance between most AMR genotypes and phenotypes but identified large genotypic diversity in clinically relevant phenotypes and the high mobility potential of AMR genes (ARGs) in this setting. We found that 84 % of ARGs identified were located on plasmids, most commonly those containing IncHI1A_1 and IncHI1B(R27)_1_R27 replicons (33%), and those containing IncHI2_1 and IncHI2A_1 replicons (31%). The vast majority (95%) of ARGS were found within 10 kbp of IS6/IS26 elements, which provide plasmids with a mechanism to exchange ARGs between plasmids and other parts of the genome. Whole genome sequencing with targeted long-read sequencing applied in a One Health context identified a comparatively limited number of insertion sequences and plasmid replicons associated with AMR. Therefore, in the context of NTS from Vietnam and likely for other settings as well, the mechanisms by which ARGs move contribute to a more successful AMR profile than the specific ARGs, facilitating the adaptation of bacteria to different environments or selection pressures.

High plasmidome diversity of extended-spectrum beta-lactam-resistant Escherichia coli isolates collected during one year in one community hospital

Plasmid-encoded antibiotic resistance encompasses many classes of currently used antibiotics. In globally distributed Escherichia coli lineages plasmids, which spread via horizontal gene transfer, are responsible for the dissemination of genes encoding extended-spectrum β-lactamases (ESBL). In this study, we combined 2nd and 3rd generation sequencing techniques to reconstruct the plasmidome of overall 97 clinical ESBL-E. coli isolates. Our results highlight the enormous plasmid diversity in respect to size, replicon-type and genetic content. Furthermore, we emphasize the diverse plasmid distribution patterns among the clinical isolates and the high intra- and extracellular mobility potential of resistance conferring genes. While the majority of resistance conferring genes were located on large plasmids of known replicon type, small cryptic plasmids seem to be underestimated resistance gene vectors. Our results contribute to a better understanding of the dissemination of resistance-conferring genes through horizontal gene transfer as well as clonal spread.

Genomic Characterization of a Uropathogenic Escherichia coli ST405 Isolate Harboring bla CTX-M-15-Encoding IncFIA-FIB Plasmid, bla CTX-M-24-Encoding IncI1 Plasmid, and Phage-Like Plasmid

Escherichia coli sequence type 405 is an emerging antibiotic-resistant clonal group associated with the global dissemination of extended-spectrum β-lactamase-producing E. coli. In this study, we report the genome assembly and characterization of a uropathogenic E. coli ST405 strain, SZESBLEC201, based on long and short reads obtained from the Nanopore and Illumina sequencing platforms, respectively. Whole-genome sequencing revealed that SZESBLEC201 harbors a 5,020,403 bp chromosome and three plasmids, namely, pSZESBLEC201-1, pSZESBLEC201-2, and pSZESBLEC201-3. pSZESBLEC201-1 (111,621 bp) belongs to the IncFIA-FIB type and harbors bla _CTX-M-15. However, this plasmid does not harbor conjugative transfer-associated genes, rendering pSZESBLEC201-1 unable to be conjugatively transferred. pSZESBLEC201-2 (95,138 bp) is a phage-like plasmid that shows a strong genome synteny with Escherichia phage P1 but with the absence of mobile genetic elements and some regulatory genes. pSZESBLEC201-3 (92,865 bp) belongs to the IncI1 type and carries bla _CTX-M-24. In contrast to pSZESBLEC201-1, pSZESBLEC201-3 retains its full active conjugation machinery and can be transferred via conjugation. The genetic features of the genome show that the SZESBLEC201 has a unique virulence pattern compared with genetically similar strains found in the same country (China). The plasmid backbones exhibit a high degree of similarity to those of geographically distant isolates, highlighting the global spread of bla _CTX-M genes and the genome plasticity of this clonal group. The coexistence of two bla _CTX-M variants in the same strain increases the risk of the emergence of new bla _CTX-M variants. Further studies on phage-like plasmids are necessary to provide insights into their biological activities and clinical significance.

Interactions between Viral Regulatory Proteins Ensure an MOI-Independent Probability of Lysogeny during Infection by Bacteriophage P1

Phage P1 is a temperate phage which makes the lytic or lysogenic decision upon infecting bacteria. During the lytic cycle, progeny phages are produced and the cell lyses, and in the lysogenic cycle, P1 DNA exists as a low-copy-number plasmid and replicates autonomously. Previous studies at the bulk level showed that P1 lysogenization was independent of multiplicity of infection (MOI; the number of phages infecting a cell), whereas lysogenization probability of the paradigmatic phage λ increases with MOI. However, the mechanism underlying the P1 behavior is unclear. In this work, using a fluorescent reporter system, we demonstrated this P1 MOI-independent lysogenic response at the single-cell level. We further observed that the activity of the major repressor of lytic functions (C1) is a determining factor for the final cell fate. Specifically, the repression activity of P1, which arises from a combination of C1, the anti-repressor Coi, and the corepressor Lxc, remains constant for different MOI, which results in the MOI-independent lysogenic response. Additionally, by increasing the distance between phages that infect a single cell, we were able to engineer a λ-like, MOI-dependent lysogenization upon P1 infection. This suggests that the large separation of coinfecting phages attenuates the effective communication between them, allowing them to make decisions independently of each other. Our work establishes a highly quantitative framework to describe P1 lysogeny establishment. This system plays an important role in disseminating antibiotic resistance by P1-like plasmids and provides an alternative to the lifestyle of phage λ.

The human oral virome: Shedding light on the dark matter

Mediators of the initiation, development, and recurrence of periodontitis include the oral microbiome embedded in subgingival plaque and the host immune response to a dysbiosis within this dynamic and complex microbial community. Although mediators have been studied extensively, researchers in the field have been unable to fully ascribe certain clinical presentations of periodontitis to their nature. Emergence of high-throughput sequencing technologies has resulted in better characterization of the microbial oral dysbiosis that extends beyond the extensively studied putative bacterial periodontopathogens to a shift in the oral virome composition during disease conditions. Although the biological dark matter inserted by retroviruses was once believed to be nonfunctional, research has revealed that it encodes historical viral-eukaryotic interactions and influences host development. The objective of this review is to evaluate the proposed association of herpesviruses to the etiology and pathogenesis of periodontal disease and survey the highly abundant prokaryotic viruses to delineate their potential roles in biofilm dynamics, as well as their interactions with putative bacterial periodontopathogens and eukaryotic cells. The findings suggest that potential novel periodontal therapies targeting or utilizing the oral virome can alleviate certain clinical presentations of periodontitis. Perhaps it is time to embrace the viral dark matter within the periodontal environment to fully comprehend the pathogenesis and systemic implications of periodontitis.

Distribution of Antimicrobial Resistance and Virulence Genes within the Prophage-Associated Regions in Nosocomial Pathogens

Prophages are often involved in host survival strategies and contribute toward increasing the genetic diversity of the host genome. Prophages also drive horizontal propagation of various genes as vehicles. However, there are few retrospective studies contributing to the propagation of antimicrobial resistance (AMR) and virulence factor (VF) genes by prophage. We extracted the complete genome sequences of seven pathogens, including ESKAPE bacteria and Escherichia coli from a public database, and examined the distribution of both the AMR and VF genes in prophage-like regions. We found that the ratios of AMR and VF genes greatly varied among the seven species. More than 70% of Enterobacter cloacae strains had VF genes, but only 1.2% of Klebsiella pneumoniae strains had VF genes from prophages. AMR and VF genes are unlikely to exist together in the same prophage region except in E. coli and Staphylococcus aureus, and the distribution patterns of prophage types containing AMR genes are distinct from those of VF gene-carrying prophage types. AMR genes in the prophage were located near transposase and/or integrase. The prophage containing class 1 integrase possessed a significantly greater number of AMR genes than did prophages with no class 1 integrase. The results of this study present a comprehensive picture of AMR and VF genes present within, or close to, prophage-like elements and different prophage patterns between AMR- or VF-encoding prophage-like elements.

IMPORTANCE Although we believe phages play an important role in horizontal gene transfer in exchanging genetic material, we do not know the distribution of the antimicrobial resistance (AMR) and/or virulence factor (VF) genes in prophages. We collected different prophage elements from the complete genome sequences of seven species—Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter cloacae, and Escherichia coli—and characterized the distribution of antimicrobial resistance and virulence genes located in the prophage region. While virulence genes in prophage were species specific, antimicrobial resistance genes in prophages were highly conserved in various species. An integron structure was detected within specific prophage regions such as P1-like prophage element. Maximum of 10 antimicrobial resistance genes were found in a single prophage region, suggesting that prophages act as a reservoir for antimicrobial resistance genes. The results of this study show the different characteristic structures between AMR- or VF-encoding prophages.

Bacteria have numerous distinctive groups of phage-plasmids with conserved phage and variable plasmid gene repertoires

Plasmids and temperate phages are key contributors to bacterial evolution. They are usually regarded as very distinct. However, some elements, termed phage–plasmids, are known to be both plasmids and phages, e.g. P1, N15 or SSU5. The number, distribution, relatedness and characteristics of these phage–plasmids are poorly known. Here, we screened for these elements among ca. 2500 phages and 12000 plasmids and identified 780 phage–plasmids across very diverse bacterial phyla. We grouped 92% of them by similarity of gene repertoires to eight defined groups and 18 other broader communities of elements. The existence of these large groups suggests that phage–plasmids are ancient. Their gene repertoires are large, the average element is larger than an average phage or plasmid, and they include slightly more homologs to phages than to plasmids. We analyzed the pangenomes and the genetic organization of each group of phage–plasmids and found the key phage genes to be conserved and co-localized within distinct groups, whereas genes with homologs in plasmids are much more variable and include most accessory genes. Phage–plasmids are a sizeable fraction of the sequenced plasmids (∼7%) and phages (∼5%), and could have key roles in bridging the genetic divide between phages and other mobile genetic elements.

Plasmid- and strain-specific factors drive variation in ESBL-plasmid spread in vitro and in vivo

Horizontal gene transfer, mediated by conjugative plasmids, is a major driver of the global rise of antibiotic resistance. However, the relative contributions of factors that underlie the spread of plasmids and their roles in conjugation in vivo are unclear. To address this, we investigated the spread of clinical Extended Spectrum Beta-Lactamase (ESBL)-producing plasmids in the absence of antibiotics in vitro and in the mouse intestine. We hypothesised that plasmid properties would be the primary determinants of plasmid spread and that bacterial strain identity would also contribute. We found clinical Escherichia coli strains natively associated with ESBL-plasmids conjugated to three distinct E. coli strains and one Salmonella enterica serovar Typhimurium strain. Final transconjugant frequencies varied across plasmid, donor, and recipient combinations, with qualitative consistency when comparing transfer in vitro and in vivo in mice. In both environments, transconjugant frequencies for these natural strains and plasmids covaried with the presence/absence of transfer genes on ESBL-plasmids and were affected by plasmid incompatibility. By moving ESBL-plasmids out of their native hosts, we showed that donor and recipient strains also modulated transconjugant frequencies. This suggests that plasmid spread in the complex gut environment of animals and humans can be predicted based on in vitro testing and genetic data.

Extensive antimicrobial resistance mobilization via multicopy plasmid encapsidation mediated by temperate phages

OBJECTIVES

To investigate the relevance of multicopy plasmids in antimicrobial resistance and assess their mobilization mediated by phage particles.

METHODS

Several databases with complete sequences of plasmids and annotated genes were analysed. The 16S methyltransferase gene armA conferring high-level aminoglycoside resistance was used as a marker in eight different plasmids, from different incompatibility groups, and with differing sizes and plasmid copy numbers. All plasmids were transformed into Escherichia coli bearing one of four different lysogenic phages. Upon induction, encapsidation of armA in phage particles was evaluated using qRT-PCR and Southern blotting.

RESULTS

Multicopy plasmids carry a vast set of emerging clinically important antimicrobial resistance genes. However, 60% of these plasmids do not bear mobility (MOB) genes. When carried on these multicopy plasmids, mobilization of a marker gene armA into phage capsids was up to 10000 times more frequent than when it was encoded by a large plasmid with a low copy number.

CONCLUSIONS

Multicopy plasmids and phages, two major mobile genetic elements (MGE) in bacteria, represent a novel high-efficiency transmission route of antimicrobial resistance genes that deserves further investigation.

A recently isolated human commensal Escherichia coli ST10 clone member mediates enhanced thermotolerance and tetrathionate respiration on a P1 phage-derived IncY plasmid

The ubiquitous human commensal Escherichia coli has been well investigated through its model representative E. coli K‐12. In this work, we initially characterized E. coli Fec10, a recently isolated human commensal strain of phylogroup A/sequence type ST10. Compared to E. coli K‐12, the 4.88 Mbp Fec10 genome is characterized by distinct single‐nucleotide polymorphisms and acquisition of genomic islands. In addition, E. coli Fec10 possesses a 155.86 kbp IncY plasmid, a composite element based on phage P1. pFec10 harbours multiple cargo genes such as coding for a tetrathionate reductase and its corresponding regulatory two‐component system. Among the cargo genes is also the Transmissible Locus of Protein Quality Control (TLPQC), which mediates tolerance to lethal temperatures in bacteria. The disaggregase ClpG_GI of TLPQC constitutes a major determinant of the thermotolerance of E. coli Fec10. We confirmed stand‐alone disaggregation activity, but observed distinct biochemical characteristics of ClpG_GI‐Fec10 compared to the nearly identical Pseudomonas aeruginosa ClpG_GI‐SG17M. Furthermore, we noted a unique contribution of ClpG_GI‐Fec10 to the exquisite thermotolerance of E. coli Fec10, suggesting functional differences between both disaggregases in vivo. Detection of thermotolerance in 10% of human commensal E. coli isolates hints to the successful establishment of food‐borne heat‐resistant strains in the human gut.

Plasmid diversity among genetically related Klebsiella pneumoniae blaKPC-2 and blaKPC-3 isolates collected in the Dutch national surveillance

Carbapenemase-producing Klebsiella pneumoniae emerged as a nosocomial pathogen causing morbidity and mortality in patients. For infection prevention it is important to track the spread of K. pneumoniae and its plasmids between patients. Therefore, the major aim was to recapitulate the contents and diversity of the plasmids of genetically related K. pneumoniae strains harboring the beta-lactamase gene bla_KPC-2 or bla_KPC-3 to determine their dissemination in the Netherlands and the former Dutch Caribbean islands from 2014 to 2019. Next-generation sequencing was combined with long-read third-generation sequencing to reconstruct 22 plasmids. wgMLST revealed five genetic clusters comprised of K. pneumoniae bla_KPC-2 isolates and four clusters consisted of bla_KPC-3 isolates. KpnCluster-019 bla_KPC-2 isolates were found both in the Netherlands and the Caribbean islands, while bla_KPC-3 cluster isolates only in the Netherlands. Each K. pneumoniae bla_KPC-2 or bla_KPC-3 cluster was characterized by a distinct resistome and plasmidome. However, the large and medium plasmids contained a variety of antibiotic resistance genes, conjugation machinery, cation transport systems, transposons, toxin/antitoxins, insertion sequences and prophage-related elements. The small plasmids carried genes implicated in virulence. Thus, implementing long-read plasmid sequencing analysis for K. pneumoniae surveillance provided important insights in the transmission of a KpnCluster-019 bla_KPC-2 strain between the Netherlands and the Caribbean.

Genomic Characterisation of a Multiple Drug Resistant IncHI2 ST4 Plasmid in Escherichia coli ST744 in Australia

Antibiotic resistance genes (ARGs) including those from the bla_CTX-M family and mcr-1 that encode resistance to extended spectrum β–lactams and colistin, respectively, have been linked with IncHI2 plasmids isolated from swine production facilities globally but not in IncHI2 plasmids from Australia. Here we describe the first complete sequence of a multiple drug resistance Australian IncHI2-ST4 plasmid, pTZ41_1P, from a commensal E. coli from a healthy piglet. pTZ41_1P carries genes conferring resistance to heavy-metals (copper, silver, tellurium and arsenic), β-lactams, aminoglycosides and sulphonamides. The ARGs reside within a complex resistance locus (CRL) that shows considerable sequence identity to a CRL in pSDE_SvHI2, an IncHI2:ST3 plasmid from an enterotoxigenic E. coli with serotype O157:H19 of porcine origin that caused substantial losses to swine production operations in Australia in 2007. pTZ41_1P is closely related to IncHI2 plasmids found in E. coli and Salmonella enterica from porcine, avian and human sources in Europe and China but it does not carry genes encoding resistance to clinically-important antibiotics. We identified regions of IncHI2 plasmids that contribute to the genetic plasticity of this group of plasmids and highlight how they may readily acquire new resistance gene cargo. Genomic surveillance should be improved to monitor IncHI2 plasmids.

Duplication and diversification of a unique chromosomal virulence island hosting the subtilase cytotoxin in Escherichia coli ST58

The AB5 cytotoxins are important virulence factors in Escherichia coli. The most notable members of the AB5 toxin families include Shiga toxin families 1 (Stx1) and 2 (Stx2), which are associated with enterohaemorrhagic E. coli infections causing haemolytic uraemic syndrome and haemorrhagic colitis. The subAB toxins are the newest and least well understood members of the AB5 toxin gene family. The subtilase toxin genes are divided into a plasmid-based variant, subAB1, originally described in enterohaemorrhagic E. coli O113:H21, and distinct chromosomal variants, subAB2, that reside in pathogenicity islands encoding additional virulence effectors. Previously we identified a chromosomal subAB2 operon within an E. coli ST58 strain IBS28 (ONT:H25) taken from a wild ibis nest at an inland wetland in New South Wales, Australia. Here we show the subAB2 toxin operon comprised part of a 140 kb tRNA-Phe chromosomal island that co-hosted tia, encoding an outer-membrane protein that confers an adherence and invasion phenotype and additional virulence and accessory genetic content that potentially originated from known virulence island SE-PAI. This island shared a common evolutionary history with a secondary 90 kb tRNA-Phe pathogenicity island that was presumably generated via a duplication event. IBS28 is closely related [200 single-nucleotide polymorphisms (SNPs)] to four North American ST58 strains. The close relationship between North American isolates of ST58 and IBS28 was further supported by the identification of the only copy of a unique variant of IS26 within the O-antigen gene cluster. Strain ISB28 may be a historically important E. coli ST58 genome sequence hosting a progenitor pathogenicity island encoding subAB.