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Harris EB, Ewool KKK, Bowden LC, Fierro J, Johnson D, Meinzer M, Tayler S, Grose JH. Genomic and Proteomic Analysis of Six Vi01-like Phages Reveals Wide Host Range and Multiple Tail Spike Proteins. Viruses 2024; 16:289. [PMID: 38400064 PMCID: PMC10892097 DOI: 10.3390/v16020289] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2023] [Revised: 02/05/2024] [Accepted: 02/07/2024] [Indexed: 02/25/2024] Open
Abstract
Enterobacteriaceae is a large family of Gram-negative bacteria composed of many pathogens, including Salmonella and Shigella. Here, we characterize six bacteriophages that infect Enterobacteriaceae, which were isolated from wastewater plants in the Wasatch front (Utah, United States). These phages are highly similar to the Kuttervirus vB_SenM_Vi01 (Vi01), which was isolated using wastewater from Kiel, Germany. The phages vary little in genome size and are between 157 kb and 164 kb, which is consistent with the sizes of other phages in the Vi01-like phage family. These six phages were characterized through genomic and proteomic comparison, mass spectrometry, and both laboratory and clinical host range studies. While their proteomes are largely unstudied, mass spectrometry analysis confirmed the production of five hypothetical proteins, several of which unveiled a potential operon that suggests a ferritin-mediated entry system on the Vi01-like phage family tail. However, no dependence on this pathway was observed for the single host tested herein. While unable to infect every genus of Enterobacteriaceae tested, these phages are extraordinarily broad ranged, with several demonstrating the ability to infect Salmonella enterica and Citrobacter freundii strains with generally high efficiency, as well as several clinical Salmonella enterica isolates, most likely due to their multiple tail fibers.
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Affiliation(s)
| | | | | | | | | | | | | | - Julianne H. Grose
- Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT 84604, USA; (E.B.H.); (K.K.K.E.)
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2
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Li D, Liang W, Hu Q, Ren J, Xue F, Liu Q, Tang F. The effect of a spontaneous induction prophage, phi458, on biofilm formation and virulence in avian pathogenic Escherichia coli. Front Microbiol 2022; 13:1049341. [PMID: 36452923 PMCID: PMC9701743 DOI: 10.3389/fmicb.2022.1049341] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2022] [Accepted: 10/24/2022] [Indexed: 12/25/2023] Open
Abstract
Prophage sequences are present in most bacterial genomes and account for up to 20% of its host genome. Integration of temperate phages may have an impact on the expression of host genes, while some prophages could turn into the lytic cycle and affect bacterial host biological characteristics. We investigated the role of spontaneous induction prophages in avian pathogenic Escherichia coli (APEC), which is the causative agent of avian colibacillosis in poultry, and considered a potential zoonotic bacterium related to the fact it serves as an armory of extraintestinal pathogenic E. coli. We found that APEC strain DE458 had a high spontaneous induction rate in vivo and in vitro. The released phage particles, phi458, were isolated, purified, and sequenced, and the deletion mutant, DE458Δphi458, was constructed and characterized. Biofilm formation of DE458Δphi458 was strongly decreased compared to that of the wild-type strain (p < 0.01). In addition, while the addition of DNase (100 μg/ml) did not affect prophage release but could digest eDNA, it significantly reduced the biofilm production of DE458 biofilm to a level close to that of DE458Δphi458. Compared to DE458, the adhesion and invasion abilities of DE458Δphi458 increased by approximately 6-20 times (p < 0.05). The virulence of DE458Δphi458 was enhanced by approximately 10-fold in chickens based on a 50% lethal dose. Furthermore, avian infection assays showed that the bacterial loads of DE458Δphi458 in the lung and liver were increased by 16.5- and 10-fold (p < 0.05), respectively, compared with those of the WT strain. The qRT-PCR revealed that deletion of phi458 led to upregulation of type I fimbriate-related gene fimH and curli-related gene csgC by 3- and 2.8-fold, respectively (p < 0.01). Our study revealed that phi458 promoted biofilm formation by spontaneously inducing and decreasing virulence by repressing virulence genes.
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Affiliation(s)
- Dezhi Li
- School of Health Science and Engineering, University of Shanghai for Science and Technology, Shanghai, China
- MOE Joint International Research Laboratory of Animal Health and Food Safety, Key Laboratory of Animal Bacteriology, Ministry of Agriculture, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China
| | - Wei Liang
- The Fourth Affiliated Hospital of Guangxi Medical University, Liuzhou, Guangxi, China
| | - Qingyue Hu
- School of Health Science and Engineering, University of Shanghai for Science and Technology, Shanghai, China
| | - Jianluan Ren
- MOE Joint International Research Laboratory of Animal Health and Food Safety, Key Laboratory of Animal Bacteriology, Ministry of Agriculture, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China
| | - Feng Xue
- MOE Joint International Research Laboratory of Animal Health and Food Safety, Key Laboratory of Animal Bacteriology, Ministry of Agriculture, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China
| | - Qing Liu
- School of Health Science and Engineering, University of Shanghai for Science and Technology, Shanghai, China
| | - Fang Tang
- MOE Joint International Research Laboratory of Animal Health and Food Safety, Key Laboratory of Animal Bacteriology, Ministry of Agriculture, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China
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Excision and integration of unconventional circularizable structures involving the erm(B) gene in enterococci. Vet Microbiol 2022; 273:109542. [PMID: 35969915 DOI: 10.1016/j.vetmic.2022.109542] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2022] [Revised: 08/04/2022] [Accepted: 08/07/2022] [Indexed: 11/22/2022]
Abstract
Traditionally, insertion sequences (ISs) play a major role in disseminating antimicrobial resistance genes (ARGs) in bacteria through transposition and translocation, forming regions that contain multiple ARGs flanked by single or multiple copies of IS. In addition, unconventional circularizable structures (UCSs), lacking recombinase genes but being surrounded by directly repeated sequences (DRs) of various sizes which do not contain transposase genes, were reported to be involved in the dissemination of ARGs. In this study, a novel UCS was identified on plasmid pE508-2 in E. faecalis E508, which carried a 24,411 bp multiresistance gene cluster, consisting of the resistance genes aphA3, lnu(B), lsa(E), spw, aac(A)-aph(D), lnu(B), dfrG, and two copies of aadE flanked by copies of erm(B). PCR assays revealed that three types of UCSs with lengths of 7235, 16,437, and 23,673 bp were formed, each of which contained the respective resistance genes and one copy of erm(B). Using erm(B)-negative and -positive strains, we demonstrated that erm(B)-carrying UCSs failed to transfer into an erm(B)-negative strain, but could integrate into an erm(B)-positive strain in a new site adjacent to a pre-existing erm(B) gene by natural transformation. Database searches revealed that erm(B)-flanked multiresistance gene regions, which might be able to form the respective UCSs, are present among various bacteria from different sources in various countries. In summary, this study experimentally demonstrated the excision and integration of UCS involving structures that include erm(B). The widespread presence of these UCSs in various Gram-positive bacteria highlights its role in the dissemination of ARGs among bacterial pathogens.
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Yu R, Chen Z, Li D, Schwarz S, Wang X, Du XD. Studies on the Transmission of a Tigecycline Resistance-Mediating tet(A) Gene Variant from Enterobacter hormaechei via a Two-Step Recombination Process. Microbiol Spectr 2022; 10:e0049622. [PMID: 35579466 PMCID: PMC9241890 DOI: 10.1128/spectrum.00496-22] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2022] [Accepted: 04/27/2022] [Indexed: 12/13/2022] Open
Abstract
To investigate the contribution of a tet(A) variant to tigecycline resistance in Enterobacter hormaechei and the recombination events that occurred during transmission of this variant. MICs were determined by broth microdilution. E. hormaechei G17 was characterized by PCR, transfer assay, S1-PFGE, Southern blot hybridization, and WGS analysis. A tet(A) variant conferring resistance to tigecycline was present in E. hormaechei G17. This strain harbored two resistance plasmids (pG17-1, 264,084 bp and pG17-2, 68,610 bp) and its E. coli transformant Tm-G17TGC one resistance plasmid (pTm-G17, 93,013 bp). The comparative analysis of pG17-1, pG17-2, and pTm-G17 showed that a tet(A) variant-carrying multiresistance gene cluster (~23 kb) originating from pG17-1 had integrated into pG17-2, forming the novel plasmid pTm-G17. In a first step, this multiresistance gene cluster was excised from pG17-1 by recombination of homologous sequences, including △TnAs1 at both termini, thereby generating an unconventional circularizable structure (UCS). In a second step, this UCS integrated into pG17-2 via recombination between homologous sequences, including IS26 present on both, the UCS and pG17-2, thereby giving rise to the new plasmid pTm-G17. In summary, a tet(A) variant conferring resistance to tigecycline was reported in E. hormaechei. Transfer of a tet(A) variant-carrying multiresistance gene cluster between plasmids occurred in a two-step recombination process, in which homologous sequences, including either △TnAs1 or IS26, were involved. IMPORTANCE Tigecycline is an important last-resort broad spectrum antimicrobial agent. This study describes the two-step recombination processes resulting in the transfer of the tet(A) variant gene between different plasmids in E. hormaechei, which depicts the role of recombination processes in the generation of UCSs and new plasmids, both carrying a tet(A) variant conferring resistance to tigecycline. Such processes enhance the dissemination of resistance genes, which is of particular relevance for resistance genes, such as the tet(A) variant. The presence and transmission of a tet(A) variant in E. hormaechei will compromise the efficacy of tigecycline treatment for E. hormaechei associated infection.
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Affiliation(s)
- Runhao Yu
- College of Veterinary Medicine, Henan Agricultural University, Zhengzhou, People’s Republic of China
| | - Zheng Chen
- College of Veterinary Medicine, Henan Agricultural University, Zhengzhou, People’s Republic of China
| | - Danyang Li
- College of Veterinary Medicine, Henan Agricultural University, Zhengzhou, People’s Republic of China
| | - Stefan Schwarz
- Institute of Microbiology and Epizootics, Centre for Infection Medicine, Department of Veterinary Medicine, Freie Universität Berlin, Berlin, Germany
- Veterinary Centre for Resistance Research (TZR), Freie Universität Berlin, Berlin, Germany
| | - Xinwei Wang
- College of Veterinary Medicine, Henan Agricultural University, Zhengzhou, People’s Republic of China
| | - Xiang-Dang Du
- College of Veterinary Medicine, Henan Agricultural University, Zhengzhou, People’s Republic of China
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Liu B, Hou W, Li K, Chen Q, Liu Y, Yue T. Specific gene SEN1393 contributes to higher survivability of Salmonella Enteritidis in egg white by regulating sulfate assimilation pathway. Int J Food Microbiol 2020; 337:108927. [PMID: 33152571 DOI: 10.1016/j.ijfoodmicro.2020.108927] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2020] [Revised: 10/09/2020] [Accepted: 10/12/2020] [Indexed: 11/16/2022]
Abstract
Salmonella enterica serovar Enteritidis (S. Enteritidis) presents an excellent capacity to survive in egg white, which is a hostile environment for bacterial growth. To reveal its survival mechanism, this study focuses on the specific gene SEN1393, which has been found to exist only in the genomic sequence of S. Enteritidis. The survival capacity of the deletion mutant strain ΔSEN1393 was proven to be significantly reduced after incubation in egg white. RNA sequencing and RT-qPCR results demonstrate that the expression levels of 19 genes were up-regulated, while the expression levels of 9 genes were down-regulated in egg white. These genes were classified into 6 groups based on their functional categories, namely the sulfate assimilation pathway, arginine biosynthesis, the tricarboxylic acid cycle, the fimbrial protein, the transport and chelation of metal ion, and others (sctT, rhs, and pspG). The strain ΔSEN1393 was deduced to damage FeS cluster enzymes and increase the sulfate and iron requirements, and to reduce bacterial motility and copper homeostasis. Via InterProScan analysis, the gene SEN1393 was speculated to encode a TerB-like and/or DjlA-like protein, and therefore, together with cysJ, possibly reduced the oxidative toxicities resulting from oxyanions such as tellurite, and/or improved CysPUWA conformation to restrain the uptake of the toxic oxyanions. In summary, the gene SEN1393 enabled the higher survival of S. Enteritidis in egg white as compared to other pathogens by regulating the sulfate assimilation pathway.
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Affiliation(s)
- Bin Liu
- College of Food Science and Engineering, Northwest A&F University, Yangling, China; Laboratory of Quality and Safety Risk Assessment for Agro-Products, Ministry of Agriculture, Yangling, China; National Engineering Research Center of Agriculture Integration Test, Yangling, China.
| | - Wanwan Hou
- College of Food Science and Engineering, Northwest A&F University, Yangling, China; Laboratory of Quality and Safety Risk Assessment for Agro-Products, Ministry of Agriculture, Yangling, China; National Engineering Research Center of Agriculture Integration Test, Yangling, China
| | - Ke Li
- Zhejiang Academy of Science & Technology for Inspection & Quarantine, Hangzhou, China
| | - Qing Chen
- College of Food Science and Engineering, Northwest A&F University, Yangling, China; Laboratory of Quality and Safety Risk Assessment for Agro-Products, Ministry of Agriculture, Yangling, China; National Engineering Research Center of Agriculture Integration Test, Yangling, China
| | - Yaxin Liu
- College of Food Science and Engineering, Northwest A&F University, Yangling, China; Laboratory of Quality and Safety Risk Assessment for Agro-Products, Ministry of Agriculture, Yangling, China; National Engineering Research Center of Agriculture Integration Test, Yangling, China
| | - Tianli Yue
- College of Food Science and Engineering, Northwest A&F University, Yangling, China; Laboratory of Quality and Safety Risk Assessment for Agro-Products, Ministry of Agriculture, Yangling, China; National Engineering Research Center of Agriculture Integration Test, Yangling, China
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6
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Zhang X, Payne M, Lan R. In silico Identification of Serovar-Specific Genes for Salmonella Serotyping. Front Microbiol 2019; 10:835. [PMID: 31068916 PMCID: PMC6491675 DOI: 10.3389/fmicb.2019.00835] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2018] [Accepted: 04/01/2019] [Indexed: 11/23/2022] Open
Abstract
Salmonella enterica subspecies enterica is a highly diverse subspecies with more than 1500 serovars and the ability to distinguish serovars within this group is vital for surveillance. With the development of whole-genome sequencing technology, serovar prediction by traditional serotyping is being replaced by molecular serotyping. Existing in silico serovar prediction approaches utilize surface antigen encoding genes, core genome MLST and serovar-specific gene markers or DNA fragments for serotyping. However, these serovar-specific gene markers or DNA fragments only distinguished a small number of serovars. In this study, we compared 2258 Salmonella accessory genomes to identify 414 candidate serovar-specific or lineage-specific gene markers for 106 serovars which includes 24 polyphyletic serovars and the paraphyletic serovar Enteritidis. A combination of several lineage-specific gene markers can be used for the clear identification of the polyphyletic serovars and the paraphyletic serovar. We designed and evaluated an in silico serovar prediction approach by screening 1089 genomes representing 106 serovars against a set of 131 serovar-specific gene markers. The presence or absence of one or more serovar-specific gene markers was used to predict the serovar of an isolate from genomic data. We show that serovar-specific gene markers have comparable accuracy to other in silico serotyping methods with 84.8% of isolates assigned to the correct serovar with no false positives (FP) and false negatives (FN) and 10.5% of isolates assigned to a small subset of serovars containing the correct serovar with varied FP. Combined, 95.3% of genomes were correctly assigned to a serovar. This approach would be useful as diagnosis moves to culture-independent and metagenomic methods as well as providing a third alternative to confirm other genome-based analyses. The identification of a set of gene markers may also be useful in the development of more cost-effective molecular assays designed to detect specific gene markers of the all major serovars in a region. These assays would be useful in serotyping isolates where cultures are no longer obtained and traditional serotyping is therefore impossible.
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Affiliation(s)
- Xiaomei Zhang
- School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, NSW, Australia
| | - Michael Payne
- School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, NSW, Australia
| | - Ruiting Lan
- School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, NSW, Australia
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Neutral barcoding of genomes reveals the dynamics of Salmonella colonization in cattle and their peripheral lymph nodes. Vet Microbiol 2018; 220:97-106. [PMID: 29885808 DOI: 10.1016/j.vetmic.2018.05.007] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2018] [Revised: 05/15/2018] [Accepted: 05/15/2018] [Indexed: 12/22/2022]
Abstract
Feedlot cattle often contain Salmonella. The number of bacteria that initiate colonization of different cattle organs and the bacterial migration within these large animals are poorly understood. To investigate these questions, we constructed wild-type isogenic tagged strains (WITS) of Salmonella by inserting 21-base barcodes flanked by Illumina sequencing primers into a neutral genome location. We then delivered several different pools of uniquely barcoded clones orally and into multiple intradermal sites, in individual Holstein steers, and subsequently performed Salmonella-directed sequence tag-based analysis of microbial populations (STAMP). Using high-throughput sequencing of the barcodes of Salmonella grown from steer lymph nodes, organs and feces, we monitored how individual barcoded clones travel from different entry sites within animals. Data showed that gastrointestinal colonization was established by up to hundreds of Salmonella founder cells, whereas peripheral lymph nodes were usually colonized by very low numbers of founding bacteria, often originating from the nearest draining intradermal delivery site. Transmission of Salmonella from the gastrointestinal tract to the lymphatic system was frequently observed, whereas entry of intradermally delivered bacteria into the gut was rare. Bacteria undergo limited extraintestinal proliferation within or prior to arrival at peripheral lymph nodes. Overall, the application of the STAMP technique facilitated characterization of the migration routes and founder population size of Salmonella within feedlot cattle and their organs and lymph nodes in unprecedented detail.
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Comparative genomics identifies distinct lineages of S. Enteritidis from Queensland, Australia. PLoS One 2018; 13:e0191042. [PMID: 29338017 PMCID: PMC5770046 DOI: 10.1371/journal.pone.0191042] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2017] [Accepted: 12/27/2017] [Indexed: 11/19/2022] Open
Abstract
Salmonella enterica is a major cause of gastroenteritis and foodborne illness in Australia where notification rates in the state of Queensland are the highest in the country. S. Enteritidis is among the five most common serotypes reported in Queensland and it is a priority for epidemiological surveillance due to concerns regarding its emergence in Australia. Using whole genome sequencing, we have analysed the genomic epidemiology of 217 S. Enteritidis isolates from Queensland, and observed that they fall into three distinct clades, which we have differentiated as Clades A, B and C. Phage types and MLST sequence types differed between the clades and comparative genomic analysis has shown that each has a unique profile of prophage and genomic islands. Several of the phage regions present in the S. Enteritidis reference strain P125109 were absent in Clades A and C, and these clades also had difference in the presence of pathogenicity islands, containing complete SPI-6 and SPI-19 regions, while P125109 does not. Antimicrobial resistance markers were found in 39 isolates, all but one of which belonged to Clade B. Phylogenetic analysis of the Queensland isolates in the context of 170 international strains showed that Queensland Clade B isolates group together with the previously identified global clade, while the other two clades are distinct and appear largely restricted to Australia. Locally sourced environmental isolates included in this analysis all belonged to Clades A and C, which is consistent with the theory that these clades are a source of locally acquired infection, while Clade B isolates are mostly travel related.
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Azpiroz MF, Laviña M. Analysis of RecA-independent recombination events between short direct repeats related to a genomic island and to a plasmid in Escherichia coli K12. PeerJ 2017; 5:e3293. [PMID: 28503377 PMCID: PMC5426353 DOI: 10.7717/peerj.3293] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2017] [Accepted: 04/10/2017] [Indexed: 02/03/2023] Open
Abstract
RecA-independent recombination events between short direct repeats, leading to deletion of the intervening sequences, were found to occur in two genetic models in the Escherichia coli K12 background. The first model was a small E. coli genomic island which had been shown to be mobile in its strain of origin and, when cloned, also in the E. coli K12 context. However, it did not encode a site-specific recombinase as mobile genomic islands usually do. It was then deduced that the host cells should provide the recombination function. This latter was searched for by means of a PCR approach to detect the island excision in E. coli K12 mutants affected in a number of recombination functions, including the 16 E. coli K12 site-specific recombinases, the RecET system, and multiple proteins that participate in the RecA-dependent pathways of homologous recombination. None of these appeared to be involved in the island excision. The second model, analyzed in a RecA deficient context, was a plasmid construction containing a short direct repeat proceeding from Saccharomyces cerevisiae, which flanked the cat gene. The excision of this gene by recombination of the DNA repeats was confirmed by PCR and through the detection, recovery and characterization of the plasmid deleted form. In sum, we present new evidence on the occurrence of RecA-independent recombination events in E. coli K12. Although the mechanism underlying these processes is still unknown, their existence suggests that RecA-independent recombination may confer mobility to other genetic elements, thus contributing to genome plasticity.
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Affiliation(s)
- María F Azpiroz
- Fisiología y Genética Bacterianas, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay
| | - Magela Laviña
- Fisiología y Genética Bacterianas, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay
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10
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Nieto PA, Pardo-Roa C, Salazar-Echegarai FJ, Tobar HE, Coronado-Arrázola I, Riedel CA, Kalergis AM, Bueno SM. New insights about excisable pathogenicity islands in Salmonella and their contribution to virulence. Microbes Infect 2016; 18:302-9. [DOI: 10.1016/j.micinf.2016.02.001] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2015] [Revised: 02/05/2016] [Accepted: 02/09/2016] [Indexed: 12/15/2022]
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Gómez RS, Ramirez BA, Céspedes PF, Cautivo KM, Riquelme SA, Prado CE, González PA, Kalergis AM. Contribution of Fcγ receptors to human respiratory syncytial virus pathogenesis and the impairment of T-cell activation by dendritic cells. Immunology 2016; 147:55-72. [PMID: 26451966 PMCID: PMC4693880 DOI: 10.1111/imm.12541] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2015] [Revised: 09/16/2015] [Accepted: 09/29/2015] [Indexed: 12/11/2022] Open
Abstract
Human respiratory syncytial virus (hRSV) is the leading cause of infant hospitalization related to respiratory disease. Infection with hRSV produces abundant infiltration of immune cells into the airways, which combined with an exacerbated pro-inflammatory immune response can lead to significant damage to the lungs. Human RSV re-infection is extremely frequent, suggesting that this virus may have evolved molecular mechanisms that interfere with host adaptive immunity. Infection with hRSV can be reduced by administering a humanized neutralizing antibody against the virus fusion protein in high-risk infants. Although neutralizing antibodies against hRSV effectively block the infection of airway epithelial cells, here we show that both, bone marrow-derived dendritic cells (DCs) and lung DCs undergo infection with IgG-coated virus (hRSV-IC), albeit abortive. Yet, this is enough to negatively modulate DC function. We observed that such a process is mediated by Fcγ receptors (FcγRs) expressed on the surface of DCs. Remarkably, we also observed that in the absence of hRSV-specific antibodies FcγRIII knockout mice displayed significantly less cellular infiltration in the lungs after hRSV infection, compared with wild-type mice, suggesting a potentially harmful, IgG-independent role for this receptor in hRSV disease. Our findings support the notion that FcγRs can contribute significantly to the modulation of DC function by hRSV and hRSV-IC. Further, we provide evidence for an involvement of FcγRIII in the development of hRSV pathogenesis.
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MESH Headings
- Adaptive Immunity
- Animals
- Antibodies, Neutralizing/pharmacology
- Antibodies, Viral/immunology
- Antibodies, Viral/metabolism
- Antiviral Agents/pharmacology
- Cells, Cultured
- Coculture Techniques
- Cytokines/metabolism
- Dendritic Cells/drug effects
- Dendritic Cells/immunology
- Dendritic Cells/metabolism
- Dendritic Cells/virology
- Disease Models, Animal
- Immunoglobulin G/immunology
- Immunoglobulin G/metabolism
- Lung/drug effects
- Lung/immunology
- Lung/metabolism
- Lung/virology
- Lymphocyte Activation/drug effects
- Mice, Inbred C57BL
- Mice, Knockout
- Palivizumab/pharmacology
- Receptors, IgG/deficiency
- Receptors, IgG/genetics
- Receptors, IgG/immunology
- Receptors, IgG/metabolism
- Respiratory Syncytial Virus Infections/drug therapy
- Respiratory Syncytial Virus Infections/genetics
- Respiratory Syncytial Virus Infections/immunology
- Respiratory Syncytial Virus Infections/metabolism
- Respiratory Syncytial Virus Infections/virology
- Respiratory Syncytial Virus, Human/drug effects
- Respiratory Syncytial Virus, Human/immunology
- Respiratory Syncytial Virus, Human/pathogenicity
- Signal Transduction
- T-Lymphocytes/drug effects
- T-Lymphocytes/immunology
- T-Lymphocytes/metabolism
- T-Lymphocytes/virology
- Viral Load
- Virus Replication
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Affiliation(s)
- Roberto S. Gómez
- Millennium Institute on Immunology and ImmunotherapyDepartamento de Genética Molecular y MicrobiologíaFacultad de Ciencias BiológicasPontificia Universidad Católica de ChileSantiago de ChileChile
| | - Bruno A. Ramirez
- Millennium Institute on Immunology and ImmunotherapyDepartamento de Genética Molecular y MicrobiologíaFacultad de Ciencias BiológicasPontificia Universidad Católica de ChileSantiago de ChileChile
| | - Pablo F. Céspedes
- Millennium Institute on Immunology and ImmunotherapyDepartamento de Genética Molecular y MicrobiologíaFacultad de Ciencias BiológicasPontificia Universidad Católica de ChileSantiago de ChileChile
| | - Kelly M. Cautivo
- Millennium Institute on Immunology and ImmunotherapyDepartamento de Genética Molecular y MicrobiologíaFacultad de Ciencias BiológicasPontificia Universidad Católica de ChileSantiago de ChileChile
| | - Sebastián A. Riquelme
- Millennium Institute on Immunology and ImmunotherapyDepartamento de Genética Molecular y MicrobiologíaFacultad de Ciencias BiológicasPontificia Universidad Católica de ChileSantiago de ChileChile
- INSERM U1064NantesFrance
| | - Carolina E. Prado
- Millennium Institute on Immunology and ImmunotherapyDepartamento de Genética Molecular y MicrobiologíaFacultad de Ciencias BiológicasPontificia Universidad Católica de ChileSantiago de ChileChile
| | - Pablo A. González
- Millennium Institute on Immunology and ImmunotherapyDepartamento de Genética Molecular y MicrobiologíaFacultad de Ciencias BiológicasPontificia Universidad Católica de ChileSantiago de ChileChile
| | - Alexis M. Kalergis
- Millennium Institute on Immunology and ImmunotherapyDepartamento de Genética Molecular y MicrobiologíaFacultad de Ciencias BiológicasPontificia Universidad Católica de ChileSantiago de ChileChile
- INSERM U1064NantesFrance
- Departamento de ReumatologíaFacultad de Medicina. Pontificia Universidad Católica de ChileSantiago de ChileChile
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Mucosal immunization of BALB/c mice with DNA vaccines encoding the SEN1002 and SEN1395 open reading frames of Salmonella enterica serovar Enteritidis induces protective immunity. Epidemiol Infect 2015; 144:247-56. [PMID: 26113459 DOI: 10.1017/s095026881500120x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Salmonella Enteritidis is the main cause of foodborne salmonellosis worldwide. The limited effectiveness of current interventions against this pathogen has been the main incentive to develop new methods for the efficient control of this infection. To investigate the use of DNA vaccines against S. Enteritidis in humans, immune responses stimulated by two plasmids containing the genes designated SEN1002, located in the pathogenicity island SPI-19 and encoding a Hcp protein involved in transport mechanisms, and SEN1395, located in the genomic island ΦSE14 and encoding a protein of a new superfamily of lysozymes, were evaluated. Humoral and cellular responses following intranasal immunization of two groups of BALB/c mice with the plasmids pV1002 and pV1395 plus adjuvant were evaluated and it was observed that the IgG2a/IgG1 ratios were sixfold higher than control groups. Both plasmids stimulated specific secretory IgA production. Increased proliferation of lymphocytes and IFN-γ production were detected in both experimental groups. DNA-vaccinated mice developed protective immunity against a virulent strain of S. Enteritidis, with nearly 2 logs of protection level compared to the negative control values in the spleen. Therefore, DNA vaccines are efficient at stimulating cellular and humoral immune responses at systemic and mucosal levels.
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13
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Microarray-based detection of Salmonella enterica serovar Enteritidis genes involved in chicken reproductive tract colonization. Appl Environ Microbiol 2014; 80:7710-6. [PMID: 25281378 DOI: 10.1128/aem.02867-14] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Salmonella enterica serovar Enteritidis has developed the potential to contaminate table eggs internally, by colonization of the chicken reproductive tract and internalization in the forming egg. The serotype Enteritidis has developed mechanisms to colonize the chicken oviduct more successfully than other serotypes. Until now, the strategies exploited by Salmonella Enteritidis to do so have remained largely unknown. For that reason, a microarray-based transposon library screen was used to identify genes that are essential for the persistence of Salmonella Enteritidis inside primary chicken oviduct gland cells in vitro and inside the reproductive tract in vivo. A total of 81 genes with a potential role in persistence in both the oviduct cells and the oviduct tissue were identified. Major groups of importance include the Salmonella pathogenicity islands 1 and 2, genes involved in stress responses, cell wall, and lipopolysaccharide structure, and the region-of-difference genomic islands 9, 21, and 40.
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14
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Unconventional circularizable bacterial genetic structures carrying antibiotic resistance determinants. Antimicrob Agents Chemother 2013; 57:2440-1. [PMID: 23580584 DOI: 10.1128/aac.02548-12] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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The type VI secretion system encoded in Salmonella pathogenicity island 19 is required for Salmonella enterica serotype Gallinarum survival within infected macrophages. Infect Immun 2013; 81:1207-20. [PMID: 23357385 DOI: 10.1128/iai.01165-12] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Salmonella enterica serotype Gallinarum is the causative agent of fowl typhoid, a disease characterized by high morbidity and mortality that causes major economic losses in poultry production. We have reported that S. Gallinarum harbors a type VI secretion system (T6SS) encoded in Salmonella pathogenicity island 19 (SPI-19) that is required for efficient colonization of chicks. In the present study, we aimed to characterize the SPI-19 T6SS functionality and to investigate the mechanisms behind the phenotypes previously observed in vivo. Expression analyses revealed that SPI-19 T6SS core components are expressed and produced under in vitro bacterial growth conditions. However, secretion of the structural/secreted components Hcp1, Hcp2, and VgrG to the culture medium could not be determined, suggesting that additional signals are required for T6SS-dependent secretion of these proteins. In vitro bacterial competition assays failed to demonstrate a role for SPI-19 T6SS in interbacterial killing. In contrast, cell culture experiments with murine and avian macrophages (RAW264.7 and HD11, respectively) revealed production of a green fluorescent protein-tagged version of VgrG soon after Salmonella uptake. Furthermore, infection of RAW264.7 and HD11 macrophages with deletion mutants of SPI-19 or strains with genes encoding specific T6SS core components (clpV and vgrG) revealed that SPI-19 T6SS contributes to S. Gallinarum survival within macrophages at 20 h postuptake. SPI-19 T6SS function was not linked to Salmonella-induced cytotoxicity or cell death of infected macrophages, as has been described for other T6SS. Our data indicate that SPI-19 T6SS corresponds to a novel tool used by Salmonella to survive within host cells.
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Transposon mutagenesis of Salmonella enterica serovar Enteritidis identifies genes that contribute to invasiveness in human and chicken cells and survival in egg albumen. Infect Immun 2012; 80:4203-15. [PMID: 22988017 DOI: 10.1128/iai.00790-12] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Salmonella enterica serovar Enteritidis is an important food-borne pathogen, and chickens are a primary reservoir of human infection. While most knowledge about Salmonella pathogenesis is based on research conducted on Salmonella enterica serovar Typhimurium, S. Enteritidis is known to have pathobiology specific to chickens that impacts epidemiology in humans. Therefore, more information is needed about S. Enteritidis pathobiology in comparison to that of S. Typhimurium. We used transposon mutagenesis to identify S. Enteritidis virulence genes by assay of invasiveness in human intestinal epithelial (Caco-2) cells and chicken liver (LMH) cells and survival within chicken (HD-11) macrophages as a surrogate marker for virulence. A total of 4,330 transposon insertion mutants of an invasive G1 Nal(r) strain were screened using Caco-2 cells. This led to the identification of attenuating mutations in a total of 33 different loci, many of which include genes previously known to contribute to enteric infection (e.g., Salmonella pathogenicity island 1 [SPI-1], SPI-4, SPI-5, CS54, fliH, fljB, csgB, spvR, and rfbMN) in S. Enteritidis and other Salmonella serovars. Several genes or genomic islands that have not been reported previously (e.g., SPI-14, ksgA, SEN0034, SEN2278, and SEN3503) or that are absent in S. Typhimurium or in most other Salmonella serovars (e.g., pegD, SEN1152, SEN1393, and SEN1966) were also identified. Most mutants with reduced Caco-2 cell invasiveness also showed significantly reduced invasiveness in chicken liver cells and impaired survival in chicken macrophages and in egg albumen. Consequently, these genes may play an important role during infection of the chicken host and also contribute to successful egg contamination by S. Enteritidis.
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Streptococcus pneumoniae transposon Tn1545/Tn6003 changes to Tn6002 due to spontaneous excision in circular form of the erm(B)- and aphA3-containing macrolide-aminoglycoside-streptothricin (MAS) element. Antimicrob Agents Chemother 2012; 56:5994-7. [PMID: 22890760 DOI: 10.1128/aac.01487-12] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The macrolide-aminoglycoside-streptothricin (MAS) element, an ∼4.2-kb insertion containing erm(B) and aphA3 resistance determinants, distinguishes Streptococcus pneumoniae transposon Tn1545/Tn6003 from Tn6002. Here, it is shown to be an unstable genetic element that, although it lacks recombinase genes, can exploit long, erm(B)-containing direct repeats acting as att sites for spontaneous excision that may result in loss. Consequent to excision, which is RecA independent, Tn1545/Tn6003 changes to Tn6002. In pneumococcal populations harboring Tn1545/Tn6003, the latter appears to coexist with Tn6002.
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18
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Characterization of a Streptococcus suis tet(O/W/32/O)-carrying element transferable to major streptococcal pathogens. Antimicrob Agents Chemother 2012; 56:4697-702. [PMID: 22710115 DOI: 10.1128/aac.00629-12] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mosaic tetracycline resistance determinants are a recently discovered class of hybrids of ribosomal protection tet genes. They may show different patterns of mosaicism, but their final size has remained unaltered. Initially thought to be confined to a small group of anaerobic bacteria, mosaic tet genes were then found to be widespread. In the genus Streptococcus, a mosaic tet gene [tet(O/W/32/O)] was first discovered in Streptococcus suis, an emerging drug-resistant pig and human pathogen. In this study, we report the molecular characterization of a tet(O/W/32/O) gene-carrying mobile element from an S. suis isolate. tet(O/W/32/O) was detected, in tandem with tet(40), in a circular 14,741-bp genetic element (39.1% G+C; 17 open reading frames [ORFs] identified). The novel element, which we designated 15K, also carried the macrolide resistance determinant erm(B) and an aminoglycoside resistance four-gene cluster including aadE (streptomycin) and aphA (kanamycin). 15K appeared to be an unstable genetic element that, in the absence of recombinases, is capable of undergoing spontaneous excision under standard growth conditions. In the integrated form, 15K was found inside a 54,879-bp integrative and conjugative element (ICE) (50.5% G+C; 55 ORFs), which we designated ICESsu32457. An ∼1.3-kb segment that apparently served as the att site for excision of the unstable 15K element was identified. The novel ICE was transferable at high frequency to recipients from pathogenic Streptococcus species (S. suis, Streptococcus pyogenes, Streptococcus pneumoniae, and Streptococcus agalactiae), suggesting that the multiresistance 15K element can successfully spread within streptococcal populations.
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Characterization of the ELPhiS prophage from Salmonella enterica serovar Enteritidis strain LK5. Appl Environ Microbiol 2012; 78:1785-93. [PMID: 22247173 DOI: 10.1128/aem.07241-11] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Phages are a primary driving force behind the evolution of bacterial pathogens by transferring a variety of virulence genes into their hosts. Similar to other bacterial genomes, the Salmonella enterica serovar Enteritidis LK5 genome contains several regions that are homologous to phages. Although genomic analysis demonstrated the presence of prophages, it was unable to confirm which phage elements within the genome were viable. Genetic markers were used to tag one of the prophages in the genome to allow monitoring of phage induction. Commonly used laboratory strains of Salmonella were resistant to phage infection, and therefore a rapid screen was developed to identify susceptible hosts. This approach showed that a genetically tagged prophage, ELPhiS (Enteritidis lysogenic phage S), was capable of infecting Salmonella serovars that are diverse in host range and virulence and has the potential to laterally transfer genes between these serovars via lysogenic conversion. The rapid screen approach is adaptable to any system with a large collection of isolates and may be used to test the viability of prophages found by sequencing the genomes of various bacterial pathogens.
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20
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Infection of mice by Salmonella enterica serovar Enteritidis involves additional genes that are absent in the genome of serovar Typhimurium. Infect Immun 2011; 80:839-49. [PMID: 22083712 DOI: 10.1128/iai.05497-11] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Salmonella enterica serovar Enteritidis causes a systemic, typhoid-like infection in newly hatched poultry and mice. In the present study, a library of 54,000 transposon mutants of S. Enteritidis phage type 4 (PT4) strain P125109 was screened for mutants deficient in the in vivo colonization of the BALB/c mouse model using a microarray-based negative-selection screening. Mutants in genes known to contribute to systemic infection (e.g., Salmonella pathogenicity island 2 [SPI-2], aro, rfa, rfb, phoP, and phoQ) and enteric infection (e.g., SPI-1 and SPI-5) in this and other Salmonella serovars displayed colonization defects in our assay. In addition, a strong attenuation was observed for mutants in genes and genomic islands that are not present in S. Typhimurium or in most other Salmonella serovars. These genes include a type I restriction/modification system (SEN4290 to SEN4292), the peg fimbrial operon (SEN2144A to SEN2145B), a putative pathogenicity island (SEN1970 to SEN1999), and a type VI secretion system remnant SEN1001, encoding a hypothetical protein containing a lysin motif (LysM) domain associated with peptidoglycan binding. Proliferation defects for mutants in these individual genes and in exemplar genes for each of these clusters were confirmed in competitive infections with wild-type S. Enteritidis. A ΔSEN1001 mutant was defective for survival within RAW264.7 murine macrophages in vitro. Complementation assays directly linked the SEN1001 gene to phenotypes observed in vivo and in vitro. The genes identified here may perform novel virulence functions not characterized in previous Salmonella models.
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Quiroz TS, Nieto PA, Tobar HE, Salazar-Echegarai FJ, Lizana RJ, Quezada CP, Santiviago CA, Araya DV, Riedel CA, Kalergis AM, Bueno SM. Excision of an unstable pathogenicity island in Salmonella enterica serovar Enteritidis is induced during infection of phagocytic cells. PLoS One 2011; 6:e26031. [PMID: 22039432 PMCID: PMC3198454 DOI: 10.1371/journal.pone.0026031] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2011] [Accepted: 09/15/2011] [Indexed: 12/28/2022] Open
Abstract
The availability of the complete genome sequence of several Salmonella enterica serovars has revealed the presence of unstable genetic elements in these bacteria, such as pathogenicity islands and prophages. This is the case of Salmonella enterica serovar Enteritidis (S. Enteritidis), a bacterium that causes gastroenteritis in humans and systemic infection in mice. The whole genome sequence analysis for S. Enteritidis unveiled the presence of several genetic regions that are absent in other Salmonella serovars. These regions have been denominated “regions of difference” (ROD). In this study we show that ROD21, one of such regions, behaves as an unstable pathogenicity island. We observed that ROD21 undergoes spontaneous excision by two independent recombination events, either under laboratory growth conditions or during infection of murine cells. Importantly, we also found that one type of excision occurred at higher rates when S. Enteritidis was residing inside murine phagocytic cells. These data suggest that ROD21 is an unstable pathogenicity island, whose frequency of excision depends on the environmental conditions found inside phagocytic cells.
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Affiliation(s)
- Tania S. Quiroz
- Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Millennium Institute on Immunology and Immunotherapy, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Pamela A. Nieto
- Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Millennium Institute on Immunology and Immunotherapy, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Hugo E. Tobar
- Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Millennium Institute on Immunology and Immunotherapy, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Francisco J. Salazar-Echegarai
- Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Millennium Institute on Immunology and Immunotherapy, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Rodrigo J. Lizana
- Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Millennium Institute on Immunology and Immunotherapy, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Carolina P. Quezada
- Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, Santiago, Chile
| | - Carlos A. Santiviago
- Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, Santiago, Chile
| | - Daniela V. Araya
- Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Millennium Institute on Immunology and Immunotherapy, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Claudia A. Riedel
- Facultad de Ciencias Biológicas y Facultad de Medicina, Millennium Institute on Immunology and Immunotherapy, Universidad Andrés Bello, Santiago, Chile
| | - Alexis M. Kalergis
- Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Millennium Institute on Immunology and Immunotherapy, Pontificia Universidad Católica de Chile, Santiago, Chile
- Departamento de Reumatología, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Susan M. Bueno
- Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Millennium Institute on Immunology and Immunotherapy, Pontificia Universidad Católica de Chile, Santiago, Chile
- * E-mail:
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Azpiroz MF, Bascuas T, Laviña M. Microcin H47 system: an Escherichia coli small genomic island with novel features. PLoS One 2011; 6:e26179. [PMID: 22022554 PMCID: PMC3191183 DOI: 10.1371/journal.pone.0026179] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2011] [Accepted: 09/21/2011] [Indexed: 11/19/2022] Open
Abstract
Genomic islands are DNA regions containing variable genetic information related to secondary metabolism. Frequently, they have the ability to excise from and integrate into replicons through site-specific recombination. Thus, they are usually flanked by short direct repeats that act as attachment sites, and contain genes for an integrase and an excisionase which carry out the genetic exchange. These mobility events would be at the basis of the horizontal transfer of genomic islands among bacteria. Microcin H47 is a ribosomally-synthesized antibacterial peptide that belongs to the group of chromosome-encoded microcins. The 13 kb-genetic system responsible for its production resides in the chromosome of the Escherichia coli H47 strain and is flanked by extensive and imperfect direct repeats. In this work, both excision and integration of the microcin H47 system were experimentally detected. The analyses were mainly performed in E. coli K12 cells carrying the microcin system cloned in a multicopy plasmid. As expected of a site-specific recombination event, the genetic exchange also occurred in a context deficient for homologous recombination. The DNA sequence of the attachment sites resulting from excision were hybrid between the sequences of the direct repeats. Unexpectedly, different hybrid attachment sites appeared which resulted from recombination in four segments of identity between the direct repeats. Genes encoding the trans-acting proteins responsible for the site-specific recombination were shown to be absent in the microcin H47 system. Therefore, they should be provided by the remaining genetic context, not only in the H47 strain but also in E. coli K12 cells, where both excision and integration occurred. Moreover, a survey of the attachment sites in data banks revealed that they are widely spread among E. coli strains. It is concluded that the microcin system is a small island –H47 genomic island- that would employ a parasitic strategy for its mobility.
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Affiliation(s)
- María F Azpiroz
- Sección Fisiología y Genética Bacterianas, Facultad de Ciencias, Montevideo, Uruguay.
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Distribution of classical and nonclassical virulence genes in enterotoxigenic Escherichia coli isolates from Chilean children and tRNA gene screening for putative insertion sites for genomic islands. J Clin Microbiol 2011; 49:3198-203. [PMID: 21775541 DOI: 10.1128/jcm.02473-10] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Enterotoxigenic Escherichia coli (ETEC) is an important cause of diarrhea. Three adhesins (Tia, TibA, EtpA), an iron acquisition system (Irp1, Irp2, and FyuA), a GTPase (LeoA), and an autotransporter (EatA) are ETEC virulence-related proteins that, in contrast to the classical virulence factors (enterotoxins and fimbrial colonization factors) have not heretofore been targets in characterizing isolates from epidemiological studies. Here, we determined the occurrence of these nonclassical virulence genes in 103 ETEC isolates from Chilean children with diarrhea and described their association with O serogroups and classical virulence determinants. Because tia, leoA, irp2, and fyuA are harbored by pathogenicity islands inserted into the selC and asnT tRNA genes (tDNAs), we analyzed the regions flanking these loci. Ten additional tDNAs were also screened to identify hot spots for genetic insertions. Associations between the most frequent serogroups and classical colonization factor (CF)-toxin profiles included O6/LT-STh/CS1-CS3-CS21 (i.e., O6 serogroup, heat-labile [LT] and human heat-stable [STh] enterotoxins, and CFs CS1, -3 and -21), O6/LT-STh/CS2-CS3-CS21, and O104-O127/STh/CFAI-CS21. The eatA and etpA genes were detected in more than 70% of the collection, including diverse serogroups and virulence profiles. Sixteen percent of the ETEC strains were negative for classical and nonclassical adhesins, suggesting the presence of unknown determinants of adhesion. The leuX, thrW, and asnT tDNAs were disrupted in more than 65% of strains, suggesting they are hot spots for the insertion of mobile elements. Sequences similar to integrase genes were identified next to the thrW, asnT, pheV, and selC tDNAs. We propose that the eatA and etpA genes should be included in characterizations of ETEC isolates in future epidemiological studies to determine their prevalence in other geographical regions. Sequencing of tDNA-associated genetic insertions might identify new ETEC virulence determinants.
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