RESUMO
BACKGROUND: Plant pathogens are under significant selective pressure by the plant host. Consequently, they are expected to have adapted to this condition or contribute to evading plant defenses. In order to acquire long-term fitness, plant bacterial pathogens are usually forced to maintain advantageous genetic diversity in populations. This strategy ensures that different alleles in the pathogen's gene pool are maintained in a population at frequencies larger than expected under neutral evolution. This selective process, known as balancing selection, is the subject of this work in the context of a common bacterial phytopathogen. We performed a genome-wide scan of Ralstonia solanacearum species complex, an aggressive plant bacterial pathogen that shows broad host range and causes a devastating disease called 'bacterial wilt'. RESULTS: Using a sliding window approach, we analyzed 57 genomes from three phylotypes of the R. solanacearum species complex to detect signatures of balancing selection. A total of 161 windows showed extreme values in three summary statistics of population genetics: Tajima's D, θw and Fu & Li's D*. We discarded any confounding effects due to demographic events by means of coalescent simulations of genetic data. The prospective windows correspond to 78 genes with known function that map in any of the two main replicons (1.7% of total number of genes). The candidate genes under balancing selection are related to primary metabolism and other basal activities (51.3%) or directly associated to virulence (48.7%), the latter being involved in key functions targeted to dismantle plant defenses or to participate in critical stages in the pathogenic process. CONCLUSIONS: We identified various genes under balancing selection that play a significant role in basic metabolism as well as in virulence of the R. solanacearum species complex. These genes are useful to understand and monitor the evolution of bacterial pathogen populations and emerge as potential candidates for future treatments to induce specific plant immune responses.
Assuntos
Ralstonia solanacearum/genética , Ralstonia solanacearum/patogenicidade , Evolução Biológica , Genoma Bacteriano , Especificidade de Hospedeiro , Doenças das Plantas/microbiologia , Plantas , Estudos Prospectivos , Ralstonia solanacearum/citologia , VirulênciaRESUMO
Enteroaggregative E. coli strains are important causes of diarrhea worldwide and are the second most important bacterial cause of travelers' diarrhea (TD). Pathogenicity of EAEC is not completely understood. We investigated the occurrence of putative virulence related genes (VRG), aatA, aggR and aaiC, in a nested case-control study of a cohort of US travelers >18 years of age, visited either Guatemala or Mexico. Fecal samples were collected between 2008 and 2012 from patients with TD from whom a HEp-2â¯cell adherent EAEC strain was identified (Cases) and from healthy subjects in the same locale without diarrhea from whom enteric pathogens were not isolated (Controls). Thirty-one subjects with acquired TD at destination was compared with 32 healthy controls. aaiC was the most expressed virulence related gene in 21 (67.7%) cases vs. 2 (6.3%) controls, (Pâ¯<â¯0.000). aggR was found in 18 (58.1%) cases vs. 1 (3.1%) control, (Pâ¯<â¯0.000). aatA in 9 (29.0%) cases vs. 1 (3.1%) control (Pâ¯<â¯0.006). With genes combined, aaiC+aggR were seen together in 18 (58.1%) cases vs. 1 (3.1%) control (Pâ¯<â¯0.000); aaiC+aatA were identified in 9 (29.0%) cases vs. 1 (3.1%) control (Pâ¯<â¯0.006); aggR+aatA were present in 9 (29.0%) cases vs. 1 (3.1%) control, (Pâ¯<â¯0.006). All three putative genes, aaiC+aggR+aatA were found in 9 (29.0%) cases vs. 1 (3.1%) control, (Pâ¯<â¯0.006). The PCR products showed that aaiC, aggR, and aatA occurred in higher frequency and were more commonly associated with EAEC in cases of TD acquired in the two countries of study, as compared to controls. aaiC was found in all cases from Guatemala. Further research is needed to study geographic and host factors in EAEC-causing travelers' diarrhea.
Assuntos
Proteínas da Membrana Bacteriana Externa/genética , Diarreia/microbiologia , Proteínas de Escherichia coli/genética , Escherichia coli/genética , Genes Bacterianos/genética , Transativadores/genética , Viagem , Fatores de Virulência/genética , Adulto , Estudos de Casos e Controles , Diarreia/epidemiologia , Infecções por Escherichia coli/epidemiologia , Infecções por Escherichia coli/microbiologia , Fezes/microbiologia , Guatemala/epidemiologia , Humanos , México/epidemiologia , Prevalência , Virulência/genéticaRESUMO
Molecular characterization of virulence and antimicrobial resistance profiles were determined for Shigella species isolated from children with diarrhea in Fortaleza, Brazil. Fecal specimens were collected along with socioeconomic and clinical data from children with moderate to severe diarrhea requiring emergency care. Shigella spp. were isolated by standard microbiological techniques, and we developed 4 multiplex polymerase chain reaction assays to detect 16 virulence-related genes (VRGs). Antimicrobial susceptibility tests were performed using disk diffusion assays. S. flexneri and S. sonnei were the predominant serogroups. S. flexneri was associated with low monthly incomes; more severe disease; higher number of VRGs; and presence of pic, set, and sepA genes. The SepA gene was associated with more intense abdominal pain. S. flexneri was correlated with resistance to ampicillin and chloramphenicol, whereas S. sonnei was associated with resistance to azithromycin. Strains harboring higher numbers of VRGs were associated with resistance to more antimicrobials. We highlight the correlation between presence of S. flexneri and sepA, and increased virulence and suggest a link to socioeconomic change in northeastern Brazil. Additionally, antimicrobial resistance was associated with serogroup specificity in Shigella spp. and increased bacterial VRGs.
Assuntos
Antibacterianos/farmacologia , Disenteria Bacilar/microbiologia , Shigella flexneri/genética , Shigella flexneri/patogenicidade , Shigella sonnei/genética , Shigella sonnei/patogenicidade , Ampicilina/farmacologia , Azitromicina/farmacologia , Proteínas de Bactérias/genética , Brasil , Cloranfenicol/farmacologia , Testes de Sensibilidade a Antimicrobianos por Disco-Difusão , Farmacorresistência Bacteriana , Disenteria Bacilar/tratamento farmacológico , Humanos , Reação em Cadeia da Polimerase Multiplex/métodos , Serina Proteases/genética , Shigella flexneri/efeitos dos fármacos , Shigella flexneri/isolamento & purificação , Shigella sonnei/efeitos dos fármacos , Shigella sonnei/isolamento & purificação , Virulência/genéticaRESUMO
Yersina enterocolitica-like species have not been extensively studied regarding its pathogenic potential. This work aimed to assess the pathogenic potential of some Y. enterocolitica-like strains by evaluating the presence of virulence-related genes by PCR and their ability to adhere to and invade Caco-2 and HEp-2 cells. A total of 50 Y. frederiksenii, 55 Y. intermedia and 13 Y. kristensenii strains were studied. The strains contained the following genes: Y. frederiksenii, fepA(44%), fes(44%) and ystB(18%); Y. intermedia, ail(53%), fepA (35%), fepD(2%), fes(97%), hreP(2%), ystB(2%) and tccC(35%); Y. kristensenii, ail(62%), ystB(23%), fepA(77%), fepD(54%), fes(54%) and hreP(77%). Generally, the Y. enterocolitica-like strains had a reduced ability to adhere to and invade mammalian cells compared to the highly pathogenic Y. enterocolitica 8081. However, Y. kristensenii FCF410 and Y. frederiksenii FCF461 presented high invasion potentials in Caco-2 cells after five days of pre-incubation increased by 45- and 7.2-fold compared to Y. enterocolitica 8081, respectively; but, the ail gene was not detected in these strains. The presence of virulence-related genes in some of the Y. enterocolitica-like strains indicated their possible pathogenic potential. Moreover, the results suggest the existence of alternative virulence mechanisms and that the pathogenicity of Y. kristensenii and Y. frederiksenii may be strain-dependent.
Assuntos
Aderência Bacteriana/genética , Virulência/genética , Yersinia enterocolitica/genética , Yersinia enterocolitica/patogenicidade , Linhagem Celular , Células Cultivadas , Genes Bacterianos , Humanos , Análise de Sequência de DNA , Fatores de Virulência/genética , Yersiniose/microbiologia , Yersinia enterocolitica/ultraestruturaRESUMO
The presence of iron uptake (irp-2, fyuA, sitA, fepC, iucA), adhesion (iha, lpfA O157/O141, lpfA O157/O154, efa, toxB) and invasion (inv, ial-related DNA sequences and assignment to the four main Escherichia coli phylogenetic groups (A, B1, B2 e D) were determined in 30 commensal E. coli strains isolated from healthy chickens and in 49 APEC strains isolated from chickens presenting clinical signs of septicemia (n=24) swollen head syndrome (n=14) and omphalitis (n=11) by PCR. None of the strains presented DNA sequences related to the inv, ial, efa, and toxB genes. DNA sequences related to lpfA O157/O154, iucA, fepC, and irp-2 genes were significantly found among pathogenic strains, where iucA gene was associated with septicemia and swollen head syndrome and fepC and irp-2 genes were associated with swollen head syndrome strains. Phylogenetic typing showed that commensal and omphalitis strains belonged mainly to phylogenetic Group A and swollen head syndrome to phylogenetic Group D. Septicemic strains were assigned in phylogenetic Groups A and D. These data could suggest that clonal lineage of septicemic APEC strains have a multiple ancestor origin; one from a pathogenic bacteria ancestor and other from a non-pathogenic ancestor that evolved by the acquisition of virulence related sequences through horizontal gene transfer. Swollen head syndrome may constitute a pathogenic clonal group. By the other side, omphalitis strains probably constitute a non-pathogenic clonal group, and could cause omphalitis as an opportunistic infection. The sharing of virulence related sequences by human pathogenic E. coli and APEC strains could indicate that APEC strains could be a source of virulence genes to human strains and could represent a zoonotic risk.(AU)
A presença de seqüências de DNA associadas à capacidade de captação de ferro (irp-2, fyuA, sitA, fepC, iucA), adesão (iha, lpfA O157/O141, lpfA O157/O154, efa, toxB) e de invasão (inv, ial) e a classificação dentro dos quatro grupos filogenéticos principais de Escherichia coli (Grupos A, B1, B2 e D) foram determinadas, através de PCR, em 30 amostras comensais de E. coli isoladas de frangos e de 49 linhagens APEC (24 isoladas de frangos com septicemia, 14 isoladas de frangos com síndrome da cabeça inchada e 11 isoladas de embriões de galinhas com onfalite). Nenhuma das linhagens apresentou os genes inv, ial, efa, e toxB. Os genes lpfA O157/O154, iucA, fepC e irp-2 foram encontrados em freqüências significativas entre as amostras patogênicas. O gene iucA foi associado com amostras causadoras de septicemia e de síndrome da cabeça inchada. Os genes fepC e irp-2 foram associados a amostras causadoras de síndrome da cabeça inchada. A análise filogenética demonstrou que linhagens comensais e causadoras de onfalite pertenceram principalmente ao Grupo filogenético A, não patogênico. Amostras causadoras de síndrome da cabeça inchada pertenceram, em sua maioria, ao Grupo patogênico D. Linhagens causadoras de septicemia pertenceram aos Grupos A e D. Estes dados sugerem que linhagens APEC causadoras de septicemia provavelmente têm uma origem ancestral múltipla: uma derivada de uma linhagem patogênica e outra de uma linhagem não patogênica que possivelmente evoluiu através da aquisição horizontal de genes de virulência. Amostras causadoras de síndrome da cabeça inchada possivelmente constituem um grupo clonal patogênico. Por outro lado, amostras causadoras de onfalite possivelmente constituem um grupo clonal não patogênico, que, possivelmente causam onfalite devido a uma infecção oportunista. A presença de genes de virulência também encontrados em E. coli de origem humana pode indicar a possível ocorrência de zoonoses causadas por APEC.(AU)