Identificação de Clostridium perfringens e Salmonella spp. em suínos adultos utilizando a técnica de PCR (Reação em Cadeia da Polimerase)

Pós-graduação em Microbiologia Agropecuária - FCAV

Detection of type III secretion genes as a general indicator of bacterial virulence

Type III secretion systems of Gram-negative bacteria are specific export machineries for virulence factors which allow their translocation to eukaryotic cells. Since they correlate with bacterial pathogenicity, their presence is used as a general indicator of bacterial virulence. By comparing the genetic relationship of the major type III secretion systems we found the family of genes encoding the inner-membrane channel proteins represented by the Yersinia enterocolitica lcrD (synonym yscV) and its homologous genes from other species an ideal component for establishing a general detection approach for type III secretion systems. Based on the genes of the lcrD family we developed gene probes for Gram-negative human, animal and plant pathogens. The probes comprise lcrD from Y. enterocolitica, sepA from enteropathogenic Escherichia coli, invA from Salmonella typhimurium, mxiA from Shigella sonnei, as well as hrcV from Erwinia amylovora. In addition we included as a control probe the flhA gene from E. coli K-12 to validate our approach. FlhA is part of the flagellar export apparatus which shows a high degree of similarity with type III secretions systems, but is not involved in pathogenicity. The probes were evaluated by screening a series of pathogenic as well as non-pathogenic bacteria. The probes detected type III secretion in pathogens where such systems were either known or were expected to be present, whereas no positive hybridization signals could be found in non-pathogenic Gram-negative bacteria. Gram-positive bacteria were devoid of known type III secretion systems. No interference due to the genetic similarity between the type III secretion system and the flagellar export apparatus was observed. However, potential type III secretion systems could be detected in bacteria where no such systems have been described yet. The presented approach provides therefore a useful tool for the assessment of the virulence potential of bacterial isolates of human, animal and plant origin. Moreover, it is a powerful means for a first safety assessment of poorly characterized strains intended to be used in biotechnological applications.

Relationship between evolutionary rate and cellular location among the Inv/Spa invasion proteins of Salmonella enterica.

For 21 strains of Salmonella enterica, nucleotide sequences were obtained for three invasion genes, spaO, spaP, and spaQ, of the chromosomal inv/spa complex, the products of which form a protein export system required for entry of the bacteria into nonphagocytic host cells. These genes are present in all eight subspecies of the salmonellae, and homologues occur in a variety of other bacteria, including the enteric pathogens Shigella and Yersinia, in which they are plasmid borne. Evolutionary diversification of the invasion genes among the subspecies of S. enterica has been generally similar in pattern and average rate to that of housekeeping genes. However, the range of variation in evolutionary rate among the invasion genes is unusually large, and there is a relationship between the evolutionary rate and cellular location of the invasion proteins, possibly reflecting diversifying selection on exported proteins in adaptation to variable host factors in extracellular environments. The SpaO protein, which is hypervariable in S. enterica and exhibits only 24% sequence identity with its homologues in Shigella and Yersinia, is secreted. In contrast, the membrane-associated proteins SpaP, SpaQ, and InvA are weakly polymorphic and have > 60% sequence identity with the corresponding proteins of other enteric bacteria. Acquisition of the inv/spa genes may have been a key event in the evolution of the salmonellae as pathogens, following which the invention of flagellar phase shifting facilitated niche expansion to include warm-blooded vertebrates.

Características de virulência, resistência e diversidade genética de sorovares de Salmonella com impacto na saúde pública, isolados de frangos de corte no Brasil /

Salmonella Enteritidis, S. Typhimurium and S. Infantis are often associated with cases of human infections worldwide and is transmitted through consumption of contaminated food, particularly those of animal origin, especially chicken meat. This thesis was fractionated into three chapters, the first one relating to general considerations about the topics discussed in the following chapters. The second chapter aimed to evaluate virulence characteristics, antimicrobial resistance and the genetic similarity of 51 strains of S. Infantis isolated in samples of poultry origin from an industry located in the state of São Paulo, Brazil, during the 2009 to 2010 period. The third chapter aimed to analyze 111 strains of S. Enteritidis, 45 of Salmonella Typhimurium and 31 of Salmonella Typhimurium monophasic variant I 4, [5], 12:i:- isolated from chicken carcasses in different brazilian slaughterhouses from 2009 to 2011, and to estimate the risk to human health, based on the presence of virulence genes and antimicrobial resistance, correlating to the pathogenicity profiles (antimicrobial resistance and presence of virulence and resistance genes) with the genetic profile (ribogroup) of the isolates. To evaluate the antimicrobial susceptibility was performed the disk diffusion test for all serotypes of Salmonella, and exclusively to S. Enteritidis and S. Typhimurium, was also verified the minimum inhibitory concentration for ciprofloxacin and ceftazidime antibiotics. The presence of virulence genes invA (invasion), lpfA (fimbriae-adhesion), agfA (fimbriae-biofilm) and sefA (fimbriae-adhesion) were evaluated by PCR. The strains that showed resistance to antibiotics of β-lactams class were evaluated for the presence of resistance genes blaTEM, blaSHV, blaCTX-M and blaAmpC. For resistant strains to quinolones and fluoroquinolones antibiotics classes were searched the qnrA and qnrS genes. The phylogenetic relationship among the isolates was determined by RAPD method for S. Infantis strains, and by ribotyping technique to S. Enteritidis and S. Typhimurium.

Prevalence of Escherichia coli Virulence Genes in Patients with Diarrhea and a Subpopulation of Healthy Volunteers in Madrid, Spain

Etiological diagnosis of diarrheal diseases may be complicated by their multi-factorial nature. In addition, Escherichia coli strains present in the gut can occasionally harbor VGs without causing disease, which complicates the assessment of their clinical significance in particular. The aim of this study was to detect and quantify nine VGs (stx1, stx2, eae, aggR, ehxA, invA, est and elt) typically present in five E. coli enteric pathotypes (EHEC, ETEC, EPEC, EAEC and EIEC) in fecal samples collected from 49 patients with acute diarrhea and 32 healthy controls from Madrid, Spain. In addition, the presence of four serotype-related genes (wzxO104 and fliCH4, rbfO157 and fliCH7) was also determined. Presence of target genes was assessed using a quantitative real-time PCR assay previously developed, and the association of presence and burden of VGs with clinical disease and/or other risk factors was explored. Prevalence of ehxA (typically associated with STEC and EPEC), invA (EIEC) and the rbfO157+fliCH7 (STEC and/or STEC/EAEC) combination were significantly (p<0.02) higher in the diarrheic group, while the wzxO104+fliCH4 combination was significantly (p=0.014) more prevalent in the control group. On the other hand, eae was detected in more than 90% of the individuals in both patient and control populations, and it was not associated with bfpA, suggesting the absence of typical EPEC. No significant differences in the quantitative values were detected for any VG among study groups, but the difference in the load of aggR (EAEC) and invA in the patients with respect to the controls was close to the significance, suggesting a potential role of these VGs in the clinical signs observed when they are present at high levels.