Genomic diversity and virulence profiles of historical Escherichia coli O157 strains isolated from clinical and environmental sources

Rapid Detection of Single Viable Escherichia coli O157 Cells in Fresh Lettuce and Strawberry by Immunomagnetic Flow Cytometry in Combination with Pre-Enrichment

Enterohemorrhagic Escherichia coli are an important pathogen causing food poisoning. The rapid detection of viable E. coli O157 in vegetables and fruits at single-cell level is critical because of the low infective dose of this pathogen. In this study, an immunomagnetic flow cytometry (IMFC)-based method was developed to detect E. coli O157 in lettuce and strawberries inoculated with 1 CFU/25 g. This method developed immunomagnetic (IM)-beads to capture E. coli O157 cells. The pre-enrichment of E. coli O157 and IM-bead separation rapidly increased the concentration of cells to a detectable range for flow cytometry. Compared with the plate-based method, the diagnostic sensitivity and specificity of the IMFC-based method were 100% in 166 samples, including 100 artificially contaminated samples, 60 retail samples, and six O157-positive samples for proficiency testing. The developed IMFC-based method was found to be effective in detecting E. coli O157 at single-cell level in 25 g of lettuce or strawberry with relatively shorter associated time to results of 5.7 h. Therefore, the IMFC-based method could improve detection efficiency and also make early warnings in a short time.

Immunogenicity and efficacy of two DNA vaccines encoding antigenic PspA and TerD against Nocardia seriolae in hybrid snakehead

Fish nocardiosis is a widespread chronic granulomatous disease in aquatic environment, which was particularly caused by Nocardia seriolae. The phage shock protein A (PspA) and tellurium resistance protein D (TerD) were identified to be the immunodominant antigens of the wild-type N. seriolae strain ZJ0503 in our previous study. In an attempt to develop effective DNA vaccines against this pathogen, PspA and TerD were used as candidates to ligate with pcDNA3.1-Flag plasmids, respectively. In addition, the abilities of these two DNA vaccines to elicit various immune responses in hybrid snakehead and supply protective efficacy against artificial challenge with N. seriolae were determined in the present study. The results showed that intramuscular injection with pcDNA-PspA and pcDNA-TerD did not exhibit cytotoxic activities in hybrid snakehead via histopathological examination. Besides, hybrid snakehead immunization with pcDNA-PspA and pcDNA-TerD could increase several non-specific immune paraments in serum, including LYZ, POD, ACP, AKP and SOD activities. Meanwhile, the pcDNA-TerD DNA vaccine could induce strongly specific antibody (IgM) titer in hybrid snakehead with a relative percent of survival (RPS) value of 83.14% against N. seriolae, while that of pcDNA-PspA DNA vaccine was displayed comparably low IgM titer with RPS value of 57.83%. Furthermore, quantitative real-time PCR assays presented that the expression of immune-related genes (MHCIα, MHCIIα, CD4, CD8α, IL-1β and TNFα) were up-regulated to various degrees after vaccination with pcDNA-PspA or pcDNA-TerD, indicating that these two DNA vaccines were able to boost humoral and cell-mediated immune responses in hybrid snakehead. Taken together, both the pcDNA-PspA and pcDNA-TerD DNA vaccines were proved to be safe, immunogenic and effective in protecting hybrid snakehead against N. seriolae infection, which can promote the development and application of DNA vaccines to control fish nocardiosis in aquaculture.

Comparative Performance Evaluation of Real-Time PCR and Dual-Labeled Fluorescence Resonance Energy Transfer Probe-Based Melt Peak Analysis for the Detection of Escherichia coli O157:H7 in Beef Products

Contaminated beef and beef products remain a frequent vehicle for the transmission of Escherichia coli O157:H7. The current U.S. Department of Agriculture (USDA) Food Safety and Inspection Service (FSIS) regulatory testing for E. coli O157:H7 uses the method described in the USDA-FSIS Microbiology Laboratory Guidebook (MLG), chapter 5. At times, described presumptive test results are nonconfirmable, suggesting that recent PCR technological advancements and presumed enhanced sensitivity and specificity may offer beneficial changes. Here, we have evaluated the precision and sensitivity of a fluorescence resonance energy transfer-based real-time PCR assay called ECO for the detection of E. coli O157:H7. ECO detects the gene target specific to both E. coli O157:H7 and E. coli O157:non-H7 but distinguishes the two by using a melt curve analysis. A total of 3,113 O157:H7 and O157:non-H7 isolates were used to define this melting temperature-based criteria. The simulated comparative performance evaluation in the spiked beef samples indicated detection of 3 of 3 samples by ECO at <3.3 log CFU/mL, whereas MLG only detected 1 of 3 (<3.3 log CFU/mL). Using modified tryptic soy broth-enriched natural beef and veal product samples ( n = 452), the comparative sensitivity, specificity, false-positive rate, and false-negative rate against culture between MLG and ECO were 75 versus 92%, 91 versus 99%, 8.9 versus 0.77%, and 25 versus 8.3%, respectively. Positive predictive value, negative predictive value, and the overall accuracy were found to be 56 versus 94%, 96 versus 98%, and 88 versus 98%, for MLG and ECO, respectively. These data demonstrate that the ECO assay is comparable to MLG detection of E. coli O157:H7 and offers improved sensitivity.

Molecular Testing in Emerging Infectious Diseases

It was widely believed in the late 1960s that infectious diseases had been conquered by vaccines and antibiotics and humans were no longer under threat by microbial pathogens. Yet, since that time more than 60 pathogens have been discovered that can cause serious emerging infectious diseases. Molecular methods have played critical roles in the discovery, monitoring, and clinical diagnostics of emerging pathogens. In this chapter, we present well-recognized emerging pathogens. We provide examples of the utility of molecular assays in research and clinical care of emerging infectious diseases. We also discuss some theoretical and practical limitations of molecular tests and the future prospects of expanding molecular diagnostics for emerging pathogens based on new advances of knowledge and technologies.

Subtyping Escherichia coli Virulence Genes Isolated from Feces of Beef Cattle and Clinical Cases in Alberta

Clinical outcomes of Shiga toxin (stx)-producing Escherichia coli infection are largely determined by virulence gene subtypes. This study used a polymerase chain reaction (PCR)-pyrosequencing assay to analyze single-nucleotide polymorphisms for subtyping three major virulence genes (stx₁, stx₂, eae) of pathogenic E. coli (O157, O26, O111, and O103) isolated from cattle over a 2-year interval (n = 465) and human clinical cases (n = 42) in western Canada. Most bovine isolates were PCR positive for at least one target virulence gene (367/465), whereas 100% of human isolates harbored eae in combination with at least one stx gene. Four Shiga toxin (1a, 2a, 2c, and 2e) and four eae (λ/γ1-eae, ɛ-eae, θ/γ2-eae, and β-eae) subtypes were identified in over 25 distinct virulence genotypes. Among cattle isolates, every serogroup, but O103, presented a dominant genotype (O157: stx_1a+stx_2a+λ/γ1-eae, O26: β-eae alone, and O111: stx_1a+θ/γ2-eae). Similar patterns were found in human isolates, although it was not possible to establish a clear genotypic association between the two sources. Many O157 and non-O157 cattle isolates lacked stx genes; the absence was greater in non-O157 (75/258) and O157:non-H7 (19/40) than in O157:H7 strains (1/164). In addition, there was a greater diversity of virulence genotypes of E. coli isolated from cattle than those of human diseases, which could be due to sample characteristics (e.g., source and clinical condition). However, the majority of cattle strains had virulence profiles identical to those of clinical cases. Consequently, determining the presence of certain stx (stx_1a and stx_2a) and eae (λ/γ1-eae) subtypes known to cause human disease would be a valuable tool for risk assessment and prediction of disease outcome along the farm-to-fork continuum.

Genome Sequences of 64 Non-O157:H7 Shiga Toxin-Producing Escherichia coli Strains

Shiga toxin-producing Escherichia coli (STEC) strains are human pathogens. Although >400 non-O157 serotypes have been involved in human disease, whole-genome sequencing information is missing for many serotypes. We sequenced 64 STEC strains comprising 38 serotypes, isolated from clinical sources, animals, and environmental samples, to improve the phylogenetic understanding of these important foodborne pathogens.