Detection of Virulence-Associated Genes in Escherichia coli O157 and Non-O157 Isolates from Beef Cattle, Humans, and Chickens

Abstract

Food-producing animals can be reservoirs of pathogenic Escherichia coli strains that can induce diseases in animals or humans. Contamination of food by E. coli O157:H7 raises immediate concerns about public health, although it is not clear whether all E. coli O157 isolates of animal origin are equally harmful to humans. Inversely, the pathogenic potential of atypical E. coli O157 isolates and several non-O157 serotypes often is ignored. We used a DNA microarray capable of detecting a subset of 346 genes to compare the virulence-associated genes present in eight E. coli O157 isolates from human cases, 14 antibiotic-resistant and/or hypermutable E. coli O157 isolates from beef cattle, and four antibiotic-resistant, sorbitol-negative, non-O157 E. coli isolates from healthy broiler chickens. Hybridization on arrays (HOA) revealed that O157 isolates from beef cattle and humans were genetically distinct, although they possessed most of the same subset of virulence genes. HOA allowed discrimination between hypermutable and antibiotic-resistant O157 isolates from beef cattle based on hybridization results for the stx2 and ycgG genes (hypermutable) or ymfL, stx1, stx2, and hlyE(avian) genes (resistant). However, the absence of hybridization to gene yfdR characterized human isolates. HOA also revealed that an atypical sorbitol-fermenting bovine O157 isolate lacked some genes of the type 3 secretion system, plasmid pO157, and the stx1 and stx2 genes. This isolate had a particular pathotype (eaeA(beta) tir(alpha) espA(alpha) espB(alpha) espD(alpha)) not found in typical E. coli O157:H7. HOA revealed that some non-O157 E. coli isolates from healthy chickens carried genes responsible for salmochelin- and yersiniabactin-mediated iron uptake generally associated with pathogenic strains.

Relative Cytotoxicity ofEscherichia coliO157:H7 Isolates from Beef Cattle and Humans

“…Differences between those lineages were recently highlighted by us and others (Maldonado et al, 2005;Dowd and Ishizaki, 2006;Rashid et al, 2006;Besser et al, 2007;Lefebvre et al, 2008). Indeed, using DNA hybridization on arrays, we previously showed that O157:H7 isolates from beef cattle were genetically different from human isolates but possessed a similar virulence potential or, more precisely, a similar set of virulence genes (Lefebvre et al, 2008).…”

“…Bovine isolates are identified by a number in parentheses, followed by a typing code (1-12), a pen number (1-16), and the sampling day (4-165) of the longitudinal study described before (Lefebvre et al, 2005). Isolates identified by a black dot were also previously compared by microarray analysis (Lefebvre et al, 2008). often different based on the presence or absence of some genomic regions and Stx-encoding bacteriophage insertion sites (Besser et al, 2007;Steele et al, 2007;Zhang et al, 2007). In a previous study, we also confirmed that O157:H7 isolates from beef cattle and human clinical cases clustered distinctly, supporting thus the existence of at least two different lineages of O157:H7 (Lefebvre et al, 2008).…”

“…Isolates identified by a black dot were also previously compared by microarray analysis (Lefebvre et al, 2008). often different based on the presence or absence of some genomic regions and Stx-encoding bacteriophage insertion sites (Besser et al, 2007;Steele et al, 2007;Zhang et al, 2007). In a previous study, we also confirmed that O157:H7 isolates from beef cattle and human clinical cases clustered distinctly, supporting thus the existence of at least two different lineages of O157:H7 (Lefebvre et al, 2008). However, we found that both genetic clusters (bovine and human isolates) clearly possessed a similar set of virulence factors, indicating a similar pathogenic potential.…”

Multiplexed optical pathogen detection with lab‐on‐a‐chip devices

“…The technology which provided the key step change in enabling highly multiplexed molecular analysis is DNA microarrays. It has been used for bacterial and viral typing since their early days and systems for microbial species typing [3,4], antibiotic resistance detection [5][6][7][8] and virulence assessment [9,10] have been described. For a review closest to the field see [11] and [12].…”

“…Further promising technologies employ protein binders, peptides, aptamers, etc. as recognition elements often in an arrayed format to increase the multiplexing capability [10,15,16]. Diagnostics of infectious diseases can be also approached from the host response to infection by measurement of nucleic acid [17,18] and metabolomic biomarkers [19].…”