scholarly journals Phenotypic Diversity Caused by Differential RpoS Activity among Environmental Escherichia coli Isolates

2011 ◽  
Vol 77 (22) ◽  
pp. 7915-7923 ◽  
Author(s):  
Sarah M. Chiang ◽  
Tao Dong ◽  
Thomas A. Edge ◽  
Herb E. Schellhorn
Keyword(s):  
Escherichia Coli ◽  
Phenotypic Diversity ◽  
Carbon Sources ◽  
Enteric Bacteria ◽  
Environmental Isolates ◽  
Bacterial Populations ◽  
Content Type ◽  
Phenotypic Differences ◽  
Adaptive Mutations ◽  
E Coli

ABSTRACTEnteric bacteria deposited into the environment by animal hosts are subject to diverse selective pressures. These pressures may act on phenotypic differences in bacterial populations and select adaptive mutations for survival in stress. As a model to study phenotypic diversity in environmental bacteria, we examined mutations of the stress response sigma factor, RpoS, in environmentalEscherichia coliisolates. A total of 2,040 isolates from urban beaches and nearby fecal pollution sources on Lake Ontario (Canada) were screened for RpoS function by examining growth on succinate and catalase activity, two RpoS-dependent phenotypes. TherpoSsequence was determined for 45 isolates, including all candidate RpoS mutants, and of these, six isolates were confirmed as mutants with the complete loss of RpoS function. Similarly to laboratory strains, the RpoS expression of these environmental isolates was stationary phase dependent. However, the expression of RpoS regulon members KatE and AppA had differing levels of expression in several environmental isolates compared to those in laboratory strains. Furthermore, after platingrpoS+isolates on succinate, RpoS mutants could be readily selected from environmentalE. coli. Naturally isolated and succinate-selected RpoS mutants had lower generation times on poor carbon sources and lower stress resistance than theirrpoS+isogenic parental strains. These results show that RpoS mutants are present in the environment (with a frequency of 0.003 among isolates) and that, similarly to laboratory and pathogenic strains, growth on poor carbon sources selects forrpoSmutations in environmentalE. coli. RpoS selection may be an important determinant of phenotypic diversification and, hence, the survival ofE. coliin the environment.

scholarly journals Functional Analysis of Genes Comprising the Locus of Heat Resistance in Escherichia coli

2017 ◽  
Vol 83 (20) ◽  
Author(s):  
Ryan Mercer ◽  
Oanh Nguyen ◽  
Qixing Ou ◽  
Lynn McMullen ◽  
Michael G. Gänzle
Keyword(s):  
Escherichia Coli ◽  
Heat Shock ◽  
Heat Shock Proteins ◽  
Heat Resistance ◽  
Growth Phase ◽  
Genomic Island ◽  
Enteric Bacteria ◽  
Content Type ◽  
E Coli ◽  
Shock Proteins

ABSTRACT The locus of heat resistance (LHR) is a 15- to 19-kb genomic island conferring exceptional heat resistance to organisms in the family Enterobacteriaceae, including pathogenic strains of Salmonella enterica and Escherichia coli. The complement of LHR-comprising genes that is necessary for heat resistance and the stress-induced or growth-phase-induced expression of LHR-comprising genes are unknown. This study determined the contribution of the seven LHR-comprising genes yfdX1 GI, yfdX2, hdeD GI, orf11, trx GI, kefB, and psiE GI by comparing the heat resistances of E. coli strains harboring plasmid-encoded derivatives of the different LHRs in these genes. (Genes carry a subscript “GI” [genomic island] if an ortholog of the same gene is present in genomes of E. coli.) LHR-encoded heat shock proteins sHSP20, ClpKGI, and sHSPGI are not sufficient for the heat resistance phenotype; YfdX1, YfdX2, and HdeD are necessary to complement the LHR heat shock proteins and to impart a high level of resistance. Deletion of trx GI, kefB, and psiE GI from plasmid-encoded copies of the LHR did not significantly affect heat resistance. The effect of the growth phase and the NaCl concentration on expression from the putative LHR promoter p2 was determined by quantitative reverse transcription-PCR and by a plasmid-encoded p2:GFP promoter fusion. The expression levels of exponential- and stationary-phase E. coli cells were not significantly different, but the addition of 1% NaCl significantly increased LHR expression. Remarkably, LHR expression in E. coli was dependent on a chromosomal copy of evgA. In conclusion, this study improved our understanding of the genes required for exceptional heat resistance in E. coli and factors that increase their expression in food. IMPORTANCE The locus of heat resistance (LHR) is a genomic island conferring exceptional heat resistance to several foodborne pathogens. The exceptional level of heat resistance provided by the LHR questions the control of pathogens by current food processing and preparation techniques. The function of LHR-comprising genes and their regulation, however, remain largely unknown. This study defines a core complement of LHR-encoded proteins that are necessary for heat resistance and demonstrates that regulation of the LHR in E. coli requires a chromosomal copy of the gene encoding EvgA. This study provides insight into the function of a transmissible genomic island that allows otherwise heat-sensitive enteric bacteria, including pathogens, to lead a thermoduric lifestyle and thus contributes to the detection and control of heat-resistant enteric bacteria in food.

scholarly journals Bacterial Secretions of Nonpathogenic Escherichia coli Elicit Inflammatory Pathways: a Closer Investigation of Interkingdom Signaling

mBio ◽  
2015 ◽  
Vol 6 (2) ◽  
Author(s):  
Amin Zargar ◽  
David N. Quan ◽  
Karen K. Carter ◽  
Min Guo ◽  
Herman O. Sintim ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Epithelial Cells ◽  
Negative Feedback ◽  
Cell Contact ◽  
Bacterial Cells ◽  
Content Type ◽  
Phenotypic Differences ◽  
E Coli ◽  
Autoinducer 2 ◽  
Human Epithelial Cells

ABSTRACTThere have been many studies on the relationship between nonpathogenic bacteria and human epithelial cells; however, the bidirectional effects of the secretomes (secreted substances in which there is no direct bacterium-cell contact) have yet to be fully investigated. In this study, we use a transwell model to explore the transcriptomic effects of bacterial secretions from two different nonpathogenicEscherichia colistrains on the human colonic cell line HCT-8 using next-generation transcriptome sequencing (RNA-Seq).E. coliBL21 and W3110, while genetically very similar (99.1% homology), exhibit key phenotypic differences, including differences in their production of macromolecular structures (e.g., flagella and lipopolysaccharide) and in their secretion of metabolic byproducts (e.g., acetate) and signaling molecules (e.g., quorum-sensing autoinducer 2 [AI-2]). After analysis of differential epithelial responses to the respective secretomes, this study shows for the first time that a nonpathogenic bacterial secretome activates the NF-κB-mediated cytokine-cytokine receptor pathways while also upregulating negative-feedback components, including the NOD-like signaling pathway. Because of AI-2's relevance as a bacterium-bacterium signaling molecule and the differences in its secretion rates between these strains, we investigated its role in HCT-8 cells. We found that the expression of the inflammatory cytokine interleukin 8 (IL-8) responded to AI-2 with a pattern of rapid upregulation before subsequent downregulation after 24 h. Collectively, these data demonstrate that secreted products from nonpathogenic bacteria stimulate the transcription of immune-related biological pathways, followed by the upregulation of negative-feedback elements that may serve to temper the inflammatory response.IMPORTANCEThe symbiotic relationship between the microbiome and the host is important in the maintenance of human health. There is a growing need to further understand the nature of these relationships to aid in the development of homeostatic probiotics and also in the design of novel antimicrobial therapeutics. To our knowledge, this is the first global-transcriptome study of bacteria cocultured with human epithelial cells in a model to determine the transcriptional effects of epithelial cells in which epithelial and bacterial cells are allowed to “communicate” with each other only through diffusible small molecules and proteins. By beginning to demarcate the direct and indirect effects of bacteria on the gastrointestinal (GI) tract, two-way interkingdom communication can potentially be mediated between host and microbe.

scholarly journals Genomewide Mutational Diversity in Escherichia coli Population Evolving in Prolonged Stationary Phase

mSphere ◽  
2017 ◽  
Vol 2 (3) ◽  
Author(s):  
Savita Chib ◽  
Farhan Ali ◽  
Aswin Sai Narain Seshasayee
Keyword(s):  
Escherichia Coli ◽  
Genetic Diversity ◽  
Stationary Phase ◽  
Phenotypic Diversity ◽  
Model System ◽  
Content Type ◽  
Neutral Drift ◽  
E Coli ◽  
Evolution By Natural Selection ◽  
Over Time

ABSTRACT Prolonged stationary phase in bacteria, contrary to its name, is highly dynamic, with extreme nutrient limitation as a predominant stress. Stationary-phase cultures adapt by rapidly selecting a mutation(s) that confers a growth advantage in stationary phase (GASP). The phenotypic diversity of starving E. coli populations has been studied in detail; however, only a few mutations that accumulate in prolonged stationary phase have been described. This study documented the spectrum of mutations appearing in Escherichia coli during 28 days of prolonged starvation. The genetic diversity of the population increases over time in stationary phase to an extent that cannot be explained by random, neutral drift. This suggests that prolonged stationary phase offers a great model system to study adaptive evolution by natural selection. Prolonged stationary phase is an approximation of natural environments presenting a range of stresses. Survival in prolonged stationary phase requires alternative metabolic pathways for survival. This study describes the repertoire of mutations accumulating in starving Escherichia coli populations in lysogeny broth. A wide range of mutations accumulates over the course of 1 month in stationary phase. Single nucleotide polymorphisms (SNPs) constitute 64% of all mutations. A majority of these mutations are nonsynonymous and are located at conserved loci. There is an increase in genetic diversity in the evolving populations over time. Computer simulations of evolution in stationary phase suggest that the maximum frequency of mutations observed in our experimental populations cannot be explained by neutral drift. Moreover, there is frequent genetic parallelism across populations, suggesting that these mutations are under positive selection. Finally, functional analysis of mutations suggests that regulatory mutations are frequent targets of selection. IMPORTANCE Prolonged stationary phase in bacteria, contrary to its name, is highly dynamic, with extreme nutrient limitation as a predominant stress. Stationary-phase cultures adapt by rapidly selecting a mutation(s) that confers a growth advantage in stationary phase (GASP). The phenotypic diversity of starving E. coli populations has been studied in detail; however, only a few mutations that accumulate in prolonged stationary phase have been described. This study documented the spectrum of mutations appearing in Escherichia coli during 28 days of prolonged starvation. The genetic diversity of the population increases over time in stationary phase to an extent that cannot be explained by random, neutral drift. This suggests that prolonged stationary phase offers a great model system to study adaptive evolution by natural selection.

scholarly journals Inactivation of Escherichia coli by Polychromatic Simulated Sunlight: Evidence for and Implications of a Fenton Mechanism Involving Iron, Hydrogen Peroxide, and Superoxide

2013 ◽  
Vol 80 (3) ◽  
pp. 935-942 ◽  
Author(s):  
Michael B. Fisher ◽  
Kara L. Nelson
Keyword(s):  
Escherichia Coli ◽  
Hydrogen Peroxide ◽  
Enteric Bacteria ◽  
Growth Conditions ◽  
Simulated Sunlight ◽  
Wild Type ◽  
Intracellular Iron ◽  
Content Type ◽  
E Coli ◽  
Degree Of Sensitization

ABSTRACTSunlight inactivation ofEscherichia colihas previously been shown to accelerate in the presence of oxygen, exogenously added hydrogen peroxide, and bioavailable forms of exogenously added iron. In this study, mutants unable to effectively scavenge hydrogen peroxide or superoxide were found to be more sensitive to polychromatic simulated sunlight (without UVB wavelengths) than wild-type cells, while wild-type cells grown under low-iron conditions were less sensitive than cells grown in the presence of abundant iron. Furthermore, prior exposure to simulated sunlight was found to sensitize cells to subsequent hydrogen peroxide exposure in the dark, but this effect was attenuated for cells grown with low iron. Mutants deficient in recombination DNA repair were sensitized to simulated sunlight (without UVB wavelengths), but growth in the presence of iron chelators reduced the degree of sensitization conferred by this mutation. These findings support the hypothesis that hydrogen peroxide, superoxide, and intracellular iron all participate in the photoinactivation ofE. coliand further suggest that the inactivation rate of enteric bacteria in the environment may be strongly dependent on iron availability and growth conditions.

scholarly journals Effects of Cover Crop Species and Season on Population Dynamics of Escherichia coli and Listeria innocua in Soil

2016 ◽  
Vol 82 (6) ◽  
pp. 1767-1777 ◽  
Author(s):  
Neiunna L. Reed-Jones ◽  
Sasha Cahn Marine ◽  
Kathryne L. Everts ◽  
Shirley A. Micallef
Keyword(s):  
Escherichia Coli ◽  
Cover Crops ◽  
Cover Crop ◽  
Green Manure ◽  
Listeria Innocua ◽  
Hairy Vetch ◽  
Bacterial Populations ◽  
Content Type ◽  
E Coli ◽  
Crimson Clover

ABSTRACTCover crops provide several ecosystem services, but their impact on enteric bacterial survival remains unexplored. The influence of cover cropping on foodborne pathogen indicator bacteria was assessed in five cover crop/green manure systems: cereal rye, hairy vetch, crimson clover, hairy vetch-rye and crimson clover-rye mixtures, and bare ground. Cover crop plots were inoculated withEscherichia coliandListeria innocuain the fall of 2013 and 2014 and tilled into the soil in the spring to form green manure. Soil samples were collected and the bacteria enumerated. Time was a factor for all bacterial populations studied in all fields (P< 0.001).E. colilevels declined when soil temperatures dipped to <5°C and were detected only sporadically the following spring.L. innocuadiminished somewhat but persisted, independently of season. In an organic field, the cover crop was a factor forE. coliin year 1 (P= 0.004) and forL. innocuain year 2 (P= 0.011). In year 1,E. colilevels were highest in the rye and hairy vetch-rye plots. In year 2,L. innocualevels were higher in hairy vetch-rye (P= 0.01) and hairy vetch (P= 0.03) plots than in the rye plot. Bacterial populations grew (P< 0.05) or remained the same 4 weeks after green manure incorporation, although initial reductions inL. innocuanumbers were observed after tilling (P< 0.05). Green manure type was a factor only forL. innocuaabundance in a transitional field (P< 0.05). Overall, the impacts of cover crops/green manures on bacterial population dynamics in soil varied, being influenced by bacterial species, time from inoculation, soil temperature, rainfall, and tillage; this reveals the need for long-term studies.

scholarly journals Adjacent Terrestrial Landscapes Impact the Biogeographical Pattern of Soil Escherichia coli Strains in Produce Fields by Modifying the Importance of Environmental Selection and Dispersal

2021 ◽  
Vol 87 (6) ◽  
Author(s):  
Jingqiu Liao ◽  
Peter Bergholz ◽  
Martin Wiedmann
Keyword(s):  
Public Health ◽  
Escherichia Coli ◽  
Land Use ◽  
Enteric Bacteria ◽  
Content Type ◽  
E Coli ◽  
Biogeographic Pattern ◽  
Environmental Selection ◽  
Forest Sites ◽  
Land Use Types

ABSTRACT High-quality habitats for wildlife (e.g., forest) provide essential ecosystem services while increasing species diversity and habitat connectivity. Unfortunately, the presence of such habitats adjacent to produce fields may increase risk for contamination of fruits and vegetables by enteric bacteria, including Escherichia coli. E. coli survives in extrahost environments (e.g., soil) and could be dispersed across landscapes by wildlife. Understanding how terrestrial landscapes impact the distribution of soil E. coli strains is of importance in assessing the contamination risk of agricultural products. Here, using multilocus sequence typing, we characterized 938 E. coli soil isolates collected from two watersheds with different landscape patterns in New York State, USA, and compared the distribution of E. coli and the influence that environmental selection and dispersal have on the distribution between these two watersheds. Results showed that for the watershed with widespread produce fields, sparse forests, and limited interaction between the two land use types, E. coli composition was significantly different between produce field sites and forest sites; this distribution appears to be shaped by relatively strong environmental selection, likely from soil phosphorus, and slight dispersal limitation. For the watershed with more forested areas and stronger interaction between produce field sites and forest sites, E. coli composition between these two land use types was relatively homogeneous; this distribution appeared to be a consequence of wildlife-driven dispersal, inferred by competing models. Collectively, our results suggest that terrestrial landscape attributes could impact the biogeographic pattern of enteric bacteria by adjusting the importance of environmental selection and dispersal. IMPORTANCE Understanding the ecology of enteric bacteria in extrahost environments is important for the development and implementation of strategies to minimize preharvest contamination of produce with enteric pathogens. Our findings suggest that watershed landscape is an important factor influencing the importance of ecological drivers and dispersal patterns of E. coli. Agricultural areas in such watersheds may have a higher risk of produce contamination due to fewer environmental constraints and higher potential of dispersal of enteric bacteria between locations. Thus, there is a perceived trade-off between priorities of environmental conservation and public health in on-farm food safety, with limited ecological data supporting or refuting the role of wildlife in dispersing pathogens under normal operating conditions. By combining field sampling and spatial modeling, we explored ecological principles underlying the biogeographic pattern of enteric bacteria at the regional level, which can benefit agricultural, environmental, and public health scientists who aim to reduce the risk of food contamination by enteric bacteria while minimizing negative impacts on wildlife habitats.

scholarly journals Production in Escherichia coli of Poly(3-Hydroxybutyrate-co-3-Hydroxyvalerate) with Differing Monomer Compositions from Unrelated Carbon Sources

2011 ◽  
Vol 77 (14) ◽  
pp. 4886-4893 ◽  
Author(s):  
Quan Chen ◽  
Qian Wang ◽  
Guoqing Wei ◽  
Quanfeng Liang ◽  
Qingsheng Qi
Keyword(s):  
Escherichia Coli ◽  
Control Strategy ◽  
Biosynthetic Pathway ◽  
Feedback Inhibition ◽  
Carbon Sources ◽  
Threonine Deaminase ◽  
Content Type ◽  
E Coli ◽  
Key Factor ◽  
Threonine Biosynthesis

ABSTRACTThe industrial production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) has been hindered by high cost and a complex control strategy caused by the addition of propionate. In this study, based on analysis of the PHBV biosynthesis process, we developed a PHBV biosynthetic pathway from a single unrelated carbon source via threonine biosynthesis inEscherichia coli. To accomplish this, we (i) overexpressed threonine deaminase, which is the key factor for providing propionyl-coenzyme A (propionyl-CoA), from different host bacteria, (ii) removed the feedback inhibition of threonine by mutating and overexpressing thethrABCoperon inE. coli, and (iii) knocked out the competitive pathways of catalytic conversion of propionyl-CoA to 3-hydroxyvaleryl-CoA. Finally, we constructed a series of strains and mutants which were able to produce the PHBV copolymer with differing monomer compositions in a modified M9 medium supplemented with 20 g/liter xylose. The largest 3-hydroxyvalerate fraction obtained in the copolymer was 17.5 mol%.

scholarly journals Genotypic-Phenotypic Discrepancies between Antibiotic Resistance Characteristics of Escherichia coli Isolates from Calves in Management Settings with High and Low Antibiotic Use

2011 ◽  
Vol 77 (10) ◽  
pp. 3293-3299 ◽  
Author(s):  
Margaret A. Davis ◽  
Thomas E. Besser ◽  
Lisa H. Orfe ◽  
Katherine N. K. Baker ◽  
Amelia S. Lanier ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Resistance Gene ◽  
Resistance Genes ◽  
Antibiotic Use ◽  
Dairy Calf ◽  
Bacterial Populations ◽  
Content Type ◽  
Exact Test ◽  
E Coli ◽  
Fisher’S Exact Test

ABSTRACTWe hypothesized that bacterial populations growing in the absence of antibiotics will accumulate more resistance gene mutations than bacterial populations growing in the presence of antibiotics. If this is so, the prevalence of dysfunctional resistance genes (resistance pseudogenes) could provide a measure of the level of antibiotic exposure present in a given environment. As a proof-of-concept test, we assayed field strains ofEscherichia colifor their resistance genotypes using a resistance gene microarray and further characterized isolates that had resistance phenotype-genotype discrepancies. We found a small but significant association between the prevalence of isolates with resistance pseudogenes and the lower antibiotic use environment of a beef cow-calf operation versus a higher antibiotic use dairy calf ranch (Fisher's exact test,P= 0.044). Other significant findings include a very strong association between the dairy calf ranch isolates and phenotypes unexplained by well-known resistance genes (Fisher's exact test,P< 0.0001). Two novel resistance genes were discovered inE. coliisolates from the dairy calf ranch, one associated with resistance to aminoglycosides and one associated with resistance to trimethoprim. In addition, isolates resistant to expanded-spectrum cephalosporins but negative forblaCMY-2had mutations in the promoter regions of the chromosomalE. coliampCgene consistent with reported overexpression of native AmpC beta-lactamase. Similar mutations in hospitalE. coliisolates have been reported worldwide. Prevalence or rates ofE. coliampCpromoter mutations may be used as a marker for high expanded-spectrum cephalosporin use environments.

scholarly journals Indole Production Promotes Escherichia coli Mixed-Culture Growth with Pseudomonas aeruginosa by Inhibiting Quorum Signaling

2011 ◽  
Vol 78 (2) ◽  
pp. 411-419 ◽  
Author(s):  
Weihua Chu ◽  
Tesfalem R. Zere ◽  
Mary M. Weber ◽  
Thomas K. Wood ◽  
Marvin Whiteley ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Pseudomonas Aeruginosa ◽  
Mixed Culture ◽  
Receptor Gene ◽  
Enteric Bacteria ◽  
Wild Type ◽  
Content Type ◽  
E Coli ◽  
Culture Growth ◽  
Indole Production

ABSTRACTIndole production byEscherichia coli, discovered in the early 20th century, has been used as a diagnostic marker for distinguishingE. colifrom other enteric bacteria. By using transcriptional profiling and competition studies with defined mutants, we show that cyclic AMP (cAMP)-regulated indole formation is a major factor that enablesE. coligrowth in mixed biofilm and planktonic populations withPseudomonas aeruginosa. Mutants deficient in cAMP production (cyaA) or the cAMP receptor gene (crp), as well as indole production (tnaA), were not competitive in coculture withP. aeruginosabut could be restored to wild-type competitiveness by supplementation with a physiologically relevant indole concentration.E. colisdiAmutants, which lacked the receptor for both indole andN-acyl-homoserine lactones (AHLs), showed no change in competitive fitness, suggesting that indole acted directly onP. aeruginosa. AnE. colitnaAmutant strain regained wild-type competiveness if grown withP. aeruginosaAHL synthase (rhlIandrhlI lasI) mutants. In contrast to the wild type,P. aeruginosaAHL synthase mutants were unable to degrade indole. Indole produced during mixed-culture growth inhibited pyocyanin production and other AHL-regulated virulence factors inP. aeruginosa. Mixed-culture growth withP. aeruginosastimulated indole formation inE. colicpdA, which is unable to regulate cAMP levels, suggesting the potential for mixed-culture gene activation via cAMP. These findings illustrate how indole, an early described feature ofE. colicentral metabolism, can play a significant role in mixed-culture survival by inhibiting quorum-regulated competition factors inP. aeruginosa.

scholarly journals Evaluating the Pathogenic Potential of Environmental Escherichia coli by Using the Caenorhabditis elegans Infection Model

2013 ◽  
Vol 79 (7) ◽  
pp. 2435-2445 ◽  
Author(s):  
Alexandra Merkx-Jacques ◽  
Anja Coors ◽  
Roland Brousseau ◽  
Luke Masson ◽  
Alberto Mazza ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Caenorhabditis Elegans ◽  
Virulence Genes ◽  
Human Health Risk ◽  
Environmental Isolates ◽  
Pathogenic Potential ◽  
Content Type ◽  
E Coli ◽  
C Elegans ◽  
Infection Assay

ABSTRACTThe detection and abundance ofEscherichia coliin water is used to monitor and mandate the quality of drinking and recreational water. Distinguishing commensal waterborneE. coliisolates from those that cause diarrhea or extraintestinal disease in humans is important for quantifying human health risk. A DNA microarray was used to evaluate the distribution of virulence genes in 148E. colienvironmental isolates from a watershed in eastern Ontario, Canada, and in eight clinical isolates. Their pathogenic potential was evaluated withCaenorhabditis elegans, and the concordance between the bioassay result and the pathotype deduced by genotyping was explored. Isolates identified as potentially pathogenic on the basis of their complement of virulence genes were significantly more likely to be pathogenic toC. elegansthan those determined to be potentially nonpathogenic. A number of isolates that were identified as nonpathogenic on the basis of genotyping were pathogenic in the infection assay, suggesting that genotyping did not capture all potentially pathogenic types. The detection of the adhesin-encoding genessfaD,focA, andfocG, which encode adhesins; ofiroN2, which encodes a siderophore receptor; ofpic, which encodes an autotransporter protein; and ofb1432, which encodes a putative transposase, was significantly associated with pathogenicity in the infection assay. Overall,E. coliisolates predicted to be pathogenic on the basis of genotyping were indeed so in theC. elegansinfection assay. Furthermore, the detection ofC. elegans-infective environmental isolates predicted to be nonpathogenic on the basis of genotyping suggests that there are hitherto-unrecognized virulence factors or combinations thereof that are important in the establishment of infection.

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