scholarly journals Divergent Evolution of the repFII Replicon of IncF Plasmids Carrying Cytotoxic Necrotizing Factorcnf2, Cytolethal Distending ToxincdtIII, andf17AeFimbrial Variant Genes in Type 2 Necrotoxigenic Escherichia coli Isolates from Calves

2015 ◽  
Vol 82 (2) ◽  
pp. 510-517
Author(s):  
Morgan Bihannic ◽  
Marisa Haenni ◽  
Eric Oswald ◽  
Jean-Yves Madec
Keyword(s):  
Escherichia Coli ◽  
Driving Forces ◽  
Divergent Evolution ◽  
Virulence Determinants ◽  
Genetic Determinants ◽  
Content Type ◽  
E Coli ◽  
Fimbrial Adhesins ◽  
Evolutionary Paths

ABSTRACTAmong the pathovars ofEscherichia coliin cattle, necrotoxigenicE. coli(NTEC) is defined by the production of cytotoxic necrotizing factors (CNFs). In particular, type 2 NTEC (NTEC2) strains are frequent in diarrheic and septicemic calves and usually coproduce CNF type 2 (CNF2), cytolethal distending toxin type III (CDTIII), and fimbrial adhesins of the F17 family, whose genetic determinants have frequently been reported on the same Vir-like plasmid. In this study, we investigated the genetic environment of thecnf2,f17Ae, andcdtIIIgenes in a collection of fecalE. coliisolates recovered from 484 French and 58 Iranian calves. In particular, we highlighted the spread ofcnf2,f17Ae, andcdtIIIon similar 150-kb IncF plasmids harboring the newly assigned repFII replicon allele F74 in NTEC2 isolates. Interestingly, this 150-kb IncF plasmid differed from the 140-kb IncF plasmid harboring the newly assigned repFII replicon allele F75 and carryingcnf2alone. These results suggest two divergent lineages ofcnf2-carrying IncF plasmids depending on the presence of thef17AeandcdtIIIgenes. This partition was observed inE. colistrains of unrelated backgrounds, suggesting two different evolutionary paths ofcnf2-carrying IncF plasmids rather than divergent evolutions of NTEC2 clones. The driving forces for such divergent evolutions are not known, and further studies are required to clarify the selection of plasmid subtypes spreading virulence determinants inE. coli, in particular, plasmids of the IncF family.

scholarly journals Phylogenetic Grouping and Virulence Potential of Extended-Spectrum-β-Lactamase-Producing Escherichia coli Strains in Cattle

2012 ◽  
Vol 78 (13) ◽  
pp. 4677-4682 ◽  
Author(s):  
Charlotte Valat ◽  
Frédéric Auvray ◽  
Karine Forest ◽  
Véronique Métayer ◽  
Emilie Gay ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Virulence Determinants ◽  
Phylogenetic Groups ◽  
Content Type ◽  
E Coli ◽  
Extended Spectrum ◽  
Specific Distribution ◽  
Extended Spectrum Beta Lactamases ◽  
Phylogenetic Grouping ◽  
Almost All

ABSTRACTIn line with recent reports of extended-spectrum beta-lactamases (ESBLs) inEscherichia coliisolates of highly virulent serotypes, such as O104:H4, we investigated the distribution of phylogroups (A, B1, B2, D) and virulence factor (VF)-encoding genes in 204 ESBL-producingE. coliisolates from diarrheic cattle. ESBL genes, VFs, and phylogroups were identified by PCR and a commercial DNA array (Alere, France). ESBL genes belonged mostly to the CTX-M-1 (65.7%) and CTX-M-9 (27.0%) groups, whereas those of the CTX-M-2 and TEM groups were much less represented (3.9% and 3.4%, respectively). One ESBL isolate wasstx1andeaepositive and belonged to a major enterohemorrhagicE. coli(EHEC) serotype (O111:H8). Two other isolates wereeaepositive butstxnegative; one of these had serotype O26:H11. ESBL isolates belonged mainly to phylogroup A (55.4%) and, to lesser extents, to phylogroups D (25.5%) and B1 (15.6%), whereas B2 strains were quasi-absent (1/204). The number of VFs was significantly higher in phylogroup B1 than in phylogroups A (P= 0.04) and D (P= 0.02). Almost all of the VFs detected were found in CTX-M-1 isolates, whereas only 64.3% and 33.3% of them were found in CTX-M-9 and CTX-M-2 isolates, respectively. These results indicated that the widespread dissemination of theblaCTX-Mgenes within theE. colipopulation from cattle still spared the subpopulation of EHEC/Shiga-toxigenicE. coli(STEC) isolates. In contrast to other reports on non-ESBL-producing isolates from domestic animals, B1 was not the main phylogroup identified. However, B1 was found to be the most virulent phylogroup, suggesting host-specific distribution of virulence determinants among phylogenetic groups.

scholarly journals Variability of Escherichia coli O157 Strain Survival in Manure-Amended Soil in Relation to Strain Origin, Virulence Profile, and Carbon Nutrition Profile

2011 ◽  
Vol 77 (22) ◽  
pp. 8088-8096 ◽  
Author(s):  
Eelco Franz ◽  
Angela H. A. M. van Hoek ◽  
El Bouw ◽  
Henk J. M. Aarts
Keyword(s):  
Escherichia Coli ◽  
Survival Time ◽  
Metabolic Profiling ◽  
Virulence Determinants ◽  
Survival Times ◽  
O157 Strain ◽  
Phenotypic Marker ◽  
Content Type ◽  
E Coli ◽  
Amended Soil

ABSTRACTThe variation in manure-amended soil survival capability among 18Escherichia coliO157 strains (8 animal, 1 food, and 9 human isolates) was studied using a single sandy soil sample and a single sample of cattle manure as the inoculum carrier. The virulence profiles ofE. coliO157 strains were characterized by detection of virulence determinants (73 genes, 122 probes in duplicate) by using the IdentibacE. coligenotyping DNA miniaturized microarray. Metabolic profiling was done by subjecting all strains to the Biolog phenotypic carbon microarray. Survival times (calculated as days needed to reach the detection limit using the Weibull model) ranged from 47 to 266 days (median, 120 days). Survival time was significantly higher for the group of human isolates (median, 211 days; minimum [min.], 71; maximum [max.], 266) compared to the group of animal isolates (median, 70 days; min., 47; max., 249) (P= 0.025). Although clustering of human versus animal strains was observed based on pulsed-field gel electrophoresis (PFGE) patterns, no relation between survival time and the presence of virulence genes was observed. Principal component analysis on the metabolic profiling data revealed distinct clustering of short- and long-surviving strains. The oxidization rate of propionic acid, α-ketobutyric acid, and α-hydroxybutyric acid was significantly higher for the long-surviving strains than for the short-surviving strains. The oxidative capacity ofE. coliO157 strains may be regarded as a phenotypic marker for enhanced survival in manure-amended soil. The large variation observed in survival is of importance for risk assessment models.

scholarly journals Genetic Determinants of Resistance to Extended-Spectrum Cephalosporin and Fluoroquinolone in Escherichia coli Isolated from Diseased Pigs in the United States

mSphere ◽  
2020 ◽  
Vol 5 (5) ◽  
Author(s):  
Shivdeep Singh Hayer ◽  
Seunghyun Lim ◽  
Samuel Hong ◽  
Ehud Elnekave ◽  
Timothy Johnson ◽  
...  
Keyword(s):  
United States ◽  
Escherichia Coli ◽  
High Risk ◽  
The United States ◽  
Genetic Determinants ◽  
Content Type ◽  
E Coli ◽  
Extended Spectrum ◽  
Animal Populations ◽  
Swine Population

ABSTRACT Fluoroquinolones and cephalosporins are critically important antimicrobial classes for both human and veterinary medicine. We previously found a drastic increase in enrofloxacin resistance in clinical Escherichia coli isolates collected from diseased pigs from the United States over 10 years (2006 to 2016). However, the genetic determinants responsible for this increase have yet to be determined. The aim of the present study was to identify and characterize the genetic basis of resistance against fluoroquinolones (enrofloxacin) and extended-spectrum cephalosporins (ceftiofur) in swine E. coli isolates using whole-genome sequencing (WGS). blaCMY-2 (carried by IncA/C2, IncI1, and IncI2 plasmids), blaCTX-M (carried by IncF, IncHI2, and IncN plasmids), and blaSHV-12 (carried by IncHI2 plasmids) genes were present in 87 (82.1%), 19 (17.9%), and 3 (2.83%) of the 106 ceftiofur-resistant isolates, respectively. Of the 110 enrofloxacin-resistant isolates, 90 (81.8%) had chromosomal mutations in gyrA, gyrB, parA, and parC genes. Plasmid-mediated quinolone resistance genes [qnrB77, qnrB2, qnrS1, qnrS2, and aac-(6)-lb′-cr] borne on ColE, IncQ2, IncN, IncF, and IncHI2 plasmids were present in 24 (21.8%) of the enrofloxacin-resistant isolates. Virulent IncF plasmids present in swine E. coli isolates were highly similar to epidemic plasmids identified globally. High-risk E. coli clones, such as ST744, ST457, ST131, ST69, ST10, ST73, ST410, ST12, ST127, ST167, ST58, ST88, ST617, ST23, etc., were also found in the U.S. swine population. Additionally, the colistin resistance gene (mcr-9) was present in several isolates. This study adds valuable information regarding resistance to critical antimicrobials with implications for both animal and human health. IMPORTANCE Understanding the genetic mechanisms conferring resistance is critical to design informed control and preventive measures, particularly when involving critically important antimicrobial classes such as extended-spectrum cephalosporins and fluoroquinolones. The genetic determinants of extended-spectrum cephalosporin and fluoroquinolone resistance were highly diverse, with multiple plasmids, insertion sequences, and genes playing key roles in mediating resistance in swine Escherichia coli. Plasmids assembled in this study are known to be disseminated globally in both human and animal populations and environmental samples, and E. coli in pigs might be part of a global reservoir of key antimicrobial resistance (AMR) elements. Virulent plasmids found in this study have been shown to confer fitness advantages to pathogenic E. coli strains. The presence of international, high-risk zoonotic clones provides worrisome evidence that resistance in swine isolates may have indirect public health implications, and the swine population as a reservoir for these high-risk clones should be continuously monitored.

scholarly journals Characterization of Multidrug-Resistant Escherichia coli Isolates from Animals Presenting at a University Veterinary Hospital

2011 ◽  
Vol 77 (20) ◽  
pp. 7104-7112 ◽  
Author(s):  
Maria Karczmarczyk ◽  
Yvonne Abbott ◽  
Ciara Walsh ◽  
Nola Leonard ◽  
Séamus Fanning
Keyword(s):  
Escherichia Coli ◽  
Molecular Mechanisms ◽  
Gene Array ◽  
Multidrug Resistant ◽  
Genetic Determinants ◽  
Gene Encoding ◽  
Content Type ◽  
E Coli ◽  
Class 1

ABSTRACTIn this study, we examined molecular mechanisms associated with multidrug resistance (MDR) in a collection ofEscherichia coliisolates recovered from hospitalized animals in Ireland. PCR and DNA sequencing were used to identify genes associated with resistance. Class 1 integrons were prevalent (94.6%) and contained gene cassettes recognized previously and implicated mainly in resistance to aminoglycosides, β-lactams, and trimethoprim (aadA1,dfrA1-aadA1,dfrA17-aadA5,dfrA12-orfF-aadA2,blaOXA-30-aadA1,aacC1-orf1-orf2-aadA1,dfr7). Class 2 integrons (13.5%) contained thedfrA1-sat1-aadA1gene array. The most frequently occurring phenotypes included resistance to ampicillin (97.3%), chloramphenicol (75.4%), florfenicol (40.5%), gentamicin (54%), neomycin (43.2%), streptomycin (97.3%), sulfonamide (98.6%), and tetracycline (100%). The associated resistance determinants detected includedblaTEM,cat,floR,aadB,aphA1,strA-strB,sul2, andtet(B), respectively. TheblaCTX-M-2gene, encoding an extended-spectrum β-lactamase (ESβL), andblaCMY-2, encoding an AmpC-like enzyme, were identified in 8 and 18 isolates, respectively. The mobility of the resistance genes was demonstrated using conjugation assays with a representative selection of isolates. High-molecular-weight plasmids were found to be responsible for resistance to multiple antimicrobial compounds. The study demonstrated that animal-associated commensalE. coliisolates possess a diverse repertoire of transferable genetic determinants. Emergence of ESβLs and AmpC-like enzymes is particularly significant. To our knowledge, theblaCTX-M-2gene has not previously been reported in Ireland.

scholarly journals Evolutionary Silence of the Acid Chaperone Protein HdeB in Enterohemorrhagic Escherichia coli O157:H7

2011 ◽  
Vol 78 (4) ◽  
pp. 1004-1014 ◽  
Author(s):  
Michelle Q. Carter ◽  
Jacqueline W. Louie ◽  
Clifton K. Fagerquist ◽  
Omar Sultan ◽  
William G. Miller ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Acid Resistance ◽  
Significant Loss ◽  
Enterohemorrhagic Escherichia Coli ◽  
Survival Strategies ◽  
Start Codon ◽  
Divergent Evolution ◽  
Content Type ◽  
E Coli ◽  
K 12

ABSTRACTThe periplasmic chaperones HdeA and HdeB are known to be important for cell survival at low pH (pH < 3) inEscherichia coliandShigellaspp. Here we investigated the roles of HdeA and HdeB in the survival of various enterohemorrhagicE. coli(EHEC) following exposure to pH 2.0. Similar to K-12 strains, the acid protections conferred by HdeA and HdeB in EHEC O145 were significant: loss of HdeA and HdeB led to over 100- to 1,000-fold reductions in acid survival, depending on the growth condition of prechallenge cells. However, this protection was much less inE. coliO157:H7 strains. Deletion ofhdeBdid not affect the acid survival of cells, and deletion ofhdeAled to less than a 5-fold decrease in survival. Sequence analysis of thehdeABoperon revealed a point mutation at the putative start codon of thehdeBgene in all 26E. coliO157:H7 strains analyzed, which shifted the ATG start codon to ATA. This mutation correlated with the lack of HdeB inE. coliO157:H7; however, the plasmid-borne O157-hdeBwas able to restore partially the acid resistance in anE. coliO145ΔhdeABmutant, suggesting the potential function of O157-HdeB as an acid chaperone. We conclude thatE. coliO157:H7 strains have evolved acid survival strategies independent of the HdeA/B chaperones and are more acid resistant than nonpathogenic K-12 for cells grown under nonfavorable culturing conditions such as in Luria-Bertani no-salt broth at 28°C. These results suggest a divergent evolution of acid resistance mechanisms withinE. coli.

scholarly journals An Environmental Shiga Toxin-Producing Escherichia coli O145 Clonal Population Exhibits High-Level Phenotypic Variation That Includes Virulence Traits

2015 ◽  
Vol 82 (4) ◽  
pp. 1090-1101 ◽  
Author(s):  
Michelle Qiu Carter ◽  
Beatriz Quinones ◽  
Xiaohua He ◽  
Wayne Zhong ◽  
Jacqueline W. Louie ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Shiga Toxin ◽  
Virulence Determinants ◽  
Content Type ◽  
Clinical Strains ◽  
Production Region ◽  
E Coli ◽  
Virulence Traits ◽  
Virulence Potential ◽  
High Level

ABSTRACTShiga toxin-producingEscherichia coli(STEC) serotype O145 is one of the major non-O157 serotypes associated with severe human disease. Here we examined the genetic diversity, population structure, virulence potential, and antimicrobial resistance profiles of environmental O145 strains recovered from a major produce production region in California. Multilocus sequence typing analyses revealed that sequence type 78 (ST-78), a common ST in clinical strains, was the predominant genotype among the environmental strains. Similarly, all California environmental strains belonged to H28, a common H serotype in clinical strains. Although most environmental strains carried an intactfliCgene, only one strain retained swimming motility. Diversestxsubtypes were identified, includingstx1a,stx2a,stx2c, andstx2e. Although no correlation was detected between thestxgenotype and Stx1 production, high Stx2 production was detected mainly in strains carryingstx2aonly and was correlated positively with the cytotoxicity of Shiga toxin. All environmental strains were capable of producing enterohemolysin, whereas only 10 strains were positive for anaerobic hemolytic activity. Multidrug resistance appeared to be common, as nearly half of the tested O145 strains displayed resistance to at least two different classes of antibiotics. The core virulence determinants of enterohemorrhagicE. coliwere conserved in the environmental STEC O145 strains; however, there was large variation in the expression of virulence traits among the strains that were highly related genotypically, implying a trend of clonal divergence. Several cattle isolates exhibited key virulence traits comparable to those of the STEC O145 outbreak strains, emphasizing the emergence of hypervirulent strains in agricultural environments.

scholarly journals Assessment of Adhesins as an Indicator of Pathovar-Associated Virulence Factors in Bovine Escherichia coli

2014 ◽  
Vol 80 (23) ◽  
pp. 7230-7234 ◽  
Author(s):  
Charlotte Valat ◽  
Karine Forest ◽  
Frédéric Auvray ◽  
Véronique Métayer ◽  
Thomas Méheut ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Beta Lactamase ◽  
Esbl Production ◽  
Content Type ◽  
Extended Spectrum Beta Lactamase ◽  
E Coli ◽  
Heat Stable ◽  
Significant Difference ◽  
Fimbrial Adhesins ◽  
The Relationship

ABSTRACTThe CS31A, F17, and F5 adhesins are usually targeted by serology-based methods to detect pathogenicEscherichia coliassociated with calf enteritis. However, the virulence traits of the selected isolates are still poorly described. Here, from a set of 349 diarrheagenicE. coliisolates from cattle, we demonstrated a 70.8% concordance rate (Cohen's kappa, 0.599) between serology- and PCR-based approaches for the detection of adhesins under field conditions. A 79% to 82.4% correspondence between the two methods was found for fimbrial adhesins, whereas major discrepancies (33%) were observed for CS31A-type antigens. Various F17A variants were found, such as F17Ac (20K) (50%), F17Aa (FY) (18.9%), F17Ab (8.1%), and F17Ad (111K) (5.4%), including a high proportion (17.6%) of new F17A internal combinations (F17Aab, F17Aac, and F17Abc) or untypeable variants. In addition, the highest proportion of pathovar-associated virulence factor (VF) genes was observed amongE. coliisolates that produced F5/F41 adhesins. A specific link between the heat-stable toxins related to the enterotoxigenicE. coli(ETEC) pathovar and adhesins was identified. STa was significantly linked to F5/F41 and EAST1 to CS31A adhesins (P< 0.001), respectively, whereas NTEC was associated with F17 adhesin (P= 0.001). Clustering between phylogroups according to the adhesin types was also observed. Also, few Shiga toxin-producingE. coli(STEC) or enteropathogenicE. coli(EPEC) pathovars were identified. Finally, no statistically significant difference was observed in the occurrence of extended-spectrum beta lactamase (ESBL) production according to the adhesins expressed by the isolates (P= 0.09). Altogether, this study gives new insights into the relationship between adhesins, VF, and antimicrobial resistance in calf enteritis and supports the need for further standardization of methodologies for such approaches.

scholarly journals Identification of Genes Important for Growth of Asymptomatic Bacteriuria Escherichia coli in Urine

2012 ◽  
Vol 80 (9) ◽  
pp. 3179-3188 ◽  
Author(s):  
Rebecca M. Vejborg ◽  
Mari R. de Evgrafov ◽  
Minh Duy Phan ◽  
Makrina Totsika ◽  
Mark A. Schembri ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Human Urine ◽  
Asymptomatic Bacteriuria ◽  
Genetic Determinants ◽  
Content Type ◽  
E Coli ◽  
Growth Defects ◽  
Cell Densities ◽  
Tract Infections

ABSTRACTEscherichia coliis the most important etiological agent of urinary tract infections (UTIs). Unlike uropathogenicE. coli, which causes symptomatic infections, asymptomatic bacteriuria (ABU)E. colistrains typically lack essential virulence factors and colonize the bladder in the absence of symptoms. While ABUE. colican persist in the bladder for long periods of time, little is known about the genetic determinants required for its growth and fitness in urine. To identify such genes, we have employed a transposon mutagenesis approach using the prototypic ABUE. colistrain 83972 and the clinical ABUE. colistrain VR89. Six genes involved in the biosynthesis of various amino acids and nucleobases were identified (carB,argE,argC,purA,metE, andilvC), and site-specific mutants were subsequently constructed inE. coli83972 andE. coliVR89 for each of these genes. In all cases, these mutants exhibited reduced growth rates and final cell densities in human urine. The growth defects could be complemented intransas well as by supplementation with the appropriate amino acid or nucleobase. When assessedin vivoin a mouse model,E. coli83972carABand 83972argCshowed a significantly reduced competitive advantage in the bladder and/or kidney during coinoculation experiments with the parent strain, whereas 83972metEand 83972ilvCdid not. Taken together, our data have identified several biosynthesis pathways as new important fitness factors associated with the growth of ABUE. coliin human urine.

scholarly journals Fimbrial Adhesins Produced by Atypical Enteropathogenic Escherichia coli Strains

2011 ◽  
Vol 77 (23) ◽  
pp. 8391-8399 ◽  
Author(s):  
Rodrigo T. Hernandes ◽  
Irina Velsko ◽  
Suely C. F. Sampaio ◽  
Waldir P. Elias ◽  
Roy M. Robins-Browne ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Phenotypic Expression ◽  
Complex Nature ◽  
Content Type ◽  
E Coli ◽  
Type 1 Pili ◽  
Gut Mucosa ◽  
Fimbrial Adhesins ◽  
Laminin Binding

ABSTRACTAtypical enteropathogenicEscherichia coli(aEPEC) has emerged as a significant cause of pediatric diarrhea worldwide; however, information regarding its adherence mechanisms to the human gut mucosa is lacking. In this study, we investigated the prevalence of several (fimA,ecpA,csgA,elfA, andhcpA) fimbrial genes in 71 aEPEC strains isolated from children with diarrhea (54 strains) and healthy individuals (17 strains) in Brazil and Australia by PCR. These genes are associated with adhesion and/or biofilm formation of pathogenic and commensalE. coli. Here, the most prevalent fimbrial genes found, in descending order, werehcpA(98.6%),ecpA(86%),fimA(76%),elfA(72%), andcsgA(19.7%). Phenotypic expression of pili in aEPEC strains was assessed by several approaches. We were not able to detect the hemorrhagic coli pilus (HCP) or theE. colilaminin-binding fimbriae (ELF) in these strains by using immunofluorescence. Type 1 pili and curli were detected in 59% (by yeast agglutination) and 2.8% (by Congo red binding and immunofluorescence) of the strains, respectively. TheE. colicommon pilus (ECP) was evidenced in 36.6% of the strains on bacteria adhering to HeLa cells by immunofluorescence, suggesting that ECP could play an important role in cell adherence for some aEPEC strains. This study highlights the complex nature of the adherence mechanisms of aEPEC strains involving the coordinated function of fimbrial (e.g., ECP) and nonfimbrial (e.g., intimin) adhesins and indicates that these strains bear several pilus operons that could potentially be expressed in different niches favoring colonization and survival in and outside the host.

scholarly journals Phylogenetically Related Argentinean and Australian Escherichia coli O157 Isolates Are Distinguished by Virulence Clades and Alternative Shiga Toxin 1 and 2 Prophages

2012 ◽  
Vol 78 (13) ◽  
pp. 4724-4731 ◽  
Author(s):  
Glen E. Mellor ◽  
Eby M. Sim ◽  
Robert S. Barlow ◽  
Beatriz A. D'Astek ◽  
Lucia Galli ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Shiga Toxin ◽  
Polymorphism Analysis ◽  
Escherichia Coli O157 ◽  
The Novel ◽  
Virulence Determinants ◽  
Content Type ◽  
E Coli ◽  
Uremic Syndrome ◽  
Insight Into

ABSTRACTShiga toxigenicEscherichia coliO157 is the leading cause of hemolytic uremic syndrome (HUS) worldwide. The frequencies ofstxgenotypes and the incidences of O157-related illness and HUS vary significantly between Argentina and Australia. Locus-specific polymorphism analysis revealed that lineage I/II (LI/II)E. coliO157 isolates were most prevalent in Argentina (90%) and Australia (88%). Argentinean LI/II isolates were shown to belong to clades 4 (28%) and 8 (72%), while Australian LI/II isolates were identified as clades 6 (15%), 7 (83%), and 8 (2%). Clade 8 was significantly associated with Shiga toxin bacteriophage insertion (SBI) typestx2(locus of insertion,argW) in Argentinean isolates (P< 0.0001). In Argentinean LI/II strains,stx2is carried by a prophage inserted atargW, whereas in Australian LI/II strains theargWlocus is occupied by the novelstx1prophage. In both Argentinean and Australian LI/II strains,stx2cis almost exclusively carried by a prophage inserted atsbcB. However, alternativeq933- orq21-related alleles were identified in the Australianstx2cprophage. Argentinean LI/II isolates were also distinguished from Australian isolates by the presence of the putative virulence determinant ECSP_3286 and the predominance of motile O157:H7 strains. Characteristics common to both Argentinean and Australian LI/II O157 strains included the presence of putative virulence determinants (ECSP_3620, ECSP_0242, ECSP_2687, ECSP_2870, and ECSP_2872) and the predominance of thetir255T allele. These data support further understanding of O157 phylogeny and may foster greater insight into the differential virulence of O157 lineages.

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