Enteroaggregative Escherichia coli O78:H10, the cause of an outbreak of urinary tract infection.

In 1991, multiresistant Escherichia coli O78:H10 strains caused an outbreak of urinary tract infections in Copenhagen, Denmark. The phylogenetic origin, clonal background, and virulence characteristics of the outbreak isolates, and their relationship to nonoutbreak O78:H10 strains according to these traits and resistance profiles, are unknown. Accordingly, we extensively characterized 51 archived E. coli O78:H10 isolates (48 human isolates from seven countries, including 19 Copenhagen outbreak isolates, and 1 each of calf, avian, and unknown-source isolates), collected from 1956 through 2000. E. coli O78:H10 was clonally heterogeneous, comprising one dominant clonal group (61% of isolates, including all 19 outbreak isolates) from ST10 (phylogenetic group A) plus several minor clonal groups (phylogenetic groups A and D). All ST10 isolates, versus 25% of non-ST10 isolates, were identified by molecular methods as enteroaggregative E. coli (EAEC) (P < 0.001). Genes present in >90% of outbreak isolates included fimH (type 1 fimbriae; ubiquitous in E. coli); fyuA, traT, and iutA (associated with extraintestinal pathogenic E. coli [ExPEC]); and sat, pic, aatA, aggR, aggA, ORF61, aaiC, aap, and ORF3 (associated with EAEC). An outbreak isolate was lethal in a murine subcutaneous sepsis model and exhibited characteristic EAEC "stacked brick" adherence to cultured epithelial cells. Thus, the 1991 Copenhagen outbreak was caused by a tight, non-animal-associated subset within a broadly disseminated O78:H10 clonal group (ST10; phylogenetic group A), members of which exhibit both ExPEC and EAEC characteristics, whereas O78:H10 isolates overall are phylogenetically diverse. Whether ST10 O78:H10 EAEC strains are both uropathogenic and diarrheagenic warrants further investigation.

Global distribution and epidemiologic associations of Escherichia coli clonal group A, 1998-2007.

Escherichia coli clonal group A (CGA) was first reported in 2001 as an emerging multidrug-resistant extraintestinal pathogen. Because CGA has considerable implications for public health, we examined the trends of its global distribution, clinical associations, and temporal prevalence for the years 1998-2007. We characterized 2,210 E. coli extraintestinal clinical isolates from 32 centers on 6 continents by CGA status for comparison with trimethoprim/sulfamethoxazole (TMP/SMZ) phenotype, specimen type, inpatient/outpatient source, and adult/child host; we adjusted for clustering by center. CGA prevalence varied greatly by center and continent, was strongly associated with TMP/SMZ resistance but not with other epidemiologic variables, and exhibited no temporal prevalence trend. Our findings indicate that CGA is a prominent, primarily TMP/SMZ-resistant extraintestinal pathogen concentrated within the Western world, with considerable pathogenic versatility. The stable prevalence of CGA over time suggests full emergence by the late 1990s, followed by variable endemicity worldwide as an antimicrobial drug-resistant public health threat.

The entomopathogenic bacterial endosymbionts Xenorhabdus and Photorhabdus: convergent lifestyles from divergent genomes.

Members of the genus Xenorhabdus are entomopathogenic bacteria that associate with nematodes. The nematode-bacteria pair infects and kills insects, with both partners contributing to insect pathogenesis and the bacteria providing nutrition to the nematode from available insect-derived nutrients. The nematode provides the bacteria with protection from predators, access to nutrients, and a mechanism of dispersal. Members of the bacterial genus Photorhabdus also associate with nematodes to kill insects, and both genera of bacteria provide similar services to their different nematode hosts through unique physiological and metabolic mechanisms. We posited that these differences would be reflected in their respective genomes. To test this, we sequenced to completion the genomes of Xenorhabdus nematophila ATCC 19061 and Xenorhabdus bovienii SS-2004. As expected, both Xenorhabdus genomes encode many anti-insecticidal compounds, commensurate with their entomopathogenic lifestyle. Despite the similarities in lifestyle between Xenorhabdus and Photorhabdus bacteria, a comparative analysis of the Xenorhabdus, Photorhabdus luminescens, and P. asymbiotica genomes suggests genomic divergence. These findings indicate that evolutionary changes shaped by symbiotic interactions can follow different routes to achieve similar end points.

Three-decade epidemiological analysis of Escherichia coli O15:K52:H1.

The successful Escherichia coli O15:K52:H1 clonal group provides a case study for the emergence of multiresistant clonal groups of Enterobacteriaceae generally. Accordingly, we tested the hypotheses that, over time, the O15:K52:H1 clonal group has become increasingly (i) virulent and (ii) resistant to antibiotics. One hundred archived international E. coli O15:K52:[H1] clinical isolates from 100 unique patients (1975 to 2006) were characterized for diverse phenotypic and molecular traits. All 100 isolates derived from phylogenetic group D and, presumptively, sequence type ST393. They uniformly carried the F16 papA allele and papG allele II (P fimbria structural subunit and adhesin variants), iha (adhesin-siderophore), fimH (type 1 fimbriae), fyuA (yersiniabactin receptor), iutA (aerobactin receptor), and kpsM II (group 2 capsule); 85% to 89% of them contained a complete copy of the pap operon and ompT (outer membrane protease). Slight additional virulence profile variation was evident, particularly within a minor diarrhea-associated subset (biotype C). However, in contrast to the clonal group's fairly stable virulence profiles over the past 30+ years, during the same interval the clonal group members' antimicrobial resistance profiles increased by a mean of 2.8 units per decade (P < 0.001). Moreover, the numbers of virulence genes and resistance markers were positively associated (P = 0.046), providing evidence against antimicrobial resistance and virulence being mutually exclusive in these strains. Thus, the O15:K52:H1 clonal group has become increasingly resistant to antimicrobials while maintaining (or expanding) its virulence potential, a particularly concerning trend if other emerging multiresistant enterobacterial clonal groups follow a similar pattern.

Epidemic clonal groups of Escherichia coli as a cause of antimicrobial-resistant urinary tract infections in Canada, 2002 to 2004.

The extent to which clonal spread contributes to emerging antimicrobial resistance in Escherichia coli is incompletely defined. To address this question within a recent, nationally representative strain collection, three established drug-resistant E. coli clonal groups (i.e., clonal group A, E. coli O15:K52:H1, and sequence type 131 [ST131]) were sought among 199 E. coli urine isolates recovered from across Canada from 2002 to 2004, with stratification by resistance to trimethoprim-sulfamethoxazole (TS) and fluoroquinolones (FQs). The isolates' clonal backgrounds, virulence genotypes, and macrorestriction profiles were assessed. The three clonal groups were found to account for 37.2% of isolates overall, but accounted for 0% of TS-susceptible (TS-S) and FQ-susceptible (FQ-S) isolates, 20% of TS-resistant (TS-R) and FQ-S isolates, 60% of TS-S and FQ-R isolates, and 68% of TS-R and FQ-R isolates (P < 0.001). E. coli ST131, the most prevalent clonal group, accounted for 23.1% of isolates overall and for 44% of the FQ-R isolates. Nearly all ST131 isolates were FQ-R (96%) but, notably, cephalosporin susceptible (98%). Although the distinctive virulence profiles of the FQ-R clonal group isolates were less extensive than those of the susceptible isolates, they were significantly more extensive than those of the other FQ-R isolates. These findings indicate that among the E. coli urine isolates studied, resistance to TS and FQs has a prominent clonal component, with the O15:K52:H1 clonal group and especially E. coli ST131 being the major contributors. These clonal groups appear to be more virulent than comparably resistant isolates, possibly contributing to their success as emerging multi-drug-resistant pathogens.

Clonal variation in Xenorhabdus nematophila virulence and suppression of Manduca sexta immunity.

Virulence of the insect pathogen Xenorhabdus nematophila is attributed in part to its ability to suppress immunity. For example, X. nematophila suppresses transcripts encoding several antimicrobial proteins, even in the presence of Salmonella enterica, an inducer of these transcripts. We show here that virulence and immune suppression phenotypes can be lost in a subpopulation of X. nematophila. Cells that have undergone 'virulence modulation' (vmo) have attenuated virulence and fail to suppress antimicrobial transcript levels, haemocyte aggregation and nodulation in Manduca sexta insects. When plated on certain media, vmo cells have a higher proportion of translucent (versus opaque) colonies compared with non-vmo cells. Like vmo strains, translucent colony isolates are defective in virulence and immune suppression. The X. nematophila genome encodes two 'opacity' genes with similarity to the Ail/PagC/Rck family of outer membrane proteins involved in adherence, invasion and serum resistance. Quantitative polymerase chain reaction analysis shows that RNA levels of one of these opacity genes, opaB, are higher in opaque relative to translucent colonies. We propose that in X. nematophila opaB may be one of several factors involved in immune suppression during infection, and expression of these factors can be co-ordinately eliminated in a subpopulation, possibly through a phase variation mechanism.

Determination of Escherichia coli O types by allele-specific polymerase chain reaction: application to the O types involved in human septicemia.

Escherichia coli can be serotyped by determination of somatic (O), capsular (K), and flagellar (H) antigens, and clear associations exist between specific O antigens and pathogenic behavior. However, E. coli is very challenging to O type with traditional serologic methods, making new methods for E. coli somatic antigen detection highly desirable. Here, we describe a simple alternative molecular method for determination of the E. coli O type based on allele-specific polymerase chain reaction amplification of the 5' portion of the rfb locus. We present our application of this new method to the detection of the 12 principal O types (O1, O2, O4, O6, O7, O12, O15, O16, O18, O25, O75, and O157) found among bloodstream isolates of E. coli. This method allowed us to determine the O types of 153 strains previously typed using reference methods with an accuracy exceeding 90%. Moreover, some rough or nonagglutinating strains can be successfully typed.

Experimental mouse lethality of Escherichia coli isolates, in relation to accessory traits, phylogenetic group, and ecological source.

BACKGROUND: Whether accessory traits, phylogenetic background, or ecological source best predicts extraintestinal virulence within Escherichia coli is undefined. METHODS: A total of 90 E. coli strains (18 fecal isolates and 72 extraintestinal-infection isolates) were characterized for 55 accessory traits and phylogenetic group (A, B1, B2, or D). Bacterial traits and ecological source were compared with experimental mouse lethality. RESULTS: Of the 90 strains, 41% were "killers" (i.e., killed > or =90% of mice). By univariate analysis, multiple group B2-associated traits (including malX [pathogenicity-island marker], pap [P fimbriae] elements, usp [uropathogenic-specific protein], and fyuA [yersiniabactin system]) were most closely associated with killer status, followed by group B2 (or non-group A) status and then by nonfecal origin. Stepwise multivariate analysis identified pap, malX, usp, fyuA, and B2 (all of which were positive predictors) and ireA (which was a negative predictor) as significant predictors of killer status. Killer strains segregated significantly from nonkiller strains, according to accessory-trait profiles. Factorial analysis of correspondence placed group B2 among the traits most closely associated with killer status, but not as the closest. CONCLUSIONS: Specific group B2-associated accessory traits are more potent predictors of experimental virulence among E. coli isolates than is either phylogenetic background or ecological source. Molecular typing can estimate an E. coli isolate's extraintestinal virulence potential, regardless of source.

Similarity between human and chicken Escherichia coli isolates in relation to ciprofloxacin resistance status.

BACKGROUND: The food supply is suspected to be a source of fluoroquinolone-resistant Escherichia coli that cause disease in humans, but supporting molecular data are lacking. METHODS: We performed a molecular-epidemiological comparison, in Barcelona, Spain (1996-1998), of 117 contemporaneous, geographically matched E. coli isolates from humans (35 blood isolates and 33 fecal) or chickens (49 fecal) that were either susceptible (n = 57) or resistant (n = 60) to ciprofloxacin and analyzed them by phylogenetic group, virulence genotype, and O antigens using random amplified polymorphic DNA (RAPD) analysis and pulsed-field gel electrophoresis (PFGE). RESULTS: When analyzed by phylogenetic distribution, virulence profiles, and O antigens, resistant human isolates were distinct from susceptible human isolates but were largely indistinguishable from chicken isolates, whereas resistant and susceptible chicken isolates were similar. Susceptible human isolates contained more virulence-associated genes and more frequently expressed virulence-associated O antigens than did resistant human or any chicken isolates. Certain resistant human isolates closely resembled chicken isolates by RAPD and PFGE analysis. CONCLUSIONS: Ciprofloxacin-resistant E. coli may arise de novo in poultry from susceptible progenitors, be transmitted to humans via the food supply, and go on to cause potentially life-threatening infections. If confirmed, these findings would mandate efforts to eliminate this reservoir of drug-resistant pathogens and/or to block their transmission to humans.

Virulence factors of Escherichia coli isolates that produce CTX-M-type extended-spectrum beta-lactamases.

This study determined the phylogenetic groups and virulence factors of 37 Escherichia coli isolates producing types of CTX-M compared with those of 19 isolates producing different types of extended-spectrum beta-lactamases (ESBLs) in a well-defined North American population. Most CTX-M-14 producers (97%) were from phylogenic group D; 67% of the CTX-M-15 producers were from group B2. A single CTX-M-14-producing strain belonged to clonal group A. There were significant prevalence differences for individual virulence factors among CTX-M producers and nonproducers; however, aggregate virulence factor scores were similar. CTX-M producers more commonly caused repeat urinary tract infections. Our results indicate that CTX-M type predicts phylogenetic background, and the virulence potential of ESBL-producing E. coli isolates is a complex issue, requiring further study and ongoing surveillance.

Xenorhabdus nematophila requires an intact iscRSUA-hscBA-fdx operon to colonize Steinernema carpocapsae nematodes.

An insertion between iscA and hscB of the Xenorhabdus nematophila iscRSUA-hscBA-fdx locus, predicted to encode Fe-S assembly machinery, prevented colonization of Steinernema carpocapsae nematodes. The insertion disrupted cotranscription of iscA and hscB, but did not reduce hscBA expression, suggesting that X. nematophila requires coordinated expression of the isc-hsc-fdx locus for colonization.