Structural and functional studies of Escherichia coli aggregative adherence fimbriae (AAF/V) reveal a deficiency in extracellular matrix binding

Detection and characterization of potentially hybrid enteroaggregative Escherichia coli (EAEC) strains isolated from urinary tract infection

Uropathogenic Escherichia coli (UPEC) have the potential to receive the virulence markers of intestinal pathotypes and transform into various important hybrid pathotypes. This study aimed to investigate the frequency and characteristics of hybrid enteroaggregative E. coli (EAEC)/UPEC strains. Out of 202 UPEC strains, nine (4.5%) were detected as hybrid EAEC/UPEC. These strains carried one to four iron uptake systems. Among nine investigated pathogenicity islands (PAIs), PAI IV536, PAI II536, and PAI ICFT073 were found in 9 (100%), 3 (33.3%), and 1 (11.1%) strains, respectively. The chuA and sitA genes were detected in 5 (55.5%) and 3 (33.3%) hybrid strains, respectively. Six hybrid strains were found to be typical extraintestinal pathogenic E. coli (ExPEC) according to their virulence traits. Most of the hybrid strains belonged to the phylogenetic group E (6/9). Among the hybrid strains, seven (7/9) were able to form biofilm and adhere to cells; however, only two strains penetrated into the HeLa cells. Our findings reveal some of the virulence characteristics of hybrid strains that lead to fitness and infection in the urinary tract. These strains, with virulence factors of intestinal and non-intestinal pathotypes, may become emerging pathogens in clinical settings; therefore, further studies are needed to reveal their pathogenicity mechanisms and so that preventive measures can be taken.

Aggregative adherence fimbriae form compact structures as seen by SAXS

Bacterial colonization is mediated by fimbriae, which are thin hair-like appendages dispersed from the bacterial surface. The aggregative adherence fimbriae from enteroaggregative E. coli are secreted through the outer membrane and consist of polymerized minor and major pilin subunits. Currently, the understanding of the structural morphology and the role of the minor pilin subunit in the polymerized fimbriae are limited. In this study we use small-angle X-ray scattering to reveal the structural morphology of purified fimbriae in solution. We show that the aggregative fimbriae are compact arrangements of subunit proteins Agg5A + Agg3B which are assembled pairwise on a flexible string rather than extended in relatively straight filaments. Absence of the minor subunit leads to less compact fimbriae, but did not affect the length. The study provides novel insights into the structural morphology and assembly of the aggregative adherence fimbriae. Our study suggests that the minor subunit is not located at the tip of the fimbriae as previously speculated but has a higher importance for the assembled fimbriae by affecting the global structure.

Diversity in Genetic Regulation of Bacterial Fimbriae Assembled by the Chaperone Usher Pathway

Bacteria express different types of hair-like proteinaceous appendages on their cell surface known as pili or fimbriae. These filamentous structures are primarily involved in the adherence of bacteria to both abiotic and biotic surfaces for biofilm formation and/or virulence of non-pathogenic and pathogenic bacteria. In pathogenic bacteria, especially Gram-negative bacteria, fimbriae play a key role in bacteria-host interactions which are critical for bacterial invasion and infection. Fimbriae assembled by the Chaperone Usher pathway (CUP) are widespread within the Enterobacteriaceae, and their expression is tightly regulated by specific environmental stimuli. Genes essential for expression of CUP fimbriae are organised in small blocks/clusters, which are often located in proximity to other virulence genes on a pathogenicity island. Since these surface appendages play a crucial role in bacterial virulence, they have potential to be harnessed in vaccine development. This review covers the regulation of expression of CUP-assembled fimbriae in Gram-negative bacteria and uses selected examples to demonstrate both dedicated and global regulatory mechanisms.

Adhesin related genes as potential markers for the enteroaggregative Escherichia coli category

Enteroaggregative Escherichia coli (EAEC) is an important cause of diarrhea in children and adults worldwide. This pathotype is phenotypically characterized by the aggregative-adherence (AA) pattern in HEp-2 cells and genetically associated to the presence of the aatA gene. EAEC pathogenesis relies in different virulence factors. At least, three types of adhesins have been specifically associated with EAEC strains: the five variants of the aggregative adherence fimbriae (AAF), the aggregative forming pilus (AFP) and more recently, a fibrilar adhesin named CS22. Our study aimed to evaluate the presence of AAF, AFP and CS22-related genes among 110 EAEC strains collected from feces of children with diarrhea. The presence of aggR (EAEC virulence regulator) and genes related to AAFs (aggA, aafA, agg3A, agg4A, agg5A and agg3/4C), AFP (afpA1 and afpR) and CS22 (cseA) was detected by PCR, and the adherence patterns were evaluated on HeLa cells. aggR-positive strains comprised 83.6% of the collection; among them, 80.4% carried at least one AAF-related gene and presented the AA pattern. aggA was the most frequent AAF-related gene (28.4% of aggR+ strains). cseA was detected among aggR+ (16.3%) and aggR- strains (22.2%); non-adherent strains or strains presenting AA pattern were observed in both groups. afpR and afpA1 were exclusively detected among aggR- strains (77.8%), most of which (71.4%) also presented AA pattern. Our results indicate that AAF- and AFP-related genes may contribute to identify EAEC strains, while the presence of cseA and its importance as an EAEC virulence factor and genotypic marker needs to be further evaluated.

Characterization of Uropathogenic Escherichia coli Reveals Hybrid Isolates of Uropathogenic and Diarrheagenic (UPEC/DEC) E. coli

(1) Background: Pathogenic Escherichia coli are divided into two groups: diarrheagenic (DEC) and extraintestinal pathogenic (ExPEC) E. coli. ExPEC causing urinary tract infections (UTIs) are termed uropathogenic E. coli (UPEC) and are the most common cause of UTIs worldwide. (2) Methods: Here, we characterized 112 UPEC in terms of phylogroup, serotype, the presence of virulence factor-encoding genes, and antimicrobial resistance. (3) Results: The majority of the isolates were assigned into the phylogroup B2 (41.07%), and the serogroups O6 (12.5%) and O25 (8.9%) were the most frequent. Five hybrid UPEC (4.5%), with markers from two DEC pathotypes, i.e., atypical enteropathogenic (aEPEC) and enteroaggregative (EAEC) E. coli, were identified, and designated UPEC/aEPEC (one isolate) and UPEC/EAEC (four isolates), respectively. Three UPEC/EAEC harbored genes from the pap operon, and the UPEC/aEPEC carried ibeA. The highest resistance rates were observed for ampicillin (46.4%) and trimethoprim/sulfamethoxazole (34.8%), while 99.1% of the isolates were susceptible to nitrofurantoin and/or fosfomycin. Moreover, 9.8% of the isolates were identified as Extended Spectrum β-Lactamase producers, including one hybrid UPEC/EAEC. (4) Conclusion: Our data reinforce that hybrid UPEC/DEC are circulating in the city of Botucatu, Brazil, as uropathogens. However, how and whether these combinations of genes influence their pathogenicity is a question that remains to be elucidated.

Identification and characterisation of enteroaggregative Escherichia coli subtypes associated with human disease

Enteroaggregative E. coli (EAEC) are a major cause of diarrhoea worldwide. Due to their heterogeneity and carriage in healthy individuals, identification of diagnostic virulence markers for pathogenic strains has been difficult. In this study, we have determined phenotypic and genotypic differences between EAEC strains of sequence types (STs) epidemiologically associated with asymptomatic carriage (ST31) and diarrhoeal disease (ST40). ST40 strains demonstrated significantly enhanced intestinal adherence, biofilm formation, and pro-inflammatory interleukin-8 secretion compared with ST31 isolates. This was independent of whether strains were derived from diarrhoea patients or healthy controls. Whole genome sequencing revealed differences in putative virulence genes encoding aggregative adherence fimbriae, E. coli common pilus, flagellin and EAEC heat-stable enterotoxin 1. Our results indicate that ST40 strains have a higher intrinsic potential of human pathogenesis due to a specific combination of virulence-related factors which promote host cell colonization and inflammation. These findings may contribute to the development of genotypic and/or phenotypic markers for EAEC strains of high virulence.

Analysis of the Virulence Profile and Phenotypic Features of Typical and Atypical Enteroaggregative Escherichia coli (EAEC) Isolated From Diarrheal Patients in Brazil

Enteroaggregative Escherichia coli (EAEC) is an important agent of acute and persistent diarrhea in children and adults worldwide. Here we report a characterization of 220 EAEC isolates, 88.2% (194/220) of which were typical and 11.8% (26/220) were atypical, obtained from diarrheal patients during seven years (2010-2016) of epidemiological surveillance in Brazil. The majority of the isolates were assigned to phylogroups A (44.1%, 97/220) or B1 (21.4%, 47/220). The aggregative adherence (AA) pattern was detected in 92.7% (204/220) of the isolates, with six of them exhibiting AA concomitantly with a chain-like adherence pattern; and agg5A and agg4A were the most common adhesin-encoding genes, which were equally detected in 14.5% (32/220) of the isolates. Each of 12 virulence factor-encoding genes (agg4A, agg5A, pic, aap, aaiA, aaiC, aaiG, orf3, aar, air, capU, and shf) were statistically associated with typical EAEC (P < 0.05). The genes encoding the newly described aggregate-forming pili (AFP) searched (afpB, afpD, afpP, and afpA2), and/or its regulator (afpR), were exclusively detected in atypical EAEC (57.7%, 15/26), and showed a significant association with this subgroup of EAEC (P < 0.001). In conclusion, we presented an extensive characterization of the EAEC circulating in the Brazilian settings and identified the afp genes as putative markers for increasing the efficiency of atypical EAEC diagnosis.

Enteroaggregative Escherichia coli subclinical and clinical infections

PURPOSE OF REVIEW

The current review is to update the results on epidemiology, pathobiology, and genes related to virulence, clinical presentation, molecular diagnosis, antimicrobial resistance, and extraintestinal infection of enteroaggregative Escherichia coli (EAEC).

RECENT FINDINGS

EAEC subclinical infection was significantly associated with reduced length at 2 years of age and EAEC and coinfections were associated with reduced delta weight-for-length and weight-for-age z-scores in the first 6 months of age in the MAL-ED birth cohort study. EAEC was associated with malnutrition in children 6-24 months of age in prospective case-control studies in Bangladesh and Brazil. Virulence gene-based studies have suggested aggregative fimbriae II may be a major contributor to disease, whereas AggR-activated regulator a marker of less severe disease. The high ability of EAEC colonization likely exacerbates effects of other microbial virulence strategies. Molecular diagnosis has been useful for understanding EAEC burden, although different criteria may relate to different pathogenic outcomes.

SUMMARY

EAEC gained special interest in the past few years, especially due to association with growth decrements in children with subclinical infections and its important role as a copathogen. Understanding of EAEC pathogenesis advanced but further research is needed for elucidating both microbial and host factors influencing infection outcomes.

Diversity of strategies used by atypical enteropathogenic Escherichia coli to induce attaching and effacing lesion in epithelial cells

PURPOSE

This study aimed to characterize 82 atypical enteropathogenic Escherichia coli (aEPEC) isolates, obtained from patients with diarrhea in Brazil, regarding their adherence patterns on HeLa cells and attaching and effacing (AE) lesion pathways.

METHODOLOGY

The adherence and fluorescence-actin staining (FAS) assays were performed using HeLa cells. AE lesion pathways were determined through the detection of tyrosine residue 474 (Y474) phosphorylation in the Tir protein, after its translocation to host cells, and by PCR assays for tir genotyping and detection of Tir-cytoskeleton coupling protein (tccP) genes.

RESULTS

Regarding the adherence pattern, determined in the presence of d-mannose, 12 isolates (14.6 %) showed the localized adherence (LA)-like pattern, 3 (3.7  %) the aggregative adherence pattern and 4 (4.9  %) a hybrid LA/diffuse adherence pattern. In addition, 36 (43.9  %) isolates displayed an undefined adherence, and 26 (31.7  %) were non-adherent (NA), while one (1.2 %) caused cell detachment. Among the 26 NA aEPEC isolates, 11 showed a type 1 pilus-dependent adherence in assays performed without d-mannose, while 15 remained NA. Forty-eight (58.5 %) aEPEC were able to trigger F-actin accumulation underneath adherent bacteria (FAS-positive), which is an important feature of AE lesions. The majority (58.3 %) of these used the Tir-Nck pathway, while 39.6  % may use both Tir-Nck and Tir-TccP pathways to induce AE lesions.

CONCLUSION

Our results reveal the diversity of strategies used by aEPEC isolates to interact with and damage epithelial host cells, thereby causing diarrheal diseases.