Shiga toxin 2a in Escherichia albertii

Detection of prolong excretion of Escherichia albertii in stool specimens of a 7-year-old child by a newly developed Eacdt gene-based quantitative real-time PCR method and molecular characterization of the isolates

Escherichia albertii is an emerging zoonotic foodborne pathogen. The clinical significance of this bacterium has increasingly been recognized worldwide. However, diagnostic method has not yet been established and its clinical manifestations are not fully understood. Here, we show that an Eacdt gene-based quantitative real-time PCR (qRT-PCR) developed in this study is 100% specific and sensitive when tested with 39 E. albertii and 36 non-E. albertii strains, respectively. Detection limit of the real-time PCR was 10 colony forming unit (CFU) and 1 pg of genomic DNA per PCR tube. When E. albertii was spiked with 4 × 100-106 CFU per mL to stool of healthy person, detection limit was 4.0 × 103 and 4.0 CFU per mL before and after enrichment culture, respectively. Moreover, the qRT-PCR was able to detect E. albertii in five children out of 246 (2%) but none from 142 adults suffering from gastroenteritis. All five E. albertii strains isolated carried eae and paa genes, however, only one strain harbored stx2f genes. Long-term shedding of stx2f gene-positive E. albertii in a child stool could be detected because of the qRT-PCR developed in this study which might have been missed if only conventional PCR and culture methods were employed. Furthermore, E. albertii isolated from siblings with diarrhea showed clonality by PFGE analysis. Taken together, these data suggest that the Eacdt gene-based qRT-PCR developed for the detection of E. albertii is useful and will assist in determining the real burden and clinical manifestation of E. albertii infections.

An interlaboratory study on the detection method for Escherichia albertii in food using real time PCR assay and selective agars

Escherichia albertii is an emerging enteropathogen. Although E. albertii-specific detection and isolation methods have been developed, their efficiency on food samples have not yet been systematically studied. To establish a series of effective methods for detecting E. albertii in food, an interlaboratory study was conducted in 11 laboratories using enrichment with modified E. coli broth supplemented with cefixime and tellurite (CT-mEC), real-time PCR assay, and plating on four kinds of selective agars. This study focused on the detection efficiency of an E. albertii-specific real-time PCR assay (EA-rtPCR) and plating on deoxycholate hydrogen sulfide lactose agar (DHL), MacConkey agar (MAC), DHL supplemented with rhamnose and xylose (RX-DHL), and MAC supplemented with rhamnose and xylose (RX-MAC). Chicken and bean sprout samples were inoculated with E. albertii either at 17.7 CFU/25 g (low inoculation level) or 88.5 CFU/25 g (high inoculation level), and uninoculated samples were used as controls. The sensitivity of EA-rtPCR was 1.000 for chicken and bean sprout samples inoculated with E. albertii at low and high inoculation levels. The Ct values of bean sprout samples were higher than those of the chicken samples. Analysis of microbial distribution by 16S rRNA gene amplicon sequencing in enriched cultures of bean sprout samples showed that approximately >96 % of the population comprised unidentified genus of family Enterobacteriaceae and genus Acinetobacter in samples which E. albertii was not isolated. The sensitivity of the plating methods for chicken and bean sprout samples inoculated with a high inoculation level of E. albertii was 1.000 and 0.848-0.970, respectively. The sensitivity of the plating methods for chicken and bean sprout samples inoculated with a low inoculation level of E. albertii was 0.939-1.000 and 0.515-0.727, respectively. The E. albertii-positive rate in all colonies isolated in this study was 89-90 % in RX-DHL and RX-MAC, and 64 and 44 % in DHL and MAC, respectively. Therefore, the sensitivity of RX-supplemented agar was higher than that of the agars without these sugars. Using a combination of enrichment in CT-mEC and E. albertii isolation on selective agars supplemented with RX, E. albertii at an inoculation level of over 17.5 CFU/25 g of food was detected with a sensitivity of 1.000 and 0.667-0.727 in chicken and bean sprouts, respectively. Therefore, screening for E. albertii-specific genes using EA-rtPCR followed by isolation with RX-DHL or RX-MAC is an efficient method for E. albertii detection in food.

A Comprehensive Review on Shiga Toxin Subtypes and Their Niche-Related Distribution Characteristics in Shiga-Toxin-Producing E. coli and Other Bacterial Hosts

Shiga toxin (Stx), the main virulence factor of Shiga-toxin-producing E. coli (STEC), was first discovered in Shigella dysenteriae strains. While several other bacterial species have since been reported to produce Stx, STEC poses the most significant risk to human health due to its widespread prevalence across various animal hosts that have close contact with human populations. Based on its biochemical and molecular characteristics, Shiga toxin can be grouped into two types, Stx1 and Stx2, among which a variety of variants and subtypes have been identified in various bacteria and host species. Interestingly, the different Stx subtypes appear to vary in their host distribution characteristics and in the severity of diseases that they are associated with. As such, this review provides a comprehensive overview on the bacterial species that have been recorded to possess stx genes to date, with a specific focus on the various Stx subtype variants discovered in STEC, their prevalence in certain host species, and their disease-related characteristics. This review provides a better understanding of the Stx subtypes and highlights the need for rapid and accurate approaches to toxin subtyping for the proper evaluation of the health risks associated with Shiga-toxin-related bacterial food contamination and human infections.

Genetic Diversity and Expression of Intimin in Escherichia albertii Isolated from Humans, Animals, and Food

Escherichia albertii (E. albertii) is an emerging diarrheagenic pathogen associated with sporadic infections and human gastroenteric outbreaks. The eae gene, which encodes intimin in the locus of enterocyte effacement (LEE) operon, contributes to the establishment of the attaching and effacing (A/E) lesion. Increasing collection of E. albertii strains from various sources has resulted in a rapid increase in the number of eae subtypes. This study systematically investigated the prevalence and genetic diversity of eae among E. albertii strains isolated from humans, animals, and food. The eae gene was present in 452/459 (98.5%) strains and 23 subtypes were identified including two novel subtypes, named eae-α11 and η3. The eae-σ subtype was the most predominant among humans, animals, and food-derived strains, while eae-γ3, τ, and α11 were unique in human-derived strains. Additionally, the LEE island was also analyzed at genomic, transcriptional, and functional levels through genomic analysis, quantitative reverse transcription PCR, and HEp-2 cell adherence assays, respectively. The eae transcript levels were variable and associated with eae subtypes. Three different adherence patterns, including localized adherence-like (LAL), diffuse adherence (DA), and detachment (DE), were observed among E. albertii strains. This study demonstrated a high diversity of functional intimin in E. albertii strains isolated from humans, animals, and food. Further in vivo and in vitro studies are warranted to better elucidate the role of intimin or LEE in different genetic backgrounds.

Genomic and Phenotypic Characterization of Shiga Toxin-Producing Escherichia albertii Strains Isolated from Wild Birds in a Major Agricultural Region in California

Escherichia albertii is an emerging foodborne pathogen. To better understand the pathogenesis and health risk of this pathogen, comparative genomics and phenotypic characterization were applied to assess the pathogenicity potential of E. albertii strains isolated from wild birds in a major agricultural region in California. Shiga toxin genes stx2f were present in all avian strains. Pangenome analyses of 20 complete genomes revealed a total of 11,249 genes, of which nearly 80% were accessory genes. Both core gene-based phylogenetic and accessory gene-based relatedness analyses consistently grouped the three stx2f-positive clinical strains with the five avian strains carrying ST7971. Among the three Stx2f-converting prophage integration sites identified, ssrA was the most common one. Besides the locus of enterocyte effacement and type three secretion system, the high pathogenicity island, OI-122, and type six secretion systems were identified. Substantial strain variation in virulence gene repertoire, Shiga toxin production, and cytotoxicity were revealed. Six avian strains exhibited significantly higher cytotoxicity than that of stx2f-positive E. coli, and three of them exhibited a comparable level of cytotoxicity with that of enterohemorrhagic E. coli outbreak strains, suggesting that wild birds could serve as a reservoir of E. albertii strains with great potential to cause severe diseases in humans.

Escherichia albertii as a Potential Enteropathogen in the Light of Epidemiological and Genomic Studies

Escherichia albertii is a new enteropathogen of humans and animals. The aim of the study was to assess the prevalence and pathogenicity of E. albertii strains isolated in northeastern Poland using epidemiological and genomic studies. In 2015-2018, a total of 1154 fecal samples from children and adults, 497 bird droppings, 212 food samples, 92 water samples, and 500 lactose-negative E. coli strains were tested. A total of 42 E. albertii strains were isolated. The PCR method was suitable for their rapid identification. In total, 33.3% of E. albertii isolates were resistant to one antibiotic, and 16.7% to two. Isolates were sensitive to cefepime, imipenem, levofloxacin, gentamicin, trimethoprim/sulfamethoxazole, and did not produce ESBL β-lactamases. High genetic variability of E. albertii has been demonstrated. In the PFGE method, 90.5% of the strains had distinct pulsotypes. In MLST typing, 85.7% of strains were assigned distinct sequence types (STs), of which 64% were novel ST types. Cytolethal distending toxin (CDT) and Paa toxin genes were found in 100% of E. albertii isolates. Genes encoding toxins, IbeA, CdtB type 2, Tsh and Shiga (Stx2f), were found in 26.2%, 9.7%, 1.7%, and 0.4% of E. albertii isolates, respectively. The chromosome size of the tested strains ranged from 4,573,338 to 5,141,010 bp (average 4,784,003 bp), and at least one plasmid was present in all strains. The study contributes to a more accurate assessment of the genetic diversity of E. albertii and the potential threat it poses to public health.

Melibiose–X-Gal–MacConkey Agar for Presumptive Differentiation of Escherichia albertii from E. coli and Salmonella from Poultry Meat

The bacterial foodborne enteropathogen Escherichia albertii, despite enjoying increased attention paid to its pathogenesis, global dissemination, and antimicrobial resistance capacity, remains difficult to identify from human foods. The primary objective of this study was to develop and test a selective and differential plating medium for the isolation of E. albertii from enteric pathogens commonly transmitted via fresh poultry meat, namely E. coli and Salmonella enterica. MacConkey agar supplemented with α-D-+-melibiose and the lactose analogue X-gal was prepared and used to differentially enumerate E. albertii, Salmonella, and E. coli from inoculated ground chicken meat. The medium, MXgMac agar, differentiated the inoculated pathogens with a greater degree of efficiency than did the previously developed E. albertii-selective medium xylose–rhamnose–melibiose (XRM) MacConkey agar, based on differential usage of the lactose analogue and melibiose. Chicken-derived feces and litter samples were subsequently tested using the medium and found not to contain E. albertii by 16S rRNA gene amplification. MXgMac agar facilitates improved differential recovery of E. albertii and other enteric pathogens from poultry meat versus other E. albertii selective/differential media.

Identification and Genomic Characterization of Escherichia albertii in Migratory Birds from Poyang Lake, China

Escherichia albertii is an emerging zoonotic foodborne enteropathogen leading to human gastroenteritis outbreaks. Although E. albertii has been isolated from birds which have been considered as the potential reservoirs of this bacterium, its prevalence in migratory birds has rarely been described. In this study, E. albertii in migratory birds from Poyang Lake was investigated and characterized using whole genome sequencing. Eighty-one fecal samples from nine species of migratory birds were collected and 24/81 (29.6%) tested PCR-positive for E. albertii-specific genes. A total of 47 isolates was recovered from 18 out of 24 PCR-positive samples. All isolates carried eae and cdtB genes. These isolates were classified into eight E. albertii O-genotypes (EAOgs) (including three novel EAOgs) and three E. albertii H-genotypes (EAHgs). Whole genome phylogeny separated migratory bird-derived isolates into different lineages, some isolates in this study were phylogenetically closely grouped with poultry-derived or patient-derived strains. Our findings showed that migratory birds may serve as an important reservoir for heterogeneous E. albertii, thereby acting as potential transmission vehicles of E. albertii to humans.

Development of a Novel Real-Time Polymerase Chain Reaction Assay to Detect Escherichia albertii in Chicken Meat

Escherichia albertii is an emerging enteropathogen. Several foodborne outbreaks of E. albertii have been reported in Japan; however, foods associated with most outbreaks remain unidentified. Therefore, polymerase chain reaction (PCR) assays detecting E. albertii specifically and sensitively are required. Primers and probe for real-time PCR assays targeting E. albertii-specific gene (EA-rtPCR) was designed. With 74 strains, including 43 E. albertii strains and several of its close relatives, EA-rtPCR specifically amplified E. albertii; therefore, the sensitivity of EA-rtPCR was then evaluated. The detection limits were 2.8 and 2.0-3.2 log colony-forming unit (CFU)/mL for E. albertii culture and enriched chicken culture inoculated with the pathogen, respectively. In addition, E. albertii was detected from 25 g of chicken meat inoculated with 0.1 log CFU of the pathogen by EA-rtPCR. The detection of E. albertii from chicken meat by EA-rtPCR was also evaluated by comparing with the nested-PCR assay, and 28 retail chicken meat and 193 dissected body parts from 21 chicken carcass were tested. One and three chicken meat were positive in the nested-PCR assay and EA-rtPCR, respectively. Fourteen carcasses had at least one body part that was positive for EA-rtPCR, and 36 and 48 samples were positive for the nested-PCR assay and EA-rtPCR, respectively. A total of 37 strains of E. albertii were isolated from seven PCR-positive samples obtained from six chicken carcass. All E. albertii isolates harbored eae gene, and were classified as E. albertii O-genotype (EAOg)3 or EAOg4 by EAO-genotyping. The EA-rtPCR developed in this study has potential to improve E. albertii detection in food and advance research on E. albertii infection.

Isolation and characterization of Escherichia albertii from wild and safeguarded animals in Okayama Prefecture and its prefectural borders, Japan

Escherichia albertii has recently been recognized as a zoonotic enteropathogen associated with food poisoning. The reservoirs and transmission routes of this bacterium to humans are still unclear. In this study, we performed a survey of E. albertii in fecal specimens of wild and safeguarded animals in Okayama Prefecture and its prefectural borders, Japan to understand its reservoir in the environment. Forty-two E. albertii were isolated from 10 and 31 droppings of 59 crows and 125 starlings, respectively. Fifty-two E. albertii were isolated from 906 mammal droppings, and out of 52 isolates, origin of 33, 6 and 1 isolates were from martens, foxes, and rabbit, respectively, however, origin of 12 isolates remained unknown. Three E. albertii were isolated from two and one feces of 159 dogs and 76 cats, respectively. Pulsed-filed gel electrophoresis analysis grouped 97 E. albertii strains into 66 pulsotypes including 36 and 30 pulsotypes of isolates from mammals and birds, respectively. E. albertii strains isolated in this study were genetically diverse. Although clonal relationship was not observed between mammal and bird isolates, there were intra- and inter-species relationship in mammalian isolates. All E. albertii strains were positive for eae and Eacdt virulence genes. Furthermore, 20 and 7 strains also carried Eccdt-I and stx2f genes, respectively. Taken together, the results indicate that genetically diverse and potentially virulent E. albertii are distributed among various wild and safeguarded animals in Okayama Prefecture, and the animals could also be reservoirs of E. albertii.

Microbiology and Epidemiology of Escherichia albertii—An Emerging Elusive Foodborne Pathogen

Escherichia albertii, a close relative of E. coli, is an emerging zoonotic foodborne pathogen associated with watery diarrhea mainly in children and immunocompromised individuals. E. albertii was initially classified as eae-positive Hafnia alvei, however, as more genetic and biochemical information became available it was reassigned to its current novel taxonomy. Its infections are common under conditions of poor hygiene with confirmed transmission via contaminated water and food, mainly poultry-based products. This pathogen has been isolated from various domestic and wild animals, with most isolates being derived from birds, implying that birds among other wild animals might act as its reservoir. Due to the absence of standardized isolation and identification protocols, E. albertii can be misidentified as other Enterobacteriaceae. Exploiting phenotypes such as its inability to ferment rhamnose and xylose and PCR assays targeting E. albertii-specific genes such as the cytolethal distending toxin and the DNA-binding transcriptional activator of cysteine biosynthesis encoding genes can be used to accurately identify this pathogen. Several gaps exist in our knowledge of E. albertii and need to be bridged. A deeper understanding of E. albertii epidemiology and physiology is required to allow the development of effective measures to control its transmission and infections. Overall, current data suggest that E. albertii might play a more significant role in global infectious diarrhea cases than previously assumed and is often overlooked or misidentified. Therefore, simple, and efficient diagnostic tools that cover E. albertii biodiversity are required for effective isolation and identification of this elusive agent of diarrhea.

Improved Genomic Identification, Clustering, and Serotyping of Shiga Toxin-Producing Escherichia coli Using Cluster/Serotype-Specific Gene Markers

Shiga toxin-producing Escherichia coli (STEC) have more than 470 serotypes. The well-known STEC O157:H7 serotype is a leading cause of STEC infections in humans. However, the incidence of non-O157:H7 STEC serotypes associated with foodborne outbreaks and human infections has increased in recent years. Current detection and serotyping assays are focusing on O157 and top six (“Big six”) non-O157 STEC serogroups. In this study, we performed phylogenetic analysis of nearly 41,000 publicly available STEC genomes representing 460 different STEC serotypes and identified 19 major and 229 minor STEC clusters. STEC cluster-specific gene markers were then identified through comparative genomic analysis. We further identified serotype-specific gene markers for the top 10 most frequent non-O157:H7 STEC serotypes. The cluster or serotype specific gene markers had 99.54% accuracy and more than 97.25% specificity when tested using 38,534 STEC and 14,216 non-STEC E. coli genomes, respectively. In addition, we developed a freely available in silico serotyping pipeline named STECFinder that combined these robust gene markers with established E. coli serotype specific O and H antigen genes and stx genes for accurate identification, cluster determination and serotyping of STEC. STECFinder can assign 99.85% and 99.83% of 38,534 STEC isolates to STEC clusters using assembled genomes and Illumina reads respectively and can simultaneously predict stx subtypes and STEC serotypes. Using shotgun metagenomic sequencing reads of STEC spiked food samples from a published study, we demonstrated that STECFinder can detect the spiked STEC serotypes, accurately. The cluster/serotype-specific gene markers could also be adapted for culture independent typing, facilitating rapid STEC typing. STECFinder is available as an installable package (https://github.com/LanLab/STECFinder) and will be useful for in silico STEC cluster identification and serotyping using genome data.

Detection of Escherichia albertii in Retail Oysters

ABSTRACT

Escherichia albertii is an emerging foodborne pathogen. Owing to its distribution in river water, it is important to determine the presence of E. albertii in aquaculture-related foods. In this study, we investigated the distribution of E. albertii in retail oyster samples. A total of 427 raw oyster samples (385 Pacific oysters and 42 Japanese rock oysters) were enriched in modified Escherichia coli broth (mEC) or mEC supplemented with novobiocin (NmEC) at 42°C. The cultures were used for E. albertii-specific nested PCR assay, as well as for E. albertii isolation using deoxycholate hydrogen sulfide lactose agar (DHL), DHL supplemented with rhamnose and xylose, and MacConkey agar supplemented with rhamnose and xylose. The population of E. albertii in nested PCR-positive samples was determined using the most-probable-number (MPN) method. E. albertii isolates were subjected to biochemical and genetic characterization. E. albertii was detected in 5 (1.6%) of 315 Pacific oyster samples (one piece each), 2 (2.9%) of 70 Pacific oyster samples (25 g each), and 2 (4.8%) of 42 Japanese rock oyster samples procured from four geographically distinct regions. A total of 64 E. albertii strains were isolated from eight of the nine nested PCR assay-positive oyster samples, and the MPN value was under the detection limit (<3 MPN/10 g). A specific season or month for detecting E. albertii was not observed in this study, suggesting that the pathogen is present in seawater. All the E. albertii isolates, except one, were positive for the virulence factor eae, indicating that these isolates have the potential to infect humans.

HIGHLIGHTS

[Molecular epidemiology of Escherichia albertii, emerging zoonotic enteropathogen]

Escherichia albertii is an emerging zoonotic enteric pathogen, closely related to E. coli. Several foodborne outbreaks caused by E. albertii accounting for >100 patients have recently occurred in Japan. This bacterium carries eae gene, similar to enteropathogenic E. coli. Some of them harbor Shiga toxin 2 (stx2a, stx2f) genes, primary virulence factor of enterohemorrhagic E. coli (EHEC), suggesting that the Stx2 producers could cause severe diseases such as HUS in humans. However, due to lack of the knowledges about its bacteriological characteristics and of the diagnostic methods, E. albertii-related infections might have been underestimated, and the infection sources and routes have not yet been understood. We had continuously performed molecular epidemiological studies targeting for cytolethal distending toxin-producing E. coli, and unexpectedly found that cdt-II gene-positive isolates were not E. coli but E. albertii. This finding led us to initiate research more focusing on E. albertii. We have constructed simple, efficient and reliable methods for the detection, isolation and identification of this bacterium by developing an E. albertii-specific PCR assay targeting Eacdt genes and E. albertii-selective isolation medium named XRM-MacConkey agar. We have also identified raccoons as a potential natural reservoir of E. albertii through wildlife survey using these methods. Here, I describe what I have studied with my colleagues.

Inconsistent PCR detection of Shiga toxin-producing Escherichia coli: Insights from whole genome sequence analyses

Shiga toxin-producing Escherichia coli (STEC) have been linked to food-borne disease outbreaks. As PCR is routinely used to screen foods for STEC, it is important that factors leading to inconsistent detection of STEC by PCR are understood. This study used whole genome sequencing (WGS) to investigate causes of inconsistent PCR detection of stx1, stx2, and serogroup-specific genes. Fifty strains isolated from Alberta feedlot cattle from three different studies were selected with inconsistent or consistent detection of stx and serogroup by PCR. All isolates were initially classified as STEC by PCR. Sequencing was performed using Illumina MiSeq® with sample library by Nextera XT. Virtual PCRs were performed using Geneious and bacteriophage content was determined using PHASTER. Sequencing coverage ranged from 47 to 102x, averaging 74x, with sequences deposited in the NCBI database. Eleven strains were confirmed by WGS as STEC having complete stxA and stxB subunits. However, truncated stx fragments occurred in twenty-two other isolates, some having multiple stx fragments in the genome. Isolates with complete stx by WGS had consistent stx1 and stx2 detection by PCR, although one also having a stx2 fragment had inconsistent stx2 PCR. For all STEC and 18/39 non-STEC, serogroups determined by PCR agreed with those determined by WGS. An additional three WGS serotypes were inconclusive and two isolates were Citrobacter spp. Results demonstrate that stx fragments associated with stx-carrying bacteriophages in the E. coli genome may contribute to inconsistent detection of stx1 and stx2 by PCR. Fourteen isolates had integrated stx bacteriophage but lacked complete or fragmentary stx possibly due to partial bacteriophage excision after sub-cultivation or other unclear mechanisms. The majority of STEC isolates (7/11) did not have identifiable bacteriophage DNA in the contig(s) where stx was located, likely increasing the stability of stx in the bacterial genome and its detection by PCR.

Detection, isolation and molecular characterization of Escherichia albertii in wild birds in West Japan

Escherichia albertii is an emerging zoonotic foodborne pathogen. Several outbreaks of E. albertii have occurred particularly in Japan. Although birds have been considered as one of the most important reservoirs of this bacterium, information regarding the prevalence in birds is still scanty. We performed a survey of E. albertii in wild birds in Japan, and examined characteristics of the isolates. E. albertii specific gene was detected in 5 cloacal swabs out of 156 birds by PCR. Four E. albertii were isolated from a swallow with 2 different E. albertii strains and 2 pigeons in a flock by XRM-MacConkey agar. These isolates were assigned to biogroup 3, shown no resistance to any antimicrobials tested, and classified into 2 EAO-genotypes (EAOg2 and EAOg33) and untypable. Similar to clinical E. albertii strains, these isolates carried virulence genes including eae (n=4), paa (n=4), Eccdt-I (n=2) and stx2f (n=1) in addition to Eacdt. Interestingly, stx2f genes in a strain were located on an inducible bacteriophage, which can confer the ability to produce Stx2f to E. coli. In conclusion, Japanese wild birds carried E. albertii at the similar levels to the reported prevalence in birds. These isolates may have a potential to cause gastroenteritis in humans.

Prevalence of Escherichia albertii in Raccoons (Procyon lotor), Japan

Natural reservoirs of Escherichia albertii remain unclear. In this study, we detected E. albertii by PCR in 248 (57.7%) of 430 raccoons from Osaka, Japan, and isolated 143 E. albertii strains from the 62 PCR-positive samples. These data indicate that raccoons could be a natural reservoir of E. albertii in Japan.

Evaluating Methods for Detecting Escherichia albertii in Chicken Meat

ABSTRACT

Escherichia albertii is an emerging foodborne pathogen. The source of the E. albertii infection in most foodborne outbreaks is unknown because E. albertii is difficult to isolate from suspected food or water. E. albertii has a broad host range among birds and can be isolated from chicken meat. In this study, PCR assay, enrichment, and isolation conditions for detecting E. albertii in chicken meat were evaluated. The growth of 47 E. albertii strains isolated in Japan between 1994 and 2018 and a type strain was evaluated in modified EC broth (mEC) and mEC supplemented with novobiocin (NmEC) and on media containing carbohydrates. The enzyme used for the nested PCR, the enrichment conditions, the most-probable-number (MPN) method, and agar media were also evaluated with chicken meat. To distinguish E. albertii from presumptive non-E. albertii bacteria, desoxycholate hydrogen sulfide lactose agar (DHL), MacConkey agar (MAC), and these agars supplemented with rhamnose and xylose (RX-DHL and RX-MAC, respectively) were used. All E. albertii strains grew in mEC and NmEC at both 36 and 42°C and did not utilize rhamnose, sucrose, or xylose. Both the first and nested PCRs with TaKaRa Ex Taq, which was 10 to 100 times more active than the other enzymes, produced positive results in enrichment culture of 25 g of chicken meat inoculated with >20 CFU of E. albertii and incubated in mEC and NmEC at 42°C for 22 ± 2 h. Thus, the first PCR was sensitive enough to detect E. albertii in chicken meat. The MPN values in mEC and NmEC were 0.5- and 2.3-fold higher than the original inoculated bacterial levels, respectively. E. albertii in chicken meat was more efficiently isolated with enrichment in NmEC (70.1 to 100%) and plating onto RX-DHL (85.4%) and RX-MAC (100%) compared with enrichment in mEC (53.5 to 83.3%) and plating onto DHL (70.1%) and MAC (92.4%). Thus, optimized conditions for the surveillance of E. albertii contamination in food and investigations of E. albertii outbreaks, including the infectious dose, were clarified.

HIGHLIGHTS

Detection of Escherichia Albertii in Urinary and Gastrointestinal Infections in Kermanshah, Iran

Background: Escherichia albertii has been recently isolated from the feces of people with gastroenteritis as a pathogen that causes diarrhea. Due to insufficient information on the phenotypic and biochemical characteristics of E. albertii, it is difficult to distinguish it from other species of the Enterobacteriaceae family and, therefore, it is mistakenly identified as Escherichia coli or even Hafnia alvei. Objective: The present study which was conducted for the first time in Iran aimed to identify E. albertii in samples from individuals afflicted with urinary and gastrointestinal infections by using the polymerase chain reaction (PCR) method. The required samples were obtained from clinical laboratories in Kermanshah. Materials and Methods: Firstly, a total of 60 urinary and 40 fecal samples identified as E. coli in clinical laboratories were re-evaluated in terms of specific phenotypic and biochemical characteristics of E. coli. Then, two lysP and mdh genes were detected for E. albertii, and the uidA gene was found for E. coli by PCR using specific primers pairs. Results: The results from phenotypic and biochemical tests indicated that all samples shared common characteristics with E. coli. However, PCR findings demonstrated that out of 100 samples, 6 samples (6%) contained specific genes of E. coli while 94 remaining samples (94%) showed the uidA gene. Out of the given 6 samples, 5 samples carried urinary tract infections and only one showed gastrointestinal infection. Conclusion: Our study findings revealed that E. albertii could have been considered as one of the causes for urinary and gastrointestinal infections in Iran, and that it was mistakenly identified as E. coli in clinical laboratories.

The Changing Face of the Family Enterobacteriaceae (Order: "Enterobacterales"): New Members, Taxonomic Issues, Geographic Expansion, and New Diseases and Disease Syndromes

The family Enterobacteriaceae has undergone significant morphogenetic changes in its more than 85-year history, particularly during the past 2 decades (2000 to 2020). The development and introduction of new and novel molecular methods coupled with innovative laboratory techniques have led to many advances. We now know that the global range of enterobacteria is much more expansive than previously recognized, as they play important roles in the environment in vegetative processes and through widespread environmental distribution through insect vectors. In humans, many new species have been described, some associated with specific disease processes. Some established species are now observed in new infectious disease settings and syndromes. The results of molecular taxonomic and phylogenetics studies suggest that the current family Enterobacteriaceae should possibly be divided into seven or more separate families. The logarithmic explosion in the number of enterobacterial species described brings into question the relevancy, need, and mechanisms to potentially identify these taxa. This review covers the progression, transformation, and morphogenesis of the family from the seminal Centers for Disease Control and Prevention publication (J. J. Farmer III, B. R. Davis, F. W. Hickman-Brenner, A. McWhorter, et al., J Clin Microbiol 21:46-76, 1985, https://doi.org/10.1128/JCM.21.1.46-76.1985) to the present.

Isolation and characterization of Escherichia albertii in poultry at the pre-harvest level

Escherichia albertii, often misidentified as Escherichia coli, has become an emerging foodborne human enteric pathogen. However, the prevalence and major animal reservoirs of this significant pathogen are still not clear. Here, we performed comprehensive microbiological, molecular, comparative genomics and animal studies to understand the status and features of E. albertii in the US domestic and food animals. Although no E. albertii was identified in a total of 1,022 diverse E. coli strains isolated from pets and food animals in a retrospective screening, in a pilot study, E. albertii was successfully isolated from a broiler farm (6 out of 20 chickens). The chicken E. albertii isolates showed clonal relationship as indicated by both pulsed-field gel electrophoresis (PFGE) and whole-genome sequence analysis. The isolated chicken E. albertii displayed multidrug resistance; all the resistance determinants including the extended-spectrum beta-lactamase gene, carried by plasmids, could be conjugatively transferred to E. coli, which was further confirmed by S1-PFGE and Southern hybridization. Whole-genome sequence-based phylogenetic analysis showed the chicken E. albertii strains were phylogenetically close to those of human origins. Challenge experiment demonstrated that the E. albertii strains isolated from human and wild bird could successfully colonize in the chicken intestine. Together, this study, for the first time, reported the isolation of E. albertii in poultry at the pre-hrvest level. The findings from multi-tier characterization of the chicken E. albertii strains indicated the importance of chickens as a reservoir for E. albertii. A large scale of E. albertii survey in poultry production at the pre-harvest level is highly warranted in the future.

Escherichia albertii Pathogenesis

Escherichia albertii is an emerging enteropathogen of humans and many avian species. This bacterium is a close relative of Escherichia coli and has been frequently misidentified as enteropathogenic or enterohemorrhagic E. coli due to their similarity in phenotypic and genetic features, such as various biochemical properties and the possession of a type III secretion system encoded by the locus of enterocyte effacement. This pathogen causes outbreaks of gastroenteritis, and some strains produce Shiga toxin. Although many genetic and phenotypic studies have been published and the genome sequences of more than 200 E. albertii strains are now available, the clinical significance of this species is not yet fully understood. The apparent zoonotic nature of the disease requires a deeper understanding of the transmission routes and mechanisms of E. albertii to develop effective measures to control its transmission and infection. Here, we review the current knowledge of the phylogenic relationship of E. albertii with other Escherichia species and the biochemical and genetic properties of E. albertii, with particular emphasis on the repertoire of virulence factors and the mechanisms of pathogenicity, and we hope this provides a basis for future studies of this important emerging enteropathogen.

O-antigen biosynthesis gene clusters of Escherichia albertii: their diversity and similarity to Escherichia coli gene clusters and the development of an O-genotyping method

Escherichia albertii is a recently recognized human enteropathogen that is closely related to Escherichia coli. In many Gram-negative bacteria, including E. coli, O-antigen variation has long been used for the serotyping of strains. In E. albertii, while eight O-serotypes unique to this species have been identified, some strains have been shown to exhibit genetic or serological similarity to known E. coli/Shigella O-serotypes. However, the diversity of O-serotypes and O-antigen biosynthesis gene clusters (O-AGCs) of E. albertii remains to be systematically investigated. Here, we analysed the O-AGCs of 65 E. albertii strains and identified 40 E. albertii O-genotypes (EAOgs) (named EAOg1–EAOg40). Analyses of the 40 EAOgs revealed that as many as 20 EAOgs exhibited significant genetic and serological similarity to the O-AGCs of known E. coli/Shigella O-serotypes, and provided evidence for the inter-species horizontal gene transfer of O-AGCs between E. albertii and E. coli. Based on the sequence variation in the wzx gene among the 40 EAOgs, we developed a multiplex PCR-based O-genotyping system for E. albertii (EAO-genotyping PCR) and verified its usefulness by genotyping 278 E. albertii strains from various sources. Although 225 (80.9 %) of the 278 strains could be genotyped, 51 were not assigned to any of the 40 EAOgs, indicating that further analyses are required to better understand the diversity of O-AGCs in E. albertii and improve the EAO-genotyping PCR method. A phylogenetic view of E. albertii strains sequenced so far is also presented with the distribution of the 40 EAOgs, which provided multiple examples for the intra-species horizontal transfer of O-AGCs in E. albertii.

Accurate identification of Escherichia albertii by matrix-assisted laser desorption ionization-time of flight mass spectrometry

A specific identification protocol for Escherichia albertii by using a MALDI-TOF/MS method was developed. For this purpose, a novel database was established which can differentiate E. albertii from E. coli by combining the mass spectra obtained from 58 E. albertii and 36 E. coli strains.

Hypoosmotic stress induces flagellar biosynthesis and swimming motility in Escherichia albertii

Bacteria use flagella as propellers to move to favorable environments. Escherichia albertii, a growing cause of foodborne illness and diarrhea, is reportedly non-motile and lacks flagella on its surface. Here, we report that 27 out of 59 E. albertii strains, collected mainly from humans and birds, showed swimming motility when cultured at low osmotic pressure. The biosynthesis of flagella in E. albertii cells was induced under ambient temperature and hypoosmotic pressure: conditions which resemble aquatic environments. Flagellar induction increased E. albertii survival in the intestinal epithelial cell culture containing gentamicin. Although genes involved in chemotaxis are not present in the E. albertii genome, the addition of glutamic acid, an amino acid known to regulate the internal cell osmolarity, augmented the proportion of swimming cells by 35-fold. These results suggest that flagellar biosynthesis and motility in E. albertii cells are controlled by their internal and external osmolarity.

Ikeda et al. report that enteropathogen E. albertii, thought to be a non-motile microorganism, may form flagella and acquire swimming motility in a hypoosmotic environment and ambient temperatures. Further addition of glutamic acid, an amino acid known to regulate the internal cell osmolarity, augments the proportion of swimming cells.

Escherichia albertii EA046 (O9) harbors two polysaccharide gene clusters for synthesis of the O-antigen by the Wzx/Wzy-dependent pathway and a mannan shared by Escherichia coli O8 by the Wzm/Wzt-dependent pathway

O antigen is a polysaccharide chain of a lipopolysaccharide on the outer membrane of Gram-negative bacteria. O-antigen-based serotyping and molecular typing are widely used for epidemiological and surveillance purposes. Two polysaccharides were isolated by Sephadex G-50 gel-permeation chromatography following mild acid degradation of the lipopolysaccharide of Escherichia albertii EA046 assigned to serotype O9. The polysaccharide eluted first was considered as the O-antigen. It was composed of tetrasaccharide repeating units containing two residues of d-Man and one residue each of d-Gal and d-GlcNAc as well as glycerol phosphate. It had the following unique structure which was established by NMR spectroscopy applied to the initial and dephosphorylated polysaccharides: The polysaccharide eluted from the gel second was identified as a mannan with a → 3)-β-d-Manp-(1 → 2)-α-d-Manp-(1 → 2)-α-d-Manp-(1 → trisaccharide repeating unit. In E. albertii EA046, two polysaccharide gene clusters were found at a chromosomal locus flanked by the conserved galF gene and the histidine synthesis operon (his). They were suggested to drive the biosynthesis of the O-antigen by the Wzy/Wzy-dependent pathway and the mannan by the Wzm/Wzt-dependent pathway. The mannan shares the structure and gene cluster with a polysaccharide isolated earlier from the lipopolysaccharide of Escherichia coli O8.

Development of a specific cytolethal distending toxin (cdt) gene (Eacdt)-based PCR assay for the detection of Escherichia albertii

Many Escherichia albertii isolates, an emerging pathogen of human and birds, might have been misidentified due to the difficulty of differentiating this bacterium from Escherichia coli and Shigella spp. by routine biochemical tests, resulting in underestimation of E. albertii infections. We have developed a polymerase chain reaction (PCR) assay that targets E. albertii cytolethal distending toxin (Eacdt) genes, which include the genes previously identified as Escherichia coli cdt-II. This assay could generate a single 449-bp PCR product in each of 67 confirmed E. albertii strains but failed to produce PCR product from any of the tested non-E. albertii enteric strains belonging to 37 different species, indicating 100% sensitivity and specificity of the PCR assay. The detection limit was 10 CFU per PCR tube and could detect 10⁵ CFU E. albertii per gram of spiked healthy human stool. The Eacdt gene-based PCR could be useful for simple, rapid, and accurate detection and identification of E. albertii.

Hazard Identification and Characterization: Criteria for Categorizing Shiga Toxin-Producing Escherichia coli on a Risk Basis†

Shiga toxin-producing Escherichia coli (STEC) comprise a large, highly diverse group of strains. Since the emergence of STEC serotype O157:H7 as an important foodborne pathogen, serotype data have been used for identifying STEC strains, and this use continued as other serotypes were implicated in human infections. An estimated 470 STEC serotypes have been identified, which can produce one or more of the 12 known Shiga toxin (Stx) subtypes. The number of STEC serotypes that cause human illness varies but is probably higher than 100. However, many STEC virulence genes are mobile and can be lost or transferred to other bacteria; therefore, STEC strains that have the same serotype may not carry the same virulence genes or pose the same risk. Although serotype information is useful in outbreak investigations and surveillance studies, it is not a reliable means of assessing the human health risk posed by a particular STEC serotype. To contribute to the development of a set of criteria that would more reliably support hazard identification, this review considered each of the factors contributing to a negative human health outcome: mild diarrhea, bloody diarrhea, and hemolytic uremic syndrome (HUS). STEC pathogenesis involves entry into the human gut (often via ingestion), attachment to the intestinal epithelial cells, and elaboration of Stx. Production of Stx, which disrupts normal cellular functions and causes cell damage, alone without adherence of bacterial cells to gut epithelial cells is insufficient to cause severe illness. The principal adherence factor in STEC is the intimin protein coded by the eae gene. The aggregative adherence fimbriae adhesins regulated by the aggR gene of enteroaggregative E. coli strains are also effective adherence factors. The stx_2a gene is most often present in locus of enterocyte effacement ( eae)-positive STEC strains and has consistently been associated with HUS. The stx_2a gene has also been found in eae-negative, aggR-positive STEC that have caused HUS. HUS cases where other stx gene subtypes were identified indicate that other factors such as host susceptibility and the genetic cocktail of virulence genes in individual isolates may affect their association with severe diseases.

The Evasive Enemy: Insights into the Virulence and Epidemiology of the Emerging Attaching and Effacing Pathogen Escherichia albertii

The diarrheic attaching and effacing (A/E) pathogen Escherichia albertii was first isolated from infants in Bangladesh in 1991, although the bacterium was initially classified as Hafnia alvei Subsequent genetic and biochemical interrogation of these isolates raised concerns about their initial taxonomic placement. It was not until 2003 that these isolates were reassigned to the novel taxon Escherichia albertii because they were genetically more closely related to E. coli, although they had diverged sufficiently to warrant a novel species name. Unfortunately, new isolates continue to be mistyped as enteropathogenic E. coli (EPEC) or enterohemorrhagic E. coli (EHEC) owing to shared traits, most notably the ability to form A/E lesions. Consequently, E. albertii remains an underappreciated A/E pathogen, despite multiple reports demonstrating that many provisional EPEC and EHEC isolates incriminated in disease outbreaks are actually E. albertii Metagenomic studies on dozens of E. albertii isolates reveal a genetic architecture that boasts an arsenal of candidate virulence factors to rival that of its better-characterized cousins, EPEC and EHEC. Beyond these computational comparisons, studies addressing the regulation, structure, function, and mechanism of action of its repertoire of virulence factors are lacking. Thus, the paucity of knowledge about the epidemiology, virulence, and antibiotic resistance of E. albertii, coupled with its misclassification and its ability to develop multidrug resistance in a single step, highlights the challenges in combating this emerging pathogen. This review seeks to synthesize our current but incomplete understanding of the biology of E. albertii.

Development of a multiplex PCR targeting eae, stx and cdt genes in genus Escherichia and detection of a novel cdtB gene in Providencia rustigianii

This study was aimed to develop a multiplex PCR (m-PCR) for the detection of Escherichia coli attaching and effacing (eae), Shiga toxin (stx) and cytolethal distending toxin (cdt) genes encoding important virulence factors of diarrheagenic E. coli such as EPEC, STEC, and Escherichia albertii. For this purpose, the m-PCR was designed to detect eae, all the subtypes of stx (stx1, stx2a-g except stx2f) and cdt (I-V) genes. The m-PCR was validated with 58 and 55 target gene-positive and negative strains of different sources, respectively. Sensitivity and specificity of the m-PCR were 100%. The m-PCR could also detect the eae, stx and cdt genes in bacteria spiked into stool specimens with or without enrichment culture. Clinical specimens collected from children with diarrhea were tested by the m-PCR, and 27 eae and 32 cdt genes were detected. Among them, three cdt-II and one untypable cdt gene-positive bacteria were isolated and identified as E. albertii and Providencia rustigianii, respectively. This is the first report demonstrating the presence of cdtB gene in P. rustigianii. These results indicate that the m-PCR is useful for surveillance of eae, stx and cdt gene-positive bacteria, not only EPEC, STEC and E. albertii but also P. rustigianii.

Implications of stx loss for clinical diagnostics of Shiga toxin-producing Escherichia coli

The dynamics related to the loss of stx genes from Shiga toxin-producing Escherichia coli remain unclear. Current diagnostic procedures have shortcomings in the detection and identification of STEC. This is partly owing to the fact that stx genes may be lost during an infection or in the laboratory. The aim of the present study was to provide new insight into in vivo and in vitro stx loss in order to improve diagnostic procedures. Results from the study support the theory that loss of stx is a strain-related phenomenon and not induced by patient factors. It was observed that one strain could lose stx both in vivo and in vitro. Whole genome comparison of stx-positive and stx-negative isolates from the same patient revealed that different genomic rearrangements, such as complete or partial loss of the parent prophage, may be factors in the loss of stx. Of diagnostic interest, it was shown that patients can be co-infected with different E. coli pathotypes. Therefore, identification of eae-positive, but stx-negative isolates should not be interpreted as "Shiga toxin-lost" E. coli without further testing. Growth and recovery of STEC were supported by different selective agar media for different strains, arguing for inclusion of several media in STEC diagnostics.

Factors in the emergence of serious human infections associated with highly pathogenic strains of shiga toxin-producing Escherichia coli

The appearance of highly pathogenic strains of Shiga toxin (Stx)-producingEscherichia. coli (STEC) has owed largely to the acquisition of Stx-encoding prophages by strains of E. coli that have pre-existing potential as enteric pathogens, such as atypical enteropathogenic E. coli (aEPEC) and enteroaggregative E. coli (EAEC). However, while high pathogenic potential is necessary, it is not sufficient for such strains to have a serious public health impact (i.e., large outbreaks, many cases of HUS, or both). To do so requires susceptible hosts and additional elements related to transmission, such as, socio-economic, societal, and lifestyle, factors. Two examples are discussed to illustrate this. The factors involved in the emergence of serious disease associated with E. coli O157:H7 in the 1980s probably included a massive increase in population exposure to this pathogen, likely as a result of the introduction of factory farming of cattle in the 1960s, and the development and wide patronage of fast food hamburger restaurants, and, potentially, waning immunity to intimin as a result of the reduction of incidence of enteropathogenic E. coli (EPEC) infection. In the devastating outbreak of Stx2-positiveEAEC O104:H4 in 2011, the wide distribution of the proposed vehicle of transmission, imported fenugreek seeds, was decisive in the exposure of a large population in Central Europe to this pathogen. Contributing factors likely included a preference for eating raw sprouts as a healthy food choice by the affected cases, many of whom were women. Low population levels of immunity to Stx2 probably contributed to the severe clinical outcome. A better understanding of the factors responsible for the emergence of potentially dangerous STEC pathogens as well as of extensive and serious disease associated with them can enhance public health strategies to respond to them.

Draft Genome Sequence of the Intimin-Positive Enteropathogenic Escherichia albertii Strain MBT-EA1, Isolated from Lettuce

The genome of the intimin (eae)-harboring Escherichia albertii strain MBT-EA1, isolated from lettuce in Germany, was sequenced. Sequence analysis showed the assembled draft genome size to be 4,560,948 bp, containing a predicted total of 4,414 protein-encoding genes, 11 rRNAs, and 82 tRNAs. Furthermore, three plasmid sequences were found.

Multidrug-Resistant Escherichia albertii: Co-occurrence of β-Lactamase and MCR-1 Encoding Genes

Escherichia albertii is an emerging member of the Enterobacteriaceae causing human and animal enteric infections. Antimicrobial resistance among enteropathogens has been reported to be increasing in the past years. The purpose of this study was to investigate antibiotic resistance and resistance genes in E. albertii isolated from Zigong city, Sichuan province, China. The susceptibility to 21 antimicrobial agents was determined by Kirby-Bauer disk diffusion method. The highest prevalence was tetracycline resistance with a rate of 62.7%, followed by resistance to nalidixic acid and streptomycin with a rate of 56.9 and 51.0%, respectively. All isolates were sensitive or intermediate susceptible to imipenem, meropenem, amoxicillin-clavulanic acid, and levofloxacin. Among 51 E. albertii isolates, 15 were extended-spectrum β-lactamase-producing as confirmed by the double disk test. The main β-lactamase gene groups, i.e., blaTEM, blaSHV, and blaCTX-M, were detected in17, 20, and 22 isolates, respectively. Furthermore, four colistin-resistant isolates with minimum inhibitory concentrations of 8 mg/L were identified. The colistin-resistant isolates all harbored mcr-1 and blaCTX-M-55. Genome sequencing showed that E. albertii strain SP140150 carried mcr-1 and blaCTX-M-55 in two different plasmids. This study provided significant information regarding antibiotic resistance profiles and identified the co-occurrence of β-lactamase and MCR-1 encoding genes in E. albertii isolates.

Characterization of four Escherichia albertii isolates collected from animals living in Antarctica and Patagonia

Escherichia albertii is a recently discovered species with a limited number of well characterized strains. The aim of this study was to characterize four of the E. albertii strains, which were among 41 identified Escherichia strains isolated from the feces of living animals on James Ross Island, Antarctica, and Isla Magdalena, Patagonia. Sequencing of 16S rDNA, automated ribotyping, and rep-PCR were used to identify the four E. albertii isolates. Phylogenetic analyses based on multi-locus sequence typing showed these isolates to be genetically most similar to the members of E. albertii phylogroup G3. These isolates encoded several virulence factors including those, which are characteristic of E. albertii (cytolethal distending toxin and intimin) as well as bacteriocin determinants that typically have a very low prevalence in E. coli strains (D, E7). Moreover, E. albertii protein extracts caused cell cycle arrest in human cell line A375, probably because of cytolethal distending toxin activity.

Defining the Genetic Features of O-Antigen Biosynthesis Gene Cluster and Performance of an O-Antigen Serotyping Scheme for Escherichia albertii

Escherichia albertii is a newly described and emerging diarrheagenic pathogen responsible for outbreaks of gastroenteritis. Serotyping plays an important role in diagnosis and epidemiological studies for pathogens of public health importance. The diversity of O-antigen biosynthesis gene clusters (O-AGCs) provides the primary basis for serotyping. However, little is known about the distribution and diversity of O-AGCs of E. albertii strains. Here, we presented a complete sequence set for the O-AGCs from 52 E. albertii strains and identified seven distinct O-AGCs. Six of these were also found in 15 genomes of E. albertii strains deposited in the public database. Possession of wzy/wzx genes in each O-AGC strongly suggest that O-antigens of E. albertii were synthesized by the Wzx/Wzy-dependent pathway. Furthermore, we performed an O-antigen serotyping scheme for E. albertii based on specific antisera against seven O-antigens and a high throughput xTAG Luminex assay to simultaneously detect seven O-AGCs. Both methods accurately identified serotypes of 64 tested E. albertii strains. Our data revealed the high-level diversity of O-AGCs in E. albertii. We also provide valuable methods to reliably identify and serotype this bacterium.

Structures and gene clusters of the O-antigens of Escherichia albertii O3, O4, O6, and O7

The O-specific polysaccharides (OPSs) called O-antigens were obtained by mild acid degradation of the lipopolysaccharides of Escherichia albertii serotypes O3, O4, O6, and O7 and studied by sugar analysis along with 1D and 2D ¹H and ¹³C NMR spectroscopy. The following structure was established for the OPS of E. albertii O4, which, to our knowledge, is unique among known bacterial polysaccharide structures: →2)-α-l-Rhap-(1 → 2)-α-l-Fucp-(1 → 2)-β-d-Galp-(1 → 3)-α-d-GalpNAc-(1 → 3)-β-d-GlcpNAc-(1→ The OPS structure of the strain of E. albertii O7 studied was identical to that of strain LMG 20973 (= Albert 10457), whose structure has been reported earlier (R. Eserstam et al. Eur. J. Biochem. 269 (2002) 3289-3295). E. albertii O3 and O6 shared the OPS structures with Escherichia coli O181 and O3, respectively, except for the lack of O-acetylation in E. albertii O3, which is present in E. coli O181. The gene clusters driving the O-antigen biosynthesis of the E. albertii strains were sequenced, the genes were annotated by comparison with sequences in the available databases, and the predicted functions of the encoded proteins were found to be consistent with the OPS structures established. In accordance with the relatedness of the OPS structures, the O-antigen gene clusters of E. albertii O3 and O6 contain the same genes and have the same organization as those of E. coli O181 and O3, the entire gene clusters being 83% and 98% identical, respectively.

Escherichia albertii Inactivation following l-Lactic Acid Exposure or Cooking in Ground Beef

Escherichia albertii is an emerging foodborne pathogen recovered from young children and adults exhibiting symptoms of gastroenteritis via pathogenesis factors including attaching and effacing lesions, cytolethal distending toxin, and Shiga toxin variants. Study objectives were to determine E. albertii survival following (i) exposure to lactic acid as a function of solution pH and incubation period and (ii) cooking ground beef patties to different endpoint temperatures. E. albertii was incubated in phosphate buffer containing 3.0% l-lactic acid adjusted to pH 3.0, 4.0, 5.0, or 7.0; survivors were determined every 30 min for 150 min. Ground beef patties (80% lean) were cooked to temperature endpoints simulating undercooking (62°C), the minimum temperature for safe cooking (71.1°C), and cooking to well done (76°C). Maximal pathogen reduction was observed after a 30-min exposure to pH 3.0 l-lactic acid. Reductions of 3.9, 4.4, and 4.9 log CFU/g were obtained following cooking ground beef patties to 62, 71.1, and 76°C, respectively, but the reductions did not differ as a function of the endpoint cooking temperature (P ≥ 0.05). E. albertii may be controlled on beef through the proper application of antimicrobial interventions and cooking.

Lambda Red-mediated Recombineering in the Attaching and Effacing Pathogen Escherichia albertii

Background

The ability to introduce site-specific mutations in bacterial pathogens is essential towards understanding their molecular mechanisms of pathogenicity. This has been greatly facilitated by the genetic engineering technique of recombineering. In recombineering, linear double- or single-stranded DNA molecules with two terminal homology arms are electroporated into hyperrecombinogenic bacteria that express a phage-encoded recombinase. The recombinase catalyzes the replacement of the endogenous allele with the exogenous allele to generate selectable or screenable recombinants. In particular, lambda red recombinase has been instrumental in engineering mutations to characterize the virulence arsenal of the attaching and effacing (A/E) pathogens enteropathogenic Escherichia coli (EPEC), enterohemorrhagic E. coli (EHEC), and Citrobacter rodentium. Escherichia albertii is another member of this taxon; however, the virulence of E. albertii remains cryptic despite accumulating evidence that E. albertii is an emerging pathogen. Multiple retrospective studies have reported that a substantial number of EPEC and EHEC isolates (~15 %) that were previously incriminated in human outbreaks actually belong to the E. albertii lineage. Thus, there is increased urgency to reliably identify and rapidly engineer mutations in E. albertii to systematically characterize its virulence determinants. To the best of our knowledge not a single chromosomal gene has been altered by targeted mutagenesis in E. albertii since it was first isolated almost 25 years ago. This is disconcerting because an E. albertii outbreak could cause significant morbidity and mortality owing to our inadequate understanding of its virulence program.

Results

In this report we describe a modified lambda red recombineering protocol to mutagenize E. albertii. As proof of principle, we successfully deleted three distinct virulence-associated genetic loci – ler, grlRA, and hfq – and replaced each wild type allele by a mutant allele with an encodable drug resistance cassette bracketed by FRT sites. Subsequently, the FRT-site flanked drug resistance marker was evicted by FLP-dependent site-specific recombination to generate excisants containing a solitary FRT site.

Conclusions

Our protocol will enable researchers to construct marked and unmarked genome-wide mutations in E. albertii, which, in turn, will illuminate its molecular mechanisms of pathogenicity and aid in developing appropriate preventative and therapeutic approaches to combat E. albertii outbreaks.

Defining the Genome Features of Escherichia albertii, an Emerging Enteropathogen Closely Related to Escherichia coli

Escherichia albertii is a recently recognized close relative of Escherichia coli. This emerging enteropathogen possesses a type III secretion system (T3SS) encoded by the locus of enterocyte effacement, similar to enteropathogenic and enterohemorrhagic E. coli (EPEC and EHEC). Shiga toxin-producing strains have also been identified. The genomic features of E. albertii, particularly differences from other Escherichia species, have not yet been well clarified. Here, we sequenced the genome of 29 E. albertii strains (3 complete and 26 draft sequences) isolated from multiple sources and performed intraspecies and intragenus genomic comparisons. The sizes of the E. albertii genomes range from 4.5 to 5.1 Mb, smaller than those of E. coli strains. Intraspecies genomic comparisons identified five phylogroups of E. albertii. Intragenus genomic comparison revealed that the possible core genome of E. albertii comprises 3,250 genes, whereas that of the genus Escherichia comprises 1,345 genes. Our analysis further revealed several unique or notable genetic features of E. albertii, including those responsible for known biochemical features and virulence factors and a possibly active second T3SS known as ETT2 (E. coli T3SS 2) that is inactivated in E. coli. Although this organism has been observed to be nonmotile in vitro, genes for flagellar biosynthesis are fully conserved; chemotaxis-related genes have been selectively deleted. Based on these results, we have developed a nested polymerase chain reaction system to directly detect E. albertii. Our data define the genomic features of E. albertii and provide a valuable basis for future studies of this important emerging enteropathogen.

Suitability of stx-PCR directly from fecal samples in clinical diagnostics of STEC

PCR-based testing for Shiga toxin producing Escherichia coli (STEC) directly from fecal samples is increasingly being implemented in routine diagnostic laboratories. These methods aim to detect clinically relevant amounts of microbes and not stx-carrying phages or low backgrounds of STEC. We present a diagnostic procedure and results from 1 year of stx-targeted real-time PCR of fecal samples from patients with gastrointestinal symptoms in Norway. A rapid stx2 subtyping strategy is described, which aims to quickly reveal the virulence potential of the microbe. stx was detected in 22 of 3320 samples, corresponding to a PCR positive rate of 0.66%. STEC were cultured from 72% of the PCR positive samples. Four stx1 isolates, eight stx2 isolates, and four isolates with both stx1 and stx2 were identified. With the method presented, stx-carrying phages are not commonly detected. Our results support the use of molecular testing combined with classical culture techniques for routine diagnostic purposes.

First bacteraemic human infection with Escherichia albertii

The facultative anaerobic Gram-negative species Escherichia albertii has been isolated from human faeces in gastrointestinal infection and from a range of wild bird species. Here we report the first case of a febrile infection associated with E. albertii bacteraemia in a 76-year-old woman with gastric dysplasia.

Prevalence of eae-positive, lactose non-fermenting Escherichia albertii from retail raw meat in China

Escherichia albertii is a newly emerging enteric pathogen that has been associated with gastroenteritis in humans. Recently, E. albertii has also been detected in healthy and sick birds, animals, chicken meat and water. In the present study, the prevalence and characteristics of the eae-positive, lactose non-fermenting E. albertii strains in retail raw meat in China were evaluated. Thirty isolates of such strains of E. albertii were identified from 446 (6·73%) samples, including duck intestines (21·43%, 6/28), duck meat (9·52%, 2/21), chicken intestines (8·99%, 17/189), chicken meat (5·66%, 3/53), mutton meat (4·55%, 1/22) and pork meat (2·44%, 1/41). None was isolated from 92 samples of raw beef meat. Strains were identified as E. albertii by phenotypic properties, diagnostic PCR, sequence analysis of the 16S rRNA gene, and housekeeping genes. Five intimin subtypes were harboured by these strains. All strains possessed the II/III/V subtype group of the cdtB gene, with two strains carrying another copy of the I/IV subtype group. Pulsed-field gel electrophoresis showed high genetic diversity of E. albertii in raw meats. Our findings indicate that E. albertii can contaminate various raw meats, posing a potential threat to public health.