Molecular characterization of cytolethal distending toxin gene-positive Escherichia coli from healthy cattle and swine in Nara, Japan

Updates on the Virulence Factors Produced by Multidrug-Resistant Enterobacterales and Strategies to Control Their Infections

The Enterobacterales order is a massive group of Gram-negative bacteria comprised of pathogenic and nonpathogenic members, including beneficial commensal gut microbiota. The pathogenic members produce several pathogenic or virulence factors that enhance their pathogenic properties and increase the severity of the infection. The members of Enterobacterales can also develop resistance against the common antimicrobial agents, a phenomenon called antimicrobial resistance (AMR). Many pathogenic Enterobacterales members are known to possess antimicrobial resistance. This review discusses the virulence factors, pathogenicity, and infections caused by multidrug-resistant Enterobacterales, especially E. coli and some other bacterial species sharing similarities with the Enterobacterales members. We also discuss both conventional and modern approaches used to combat the infections caused by them. Understanding the virulence factors produced by the pathogenic bacteria will help develop novel strategies and methods to treat infections caused by them.

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.

Phylogenetic Groups/B2 Subgroup Distributions, Serogrouping and Identification of Virulence Factors in Extended-Spectrum Cephalosporin-Resistant Escherichia coli Strains Isolated from the Stool of Healthy Children Under 10 Years Old

Background: Segregation of Escherichia coli (E. coli) into the phylogenetic groups was observed in the experiments so that group B2 contained the enteropathogenic E. coli (EPEC) strains and extraintestinal pathogenic E. coli (ExPEC). Objectives: This study aimed to identify B2 phylogenetic groups in the extended-spectrum Cephalosporins resistant E. coli isolated from the stool of healthy children under 10 years old. Methods: One hundred E. coli resistant to broad-spectrum Cephalosporins were collected from the feces of healthy children under 10. Subsequently, we grouped phylogenetic via PCR based on the genes yjaA, chuA, arpA, as well, as TspE4.C2. Then, according to Clermont et al.’s study, we used two individual multiplex PCRs for identifying B2 sub-groups (I-X subgroups). Serogroup typing with the 12 O-antigen was analyzed via PCR, and finally, 10 virulence genes (cnf1, papG, ibeA, malX, usp, cdt, eae, bfp, and afa-Dr) were identified with PCR. Results: The age range of the healthy children was between 1 and 10 years. The B2 and unknown phylogroups were the most common strains in this study. The most common B2 subgroups were I (STc131) (2%), IX (1%), V (8%), IV, V, VII (1%), IX, V (3%), IX, V, III, I (1%), IX, V, III, VII, I (%1), V, I (6%), V, III, I (3%), and V, III, VII (1%), with each subgroup carrying distinctive sets of ExPEC virulence markers. The results also showed that 29% of E. coli in the healthy children had malX and 23% had papGII. It was also found that 32% of the strains isolated from the healthy children had antigens O2 and 36% were unknown. Conclusions: In this study, 27% of the strains belonged to B2 phylogroup and 6% to B1 phylogroup. Moreover, serogroups O2, O16, and O25 were predominant and belonged to B2 phylogroup. Moreover, malX, papGII, usp, papGIII, aggR, and eae virulence genes also had the highest to lowest supply among the tested strains, respectively. Moreover, B2 isolates were shown to have further virulence-related genes in comparison to the non B2 isolates.

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

Comparative genomics of Chinese and international isolates of Escherichia albertii: population structure and evolution of virulence and antimicrobial resistance

Escherichia albertii is a recently recognized species in the genus Escherichia that causes diarrhoea. The population structure, genetic diversity and genomic features have not been fully examined. Here, 169 E. albertii isolates from different sources and regions in China were sequenced and combined with 312 publicly available genomes (from additional 14 countries) for genomic analyses. The E. albertii population was divided into two clades and eight lineages, with lineage 3 (L3), L5 and L8 more common in China. Clinical isolates were observed in all clades/lineages. Virulence genes were found to be distributed differently among lineages: subtypes of the intimin encoding gene eae and the cytolethal distending toxin gene cdtB were lineage associated, and the second type three secretion system (ETT2) island was truncated in L3 and L6. Seven new eae subtypes and one new cdtB subtype (cdtB-VI) were identified. Alarmingly, 85.9 % of the Chinese E. albertii isolates were predicted to be multidrug-resistant (MDR) with 35.9 % harbouring genes capable of conferring resistance to 10 to 14 different drug classes. The majority of the MDR isolates were of poultry source from China and belonged to four sequence types (STs) [ST4638, ST4479, ST4633 and ST4488]. Thirty-four plasmids with some carrying MDR and virulence genes, and 130 prophages were identified from 17 complete E. albertii genomes. The 130 intact prophages were clustered into five groups, with group five prophages harbouring more virulence genes. We further identified three E. albertii specific genes as markers for the identification of this species. Our findings provided fundamental insights into the population structure, virulence variation and drug resistance of E. albertii.

[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.

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.

Isolation and Identification of Escherichia albertii in Broiler Chickens From Kermanshah

Background: F Escherichia albertii is generally recognized as a human pathogen with a limited number of strains. It has also been identified as a cause of mortality among birds. The clinical significance and prevalence of E. albertii are somewhat unknown. Objectives: The aim of the present study was to isolate and identify E. albertii as a causative agent of respiratory infections in broilers. Materials and Methods: During a three-month period (Winter 2018), 200 samples of the air sacs of 100 chickens with suspected colibacillosis were collected. Routine biochemical tests were performed and suspected isolates of E. albertii were selected for polymerase chain reaction (PCR). Results: A total of 68 suspected samples of E. albertii and Escherichia coli were isolated. Further, E. coli was detected in all the suspected samples using species-specific sequences of E. coli (uidA) and E. albertii (mdh and lysP). Conclusion: Escherichia albertii was not identified as a cause of respiratory infection in broilers.

Genomic features and antimicrobial resistance patterns of Shiga toxin-producing Escherichia coli strains isolated from food in Chile

Shiga toxin-producing Escherichia coli (STEC) is a zoonotic pathogen that causes severe illness in humans, often associated with foodborne outbreaks. Antimicrobial resistance among foodborne E. coli has increased over the last decades becoming a public health issue. In this study, the presence and features of STEC were investigated in samples of meat, seafood, vegetables and ready-to-eat street-vended food collected in Chile, using a genomic and microbiological approach. Phenotypic and genotypic antimicrobial resistance profiles were determined, and serotype, phylogroup, sequence type (ST) and phylogenomics were predicted using bioinformatic tools. Three thousand three hundred samples collected in 2019 were screened, of which 18 were positive for STEC strains (0.5%), with stx2a (61.1%) being the predominant stx subtype. The presence of the virulence genes lpfA (100%), iha and ehaA (94.4%), and ehxA, hlyA and saa (83.3%) was confirmed among the STEC strains; the Locus of adhesion and autoaggregation (LAA) was predicted in 14 (77.8%) strains. Strains displayed resistance to colistin (100%), and intermediate resistance to enrofloxacin (11.1%) and chloramphenicol (5.6%). In this regard, mutations in the two-component regulatory system genes pmrA (S29G), pmrB (D283G) and phoP (I44L), and the presence of the qnrB19 gene were confirmed. STEC strains belonged to ST11231 (38.9%), ST297 and ST58 (16.7% each), and ST1635, ST11232, ST446, ST442 and ST54 (5.6% each), and the most frequently detected serotypes were O113:H21 (44.4%), O130:H11 and O116:H21 (16.7% each), and O174:H21 (11.1%). Strains belonging to the international ST58 showed genomic relatedness with worldwide strains from human and non-human sources. Our study reports for the first time the genomic profile of STEC strains isolated from food in Chile, highlighting the presence of international clones and sequence types commonly associated with human infections in different geographical regions, as well as the convergence of virulence and resistance in STEC lineages circulating in this country.

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.

A One Health Perspective for Defining and Deciphering Escherichia coli Pathogenic Potential in Multiple Hosts

E. coli is one of the most common species of bacteria colonizing humans and animals. The singularity of E. coli 's genus and species underestimates its multifaceted nature, which is represented by different strains, each with different combinations of distinct virulence factors. In fact, several E. coli pathotypes, or hybrid strains, may be associated with both subclinical infection and a range of clinical conditions, including enteric, urinary, and systemic infections. E. coli may also express DNA-damaging toxins that could impact cancer development. This review summarizes the different E. coli pathotypes in the context of their history, hosts, clinical signs, epidemiology, and control. The pathotypic characterization of E. coli in the context of disease in different animals, including humans, provides comparative and One Health perspectives that will guide future clinical and research investigations of E. coli infections.

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.

Intestinal colonization of genotoxic Escherichia coli strains encoding colibactin and cytotoxic necrotizing factor in small mammal pets

Escherichia coli encoding colibactin (clb), cytolethal distending toxin (cdt), and hemolysin-associated cytotoxic necrotizing factor (cnf) are associated with various intestinal and extra-intestinal diseases in humans and animals. Small mammal pets are not evaluated for genotoxin-encoding E. coli. Thus, the prevalence of such strains is unknown. The objective of this study was to isolate and characterize genotoxin-encoding E. coli from healthy and ill small mammal pets examined at a veterinary clinic and at two animal adoption centers. E. coli isolates were cultured from fecal samples and biochemically characterized. A total of 65 animals, including mice, rats, rabbits, guinea pigs, and hedgehogs, were screened. Twenty-six E. coli isolates were obtained from 24 animals. Twelve of the 26 isolates (46.2 %) were PCR-positive for the pks genes clbA and clbQ. Two isolates (7.7 %) were PCR-positive for cnf. All isolates were PCR-negative for cdt. All genotoxin-encoding isolates belonged to the pathogen-associated phylogenetic group B2. Representative genotoxin-encoding isolates had serotypes previously associated with clinical disease in humans and animals. Isolates encoding pks or cnf induced megalocytosis and cytotoxicity to HeLa cells in vitro. Although most isolates were obtained from healthy pets, two guinea pigs with diarrhea had pks-positive isolates cultured from their feces. Whole genome sequencing on four representative isolates confirmed the presence of pks and cnf genes and identified other virulence factors associated with pathogenicity in animals and humans. Our results suggest that small mammalian pets may serve as a reservoir for potentially pathogenic E. coli and implicate a zoonotic risk.

Non-biogroup 1 or 2 Strains of the Emerging Zoonotic Pathogen Escherichia albertii, Their Proposed Assignment to Biogroup 3, and Their Commonly Detected Characteristics

Escherichia albertii, a zoonotic enteropathogen, is responsible for outbreaks of disease in humans. Identifying strains of E. albertii by phenotypic characterization tests is difficult because of its poorly defined properties. Screening its phenotypic characteristics is, nevertheless, a necessary prerequisite for further genetic analysis of its properties, and species-specific polymerase chain reaction (PCR) analysis can be used to type the pathogen. While two E. albertii biogroups (1 and 2) have been described, strains with characteristics divergent from both biogroups have been reported worldwide. The aim of the present study was to evaluate the characteristics of non-biogroup 1 or 2 strains, and discern the characteristics common to all of the E. albertii strains from this study. Altogether, 107/414 field isolates were selected for examination based on pulsed-field gel electrophoresis analysis. The 107 strains were isolated from 92 sources, including humans and pigeon feces, other wild birds, and retail chicken livers. All strains were then examined using various culture-based, biochemical (API 50CHE tests, API Zym test, and others) and molecular (virulence gene screening, multi-locus sequence analysis) testing methods. Our results revealed that all field strains (n = 107) showed non-biogroup 1 or 2 characteristics, with multiple sequence differences. Variations in indole production and the lysine decarboxylase activity profiles among the isolates made identification of E. albertii very difficult. Therefore, we propose that non-biogroup 1 or 2 of E. albertii should be assigned to biogroup 3 to make screening of them easier in public health and clinical laboratory settings. Clearly, having group criteria for indole-negative/lysine-positive, indole-positive/lysine-negative, and indole-positive/lysine-positive E. albertii biogroups 1, 2, and 3 strains, respectively, should provide for more accurate identification of E. albertii isolates. Based on our findings, we recommend that isolates displaying phenotype mobility-negativity (sulfide-indole-motility medium, 37°C), hydrogen sulfide production-negativity (triple sugar iron medium), acid production-negativity from xylose, negative β-glucuronidase activity properties, and showing indole production and lysine decarboxylase activity profiles in accordance with one of the three biogroups, should be further assessed using an E. albertii-specific PCR assay.

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.

Genotoxic Escherichia coli Strains Encoding Colibactin, Cytolethal Distending Toxin, and Cytotoxic Necrotizing Factor in Laboratory Rats

Although many Escherichia coli strains are considered commensals in mammals, strains encoding the cyclomodulin genotoxins are associated with clinical and subclinical disease in the urogenital and gastrointestinal tracts, meningitis, and inflammatory disorders. These genotoxins include the polyketide synthase (pks) pathogenicity island, cytolethal distending toxin (cdt), and hemolysin-associated cytotoxic necrotizing factor (cnf). E. coli strains are not excluded from rodents housed under SPF conditions in academic or vendor facilities. This study isolated and characterized genotoxin-encoding E. coli from laboratory rats obtained from 4 academic institutions and 3 vendors. A total of 69 distinct E. coli isolates were cultured from feces, rectal swab, nares, or vaginal swab of 52 rats and characterized biochemically. PCR analysis for cyclomodulin genes and phylogroup was performed on all 69 isolates. Of the 69 isolates, 45 (65%) were positive for pks, 20/69 (29%) were positive for cdt, and 4 (6%) were positive for cnf. Colibactin was the sole genotoxin identified in 21 of 45 pks+ isolates (47%), whereas cdt or cnf was also present in the remaining 24 isolates (53%); cdt and cnf were never present together or without pks. All genotoxin-associated strains were members of pathogen-associated phylogroup B2. Fisher exact and χ² tests demonstrated significant differences in genotoxin prevalence and API code distribution with regard to vendor. Select E. coli isolates were characterized by HeLa cell in vitro cytotoxicity assays, serotyped, and whole-genome sequenced. All isolates encoding cyclomodulins induced megalocytosis. Serotypes corresponded with vendor origin and cyclomodulin composition, with the cnf+ serotype representing a known human uropathogen. Whole-genome sequencing confirmed the presence of complete pks, cdt, and hemolysin-cnf pathogenicity islands. These findings indicate that genotoxin-encoding E. coli colonize laboratory rats from multiple commercial vendors and academic institutions and suggest the potential to contribute to clinical disease and introduce confounding variables into experimental rat models.

Detection of multi-drug resistant (MDR) Escherichia coli and tet gene prevalence at a pig farm in Kupang , Indonesia

OBJECTIVE

The purpose of this study was to detect the incidence of multi-drug resistant (MDR) and the spread of tet genes that encode tetracycline (TE) resistance in E. coli in pig farms in the city of Kupang, Indonesia.

MATERIALS AND METHODS

Samples of pig feces have been obtained from 96 pig farms in Kupang city, Indonesia. Escherichia coli bacteria were isolated and identified morphologically and biochemically, and finally confirmed by the API test. The disk diffusion method has been used to observe the antibiotic sensitivity effects and has been followed by observing resistant genes encoding TE resistance using the multiplex polymerase chain reaction (m-PCR) method to detect the presence of tet genes such as tet (A), tet (B), tet (C), tet (D), and tet (E), respectively.

RESULTS

A total of 82 (85.4%) of E. coli isolates have been found in all pig feces samples obtained from 96 pig farms in Kupang city. This study has shown a high level of antibiotic resistance dominated by erythromycin (85.4%) and cephalothin (58.5%) and followed by several other antibiotics with a percentage below 34.1%. The prevalence of MDR E. coli was 57.3% by showing 39 different patterns. The most common pattern was showed by the Cephalothin-Colistin-Erythromycin pattern. The resistance of E. coli to TE appears to be related to the presence of tet (A) and tet (E) genes.

CONCLUSION

This study has encouraged the need for public awareness (farmers) of the wise use of antibiotics in preventing the spread of resistant bacteria that can cause health problems in animals and humans.

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.

The Enterobacterial Genotoxins: Cytolethal Distending Toxin and Colibactin

While the DNA damage induced by ionizing radiation and by many chemical compounds and drugs is well characterized, the genotoxic insults inflicted by bacteria are only scarcely documented. However, accumulating evidence indicates that we are exposed to bacterial genotoxins. The prototypes of such bacterial genotoxins are the Cytolethal Distending Toxins (CDTs) produced by Escherichia coli and Salmonella enterica serovar Typhi. CDTs display the DNase structure fold and activity, and induce DNA strand breaks in the intoxicated host cell nuclei. E. coli and certain other Enterobacteriaceae species synthesize another genotoxin, colibactin. Colibactin is a secondary metabolite, a hybrid polyketide/nonribosomal peptide compound synthesized by a complex biosynthetic machinery. In this review, we summarize the current knowledge on CDT and colibactin produced by E. coli and/or Salmonella Typhi. We describe their prevalence, genetic determinants, modes of action, and impact in infectious diseases or gut colonization, and discuss the possible involvement of these genotoxigenic bacteria in cancer.

Molecular characterization of enterohemorrhagic Escherichia coli hemolysin gene (EHEC-hlyA)-harboring isolates from cattle reveals a diverse origin and hybrid diarrheagenic strains

In the present study we investigated the occurrence of Escherichia coli strains harboring the gene encoding enterohemorrhagic E. coli hemolysin (EHEC-HlyA) in cattle and the association of this gene with various diarrheagenic E. coli (DEC) pathotypes. First, the bovine E. coli isolates were screened for EHEC-hlyA gene by PCR, and then they were characterized for the phylogenetic groups and the presence of the major virulence genes of different DEC pathotypes. In total, 25 virulence gene profiles were observed in 54 EHEC-hlyA+ isolates that reflect a considerable heterogeneity. The EHEC-hlyA+ strains were mostly associated with EHEC (72%), while only 7.4% were enteropathogenic E. coli (EPEC). We also showed the presence of estA gene of enterotoxigenic E. coli (ETEC) in 6 isolates (11.1%). Interestingly, two of the estA+ strains showed hybrid pathotypes with one carrying eae/estA (EPEC/ETEC), and the other one stx2/astA/estA (EHEC/ETEC). None of the isolates were related to enteroaggregative E. coli (EAggEC), enteroinvasive E. coli (EIEC), and necrotoxigenic E. coli (NTEC). The EHEC-plasmid encoded genes occurred in seven different combinations with EHEC-hlyA/saa/subA/espP being the most prevalent (46.3%). All stx-/eae+ strains carried O island 57 (OI-57) molecular marker(s) that may indicate these to be the progenitors of EHEC or strains losing stx. The most prevalent phylogroup was B1 (61.1%), but the most heterogeneous strains including the hybrid strains belonged to A phylogroup. Overall, our results indicate that cattle EHEC-hlyA encoding E. coli isolates consist of diverse diarrheagenic strains with the possible existence of hybrid pathotypes. Future studies are required to clarify the evolutionary aspects and clinical significance of these strains in humans and domestic animals.

Prevalence and pathogenic potential of Escherichia coli isolates from raw milk and raw milk cheese in Egypt

The objectives of this study were to investigate prevalence and pathogenic potential of Escherichia coli contaminating raw milk and its products in Egypt. Out of 187 dairy products including 72 raw milk samples, 55 Karish cheese and 60 Ras cheese, 222 E. coli isolates including 111, 89 and 22 were obtained from 55 raw milk samples (76.4%), 41 Karish cheese (74.5%), and 13 Ras cheese (21.7%), respectively. Isolated E. coli strains were examined for 24 representative virulence genes present in diarrheagenic E. coli (DEC) and extraintestinal pathogenic E. coli (ExPEC). Among DEC and ExPEC virulence factors, genes for enteropathogenic E. coli (eaeA, bfpA, EAF), enterohemorrhagic E. coli (stx1, stx2, eaeA), enterotoxigenic E. coli (elt, est), enteroinvasive E. coli (invE), enteroaggregative E. coli (Eagg, astA), diffusely adherent E. coli (daaD), ExPEC (cdt-I to cdt-V, cnf1, cnf2, hlyA) and putative adhesins (efa1, iha, ehaA, saa, and lpfAO113) were screened by colony hybridization assay. Out of 222 E. coli strains, 104 (46.8%) isolated from 69 (36.9%) samples carried one or more virulence genes. The most prevalent gene detected was lpfAO113 (40.5%), followed by ehaA (32.4%,), astA (3.15%,), iha (1.80%), hlyA (1.35%), stx1 (0.90%), stx2 (0.90%), eaeA (0.45%), cdt-III (0.45%) and cnf2 (0.45%). Two strains isolated from Karish cheese harbored 5 virulence genes (stx1, stx2, iha, ehaA, lpfAO113). Stx subtype was determined to be stx1 (not stx1c or stx1d) and stx2d. Indeed, expression of hemolysin A, CDT-III, CNF-II, Stx1 and Stx2d was confirmed by blood agar plate, cytotoxicity assay and Western blotting, respectively. Among the 222 E. coli strains, 54 (48.6%), 38 (42.6%) and 12 (54.7%) isolated from raw milk, Karish cheese and Ras cheese were potentially virulent, respectively. O-genotyping indicated that most of the potentially virulent E. coli isolates did not belong to clinically important O serogroups except O75, O91 and O166, which have been associated with human diseases. Phylogenetic grouping revealed that 150 (67.6%), 67 (30.2%) and 5 (2.30%) strains were clustered into A, B1 and D groups, respectively, which are considered to be associated with intestinal infection, indicating that these E. coli strains might have a potential to cause gastroenteritis. To the best of our knowledge, this is the first comprehensive study regarding prevalence and pathogenic potential of E. coli in dairy products in Egypt. Raw milk, Karish cheese and Ras cheese in Egypt are highly contaminated with E. coli including potentially pathogenic strains, which may impose a public health threat.

Detection of Escherichia albertii from chicken meat and giblets

Escherichia albertii occasionally causes food-borne outbreaks of gastroenteritis in humans; however, little is known about the vehicle of transmission. To screen retail chicken products for the presence of E. albertii, 104 retail chicken products were investigated. Portions of enrichment cultures that were PCR-positive for E. albertii (n=3) were sub-cultured on agar medium. Only 2 strains obtained from 2 chicken giblet samples were identified as E. albertii by multi locus sequence typing. Antimicrobial susceptibility testing showed that 1 strain was resistant to streptomycin and sulfisoxazole. Both strains harbored the virulence genes cdt and eae. This study is the first description of E. albertii isolation from retail food, suggesting that chicken products are a potential vehicle of E. albertii transmission.

Cytolethal distending toxin A, B and C subunit proteins are necessary for the genotoxic effect of Escherichia coli CDT-V

Cytolethal distending toxins (CDT) are considered the prototype of inhibitory cyclomodulins, and are produced by a wide range of Gram-negative pathogenic bacteria, including Escherichia coli strains of various sero- and pathotypes. CDT is a heterotripartite toxin consisting of three protein subunits, CdtA, CdtB and CdtC. The active subunit, CdtB has DNase activity and causes DNA damage and cell cycle arrest in the target cell. However, several studies have highlighted different roles for CdtA and CdtC subunits. In order to reveal the necessity of CdtA and CdtC subunit proteins in the CDT-specific phenotype, expression clones containing the cdt-V subunit genes were constructed. Using cell culture assays, we demonstrated that clones expressing only the CdtB subunit or in combination with only CdtA or CdtC were unable to trigger the specific cell cycle arrest and changes in cell morphology in HeLa cells. At the same time, the recombinant clone harbouring the whole cdt-V operon caused all the CDT-associated characteristic phenotypes. All these results verify that all the three CDT subunit proteins are necessary for the genotoxic effect caused by CDT-V.