stx2vhaIs the Dominant Genotype of Shiga Toxin-ProducingEscherichia coliO157:H7 Isolated from Patients and Domestic Animals in Three Regions of China

An analytical overview of the composition and characteristics of China's food safety standards

This paper discusses the framework of China's food safety standards and provides a brief overview of the problems and developmental characteristics of food safety in China. The composition and characteristics of China's food safety standards are revealed by an analysis of the changes in China's general food standards, an overview of the characteristics of the hygiene requirements in the production and operation process, and an introduction to food product and test method standards. In conclusion, Chinese food safety standards are still being improved, but they must also be effectively implemented and followed up in real time in order to continuously improve the quality of food and reduce food safety incidents. © 2024 Society of Chemical Industry.

The NMR structure of the Ea22 lysogenic developmental protein from lambda bacteriophage

The ea22 gene resides in a relatively uncharacterized region of the lambda bacteriophage genome between the exo and xis genes and is among the earliest genes transcribed upon infection. In lambda and Shiga toxin-producing phages found in enterohemorrhagic E. coli (EHEC) associated with food poisoning, Ea22 favors a lysogenic over lytic developmental state. The Ea22 protein may be considered in terms of three domains: a short amino-terminal domain, a coiled-coiled domain, and a carboxy-terminal domain (CTD). While the full-length protein is tetrameric, the CTD is dimeric when expressed individually. Here, we report the NMR solution structure of the Ea22 CTD that is described by a mixed alpha-beta fold with a dimer interface reinforced by salt bridges. A conserved mobile loop may serve as a ligand for an unknown host protein that works with Ea22 to promote bacterial survival and the formation of new lysogens. From sequence and structural comparisons, the CTD distinguishes lambda Ea22 from homologs encoded by Shiga toxin-producing bacteriophages.

Enterohemorrhagic Escherichia coli O157:H7 - Xuzhou City, Jiangsu Province, China, 2001-2021

What is already known about this topic?

The largest and longest outbreak of diarrhea, which was complicated with hemolytic uremic syndrome (HUS) caused by enterohemorrhagic Escherichia coli (EHEC) O157:H7, occurred in Xuzhou City and its adjacent areas from 1999 to 2000 in China.

What is added by this report?

According to surveillance results from 2001 to 2021, there was a significant decrease in the isolation rate of O157:H7, and cattle and sheep remained the primary hosts. However, non-Shiga toxin-producing O157:H7 emerged as the dominant strain, with stx2+stx1- strains following closely behind.

What are the implications for public health practice?

National surveillance of O157:H7 effectively serves as an early warning system and guidance for assessing the intensity and trend of disease epidemics. It is crucial to raise awareness of the public health risks associated with Shiga toxin-producing E. coli.

Microbial Food Safety in China: Past, Present, and Future

Food safety is a major public health issue worldwide, especially in heavily populated countries such as China. As in other countries, the predominant food safety issues in China are foodborne diseases caused by microbial pathogens. Hence, this review provides a systematic overview on microbial food safety in the past, present, and future in China. Management of microbial food safety in China is generally divided into three stages: Stage I before 2000, Stage II from 2000 to 2009, and Stage III from 2010 to present. At Stage I, China's main food concern gradually shifted from food security to food safety. At Stage II, foodborne pathogen surveillance was initiated and gradually became a focus of microbial food safety marked by the establishment of national food contamination monitoring system in 2000 and the promulgation of China Food Safety Law in 2009, although chemical food safety was considered a priority issue during this stage. At Stage III, microbial food safety was recognized as a high priority supported by many national food safety policies such as the launch of a national foodborne disease molecular tracing network in 2013 and the revision of China Food Safety Law in 2015. Advancement in food safety education and research support by central and local governments has also made significant contributions to tackling and solving microbial food safety problems. Management in the future should be focused on active involvement of food industries in mitigating microbial risks by introducing ISO 22000, regulatory enforcement to oversee compliances to standards and rules, and application of molecular tools for fast detection and source tracking to support decision-making. Future research efforts may include, but are not limited to, exploitation of interaction mechanisms among pathogenic bacteria, food and gut microbiota, smart traceability of microbial hazards, and development of novel antimicrobial strategies.

Antibody recognition of Shiga toxins (Stxs): computational identification of the epitopes of Stx2 subunit A to the antibodies 11E10 and S2C4

We have recently developed a new method to predict the epitopes of the antigens that are recognized by a specific antibody. In this work, we applied the method to identify the epitopes of the Shiga toxin (Stx2 subunit A) that were bound by two specific antibodies 11E10 and S2C4. The predicted epitopes of Stx2 binding to the antibody 11E10 resembles the recognition surface constructed by the regions of Stx2 identified experimentally. For the S2C4, our results indicate that the antibody recognizes the Stx2 at two different regions on the protein surface. The first region (residues 246-254: ARSVRAVNE) is similar to the recognition region of the 11E10, while the second region is formed by two epitopes. The second region is particularly significant because it includes the amino acid sequence region that is diverse between Stx2 and other Stx (residues 176-188: QREFRQALSETAPV). This new recognition region is believed to play an important role in the experimentally observed selectivity of S2C4 to the Stx2.

Global transcriptional and phenotypic analyses of Escherichia coli O157:H7 strain Xuzhou21 and its pO157_Sal cured mutant

Escherichia coli O157:H7 is an important food-borne pathogen that can cause hemorrhagic colitis and hemolytic-uremic syndrome in humans. pO157_Sal, a novel conjugative plasmid is present in a Chinese O157:H7 outbreak strain Xuzhou21. Here we investigated the phenotypic and transcriptional differences between the wild type strain Xuzhou21 and the pO157_Sal cured mutant strain Xuzhou21m. RNA-Seq analysis found that all 52 ORFs encoded on pO157_Sal were transcribed. One hundred and sixty eight chromosomal and pO157 genes were differentially expressed (≥2 fold difference) between Xuzhou21 and Xuzhou21m. Sixty-seven and 101 genes were up-regulated and down-regulated respectively by pO157_Sal including genes related to stress response, adaption and virulence. The plasmid-cured mutant Xuzhou21m grew slower than wild type Xuzhou21 and pO157_Sal plasmid complemented strain Xuzhou21c in M9 medium under the condition of high NaCl or presence of sodium deoxycholate (NaDC), corroborating with the RNA-Seq data. Seven differentially expressed genes are associated with NaDC resistance, including the adenine-specific DNA-methyltransferase gene (dam), multidrug efflux system subunit gene mdtA, hyperosmotically inducible periplasmic protein gene osmY and oxidation-reduction related genes while two differentially expressed genes (osmY and pspD) are likely to be related to resistance to osmotic pressure. A number of differentially expressed genes were virulence associated including four genes encoding T3SS effectors from the chromosome and ehxD from pO157. Through complementation of Xuzhou21m with a plasmid construct carrying the pO157_Sal hha homolog we further showed that the pO157_Sal hha represses the expression of T3SS effectors. These findings demonstrated that the plasmid pO157_Sal affects the transcription of the chromosomal and pO157 plasmid genes and contributes to the enhanced ability to resist stress. We conclude that pO157_Sal plays an important role in regulating global gene expression and affects the virulence and adaptation of E. coli O157:H7.

stx genotype and molecular epidemiological analyses of Shiga toxin-producing Escherichia coli O157:H7/H- in human and cattle isolates

The relationship between human diseases caused by infection with Shiga toxin (Stx)-producing Escherichia coli (STEC) O157 strains and O157 strains isolated from cattle was investigated in an area where stockbreeding is prolific. For this purpose, the stx genotypes, the molecular epidemiological characteristics of 268 STEC O157 strains including 211 human-origin strains and 57 cattle-origin strains, and clinical manifestations of 210 STEC-infected people were analyzed. Of 211 human-origin strains, 92 strains (44%) were of the stx1/stx2 genotype, and 74 strains (35%) were of the stx2c genotype. Most of the people infected with stx2c genotype strains presented no symptoms or mild symptoms such as slight diarrhea, except for 3 patients with bloody diarrhea. Of the 57 cattle-origin strains, 27 strains (47%) were of the stx2c genotype and 17 strains (30%) were of the stx1/stx2 genotype. Pulsed-field gel electrophoresis (PFGE) and insertion sequence (IS) analysis demonstrated that 11 isolates (41%) of the 27 cattle isolates of the stx2c genotype had high homology (>95% identity) with human isolates. These results suggest that some genetic patterns of the stx2c genotype strains might be preserved in cattle or their surrounding environment for several years, and during these periods, they might have opportunities to infect people through various routes. Because of the mild virulence of the stx2c genotype strains, they seemed to be transmitted asymptomatically from cattle to humans and then spread from person to person. It may be a public health concern. Further, they occasionally cause severe symptoms in humans; therefore, caution is warranted for infections by stx2c genotype O157 strains, in addition to stx2-possessing genotype O157 strains.

Development of PCR assays for detection of Escherichia coli O157:H7 in meat products

A multiplex polymerase chain reaction (PCR) procedure based on fliC(h7) and rfbE genes was developed for the detection of Escherichia coli O157:H7 in raw pork meat and ready-to-eat (RTE) meat products. Two different DNA extraction procedures were evaluated for application on meat products. MasterPure™ DNA Purification kit in combination with immunomagnetic separation was found to be the best method in a meat system. The optimized PCR included an enrichment step in brilliant green bile 2% broth at 37 °C. This method was applied to artificially inoculated meat and RTE meat products with different concentrations of E. coli O157:H7. The results indicate that the PCR assay developed could sensitively and specifically detect E. coli O157:H7 in raw pork meat and RTE meat products in approximately 10h, including a 6h enrichment step. Thus, this method could be proposed for screening E. coli O157:H7 in raw pork and RTE meat products.

pO157_Sal, a novel conjugative plasmid detected in outbreak isolates of Escherichia coli O157:H7

In addition to the large virulence plasmid pO157, a novel 38-kb conjugative plasmid, pO157_Sal, was identified and sequenced from an Escherichia coli O157:H7 outbreak-associated Chinese isolate that shares high similarity with a plasmid in Salmonella enterica serovar Agona. The plasmid was found in 15 of 326 isolates, 12 of which were of the same pulsed-field gel electrophoresis type.

Prevalence and genetic characterization of shiga toxin-producing Escherichia coli isolates from slaughtered animals in Bangladesh

To determine the prevalence of Shiga toxin (Stx)-producing Escherichia coli (STEC) in slaughter animals in Dhaka, Bangladesh, we collected rectal contents immediately after animals were slaughtered. Of the samples collected from buffalo (n = 174), cows (n = 139), and goats (n = 110), 82.2%, 72.7%, and 11.8% tested positive for stx(1) and/or stx(2), respectively. STEC could be isolated from 37.9%, 20.1%, and 10.0% of the buffalo, cows, and goats, respectively. STEC O157 samples were isolated from 14.4% of the buffalo, 7.2% of the cows, and 9.1% of the goats. More than 93% (n = 42) of the STEC O157 isolates were positive for the stx(2), eae, katP, etpD, and enterohemorrhagic E. coli hly (hly(EHEC)) virulence genes. STEC O157 isolates were characterized by seven recognized phage types, of which types 14 (24.4%) and 31 (24.4%) were predominant. Subtyping of the 45 STEC O157 isolates by pulsed-field gel electrophoresis showed 37 distinct restriction patterns, suggesting a heterogeneous clonal diversity. In addition to STEC O157, 71 STEC non-O157 strains were isolated from 60 stx-positive samples from 23.6% of the buffalo, 12.9% of the cows, and 0.9% of the goats. The STEC non-O157 isolates belonged to 36 different O groups and 52 O:H serotypes. Unlike STEC O157, most of the STEC non-O157 isolates (78.9%) were positive for stx(1). Only 7.0% (n = 5) of the isolates were positive for hly(EHEC), and none was positive for eae, katP, and etpD. None of the isolates was positive for the iha, toxB, and efa1 putative adhesion genes. However, 35.2% (n = 25), 11.3% (n = 8), 12.7% (n = 9), and 12.7% (n = 9) of the isolates were positive for the lpf(O113), saa, lpfA(O157/01-141), and lpfA(O157/OI-154) genes, respectively. The results of this study provide the first evidence that slaughtered animals like buffalo, cows, and goats in Bangladesh are reservoirs for STEC, including the potentially virulent STEC strain O157.

Isolation and characterization of the Shiga toxin gene (stx)-bearing Escherichia coli O157 and non-O157 from retail meats in Shandong Province, China, and characterization of the O157-derived stx2 phages

Infection by Shiga toxin (Stx)-producing Escherichia coli of non-O157 and O157 serotypes are rare in China, but infection by O157 serotype was found in Shandong Province and three other provinces in China. To understand the reason for these rare infections and to determine the safety of retail meats in Shandong Province, we examined the distribution of Shiga toxin gene (stx)-bearing E. coli in retail meats and characterized the isolated stx-bearing strains. We used hybridization with DNA probes and isolated stx1- and/or stx2-positive E. coli from 31 (58%) of 53 retail meat samples, with beef showing the highest frequency (68%). Of 42 stx-positive isolates, none belonged to O157. Using the O157-specific immunomagnetic bead technique, we isolated E. coli O157 carrying the eae and stx2 genes from eight beef samples (26%). These strains produced little or no Stx2 and carried a unique q gene. Replication of the stx2 phages was detected in these strains, whereas stx2 phage replication was not detected in our previous study in which we examined similar stx2-bearing E. coli O157 strains from other Asian countries. Analysis of E. coli C600 lysogenized with the stx2 phages found in this study suggests that the lack of Stx2 production is due to changes in non-q gene region(s) of the phage genome or chromosomal mutation(s) in the host. Our data and reports by other workers suggest it is necessary to determine if various stx2-bearing E. coli O157 strains producing Stx2 to varying degrees are distributed in meats in various locations in China.

Prevalence and genetic profiles of Shiga toxin-producing Escherichia coli strains isolated from buffaloes, cattle, and goats in central Vietnam

We investigated the prevalence of Shiga toxin-producing Escherichia coli (STEC) in 568 healthy domestic animals (buffaloes, cattle, and goats) from 98 farms in the central region of Vietnam. The aims of this study were to determine if the prevalence of STEC in South East Asia is similar to that in other parts of the world, to characterize the virulence gene profiles from the recovered STEC and to determine if the recovered STEC belong to serotypes commonly associated with human disease. STEC and intimin-positive strains were recovered from 27% of buffaloes, 23% of cattle, and 38.5% of goats. Seventy percent of buffalo farms, 60% of cattle farms and 100% goat farms were positive for STEC. Of 170 STEC strains, 99 carried both stx1 and stx2 genes, 36 carried the stx2 gene, and 35 carried the stx1 gene. The eae gene was found in six caprine isolates, but not in buffalo or bovine isolates. Among 173 E. coli strains (170 STEC and 3 intimin-positive), 110 carried the ehxA gene, 106 possessed the saa gene. Further characterization of stx subtypes demonstrated that among 134 stx1-containing isolates, 107 belonged to the stx1c subtype and 27 were the stx1 subtype. Of the 132 stx2-containing isolates, 36 were stx2, 34 were stx2c, 43 were stx2d subtype, 3 belonged to stx2g, and 16 strains were stx2d(act). The stx2c variant was dominant in strains isolated from buffalo while the stx2d variant occurred more frequently in caprine isolates. Only 9 (5%) STEC strains contained genes encoding for serotypes O26, O91, O121, O145, and O157 LPS, which are more frequently associated with human infections. The results of this study provide data for understanding of epidemiology of STEC among domestic animals in Vietnam and indicate that buffaloes are also an important reservoir of STEC.

Phenotypic characteristics, virulence profile and genetic relatedness of O157 Shiga toxin-producing Escherichia coli isolated in Brazil and other Latin American countries

Thirty-eight Shiga toxin-producing Escherichia coli (STEC) O157:H7/H(-) strains isolated from human infections, cattle and foods in Brazil and in some other Latin American countries were compared with regard to several phenotypic and genotypic characteristics. The genetic relatedness of the strains was also determined by pulsed-field gel electrophoresis (PFGE). Similar biochemical behaviour was identified, regardless of the origin and country of the strains. Most (89.5%) strains were sensitive to the antimicrobial agents tested, but resistance to at least one drug was observed among bovine strains. Although a diversity of stx genotypes was identified, most (77.8%) of the human strains harboured stx(2) or stx(2)stx(2c(2vha)), whereas stx(2c(2vha)) prevailed (64.2%) among strains isolated from cattle. stx(1) and stx(1)stx(2c(2vha)) were the genotypes identified less frequently, and occurred exclusively among strains isolated from food and cattle, respectively. Despite differences in the stx genotypes, all strains carried eae-gamma, efa1, ehx, iha, lpf(O157) and toxB sequences. Many closely related subgroups (more than 80% of similarity) were identified by PFGE, and the presence of a particular O157:H7 STEC clone more related to human infections in Brazil, as well as a common origin for some strains isolated from different sources and countries in Latin America can be suggested.