Prevalence and antimicrobial susceptibility of Salmonella in the commercial eggs in China

Emergence of Salmonella Infantis carrying the pESI-like plasmid from eggs in egg grading and packing plants in Korea

The plasmid of emerging S. Infantis (pESI) or pESI-like plasmid in Salmonella enterica Infantis are consistently reported in poultry and humans worldwide. However, there has been limited research on these plasmids of S. Infantis isolated from eggs. Therefore, this study aimed to analyze the prevalence and characteristics of S. Infantis carrying the pESI-like plasmid from eggs in egg grading and packing plants. In this study, the pESI-like plasmid was only detected in 18 (78.3%) of 23 S. Infantis isolates, and it was absent in the other 9 Salmonella serovars. In particular, S. Infantis isolates carrying the pESI-like plasmid showed the significantly higher resistance to β-lactams, phenicols, cephams, aminoglycosides, quinolones, sulfonamides, and tetracyclines than Salmonella isolates without the pESI-like plasmid (p < 0.05). Moreover, all S. Infantis isolates carrying the pESI-like plasmid were identified as extended-spectrum β-lactamase (ESBL) producer, harboring the blaCTX-M-65 and blaTEM-1 genes, and carried non-β-lactamase resistance genes (ant(3'')-Ia, aph(4)-Ia, aac(3)-IVa, aph(3')-Ic, sul1, tetA, dfrA14, and floR) against five antimicrobial classes. However, all isolates without the pESI-like plasmid only carried the blaTEM-1 gene among the β-lactamase genes, and either had no non-β-lactamase resistance genes or harbored non-β-lactamase resistance genes against one or two antimicrobial classes. Furthermore, all S. Infantis isolates carrying the pESI-like plasmid carried class 1 and 2 integrons and the aadA1 gene cassette, but none of the other isolates without the pESI-like plasmid harbored integrons. In particular, D87Y substitution in the gyrA gene and IncP replicon type were observed in all the S. Infantis isolates carrying the pESI-like plasmid but not in the S. Infantis isolates without the pESI-like plasmid. The distribution of pulsotypes between pESI-positive and pESI-negative S. Infantis isolates was clearly distinguished, but all S. Infantis isolates were classified as sequence type 32, regardless of whether they carried the pESI-like plasmid. This study is the first to report the characteristics of S. Infantis carrying the pESI-like plasmid isolated from eggs and can provide valuable information for formulating strategies to control the spread of Salmonella in the egg industry worldwide.

Prevalence and characterization of non-typhoidal Salmonella in egg from grading and packing plants in Korea

Egg washing guidelines vary across countries; however, since 2020, Korea has required that all eggs produced from farms with more than 10,000 laying hens must be washed through egg grading and packing (GP) plant. This study investigated the prevalence and characterization of non-typhoidal Salmonella in eggs after washing at GP plants. In total, 16,800 eggs were collected from 60 egg GP plants located inside commercial layer farms, and 840 pooled eggshell and egg contents were tested for Salmonella, respectively. Of the 60 GP plants tested, 11 (18.3%) and 12 (20.0%) plants were positive for Salmonella spp. In the eggshells and egg contents, respectively. In particular, High Salmonella prevalence in the eggshells and egg contents occurred most often in farms with laying hens older than 80 weeks (33.3% and 40.0%, respectively). However, among 840 pooled eggshells and egg content samples, only 19 (2.3%) of each sample type were positive only for non-typhoidal Salmonella spp. The most common Salmonella serovar in both eggshells and egg contents was S. Infantis, which was found in five (8.3%) of 60 GP plants for both samples types. The other Salmonella serovars detected in eggshells were S. Bareilly (5.0%), S. Agona (3.3%), S. Enteritidis (1.7%), and S. Montevideo (1.7%), whereas those detected in egg contents were S. Enteritidis (5.0%), S. Agona (3.3%), S. Newport (3.3%), S. Senftenberg (3.3%), and S. Derby (1.7%). Of the 19 virulence genes tested, 14 genes were detected in all Salmonella. Interestingly, the spvB gene was detected only in S. Enteritidis, and the sefC gene was detected only in S. Enteritidis and S. Senftenberg. Moreover, all S. Infantis isolates showed multidrug resistance (MDR) against five or more classes, and the other serovars only showed MDR against three to four classes or no MDR. These results suggest that comprehensive surveillance and advanced management approaches for egg GP plants are required to minimize egg contamination with non-typhoidal Salmonella.

Prevalence, antibiotic resistance, virulence genes and molecular characteristics of Salmonella isolated from ducks and wild geese in China

Salmonella is a major foodborne pathogen and the cause of significant morbidity and mortality via consumption of contaminated meat and meat-products. The prevalence of Salmonella in ducks and wild geese in China are poorly characterized and these sources represent a potential pool that could be transferred to farm-reared fowl. In this study, we isolated 335 (18.3%) Salmonella from 1830 samples and identified 24 serotypes and most prevalent were Salmonella Indiana, Salmonella Kentucky and Salmonella Typhimurium. Whole genome sequencing revealed the presence of the dominant sequence types ST17, ST198 and ST19 for these three serotypes, respectively. In addition, these isolates were most likely clonally spread across different regions while S. Kentucky also crossed the species barrier. The majority of the Salmonella isolates possessed β-lactam and fluoroquinolone resistance and these were consistent with antibiotic resistance gene profiles. We also identified 8 plasmid replicon types and all isolates possessed virulence genes and the numbers were greatest for S. Enteritidis and S. Typhimurium isolates. This study provides novel insights concerning the epidemiology of Salmonella in ducks and wild geese and provides basic data for public health screening and management.

In Situ Cas12a-Based Allele-Specific PCR for Imaging Single-Nucleotide Variations in Foodborne Pathogenic Bacteria

In situ profiling of single-nucleotide variations (SNVs) can elucidate drug-resistant genotypes with single-cell resolution. The capacity to directly "see" genetic information is crucial for investigating the relationship between mutated genes and phenotypes. Fluorescence in situ hybridization serves as a canonical tool for genetic imaging; however, it cannot detect subtle sequence alteration including SNVs. Herein, we develop an in situ Cas12a-based amplification refractory mutation system-PCR (ARMS-PCR) method that allows the visualization of SNVs related to quinolone resistance inside cells. The capacity of discriminating SNVs is enhanced by incorporating optimized mismatched bases in the allele-specific primers, thus allowing to specifically amplify quinolone-resistant related genes. After in situ ARMS-PCR, we employed a modified Cas12a/CRISPR RNA to tag the amplicon, thereby enabling specific binding of fluorophore-labeled DNA probes. The method allows to precisely quantify quinolone-resistant Salmonella enterica in the bacterial mixture. Utilizing this method, we investigated the survival competition capacity of quinolone-resistant and quinolone-sensitive bacteria toward antimicrobial peptides and indicated the enrichment of quinolone-resistant bacteria under colistin sulfate stress. The in situ Cas12a-based ARMS-PCR method holds the potential for profiling cellular phenotypes and gene regulation with single-nucleotide resolution at the single-cell level.

Prevalence of Salmonella in Eggs from Conventional and Cage-Free Egg Production Systems and the Role of Consumers in Reducing Household Contamination

Salmonella is one of the leading causes of foodborne disease worldwide, usually related to contaminated poultry or poultry products, such as eggs. Since egg contamination with Salmonella depends on multiple factors that make it challenging to control, consumers' knowledge about food safety and the proper handling of eggs is crucial. The aims of the study were (1) to determine the prevalence of Salmonella in eggs from conventional and alternative production systems, (2) to characterize the Salmonella isolates according to phenotypic-genotypic and antimicrobial-resistant traits, and (3) to understand how consumers manage the hazards related to egg contamination in the household. A total of 426 egg samples were analyzed (conventional systems = 240; alternative systems = 186). Culture-based and molecular microbiological methods were used to identify Salmonella and bioinformatics analysis of whole genome sequences was used to determine the serotype and antimicrobial-resistant genes. Salmonella enterica serotype Enteritidis was detected only in eggs from alternative systems (1.1%, 2/186). Isolates showed resistance to nalidixic acid (100%, 2/2), and the aac(6')-Iaa gene and a mutation in the gyrA gene were identified in both isolates. Overall, consumers demonstrated knowledge regarding food safety; however, many still engage in practices that pose a risk of acquiring foodborne illnesses.

Complete Genome Sequencing and Bacteriocin Functional Characterization of Pediococcus ethanolidurans CP201 from Daqu

This study aims to sequence the whole genome of Pediococcus ethanolidurans CP201 isolated from Daqu and determine the anti-corrosion ability of bacteriocins on chicken breast. The whole genome sequence information of P. ethanolidurans CP201 was analyzed, and its gene structure and function were explored. It was found that gene1164 had annotations in the NR, Pfam, and Swiss-Prot databases, and was related to bacteriocins. The exogenous expression of the bacteriocin gene Pediocin PE-201 was analyzed based on the pET-21b vector and the host BL21, and the corresponding bacteriocin was successfully expressed under the induction of IPTG. After purification by NI-NTA column, enterokinase treatment, membrane dialysis concentration treatment, and SDS-PAGE electrophoresis, the molecular weight was about 6.5 kDa and the purity was above 90%. By applying different concentrations of bacteriocin to chicken breast with different levels of contamination, the control of pathogenic bacteria, the ordinary contamination level (OC) group, and the high contamination level (MC) group could be completely achieved with 25 mg/L bacteriocin. In conclusion, the bacteriocin produced by the newly isolated CP201 can be applied to the preservation of meat products to prevent the risk of food-borne diseases.

A review on egg pasteurization and disinfection: Traditional and novel processing technologies

Salmonella Enteritidis is a pathogen related to many foodborne outbreaks involving eggs and egg products. Regulations about whether eggs should be pasteurized are very different and inconsistent worldwide. In the United States, eggs are not required to be pasteurized. Hence, less than 3% of the eggs in the country are pasteurized. The standard pasteurization method (57°C, 57.5 min) uses a long thermal process that increases the cost of the product and affects its quality. Foodborne outbreaks can be reduced if eggs are properly pasteurized to inactivate Salmonella spp. However, the technology to pasteurize eggs needs to offer a faster and more reliable method that can be scaled up to industry settings at a low cost and without affecting product quality. Several novel technologies have been tested for eggshell disinfection and egg pasteurization. Some thermal technologies have been evaluated for the pasteurization of eggs. Microwave has limited penetration depth and is a technical challenge for egg pasteurization. However, radio frequency can penetrate eggshells effectively to inactivate Salmonella, considerably reduce processing time, and maintain the quality of the product. Nonthermal technologies such as ultraviolet, pulsed light, cold plasma, ozone, pressure carbon dioxide, electrolyzed water, and natural antimicrobials have been explored for surface cleaning of the intact egg as alternatives without affecting the internal quality. This review presents some of these novel technologies and the current challenges. It discusses the possible combination of factors to achieve the egg's internal pasteurization and the eggshell's disinfection without affecting the quality at a low cost for the consumer.

Epidemiology of foodborne diseases caused by Salmonella in Zhejiang Province, China, between 2010 and 2021

Objective

Salmonella infection is a common cause of bacterial foodborne diseases (FBDs) globally. In this study, we aimed to explore the epidemiological and etiological characteristics of Salmonella infection from 2012-2021 in Zhejiang Province, China.

Methods

Descriptive statistical methods were used to analyze the data reported by the Centers for Disease Control and Prevention at all levels in Zhejiang Province through the China National Foodborne Diseases Surveillance Network from 2012-2021.

Results

A total of 11,269 Salmonella cases were reported, with an average positive rate of 3.65%, including 1,614 hospitalizations. A significant seasonal trend was observed for Salmonella cases, with the highest rate over the summer period, peaking from May to October, accounting for 77.96%. The results indicated a higher positive rate among respondents aged 0-4 years, especially for the scattered children (P < 0.05). The highest number of Salmonella infections were caused due to contaminated fruit and fruit products. Households (54.69%) had the most common exposure settings. Serotypes analysis revealed that Salmonella typhimurium (36.07%), Salmonella enteritidis (15.17%), and Salmonella london (6.05%) were the dominant strains among the 173 serotypes. Diarrhea, abdominal pain, fever, nausea, and vomiting were the main symptoms of these serotypes.

Conclusions

FBDs caused by Salmonella are important issues for public health in Zhejiang Province, and there is a need to focus on the epidemiological and etiological characteristics to control Salmonella infections.

Cytotoxicity and Antimicrobial Resistance of Salmonella enterica Subspecies Isolated from Raised Reptiles in Beijing, China

BACKGROUND

Reptiles are asymptomatic carriers of Salmonella spp. Reptile-associated Salmonella infections have been noticed as a significant contributor to overall human salmonellosis. However, it remains unclear regarding the prevalence of reptile-associated Salmonella in China.

METHODS

Fecal and gastrointestinal mucosal samples were taken from 104 snakes, 21 lizards, and 52 chelonians and cultured on selective medium. The positive clones were validated and annotated by biochemical screening and multiplex PCR verification. In addition, the antibiotic resistance of identified Salmonella isolates was detected and followed by cytotoxic activity detection on human colon cells via co-culturation.

RESULTS

The overall prevalence of Salmonella in reptiles was 25.99%, with rates of 30.77%, 47.62%, and 7.69% in snakes, lizards, and chelonians, respectively. Further, all isolates showed variable drug-resistant activity to 18 antibiotics, of which 14 strains (30.43%) were resistant to more than eight kinds of antibiotics. More than half of isolated Salmonella strains were more toxic to host cells than the standard strain, SL1344. Whole genome sequencing (WGS) results showed that all lizard-associated strains belong to 4 serovar types, and 7 of them fall into the highly pathogenic serovars "Carmel" and "Pomona."

CONCLUSIONS

Our results highlight the potential threat of zoonotic salmonellosis from captive reptiles in the Beijing area of China.

RyhB Paralogs Downregulate the Expressions of Multiple Survival-Associated Genes and Attenuate the Survival of Salmonella Enteritidis in the Chicken Macrophage HD11

RyhB-1 and RyhB-2 are small non-coding RNAs in Salmonella that act as regulators of iron homeostasis by sensing the environmental iron concentration. Expressions of RyhB paralogs from Salmonella Typhimurium are increased within microphages. RyhB paralogs restrain the growth of S. Typhimurium in RAW264.7 macrophages by modulating the expression of Salmonella pathogenicity island 1 (SPI-1) genes sicA and rtsB. However, little is known about the regulatory role of RyhBs and their virulence-associated targets in Salmonella Enteritidis. We studied candidate targets of RyhB paralogs via RNA-Seq in conditions of iron limitation and hypoxia. RyhB paralogs were expressed when the S. Enteritidis strain CMCC(B)50336 (SE50336) interacted with the chicken macrophage line HD11. We analyzed gene expression associated with Salmonella survival and replication in macrophages in wild-type strain SE50336 and the RyhB deletion mutants after co-incubation with HD11 and screened out targets regulated by RyhBs. The expressions of both RyhB-1 and RyhB-2 were increased after co-incubation with HD11 for 8 h and several survival-associated genes within macrophages, such as ssaI, sseA, pagC, sodC, mgtC, yaeB, pocR, and hns, were upregulated in the ryhB-1 deletion mutant. Specifically, ssaI, the type-three secretion system 2 (T3SS-2) effector encoded by SPI-2, which promoted the survival of Salmonella in macrophages, was upregulated more than 3-fold in the ryhB-1 deletion mutant. We confirmed that both RyhB-1 and RyhB-2 downregulated the expression of ssaI to repress its mRNA translation by directly interacting with its coding sequence (CDS) region via an incomplete complementary base-pairing mechanism. The SPI-2 gene sseA was indirectly modulated by RyhB-1. The survival assays in macrophages showed that the ability of intracellular survival of ryhB-1 and/or ryhB-2 deletion mutants in HD11 was higher than that of the wild-type strain. These results indicate that RyhB paralogs downregulate survival-related virulence factors and attenuate the survival of S. Enteritidis inside chicken macrophage HD11.

The vertical transmission of Salmonella Enteritidis in a One-Health context

Salmonella enterica serovar Enteritidis (S. Enteritidis, SE) is a foodborne zoonotic pathogen, causing economic losses in animal husbandry and large numbers of human deaths and critically threatening economic development and public health. Human infection with SE has complex transmission routes, involving the environment, animal reservoirs, and water in a One-Health context. Food-producing animals, particularly poultry and livestock, are regarded as the most common sources of SE infection in humans. However, there is little known about the vertical transmission of SE in a One-Health context. In this review, we analyze the ecological significance of SE in a One-Health context. Importantly, we focus on the difference in vertical transmission of SE in poultry, livestock, and humans. We introduce the transmission pathway, describe the immune mechanisms, and discuss the models that could be used for studying the vertical transmission of SE and the strategy that prevention and control for vertical transmission of SE into the future from a One-Health perspective. Together, considering the vertical transmission of SE, it is helpful to provide important insights into the control and decontamination pathways of SE in animal husbandry and enhance knowledge about the prevention of fetal infection in human pregnancy.

Phenotypic and genotypic characterization of antimicrobial resistance profiles in Salmonella isolated from waterfowl in 2002–2005 and 2018–2020 in Sichuan, China

Salmonella enterica is a widespread foodborne pathogen with concerning antimicrobial resistance (AMR). Waterfowl are a major source of Salmonella transmission, but there are few systematic studies on Salmonella prevalence in waterfowl species. In this study, 126 Salmonella isolates (65 collected in 2018–2020 and 61 collected in 2002–2005) were obtained from waterfowl samples in Sichuan, China. Their serotypes, pulsed-field gel electrophoresis (PFGE) types, and phenotypic and genotypic AMR profiles were systematically examined. The isolates were distributed in 7 serotypes, including serovars Enteritidis (46.0%), Potsdam (27.8%), Montevideo (7.9%), Cerro (6.3%), Typhimurium (4.8%), Kottbus (4.0%) and Apeyeme (3.2%). Their PFGE characteristics were diverse; all isolates were distributed in four groups (cutoff value: 60.0%) and 20 clusters (cutoff value: 80.0%). Moreover, all isolates were multidrug resistant, and high rates of AMR to lincomycin (100.0%), rifampicin (100.0%), sulfadiazine (93.7%), erythromycin (89.7%), ciprofloxacin (81.0%), and gentamicin (75.4%) were observed. Finally, 49 isolates were subjected to whole-genome sequencing, and a wide variety of AMR genes were found, including multiple efflux pump genes and specific resistance genes. Interestingly, the tet(A)/tet(B) and catII resistance genes were detected in only isolates obtained in the first collection period, while the gyrA (S83F, D87N and D87G) and gyrB (E466D) mutations were detected at higher frequencies in the isolates obtained in the second collection period, supporting the findings that isolates from different periods exhibited different patterns of resistance to tetracycline, chloramphenicol and nalidixic acid. In addition, various incompatible plasmid replicon fragments were detected, including Col440I, Col440II, IncFIB, IncFII, IncX1, IncX9, IncI1-I and IncI2, which may contribute to the horizontal transmission of AMR genes and provide competitive advantages. In summary, we demonstrated that the Salmonella isolates prevalent in Sichuan waterfowl farms exhibited diverse serotypes, multiple AMR phenotypes and genotypes, and AMR changes over time, indicating their potential risks to public health.

Descriptive study of foodborne disease using disease monitoring data in Zhejiang Province, China, 2016-2020

Background

This study aimed to identify the epidemiology, seasonality, aetiology and clinical characteristics of sporadic foodborne diseases in Zhejiang province during 2016–2020.

Methods

Descriptive statistical methods were used to analyze the data from surveillance network established by the Zhejiang Provincial Center for Disease Control and Prevention. There were 31 designated hospitals in all 11 cities which were selected using probability proportionate to size sampling method.

Results

During the study period, the surveillance system received 75,124 cases with 4826 (6.42%) hospitalizations from 31 hospitals. The most common cause was Norovirus, 6120 cases (42.56%), followed by Salmonella, 3351 cases (23.30%). A significant seasonal trend was observed for the V. parahaemolyticus, with the highest rates over the summer period, peaking in August, 1171 cases (38.75%), a similar trend was also observed with Salmonella and Diarrheagenic E. coli. Norovirus infections showed the highest rate in November (904, 14.77%) and March (660,10.78%), the lowest in August, 215 cases (3.51%). Patients between 19 ~ 40 years were more likely to infected by Norovirus, V. parahaemolyticus and Diarrheagenic E. coli, patients below 1 year were the highest among patients with Salmonella infection, 881 cases (26.3%). The Norovirus, V. parahaemolyticus and Diarrheagenic E. coli infection with the highest positive detection rates among the workers were observed. The largest number cases of food categories were from aquatic product infection. The private home was the most common exposure setting.

Conclusion

Our study highlighted the necessity for conducting an active, comprehensive surveillance for pathogens in all age groups, to monitor the changing dynamics in the epidemiology and aetiology of foodborne diseases to guide policies that would reduce related illnesses.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-022-14226-1.

Clinical Characteristics and Drug Resistance Analysis of 90 Cases of Children with Salmonella Enteritis

Objective. To summarize the clinical characteristics and drug sensitivity analysis of children with Salmonella enteritis in our hospital, explore the characteristics and drug resistance of Salmonella infection, and guide the rational clinical use of drugs. Methods. The clinical data of 90 pediatric Salmonella enteritis patients treated in our hospital from January 2015 to January 2020 were selected as the observation group of this retrospective study, and 90 patients with non-Salmonella enteritis were selected at the same time as a control group. Discuss the clinical characteristics of Salmonella, drug sensitivity analysis, infection characteristics, and drug resistance and guide the rational clinical use of drugs. Results. The susceptibility rates of 15 antibiotics from high to low were imipenem and meropenem, piperacillin, cefoperazone, compound trimethoprim, chloramphenicol, and ceftazidime. Salmonella strains were both resistant to imipenem and meropenem. Salmonella is sensitive and has a low rate of resistance to quinolones (ciprofloxacin) and a high rate of resistance to cephalosporins (ceftriaxone, cefotaxime, ceftazime, and cefpiramide), both reached more than 28%. Salmonella has the highest resistance to penicillin and erythromycin, both at 85.00% and above. Among 90 children with Salmonella enteritidis food poisoning, 32 were hospitalized, 21 cases were hospitalized less than 7 days, and 11 cases were 7-14 days. The longest hospital stay was 12 days, the shortest was 1 day, and the average was 6.1 days. Seven people stayed for observation and 51 people were discharged after treatment. All the children recovered without death. Conclusion. In clinical practice, antibiotics should be used rationally based on drug susceptibility results. In the case of poor efficacy of cephalosporins, amoxicillin and potassium clavulanate, piperacillin, tazobactam, or imipenem, cephalosporin antibiotics can be considered the first choice for clinical empiric medication.

Whole Genome Sequencing, Antibiotic Resistance, and Epidemiology Features of Nontyphoidal Salmonella Isolated From Diarrheic Children: Evidence From North China

Nontyphoidal Salmonella (NTS) in children remains a growing burden on public health and often causes children to be hospitalized with diarrheic symptoms. In this work, 260 strains of human Salmonella isolated from Jilin, China were characterized by serotypes and antimicrobial resistance using whole genome sequencing (WGS). The most prevalent serotype was Salmonella enteritidis (47.3%), followed by S. I 4,[5],12:i:- (33.1%), and Salmonella Typhimurium (7.3%). Furthermore, the consistency between resistance phenotype and genotype was confirmed. Similarly, strains harbored bla_TEM−1B and tetA genes were detected, which verified the level of resistant phenotype in β-lactams and tetracyclines. The presence of a single mutation in parC, gyrA, and qnrS1 genes corresponding to quinolones was also observed. In our work, multilocus sequence typing (MLST) and core genome multilocus sequence typing (cgMLST) were found to have a high resolution to molecular traceability, and the combination of both was conducive to practical application in an actual situation. Taking all of this into account, we suggested that the comprehensive surveillance of Salmonella infection in children should be carried out to monitor antimicrobial-resistant trends from various sources and to alert on outbreaks of foodborne diseases to protect public health.

Antibiotic resistance of fecal carriage of Escherichia coli from pig farms in China: a meta-analysis

Fecal carriage of bacteria is a major source of antibiotic resistance genes (ARGs) and a public health risk, but the antibiotic resistance of Escherichia coli (E. coli) in Chinese pig farms remains a major gap in the available literature. Our goal was to conduct a meta-analysis of studies reporting antibiotic resistance of fecal carriage of E. coli from pig farms in China, calculating the pooled resistance rates and summarizing factors associated with it. We searched PubMed and Web of Science for studies published in English up to February 28, 2021. We also searched bibliographic indices and corresponded with the authors. We chose ciprofloxacin, gentamicin, tetracycline, ampicillin, and florfenicol from five major types of antibiotics to comprehensively evaluate the resistance rate of E. coli. We used a random-effects model and Freeman-Tukey double arcsine transformation to calculate the resistance rate and 95% confidence interval. Among the 120 retrieved manuscripts, 16 studies (1985 E. coli isolates) were deemed eligible for our analysis. The combined resistance rate of E. coli from feces was 58.8% (95% CI: 45.3-71.7%) to ciprofloxacin, 54.3% (95% CI: 35.3-72.6%) to gentamicin, 91.0% (95% CI: 83.1-96.7%) to tetracycline, 81.4% (95% CI: 62.0-95.1%) to ampicillin, and 65.4% (95% CI: 33.9-90.9%) to florfenicol. In conclusion, fecal carriage of E. coli in Chinese pig farms shows high resistance to ciprofloxacin, gentamicin, tetracycline, ampicillin, and florfenicol. Subgroup analysis showed that the resistance of E. coli to antibiotics was closely related to the sample size and the health condition of the pigs. Specifically, ESBL-producing E. coli has a higher ratio of resistance to other antibiotics. Future collection of antibiotic resistance and other information in pig farms should be more precise and depend on local surveys.

Risk factors associated with Salmonella prevalence, its antibiotic resistance, and egg antibiotic residues in the layer farming environment

Background and Aim:

Human salmonellosis with non-typhoidal Salmonella remains a global public health concern related to the consumption of contaminated eggs and egg-based products. This study aimed to examine the prevalence of Salmonella, antimicrobial-resistant Salmonella, and egg antibiotic residues concerning risk factors associated with Salmonella contamination in eggs, the layer farming environment, and laying hens kept in battery-cage closed-housing systems.

Materials and Methods:

This study used a repeated cross-sectional design to collect 488 samples from eggs, laying hens, and the farm environment on one laying farm for Salmonella detection according to ISO 6579:2002/AMD 1:2007. Salmonella-positive samples were further tested for serotype and antimicrobial susceptibility using the disk diffusion test. The layer farm contact person was interviewed at the sampling time to evaluate the risk factors associated with Salmonella contamination using logistic regression analysis. For each month, 24 eggs (144 eggs in total) were also randomly sampled from the collection egg area at the farm for antibiotic residue detection using the European Four Plate Test.

Results:

The highest Salmonella prevalence rates were in the samples from the layer pen floors, followed by the egg sizing machine (ESM) and eggshells at 65.5%, 52.5%, and 15%, respectively. Salmonellaenterica serovar Corvallis was the dominant serovar (48.38%), followed by Mbandaka (37.76%), Braenderup (14.29%), and Typhimurium (4.08%). Rodent presence at the farm and the frequency of changing the disinfectant foot dip were significant factors related to Salmonella contamination on the pen floors (odds ratio [OR]=22.5, 95% confidence interval [CI]=2.11-240.48, p=0.01; OR=24, 95% CI=2.78-206.96, p=0.004, respectively). Hand-washing before sorting and cleaning the ESM were the significant factors (OR=13, 95% CI=1.2-140.73, p=0.04). The most resistant Salmonella isolates were resistant to oxytetracycline. One isolate of S. enterica Typhimurium was resistant to cefotaxime, enrofloxacin, and oxytetracycline. The antibiotic residues in the egg yolks were streptomycin, enrofloxacin, and tetracycline at prevalence rates of 36.11%, 11.81%, and 7.64%, respectively. Streptomycin was the most abundant residue in the albumen and yolk, followed by tetracycline.

Conclusion:

Salmonella prevalence in layer farming with a closed-housing system is related to effective biosecurity and hygiene issues, such as rodent control, clean farm equipment, and good worker hygiene. In addition, eggs’ antibiotic residues may be related to treating antimicrobial-resistant Salmonella isolates and medicated feed with inappropriate antibiotic withdrawal time.

Resistance-Nodulation-Cell Division (RND) Transporter AcrD Confers Resistance to Egg White in Salmonella enterica Serovar Enteritidis

The excellent survival ability of Salmonella enterica serovar Enteritidis (S. Enteritidis) in egg white leads to outbreaks of salmonellosis frequently associated with eggs and egg products. Our previous proteomic study showed that the expression of multidrug efflux RND transporter AcrD in S. Enteritidis was significantly up-regulated (4.06-fold) in response to an egg white environment. In this study, the potential role of AcrD in the resistance of S. Enteritidis to egg white was explored by gene deletion, survival ability test, morphological observation, Caco-2 cell adhesion and invasion. It was found that deletion of acrD had no apparent effect on the growth of S. Enteritidis in Luria-Bertani (LB) broth but resulted in a significant (p < 0.05) decrease in resistance of S. Enteritidis to egg white and a small number of cell lysis. Compared to the wild type, a 2-log population reduction was noticed in the ΔacrD mutant with different initial concentrations after incubation with egg white for 3 days. Furthermore, no significant difference (p > 0.05) in the adhesion and invasion was found between the wild type and ΔacrD mutant in LB broth and egg white, but the invasion ability of the ΔacrD mutant in egg white was significantly (p < 0.05) lower than that in LB broth. This indicates that acrD is involved in virulence in Salmonella. Taken together, these results reveal the importance of AcrD on the resistance of S. Enteritidis to egg white.

A Severe Gastroenteritis Outbreak of Salmonella enterica Serovar Enteritidis Linked to Contaminated Egg Fried Rice, China, 2021

Salmonella contamination of eggs and egg shells has been identified as a public health problem worldwide. Here, we reported an outbreak of severe gastrointestinal symptoms caused by Salmonella enterica serovar Enteritidis (S. enteritidis) in China. We evaluated the outbreak by using epidemiological surveys, routine laboratory testing methods, and whole genome sequencing (WGS). This outbreak occurred in a canteen in Beijing, during March 9–11, 2021, 225 of the 324 diners who have eaten at the canteen showed gastrointestinal symptoms. The outbreak had characteristical epidemiological and clinical features. It caused a very high attack rate (69.4%) in a short incubation time. All patients developed diarrhea and high fever, accompanied by abdominal pain (62.3%), nausea (50.4%), and vomiting (62.7%). The average frequency of diarrhea was 12.4 times/day, and the highest frequency of diarrhea was as high as 50 times/day. The average fever temperature was 39.4°C, and the highest fever temperature was 42°C. Twenty strains of S. enteritidis were recovered, including 19 from the patients samples, and one from remained egg fried rice. Antibiotic susceptibility test showed that the 20 outbreak strains all had the same resistance pattern. PFGE results demonstrated that all 20 strains bore completely identical bands. Phylogenetic analysis based on WGS revealed that all 20 outbreak strains were tightly clustered together. So the pathogenic source of this food poisoning incident may was contaminated egg fried rice. Resistance gene analysis showed that the outbreak strains are all multi-drug resistant strains. Virulence gene analysis indicated that these outbreak strains carried a large number of virulence genes, including 2 types of Salmonella pathogenicity islands (SPI-1 and SPI-2). Other important virulence genes were also carried by the outbreak strains, such as pefABCD, rck and shdA. And the shdA gene was not in other strains located in the same evolutionary branch as the outbreak strain. We speculated that this is a significant reason for the serious symptoms of gastroenteritis in this outbreak. This outbreak caused by S. enteritidis suggested government should strengthen monitoring of the prevalence of outbreak clone strains, and take measures to mitigate the public health threat posed by contaminated eggs.

Genomic Investigation of Antimicrobial-Resistant Salmonella enterica Isolates From Dead Chick Embryos in China

Salmonella spp. is recognized as an important zoonotic pathogen. The emergence of antimicrobial resistance in Salmonella enterica poses a great public health concern worldwide. While the knowledge on the incidence and the characterization of different S. enterica serovars causing chick embryo death remains obscure in China. In this study, we obtained 45 S. enterica isolates from 2,139 dead chick embryo samples collected from 28 breeding chicken hatcheries in Henan province. The antimicrobial susceptibility assay was performed by the broth microdilution method and the results showed that 31/45 (68.8%) isolates were multidrug-resistant (≥3 antimicrobial classes). Besides the highest resistance rate was observed in the aminoglycoside class, all the isolates were susceptible to chloramphenicol, azithromycin, and imipenem. Furthermore, genomic characterization revealed that S. Enteritidis (33.33%; 15/45) was a frequent serovar that harbored a higher number of virulence factors compared to other serovars. Importantly, genes encoding β-lactamases were identified in three serovars (Thompson, Enteritidis, and Kottbus), whereas plasmid-mediated quinolone resistance genes (qnrB4) were detected in certain isolates of S. Thompson and the two S. Kottbus isolates. All the examined isolates harbored the typical virulence factors from Salmonella pathogenicity islands 1 and 2 (SPI-1 and SPI-2). Additionally, a correlation analysis between the antimicrobial resistance genes, phenotype, and plasmids was conducted among Salmonella isolates. It showed strong positive correlations (r < 0.6) between the different antimicrobial-resistant genes belonging to certain antimicrobial classes. Besides, IncF plasmid showed a strong negative correlation (r > −0.6) with IncHI2 and IncHI2A plasmids. Together, our study demonstrated antimicrobial-resistant S. enterica circulating in breeding chicken hatcheries in Henan province, highlighting the advanced approach, by using genomic characterization and statistical analysis, in conducting the routine monitoring of the emerging antimicrobial-resistant pathogens. Our findings also proposed that the day-old breeder chicks trading could be one of the potential pathways for the dissemination of multidrug-resistant S. enterica serovars.

A review on recent advances of egg byproducts: Preparation, functional properties, biological activities and food applications

The rapid development of egg industries produced vast byproducts that have not been effectively used. In this paper, the comprehensive utilization of egg byproducts was reviewed. Protein extraction and enzymatic hydrolysis were the main used ways for recycle of egg byproducts. The fact that eggshell membrane could accelerate would healing and improve facial skin of healthy people for 12 weeks was found. However, salted egg white had poor functional properties owing to high salt and ultrafiltration was an effective technology to remove 92.93% of salt. Moreover, Defatted yolk protein had the great potential to be used as food additives and functional foods. Other egg byproducts such as egg inhibitor and eggshells also were discussed. The novel applications of egg byproducts in the food field included food additives, feeds, food packaging materials and nutraceuticals based on current knowledge, but the proportion needed to be improved. This paper would provide a new insight for comprehensive utilization of egg byproducts.

Positive regulation of Type III secretion effectors and virulence by RyhB paralogs in Salmonella enterica serovar Enteritidis

Small non-coding RNA RyhB is a key regulator of iron homeostasis in bacteria by sensing iron availability in the environment. Although RyhB is known to influence bacterial virulence by interacting with iron metabolism related regulators, its interaction with virulence genes, especially the Type III secretion system (T3SS), has not been reported. Here, we demonstrate that two RyhB paralogs of Salmonella enterica serovar Enteritidis upregulate Type III secretion system (T3SS) effectors, and consequently affect Salmonella invasion into intestinal epithelial cells. Specifically, we found that RyhB-1 modulate Salmonella response to stress condition of iron deficiency and hypoxia, and stress in simulated intestinal environment (SIE). Under SIE culture conditions, both RyhB-1 and RyhB-2 are drastically induced and directly upregulate the expression of T3SS effector gene sipA by interacting with its 5′ untranslated region (5′ UTR) via an incomplete base-pairing mechanism. In addition, the RyhB paralogs upregulate the expression of T3SS effector gene sopE. By regulating the invasion-related genes, RyhBs in turn affect the ability of S. Enteritidis to adhere to and invade into intestinal epithelial cells. Our findings provide evidence that RyhBs function as critical virulence factors by directly regulating virulence-related gene expression. Thus, inhibition of RyhBs may be a potential strategy to attenuate Salmonella.