Association of Beta2-PositiveClostridium perfringensType A With Focal Duodenal Necrosis in Egg-Laying Chickens in the United States

Laser Capture Microdissection, Culture Analysis, and Bacterial Sequencing to Evaluate the Microbiota of Focal Duodenal Necrosis in Egg Layers

Focal duodenal necrosis (FDN) is a common intestinal disease of table egg layers. In this research we aimed to identify the bacteria commonly found in FDN lesions as seen with histopathological analysis. Fifty-nine ethanol-fixed duodenum samples were collected from egg layers on eight FDN-affected farms, and 42 samples had typical FDN lesions. Excision of bacteria-containing lesions using laser capture microdissection was performed, followed by 16S rRNA gene sequencing of extracted DNA for bacterial identification. Bacterial sequencing analysis revealed no consistent bacterial species identified from samples with FDN. However, analysis of the relative phylum abundance revealed differences in the duodenal microbiota between layers with FDN and healthy birds. There were differences in the abundance of Proteobacteria, Firmicutes, and Actinobacteria between FDN-positive and FDN-negative control samples compatible with intestinal dysbiosis. In addition, 10 duodenal samples with FDN lesions were collected for bacteriological analysis, yielding 47 colonies on tryptone soy agar, MacConkey agar, and blood agar plates. Using 16S rRNA gene PCR, 39/47 (53.8%) colonies were identified as Escherichia coli. PCR for E. coli virulence genes identified 21/39 (53.8%) E. coli isolates as avian pathogenic E. coli-like. PCR analysis for 19 E. coli virulence genes associated with intestinal disease strains including inflammatory bowel disease found 11/39 (28.2%) isolates containing more than 10 of these virulence genes. In conclusion, FDN appears to be a multifactorial inflammatory intestinal disease associated with intestinal dysbiosis, and Gram-negative bacteria including E. coli may contribute to the pathogenesis of this disease.

Necrotizing Hepatitis Associated with Clostridium perfringens in Broiler Chicks

In this retrospective study we describe unusual cases of clostridial hepatitis associated with high mortality in young broiler chicks. Eleven cases of necrotizing hepatitis in broiler chicks from four companies were submitted to the Poultry Diagnostic and Research Center or the Georgia Poultry Laboratory Network between 2017 and 2020. In most flocks, increased 3-day mortality was followed by an elevated 7-day mortality. Gross lesions included green to dark brown discoloration of the liver, congested lungs, serosanguineous fluid in the caudoventral aspect of the abdomen, and emphysema in the yolk sacs. In birds older than a week of age, disease with neurologic signs became evident and consisted of tremors, stargazing, and incoordination. Histopathologic evaluation revealed multifocal to coalescing fibrinoheterophilic and necrotizing hepatitis associated with gram-positive, long, rod-shaped bacteria. Formalin-fixed liver samples from six cases out of eight cases tested were positive for Clostridium perfringens by immunohistochemistry. Liver samples from two cases were culture positive for Clostridium spp., and C. perfringens was isolated from one sample. Toxinotyping by PCR performed in seven samples revealed the presence of the genes that code for alpha toxin phospholipase C (cpa or plc) and necrotic enteritis toxin B-like (netB) in six samples and as well as C. perfringens large cytotoxin (tpeL) in one sample. Broiler breeders are the suspected source of the infection, and testing revealed C. perfringens in hatchery samples and among broiler breeder flocks. Antimicrobial therapy was coupled with enhanced sanitation at the farm and hatchery in that company, markedly decreasing the mortality and clinical signs. This is the first comprehensive evaluation of clostridial necrotizing hepatitis in newly hatched chicks, and the second ever reported in the literature.

Clostridium perfringens Beta2 toxin forms highly cation-selective channels in lipid bilayers

Clostridium perfringens is a potent producer of a variety of toxins. Well studied from these are five toxins (alpha, Beta (CPB), epsilon, iota and CPE) that are produced by seven toxinotype strains (A–G) of C. perfringens. Besides these toxins, C. perfringens produces also another toxin that causes necrotizing enterocolitis in piglets. This toxin termed consensus Beta2 toxin (cCPB2) has a molecular mass of 27,620 Da and shows only little homology to CPB and no one to the other toxins of C. perfringens. Its primary action on cells remained unknown to date. cCPB2 was heterogeneously expressed as fusion protein with GST in Escherichia coli and purified to homogeneity. Although cCPB2 does not exhibit the typical structure of beta-stranded pore-forming proteins and contains no indication for the presence of amphipathic alpha-helices we could demonstrate that cCPB2 is a pore-forming component with an extremely high activity in lipid bilayers. The channels have a single-channel conductance of about 700 pS in 1 M KCl and are highly cation-selective as judged from selectivity measurements in the presence of salt gradients. The high cation selectivity is caused by the presence of net negative charges in or near the channel that allowed an estimate of the channel size being about 1.4 nm wide. Our measurements suggest that the primary effect of cCPB2 is the formation of cation-selective channels followed by necrotic enteritis in humans and animals. We searched in databases for homologs of cCPB2 and constructed a cladogram representing the phylogenetic relationship to the next relatives of cCPB2.

Role of Clostridium perfringens Necrotic Enteritis B-like Toxin in Disease Pathogenesis

Necrotic enteritis (NE) is a devastating enteric disease caused by Clostridium perfringens type A/G that impacts the global poultry industry by compromising the performance, health, and welfare of chickens. Coccidiosis is a major contributing factor to NE. Although NE pathogenesis was believed to be facilitated by α-toxin, a chromosome-encoded phospholipase C enzyme, recent studies have indicated that NE B-like (NetB) toxin, a plasmid-encoded pore-forming heptameric protein, is the primary virulence factor. Since the discovery of NetB toxin, the occurrence of NetB⁺ C. perfringens strains has been increasingly reported in NE-afflicted poultry flocks globally. It is generally accepted that NetB toxin is the primary virulent factor in NE pathogenesis although scientific evidence is emerging that suggests other toxins contribute to NE. Because of the complex nature of the host-pathogen interaction in NE pathogenesis, the interaction of NetB with other potential virulent factors of C. perfringens needs better characterization. This short review will summarize the primary virulence factors involved in NE pathogenesis with an emphasis on NetB toxin, and a new detection method for large-scale field screening of NetB toxin in biological samples from NE-afflicted commercial broiler flocks.

Research-Relevant Background Lesions and Conditions in Common Avian and Aquatic Species

Non-mammalian vertebrates including birds, fish, and amphibians have a long history of contributing to ground-breaking scientific discoveries. Because these species offer several experimental advantages over higher vertebrates and share extensive anatomic and genetic homology with their mammalian counterparts, they remain popular animal models in a variety of fields such as developmental biology, physiology, toxicology, drug discovery, immunology, toxicology, and infectious disease. As with all animal models, familiarity with the anatomy, physiology, and spontaneous diseases of these species is necessary for ensuring animal welfare, as well as accurate interpretation and reporting of study findings. Working with avian and aquatic species can be especially challenging in this respect due to their rich diversity and array of unique adaptations. Here, we provide an overview of the research-relevant anatomic features, non-infectious conditions, and infectious diseases that impact research colonies of birds and aquatic animals, including fish and Xenopus species.

Characterization of Virulent netB+/tpeL+ Clostridium perfringens Strains from Necrotic Enteritis-Affected Broiler Chicken Farms

Clostridium perfringens (CP) type A and newly created type G strains are the key etiological factors in the induction of necrotic enteritis (NE), an important enteric disease that is responsible for the annual loss of $6 billion in the worldwide poultry industry. Several CP toxin genes were found to be critical in NE pathogenesis in chickens, but limited information is available on the CP lethal toxin tpeL gene. In this study, 19 CP strains isolated from NE-affected chicken farms were characterized microbiologically and molecularly and evaluated for their pathogenicity in commercial broiler chickens. Toxin typing by PCR revealed that all strains tested were positive for the netB toxin gene, but only five strains were positive for the tpeL toxin gene (LLY-TpeL 13, -TpeL 15, -TpeL 17, -TpeL 18, and -TpeL 19, simplified as TpeL 13, TpeL 15, TpeL 17, TpeL 18, and TpeL 19). High levels of TpeL proteins were detected in the concentrated culture supernatant from strains TpeL 13, 15, 17, and 19 by western blotting. Quantitative PCR showed that strains TpeL 13, 15, 17, 18, and 19 harbored a high number of copies of tpeL genes, while TpeL 18 had the highest number of copies of the tpeL gene among all CP strains tested when normalized with copy numbers of 16S rRNA gene as a housekeeping gene marker. The in vivo NE challenge test using multiple oral CP inoculations combined with a high-protein diet showed that TpeL 17 was the most virulent in inducing typical NE lesions, followed by TpeL 19 as the next most virulent, when tested in commercial broiler chickens. Infection with TpeL 17 reduced the growth rate significantly, as shown by reduced relative body weight gain percentage at day 5 postinfection. Availability of the virulent netB⁺tpeL⁺ CP strains is essential for the development of a CP-alone NE challenge model that could provide significant tools for understanding CP pathogenesis and for development of alternative to antibiotics.

Focal duodenal necrosis in chickens: attempts to reproduce the disease experimentally and diagnostic considerations

Focal duodenal necrosis (FDN) is an intestinal disease of egg-layer chickens characterized by multifocal necrosis of the duodenal loop and proximal jejunum. Affected flocks usually have decreased egg weights and drops in egg production. Previous studies have associated this condition with Clostridium perfringens infection. We tried to reproduce FDN by experimental infection of egg-laying chickens using different netB-positive and netB-negative C. perfringens strains, and duodenal homogenate obtained from FDN lesions. Chickens challenged with C. perfringens and/or duodenal homogenate developed duodenitis after challenge. Gross lesions included mucosal erosions, hyperemia, mucosal hemorrhages, and watery intestinal content. Microscopic lesions included mild enterocyte degeneration and necrosis, and mild-to-moderate hemorrhage and lymphoplasmacytic and heterophilic infiltration of the lamina propria. Two netB-positive C. perfringens strains closely related to necrotic enteritis pathogenic strains, by genomic composition, were re-isolated from lesions. Necrosis of intestinal crypts was observed in chickens challenged with duodenal homogenate with or without C. perfringens coinfection. Characteristic microscopic FDN lesions with significant necrosis and loss of villus enterocytes were not reproduced.

Profiling of Egg Layer Flocks Affected with Focal Duodenal Necrosis Based on a Questionnaire Survey

Focal duodenal necrosis (FDN) is an intestinal disease of egg-laying chickens, characterized by multifocal mucosal erosions in the duodenal loop and proximal jejunum. It is currently considered by the Association of Veterinarians in Egg Production and the United States Animal Health Association as one of the top five disease concerns of the table egg industry in the United States. Previous studies have associated this condition with Clostridium species. The purpose of this study was to investigate the epidemiologic characteristics of table egg layer flocks affected with FDN. An online questionnaire was distributed to commercial layer operations in different states in the United States. Layer farms that had diagnosed FDN within the past 12 mo were surveyed. The questionnaire had 45 questions about management, nutrition, housing, and methods for disease prevention and control. Thirty-seven surveys were sent and 21 were completed, which represents a response rate of 56.7%. The survey results showed the presence of FDN in five egg-layer genetic lines or breed crosses of different ages, with most cases reported between 30-39 wk of age. The pullets were cage-reared in all affected flocks and the majority of flocks in production were housed in traditional cages. Most of the FDN-affected flocks received more than 12 different feed formulations from pre-lay to 60 wk of age. Distiller's dried grain with solubles was a common ingredient added to the feed in the majority of affected flocks, and all flocks were provided with limestone as a calcium source for egg production. Most surveys reported that coccidiosis and roundworm parasitism were not problems in affected flocks in production; however, pests such as flies and rodents were reported as problems in most affected flocks. Additionally, most affected farms never washed feeders, cages, and houses before disinfection, which may not be sufficient to prevent the persistency and transmission of the causative agent of FDN. In conclusion, several management practices that have been associated with enteric disease, including clostridial-associated enteritis, were described by the majority of FDN-affected flocks. Additional studies are needed to determine if management and health practices identified in this survey represent risk factors for FDN.

Complete Genome Sequence of Clostridium perfringens LLY_N11, a Necrotic Enteritis-Inducing Strain Isolated from a Healthy Chicken Intestine

Clostridium perfringens strain LLY_N11, a commensal bacterium, which previously induced necrotic enteritis in an experimental study, was isolated from the intestine of a young healthy chicken. Here, we present the complete genome sequence of this strain, which may provide a better understanding of the molecular mechanisms involved in necrotic enteritis pathogenesis.