Evidence that bacteria are not causative agents of stunting syndrome in poults

Segmented Filamentous Bacteria - Metabolism Meets Immunity

Segmented filamentous bacteria (SFB) are a group of host-adapted, commensal organisms that attach to the ileal epithelium of vertebrate and invertebrate hosts. A genetic relative of the genus Clostridium, these morphologically unique bacteria display a replication and differentiation lifecycle initiated by epithelial tissue binding and filamentation. SFB intimately bind to the surface of absorptive intestinal epithelium without inducing an inflammatory response. Rather, their presence impacts the generation of innate and differentiation of acquired immunity, which impact the clearance of extracellular bacterial or fungal pathogens in the gastrointestinal and respiratory tracts. SFB have recently garnered attention due to their role in promoting adaptive and innate immunity in mice and rats through the differentiation and maturation of Th17 cells in the intestinal tract and production of immunoglobulin A (IgA). SFB are the first commensal bacteria identified that impact the maturation and development of Th17 cells in mice. Recently, microbiome studies have revealed the presence of Candidatus Arthromitus (occasionally designated as Candidatus Savagella), a proposed candidate species of SFB, in higher proportions in higher-performing flocks as compared to matched lower-performing flocks, suggesting that SFB may serve to establish a healthy gut and protect commercial turkeys from pathogens resulting in morbidity and decreased performance. In this review we seek to describe the life cycle, host specificity, and genetic capabilities of SFB, such as bacterial metabolism, and how these factors influence the host immunity and microbiome. Although the role of SFB to induce antigen-specific Th17 cells in poultry is unknown, they may play an important role in modulating the immune response in the intestinal tract to promote resistance against some infectious diseases and promote food-safety. This review demonstrates the importance of studying and further characterizing commensal, host-specific bacteria in food-producing animals and their importance to animal health.

Emergence of enteric viruses in production chickens is a concern for avian health

Several viruses have been identified in recent years in the intestinal contents of chickens and turkeys with enteric problems, which have been observed in commercial farms worldwide, including Brazil. Molecular detection of these viruses in Brazil can transform to a big threat for poultry production due to risk for intestinal integrity. This disease is characterized by severely delayed growth, low uniformity, lethargy, watery diarrhea, delayed feed consumption, and a decreased conversion rate. Chicken astrovirus (CAstV), rotavirus, reovirus, chicken parvovirus (ChPV), fowl adenovirus of subgroup I (FAdV-1), and avian nephritis virus (ANV) were investigated using the conventional polymerase chain reaction (PCR) and the reverse transcription polymerase chain reaction (RT-PCR). In addition, the infectious bronchitis virus (IBV), which may play a role in enteric disease, was included. The viruses most frequently detected, either alone or in concomitance with other viruses, were IBV, ANV, rotavirus, and CAstV followed by parvovirus, reovirus, and adenovirus. This study demonstrates the diversity of viruses in Brazilian chicken flocks presenting enteric problems characterized by diarrhea, growth retard, loss weight, and mortality, which reflects the multicausal etiology of this disease.

A comparative molecular study of the presence of "Candidatus arthromitus" in the digestive system of rainbow trout, Oncorhynchus mykiss (Walbaum), healthy and affected with rainbow trout gastroenteritis

Observations were made using histopathological techniques in conjunction with a nested polymerase chain reaction (PCR) protocol for the specific detection of "Candidatus arthromitus" on DNA extracted from wax-embedded tissues and fresh digestive contents of rainbow trout. Samples positive for "Candidatus arthromitus" DNA included fish with rainbow trout gastroenteritis (RTGE), clinically normal cohabiting fish, and apparently healthy controls from RTGE positive and RTGE negative sites. The results obtained from the PCR were confirmed by nucleotide sequencing. "Candidatus arthromitus" DNA was found in distal intestine as well as in sections of pyloric caeca, suggesting that both these locations are appropriate for molecular detection of "Candidatus arthromitus" DNA in trout. Furthermore, rainbow trout fry distal intestinal samples from two different hatcheries where RTGE had not been reported were also positive. Differences in "Candidatus arthromitus" DNA detection between paraffin wax-embedded and fresh digestive content samples from the same fish suggested that it may be predominantly epithelium-associated in healthy trout. Parallel histopathological observations indicated that pyloric caeca are the preferred site for visualizing segmented filamentous bacteria (SFB) in trout with RTGE. The results of this study showed that the presence of SFB was not invariably associated with clinical disease and that more information is required to understand the role of these organisms.

Development of organs and intestinal mucosa leukocytes in four broiler lines that differ in susceptibility to malabsorption syndrome

Growth retardation in young broiler chicks due to poor nutrient metabolism, commonly known as malabsorption syndrome (MAS), is a widespread problem caused by enteric infections with a combination of pathogens mainly viruses. Genetic lines of broiler chickens differ in susceptibility to the syndrome. A difference in growth retardation was observed among four broiler lines (BL) after oral inoculation at 1 d of age with intestinal homogenates obtained from MAS-affected birds. Two of the lines that are more susceptible to MAS had severe weight gain depression. To uncover the factors that play a role in the susceptibility to MAS, we analyzed the growth rate of the body and vital organs and the quantity of leukocytes in the peripheral blood and intestinal mucosa. The development of the intestine, liver, bursa of Fabricius, and spleen was similar among the BL. The resistant BL had higher numbers of peripheral blood leukocytes, especially lymphocytes, at 1 d of age. A significant difference was noted in the numbers of CD4+ T cells and CD8+ T cells in the intestinal villi. At the ages of 3 and 8 d, the susceptible BL had more CD8+ T cells in the villi, whereas the ratios of CD4+:CD8+ T cells were higher in the resistant BL. This difference in the number of T-cell subpopulations in the intestinal mucosa might be an important factor in the difference in susceptibility to the enteric infections associated with MAS.

Identification by in situ hybridization of segmented filamentous bacteria in the intestine of diarrheic rainbow trout (Oncorhynchus mykiss)

Nonculturable segmented filamentous bacteria (SFB) have been described in the gut of rats, mice and chickens, and 16S rRNA sequences for these organisms are available. These organisms, peripherically related to Clostridium phylogenetic group I, have been provisionally named 'Candidatus Arthromitus'. This work reports the observation of similar bacteria in the intestinal content of the distal intestine, preferentially, in the adult rainbow trout (Oncorhynchus mykiss) that exhibited episodic acute diarrhea, usually during the summer. Abdominal distension, intestinal fluid-mucus content and epithelium detachment were observed in trout. The demonstration that the observed microorganisms are bacteria and belong in the 'Candidatus Arthromitus' group was achieved by in situ hybridization with, respectively, a eubacterial probe and an oligonucleotide probe designed to react specifically with SFB 16S rRNA (encoded by the rrs gene) sequences. The sequenced rrs gene was compared with published sequences and found to be closely related to (although distinct from) other SFB sequences. Implication of these bacteria in trout diarrheic illness remains hypothetical.

Infectious stunting syndrome associated with disturbances of mineral metabolism and bone development in broiler chickens

On a broiler farm with a rearing capacity of about 200,000 chickens, a disease characterised by growth retardation, variability in chick size, 'leg weakness', diarrhoea and increased mortality at 3 weeks of age occurred repeatedly, in several successive broiler flocks. Gross and histopathological findings were dominated by widening of the hypertrophic and ossification layers of the physes of long bones as well as by thickening, unevenness and defective calcification of the cartilage trabeculae. In the parathyroid gland, vacuolar degeneration of the cytoplasm of glandular epithelial cells, connective tissue proliferation and, here and there, cyst formation were seen. Additional findings included severe cerebellar oedema and neuronal degeneration. The pancreatic, myocardial and intestinal changes typical of infectious stunting syndrome (ISS) occurred only in a mild form. Four-week-old chickens exhibiting 'leg weakness' had significantly lower blood inorganic phosphate concentration and tibial ash content as compared to healthy chickens. The disease was successfully transmitted by oral administration of small intestinal homogenate from affected chickens. In a second experiment, however, the disease could not be transmitted with intestinal homogenate sterilized by irradiation. Large doses of vitamin D3 reduced the rate of growth retardation and defective calcification of bones. The digestive enzyme activities of the pancreas and small intestinal mucosa of 'infected' chickens were decreased as is typical of ISS.

Stunting syndrome in broilers: effect of stunting syndrome inoculum obtained from stunting syndrome affected broilers, on broilers, leghorns and turkey poults

Responses to stunting syndrome (SS) infective material obtained from affected broilers and administered per os were monitored for 3 wk in a fast-growing commercial broiler population, in slow-growing Leghorn chicks, and in turkey poults. At 2 and 3 wk, the size of the gastrointestinal tract (GIT) segments, the pH of the GIT contents, and the activities of digestive enzymes in the intestinal contents and of disaccharidases on the jejunum mucosae were determined. Inoculation affected the genetic stocks differently. In broiler chicks, growth and feed utilization were markedly reduced. In contrast, inoculation of Leghorns was accompanied by improved feed intake and growth rate. Performance of poults was affected only slightly, albeit significantly. The effect of inoculation on the pH of crop and intestinal contents in Leghorn chicks was opposite to that found in broiler chicks, i.e., a significant increase in the crop and small intestinal pH in the former vs a significant decrease in inoculated broilers. Although inoculation of the broiler chicks did not affect the pH in the proventriculus, in Leghorn chicks it was reduced by 25%. In poults, inoculation did not significantly affect GIT contents pH. The GIT segments were markedly enlarged in broiler chicks, whereas in Leghorn chicks the opposite trend was observed; namely, intestinal segment weights were significantly reduced. In poults, inoculation caused a reduction in the intestinal segments and gizzard weight at 3 wk. During this same period, the liver and pancreas relative weights were dramatically increased in broiler chicks. A higher relative heart weight at 2 wk was observed in broilers and poults; this trend persisted to Week 3 in poults but not in broiler chicks. In broiler chicks, a nonsignificant reduction was observed for all enzymes assayed at 3 wk and for chymotrypsin at 2 wk. In Leghorn chicks, inoculation was accompanied by a marked and significant increase in the activity of chymotrypsin during both periods. In poults, inoculation caused a marked increase in the activities of amylase during Week 2 and 3, and trypsin at 3 wk. Maltase and saccharase activities in the jejunum of broiler chicks were slightly depressed a t 2 and 3 wk, the depression being significant at 2 wk for maltase and at 3 wk for saccharase. In the Leghorn chicks, inoculation caused a twofold increase in the activities of both enzymes. As in Leghorns, inoculation of poults with SS infective material caused a marked increase in the activities of the disaccharidases. The different responses to SS inoculation in the different genetic stocks are discussed.

Stunting syndrome in broilers: effect of glucose or maltose supplementation on digestive organs, intestinal disaccharidases, and some blood metabolites

The effect of supplementing a cornsoybean diet (C) with glucose (G) or maltose (M) on young broilers (from hatch to 3 wk of age) affected by stunting syndrome (SS) was studied. Stunting syndrome was induced by orally administering an inoculum prepared from the intestines of SS broiler chicks. Relative to the M diet, the G diet improved growth and feed utilization and increased feed intake in naive (NA) control chickens. The C diet was intermediate in this respect. In contrast to the NA chickens, diet did not affect growth or feed utilization in SS chicks. Changes in the relative weights of the gastrointestinal tract segments were evident by 1 wk of age and hypertrophy of these segments persevered to 3 wk of age. Stunting syndrome infection was accompanied by a significant increase in pancreatic trypsin-specific activity during Weeks 1 and 2, and in chymotrypsin activity at 1 wk. During this time, amylase-specific activity was not affected. At 3 wk of age, the specific activities of amylase, trypsin, and chymotrypsin in the pancreas were lower in the inoculated vs control birds. Whereas no significant effect of SS was observed with activities of amylase in the intestinal contents, trypsin activity was higher in SS chicks at 1 wk, and that of chymotrypsin lower during Weeks 2 and 3. Relative to NA chicks, the maltase and saccharase activities of SS chicks were much lower during Week 1, but increased later on and were similar to NA chick values at 2 and 3 wk. Whereas the level of blood plasma proteins did not vary from 1 to 3 wk in the NA chicks, it increased gradually in SS chicks to a level that significantly exceeded that in their NA counterparts. Blood plasma glucose and triglyceride levels were slightly lower in the SS chicks (NS), and the blood plasma cholesterol level was significantly reduced during Week 2. Relative to NA chicks, SS infection caused a significant increase in plasma calcium during Weeks 2 and 3, accompanied by a significant reduction in blood plasma phosphorus at 2 wk only. No difference was observed in the blood plasma level of uric acid, which peaked in both treatments during Week 2, or in D-beta-hydroxybutyric acid level, which was quite stable during the experimental period. Stunting syndrome infection was accompanied by a dramatic increase in amylase and alkaline phosphatase activities in the blood plasma, and by a slight but significant decrease in activity of lactic dehydrogenase. Stunting syndrome was concluded to be an affliction not only of digestion but also of metabolism. The main depression in growth caused by SS inoculation is probably due to metabolic alterations beyond those of digestion and absorption.

Stunting syndrome in broilers: effect of age and exogenous amylase and protease on performance, development of the digestive tract, digestive enzyme activity, and apparent digestibility

Day-old male, meat-type chicks raised in brooder batteries were infected by orally administering an inoculum prepared from intestines of broiler chicks infected with stunting syndrome (SS). Naive controls were kept in a parallel room. The chicks were fed a commercial starter diet supplemented with two levels of enzyme preparations to 14 d of age. The experiment was continued to the age of 6 wk in order to estimate compensatory feed intake and growth. In a parallel study, digestibility of the feed was determined from 1 to 3 wk of age with control or inoculated chicks. The enzymes amylase and proteases were produced by Bacillus subtilis and Penicillium emersonii. Enzyme supplementation had no effect on feed intake, growth, or feed utilization, or on digestibility of fat, starch, protein, or energy. Because enzyme supplementation did not consistently affect performance of chicks and no interactions were observed between enzyme supplementation and infection status, data are presented for effects of infection only. Inoculation of SS-infective material reduced performance to 4 wk. Compensatory growth and feed intake were observed from the age of 4 wk onward. At the age of 6 wk the slight retardation of the inoculated chicks was not significant. On Week 1, retention of fat, starch, protein, and energy was significantly depressed in the inoculated chicks. At the age of 2 wk, retention of starch was not depressed, and at the age of 3 wk, the only consistent depression was that observed for fat. The proventriculus weight and content were consistently higher in inoculated chicks, as were the small intestine and intestinal content. The pH of the gizzard content was higher, and that of the small intestine content was lower, in the inoculated birds than in their control counterparts. Stunting syndrome infection was accompanied by a significant depression of trypsin activity in the pancreas at the age of 1 and 2 wk. At these periods, amylase and chymotrypsin were not affected. At 6 wk of age, the activities of amylase, trypsin, and chymotrypsin in the pancreas were higher in the inoculated than in the control birds. In the intestinal chime, amylase, trypsin, and chymotrypsin activities were lower in the inoculated birds on Week 1 and 2 (NS for amylase on Week 1). On Week 6, the activity of all enzymes assayed was higher in the inoculated birds (NS for amylase). It is suggested that the main factors depressing feed intake and growth in SS-infected birds are most probably beyond those of digestion.

Stunting syndrome in broilers: physical, physiological, and behavioral aspects

The effect of stunting syndrome (SS) on young broilers induced by orally administering an inoculum prepared from intestines of SS-affected broiler chicks was studied in two experiments. Depression of growth, feed intake, and feed utilization, respectively, was negatively related to the age of inoculation, i.e., highest at posthatch inoculation (63, 57, and 61%), and intermediate at the ages of 3 (42, 45, and 50%) and 7 d (29, 34, and 53%), whereas at the age of 14 d inoculation was ineffectual and the inoculated chicks performed similarly to the naive controls. Eating behavior was determined by periodically recording the number of chicks in each treatment group exhibiting this behavior, i.e., pecking mash in the feeder or pecking the litter. Eating activity was much higher in inoculated chicks (about 20 to 24%) than in the naive controls (6 to 12%) and as with performance negatively related to the age of inoculation. In chicks inoculated at the age of 14 d, eating activity was quite similar to that of the naive control chicks. Noninoculated chickens raised in the same room as their inoculated counterparts were infected by the disease agents. In some respects the consequences of horizontal infection were similar to those observed in inoculated chicks, i.e., depressed feed intake, growth, and feed utilization and a heavier heart, crop, proventriculus, gizzard, intestine, and gastrointestinal contents. In contrast, the activities of the pancreatic digestive enzymes were more similar to those of the naive controls than to those of the inoculated groups. At the age of 14 d, activities of amylase, trypsin, chymotrypsin, and lipase in the pancreas were lower in the inoculated than in the naive control birds. At the age of 21 d, the results were reversed and activity in the inoculated birds was higher than in the naive control birds. During both periods, the activity of pancreatic lipase was higher in the naive controls than in the inoculated birds. The hyperactivity estimated via a determination of eating activity suggests that SS is an affliction not only of digestion but also of metabolism.