Effect of avian intestinal microflora possessing adhering and hydrophobic properties on competitive exclusion of Salmonella typhimurium from chicks

Foodborne Salmonella ecology in the avian gastrointestinal tract

Foodborne Salmonella continues to be a major cause of salmonellosis with Salmonella Enteritidis and S. Typhimurium considered to be responsible for most of the infections. Investigation of outbreaks and sporadic cases has indicated that food vehicles such as poultry and poultry by-products including raw and uncooked eggs are among the most common sources of Salmonella infections. The dissemination and infection of the avian intestinal tract remain somewhat unclear. In vitro incubation of Salmonella with mammalian tissue culture cells has shown that invasion into epithelial cells is complex and involves several genetic loci and host factors. Several genes are required for the intestinal phase of Salmonella invasion and are located on Salmonella pathogenicity island 1 (SPI 1). Salmonella pathogenesis in the gastrointestinal (GI) tract and the effects of environmental stimuli on gene expression influence bacterial colonization and invasion. Furthermore, significant parameters of Salmonella including growth physiology, nutrient availability, pH, and energy status are considered contributing factors in the GI tract ecology. Approaches for limiting Salmonella colonization have been primarily based on the microbial ecology of the intestinal tract. In vitro studies have shown that the toxic effects of short chain fatty acids (SCFA) to some Enterobacteriaceae, including Salmonella, have resulted in a reduction in population. In addition, it has been established that native intestinal microorganisms such as Lactobacilli provide protective mechanisms against Salmonella in the ceca. A clear understanding of the key factors involved in Salmonella colonization in the avian GI tract has the potential to lead to better approach for more effective control of this foodborne pathogen.

Prospects for 'competitive exclusion' treatment to control salmonellas and other foodborne pathogens in poultry

In newly hatched chicks, the rapid establishment of an adult-type intestinal microflora, via the oral route, produces almost immediate resistance to colonization by any food poisoning salmonellas that gain access to the rearing environment. Exploitation of the 'competitive exclusion' (CE) effect is now an accepted part of the overall strategy by which poultry-associated salmonellas are being controlled in some countries. This review covers practical aspects of CE treatment and factors affecting efficacy in both laboratory-scale trials and field studies. It also considers possible applications in preventing colonization of poultry with Escherichia coli O157 and Campylobacter jejuni. For the latter, evidence suggests that the 'protective' organisms are different from those involved in salmonella control.

The application of ecological principles and fermentable fibers to manage the gastrointestinal tract ecosystem

Because diet can influence the structure and functions of the gastrointestinal tract, there are opportunities for using diet as a "management tool" to affect the resident microbiota. Fermentable fibers increase the densities of beneficial bacteria and stimulate growth and functions of the healthy intestine. Recent findings show that after acute diarrhea, the use of an oral electrolyte solution with the fermentable fiber oligofructose accelerates recovery of beneficial bacteria, reduces the relative abundance of detrimental bacteria, stimulates mucosal growth and enhances digestive and immune functions. This review will focus on how the principles of stream ecology can be applied to better understand the distribution of bacteria along the length of the gastrointestinal tract, the effect of diarrhea on the gastrointestinal ecosystem and how fermentable fibers can be used as a "management tool" to promote gastrointestinal health in normal states and during recovery from diarrhea.

Identification of a new intestinal spirochete with pathogenicity for chickens

Two intestinal spirochete isolates obtained from chickens with diarrhea were examined by electron microscopy, biochemical tests, rRNA gene restriction pattern analysis, and multilocus enzyme electrophoresis. One isolate (strain 91-1207/C1) was pathogenicity tested in vivo in chickens. The chicken spirochetes were morphologically indistinguishable from Serpulina innocens and Serpulina hyodysenteriae and phenotypically similar to S. innocens. However, the chicken spirochetes could be distinguished from S. innocens, S. hyodysenteriae, and other swine intestinal spirochetes by rRNA gene restriction pattern analysis and multilocus enzyme electrophoresis. In pathogenicity tests in 1-day-old chicks and 14-month-old hens, chicken spirochete 91-1207/C1 produced pale-yellow, watery cecal contents and mild lymphocytic typhlitis. These findings support the conclusion that avian intestinal spirochetes can be pathogenic to commercial poultry and that the microorganisms are different from intestinal spirochetes that infect pigs.

Comparison of probiotics maintained by in vivo passage through laying hens and broilers

Cecal colonization by salmonellae may be greatly reduced by inoculating chickens with normal cecal microflora, a phenomenon known as competitive exclusion. Unfortunately, it has not been possible to reliably store active cecal microflora over long time periods, and it is difficult to obtain consistent experimental results with different batches of microflora. In order to overcome these problems, the present authors have maintained active cecal flora through a 2-yr period by in vivo passage through both broiler chicks and layers that were fed a diet containing 5% lactose. Competitive exclusion cultures maintained in laying hens worked as well as cultures from broilers. Cecal microflora from either source excluded both nonlactose-fermenting and lactose-fermenting Salmonella strains. Colonization by both types of Salmonella was reduced even when the competitive exclusion organisms were given as late as 3 days after oral challenge inoculation with Salmonella typhimurium.

Defined cultures and prospects

Resistance of young chicks to Salmonella colonization can be increased by treating them with suspensions or anaerobic cultures of gut content from healthy, adult birds. Unfortunately, such treatments have an unknown bacterial composition and are therefore not acceptable to regulatory agencies in some countries. Efforts are continuing to identify components in the gut microflora that are involved in the protective process. The ultimate aim is to identify bacteria that may be used, either alone or in mixtures (defined cultures), as a prophylactic treatment of chicks against Salmonella colonization. Although much research has been done in this area, a defined culture treatment with a potency and stability equivalent to that of undefined culture has not been developed. Since the mechanism of protection is not clear, there are no reliable criteria for selecting potentially protective strains. The most effective mixtures contain large numbers of bacterial cultures (about 50 isolates). These mixtures are comparable to undefined faecal cultures in protecting chicks against challenge levels of up to 10(4) Salmonella/chick. However, they are not protective for turkey poults. Mixtures containing lower number of strains are generally less protective. It appears that obligate and facultative anaerobes from different genera are required for protection. Mixtures containing strains from only one genus, e.g. Lactobacillus or Bifidobacterium, are generally not effective. Maintenance of intestinal isolates on laboratory media, as well as in storage at -70 degrees C, results in a progressive decrease in their protective ability. The protective ability of mixtures or individual strains can be partially restored by in vivo passage. A promising criterion for isolating and/or screening potentially protective isolates is based on the adherence of native microflora to the caecal wall of treated chicks. Despite substantial efforts and some progress in the development of defined cultures, the prospects are not very encouraging. Until the exact mechanism of protection is elucidated, the basis for selecting the required strains will be difficult to define.