Conventional Animals

Conventional (CV) animals, being those which have a natural occurring microbiota, may be used to stimulate the human GIT. However, due to differences between the human and animal microbiota, the results from studies in CV animals may be quite different from corresponding studies conducted in humans. CV animal models are useful in studies on orally administrated human microorganisms in vivo, where the activities of the indigenous microbiota are acceptable. CV rodent models have been used for studies of probiotic cultures and particularly their effect on infectious disease. CV animals may also be used to assess the survival of probiotic cultures in vivo. Although the GI conditions of CV animal models are quite different from those of the human, the conditions of the animal GIT are most likely closer to human than what can be simulated in vitro.

There are several examples of studies where CV animals have been used to assess the protective effects of probiotics. These include studies in which Salmonella (32,56,58-60), E. coli (61,62) and Listeria (63,64) have been used as model pathogens. Specific Pathogen Free (SPF) mice have been useful in similar studies where animals were given single or mixed cultures that were considered to be probiotic, before being challenged with Salmonella. The progress of infection is determined by monitoring (1) translocation of pathogen to internal organs (31,43), (2) change in animal body weight, and (3) mortality (65) following the challenge. Out of these three general methods, monitoring changes in animal body weight is convenient and relevant in most cases. The virulence of a model pathogen is relevant in this regard, since the virulence will affect the progress of infection. A too virulent strain may induce an unnecessarily severe infection (66). In other cases, human pathogens may not colonize, infect or give a demonstrable effect in an animal model (64,67). If this is the case, then a human pathogen may be replaced with a strain known to be virulent in animals. Examples given so far relate to models used for the monitoring of GI infection and translocation to areas such as MLN and intestinal organs. The protective effect of probiotic cultures can also be monitored by assessing the clearance rate of a specific pathogen from the feces of animals challenged with that pathogen (65). The clearance rate of Listeria was measured in the feces of animals that were fed probiotic cultures and meat starter cultures in order to identify specific probiotic cultures that eliminated this particular pathogen (64).

CV animals may also be used as a model system to assess the survival and colonization of probiotic cultures and other microorganisms of human origin. The survival, during passage through the GIT, can be monitored as long as appropriate methods of detection are available. Traditional culturing methods have been important tools used in monitoring the survival of probiotic cultures during GI transit (68-70). Recent years have seen other more efficient detection methods such as molecular probes, which have been developed for the accurate assessments of population sizes of particular probiotic cultures in feces (71). Probes of this type may be used to confirm the identity of particular probiotic strains (72-74) and detect specific strains even at very sparse population levels (75).

GI microbiota is obviously important for the biochemical profile of the GIT. However, simply identifying the survival of microorganisms in feces gives little information about the details of their activity in the GIT. In vivo investigations into the activity of particular microorganisms require methods other than those used for that of detection. Mice or rats may be used to characterize the activity of cultures at specific sites throughout the GIT, something that is very difficult to assess in humans. Traditionally this type of study has been conducted on animals containing microorganisms of interest by describing the biochemical profile of the animal's GI contents. This methodology is adequate in instances where the sum of all microbial and host activities are investigated at the time of sampling. However, it is less appropriate if the activities of specific microorganisms are assessed, where these microorganisms are a part of a complex microbial system. In vivo studies on the activities of specific cultures in a complex ecosystem require different animal models. The development of a lactobacillus free mouse model has provided the opportunity to study the effects of lactobacillus colonization on host physiology, including the effects on fecal bile acids and enzyme activities (76-78). This type of model may be used in studies on the effect of human lactobacillus strains if animals are colonized by strains of human origin.

Pregnancy And Childbirth

Pregnancy And Childbirth

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