<p>Allergic diseases, for example asthma and eczema, are nowadays considered belonging to the most common chronic diseases amongst children in the West, but the cause for this increase in allergy prevalence is unknown. Since studies have indicated a connection between children's exposure of microorganisms during infancy and risk of developing allergic disease, it is suggested that this exposure is a crucial factor in question of allergy development or not. Other studies have established differences in microflora composition between healthy children and children with allergic disease, and several studies have shown that probiotic therapy can give positive results in both prevention and treatment of allergic diseases.</p><p>The aim of this master's thesis was to develop a method, using PCR and denaturing gradient gel electrophoresis, to study the diversity of <em>Lactobacillus spp</em>. in fecal samples retrieved from a study of the probiotic strain<em> L. reuteri</em> ATCC 55730. The developed method was successful in detecting lactobacilli in fecal samples, but three other bacterial genera commonly found in humans were also amplified. Comparison of average numbers of detected bacterial strains and lactobacilli strains between samples belonging to the probiotics and placebo groups, respectively, showed higher numbers for the probiotics group. Also, the only fecal samples that contained <em>L. reuteri</em> belonged to the probiotics group. Although the results are far from statistically significant, they support the theories that probiotics may influence the intestinal microbiota.</p>

Allergic diseases, for example asthma and eczema, are nowadays considered belonging to the most common chronic diseases amongst children in the West, but the cause for this increase in allergy prevalence is unknown. Since studies have indicated a connection between children's exposure of microorganisms during infancy and risk of developing allergic disease, it is suggested that this exposure is a crucial factor in question of allergy development or not. Other studies have established differences in microflora composition between healthy children and children with allergic disease, and several studies have shown that probiotic therapy can give positive results in both prevention and treatment of allergic diseases. The aim of this master's thesis was to develop a method, using PCR and denaturing gradient gel electrophoresis, to study the diversity of Lactobacillus spp. in fecal samples retrieved from a study of the probiotic strain L. reuteri ATCC 55730. The developed method was successful in detecting lactobacilli in fecal samples, but three other bacterial genera commonly found in humans were also amplified. Comparison of average numbers of detected bacterial strains and lactobacilli strains between samples belonging to the probiotics and placebo groups, respectively, showed higher numbers for the probiotics group. Also, the only fecal samples that contained L. reuteri belonged to the probiotics group. Although the results are far from statistically significant, they support the theories that probiotics may influence the intestinal microbiota.