The chicken cecum contains a great many bacteria, most of which are strict anaerobes. A strictly anaerobe culture‐based method was used in the present study, in conjunction with the 16S rDNA clone library, to elucidate bacterial diversity and the phylogenetic relationship of cecal microbiota in the chicken. A comparative 16S rDNA sequence analysis of cultivated strains and retrieved clones from cecal contents was performed. Approximately 90% of the bacterial cells detected by microscopy did not form colonies on a medium 10 in plate‐in‐bottle. The 19 isolated strains yielded 11 distinct rDNA sequences, 58% of which were classified as low G + C Gram‐positive bacteria, 26% were related to Bacteroides spp., and 16% were classified as Proteobacteria. Based on the sequence analysis of 164 clones, 24% were identified to belong to 8 known species and 76% were considered to be 65 novel phylotypes. Approximately 94% of cloned sequences were classified into low G + C Gram‐positive bacteria, 4% were related to Bacteroides spp., and 2% were classified into Proteobacteria. Clostridium subcluster XIVa (38%), Clostridium cluster IV (13%), Lactobacillus spp. (24%), and Bacteroides spp. (4%) were the major groups constituting the cecal microbiota in chicken, in which the Clostridium subcluster XIVa was the most phylogenetically diverse group in chicken cecum. The 16S rDNA sequences of Lactobacillus acidophilus, L. crispatus, L. salivarius, and L. reuteri were the most frequently found in the Lactobacillus group in chicken cecum.

We examined the effects of probiotic Lactobacillus strains of Lactobacillus agilis JCM 1048 and Lactobacillus salivarius subsp. salicinius JCM 1230 on jejunal and cecal microbiota of broiler chicken under heat stress condition using terminal restriction fragment length polymorphism (T‐RFLP) analysis. The jejunal bacterial community was limited to a few bacterial groups, mostly Lactobacillus spp. A relatively abundant and higher prevalence of Lactobacillus spp. were observed in the jejunal and cecal microbiota of the probiotic chickens compared with those of the control chickens under heat stress condition. In general, the probiotic strains did not significantly affect the abundance of L. agilis and L. salivarius in chicken intestine but clearly contributed to increasing their prevalence in the probiotic chickens. The probiotic Lactobacillus strains enriched the diversity of Lactobacillus flora in chicken jejunum and cecum by increasing the abundance and prevalence of Lactobacillus spp. inhabiting the intestine. The richness of Lactobacillus species tended to be similar among the jejunal and cecal microbiota. The bacterial community of cecum was complex and age‐dependent. The major components of the cecal microbiota were clostridia and lactobacilli. The Clostridium subcluster XIVa was the most predominant group in chicken cecum. Probiotic Lactobacillus strains restored the microbial balance and maintained the natural stability of indigenous bacterial microbiota following heat stress‐induced changes.

Eight bacterial strains isolated from the caecum of chicken, BL2T, BL66, EG3, EG6, M27, BL78T, C35T and C43, were characterized by determining their phenotypic characteristics, cellular fatty acid profiles, menaquinone profiles and phylogenetic positions based on 16S rRNA gene sequence analysis. 16S rRNA gene sequence analysis showed that these isolates belonged to the genus Bacteroides. One group of five strains (BL2T, BL66, EG3, EG6 and M27) was related most closely to Bacteroides coprocola JCM 12979T, with approximately 93 % 16S rRNA gene sequence similarity, and to Bacteroides plebeius JCM 12973T, with about 92 % similarity, and shared ⩾99.6 % similarity with each other. Strain BL78T exhibited 90.5 % similarity to B. plebeius JCM 12973T and 89.8 % similarity to B. coprocola JCM 12979T and differed from the above group of five strains at ⩾10 % sequence divergence. Strains C35T and C43 were related most closely to Bacteroides eggerthii JCM 12986T, with 95.1 % sequence similarity, to Bacteroides stercoris JCM 9496T, with 94.6 % similarity, and to Bacteroides uniformis JCM 5828T, with 94.4 % similarity, and shared 100 % similarity with each other. From results of phenotypic examination, cellular fatty acid composition analysis, menaquinone composition analysis and DNA G+C contents, the group of five strains as well as strain BL78T were shown to differ from the type strains of B. coprocola and B. plebeius. Strain BL78T differed from the others based on its menaquinone composition, which included MK-11 and MK-12. Strains C35T and C43 could also be differentiated from the type strains of B. eggerthii, B. stercoris and B. uniformis. The group of five strains, strain BL78T, B. coprocola JCM 12979T and B. plebeius JCM 12973T showed low levels of DNA–DNA relatedness (<35 %) with each other. High levels of DNA–DNA relatedness were obtained within the group of five strains (>75 %). Strains C35T and C43 exhibited a high level of DNA–DNA relatedness (>88 %) with each other, but low levels with B. eggerthii JCM 12986T (<40 %), B. stercoris JCM 9496T (<37 %) and B. uniformis JCM 5828T (<16 %). On the basis of these data, three novel Bacteroides species are proposed: Bacteroides barnesiae sp. nov. (type strain BL2T=JCM 13652T=DSM 18169T), Bacteroides salanitronis sp. nov. (type strain BL78T=JCM 13657T=DSM 18170T) and Bacteroides gallinarum sp. nov. (type strain C35T=JCM 13658T=DSM 18171T).