During the last few decades, the main focus of numerous studies has been on the human breast milk microbiota and its influence on the infant intestinal microbiota and overall health. The presence of lactic acid bacteria in breast milk affects both the quantitative and qualitative composition of the infant gut microbiota. The aim of this study was to assess the most frequently detected cultivable rod-shaped lactobacilli, specific for breast milk of healthy Bulgarian women and fecal samples of their infants over the first month of life, in 14 mother–infant tandem pairs. Additionally, we evaluated the strain diversity among the most common isolated species. A total of 68 Gram-positive and catalase-negative strains were subjected to identification using the MALDI-TOF technique. Predominant cultivable populations belonging to the rod-shaped lactic acid bacteria have been identified as Lacticaseibacillus rhamnosus, Limosilactobacillus fermentum, Lacticaseibacillus paracasei, and Limosilactobacillus reuteri. Also, we confirmed the presence of Lactiplantibacillus plantarum and Lactobacillus gasseri. Up to 26 isolates were selected as representatives and analyzed by 16S rRNA sequencing for strain identity confirmation and a phylogenetic tree based on 16S rRNA gene sequence was constructed. Comparative analysis by four RAPD primers revealed genetic differences between newly isolated predominant L. rhamnosus strains. This pilot study provides data for the current first report concerning the investigation of the characteristic cultivable lactobacilli isolated from human breast milk and infant feces in Bulgaria.

During the last few decades, the main focus of numerus studies has been on the human breast milk microbiota and its influence on the infant intestinal microbiota and overall health. The presence of lactic acid bacteria in breast milk affects both the quantitative and qualitative composition of the infant gut microbiota. The aim of this study was to assess the dominant cultivable rod-shaped lactic acid bacteria, specific for breast milk of healthy Bulgarian women and fecal samples of their infants over the first month of life, in 14 mother-infant tandem pairs. Additionally, we evaluated strain diversity among the dominant newly isolated species. 68 gram-positive and catalase negative strains were subjected to identification by using MALDI-TOF technique. Predominant culturable populations belonging to the rod-shaped lactic acid bacteria have been identified as Lacticaseibacillus rhamnosus, Limosilactobacillus fermentum, Lacticaseibacillus paracasei and Limosilactobacillus reuteri. Also, we confirmed the presence of Lactiplantibacillus plantarum and Lactobacillus gasseri. 27 isolates were selected as representatives and analyzed by 16S rDNA sequencing for strain identity confirmation and a phylogenetic tree based on 16S rDNA gene sequence was constructed. Comparative analysis by four RAPD primers revealed genetic differences between newly isolated L. rhamnosus strains. This pilot study provides data for the current first report concerning investigation on characteristic microbiota of human breast milk and infant feces in Bulgaria.

Colostrum harbors a highly diverse microbial community, predominantly composed of genera such as Staphylococcus, Streptococcus, Lactobacillus, Bifidobacterium, and Enterococcus. The composition and diversity of this microbiota are influenced by maternal factors—including age, body mass index, lactation activity, stress levels, and gestational diabetes—as well as external factors such as mode of delivery, antibiotic exposure, diet, and geographic location. This microbial community plays a critical role in maternal and neonatal health by contributing to early gut colonization, supporting digestion, promoting immune system development, and protecting against pathogenic microorganisms through mechanisms such as antimicrobial peptide production by lactic acid bacteria. The primary aim of this study was to evaluate the impact of mode of delivery on colostrum microbiota by comparing mothers who delivered vaginally with those who underwent cesarean section. Colostrum samples from 15 mothers were subjected to DNA extraction, high-throughput sequencing, and bioinformatic analyses to characterize microbial composition and predicted functional profiles. Although substantial inter-individual variability was observed, no statistically significant differences were detected in overall microbial diversity or community structure between the two delivery groups. However, distinct bacterial taxa and functional characteristics were identified that were specific to each mode of delivery, suggesting subtle delivery-related influences on colostrum microbiota composition.