The milk and mammary gland (MG) microbiome can be influenced by several factors, such as mode of delivery, breastfeeding, maternal lifestyle, health status, and diet. An increasing number of studies show a variety of positive effects of consumption of probiotics during pregnancy and breastfeeding on the mother and the newborn. The aim of this study was to investigate the effect of oral administration of probiotics Lactobacillus gasseri K7 (LK7) and Lactobacillus rhamnosus GG (LGG) during pregnancy and lactation on microbiota of the mouse mesenteric lymph nodes (MLN), MG, and milk. Pregnant FVB/N mice were fed skim milk or probiotics LGG or LK7 resuspended in skim milk during gestation and lactation. On d 3 and 8 postpartum, blood, feces, MLN, MG, and milk were analyzed for the presence of LGG or LK7. The effects of probiotics on MLN, MG, and milk microbiota was evaluated by real-time PCR and by 16S ribosomal DNA 454-pyrosequencing. In 5 of 8 fecal samples from the LGG group and in 5 of 8 fecal samples from the LK7 group, more than 1 × 10(3) of live LGG or LK7 bacterial cells were detected, respectively, whereas no viable LGG or LK7 cells were detected in the control group. Live lactic acid bacteria but no LGG or LK7 were detected in blood, MLN, and MG. Both probiotics significantly increased the total bacterial load as assessed by copies of 16S ribosomal DNA in MLN, and a similar trend was observed in MG. Metagenomic sequencing revealed that both probiotics increased the abundance of Firmicutes in MG, especially the abundance of lactic acid bacteria. The Lactobacillus genus appeared exclusively in MG from probiotic groups. Both probiotics influenced MLN microbiota by decreasing diversity (Chao1) and increasing the distribution of species (Shannon index). The LGG probiotic also affected the MG microbiota as it increased diversity and distribution of species and proportions of the genera Lactobacillus and Bifidobacterium. These results provide evidence that probiotics can modulate the bacterial composition of MLN and MG microbiota in ways that could improve the health of the MG and, ultimately, the health of the newborn.

The adequate survival of probiotics in the harsh environment of the gastrointestinal (GI) tract plays a crucial role in the expression of their functional properties. The aim of the present study was to evaluate the survival of commercial probiotics during digestion using a standardised INFOGEST 2.0 model extended with three food matrices simulating three scenarios for the consumption of probiotics: on an empty stomach, with juice, or with food (porridge). All eight products matched the bacterial content stated on the label. After simulated digestion, we observed an average decrease in viability of 1.6 log10 colony forming units (CFU) when the product was co-digested with water, a 2.5 log10 CFU decrease in the presence of juice, and a 1.2 log10 CFU decrease in the presence of porridge. The survival rate of the probiotics was statistically higher in the test samples with porridge (91.8%) than in those with juice (79.0%). For two products, the number of lactobacilli and bifidobacteria strains after digestion was less than <3 × 10⁵ CFU, which can be considered insufficient. The present study has shown that the survival of probiotic strains during GI passage depends not only on their ability to withstand these harsh conditions but may also be influenced by the manufacturing process and by the foods consumed together with the probiotics.

The aim of the present study was to characterize human milk microbiota (HMM) with 16S rRNA gene amplicon next-generation sequencing and cultivation/matrix-assisted laser desorption/ionization (MALDI)-time of flight (TOF) mass spectrometry (MS) identification approaches. We analyzed 31 human milk samples from healthy Slovenian mothers. To check the accuracy of MALDI-TOF MS identification, several colonies representing most abundant genera and those, which could not be reliably identified by MALDI-TOF, were subjected to Sanger sequencing of their 16S rRNA gene. We showed that cultivation/MALDI-TOF MS was a suitable tool for culture-dependent determination of HMM. With both approaches, Staphylococcus and Streptococcus were found as predominant genera in HMM and the abundance of Staphylococcus was associated with decreased microbial diversity. In addition, we characterized factors that might influence HMM. The use of a breast pump was significantly associated with composition of HMM, lower microbial load, and higher abundance of cultivable staphylococci. Moreover, our study suggests that administration of probiotics to the suckling infant might influence HMM by increased abundance of lactobacilli and the presence of viable probiotic bacteria in human milk. However, since our study was observational with relatively small sample size, more targeted studies are needed to study possible transfer of probiotics to the mammary gland via an external route and the physiological relevance of these events.

Since health benefits conferred by probiotics are strain-specific, identification to the strain level is mandatory to allow the monitoring of the presence and the abundance of specific probiotic in a product or in a gastrointestinal tract. Compared to standard plate counts, the reduced duration of the assays and higher specificity makes PCR-based methods (standard PCR and quantitative PCR) very appropriate for detection or quantification of probiotics. Development of strain-specific assay consists of 4 main stages: (1) strain-specific marker identification; (2) construction of potential strain-specific primers; (3) validation on DNA from pure cultures of target and related strains; and (4) validation on spiked samples. The most important and also the most challenging step is the identification of strain-specific sequences, which can be subsequently targeted by specific primers or probes. Such regions can be identified on sequences derived from 16S-23S internally transcribed spacers, randomly amplified polymorphic DNA, representational difference analysis and suppression subtractive hybridisation. Already known phenotypic or genotypic characteristics of the target strain can also be used to develop the strain-specific assay. However, the initial stage of strain-specific assay development can be replaced by comparative genomics analysis of target genome with related genomes in public databases. Advances in whole genome sequencing (WGS) have resulted in a cost reduction for bacterial genome sequencing and consequently have made this approach available to most laboratories. In the present paper I reviewed the available literature on PCR and qPCR assays developed for detection of a specific probiotic strain and discussed future WGS and comparative genomics-based approaches.

Lactobacillus gasseri K7 is an isolate from infant feces and has in vitro and in vivo established probiotic properties. Here, we report the improved version of the draft genome sequence, which comprises 8 scaffolds (13 contigs), a total length of 1.99 Mb, and 1,841 predicted protein-coding sequences.