Background: Human milk, considered ideal with respect to the optimal nutrition for the infants, not only contains nutritional substrates but also commensal bacteria such as Lactobacillus and Bifidobacterium species. It can be postulated that mothers in rural areas have higher incidence of these bacteria compared to mothers from urban environments.
Aim: To investigate the occurrence of lactobacilli, particularly L. reuteri and bifidobacteria in the milk of nursing mothers and to compare the frequencies in different countries and between different areas within those countries.
Methods: Breast milk samples were collected from 226 women living in urban or rural areas in Sweden, Israel, South Africa, Japan, Peru, Korea and Denmark. The numbers of total lactobacilli, L. reuteri and bifidobacteria were analysed using conventional bacterial cultivation methods.
Results: The isolation rates varied from 50% L. reuteri positive samples from rural areas in Japan and Sweden to negative samples from urban areas in Peru, Denmark and Israel. Overall, 12% of the mothers had detectable L. reuteri counts. 100 percent of mothers milk from rural samples from Japan and 79% from Korea was positive for bifidobacteria whilst mothers from these areas in Denmark, Peru and Sweden had low or non-detectable levels. Among the samples from the rural areas approximately 50% of the Israeli, Japanese and Korean samples had positive total lactobacilli levels. In comparison the urban samples from Israel, Peru and Denmark contain about 20% positive total lactobacilli counts.
Conclusion: Breast milk microbiota varies between different countries and parts of the world. Japanese breast milk shows the highest frequency of colonisation with L. reuteri and Japanese and Korean mothers have higher bifidobacteria and total lactobacilli counts in their breast milk compared to mothers from other countries. Breast milk from rural areas contains more lactic acid bacteria than milk from urban areas.