Culture-dependent assessment of bacterial diversity from human milk with lactational mastitis

Mastitis, an inflammation of mammary gland, is a deliberately painful condition experienced by lactating women. Etiology of mastitis is still underexplored due to the paucity of research conducted on it. The objective of this study was to explore culturable bacterial diversity present in the breast milk of mastitis-suffering women by 16S rDNA sequencing and evaluate its antibiotic susceptibility. The culturable bacteria present in the breast milk of 32 women with lactational mastitis were studied. Thirty-seven bacterial isolates comprised of distinct colony characteristics were checked for antibiotic susceptibility and identified by 16S rDNA sequencing. Sequencing of 16S rDNA and BLAST analysis revealed the presence of 17 genera and 30 different species indicating highly diverse community in mastitis milk. The Proteobacteria (51.35 % of total clones) and Firmicutes (37.83 %) were the most abundant phyla and included representatives from the class Gammaproteobacteria, Alphaproteobacteria, and Bacilli. Pseudomonas (6 species) and Staphylococcus (4 species) were the most prevalent genera while Brevundimonas, Bacillus, Enterococcus, Micrococcus, and Macrococcus were infrequently isolated. Staphylococcus sp. (87.5 % of mastitis samples), Staphylococcus aureus (75 %), Pseudomonas aeruginosa (53.12 %), Klebsiella pneumoniae (43.75 %), and Brevundimonas diminuta (37.5 %) were frequently isolated from mastitis milk. Antibiotics like chloramphenicol, gentamicin, ofloxacin, and ciprofloxacin proved to be most effective against mastitis pathogens. Overall analysis suggested that high bacterial diversity in diseased condition could be the result of colonization of mammary gland by opportunistic pathogens but the actual role of bacteria in mastitis is still a debatable question.