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Only a decade after we thought that breastmilk was sterile, research has discovered that breastmilk in fact has its own microbiome and uncovered fascinating new findings we can apply in clinical practice for therapeutic outcomes.

What is the Breastmilk Microbiome?

In the early days, the microbiome (collection of microbes, genetic material and the ecosystem in which it lives) was generally discussed in context of ‘the gut’, where the greatest concentration lives in the human body.

But as research evolved, we have learned that each body site has its own microbiome, with each playing a significant role in the health and function of that particular site and collectively works to support the overall health and function of the human organism as a whole.

How the microbiome relates to mastitis and other breastfeeding complications

Dysbiosis describes the ‘imbalance’ in our microbiome, and typically involves loss of beneficial bacteria and an overgrowth of pathogenic bacteria”(1)

Many breastfeeding mothers have a compromised microbiome for which there can be many contributing factors;(2)

  • Diet, lifestyle and maternal health status
  • Geographical location and environmental toxins
  • Mode of delivery
  • Stress and birth trauma
  • Gestational age
  • C-section and GBS (intrapartum antibiotics)
  • Antibiotics, PPIs – from preconception throughout pregnancy
  • ‘Other’ medications – including epidurals and pain medications
  • Lactation stage and mode of feeding (breast vs expressing)

Understanding the roles of the microbes themselves and the ‘environment /ecosystem’ in which they need to thrive – it’s easy to see how dysbiosis can contribute to many breastfeeding complications, including:

  • Breast pain and inflammation
  • Nipple ‘thrush’
  • Blocked ducts and blebs
  • Mild inflammatory Mastitis
  • Bacterial mastitis and abscess
  • The cessation of breastfeeding

How evidence-based Probiotics can improve Breastfeeding Outcomes

It’s important to remember not all probiotics are created equal. Learning how a supplemental probiotic behaves in the human body takes clinical research and strain specificity (meaning only the research done on that specific strain can be attributed to the expected outcomes).

For example, Lactobacillus Fermentum CECT5716 (recently reclassified to Limosilactobacillus fermentum CECT5716) has been researched for reducing pathobiont overgrowth and for being the onlyL.Fermentum strain to help  relieve symptoms and reducing the occurrence of mastitis (3,4,5).

‘Mechanisms of action’ are crucial to understanding what makes a probiotic effective and when to use them in clinical practice.  Some actions are unique to certain strains, while some strains show more ‘actions’ than others.

Mechanisms of action demonstrated in  L. Fermentum CECT5716;(6)

  • Survives the gastrointestinal tract and translocates easily and quickly
  • Maternal transfer*
  • Reduces inflammation – locally and systemically
  • Modulates immune response – locally and systemically
  • Kills pathogens and reduces pathobionts (when ‘overgrown’)
  • Strong adherence to membranes (competitive exclusion)
  • Infiltrates biofilm
  • Improves health and function of mammary tissue, ducts and membranes
  • Produces beneficial metabolites (‘postbiotics’)
  • Stimulates SIgA and mucin production (improves membrane integrity)
  • Encourages regeneration of indigenous flora

Maternal transfer:  After a mother takes a probiotic orally, the probiotic ‘transfers’ to her breast tissue and breast milk through entero-mammary circulation (7).

How evidence-based Probiotics can help Mild (Inflammatory) Mastitis

The 2022 Mastitis Protocol Update published by the Academy of Breastfeeding Medicine, mentions L.Fermentum CECT5716 as beneficial for mild (inflammatory) mastitis and recommended the use of this probiotic strain as part of the ‘spectrum wide’ recommendations for mastitis.

  1. Fermentum CECT5716 is a ‘breastmilk strain’ – meaning it has been originally isolated from healthy human milk, as opposed to bowel flora or food as in other probiotic strains.

Considering the new insights outlined in the protocol it is easy to understand why correct strains of evidence-based probiotics can help through;

  • Translocating into the breast tissue and milk
  • Addressing the dysbiosis in breast tissue
  • Reducing inflammation at the local site
  • Improving membrane integrity
  • Suppressing pathobiont overgrowth
  • Helping restore beneficial flora


Among other influences, breastfeeding (by design) establishes and develops an infant’s microbiome impacting babies health over their lifetime and for future generations.  Which is why the WHO recommends initiation of breastfeeding withing one hour of birth, exclusive breastfeeding for the first six months of life, and continuation for up to 2 years of age or beyond.

Along with balanced medical practices, continued education around diet and lifestyle, evidence-based probiotics such as L Fermentum CECT5716 are extremely effective in reducing the symptoms and occurrence of mastitis, and can be considered as prophylactic AND first line treatments.

Written by:  Emma Park – Functional Nutritionist from Qiara Probiotics


Martinez JE et al Unhealthy Lifestyle and Gut Dysbiosis: A Better Understanding of the Effects of Poor Diet and Nicotine on the Intestinal Microbiome. Front Endocrinol (Lausanne). 2021 Jun 8;12:667066.

(1)    Mantziari & Rautava 2021 Factors influencing the microbial composition of human milk, Seminars in Perinatology; 45(8)

(2)    Arroyo et al, 2010 Treatment of Infectious Mastitis during Lactation: Antibiotics versus Oral Administration of Lactobacilli Isolated from Breast Milk, Clinical Infectious Diseases, Volume 50, Issue 12, 15 June 2010, Pages 1551–1558,

(3)    Maldonado-Lobón, et al Lactobacillus fermentum CECT 5716 Reduces Staphylococcus Load in the Breastmilk of Lactating Mothers Suffering Breast Pain: A Randomized Controlled Trial. Breastfeeding Medicine.Nov 2015.425-432.

(4)    Hurtado et al 2017 Oral Administration to Nursing Women of Lactobacillus fermentum CECT5716 Prevents Lactational Mastitis Development: A Randomized Controlled Trial. Breastfeed Med. 2017 May 1;12(4):202–9. 10.1089/bfm.2016.0173.

(5)    Rodríguez-Sojoet al. Limosilactobacillus fermentum CECT5716: Mechanisms and Therapeutic Insights. Nutrients. 2021 Mar 21;13(3):1016. doi: 10.3390/nu13031016. PMID: 33801082; PMCID: PMC8003974.

(6)    Selvamani, S et all (2021) An Insight into Probiotics Bio-Route: Translocation from the Mother’s Gut to the Mammary Gland. Appl. Sci. 2021, 11, 7247.

(7)    Mitchell KB et al 2022 Academy of Breastfeeding Medicine Clinical Protocol #36: The Mastitis Spectrum, Revised 2022. Breastfeed Med. 2022 May;17(5):360-376.