Abstract
To the Editor,
We appreciate the interest from Cullinane and Amir regarding our study (Mediano et al., 2017).
The authors expressed concern about the inclusion criteria for mastitis and the absence of a control group in the study. Women with acute mastitis were recruited either on first presentation or as a recurrent episode after failure of initial empiric antibiotic treatment, whereas women with symptoms of subacute mastitis were recruited after several weeks of painful breastfeeding and having been unsuccessfully checked for other potential causes (feeding position, ankyloglossia, etc.). Breastfeeding women whose symptoms were relieved with management practices were not referred to our lab.
The aim of this work was to describe the culturable microbial diversity in milk samples from women suffering from mastitis and not to compare microbiological results from those of healthy women. Several studies characterizing the human milk microbiota in physiological conditions have been previously reported. Healthy milk microbiota contains a balanced composition of different microorganisms at a moderated concentration (< 103 CFU/ml), whereas mastitis milk cultures are usually characterized by the presence of a few predominant species at a higher concentration (> 104 CFU/ml). This change in the composition of milk microbiota, referred to as dysbiosis, is involved in the development of lactational mastitis (Rodríguez & Fernández, 2017). In the last decade, emerging evidence supports that dysbiosis processes are involved in the development of a wide range of diseases (Petersen & Round, 2014). For most bacterial species, pathogenicity depends on the state of the host and also on the strain, a key concept to understand the etiopathogenicity of mastitis. It is common to isolate small concentrations of different Staphylococcus epidermidis strains in the milk of a healthy mother but also to find a high concentration of a single S. epidermidis strain in milk of women with mastitis. The current definition of mastitis (applied only to describe acute cases of mastitis) should be revised in light of new scientific knowledge to include subacute mastitis, caused mainly by coagulase-negative staphylococci and viridans group streptococci. Their presence at a high concentration explains many cases of local symptoms such as breast engorgement, pain, and reduced milk secretion. The milk samples included in the study met the microbiological criteria endorsed by the Spanish Society of Infectious Diseases and Clinical Microbiology (Delgado, García-Garrote, Padilla, Rodríguez Gómez, & Romero, 2015). It was advised that milk samples be collected from each breast since both breasts may be affected by the dysbiosis process, as this and previous results have shown.
The authors also expressed that microbiological confirmation may be impractical. However, one of the main advantages of culture-dependent techniques is that they allow further studies of bacterial isolates. Human milk cultures and antibiotic susceptibility testing are key to ensuring an early and effective diagnosis and treatment, since human mastitis pathogens have shown high rates of antimicrobial resistance to the antibiotics usually prescribed for mastitis, including the emergence of multidrug-resistant strains (Marín, Arroyo, Espinosa-Martos, Fernández, & Rodríguez, 2017). Therefore, the results of this work can be useful to reinforce the need of milk cultures to avoid increasing antibiotic resistance, which is a worldwide threat to public health.
Our knowledge on human mastitis is still limited and further studies are needed to prevent this condition and eventually avoid premature weaning. This task will certainly require enhancing interdisciplinary cooperation and collaboration in the frame of the One Health Initiative (http://www.onehealthinitiative.com/).