Studies carried in the last years have revealed that human milk contains a site-specific microbiota and constitutes a source of potentially beneficial bacteria to the infant gut. Once in the infant gut, these bacteria contribute to the assembly of a physiological gut microbiota and may play several functions, contributing to infant metabolism, protection against infections, immunomodulation or neuromodulation. Many preterm neonates are fed with pasteurized donor’s human milk (DHM) or formula and, therefore, are devoid of contact with human milk microbes. As a consequence, new strategies are required to allow the exposition of a higher number of preterm infants to the human milk microbiota early in life. The first strategy would be to promote and to increase the use of own mother’s milk (OMM) in Neonatal Intensive Care Units (NICUs). Even small quantities of OMM can be very valuable since they would be added to DHM in order to microbiologically “customize” it. When OMM is not available, a better screening of donor women, including routine cytomegalovirus (CMV) screening of milk, may help to avoid the pasteurization of the milk provided by, at least, a relevant proportion of donors. Finally, when pasteurized DHM or formula are the only feeding option, their supplementation with probiotic bacteria isolated from human milk, such as lactic acid bacteria or bifidobacteria, may be an alternative to try to restore a human milk-like microbiota before feeding the babies. In the future, the design of human milk bacterial consortia (minimal human milk microbiotas), including well characterized strains representative of a healthy human milk microbiota, may be an attractive strategy to provide a complex mix of strains specifically tailored to this target population.

No abstract

In some conditions, bacteria self-organize into biofilms, supracellular structures made of a self-produced embedding matrix, mainly composed of polysaccharides, DNA, proteins, and lipids. It is known that bacteria change their colony/matrix ratio in the presence of external stimuli such as hydrodynamic stress. However, little is still known about the molecular mechanisms driving this self-adaptation. In this work, we monitor structural features of Pseudomonas fluorescens biofilms grown with and without hydrodynamic stress. Our measurements show that the hydrodynamic stress concomitantly increases the cell density population and the matrix production. At short growth timescales, the matrix mediates a weak cell-cell attractive interaction due to the depletion forces originated by the polymer constituents. Using a population dynamics model, we conclude that hydrodynamic stress causes a faster diffusion of nutrients and a higher incorporation of planktonic bacteria to the already formed microcolonies. This results in the formation of more mechanically stable biofilms due to an increase of the number of crosslinks, as shown by computer simulations. The mechanical stability also relies on a change in the chemical compositions of the matrix, which becomes enriched in carbohydrates, known to display adhering properties. Overall, we demonstrate that bacteria are capable of self-adapting to hostile hydrodynamic stress by tailoring the biofilm chemical composition, thus affecting both the mesoscale structure of the matrix and its viscoelastic properties that ultimately regulate the bacteria-polymer interactions.

The nasogastric enteral feeding tubes (NEFTs) used to feed preterm infants are commonly colonized by bacteria with the ability to form complex biofilms in their inner surfaces. Among them, staphylococci (mainly Staphylococcus epidermidis and Staphylococcus aureus) and some species belonging to the Family Enterobacteriaceae are of special concern since they can cause nosocomial infections in this population. NETF-associated biofilms can also include lactic acid bacteria (LAB), with the ability to compete with pathogenic species for nutrients and space. Ecological interactions among the main colonizers of these devices have not been explored yet; however, such approach could guide future strategies involving the pre-coating of the inner surfaces of NEFTs with well adapted LAB strains in order to reduce the rates of nosocomial infections in neonatal intensive care units (NICUs). In this context, this work implied the formation of dual-species biofilms involving one LAB strain (either Ligilactobacillus salivarius 20SNG2 or Limosilactobacillus reuteri 7SNG3) and one nosocomial strain (either Klebsiella pneumoniae 9SNG3, Serratia marcescens 10SNG3, Staphylococcus aureus 45SNG3 or Staphylococcus epidermidis 46SNG3). The six strains used in this study had been isolated from the inner surface of NEFTs. Changes in adhesion ability of the pathogens were characterized using a culturomic approach. Species interactions and structural changes of the resulting biofilms were analyzed using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). No aggregation was observed in dual-species biofilms between any of the two LAB strains and either K. pneumoniae 9SNG3 or S. marcescens 10SNG3. In addition, biofilm thickness and volume were reduced, suggesting that both LAB strains can control the capacity to form biofilms of these enterobacteria. In contrast, a positive ecological relationship was observed in the combination L. reuteri 7SNG3-S. aureus 45SNG3. This relationship was accompanied by a stimulation of S. aureus matrix production when compared with its respective monospecies biofilm. The knowledge provided by this study may guide the selection of potentially probiotic strains that share the same niche with nosocomial pathogens, enabling the establishment of a healthier microbial community inside NEFTs.