Glycans are major nutrients for the human gut microbiota (HGM). Arabinogalactan proteins (AGPs) comprise a heterogenous group of plant glycans in which a β1,3-galactan backbone and β1,6-galactan side chains are conserved. Diversity is provided by the variable nature of the sugars that decorate the galactans. The mechanisms by which nutritionally relevant AGPs are degraded in the HGM are poorly understood. Here we explore how the HGM organism Bacteroides thetaiotaomicron metabolises AGPs. We propose a sequential degradative model in which exo-acting glycoside hydrolase (GH) family 43 β1,3-galactanases release the side chains. These oligosaccharide side chains are depolymerized by the synergistic action of exo-acting enzymes in which catalytic interactions are dependent on whether degradation is initiated by a lyase or GH. We identified two GHs that establish two previously undiscovered GH families. The crystal structures of the exo-β1,3-galactanases identified a key specificity determinant and departure from the canonical catalytic apparatus of GH43 enzymes. Growth studies of Bacteroidetes spp. on complex AGP revealed three keystone organisms that facilitated utilisation of the glycan by 17 recipient bacteria, which included B. thetaiotaomicron . A surface endo-β1,3-galactanase, when engineered into B. thetaiotaomicron , enabled the bacterium to utilise complex AGPs and act as a keystone organism.

Staphylococcus aureus is a virulent pathogen and a major causative agent of superficial and invasive skin and soft tissue infections (SSSTIs). Antibiotic resistance in S. aureus, among other bacterial pathogens, has rapidly increased, and this is placing an enormous burden on the health care sector and has serious implications for infected individuals, especially immunocompromised patients. Alternative treatments thus need to be explored to continue to successfully treat infections caused by S. aureus, including antibiotic-resistant strains of S. aureus. In this study, an antimicrobial nanofiber wound dressing was generated by electrospinning nisin (Nisaplin) into poly(ethylene oxide) and poly(D,L-lactide) (50:50) blend nanofibers. Active nisin diffused from the nanofiber wound dressings for at least 4 days in vitro, as shown by consecutive transfers onto plates seeded with strains of methicillin-resistant S. aureus (MRSA). The nisin-containing nanofiber wound dressings significantly reduced S. aureus Xen 36 bioluminescence in vivo and viable cell numbers in a murine excisional skin infection model. The bacterial burden of wounds treated with nisin-containing nanofiber wound dressings was 4.3 ؋ 10 2 CFU/wound, whereas wounds treated with control nanofiber wound dressings had 2.2 ؋ 10 7 CFU/wound on the last day of the trial (day 7). Furthermore, the wound dressings stimulated wound closure of excisional wounds, and no adverse effects were observed by histological analysis. Nisin-containing nanofiber wound dressings have the potential to treat S. aureus skin infections and to potentially accelerate wound healing of excisional wounds.

Acid tolerance is considered an important characteristic of probiotic bacteria. Lactobacillus plantarum 423 tolerates acidic pH and is the ideal candidate in which to study molecular mechanisms that acid-tolerant lactic acid bacteria employ to survive such conditions. In this study we recorded changes in the protein profile of L. plantarum 423 when exposed to pH 2.5 by using a gel-free nanoLC-MS/MS proteomics approach. In total, 97 proteins were detected as more abundant, and 12 proteins were detected solely when strain 423 was exposed to pH 2.5. General stress response proteins, the utilization of a variety of carbohydrate sources in a glucose rich environment, altered pyruvate metabolism, increased lysine biosynthesis, and a significant oxidative stress response was observed in acid-stressed cells. The accumulation of basic compounds also seemed to play an integral role in the response to acid stress. We observed a marked decrease in proteins involved in cell wall and phospholipid biosynthesis, transcription, translation, and cell division. The most abundant protein detected was an uncharacterized protein, JDM1_2142. Functional analysis revealed that this protein plays a role in survival during acid stress. Our results contribute to the growing body of knowledge on the molecular mechanisms employed by lactobacilli, in particular L. plantarum, to ensure survival in acidic conditions.

Plantaricin 423, produced by Lactobacillus plantarum 423, was encapsulated in nanofibers that were produced by the electrospinning of 18% (w/v) polyethylene oxide (200 000 Da). The average diameter of the nanofibers was 288 nm. Plantaricin 423 activity decreased from 51 200 AU/ml to 25 600 AU/ml and from 204 800 AU/ml to 51 200 AU/ml after electrospinning, as determined against Lactobacillus sakei DSM 20017 and Enterococcus faecium HKLHS, respectively. Cells of L. plantarum 423 encapsulated in nanofibers decreased from 2.3 × 10(10) cfu/ml before electrospinning to 4.7 × 10(8) cfu/ml thereafter. Cells entrapped in the nanofibers continued to produce plantaricin 423. This is the first report on the encapsulation of a bacteriocin and cells of L. plantarum in nanofibers. The method may be used to design a drug delivery system for bacteriocins and the encapsulation of probiotic lactic acid bacteria. The technology is currently being optimized.

Injury to the skin causes a breach in the protective layer surrounding the body. Many pathogens are resistant to antibiotics, rendering conventional treatment less effective. This led to the use of alternative antimicrobial compounds, such as silver ions, in skin treatment. In this review nanofibers, and the incorporation of natural antimicrobial compounds in these scaffolds, are discussed as an alternative way to control skin infections. Electrospinning as a technique to prepare nanofibers is discussed. The possibility of using these structures as drug delivery systems is investigated.