Green synthesis of chitosan-based membrane modified with uniformly micro-sizing selenium particles decorated graphene oxide for antibacterial application.

In this study, selenium microparticles (SeMPs) were green-synthesized by utilizing the Terminalia catappa leaves extract as an effective reducing agent. SeMPs were then decorated onto graphene oxide (GO) with the assistance of ultrasound using the ex-situ technique to obtain the SeMPs-GO composite. SeMPs and SeMPs-GO were thoroughly characterized with modern analytical methods, whereas the antibacterial performance of the composites was evaluated via the optical density method. Particularly, SeMPs-GO held up an inhibition of 99 % against both Gram-positive and Gram-negative bacteria strains as well as restrained 50 % of fungal activity. SeMPs-GO was additionally incorporated onto chitosan (CTS) to collect the SeMPs-GO/CTS membrane which was characterized by similar advanced analysis methods. The antibacterial property of the membrane was determined by the inhibition zone diameter. Furthermore, the membrane exhibited good thermal and mechanical characteristics, showing no sign of degradation at a temperature below 260 °C, and a tensile strength of 38 N/mm2. The swelling degree reached 148 % after 6 h of immersion in water, which was stable after 72 h (153 %). The obtained membrane can potentially be utilized for medical and food applications.

Comprehensive analysis of fatty acids in human milk of four Asian countries.

Human milk lipids provide not only energy but also indispensable bioactive components such as essential fatty acids. To establish the recommended daily intake value and guidelines for infant formula, a reference library of fatty acid composition has been generated from 4 Asian countries (South Korea, China, Vietnam, and Pakistan). Regardless of country, palmitic acid (C16:0), linoleic acid (C18:1), and linolenic acid (C18:2) were the 3 most abundant fatty acids in human milk and account for more than 75% of total fatty acids (total FA). However, there were several considerable differences between fatty acids, particularly n-3 and n-6 (omega-3 and omega-6) groups. Chinese mothers' milk had a high concentration of linoleic acid at 24.38 ± 10.02% of total FA, which may be due to maternal diet. Among the 4 countries, Pakistani mothers' milk contained a high amount of saturated fatty acid (56.83 ± 5.96% of total FA), and consequently, polyunsaturated fatty acids, including n-3 and n-6, were significantly lower than in other countries. It is noteworthy that docosahexaenoic acid (DHA) in Pakistani mothers' milk was 44.8 ± 33.3 mg/L, which is only 25 to 30% of the levels in the other 3 countries, suggesting the need for DHA supplementation for infants in Pakistan. Moreover, the ratio of n-6 to n-3 was also remarkably high in Pakistani mothers' milk (15.21 ± 4.96), being 1.4- to 1.7-fold higher than in other countries. The average DHA:ARA ratio in Asian human milk was 1.01 ± 0.79. Korean mothers' milk showed a high DHA:ARA ratio, with a value of 1.30 ± 0.98, but Pakistani mothers' milk had a significantly lower value (0.42 ± 0.12). The fatty acid compositions and anthropometric data of mother (body mass index, age) did not show any correlation. The obtained data might provide information about human milk compositions in the Asian region that could benefit from setting up recommended nutrient intake and infant formula for Asian babies.

Characterization of the Streptococcus mutans SMU.1703c-SMU.1702c Operon Reveals Its Role in Riboflavin Import and Response to Acid Stress.

Streptococcus mutans utilizes numerous metabolite transporters to obtain essential nutrients in the "feast or famine" environment of the human mouth. S. mutans and most other streptococci are considered auxotrophic for several essential vitamins including riboflavin (vitamin B2), which is used to generate key cofactors and to perform numerous cellular redox reactions. Despite the well-known contributions of this vitamin to central metabolism, little is known about how S. mutans obtains and metabolizes B2 The uncharacterized protein SMU.1703c displays high sequence homology to the riboflavin transporter RibU. Deletion of SMU.1703c hindered S. mutans growth in complex and defined medium in the absence of saturating levels of exogenous riboflavin, whereas deletion of cotranscribed SMU.1702c alone had no apparent effect on growth. Expression of SMU.1703c in a Bacillus subtilis riboflavin auxotroph functionally complemented growth in nonsaturating riboflavin conditions. S. mutans was also able to grow on flavin adenine dinucleotide (FAD) or flavin mononucleotide (FMN) in an SMU.1703c-dependent manner. Deletion of SMU.1703c and/or SMU.1702c impacted S. mutans acid stress tolerance, as all mutants showed improved growth at pH 5.5 compared to that of the wild type when medium was supplemented with saturating riboflavin. Cooccurrence of SMU.1703c and SMU.1702c, a hypothetical PAP2 family acid phosphatase gene, appears unique to the streptococci and may suggest a connection of SMU.1702c to the acquisition or metabolism of flavins within this genus. Identification of SMU.1703c as a RibU-like riboflavin transporter furthers our understanding of how S. mutans acquires essential micronutrients within the oral cavity and how this pathogen successfully competes within nutrient-starved oral biofilms.IMPORTANCE Dental caries form when acid produced by oral bacteria erodes tooth enamel. This process is driven by the fermentative metabolism of cariogenic bacteria, most notably Streptococcus mutans Nutrient acquisition is key in the competitive oral cavity, and many organisms have evolved various strategies to procure carbon sources or necessary biomolecules. B vitamins, such as riboflavin, which many oral streptococci must scavenge from the oral environment, are necessary for survival within the competitive oral cavity. However, the primary mechanism and proteins involved in this process remain uncharacterized. This study is important because it identifies a key step in S. mutans riboflavin acquisition and cofactor generation, which may enable the development of novel anticaries treatment strategies via selective targeting of metabolite transporters.