Dual antibacterial mechanism of [K4K15]CZS-1 against Salmonella Typhimurium: a membrane active and intracellular-targeting antimicrobial peptide.

Salmonella genus is a leading cause of food-borne infections with strong public health impact and economic ramifications. The development of antimicrobial resistance added complexity to this scenario and turned the antibiotic drug discovery into a highly important challenge. The screening of peptides has served as a successful discovery platform to design new antibiotic candidates. Motivated by this, the antimicrobial and cytotoxic properties of three cruzioseptins against Salmonella Typhimurium and RAW 264.7 murine macrophage cells, respectively, were investigated. [K4K15]CZS-1 was the most potent antimicrobial peptide identified in the screening step with a minimum inhibitory concentration (MIC) of 16 µg/mL (7.26 µM) and moderate cytotoxicity. From a structural point of view, in vitro and in silico techniques evidenced that [K4K15]CZS-1 is a α-helical cationic antimicrobial peptide. In order to capture mechanistic details and fully decipher their antibacterial action, we adopted a multidimensional approach, including spectroscopy, electron microscopy and omics analysis. In general lines, [K4K15]CZS-1 caused membrane damage, intracellular alterations in Salmonella and modulated metabolic pathways, such as the tricarboxylic acid (TCA) cycle, fatty acid biosynthesis, and lipid metabolism. Overall, these findings provide deeper insights into the antibacterial properties and multidimensional mode of action of [K4K15]CZS-1 against Salmonella Typhimurium. In summary, this study represents a first step toward the screening of membrane-acting and intracellular-targeting peptides as potential bio-preservatives to prevent foodborne outbreaks caused by Salmonella.

Myotendinous junction plasticity in aged ovariectomized rats submitted to aquatic training.

The study aims to describe the tissue plasticity of MTJ through the morphological analysis of MTJ soleus in ovariectomized aged female Wistar rats submitted to aquatic training. Forty aged Wistar rats, 1 year and 2 months of age, were divided into four groups: sedentary (S), trained (T), ovariectomized (O), and trained/ovariectomized (OT). Employing the transmission electron microscopy, the ultrastructural and morphometric elements were revealed. In the S group, changes in morphological characteristics as a consequence of the aging process were seen, demonstrated by the conical shape of the muscle cell extremity, a large area with collagen deposit, and misalignment of sarcomeres in series. The T group presented ample adjustments when revealed the organization of MTJ, through the increase of the contact area and greater lengths of sarcoplasmatic invaginations and evaginations. The O group revealed extensive tissue disorganization with muscle atrophy, reduction of MTJ contact area, and consequently, changes in sarcoplasmatic invaginations and evaginations. The OT group demonstrated extensive remodeling with restructuring MTJ through the increase of tissue contact area, extensive organization, parallel arrangement, and increased length of sarcoplasmatic invaginations and evaginations. The distal sarcomeres presented higher lengths compared to the proximal sarcomeres in both the groups. We conclude that aquatic training was effective in the organization and structural remodeling of the myotendinous interface of ovariectomized aged rats. There was a greater area of contact, and consequently, greater resistance in the myotendinous interface promoting a lower predisposition to injuries.

Ultrastructural features of the myotendinous junction of the sternomastoid muscle in Wistar rats: from newborn to aging.

The myotendinous junction (MTJ) is a major area for transmitting force from the skeletal muscle system and acts in joint position and stabilization. This study aimed to use transmission electron microscopy to describe the ultrastructural features of the MTJ of the sternomastoid muscle in Wistar rats from newborn to formation during adulthood and possible changes with aging. Ultrastructural features of the MTJ from the newborn group revealed pattern during development with interactions between muscle cells and extracellular matrix elements with thin folds in the sarcolemma and high cellular activity evidenced through numerous oval mitochondria groupings. The adult group had classical morphological features of the MTJ, with folds in the sarcolemma forming long projections called "finger-like processes" and sarcoplasmic invaginations. Sarcomeres were aligned in series, showing mitochondria near the Z line in groupings between collagen fiber bundles. The old group had altered "finger-like processes," thickened in both levels of sarcoplasmic invaginations and in central connections with the lateral junctions. We conclude that the MTJ undergoes intense activity from newborn to its formation during adulthood. With increasing age, changes to the MTJ were observed in the shapes of the invaginations and "finger-like processes" due to hypoactivity, potentially compromising force transmission and joint stability.

Ultrastructure of the myotendinous junction of the medial pterygoid muscle of adult and aged Wistar rats.

The myotendon junction (MTJ) is a specialised area into the muscle fibers where the sarcoplasmic membranes connect to the collagen fibers bundles. There are few data about plasticity of the MTJ in aging processes. The aim of this study is to analyse the ultrastructure characteristics of MTJ of medial pterygoid muscle of adult and aged rats. Employing the transmission electron microscopy method, twenty male rats Wistar (Rattus norvegicus) were divided into two groups: A (n=10) with 12 months of age; B (n=10) 24 months of age. The animals were anaesthetised with overdose the urethane (3g/kg, i.p.) and sacrified during the perfusion with modified Karnovsky solution. The specimens were post-fixed in a 1% osmium tetroxide solution, dehydrated in ascending concentration of ethanol and embedded in Spurr resin. The thin sections, of 90 nm thick, were counterstained with uranyl acetate and lead citrate solution, and examined in a Jeol 1010 transmission electron microscope. The fine structure of the MTJ of group A revealed the defined interdigitations and disposed in several levels of deep formations containing the collagen fibers. In the group B, such structures did not observed, detecting the projections irregular in shape, and large of extra matrix with in aspect of remodelling. In conclusion it was possible to identify the plasticity of MTJ in the group B which presented several morphological alterations comparing to the adult animals. These data of group B suggested the occurrence of aging processes in the MTJ in rats.