The increase in infections derived from biofilms from Staphylococcal spp. prompted us to develop novel strategies to inhibit biofilm development. Nanoscale protrusion structures (nanopillars) observed on the wings of dragonflies and cicadas have recently gained notable attention owing to their physical, antimicrobial, and bactericidal properties. Thus, they are not only expected to reduce the damage caused by chemical antimicrobial agents to human health and the environment, but also to serve as a potential countermeasure against the emergence of antimicrobial-resistant bacteria (ARB). In this study, we evaluated the anti-biofilm effects of cyclo-olefin polymer (COP) nanopillars by changing the wettability of surfaces ranging in height from 100 to 500 nm against Staphylococcus spp., such as Staphylococcus aureus NBRC 100910 (MSSA), Staphylococcus aureus JCM 8702 methicillin-resistant S. aureus (MRSA), and Staphylococcus epidermidis ATCC 35984. The results clearly show that the fabricated nanopillar structures exhibited particularly strong biofilm inhibition against MRSA, with inhibition rates ranging from 51.2% to 62.5%. For MSSA, anti-biofilm effects were observed only at nanopillar heights of 100–300 nm, with relatively low hydrophobicity, with inhibition rates ranging from 23.9% to 40.8%. Conversely, no significant anti-biofilm effect was observed for S. epidermidis in any of the nanopillar structures. These findings suggest that the anti-biofilm properties of nanopillars vary among bacteria of the same species. In other words, by adjusting the height of the nanopillars, selective anti-biofilm effects against specific bacterial strains can be achieved.

There is an urgent need to discover and develop novel antibacterial agents. Accordingly, we synthesised 2-(piperazin-1-yl)naphtho[2,3-d]thiazole-4,9-dione (PNT), which exhibits antimicrobial activity. The aim of this study was to characterise PNT as an effective antimicrobial agent. Fluorescence microscopy was used to measure PNT’s uptake into microbial cells (strains of Staphylococcus epidermidis, Staphylococcus aureus, and methicillin-resistant S. aureus (MRSA)), transmission electron microscopy (TEM) was used to investigate the influence of PNT on the configuration of microbial cells, and a DNA gyrase supercoiling assay was used to investigate whether PNT inhibits DNA gyrase. PNT was taken up by more than 50% of microbial cells within 30 min. Using TEM, hollowed-out bacterial cytoplasms were observed in the specimen treated with PNT, although there was no disintegration of the bacterial membrane. In the DNA gyrase supercoiling assay, a dose-dependent reduction in fluorescence intensity was observed as the concentration of PNT increased. This suggests that PNT is taken up by microbial cells, resulting in cell disruption, and it reveals that one of the mechanisms underlying the antimicrobial activity of PNT is the inhibition of DNA gyrase.

The chemical reaction of 2-(methylsulfinyl)naphtho[2,3-d]thiazole-4,9-dione (3) using different amines, including benzylamine (4a), morpholine (4b), thiomorpholine (4c), piperidine (4d), and 4-methylpiperazine (4e), produced corresponding new tricyclic naphtho[2,3-d]thiazole–4,9–dione compounds (5a–e) in moderate-to-good yields. The photophysical properties and antimicrobial activities of these compounds (5a–e) were then characterized. Owing to the extended π-conjugated system of naphtho[2,3-d]thiazole–4,9–dione skeleton and substituent effect, 5a–e showed fluorescence both in solution and in the solid state. The introduction of nitrogen-containing heterocycles at position 2 of the thiazole ring on naphtho[2,3-d]thiazole-4,9-dione led to large bathochromic shifts in solution, and 5b–e exhibited orange-red fluorescence with emission maxima of over 600 nm in highly polar solvents. Staphylococcus aureus (S. aureus) is a highly pathogenic bacterium, and infection with its antimicrobial-resistant pathogen methicillin-resistant S. aureus (MRSA) results in serious clinical problems. In this study, we also investigated the antimicrobial activities of 5a–e against S. aureus, MRSA, and S. epidermidis. Compounds 5c with thiomorpholine group and 5e with 4-methylpiperazine group showed potent antimicrobial activity against these bacteria. These results will lead to the development of new fluorescent dyes with antimicrobial activity in the future.

Cutibacterium acnes is abundant and commonly exists as a superficial bacteria on human skin. Recently, the resistance of C. acnes to antimicrobial agents has become a serious concern, necessitating the development of alternative pharmaceutical products with antimicrobial activity against C. acnes. To address this need, we evaluated the antimicrobial activity of CKR-13—a mutant oligopeptide of FK-13 with increased net charge and theoretical α-helical content—against C. acnes in modified Gifu Anaerobic Medium broth by determining the minimum inhibitory concentration (MIC). CKR-13 exerted greater antimicrobial activity against C. acnes than FK-13 in the broth at pH 7.0. The antimicrobial activity of CKR-13 with RXM against C. albicans was pH-dependent. The ionization of CKR-13 and pH-dependent growth delay of C. albicans was suggested to be associated with the increase in CKR-13 antimicrobial activity.

In this paper, the antifungal activity of medium-chain fatty acids with 8 to 11 carbon atoms in their chemical structures, medium-chain fatty acid lactones, and a partially fluorinated medium-chain fatty acid was determined. As the length of the alkyl chain increased in medium-chain fatty acids with 8 to 11 carbon atoms, the MIC and MFC became smaller, with increased antifungal activity (octanoic acid, 225 µg/mL(MIC), 450 µg/mL (MFC); nonanoic acid, 225 µg/mL (MIC), 450 µg/mL (MFC); decanoic acid, 112.5 µg/mL (MIC), 225 µg/mL (MFC); undecanoic acid, 112.5 µg/mL (MIC), 225 µg/mL (MFC)), whereas the antifungal activity of γ-undecalactone, in which the carboxyl group of the medium-chain fatty acid with 11 carbon atoms was converted to a five-membered lactone ring, also had antifungal activity (γ-undecalactone, 112.5 µg/mL (MIC), 225 µg/mL (MFC)). The antifungal activity of the partially fluorinated fatty acid with 11 carbon atoms and δ-undecalactone was not observed and their MICs were not evaluated in this study. The equation derived through multiple regression analysis revealed that the polarizability value was significantly related to the MICs or MFCs of fatty acids containing 8 to 11 carbon atoms and γ-undecalactone (R² = 0.78, p < 0.05). C. albicans cultured at 37 °C with γ-undecalactone at the MIC formed hyphae or biofilms, which were observed using scanning electron microscopy in this study. Dead C. albicans were observed when cultured at 37 °C with γ-undecalactone at the MFC, indicating that in order to demonstrate complete killing, C. albicans must be killed at or above the MFC of γ-undecalactone when cultured at 37 °C. γ-undecalactone exhibited no hemolytic activity at the MFC, similar to negative controls. Our results show that γ-undecalactone has an antifungal effect against C. albicans over the MFC, without hemodialysis as the observed cytotoxicity.

Staphylococcus aureus（S. aureus，黄色ブドウ球菌）はアトピー性皮膚炎の炎症部で顕著に増加して炎症を増悪化する。一方，健常者の皮膚に多いStaphylococcus epidermidis（S. epidermidis，表皮ブドウ球菌）はS. aureusの生育抑制などの有用機能を保持する。多数の脂肪酸のS. aureusとS. epidermidisに対する抗菌活性を調べたところ，6-cis-C16：1，7-cis-C16：1，および9-cis-C16：1はS. aureusの生育を抑制し，S. epidermidisの生育を抑制しない選択的抗菌活性を保持し，アトピー性皮膚炎の炎症緩和に寄与することが期待される。皮脂中に存在する6-cis-C16：1は天然油脂中に存在しないことから，7-cis-C16：1と9-cis-C16：1を微生物法で生産することを試みた。Aeromonas hydrophilaおよびAcinetobacter sp.は，9-cis-C18：1を含む植物油を基質としたとき，9-cis-C18：1の炭素数を小さくした7-cis-C16：1に変換した。種々の遺伝子組換えを施したSaccharomyces cerevisiaeは高含量の9-cis-C16：1を含む油脂を生産した。さらに精製条件の検討により9-cis-C16：1含量を98％まで高めることができた。また，消費者の認知度の高いBifidobacterium sp. JCM 7042株は菌体内に7-cis-C16：1を生産した。