Browsing by Subject "Antimicrobial activity"

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  • Kuosmanen, Soile (Helsingfors universitet, 2013)
    The lower respiratory infection tuberculosis (TB) has been the leading cause of death for centuries causing millions of deaths worldwide. The development of antibiotic therapy has reduced the morbidity and mortality during the 20th century, at least in the developed countries. However, tuberculosis is still the world's second leading cause of death from infectious diseases. Although TB can be treated and even cured with drug therapy, the treatment is extremely long and requires 6-9 months constant drug therapy. This prolonged treatment causes poor patient compliance, which is usually the reason for the selection of drug resistant and often multidrug (MDR-TB) or even extensively drug-resistant (XDR-TB) TB bacteria. Limitations of available therapies and the emergence of drug-resistant strains have intensified the search for new drugs from natural sources. Marine micro- and macro-organisms have proven to be an excellent source of structurally unique biologically active natural products. EU FP7 -funded MAREX project, launched in 2010, aims at identifying new biologically active compounds from marine sources. This Master's thesis was carried out as a part of the MAREX project. The aim of this study was to optimize and validate a reproducible method to determine antimicrobial activity of natural products against Mycobacterium smegmatis, which is a widely used non-pathogenic surrogate model for TB. In the present study, spectrophotometric microplate assay was optimized and validated using existing antibacterial agents ciprofloxacin and rifampicin as reference compounds. The assay was performed on 96-well plate by using two detection techniques, absorbance measurement and a colorimetric indicator, for the antibacterial MIC end-point determination. The results obtained by the described methods were compared with each other in order to achieve the most optimal assay conditions. The quality control parameters S/B, S/N and Z' factor were used in order to determine the optimal experimental conditions for the assay. Obtaining reliable results with the turbidimetric method required incubation for two days in the case of ciprofloxacin, and for five days with rifampicin. Colorimetric measurement led to similar results as the turbidimetric measurement for both of the reference compounds. The method was further used for the screening of a group of marine extracts. None of the 21 samples tested showed significant activity against M. smegmatis.
  • Puupponen-Pimiä, Riitta; Nohynek, Liisa; Juvonen, Riikka; Kössö, Tuija; Truchado, Pilar; Westerlund-Wikström, Benita Alice; Leppänen, Tiina; Moilanen, Eeva; Oksman-Caldentey, Kirsi-Marja (2015)
  • Cruz, Cristina D; Wrigstedt, Pauli; Moslova, Karina; Iashin, Vladimir; Mäkkylä, Heidi; Ghemtio, Leo; Heikkinen, Sami; Tammela, Päivi; Perea-Buceta, Jesus Enrique (2021)
    N-aryl-oxazolidinones is a prominent family of antimicrobials used for treating infections caused by clinically prevalent Gram-positive bacteria. Recently, boron-containing compounds have displayed intriguing potential in the antibiotic discovery setting. Herein, we report the unprecedented introduction of a boron-containing moiety such as an aryl boronic acid in the external region of the oxazolidinone structure via a chemoselective acyl coupling reaction. As a result, we accessed a series of analogues with a distal aryl boronic pharmacophore on the oxazolidinone scaffold. We identified that a peripheric linear conformation coupled with freedom of rotation and no further substitution on the external aryl boronic ring, an amido linkage with hydrogen bonding character, in addition to a para-relative disposition between boronic group and linker, are the optimal combination of structural features in this series for antimicrobial activity. In comparison to linezolid, the analogue comprising all those features, compound 20b, displayed levels of antimicrobial activity augmented by an eight-fold to a thirty-two-fold against a panel of Gram-positive strains, and a near one hundred-fold against Escherichia coli JW5503, a Gram-negative mutant strain with a defective efflux capability.
  • Liu, Shanna; Liu, Yongjun; Takala, Timo M.; Zhang, Pingping; Wang, Suhua (2020)
    Listeria ivanovii is one of the two pathogenic species within the genus Listeria, the other being L. monocytogenes. In this study, we generated a stable pediocin resistant mutant Liv-r1 of a L. ivanovii strain, compared phenotypic differences between the wild-type and the mutant, localised the pediocin-induced mutations in the chromosome, and analysed the mechanisms behind the bacteriocin resistance. In addition to pediocin resistance, Liv-r1 was also less sensitive to nisin. The growth of Liv-r1 was significantly reduced with glucose and mannose, but less with cellobiose. The cells of Liv-r1 adsorbed less pediocin than the wild-type cells. Consequently, with less pediocin on the cell surface, the mutant was also less leaky, as shown as the release of intracellular lactate dehydrogenase to the supernatant. The surface of the mutant cells was more hydrophobic than that of the wild-type. Whole genome sequencing revealed numerous changes in the Liv-r1 chromosome. The mutations were found e.g., in genes encoding sigma-54-dependent transcription regulator and internalin B, as well as in genes involved in metabolism of carbohydrates such as glucose and cellobiose. Genetic differences observed in the mutant may be responsible for resistance to pediocin but no direct evidence is provided.