Den 1 densitometer

Manufactured by Biosan

Sourced in Latvia

The DEN-1 densitometer is a laboratory instrument used for measuring the optical density of liquid samples, such as bacterial cultures or protein solutions. It provides a quantitative assessment of the turbidity or concentration of the sample. The DEN-1 densitometer uses a light source and a detector to measure the absorbance of light passing through the sample, which is then converted into an optical density value.

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Lab products found in correlation

Tryptic soy broth (tsb), by Thermo Fisher Scientific (1 mentions) Nutrient agar, by HiMedia (1 mentions) Mueller hinton agar (mha), by Condalab (1 mentions) Menadione, by Merck Group (1 mentions) Carbonyl cyanide 3 chlorophenylhydrazone cccp, by Merck Group (1 mentions) Mrs broth, by Merck Group (1 mentions) Tryptic soy broth (tsb), by Merck Group (1 mentions) M17 broth, by Merck Group (1 mentions) Bhi broth, by HiMedia (1 mentions) Sabouraud broth, by HiMedia (1 mentions) Rpmi 1640, by Merck Group (1 mentions)

Spelling variants of this product

DEN-1 (26 citations) DEN-1 McFarland densitometer (12 citations)

11 protocols using den 1 densitometer

Evaluating Antifungal Potency of AgNP and KTZ

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In order to evaluate the inhibitory activity of synthesized AgNP and KTZ (Sigma-Aldrich, Buenos Aires, Argentina), MIC were determined by broth microdilution method in accordance with CLSI M27-A3 document (Clinical and Laboratory Standards Institute 2008 ) with modifications proposed by Rojas et al. (2014 (link)).
All inoculum suspensions were prepared in sterile saline solution and turbidity was adjusted to a 1 McFarland scale by densitometer (DEN-1 densitometer, Biosan). This inoculum was diluted 1:100 in supplemented RPMI medium to achieve a final concentration of 0.5–2.5 × 10⁵ CFU/mL.
AgNP and KTZ solutions were prepared using dimethyl sulfoxide (DMSO) as solvent (final concentration ≤ 1%) and RPMI medium as diluents. A twofold dilution serial of the drugs was performed to obtain a final concentration range from 4 to 0.008 mg/L. The microtiter plates with 96 U wells (Greiner bio-One, Buenos Aires, Argentina) were incubated for 3 days at 32 °C.
MIC for AgNP solution was determined by visual reading of growth inhibition at two endpoints: MIC-2 as the lowest concentration capable of inhibiting ≥ 50% growth as compared with the AgNP-free growth-control well and MIC-0 as the lowest concentration that completely inhibit yeast growth. For KTZ, the MIC endpoint was MIC-2 (Clinical and Laboratory Standards Institute 2008 ).

Mussin J.E., Roldán M.V., Rojas F., Sosa M.D., Pellegri N, & Giusiano G. (2019). Antifungal activity of silver nanoparticles in combination with ketoconazole against Malassezia furfur. AMB Express, 9, 131.

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Quorum Sensing Inhibition Assay

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Tests were performed with S. aureus ATCC 25923 and E. coli isolated from pork meat. Isolation was carried out according to the standard method [21 ]. Each MO was cultured on tryptone soy agar (TSA, LabM, Lancashire, UK) for 24 h at 37 °C. After incubation, 2 to 3 individual colonies were transferred to 10 mL of tryptone soy broth (TSB, Oxoid, Hampshire, UK). The suspensions were incubated at 37 °C for 18 h. The final concentration of the bacterial suspensions used in the experiments was obtained by adjusting the cell density according to the 1.0 McFarland standard (~3 × 10⁸ CFU/mL) using a DEN-1 densitometer (Biosan, Riga, Latvia). The quorum biosensor bacterial strain Chromobacterium violaceum CV026 (a double mini-Tn5 mutant derived from Chromobacterium violaceum ATCC 31532) was used for anti-QS disinfectant activity testing [22 (link)].

Todorić O., Pezo L., Šarić L., Kolarov V., Varga A., Čabarkapa I, & Kocić-Tanackov S. (2023). Comparison of the Efficiency of Selected Disinfectants against Planktonic and Biofilm Populations of Escherichia coli and Staphylococcus aureus. Microorganisms, 11(6), 1593.

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Isolation and Characterization of S. mutans Strains

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Twenty-six isolates of S. mutans clinical strains were obtained from a dental clinic at Nopphitam Hospital in Nakhon Si Thammarat, Thailand. The isolates were identified by bacterial growth on Mitis-sucrose-bacitracin (MSB) agar (Difco, USA) and confirmatory tests with biochemical test kits (RapIDTM Systems, Thermo Fisher Scientific, USA). The bacterial isolates were cultured in sterile brain heart infusion (BHI) broth and incubated at 37 °C in the presence of 5% CO₂. After 48 h of incubation, Gram staining was performed, and the cultures were replated to verify bacterial isolation. The bacteria were transferred to broth media for antibacterial activity testing. The bacterial suspensions were adjusted to a concentration equal to the No. 0.5 McFarland standards (1.5 × 10⁸ CFU/mL) (DEN-1 Densitometer; suspension turbidity detector, BIOSAN, Latvia) and further diluted in normal saline solution (NSS) to obtain a bacterial concentration of 1 × 10⁶ CFU/mL. The identified isolates were named clinical Streptococcus mutans (CSM01-CSM26). S. mutans ATCC 25,175 was obtained from the American-type culture collection for use as a reference strain in this study.

Karnjana K., Jewboonchu J., Niyomtham N., Tangngamsakul P., Bunluepuech K., Goodla L, & Mordmuang A. (2022). The potency of herbal extracts and its green synthesized nanoparticle formulation as antibacterial agents against Streptococcus mutans associated biofilms. Biotechnology Reports, 37, e00777.

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Antibacterial Activity of A. ursinum Extract

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The antibacterial activity of the A. ursinum extract was tested against selected Gram-negative (Escherichia coli ATCC 10536, Escherichia coli ATCC 8739, Salmonella Enteritidis ATCC 13076, Proteus hauseri ATCC 13315) and Gram-positive bacteria (Listeria monocytogenes ATCC 19111, Enterococcus faecalis ATCC 29212). Lyophilized bacteria were stored in the refrigerator until the moment of activation. Reconstitution was performed according to the manufacturer’s instructions. Refrigerated slant cultures (Nutrient agar, Himedia, India) were sub-cultured weekly. Prior to each antibacterial test, selected bacterial strains were sub-cultured on Nutrient agar (Himedia, India) and incubated at 37 ± 1 °C for 18–24 h. After incubation, bacteria were aseptically transferred to 0.1% peptone salt solution (Himedia, India) and well homogenized. The density of the bacterial suspensions was adjusted to the turbidity of a 0.5 McFarland standard using the DEN-1 densitometer (Biosan, Latvia). These initial suspensions were used to prepare further decimal dilutions in 0.1% peptone salt solution intended for preparation of artificially contaminated samples of A. ursinum extract.

Stupar A., Šarić L., Vidović S., Bajić A., Kolarov V, & Šarić B. (2022). Antibacterial Potential of Allium ursinum Extract Prepared by the Green Extraction Method. Microorganisms, 10(7), 1358.

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Antibacterial Activity Evaluation

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The antibacterial activity of the DM was tested against E. coli ATCC 8739, S. aureus ATCC 25923 and L. monocytogenes ATCC 19111. After overnight incubation on nutrient agar at 37 ± 1 °C, well-isolated colonies of each tested bacteria were selected and transferred with an inoculating loop into a tube containing sterile saline and mixed thoroughly. A DEN-1 densitometer (Biosan, Riga, Latvia) was used to prepare the bacterial suspension whose turbidity was equal to the 0.5 McFarland standard. Ten-fold sequential dilutions of the bacterial suspensions were made in 0.1% peptone saline.

Šarić L., Premović T., Šarić B., Čabarkapa I., Todorić O., Miljanić J., Lazarević J, & Karabasil N. (2023). Microbiological Quality of Raw Donkey Milk from Serbia and Its Antibacterial Properties at Pre-Cooling Temperature. Animals : an Open Access Journal from MDPI, 13(3), 327.

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Antimicrobial Activity of Polymer Films

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The antimicrobial activity of the films was determined by the agar disc diffusion method against S. aureus (ATCC 29213) and E. coli (BC1402) strains. The isolates were incubated at 37 °C for 24 h in nutrient agar (NA, Merck, Darmstadt, Germany) to obtain early stationary phase cells. The turbidity of the cultures was set to 0.5 McFarland (DEN-1 densitometer; Biosan, Riga, Latvia) (10⁸ cfu/mL). One hundred microliters of the bacterial suspensions was spread on a Mueller–Hinton agar (Condalab, Madrid, Spain) plate. Then, the films were cut into 1 cm diameter discs and placed on the plates in an appropriate manner. The plates were incubated at 37 °C for 24 h. At the end of the incubation, the diameters of the inhibition zones formed around the discs were measured. The tests were performed in triplicate [24 (link)].

Hasan R., Sumnu G., Sahin S., Oz E, & Oz F. (2023). The Effects of Citric Acid Crosslinking on Fabrication and Characterization of Gelatin/Curcumin-Based Electrospun Antioxidant Nanofibers. Antioxidants, 12(7), 1387.

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Bacterial Cultivation and Hemolysis Assays

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Stocks of our own clinical isolates of Escherichia coli strain 508 and Staphylococcus aureus strain 92 were stored at −80 °C in 30% (v/v) sterile glycerol until use. Columbia sheep blood agar plate were seeded and incubated overnight in aerobic conditions at 37 °C. Single colonies were thereafter incubated on Luria Bertani agar plates for 24 h incubation aerobic atmosphere at 37 °C. Cells were washed with 5 ml phosphate-buffer saline (PBS, 150 mM, pH 7.4). McFarland density values were determined with a DEN-1 densitometer (Biosan, USA). For calorimetry studies, samples were diluted in PBS and used immediately thereafter. For hemolysis assays on plates, 100 μL of each bacterial suspension was incubated at physiological (37 °C) and fever temperatures (38.5 °C, 39.5 °C and 40.5 °C), on Columbia sheep blood agar plates for 24 h. Images of plates were processed using ImageJ (NIH, USA). Colony forming units counting was performed using OpenCFU 3.8.

Palela M., Giol E.D., Amzuta A., Ologu O.G, & Stan R.C. (2022). Fever temperatures impair hemolysis caused by strains of Escherichia coli and Staphylococcus aureus. Heliyon, 8(2), e08958.

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Awakening and Characterizing Bacterial Persisters

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The SH1000 strain was grown at 37°C in cation-adjusted Mueller-Hinton broth with 125 ng mL⁻¹ tetracycline under shaking at 300 rpm for 8 h. Where indicated, the culture was then exposed to 80 μM menadione (Sigma), 6 μM carbonyl cyanide 3-chlorophenylhydrazone (CCCP) (Sigma), or 0.25 mg L⁻¹ gentamicin (0.5× the MIC; Sigma) for 24 h prior to CFU counting, flow cytometry, ATP measurements, bright-filter-mode microscopy, SDS-PAGE, or RNA extraction. For single-cell awakening experiments, persisters recovered from macrophages were reinoculated in fresh MHB-CA medium, starting from of a single FACS event. Lag times were calculated in comparison with the time needed to reach the detection limit in exponential cultures, using a DEN-1 densitometer (Biosan).

Peyrusson F., Nguyen T.K., Najdovski T, & Van Bambeke F. (2022). Host Cell Oxidative Stress Induces Dormant Staphylococcus aureus Persisters. Microbiology Spectrum, 10(1), e02313-21.

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Optimizing Bacterial Growth Conditions

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The aim of this step was to find the best culture conditions for the cultivation of the selected bacteria in view of biomass preparation for future starter cultures. To determine the optimal growth conditions, bacterial suspensions with optical densities of 0.5 McF were prepared in liquid culture media. The following media were used: MRS broth (Sigma Aldrich, Steinheim, Germany), tryptic soy broth (Sigma Aldrich, Steinheim, Germany), M-17 broth (Sigma Aldrich, Steinheim, Germany), and LAPTg. The LAPTg medium was prepared by dissolving the following ingredients in 1 L of water: 10 g of yeast extract, 15 g of peptone, 1 mL of Tween 80, 10 g of tryptone, and 18 g of lactose (pH approx. 6.5). The bacterial suspensions were incubated at 20 and 30 °C. The optical density of each sample after 6, 24, and 48 h was measured in triplicate. A DEN-1 densitometer (Biosan) was used for the measurements.

Maślak E., Złoch M., Arendowski A., Sugajski M., Janczura I., Rudnicka J., Walczak-Skierska J., Buszewska-Forajta M., Rafińska K., Pomastowski P., Białczak D, & Buszewski B. (2022). Isolation and Identification of Lactococcus lactis and Weissella cibaria Strains from Fermented Beetroot and an Investigation of Their Properties as Potential Starter Cultures and Probiotics. Foods, 11(15), 2257.

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Biofilm Formation on Collagen Membranes

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After activation, a few colonies of each bacterial species were transferred to a suitable medium (Table 2). Bacterial suspensions of each species were centrifuged (10 min, 3000 rpm), the supernatant was discarded, and the pellet was resuspended in PBS (1.0 McFarland standard ≈ 10⁸ cells/mL) (DEN-1 densitometer, Biosan, Riga, Latvia). The final value of CFU/mL of around 10⁵ was obtained by further dilutions in the suitable medium (Table 2).
Sterile collagen membranes (5 mm × 5 mm) were placed with sterile tweezers in a sterile 96-well dish. In order to form a primary pellicle and mimic the conditions of biofilm formation in vivo, collagen membranes were first embedded in 100 μL of artificial saliva (Pharmacy Belgrade, Belgrade, Serbia) for 4 h at 37 °C. This step was followed by the addition of 200 μL of the previously prepared bacterial suspension (around 10⁵ CFU/mL). Incubation was performed in static conditions, as listed in Table 2.

Lazarevic M., Petrovic S., Pierfelice T.V., Ignjatovic N., Piattelli A., Vlajic Tovilovic T, & Radunovic M. (2023). Antimicrobial and Osteogenic Effects of Collagen Membrane Decorated with Chitosan–Nano-Hydroxyapatite. Biomolecules, 13(4), 579.

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