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A Synergistic Interaction Between Citrus Hystrix Peel Essential Oil and Tetracycline and Evaluation of their Antibacterial Mechanism of Action in Vitro and in Silico Against Escherichia Coli

Aini Khairunnisa N, Yuandani, Raina Nasution H, Sari Utami D, Frimayanti N, Jantan I, et al.

Chem Biodivers, 2025 Jan;22(1):e202401291.
PMID: 39246102 DOI: 10.1002/cbdv.202401291

Citrus hystrix essential oil (CHEO) have shown various pharmacological properties including antibacterial activity. This EO also possessed antibacterial effect against foodborne pathogens. There is less information available about the synergy interaction between CHEO and tetracycline, as well as their mechanism of action. Therefore, this study was conducted to evaluate the synergistic effect of CHEO and tetracycline against clinical isolate of Escherichia coli. Antibiofilm, bacteriolytic, and efflux pump inhibitor activities were also performed. The chemical composition of CHEO was analysed using GC-MS. Three major compounds, D-limonene (25.02 %), β-pinene (23.37 %), and β-sabinene (22.20 %) were identified. CHEO exhibited moderate antibacterial activity with MIC value of 250 μg/mL. The combination of CHEO (7.8 μg/mL) and tetracycline (62.5 μg/mL) produced a synergistic effect on E. coli with fractional inhibitory concentration index of 0.5. This mixture inhibited biofilm formation in E. coli. The combination of 7.8 μg/mL CHEO and 62.5 μg/mL tetracycline demonstrated bacteriolytic activity. In addition, the CHEO at 250 μg/mL showed a significant effect in inhibiting efflux pump. D-limonene has a binding free energy value of -20.13 kcal/mol with ompA transmembrane domain of E. coli. This finding indicates that CHEO has a potency to be developed as natural antibacterial against E. coli.
Fulltext Material Characterization of a Magnetorheological Fluid Subjected to Long-Term Operation in Damper

Utami D, Ubaidillah, Mazlan SA, Imaduddin F, Nordin NA, Bahiuddin I, et al.

Materials (Basel), 2018 Nov 06;11(11).
PMID: 30404193 DOI: 10.3390/ma11112195

This paper investigates the field-dependent rheological properties of magnetorheological (MR) fluid used to fill in MR dampers after long-term cyclic operation. For testing purposes, a meandering MR valve was customized to create a double-ended MR damper in which MR fluid flowed inside the valve due to the magnetic flux density. The test was conducted for 170,000 cycles using a fatigue dynamic testing machine which has 20 mm of stroke length and 0.4 Hz of frequency. Firstly, the damping force was investigated as the number of operating cycles increased. Secondly, the change in viscosity of the MR fluid was identified as in-use thickening (IUT). Finally, the morphological observation of MR particles was undertaken before and after the long-term operation. From these tests, it was demonstrated that the damping force increased as the number of operating cycles increases, both when the damper is turn on (on-state) and off (off-state). It is also observed that the particle size and shape changed due to the long operation, showing irregular particles.
Biocompatibility assessment of an integrated contraceptive and RFID-based intravaginal device in cats (Felis catus): A preliminary study

Santoso MIB, Ainun SS, Utami D, Aziz FA, Puspitaningsih R, Ashar Y, et al.

Open Vet J, 2024 Sep;14(9):2348-2360.
PMID: 39553770 DOI: 10.5455/OVJ.2024.v14.i9.23

BACKGROUND: An intravaginal device (IVD) made from polyethylene plastic and copper wire, integrated with a radio frequency identification (RFID) chip, was developed as a biocompatible contraceptive and identity device for cats.
AIM: This study evaluates the local and systemic biocompatibility of IVD in five non-pregnant female cats.
METHODS: The IVD was successfully inserted into the vaginal lumen after estrogen administration. Radiographic imaging confirmed the IVD's position, which lasted up to two days post-insertion.
RESULTS: Systemic response, assessed through hematological examinations on days 0, 1, and 3 post-insertion, showed no significant changes in erythrogram and leukogram parameters. Local response, evaluated through vulvar inspection and vaginal cytology on days 0, 1, 3, and 7, revealed no neutrophil infiltration in 4 out of 5 cats, indicating compatibility with vaginal tissue. Furthermore, epithelial cell profile changes were observed, showing an increase in superficial cells, which is typical during the estrus phase.
CONCLUSION: These findings suggest that the IVD is biocompatible and suitable for use as a contraceptive and identity device in cats. However, further long-term studies are necessary to evaluate the device's prolonged efficacy and potential for contraception failure prevention by mating trials.

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