In this work, we report the adaptation of bacteria to stress conditions that induce instability of their cultural, morphological, and enzymatic characters, on which the identification of pathogenic bacteria is based. These can raise serious issues during the characterization of bacteria. The timely detection of pathogens is also a subject of great importance. For this reason, our objective is oriented towards developing an immunosensing system for rapid detection and quantification of Staphylococcus aureus. Polyclonal anti-S. aureus are immobilized onto modified gold electrode by self-assembled molecular monolayer (SAM) method. The electrochemical performances of the developed immunosensor were evaluated by impedance spectroscopy through the monitoring of the charge transfer resistance at the modified solid/liquid interface using ferri-/ferrocyanide as redox probe. The developed immunosensor was applied to detect stressed and resuscitate bacteria. As a result, a stable and reproducible immunosensor with sensitivity of 15 kΩ/decade and a detection limit of 10 CFU/mL was obtained for the S. aureus concentrations ranging from 10(1) to 10(7) CFU/mL. A low deviation in the immunosensor response (±10 %) was signed when it is exposed to stressed and not stressed bacteria.
The use of response surface methodology based on statistical design of experiments is becoming increasingly widespread in several sciences such as analytical and environmental chemistry. In the present study, the decolourization and the degradation efficiency of CI Reactive Violet 5 (CIRV5) was studied using a novel bacterial consortium. CIRV5 (1000 p.p.m.) biodegradation was investigated under shaking condition in mineral salt medium solution (MSM) at a 7.5 pH and a 25°C temperature. The degradation pathways were also predicted, using UV‐visible spectroscopy analysis. Under optimal conditions, the bacterial consortium was able to decolourize the dye completely (>99%) within 8 h. The colour and chemical oxygen demand (COD) removal were 99.29 and 94.93%, respectively. Polymerase chain reaction (PCR) technique was utilized to detect the adhesin genes ‘icaA’ and ‘icaD.’ Our results showed that Staphylococcus aureus had a high decolourization capacity. Phytotoxicity study using Triticum turgidum ssp durum showed the no toxicity of the produced products.
In this study, we incubated four strains of Staphylococcus aureus for 8 months in seawater microcosms. The biofilm formation on microplates and on glass and the surface hydrophobicity of starved cells were investigated. Our results showed that the stressed cells increased their hydrophobicity from 12 to 44% and also their capacity for producing biofilm. Indeed, after 8 months of incubation in seawater microcosms, all strains became slime positive on CRA plates and very adherent to polystyrene microplates or glass wells.
We investigated the chemical composition (by gas chromatography) and anti-microbial activity of the Tunisian Nigella sativa fixed oil against different standard Gram-negative and Gram-positive strains and Candida isolates by disc diffusion method, and determined the minimal inhibitory concentration (MIC), minimal bactericidal concentration (MBC) and minimal fungicidal concentration (MFC) values. Twenty three fatty acids were identified in N. sativa fixed oil. Palmitic acid was the major saturated fatty acids (SFA) accounted for 12.2% of the total fatty acid (TFA). For monounsaturated fatty acids (MUFA), oleic acid was the major one with 21.67% of TFA. Linoleic acid has the most important percentage (58.73% of TFA) and was the major polyunsaturated fatty acids (PUFA). For the antibacterial activity, the best inhibition was seen against Staphylococcus aureus ATCC 25923 (16.66 mm) and Salmonella typhimurium ATCC 14028 (15.33 mm). The best antifugal activity was found against Candida parapsilosis ATCC 22019 (13.33 mm) and Candida glabata ATCC 90030 (12 mm). This fixed oil can be used as an antibacterial and antifungal agent each time the MIC values have a good effect on the antibacterial and antifungal activities of the Tunisian N. sativa fixed oil. Our results demonstrate important antibacterial and antifungal activities of the Tunisian N. sativa fixed oil; these effects further validate the traditional use of N. sativa in the folk medicine against bacterial and fungal infection.
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