Model Gram-negative Bacterium Research Articles

Gold nanoparticles as colorimetric sensor: A case study on E. coli O157:H7 as a model for Gram-negative bacteria

A novel and sensitive colorimetric method for assay of Escherichia coli O157:H7 was developed as a model for Gram-negative bacteria by a mercaptoethylamine-modified gold nanoparticles (MEA-AuNPs) sensor. Mercaptoethylamine (MEA) molecule binded with E. coli O157:H7 via electrostatic adhesion between the positive electricity of MEA and the negative electricity of E. coli O157:H7. Furthermore MEA can be easily conjugated to AuNPs through –SH group. Thus, the MEA-AuNPs can be cross linked in the presence of certain amount of E. coli O157:H7, resulting in a dramatic color change from red to blue. It is worth noting that the absorption ratio ( A 625/ A 520) of the modified AuNPs exhibited a linear correlation with E. coli O157:H7 concentration. Therefore, the concentration of E. coli O157:H7 can be detected by the naked eyes. This bioassay is rapid, takes less than 5 min from bacterium binding to detection and analysis, and is also convenient. Therefore, MEA-AuNPs system as a novel, on-site, real-time and low-cost Gram-negative bacteria sensor, would have a wide range of practical applications.

Simultaneous Electrokinetic and Hydrodynamic Injection for High Sensitivity Bacteria Analysis in Capillary Electrophoresis

A repeatable preconcentration electrophoretic methodology for the analysis of bacteria was developed. This method is based on an isotachophoretic mode coupled with a simultaneous hydrodynamic-electrokinetic injection in conditions of field-amplified sample injection. This electrophoretic method allows the quantification of Enterobacter cloacae (studied as a model of Gram negative bacteria) with a limit of detection of 2 × 10(4) cells/mL. With the optimized conditions, a preconcentration factor of about 500-fold was obtained as compared to a standard hydrodynamic injection. The RSD (n = 5) on the migration time and on the peak area were 3% and 5%, respectively. This capillary electrophoretic methodology has been applied for the quantification of microbes in natural water (river and natural spring waters). Filtration of the sample prior to injection was required to remove ions present in the water and to keep the field-amplified sample injection condition at the injection. Filtrated bacteria were then recovered in terminating electrolyte diluted 10 times with water. Good agreements were obtained between cellular ATP measurements and the proposed CE methodology for the quantification of bacteria in waters.

Synthesis of TiO 2–Ag nanocomposite with sol–gel method and investigation of its antibacterial activity against E. coli

TiO 2–Ag nanocomposite was prepared by the sol–gel method and an azeotropic distillation with benzene was used for dehydration of the gel. Because of gel dehydration by distillation method a nanopowder with a surface area of 230 m 2/g was produced which decreased to 80 m 2/g after calcination. TEM micrographs and XRD patterns showed that spherical nanosized Ag particles (≈ 10 nm) were deposited among TiO 2 particles. The antibacterial activity of calcined powder at 300 and 500 °C was studied in the presence and in the absence of UV irradiation against Escherichia coli as a model for Gram-negative bacteria. The antibacterial tests confirmed the powder calcined at 300 °C possessed more antibacterial activity than the pure TiO 2, amorphous powder and the powder calcined at 500 °C under UV irradiation. In the absence of UV, the reduction in viable cells was observed only with calcinated powder at 300 °C.

Antimicrobial finishing of cotton textile based on water glass by sol–gel method

A low temperature and cost-effective process for antimicrobial finishing of cotton textiles has been developed by sol–gel method. The antimicrobial treatment was performed by treating cotton textile with silica sols from water glass and then with silver nitrate solution. The antimicrobial activity was determined by using E. coli as a model for Gram-negative bacteria. The results showed that the treated textile has an excellent antimicrobial effect and laundering durability. SEM analysis showed coarse surface morphological change on the water glass treated cotton textile. The residual concentration of silver ion on fabrics was informed by ICP-MS. XPS results indicated that two different states of silver were present on the surface of the antimicrobial textile.

Silver nanoparticles as antimicrobial agent: a case study on E. coli as a model for Gram-negative bacteria

The antimicrobial activity of silver nanoparticles against E. coli was investigated as a model for Gram-negative bacteria. Bacteriological tests were performed in Luria–Bertani (LB) medium on solid agar plates and in liquid systems supplemented with different concentrations of nanosized silver particles. These particles were shown to be an effective bactericide. Scanning and transmission electron microscopy (SEM and TEM) were used to study the biocidal action of this nanoscale material. The results confirmed that the treated E. coli cells were damaged, showing formation of “pits” in the cell wall of the bacteria, while the silver nanoparticles were found to accumulate in the bacterial membrane. A membrane with such a morphology exhibits a significant increase in permeability, resulting in death of the cell. These nontoxic nanomaterials, which can be prepared in a simple and cost-effective manner, may be suitable for the formulation of new types of bactericidal materials.