Detection of bacteria by surface-enhanced Raman spectroscopy

The detection and identification of dilute bacterial samples by surface-enhanced Raman spectroscopy has been explored by mixing aqueous suspensions of bacteria with a suspension of nanocolloidal silver particles. An estimate of the detection limit of E. coli was obtained by varying the concentration of bacteria. By correcting the Raman spectra for the broad librational OH band of water, reproducible spectra were obtained for E. coli concentrations as low as approximately 10³ cfu/mL. To aid in the assignment of Raman bands, spectra for E. coli in D₂O are also reported. Figure Light scattering apparatus used to detect bacteria     

Effect of hydrophobic modifications in antimicrobial peptides

With increasing resistance development against conventional antibiotics, there is an urgent need to identify novel approaches for infection treatment. Antimicrobial peptides may offer opportunities in this context, hence there has been considerable interest in identification and optimization of such peptides during the last decade in particular, with the long-term aim of developing these to potent and safe therapeutics. In the present overview, focus is placed on hydrophobic modifications of antimicrobial peptides, and how these may provide opportunities to combat also more demanding pathogens, including multi-resistant strains, yet not provoking unacceptable toxic responses. In doing so, physicochemical factors affecting peptide interactions with bacterial and eukaryotic cell membranes are discussed. Throughout, an attempt is made to illustrate how physicochemical studies on model lipid membranes can be correlated to result from bacterial and cell assays, and knowledge from this translated into therapeutic considerations.     

1,8-Bis(dimethylamino)naphthalene/9-aminoacridine: A new binary matrix for lipid fingerprinting of intact bacteria by matrix assisted laser desorption ionization mass spectrometry

The effectiveness of a novel binary matrix composed of 1,8-bis(dimethylamino)naphthalene (DMAN; proton sponge) and 9-aminoacridine (9AA) for the direct lipid analysis of whole bacterial cells by matrix assisted laser desorption ionization mass spectrometry (MALDI MS) is demonstrated. Deprotonated analyte signals nearly free of matrix-related ions were observed in negative ion mode. The effect of the most important factors (laser energy, pulse voltage, DMAN/9AA ratio, analyte/matrix ratio) was investigated using a Box–Behnken response surface design followed by multi-response optimization in order to simultaneously maximize signal-to-noise (S/N) ratio and resolution. The chemical surface composition of single or mixed matrices was explored by X-ray photoelectron spectroscopy (XPS). Moreover, XPS imaging was used to map the spatial distribution of a model phospholipid in single or binary matrices.     

SIMPLISMA applied to two-dimensional wavelet compressed ion mobility spectrometry data

A modified SIMPLe-to-use Interactive Self-modeling Mixture Analysis (SIMPLISMA) algorithm, referred to as real-time (RT) SIMPLISMA has been combined with two-dimensional (2D) wavelet compression (WC²). This tool was evaluated with datasets of drugs and bacteria that were acquired from two different ion mobility spectrometers and published reference data that comprised Raman, FTIR microscopy, near-infrared (NIR) and mass spectral data. RTSIMPLISMA is amenable for real-time modeling and is able to determine the number of components automatically. The 2D wavelet compression, which compresses both acquisition and drift time dimensions of measurement, was applied to the datasets prior to RTSIMPLISMA modeling. RTSIMPLISMA models obtained from the compressed data were wavelet transformed back to the uncompressed representation. The effects of wavelet filter types and compression levels were investigated. The relative root-mean-square errors (RRMSE) of reconstruction, which calculate the relative difference between the extracted models with and without 2D compressions, were used to evaluate the effects of compression on self-modeling. The results showed that satisfactory models could be obtained when a data was compressed to 1/256 of its size.     

Effect of high pressure on mesophilic starters for cheesemaking

In the experiment, the effect of pressurization on the survival as well as acidifying and proteolytic activity of mesophilic commercial starters used for cheesemaking was studied. The samples were exposed to a single and a double (after 24 h) pressurization in the range of 200-800 MPa, for 15 minutes, at 20 °C. Analyses were performed immediately after the processing as well as after 1, 2, and 3 weeks of storage at 4 °C. A double processing at 600 and 800 MPa caused an irreversible reduction in the number of microorganisms, inhibited the process of milk acidification but preserved approximately 20% of the initial proteolytic activity of the bacterial enzymes.     

Influence of high pressure on some biochemical properties of kefir microflora (effect of HPP on kefir microflora)

The effect of high pressure on some biochemical properties of lactic acid bacteria present in kefir was investigated. Three strains of lactococci and three strains of lactobacilli, isolated from lyophilised kefir culture, were activated in milk and subjected, at room temperature, to pressurisation at 500 MPa, for 15 minutes. Both in the unpressurised and pressurised culture the following factors were determined: survivability of microorganisms, aroma-producing activity, acidity, ability to ferment lactose and antibacterial activity. As a result of pressurisation, the initial number of bacteria decreased by ca. 2-4 order of magnitude in the case of lactococci and by ca. 5-6 order of magnitude in case of lactobacilli. After pressurisation, decrease in ability of bacteria to produce aroma was observed. Following pressurisation, an increase of acidity (pH) and slight decrease of titratable acidity (°SH) in the cultures was observed. As compared to lactococci, acidity of lactobacilli culture was reduced to a bigger extent. Pressurisation did not effect the capability of lactococci to utilise lactose. In case of lactobacilli it was partly inhibited for the first 24 hours after processing. As a consequence of pressurisation, the studied microorganisms lost their antibacterial activity.     

High Pressure Processing at Subzero Temperature: Effect on Spoilage Microbiota of Poultry

Mechanically recovered poultry meat (MRPM) was treated at 350 and 450 MPa for 5 and 15 min at m 20 °C and then stored at 2 °C. Counts of mesophilic, psychrotrophic and lactic acid bacteria were determined at 1, 4 and 15 days of storage. Initial counts were ca. 7 log CFU/g for the three populations. High pressure induced lethalities of ca. 1.5 log CFU/g for mesophiles and psychrotrophs and, in some cases, ca. 2.5 log CFU/g for lactic acid bacteria. At 4 days, counts in pressurized samples increased less for mesophiles and psychrotrophs ( h 0.5 CFU/g) than for lactic acid bacteria ( S 1 log CFU/g). At 15 days, counts of the three populations were ca. 9 log CFU/g in all samples. High pressure processing at subzero temperature does not extend shelf-life of MRPM.     

光学扩散特征的生鲜肉细菌总数的无损检测方法

细菌总数是生鲜肉的最主要安全参数之一,肉品的光学扩散特征反映其细菌总数。对高光谱扩散数据利用不同的拟合算法处理与分析,并比对生鲜猪肉细菌总数建模的相关性差异,确定了用于最终建模的最佳扩散特征参数,为后续的装置开发提供建模依据。冰箱调至4℃恒温,在里面放置63个分割好的猪肉样品,每天间隔固定时间从里面随机取出4~5块样品,获取猪肉表面的400~1 100nm波长范围内高光谱散射图像,从高光谱图像中提取猪肉的扩散光谱曲线,利用Lorentz函数和Gompertz函数以及修正后的函数,拟合处理与分析扩散数据,拟合后的不同参数可以代表样品的特征光谱,细菌总数的标准值用平板计数法获得,然后单独用各单个参数、多个参数结合的方式,多元线性回归的统计方法,与细菌总数分别建立模型。实验结果表明,Lorentz三参数结合,Lorentz四参数结合,Gompertz四参数拟合的模型相关系数较高,其校正集和预测集相关系数分别为0.93,0.96,0.96和0.90,0.90,0.92,标准偏差分别为0.47,0.44,0.39和0.56,0.46,0.42,其中,相关性最好的是Gompertz四参数结合,在装置的开发中可以优选相关性和稳定性最好的模型导入装置系统中。     

pH-responsive deoxyribonucleic acid capture/release by polydopamine functionalized magnetic nanoparticles

Polydopamine functionalized magnetic nanoparticles (PDA@Fe₃O₄) were prepared and characterized by transmission electron microscopy, scanning electron microscopy, zeta potential and vibrating sample magnetometry. They were found to enable highly efficient capture of genomic deoxyribonucleic acid (DNA). The adsorption capacity of PDA@Fe₃O₄ for genomic DNA can reach 161 mg g⁻¹. The extraction protocol used aqueous solutions for DNA binding to and releasing from the surface of the magnetic particles based on the pH inducing the charge switch of amino and phenolic hydroxyl groups on PDA@Fe₃O₄. The extracted DNA with high quality (A₂₆₀/A₂₈₀ = 1.80) can be directly used as templates for polymerase chain reaction (PCR) followed by capillary electrophoresis (CE) analysis. None of the toxic chemical reagents and PCR inhibitors was used throughout the whole procedure. PDA@Fe₃O₄ based magnetic solid phase extraction (MSPE) method was superior to those using commercial kit and traditional phenol–chloroform extraction methods in yield of DNA. The developed PDA@Fe₃O₄ based MSPE-PCR-CE method was applied for simultaneous and fast detection of Listeria monocytogenes and Escherichia coli O157:H7 in milk.     

Role of the cell-wall structure in the retention of bacteria by microfiltration membranes

This experimental study investigates the retention of bacteria by porous membranes. The transfer of bacteria larger than the nominal pore size of microfiltration track-etched membranes has been studied for several kinds of bacterial strains. This unexpected transfer does not correlate to the hydrophobicity, neither to the surface charge of the microorganism, as suggested in previous reports. We conclude that, in our conditions, the kind of bacteria (Gram-positive or Gram-negative) is finally the most important parameter. As the distinction between those two types of bacteria is related to the cell-wall structure, we provide an experimental evidence, via the action of an antibiotic, that the cell-wall flexibility triggers the transfer of the bacteria through artificial membranes, when the pores are smaller in size than the cell.