Recognition property and preparation of Staphylococcus aureus protein A-imprinted polyacrylamide polymers by inverse-phase suspension and bulk polymerization

Staphylococcus aureus protein A-imprinted polyacrylamide gel beads (SpA-IPGB) and imprinted polyacrylamide particles (SpA-IPGP) were synthesized by inverse-phase suspension polymerization and bulk polymerization, using SpA as template, acrylamide (AM) as functional monomers. Recognition capacity studies of the prepared SpA-IPGB and SpA-IPGP on SpA and S. aureus were conducted to determine recognition specificity. Computer imitation docking studies were conducted between template proteins and acrylamide monomer to reveal the recognition mechanism of SpA molecularly imprinted polymer. The results showed that the imprinted gel beads had high adsorption capacity and specificity to the SpA and S. aureus, and the adsorption quantity could reach 6.85 × 10⁻³ μmol/g and 10³-10⁴ CFU/g. The adsorption capacities of SpA-IPGB on SpA and S. aureus were higher than that of SpA-IPGP and Non-imprinted polyacrylamide gel beads (Non-IPGB). The recognition specificity of SpA-IPGB and SpA-IPGP on S. aureus was much higher than on Escherichia coli and Streptococcus thermophilus. The formation of complementary shape, and hydrogen bonding, electrostatic, and hydrophobic interactions between the imprinting cavities and the template proteins is the driving force for effective and specific recognition of protein imprinted polymer.     

Carbon Dioxide Inhibition of Escherichia coli and Staphylococcus aureus on a pH-adjusted Surface in a Model System

Growth of Escherichia coli and Staphylococcus aureuson the surface of Trypticase Soy Agar (TSA) packaged with various CO₂ partial pressures (0, 20, 40, 60, 80, 100%, balance N₂) was compared to the control (N₂ 100%) on TSA in which the pH was adjusted to equal that in CO₂ atmospheres at 15°C and 30°C. At 15°C, the biostatic effect was noted with all CO₂ partial pressures for both species. At 30°C, the biostatic effect of CO₂ was almost completely nullified for E. coli, but that for S. aureus was still effective. S. aureus was more sensitive to the inhibitory effects of CO₂ than E. coli at both the temperatures.     

Synthesis of Mixed Refrigerant Cascade Cycles

This paper considers the synthesis of refrigeration systems with refrigerant mixtures as working fluids. The employed refrigeration topology encompasses features from industrial liquefaction of natural gas (LNG) systems. This configuration consists of a combination of horizontal and vertical cascades generalizing the vertical cascade of pure refrigerant systems. The key features of mixtures exploited here are their ability to evaporate/condense over a temperature range and their potential to generate streams with different compositions through partial condensation. The synthesis problem is formulated and solved as a nonlinear program. The proposed methodology is illustrated using an example of cooling a methane-rich stream.     

Colonization and Infection of the Skin by S. aureus: Immune System Evasion and the Response to Cationic Antimicrobial Peptides

Staphylococcus aureus (S. aureus) is a widespread cutaneous pathogen responsible for the great majority of bacterial skin infections in humans. The incidence of skin infections by S. aureus reflects in part the competition between host cutaneous immune defenses and S. aureus virulence factors. As part of the innate immune system in the skin, cationic antimicrobial peptides (CAMPs) such as the β-defensins and cathelicidin contribute to host cutaneous defense, which prevents harmful microorganisms, like S. aureus, from crossing epithelial barriers. Conversely, S. aureus utilizes evasive mechanisms against host defenses to promote its colonization and infection of the skin. In this review, we focus on host-pathogen interactions during colonization and infection of the skin by S. aureus and methicillin-resistant Staphylococcus aureus (MRSA). We will discuss the peptides (defensins, cathelicidins, RNase7, dermcidin) and other mediators (toll-like receptor, IL-1 and IL-17) that comprise the host defense against S. aureus skin infection, as well as the various mechanisms by which S. aureus evades host defenses. It is anticipated that greater understanding of these mechanisms will enable development of more sustainable antimicrobial compounds and new therapeutic approaches to the treatment of S. aureus skin infection and colonization.     

食品中金黄色葡萄球菌定量检测方法比较研究

目的：研究食品中金黄色葡萄球菌定量检测方法。方法：比较Baird—Parker平板、显色培养基A、显色培养基B、Petrifilm TM测试片等4种计数方法的生长率、选择性、检出限及人工污染食品的检验效果。结果：金黄色葡萄球菌在显色培养基A上的生长率最高,PetrifilmTM测试片的选择性最强,4种计数方法的检出限相当,检出结果与实际含菌量无显著差异。结论：选择显色培养基作为日常检验的辅助手段可大大提高检测灵敏度、缩短检验周期、节约检验成本,值得在日常检验中推广应用。     

The olive compound 4-hydroxytyrosol inactivates Staphylococcus aureus bacteria and Staphylococcal Enterotoxin A (SEA)

The foodborne pathogen Staphylococcus aureus produces the virulent staphylococcal enterotoxin A (SEA), a single chain protein which consists of 233 amino acid residues with a molecular weight of 27078 Da. SEA is a superantigen that is reported to contribute to animal (mastitis) and human (emesis, diarrhea, atopic dermatitis, arthritis, and toxic shock) syndromes. Changes in the native structural integrity may inactivate the toxin by preventing molecular interaction with cell membrane receptor sites of their host cells. In the present study, we evaluated the ability of the pure olive compound 4-hydroxytyrosol and a commercial olive powder called Hidrox-12, prepared by freeze-drying olive juice, to inhibit S. aureus bacteria and SEA's biological activity. Dilutions of both test substances inactivated the pathogens. Two independent cell assays (BrdU incorporation into newly synthesized DNA and glycyl-phenylalanyl-aminofluorocoumarin proteolysis) demonstrated that the olive compound 4-hydroxytyrosol also inactivated the biological activity of SEA at concentrations that were not toxic to the spleen cells. However, efforts to determine inhibition of the toxin by Hidrox-12 were not successful because the olive powder was cytotoxic to the spleen cells at concentrations found to be effective against the bacteria. The results suggest that food-compatible and safe antitoxin olive compounds can be used to inactivate both pathogens and toxins produced by the pathogens. Practical Application: The results of this study suggest that food-compatible and safe antitoxin olive compounds can be used to reduce both pathogens and toxins produced by the pathogens in foods.     

A Quasi-Chemical Kinetics Model for the Growth and Death of Staphylococcus aureus in Intermediate Moisture Bread

ABSTRACT: The "quasi-chemical" kinetics model accounts for all 4 phases of the microbial lifecycle based on a proposed series of chemical rate equations. The model fits continuous growth-death kinetics for Staphylococcus aureus in intermediate moisture bread in various conditions of water activity, pH, and temperature. Growth rates evaluated using the quasi-chemical model are compared with values obtained with the Gompertz model. Kinetics data obtained with the quasi-chemical model are integrated with a probabilistic approach to estimate the boundary between growth and no-growth conditions. Continuous modeling of microbial growth/death kinetics in actual foods advances predictive modeling that conventionally separates growth and death models.     

Universal bio-molecular signal transduction-based nano-electronic bio-detection system

The development of rapid and ultra-sensitive detection technologies is a long-standing goal for researchers in the bio-detection fields. Nanowire field-effect transistor (nano-FET) devices have shown great promise in label-free and ultra sensitive detection of biological agents. However, critical application problems in using this technology have not been addressed, particularly the difficulties of FET sensing surface modification for various targets and lower detection specificity in real biological samples. A novel molecular signal transduction system reported herein overcomes such problems. With this system, various complicated bio-molecular interactions are “translated” into simple signal molecules with universal sequences. These signal molecules are captured on the sensing surface of nano-FET devices through sequence-specific recognition and generate detectable electronic signals. Using this system, nano-FET devices become universal for detecting almost any bio-agents. Staphylococcus aureus was used as the target to demonstrate the detection of DNA, RNA and protein on the same nano-FET device. Detection sensitivity was achieved at 25 fM levels in pure sample.     

Antimicrobial susceptibility and coagulase gene typing of Staphylococcus aureus isolated from bovine clinical mastitis cases in Turkey

The objectives of this study were to determine antimicrobial resistance patterns of Staphylococcus aureus strains isolated from bovine clinical mastitis cases and to subtype the strains by polymerase chain reaction (PCR) technique based on coagulase gene polymorphism. Two hundred sixty-five S. aureus isolates collected from individual animals in different herds (n = 235) from 1995 to 2004 were tested for susceptibility to penicillin, ampicillin, amoxicillin-clavulanate, oxacillin, oxytetracycline, enrofloxacin, kanamycin-cephalexin, and trimethoprim-sulfamethoxazole using the agar disc diffusion test. Strains were also tested for β-lactamase production. A total of 29.8% of the strains were susceptible to all antimicrobial agents tested. The highest resistance was observed in 63.3% of the strains against β-lactam antibiotics, penicillin and ampicillin. Oxytetracycline resistance was observed in 27.9% of the strains, either alone or in combination with β-lactams. No resistance was detected for amoxicillin-clavulanate, oxacillin, enrofloxacin and kanamycin-cephalexin. β-Lactamase production and resistance to β-lactam antibiotics were usually correlated. Resistance against β-lactams increased from 43.5% in 1995 to 58 to 77% from 1999 to 2004.One hundred twenty-five strains were examined for coagulase gene polymorphism. The isolates were subtyped into 4 types by coagulase gene-based PCR. A predominant 1000-bp PCR product was observed in 60.8% of the isolates typed. The results indicate that a few coagulase gene types of S. aureus are responsible for the majority of bovine clinical mastitis cases in one province of Central Anatolia region, Turkey.     

Technological activities of Staphylococcus carnosus and Staphylococcus simulans strains isolated from fermented sausages

The aim of this study was to determine the technological properties of 2 strains of Staphylococcus simulans (Ssm12, Ssm21) and 4 strains of S. carnosus (SC28, SC31, SC54 and SC55) for the selection of a potential starter cultures to employ in the processing of dry fermented sausages. The strains were studied to evaluate nitrate reductase, proteolytic, lipolytic, decarboxylase and antioxidant activities as well as growth ability at different temperatures, pH and NaCl concentrations. Nitrate reductase activity was determined at 15, 20 and 30 °C. By spectrophotometric method all the strains were able to reduce nitrate to nitrite at the different temperatures but these results were not confirmed by the agar plate method. Antioxidant and lipolytic activities were evaluated by spectrophotometric assay. All the strains showed antioxidative enzymes superoxide dismutase (SOD) and catalase whereas all appeared unable to hydrolyse pork fat. Proteolytic activity was determined by agar plate method, spectrophotometric assay (OPA) and sodium dodecyl sulphate gel-electrophoresis (SDS–PAGE) and all strains appeared to be able to hydrolyse sarcoplasmic proteins but not myofibrillar proteins. Finally, all the strains grew at 15 and 20 °C, in presence of 10%, 15% and 20% of NaCl and at pH 5.0 and 5.5 and were unable to produce histamine, cadaverine and putrescine. The results showed that all strains studied possess useful technological activities that would make them eligible as a good starter cultures for fermented sausages.