Growth of food-borne pathogenic bacteria in oil-in-water emulsions: I—Methods for investigating the form of growth

Methods are presented for investigating the site and form of growth of bacteria in model oil-in-water emulsions and in dairy cream. Following growth of the bacteria, the continuous aqueous phase is gelled using agarose and the oil phase removed using a mixture of chloroform and methanol. Using this method, the authors have found that Listeria monocytogenes, Salmonella typhimurium and Yersinia enterocolitica grow in the form of colonies in concentrated oil-in-water emulsions. Colonies of L. monocytogenes and Y. enterocolitica also form in artificially-inoculated fresh and tinned dairy cream. If information about the precise site of growth is not required, the authors have discovered that intact colonies can be liberated from the model emulsions by dissolving away the oil phase with chloroform: methanol.     

Effect of temperature on growth parameters of psychrophilic bacteria and yeasts

Three bacterial (Pedobacter heparinus, Pedobacter piscium, Pedobacter cryoconitis) and three yeast strains (Saccharomyces cerevisiae, Leucosporidiella creatinivora, Rhodotorula glacialis) of different thermal classes (mesophiles and psychrophiles) were tested for the effect of temperature on a range of growth parameters, including optical density, viable cell numbers, and cell dry mass, in order to determine the temperature conditions under which maximum biomass formation is obtained. Maximum values of growth parameters obtained at the stationary growth phase of the strains were used for statistical calculation. Temperature had a significant (P ≤ 0.05) effect on all growth parameters for each strain; correlations between the growth parameters were significant (P ≤ 0.05–0.01). The maximum growth temperature or the temperature at which microbial growth was fastest was in no case the temperature at which the investigated strains produced the highest amount of biomass. All tested psychrophilic bacteria and yeast strains produced highest amounts of cells (as calculated per mg cell dry mass or per OD₆₀₀ unit) at 1°C, while cell numbers of mesophiles were highest at 20°C. Thus, cultivation temperatures close to the maximum growth temperature are not appropriate for studying psychrophiles.     

Influence of host and bacteriophage concentrations on the inactivation of food-borne pathogenic bacteria by two phages

To use bacteriophages (phages) to control food-borne pathogenic bacteria, it will be necessary to determine the conditions allowing optimal activity. To start exploring these conditions, a Salmonella phage (P7) and a Campylobacter phage (Cj6) were incubated with their respective hosts at 24 °C for up to 2 h at varying phage and host cell concentrations, and surviving host cells were enumerated. A quadratic polynomial equation was fitted to the inactivation data and contour maps of inactivation against log₁₀ phage and host concentrations were plotted. Inactivation of Salmonella by P7 seemed to be independent of the host concentration, with close to 100% inactivation occurring at a phage concentration of around 5 × 10⁸ PFU mL⁻¹. For Campylobacter phage Cj6, there appeared to be an interaction of both phage and host concentrations. The data obtained were largely consistent with prior work indicating that, at low host cell concentrations, the proportion of cells killed is independent of the host cell concentration. The data indicate that biocontrol of pathogens present in low numbers in liquid foods is achievable, given a sufficiently high concentration of added phages, and that it is not necessary to know the concentration of pathogens to achieve this.     

Liposome-stabilized oil-in-water emulsions as adjuvants: increased emulsion stability promotes induction of cytotoxic T lymphocytes against an HIV envelope antigen

Protective or therapeutic immunity against HIV infection is currently believed to require both antibody and CTL responses against the envelope protein. In the present study, the adjuvant activity of a unique oil-in-water emulsion, in which liposomes containing lipid A (LA) and encapsulated antigen served as the emulsifying agent, was examined in mice using oligomeric gp140 (ogp140) derived from the HIV-1 envelope as the antigen. Emulsions rendered either highly stable or unstable by altering the ratio of liposomes to oil were used to examine the effect of stability of the emulsion on adjuvant activity. Stable and unstable emulsions had similar potencies for inducing both IgG antibodies to ogp140 and antigen-specific T-lymphocyte proliferation. Stable emulsions, but not unstable emulsions, induced antigen-specific CTL responses, possibly because of the depot effect of the stable emulsions. Furthermore, stable emulsions induced lower IgG2a/IgG1 ratios than the unstable emulsions. We conclude that stable liposomal oil-in-water emulsions provide an effective means of obtaining both antibody and CTL responses against an HIV envelope antigen.     

Population structure and evolutionary dynamics of pathogenic bacteria

Evidence concerning the significance of recombination within natural bacterial populations has historically come from two main sources: multilocus enzyme electrophoresis (MLEE) and nucleotide sequence data. Here we discuss evidence from a third method, multilocus sequence typing (MLST), which is a development of MLEE based on nucleotide sequencing that combines the advantages of both approaches. MLST has confirmed both the existence of clones and the high rates of recombination for several bacterial pathogens. The data are consistent with "epidemic" population structures, where clones are superimposed upon a backdrop of frequent recombination, thus, in the short term, resisting the homogenising effect of recombination. The nature of the selective advantage of clones, however, and how this advantage relates to virulence are unclear. The current evidence also has broader implications concerning bacterial species definition, the management of antibiotic-resistant bacteria and the assessment of the dangers of releasing genetically modified organisms into the environment.     

Effect of perfluorocarbon emulsions on rheological parameters of blood

The effect of a perfluorocarbon emulsion on the rheological parameters of blood in a living organism at the hematocrit twice lower than the norm was studied. It was shown that an increase in emulsion concentration leads to an increase in blood asymptotic viscosity and the aggregation of erythrocytes. It was concluded that only a small volume of the fluorocarbon phase of particles, as compared with the total amount of erythrocytes, can improve the blood fluidity upon disturbed circulation.     

Effect of lactose monolaurate on pathogenic and nonpathogenic bacteria

The antimicrobial activities of sucrose monolaurate and a novel ester, lactose monolaurate (LML), were tested. Gram-positive bacteria were more susceptible than Gram-negative bacteria to both esters. The minimal bactericidal concentrations of LML were 5 to 9.5 mM for Listeria monocytogenes isolates and 0.2 to 2 mM for Mycobacterium isolates.     

Diallyl sulfide content and antimicrobial activity against food-borne pathogenic bacteria of chives (Allium schoenoprasum)

Chives, a member of the Alliaceae family, have been used in food and medicine in Thailand for a long time. Diallyl sulfides (diallyl monosulfide, dially disulfide, diallyl trisulfide, and diallyl tetrasulfide) are believed to be responsible for the antimicrobial activity of plants in this family. In this study, chive oil was examined for its diallyl sulfide content and its antimicrobial activity against some strains of food-borne pathogenic bacteria. Chive oil had a very low concentration of diallyl monosulfide in comparison with the other diallyl sulfides. They inhibited all pathogenic bacteria used in this study with a different degree of inhibition. Chive oil was also shown to be able to inhibit Escherichia coli O157:H7 in a food model. This study is the first report describing not only the diallyl disulfide content of chive oil, but also its antimicrobial activity against food-borne pathogens in both a test tube and food model.     

Differential effects of catecholamines on in vitro growth of pathogenic bacteria

Supplementation of minimal medium inoculated with bacterial cultures with norepinephrine, epinephrine, dopamine, or isoproterenol resulted in marked increases in growth compared to controls. Norepinephrine and dopamine had the greatest enhancing effects on growth of cultures of Pseudomonas aeruginosa and Klebsiella pneumoniae, while epinephrine and isoproterenol also enhanced growth to a lesser extent. The growth of Escherichia coli in the presence of norepinephrine was greater than growth in the presence of the three other neurochemicals used in the study. Growth of Staphylococcus aureus was also enhanced in the presence of norepinephrine, but not to the same degree as was the growth of gram negative bacteria. Addition of culture supernatants from E. coli cultures that had been grown in the presence of norepinephrine was able to enhance the growth of K. pneumoniae. Addition of the culture supernatant fluid culture from E. coli cultures that had been grown in the presence of norepinephrine did not enhance growth of P. aeruginosa or S. aureus. Culture supernatant fluids from bacteria other than E. coli grown in the presence of norepinephrine were not able to enhance the growth of any bacteria tested. The results suggest that catecholamines can enhance growth of pathogenic bacteria, which may contribute to development of pathogenesis; however, there is no uniform effect of catecholamines on bacterial growth.     

A synthetic analog of plantaricin 149 inhibiting food-borne pathogenic bacteria:evidence for alpha-helical conformation involved in bacteria-membrane interaction.

Plantaricin-149 is a bacteriocin produced by Lactobacillus plantarum NRIC 149 (a LAB isolated from pineapple), which consists of a peptidic chain made up of 22 amino acid residues [Kato et al. J. Ferment. Bioeng. 1994; 77: 277-282]. In this work, a synthetic C-terminal amidated peptide analog denoted Pln149a was prepared by SPPS-Fmoc chemistry and the antagonistic activity against gram-positive and gram-negative bacteria was tested. The secondary structure was studied by circular dichroism (CD) and the vicinity of the tyrosine residue by fluorescence spectroscopy under different conditions. We report the results of the interaction of Pln149a with reverse micelles prepared from the amphiphilic AOT in cyclohexane.Synthetic plantaricin was active against one strain of Staphylococcus aureus and four strains of Listeria genus at pH 5.5 and 7.4 and, like its natural variant, inhibited L. plantarum ATCC 8014.The data derived from spectroscopic measurements in presence of AOT reverse micelles suggest that the secondary structure of the peptide upon interaction is an alpha-helix. In this membrane model, the hydrophobic side of the alpha-helix is inserted into the micelles, leaving the lysines exposed to the solvent and interacting with the polar moieties of AOT. The fluorescence data point out that the N-terminal tyrosine residue is close to the micellar interface.     

Small colony variants: a pathogenic form of bacteria that facilitates persistent and recurrent infections

Small colony variants constitute a slow-growing subpopulation of bacteria with distinctive phenotypic and pathogenic traits. Phenotypically, small colony variants have a slow growth rate, atypical colony morphology and unusual biochemical characteristics, making them a challenge for clinical microbiologists to identify. Clinically, small colony variants are better able to persist in mammalian cells and are less susceptible to antibiotics than their wild-type counterparts, and can cause latent or recurrent infections on emergence from the protective environment of the host cell. This Review covers the phenotypic, genetic and clinical picture associated with small colony variants, with an emphasis on staphylococci, for which the greatest amount of information is available.     

Catecholamines and in vitro growth of pathogenic bacteria: enhancement of growth varies greatly among bacterial species

The purpose of this study was to examine the effects of catecholamines on in vitro growth of a range of bacterial species, including anaerobes. Bacteria tested included: Porphyromonas gingivalis, Bacteriodes fragilis, Shigella boydii, Shigella sonnie, Enterobacter Sp, and Salmonella choleraesuis. The results of the current study indicated that supplementation of bacterial cultures in minimal medium with norepinephrine or epinephrine did not result in increased growth of bacteria. Positive controls involving treatment of Escherichia coli with catecholamines did result in increased growth of that bacterial species. The results of the present study extend previous observations that showed differential capability of catecholamines to enhance bacterial growth in vitro.     

Growth inhibition of selected food-borne bacteria by tannic acid, propyl gallate and related compounds

Tannic acid, propyl gallate, gallic acid and ellagic acid were tested for their inhibitory effects on selected food-borne bacteria by the well assay technique. Tannic acid and propyl gallate were inhibitory whereas gallic acid and ellagic acid were not.     

Association with pathogenic bacteria affects life‐history traits and population growth in Caenorhabditis elegans

Determining the relationship between individual life‐history traits and population dynamics is an essential step to understand and predict natural selection. Model organisms that can be conveniently studied experimentally at both levels are invaluable to test the rich body of theoretical literature in this area. The nematode Caenorhabditis elegans, despite being a well‐established workhorse in genetics, has only recently received attention from ecologists and evolutionary biologists, especially with respect to its association with pathogenic bacteria. In order to start filling the gap between the two areas, we conducted a series of experiments aiming at measuring life‐history traits as well as population growth of C. elegans in response to three different bacterial strains: Escherichia coli OP50, Salmonella enterica Typhimurium, and Pseudomonas aeruginosa PAO1. Whereas previous studies had established that the latter two reduced the survival of nematodes feeding on them compared to E. coli OP50, we report for the first time an enhancement in reproductive success and population growth for worms feeding on S. enterica Typhimurium. Furthermore, we used an age‐specific population dynamic model, parameterized using individual life‐history assays, to successfully predict the growth of populations over three generations. This study paves the way for more detailed and quantitative experimental investigation of the ecology and evolution of C. elegans and the bacteria it interacts with, which could improve our understanding of the fate of opportunistic pathogens in the environment.     

大白菜软腐菌种群组成及优势菌致病型的研究

对黑龙江省成熟大白菜[Brassica pekinensis（Lour．）Rupr．]生产田采集的软腐病菌进行分离、纯化,并根据形态学特征分析了大白菜软腐病菌的种群组成。结果表明,引起黑龙江省秋季大白菜软腐病的主要致病菌是胡萝卜软腐欧文氏菌胡萝卜软腐亚种[Erwinia carotovora（Jones）Bergey et al．subsp、carotovora]（Ecc）;利用20个Ecc菌株的混合菌对来源于不同生态型及不同地区的大白菜品种进行接种,筛选出5个鉴别寄主,以此将20个Ecc菌株划分为5个致病力类型,其中V型为优势致病菌,其分布广且致病力强。