bluuebunny/crossref_metadata_2025_split huggingface dataset:
Estimation of
Staphylococcus aureus
Growth Parameters from Turbidity Data: Characterization of Strain Variation and Comparison of Methods
Authors: Lindqvist R. 
Published: July 2006

ABSTRACT

Turbidity methods offer possibilities for generating data required for addressing microorganism variability in risk modeling given that the results of these methods correspond to those of viable count methods. The objectives of this study were to identify the best approach for determining growth parameters based on turbidity data and use of a Bioscreen instrument and to characterize variability in growth parameters of 34
Staphylococcus aureus
strains of different biotypes isolated from broiler carcasses. Growth parameters were estimated by fitting primary growth models to turbidity growth curves or to detection times of serially diluted cultures either directly or by using an analysis of variance (ANOVA) approach. The maximum specific growth rates in chicken broth at 17°C estimated by time to detection methods were in good agreement with viable count estimates, whereas growth models (exponential and Richards) underestimated growth rates. Time to detection methods were selected for strain characterization. The variation of growth parameters among strains was best described by either the logistic or lognormal distribution, but definitive conclusions require a larger data set. The distribution of the physiological state parameter ranged from 0.01 to 0.92 and was not significantly different from a normal distribution. Strain variability was important, and the coefficient of variation of growth parameters was up to six times larger among strains than within strains. It is suggested to apply a time to detection (ANOVA) approach using turbidity measurements for convenient and accurate estimation of growth parameters. The results emphasize the need to consider implications of strain variability for predictive modeling and risk assessment.
Simulating the Contribution of Coaggregation to Interspecies Hydrogen Fluxes in Syntrophic Methanogenic Consortia
Authors: Ishii Shun'ichi , Kosaka Tomoyuki , Hotta Yasuaki , Watanabe Kazuya 
Published: July 2006

ABSTRACTA simple model (termed the syntrophy model) for simulating the contribution of coaggregation to interspecies hydrogen fluxes between syntrophic bacteria and methanogenic archaea is described. We applied it to analyzing partially aggregated syntrophic cocultures with various substrates, revealing that large fractions of hydrogen molecules were fluxed in aggregates.
Asymmetrical Interactions betweenWolbachiaandSpiroplasmaEndosymbionts Coexisting in the Same Insect Host
Authors: Goto Shunsuke , Anbutsu Hisashi , Fukatsu Takema 
Published: July 2006

ABSTRACTWe investigated the interactions between the endosymbiontsWolbachia pipientisstrainwMel andSpiroplasmasp. strain NSRO coinfecting the host insectDrosophila melanogaster. By making use of antibiotic therapy, temperature stress, and hemolymph microinjection, we established the following strains in the same host genetic background: the SW strain, infected with bothSpiroplasmaandWolbachia; the S strain, infected withSpiroplasmaonly; and the W strain, infected withWolbachiaonly. The infection dynamics of the symbionts in these strains were monitored by quantitative PCR during host development. The infection densities ofSpiroplasmaexhibited no significant differences between the SW and S strains throughout the developmental course. In contrast, the infection densities ofWolbachiawere significantly lower in the SW strain than in the W strain at the pupal and young adult stages. These results indicated that the interactions between the coinfecting symbionts were asymmetrical, i.e.,Spiroplasmaorganisms negatively affected the population ofWolbachiaorganisms, whileWolbachiaorganisms did not influence the population ofSpiroplasmaorganisms. In the host body, the symbionts exhibited their own tissue tropisms: among the tissues examined,Spiroplasmawas the most abundant in the ovaries, whileWolbachiashowed the highest density in Malpighian tubules. Strikingly, basically noWolbachiaorganisms were detected in hemolymph, the principal location ofSpiroplasma. These results suggest that different host tissues act as distinct microhabitats for the symbionts and that the lytic process in host metamorphosis might be involved in the asymmetrical interactions between the coinfecting symbionts.
Isolation and Characterization of
Listeria monocytogenes
Isolates from Ready-To-Eat Foods in Florida
Authors: Shen Yuelian , Liu Yan , Zhang Yifan , Cripe Jennifer , Conway William , Meng Jianghong , Hall Grace , Bhagwat Arvind A. 
Published: July 2006

ABSTRACT

Of 3,063 ready-to-eat food samples tested, 91 (2.97%) were positive for
Listeria monocytogenes
, and lineage 1 strains outnumbered lineage 2 strains 57 to 34. Seventy-one isolates (78%) exhibited multiple antibiotic resistance, and an
L. monocytogenes
-specific bacteriophage cocktail lysed 65 of 91 (71%) isolates. Determining phage, acid, and antibiotic susceptibility phenotypes enabled us to identify differences among strains which were otherwise indistinguishable by conventional methods.
A Functional
mobA
Gene for Molybdopterin Cytosine Dinucleotide Cofactor Biosynthesis Is Required for Activity and Holoenzyme Assembly of the Heterotrimeric Nicotine Dehydrogenases of
Arthrobacter nicotinovorans
Authors: Sachelaru Paula , Schiltz Emile , Brandsch Roderich 
Published: July 2006

ABSTRACT

Two
Arthrobacter nicotinovorans
molybdenum enzymes hydroxylate the pyridine ring of nicotine. Molybdopterin cytosine dinucleotide (MCD) was determined to be a cofactor of these enzymes. A
mobA
gene responsible for the formation of MCD could be identified and its function shown to be required for assembly of the heterotrimeric molybdenum enzymes.
Changes in the Spoilage-Related Microbiota of Beef during Refrigerated Storage under Different Packaging Conditions
Authors: Ercolini Danilo , Russo Federica , Torrieri Elena , Masi Paolo , Villani Francesco 
Published: July 2006

ABSTRACT

The microbial spoilage of beef was monitored during storage at 5°C under three different conditions of modified-atmosphere packaging (MAP): (i) air (MAP1), (ii) 60% O
2
and 40% CO
2
(MAP2), and (iii) 20% O
2
and 40% CO
2
(MAP3).
Pseudomonas
,
Enterobacteriaceae
,
Brochothrix thermosphacta
, and lactic acid bacteria were monitored by viable counts and PCR-denaturing gradient gel electrophoresis (DGGE) analysis during 14 days of storage. Moreover, headspace gas composition, weight loss, and beef color change were also determined at each sampling time. Overall, MAP2 was shown to have the best protective effect, keeping the microbial loads and color change to acceptable levels in the first 7 days of refrigerated storage. The microbial colonies from the plate counts of each microbial group were identified by PCR-DGGE of the variable V6-V8 region of the 16S rRNA gene. Thirteen different genera and at least 17 different species were identified after sequencing of DGGE fragments that showed a wide diversity of spoilage-related bacteria taking turns during beef storage in the function of the packaging conditions. The countable species for each spoilage-related microbial group were different according to packaging conditions and times of storage. In fact, the DGGE profiles displayed significant changes during time and depending on the initial atmosphere used. The spoilage occurred between 7 and 14 days of storage, and the microbial species found in the spoiled meat varied according to the packaging conditions.
Rahnella aquatilis
,
Rahnella
spp.,
Pseudomonas
spp., and
Carnobacterium divergens
were identified as acting during beef storage in air (MAP1).
Pseudomonas
spp. and
Lactobacillus sakei
were found in beef stored under MAP conditions with high oxygen content (MAP2), while
Rahnella
spp. and
L. sakei
were the main species found during storage using MAP3. The identification of the spoilage-related microbiota by molecular methods can help in the effective establishment of storage conditions for fresh meat.
Citrate Inhibition-Resistant Form of 6-Phosphofructo-1-Kinase fromAspergillus niger
Authors: Mlakar Tina , Legiša Matic 
Published: July 2006

ABSTRACTTwo forms ofAspergillus niger6-phosphofructo-1-kinase (PFK1) have been described recently, the 85-kDa native enzyme and 49-kDa shorter fragment that is formed from the former by posttranslational modification. So far, kinetic characteristics have never been determined on the enzyme purified to near homogeneity. For the first time, kinetic parameters were determined for individual enzymes with respect to citrate inhibition. The native 85-kDa enzyme was found to be moderately inhibited by citrate, with theKivalue determined to be 1.5 mM, in the system with 5 mM Mg2+ions, while increasing magnesium concentrations relieved the negative effect of citrate. An identical inhibition coefficient was determined also in the presence of ammonium ions, although ammonium acted as a strong activator of enzyme activity. On the other hand, the shorter fragment of PFK1 proved to be completely resistant to inhibition by citrate. Allosteric citrate binding sites were most probably lost after the truncation of the C-terminal part of the native protein, in which region some binding sites for inhibitor are known to be located. At near physiological conditions, characterized by low fructose-6-phosphate concentrations, a much higher efficiency of the shorter fragment was observed during an in vitro experiment. Since the enzyme became more susceptible to the positive control by specific ligands, while the negative control was lost after posttranslational modification, the shorter PFK1 fragment seems to be the enzyme most responsible for generating undisturbed metabolic flow through glycolysis inA. nigercells.
Caenorhabditis elegans
Senses Bacterial Autoinducers
Authors: Beale Elmus , Li Guigen , Tan Man-Wah , Rumbaugh Kendra P. 
Published: July 2006

ABSTRACT

Pseudomonas aeruginosa
uses virulence factors controlled by quorum sensing (QS) to kill
Caenorhabditis elegans
. Here we show that
C. elegans
is attracted to the acylated homoserine lactones (AHSLs) that mediate QS in
P. aeruginosa
. Our data also indicate that
C. elegans
can distinguish AHSLs and may use them to mediate aversive or attractive learning.
Saccharomyces cerevisiae
-Based Molecular Tool Kit for Manipulation of Genes from Gram-Negative Bacteria
Authors: Shanks Robert M. Q. , Caiazza Nicky C. , Hinsa Shannon M. , Toutain Christine M. , O'Toole George A. 
Published: July 2006

ABSTRACT

A tool kit of vectors was designed to manipulate and express genes from a wide range of gram-negative species by using in vivo recombination.
Saccharomyces cerevisiae
can use its native recombination proteins to combine several amplicons in a single transformation step with high efficiency. We show that this technology is particularly useful for vector design. Shuttle, suicide, and expression vectors useful in a diverse group of bacteria are described and utilized. This report describes the use of these vectors to mutate
clpX
and
clpP
of the opportunistic pathogen
Pseudomonas aeruginosa
and to explore their roles in biofilm formation and surface motility. Complementation of the rhamnolipid biosynthetic gene
rhlB
is also described. Expression vectors are used for controlled expression of genes in two pseudomonad species. To demonstrate the facility of building complicated constructs with this technique, the recombination of four PCR-generated amplicons in a single step at >80% efficiency into one of these vectors is shown. These tools can be used for genetic studies of pseudomonads and many other gram-negative bacteria.
Colonization Dynamics of Altered Schaedler Flora Is Influenced by Gender, Aging, and
Helicobacter hepaticus
Infection in the Intestines of Swiss Webster Mice
Authors: Ge Zhongming , Feng Yang , Taylor Nancy S. , Ohtani Masahiro , Polz Martin F. , Schauer David B. , Fox James G. 
Published: July 2006

ABSTRACT

The distribution and colonization levels of the altered Schaedler flora (ASF) in their natural hosts are poorly understood. Intestinal colonization levels of the eight ASF strains in outbred Swiss Webster mice with or without
Helicobacter hepaticus
infection were characterized by real-time quantitative PCR. All ASF strains were detected in the cecum and colon, but some strains displayed significant variation in colonization levels with host age, gender, and
H. hepaticus
infection status.
Functional Heterogeneity of RpoS in Stress Tolerance of Enterohemorrhagic
Escherichia coli
Strains
Authors: Bhagwat Arvind A. , Tan Jasmine , Sharma Manan , Kothary Mahendra , Low Sharon , Tall Ben D. , Bhagwat Medha 
Published: July 2006

ABSTRACT

The stationary-phase sigma factor (RpoS) regulates many cellular responses to environmental stress conditions such as heat, acid, and alkali shocks. On the other hand, mutations at the
rpoS
locus have frequently been detected among pathogenic as well as commensal strains of
Escherichia coli
. The objective of this study was to perform a functional analysis of the RpoS-mediated stress responses of enterohemorrhagic
E. coli
strains from food-borne outbreaks.
E. coli
strains belonging to serotypes O157:H7, O111:H11, and O26:H11 exhibited polymorphisms for two phenotypes widely used to monitor
rpoS
mutations, heat tolerance and glycogen synthesis, as well as for two others, alkali tolerance and adherence to Caco-2 cells. However, these strains synthesized the oxidative acid resistance system through an
rpoS
-dependent pathway. During the transition from mildly acidic growth conditions (pH 5.5) to alkaline stress (pH 10.2), cell survival was dependent on
rpoS
functionality. Some strains were able to overcome negative regulation by RpoS and induced higher β-galactosidase activity without compromising their acid resistance. There were no major differences in the DNA sequences in the
rpoS
coding regions among the tested strains. The heterogeneity of
rpoS
-dependent phenotypes observed for stress-related phenotypes was also evident in the Caco-2 cell adherence assay. Wild-type O157:H7 strains with native
rpoS
were less adherent than
rpoS
-complemented counterpart strains, suggesting that
rpoS
functionality is needed. These results show that some pathogenic
E. coli
strains can maintain their acid tolerance capability while compromising other RpoS-dependent stress responses. Such adaptation processes may have significant impact on a pathogen's survival in food processing environments, as well in the host's stomach and intestine.
Survival of Yogurt Bacteria in the Human Gut
Authors: Elli Marina , Callegari Maria Luisa , Ferrari Susanna , Bessi Elena , Cattivelli Daniela , Soldi Sara , Morelli Lorenzo , Goupil Feuillerat Nathalie , Antoine Jean-Michel 
Published: July 2006

ABSTRACT

Whether
Lactobacillus delbrueckii
subsp.
bulgaricus
and
Streptococcus thermophilus
can be recovered after passage through the human gut was tested by feeding 20 healthy volunteers commercial yogurt. Yogurt bacteria were found in human feces, suggesting that they can survive transit in the gastrointestinal tract.
Effects ofGPD1Overexpression inSaccharomyces cerevisiaeCommercial Wine Yeast Strains LackingALD6Genes
Authors: Cambon Brigitte , Monteil Virginie , Remize Fabienne , Camarasa Carole , Dequin Sylvie 
Published: July 2006

ABSTRACTThe utilization ofSaccharomyces cerevisiaestrains overproducing glycerol and with a reduced ethanol yield is a potentially valuable strategy for producing wine with decreased ethanol content. However, glycerol overproduction is accompanied by acetate accumulation. In this study, we evaluated the effects of the overexpression ofGPD1, coding for glycerol-3-phosphate dehydrogenase, in three commercial wine yeast strains in which the two copies ofALD6encoding the NADP+-dependent Mg2+-activated cytosolic acetaldehyde dehydrogenase have been deleted. Under wine fermentation conditions, the engineered industrial strains exhibit fermentation performance and growth properties similar to those of the wild type. Acetate was produced at concentrations similar to that of the wild-type strains, whereas sugar was efficiently diverted to glycerol. The ethanol yield of theGPD1 ald6industrial strains was 15 to 20% lower than that in the controls. However, these strains accumulated acetoin at considerable levels due to inefficient reduction to 2,3-butanediol. Due to the low taste and odor thresholds of acetoin and its negative sensorial impact on wine, novel engineering strategies will be required for a proper adjustment of the metabolites at the acetaldehyde branch point.
Phenotypic Properties and Microbial Diversity of Methanogenic Granules from a Full-Scale Upflow Anaerobic Sludge Bed Reactor Treating Brewery Wastewater
Authors: Díaz Emiliano E. , Stams Alfons J. M. , Amils Ricardo , Sanz José L. 
Published: July 2006

ABSTRACTMethanogenic granules from an anaerobic bioreactor that treated wastewater of a beer brewery consisted of different morphological types of granules. In this study, the microbial compositions of the different granules were analyzed by molecular microbiological techniques: cloning, denaturing gradient gel electrophoresis and fluorescent in situ hybridization (FISH), and scanning and transmission electron microscopy. We propose here that the different types of granules reflect the different stages in the life cycle of granules. Young granules were small, black, and compact and harbored active cells. Gray granules were the most abundant granules. These granules have a multilayer structure with channels and void areas. The core was composed of dead or starving cells with low activity. The brown granules, which were the largest granules, showed a loose and amorphous structure with big channels that resulted in fractured zones and corresponded to the older granules.Firmicutes(as determined by FISH) andNitrospiraandDeferribacteres(as determined by cloning and sequencing) were the predominantBacteria. Remarkably,Firmicutescould not be detected in the brown granules. The methanogenicArchaeaidentified wereMethanosaeta concilii(70 to 90% by FISH and cloning),Methanosarcina mazei, andMethanospirillumspp. The phenotypic appearance of the granules reflected the physiological condition of the granules. This may be valuable to easily select appropriate seed sludges to start up other reactors.
Effects of Low-Shear Modeled Microgravity on Cell Function, Gene Expression, and Phenotype in
Saccharomyces cerevisiae
Authors: Purevdorj-Gage B. , Sheehan K. B. , Hyman L. E. 
Published: July 2006

ABSTRACT

Only limited information is available concerning the effects of low-shear modeled microgravity (LSMMG) on cell function and morphology. We examined the behavior of
Saccharomyces cerevisiae
grown in a high-aspect-ratio vessel, which simulates the low-shear and microgravity conditions encountered in spaceflight. With the exception of a shortened lag phase (90 min less than controls;
P
< 0.05), yeast cells grown under LSMMG conditions did not differ in growth rate, size, shape, or viability from the controls but did differ in the establishment of polarity as exhibited by aberrant (random) budding compared to the usual bipolar pattern of controls. The aberrant budding was accompanied by an increased tendency of cells to clump, as indicated by aggregates containing five or more cells. We also found significant changes (greater than or equal to twofold) in the expression of genes associated with the establishment of polarity (
BUD5
), bipolar budding (
RAX1
,
RAX2
, and
BUD25
), and cell separation (
DSE1
,
DSE2
, and
EGT2
). Thus, low-shear environments may significantly alter yeast gene expression and phenotype as well as evolutionary conserved cellular functions such as polarization. The results provide a paradigm for understanding polarity-dependent cell responses to microgravity ranging from pathogenesis in fungi to the immune response in mammals.
The Cell Lysis Activity of the
Streptococcus agalactiae
Bacteriophage B30 Endolysin Relies on the Cysteine, Histidine-Dependent Amidohydrolase/Peptidase Domain
Authors: Donovan David M. , Foster-Frey Juli , Dong Shengli , Rousseau Geneviève M. , Moineau Sylvain , Pritchard David G. 
Published: July 2006

ABSTRACT

The
Streptococcus agalactiae
bacteriophage B30 endolysin contains three domains: cysteine, histidine-dependent amidohydrolase/peptidase (CHAP), Acm glycosidase, and the SH3b cell wall binding domain. Truncations and point mutations indicated that the Acm domain requires the SH3b domain for activity, while the CHAP domain is responsible for nearly all the cell lysis activity.
Persisting Immune Responses Indicating Long-Term Protection after Booster Dose with Meningococcal Group B Outer Membrane Vesicle Vaccine
Authors: Feiring Berit , Fuglesang Jan , Oster Philipp , Næss Lisbeth M. , Helland Oddveig S. , Tilman Sandrine , Rosenqvist Einar , Bergsaker Marianne A. R. , Nøkleby Hanne , Aaberge Ingeborg S. 
Published: July 2006

ABSTRACT

MenBvac is an outer membrane vesicle vaccine against systemic meningococcal disease caused by serogroup B
Neisseria meningitidis
. In this placebo-controlled double-blind study including 374 healthy adolescents, the safety and immunogenicity of a schedule of three primary doses 6 weeks apart followed by a fourth dose a year later were evaluated. Antibody responses to the vaccine strain and heterologous strains (non-vaccine-type strains) and the persistence of these antibodies were measured by the serum bactericidal assay (SBA) and enzyme-linked immunosorbent assay up to 1 year after the last dose. The proportion of subjects with SBA titers of ≥4 against the vaccine strain increased from 3% prevaccination to 65% after the third dose. Ten months later, this proportion had declined to 28%. The fourth dose induced a booster response demonstrated by 93% of subjects achieving a titer of ≥4. One year after the booster dose, 64% still showed SBA titers of ≥4. Cross-reacting antibodies were induced against all heterologous strains tested, although the magnitude of SBA titers differed widely between the different strains. All four doses of MenBvac were safe. Both MenBvac and the placebo had reactogenicity profiles of mild to moderate local and systemic reactions. Pain, the most common reaction, was reported with similar frequencies in both groups. No serious adverse events occurred in the MenBvac group. This study confirmed the good immunogenicity of the primary course of MenBvac and demonstrated prolonged persistence and increased cross-reactivity of functional antibodies elicited by a booster dose.
Factors Associated with Immunoglobulin G Subclass Polarization in Naturally Acquired Antibodies to
Plasmodium falciparum
Merozoite Surface Proteins: a Cross-Sectional Survey in Brazilian Amazonia
Authors: Scopel Kézia K. G. , Fontes Cor J. F. , Ferreira Marcelo U. , Braga Érika M. 
Published: July 2006

ABSTRACT

We investigated immunoglobulin G (IgG) subclass antibody responses to
Plasmodium falciparum
merozoite surface protein 1 (MSP-1) and MSP-2 in 112 malaria-exposed subjects in Brazil. IgG3 polarization was primarily epitope driven, being little affected by cumulative or current exposure to malaria and not affected by a subject's age and Fcγ receptor IIA genotype.