bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparative Evaluation of the VITEK 2, Disk Diffusion, Etest, Broth Microdilution, and Agar Dilution Susceptibility Testing Methods for Colistin in Clinical Isolates, Including Heteroresistant
Enterobacter cloacae
and
Acinetobacter baumannii
Strains
Authors: Lo-Ten-Foe Jerome R. , de Smet Anne Marie G. A. , Diederen Bram M. W. , Kluytmans Jan A. J. W. , van Keulen Peter H. J. 
Published: July 2007

ABSTRACT

Increasing antibiotic resistance in gram-negative bacteria has recently renewed interest in colistin as a therapeutic option. The increasing use of colistin necessitates the availability of rapid and reliable methods for colistin susceptibility testing. We compared seven methods of colistin susceptibility testing (disk diffusion, agar dilution on Mueller-Hinton [MH] and Isosensitest agar, Etest on MH and Isosensitest agar, broth microdilution, and VITEK 2) on 102 clinical isolates collected from patient materials during a selective digestive decontamination or selective oral decontamination trial in an intensive-care unit. Disk diffusion is an unreliable method to measure susceptibility to colistin. High error rates and low levels of reproducibility were observed in the disk diffusion test. The colistin Etest, agar dilution, and the VITEK 2 showed a high level of agreement with the broth microdilution reference method. Heteroresistance for colistin was observed in six
Enterobacter cloacae
isolates and in one
Acinetobacter baumannii
isolate. This is the first report of heteroresistance to colistin in
E. cloacae
isolates. Resistance to colistin in these isolates seemed to be induced upon exposure to colistin rather than being caused by stable mutations. Heteroresistant isolates could be detected in the broth microdilution, agar dilution, Etest, or disk diffusion test. The VITEK 2 displayed low sensitivity in the detection of heteroresistant subpopulations of
E. cloacae
. The VITEK 2 colistin susceptibility test can therefore be considered to be a reliable tool to determine susceptibility to colistin in isolates of genera that are known not to exhibit resistant subpopulations. In isolates of genera known to (occasionally) exhibit heteroresistance, an alternative susceptibility testing method capable of detecting heteroresistance should be used.
Effect of Dosing and Dosing Frequency on the Efficacy of Ceftizoxime and the Emergence of Ceftizoxime Resistance during the Early Development of Murine Abscesses Caused by
Bacteroides fragilis
and
Enterobacter cloacae
Mixed Infection
Authors: Stearne Lorna E. T. , Goessens Wil H. F. , Mouton Johan W. , Gyssens Inge C. 
Published: July 2007

ABSTRACT

The efficacy of β-lactams is thought to be dependent on the time that the unbound concentrations exceed the MIC (
fT
>MIC). However, the pharmacokinetic/pharmacodynamic index (PDI) that correlates best to the selection of resistance is not yet clear. The selection of ceftizoxime (CZX)-resistant
Enterobacter cloacae
mutant strains during the development of murine mixed-infection abscesses was studied to determine the PDI that is important for the emergence of resistance and the PDI value needed for the prevention of resistance. Studies were carried out 24 h after inoculation with
Bacteroides fragilis
ATCC 23745 and
E. cloacae
22491. Six to 1,536 mg of CZX/kg of body weight/day given every 2 h (q2h), q4h, q6h, or q8h was started 30 min before inoculation and continued for 24 h. Resistant mutants were isolated to determine mutant frequencies (MF). The
fT
>MIC varied from 9 to 98% for
E. cloacae
, the peak concentration (unbound fraction) was 0.6 to 578 mg/liter, and the area under the concentration-time curve (unbound fraction) (
f
AUC) was 1.9 to 553 mg·h/liter. The
f
AUC-to-MIC ratio best explained the in vivo efficacy. CZX-resistant
B. fragilis
and
E. cloacae
mutants were isolated from untreated controls at an MF of 10
−5
to 10
−7
. The MF of resistant
B. fragilis
did not increase during therapy. The selection of resistant
E. cloacae
strains at an MF of 10
−1
to 10
−2
was related to the
fT
>MIC and the ratio of
f
AUC to MIC following an inverse U shape. However, the ratio of
f
AUC to MIC was the stronger driver of resistance. The highest MFs were 0.7 to 0.9 at an
f
AUC-to-MIC ratio of approximately 250. We conclude that the ratio of
f
AUC to MIC is the PDI that correlated best to the in vivo efficacy of CZX and probably also to the emergence of resistant
E. cloacae
mutants. An
f
AUC-to-MIC ratio of 1,000 was needed to prevent the emergence of this resistance.
Endogenously Synthesized (−)-proto-Quercitol and Glycine Betaine Are Principal Compatible Solutes ofSchizochytriumsp. Strain S8 (ATCC 20889) and Three New Isolates of Phylogenetically Related Thraustochytrids
Authors: Jakobsen Anita N. , Aasen Inga M. , Strøm Arne R. 
Published: July 2007

ABSTRACTWe report that endogenously synthesized (−)-proto-quercitol (1d-1,3,4/2,5-cyclohexanepentol) and glycine betaine were the principal compatible solutes ofSchizochytriumsp. strain S8 (ATCC 20889) and three new osmotolerant isolates of thraustochytrids (strains T65, T66, and T67). The compatible solutes were identified and quantified by use of nuclear magnetic resonance spectroscopy, and their identity was confirmed by mass spectroscopy and measurement of the specific optical rotation. The cellular content of compatible solutes increased with increasing NaCl concentration of a defined medium. (−)-proto-Quercitol was the dominating solute at all NaCl concentrations tested (0.25 to 1.0 M), e.g., cells of S8 and T66 stressed with 1.0 M NaCl accumulated about 500 μmol (−)-proto-quercitol and 100 μmol glycine betaine per g dry weight. To our knowledge, (−)-proto-quercitol has previously been found only in eucalyptus. The 18S rRNA gene sequences of the four (−)-proto-quercitol-producing strains showed 99% identity, and they displayed the same fatty acid profile. The only polyunsaturated fatty acids accumulated were docosahexaenoic acid (78%) and docosapentaenoic acid (22%). A less osmotolerant isolate (strain T29), which was closely phylogenetically related toThraustochytrium aureum(ATCC 34304), did not contain (−)-proto-quercitol or glycine betaine. Thus, the level of osmotolerance and the osmolyte systems vary among thraustochytrids.
Transcriptional Responses of
Enterococcus faecalis
V583 to Bovine Bile and Sodium Dodecyl Sulfate
Authors: Solheim Margrete , Aakra Ågot , Vebø Heidi , Snipen Lars , Nes Ingolf F. 
Published: July 2007

ABSTRACT

Resistance to bile is a prerequisite property of the gastrointestinal bacterial flora. Bile acids are powerful detergents, and resistance to sodium dodecyl sulfate (SDS) has therefore often been considered relevant to studies of bile resistance. We have studied the effects of bovine bile (BB) and SDS on
Enterococcus faecalis
V583 by traditional growth studies and microarrays. Transcriptional responses were studied by time course experiments. In the presence of BB (V583-BB) or SDS (V583-SDS), 308 and 209 genes were identified as differentially expressed at one or more time points, respectively. In V583 treated with both BB and SDS (V583-BB-SDS), 254 genes showed differential expression. Detergents exert their toxic effects primarily on the microbial membrane. The enrichment of differentially transcribed genes that encode proteins with membrane-associated functions and/or locations indicates a major impact of all three treatments on the integrity and functionality of the cell membrane. Two gene clusters involved in fatty acid biosynthesis were repressed in V583-BB and V583-BB-SDS and partly induced in V583-SDS. Furthermore, two EmrB/QacA family drug resistance transporters and a vacuolar-type ATPase were induced in V583-BB and V583-BB-SDS. None of the putative bile salt hydrolase homologs in V583 showed differential expression during the bile treatments. The transcriptional profile of V583-BB-SDS was qualitatively more similar to the response in V583-BB than to that in V583-SDS, suggesting that the presence of bile suppresses the effects of SDS in V583-BB-SDS. The overall results presented here indicate that different mechanisms are involved in detergent resistance in
E. faecalis
.
No Evidence of an Impact on the Rhizosphere Diazotroph Community by the Expression of
Bacillus thuringiensis
Cry1Ab Toxin by Bt White Spruce
Authors: Lamarche Josyanne , Hamelin Richard C. 
Published: July 2007

ABSTRACT

Nitrogen fixation is one of the most important roles played by soil bacterial communities, as fixation supplies nitrogen to many ecosystems which are often N limited. As impacts on this functional group of bacteria might harm the ecosystem's health and reduce productivity, monitoring that particular group is important. Recently, a field trial with Bt white spruce, which constitutively expresses the Cry1Ab insecticidal toxin of
Bacillus thuringiensis
, was established. The Bt white spruce was shown to be resistant to spruce budworm. We investigated the possible impact of these genetically modified trees on soil nitrogen-fixing bacterial communities. The trial consisted of untransformed controls, GUS white spruce (transformed with the β-glucuronidase gene), and Bt/GUS white spruce (which constitutively expresses both the Cry1Ab toxin and β-glucuronidase) in a random design. Four years after planting, soil samples from the control and the two treatments from plantation as well as from two natural stands of white spruce were collected. Diazotroph diversity was assessed by extracting soil genomic DNA and amplifying a region of the nitrogenase reductase (
nifH
) gene, followed by cloning and sequencing. Analysis revealed that nitrogen-fixing communities did not differ significantly among the untransformed control, GUS white spruce, and Bt/GUS white spruce. Nevertheless, differences in diazotroph diversity were observed between white spruce trees from the plantation site and those from two natural stands, one of which grew only a few meters away from the plantation. We therefore conclude, in the absence of evidence that the presence of the
B. thuringiensis cry1Ab
gene had an effect on diazotroph communities, that either site and/or field preparation prior to planting seems to be more important in determining diazotroph community structure than the presence of Bt white spruce.
Characteristics of
Gloeophyllum trabeum
Alcohol Oxidase, an Extracellular Source of H
2
O
2
in Brown Rot Decay of Wood
Authors: Daniel Geoffrey , Volc Jindřich , Filonova Lada , Plíhal Ondřej , Kubátová Elena , Halada Petr 
Published: July 2007

ABSTRACT

A novel alcohol oxidase (AOX) has been purified from mycelial pellets of the wood-degrading basidiomycete
Gloeophyllum trabeum
and characterized as a homooctameric nonglycosylated protein with native and subunit molecular masses of 628 and 72.4 kDa, containing noncovalently bonded flavin adenine dinucleotide. The isolated
AOX
cDNA contained an open reading frame of 1,953 bp translating into a polypeptide of 651 amino acids displaying 51 to 53% identity with other published fungal AOX amino acid sequences. The enzyme catalyzed the oxidation of short-chain primary aliphatic alcohols with a preference for methanol (

K
m

= 2.3 mM,
k
cat
= 15.6 s
−1
). Using polyclonal antibodies and immunofluorescence staining, AOX was localized on liquid culture hyphae and extracellular slime in sections from degraded wood and on cotton fibers. Transmission electron microscopy immunogold labeling localized the enzyme in the hyphal periplasmic space and wall and on extracellular tripartite membranes and slime, while there was no labeling of hyphal peroxisomes. AOX was further shown to be associated with membranous or slime structures secreted by hyphae in wood fiber lumina and within the secondary cell walls of degraded wood fibers. The differences in AOX targeting compared to the known yeast peroxisomal localization were traced to a unique C-terminal sequence of the
G. trabeum
oxidase, which is apparently responsible for the protein's different translocation. The extracellular distribution and the enzyme's abundance and preference for methanol, potentially available from the demethylation of lignin, all point to a possible role for AOX as a major source of H
2
O
2
, a component of Fenton's reagent implicated in the generally accepted mechanisms for brown rot through the production of highly destructive hydroxyl radicals.
Characterization and Synergistic Interactions of
Fibrobacter succinogenes
Glycoside Hydrolases
Authors: Qi Meng , Jun Hyun-Sik , Forsberg Cecil W. 
Published: July 2007

ABSTRACT

The objectives of this study were to characterize
Fibrobacter succinogenes
glycoside hydrolases from different glycoside hydrolase families and to study their synergistic interactions. The gene encoding a major endoglucanase (endoglucanase 1) of
F. succinogenes
S85 was identified as
cel9B
from the genome sequence by reference to internal amino acid sequences of the purified native enzyme. Cel9B and two other glucanases from different families, Cel5H and Cel8B, were cloned and overexpressed, and the proteins were purified and characterized. These proteins in conjunction with two predominant cellulases, Cel10A, a chloride-stimulated cellobiosidase, and Cel51A, formerly known as endoglucanase 2 (or CelF), were assayed in various combinations to assess their synergistic interactions using ball-milled cellulose. The degree of synergism ranged from 0.6 to 3.7. The two predominant endoglucanases produced by
F. succinogenes
, Cel9B and Cel51A, were shown to have a synergistic effect of up to 1.67. Cel10A showed little synergy in combination with Cel9B and Cel51A. Mixtures containing all the enzymes gave a higher degree of synergism than those containing two or three enzymes, which reflected the complementarity in their modes of action as well as substrate specificities.
Dissection and Modulation of the Four Distinct Activities of Nisin by Mutagenesis of Rings A and B and by C-Terminal Truncation
Authors: Rink Rick , Wierenga Jenny , Kuipers Anneke , Kluskens Leon D. , Driessen Arnold J. M. , Kuipers Oscar P. , Moll Gert N. 
Published: July 2007

ABSTRACT

Nisin A is a pentacyclic antibiotic peptide produced by various
Lactococcus lactis
strains. Nisin displays four different activities: (i) it autoinduces its own synthesis; (ii) it inhibits the growth of target bacteria by membrane pore formation; (iii) it inhibits bacterial growth by interfering with cell wall synthesis; and, in addition, (iv) it inhibits the outgrowth of spores. Here we investigate the structural requirements and relevance of the N-terminal thioether rings of nisin by randomization of the ring A and B positions. The data demonstrate that: (i) mutation of ring A results in variants with enhanced activity and a modulated spectrum of target cells; (ii) for the cell growth-inhibiting activity of nisin, ring A is rather promiscuous with respect to its amino acid composition, whereas the bulky amino acid residues in ring B abolish antimicrobial activity; (iii) C-terminally truncated nisin A mutants lacking rings D and E retain significant antimicrobial activity but are unable to permeabilize the target membrane; (iv) the dehydroalanine in ring A is not essential for the inhibition of the outgrowth of
Bacillus
cells; (v) some ring A mutants have significant antimicrobial activities but have decreased autoinducing activities; (vi) the opening of ring B eliminates antimicrobial activity while retaining autoinducing activity; and (vii) some ring A mutants escape the nisin immune system(s) and are toxic to the nisin-producing strain NZ9700. These data demonstrate that the various activities of nisin can be engineered independently and provide a basis for the design and synthesis of tailor-made analogs with desired activities.
Differential Involvement of Histidine Kinase Receptors in Pseudohyphal Development, Stress Adaptation, and Drug Sensitivity of the Opportunistic Yeast
Candida lusitaniae
Authors: Chapeland-Leclerc Florence , Paccallet Paméla , Ruprich-Robert Gwenaël , Reboutier David , Chastin Christiane , Papon Nicolas 
Published: July 2007

ABSTRACT

Fungal histidine kinase receptors (HKRs) sense and transduce many extracellular signals. We investigated the role of HKRs in morphogenetic transition, osmotolerance, oxidative stress response, and mating ability in the opportunistic yeast
Candida lusitaniae
. We isolated three genes,
SLN1
,
NIK1
, and
CHK1
, potentially encoding HKRs of classes VI, III, and X, respectively. These genes were disrupted by a transformation system based upon the “
URA3
blaster” strategy. Functional analysis of disruptants was undertaken, except for the
sln1 nik1
double mutant and the
sln1 nik1 chk1
triple mutant, which are not viable in
C. lusitaniae
. The
sln1
mutant revealed a high sensitivity to oxidative stress, whereas both the
nik1
and
chk1
mutants exhibited a more moderate sensitivity to peroxide. We also showed that the
NIK1
gene was implicated in phenylpyrrole and dicarboximide compound susceptibility while HKRs seem not to be involved in resistance toward antifungals of clinical relevance. Concerning mating ability, all disruptants were still able to reproduce sexually in vitro in unilateral or bilateral crosses. The most important result of this study was that the
sln1
mutant displayed a global defect of pseudohyphal differentiation, especially in high-osmolarity and oxidative-stress conditions. Thus, the
SLN1
gene could be crucial for the
C. lusitaniae
yeast-to-pseudohypha morphogenetic transition. This implication is strengthened by a high level of
SLN1
mRNAs revealed by semiquantitative reverse transcription-PCR when the yeast develops pseudohyphae. Our findings highlight a differential contribution of the three HKRs in osmotic and oxidant adaptation during the morphological transition in
C. lusitaniae
.
FEA1
,
FEA2
, and
FRE1
, Encoding Two Homologous Secreted Proteins and a Candidate Ferrireductase, Are Expressed Coordinately with
FOX1
and
FTR1
in Iron-Deficient
Chlamydomonas reinhardtii
Authors: Allen Michael D. , del Campo José A. , Kropat Janette , Merchant Sabeeha S. 
Published: July 2007

ABSTRACT

Previously, we had identified FOX1 and FTR1 as iron deficiency-inducible components of a high-affinity copper-dependent iron uptake pathway in
Chlamydomonas
. In this work, we survey the version 3.0 draft genome to identify a ferrireductase, FRE1, and two ZIP family proteins, IRT1 and IRT2, as candidate ferrous transporters based on their increased expression in iron-deficient versus iron-replete cells. In a parallel proteomic approach, we identified FEA1 and FEA2 as the major proteins secreted by iron-deficient
Chlamydomonas reinhardtii
. The recovery of FEA1 and FEA2 from the medium of
Chlamydomonas
strain CC425 cultures is strictly correlated with iron nutrition status, and the accumulation of the corresponding mRNAs parallels that of the
Chlamydomonas FOX1
and
FTR1
mRNAs, although the magnitude of regulation is more dramatic for the
FEA
genes. Like the
FOX1
and
FTR1
genes, the
FEA
genes do not respond to copper, zinc, or manganese deficiency. The 5′ flanking untranscribed sequences from the
FEA1
,
FTR1
, and
FOX1
genes confer iron deficiency-dependent expression of
ARS2
, suggesting that the iron assimilation pathway is under transcriptional control by iron nutrition. Genetic analysis suggests that the secreted proteins FEA1 and FEA2 facilitate high-affinity iron uptake, perhaps by concentrating iron in the vicinity of the cell. Homologues of
FEA1
and
FRE1
were identified previously as high-CO
2
-responsive genes,
HCR1
and
HCR2
, in
Chlorococcum littorale
, suggesting that components of the iron assimilation pathway are responsive to carbon nutrition. These iron response components are placed in a proposed iron assimilation pathway for
Chlamydomonas
.
Human Monoclonal Antibodies against Anthrax Lethal Factor and Protective Antigen Act Independently To Protect againstBacillus anthracisInfection and Enhance Endogenous Immunity to Anthrax
Authors: Albrecht Mark T. , Li Han , Williamson E. Diane , LeButt Chris S. , Flick-Smith Helen C. , Quinn Conrad P. , Westra Hans , Galloway Darrell , Mateczun Alfred , Goldman Stanley , Groen Herman , Baillie Les W. J. 
Published: July 2007

ABSTRACTThe unpredictable nature of bioterrorism and the absence of real-time detection systems have highlighted the need for an efficient postexposure therapy forBacillus anthracisinfection. One approach is passive immunization through the administration of antibodies that mitigate the biological action of anthrax toxin. We isolated and characterized two protective fully human monoclonal antibodies with specificity for protective antigen (PA) and lethal factor (LF). These antibodies, designated IQNPA (anti-PA) and IQNLF (anti-LF), were developed as hybridomas from individuals immunized with licensed anthrax vaccine. The effective concentration of IQNPA that neutralized 50% of the toxin in anthrax toxin neutralization assays was 0.3 nM, while 0.1 nM IQNLF neutralized the same amount of toxin. When combined, the antibodies had additive neutralization efficacy. IQNPA binds to domain IV of PA containing the host cell receptor binding site, while IQNLF recognizes domain I containing the PA binding region in LF. A single 180-μg dose of either antibody given to A/J mice 2.5 h before challenge conferred 100% protection against a lethal intraperitoneal spore challenge with 24 50% lethal doses [LD50s] ofB. anthracisSterne and against rechallenge on day 20 with a more aggressive challenge dose of 41 LD50s. Mice treated with either antibody and infected withB. anthracisSterne developed detectable murine anti-PA and anti-LF immunoglobulin G antibody responses by day 17 that were dependent on which antibody the mice had received. Based on these results, IQNPA and IQNLF act independently during prophylactic anthrax treatment and do not interfere with the establishment of endogenous immunity.
Binding of Serum Mannan Binding Lectin to a Cell Integrity-DefectiveCryptococcus neoformans ccr4Δ Mutant
Authors: Panepinto John C. , Komperda Kazimierz W. , Hacham Moshe , Shin Soowan , Liu Xiaoguang , Williamson Peter R. 
Published: July 2007

ABSTRACTMannan binding lectin (MBL) is an innate immune mediator belonging to the collectin family known to bind to the surfaces of many viruses, bacteria, and fungi. However, pathogenic strains of the fungusCryptococcus neoformansare resistant to MBL binding. To dissect the mechanism of cryptococcal resistance to MBL, we compared MBL binding to an encapsulated wild-type strain, an encapsulatedccr4Δ mutant defective in cell integrity, and an acapsularcap60Δ strain. No MBL binding was detected on wild-typeC. neoformans. In contrast, theccr4Δ mutant bound MBL to the cell wall, predominantly at the ends of enlarged buds, whereas the acapsular strain bound MBL only at the bud neck and bud scars. In addition, theccr4Δ mutant was sensitive to the cell wall-active antifungal caspofungin and other cell wall stress inducers, and its virulence was reduced in a mouse model of cryptococcosis. Interestingly, treatment of wild-type cells with caspofungin also increased MBL binding toC. neoformans. These results suggest that both the presence of capsule and wild-type cell wall architecture preclude MBL binding toC. neoformans.