bluuebunny/crossref_metadata_2025_split huggingface dataset:
In Vitro Selection of Resistance in
Haemophilus influenzae
by Amoxicillin-Clavulanate, Cefpodoxime, Cefprozil, Azithromycin, and Clarithromycin
Authors: Clark Catherine , Bozdogan Bülent , Peric Mihaela , Dewasse Bonifacio , Jacobs Michael R. , Appelbaum Peter C. 
Published: October 2002

ABSTRACT

Abilities of amoxicillin-clavulanate, cefpodoxime, cefprozil, azithromycin, and clarithromycin to select resistant mutants of
Haemophilus influenzae
were tested by multistep and single-step methodologies. For multistep studies, 10 random strains were tested: 5 of these were β-lactamase positive. After 50 daily subcultures in amoxicillin-clavulanate, MICs did not increase more than fourfold. However, cefprozil MICs increased eightfold for one strain. Clarithromycin and azithromycin gave a >4-fold increase in 8 and 10 strains after 14 to 46 and 20 to 50 days, respectively. Mutants selected by clarithromycin and azithromycin were associated with mutations in 23S rRNA and ribosomal proteins L4 and L22. Three mutants selected by clarithromycin or azithromycin had alterations in ribosomal protein L4, while five had alterations in ribosomal protein L22. Two mutants selected by azithromycin had mutations in the gene encoding 23S rRNA: one at position 2058 and the other at position 2059 (
Escherichia coli
numbering), with replacement of A by G. One clone selected by clarithromycin became hypersusceptible to macrolides. In single-step studies azithromycin and clarithromycin had the highest mutation rates, while amoxicillin-clavulanate had the lowest. All resistant clones were identical to parents as observed by pulsed-field gel electrophoresis. The MICs of azithromycin for azithromycin-resistant clones were 16 to >128 μg/ml, and those of clarithromycin for clarithromycin-resistant clones were 32 to >128 μg/ml in multistep studies. For strains selected by azithromycin, the MICs of clarithromycin were high and vice versa. After 50 daily subcultures in the presence of drugs, MICs of amoxicillin-clavulanate and cefpodoxime against
H. influenzae
did not rise more than fourfold, in contrast to cefprozil, azithromycin, and clarithromycin, whose MICs rose to variable degrees.
In Vitro Interaction of Flucytosine Combined with Amphotericin B or Fluconazole against Thirty-Five Yeast Isolates Determined by both the Fractional Inhibitory Concentration Index and the Response Surface Approach
Authors: Te Dorsthorst D. T. A. , Verweij P. E. , Meletiadis J. , Bergervoet M. , Punt N. C. , Meis J. F. G. M. , Mouton J. W. 
Published: October 2002

ABSTRACT

Combination therapy could be of benefit for the treatment of invasive yeast infections. However, in vitro interaction studies are relatively scarce and the interpretation of the fractional inhibitory concentration (FIC) index can be contradictory due to various definitions used; not all information on the interaction study is used in the index, and different MIC end points exist for different classes of drugs. Fitting an interaction model to the whole response surface and estimation of an interaction coefficient alpha (ICα) would overcome these objections and has the additional advantage that confidence intervals of the interaction are obtained. The efficacy of flucytosine (5FC) in combination with amphotericin B (AB) and fluconazole (FCZ) was studied against 35 yeast isolates in triplicate (
Candida albicans
[
n
= 9],
Candida glabrata
[
n
= 9],
Candida krusei
[
n
= 9], and
Cryptococcus neoformans
[
n
= 8]) using a broth microdilution checkerboard method and measuring growth after 48 h by a spectrophotometer. The FIC index and ICα were determined, the latter by estimation from the response surface approach described by Greco et al. (W. R. Greco, G. Bravo, and J. C. Parsons, Pharmacol. Rev.
47:
331-385, 1995) by using a computer program developed for that purpose. For the 5FC-FCZ combination, the interactions determined by the ICα generally were in concordance with the interactions determined by the FIC index, but large discrepancies were found between both methods for the 5FC-AB combination. These could mainly be explained by shortcomings in the FIC approach. The in vitro interaction of 5FC-AB demonstrated variable results depending on the tested
Candida
isolate. In general, the 5FC-FCZ combination was antagonistic against
Candida
species, but for some
Candida
isolates synergism was found. For
C. neoformans
the interaction for both combinations was highly dependent on the tested isolate and the method used. Response surface approach is an alternative method for determining the interaction between antifungal agents. By using this approach, some of the problems encountered with the FIC were overcome.
The Antifungal Echinocandin Caspofungin Acetate Kills Growing Cells of
Aspergillus fumigatus
In Vitro
Authors: Bowman J. C. , Hicks P. Scott , Kurtz M. B. , Rosen H. , Schmatz D. M. , Liberator P. A. , Douglas C. M. 
Published: October 2002

ABSTRACT

Caspofungin acetate is an antifungal antibiotic that inhibits synthesis of 1,3-β-
d
-glucan, an essential component of the fungal cell wall. While caspofungin causes cell death in yeasts and dimorphic fungi such as
Candida albicans
, its effect on
Aspergillus fumigatus
is less well understood. We used the fluorescent dyes 5,(6)-carboxyfluorescein diacetate (CFDA) and bis-(1,3-dibutylbarbituric acid) trimethine oxonol (DiBAC), which stain live and dead cells, respectively, to further characterize the antifungal activity of caspofungin. For comparison, compounds whose mode of action was either fungistatic (fluconazole, itraconazole) or fungicidal (amphotericin B) were also evaluated. A correlation between caspofungin-induced loss of viability, decreased CFDA staining, and increased DiBAC staining was established first with
C. albicans
. For
A. fumigatus
, caspofungin caused similar dye-staining changes, which were quantified by fluorimetric analysis of stained hyphae grown in a medium that promoted dispersed growth. The minimum concentration of caspofungin required to produce these changes also decreased the level of growth-dependent reduction of the indicator dye Alamar Blue. We observed a differential effect of caspofungin as a function of cell position: 88% of apical cells and 61% of subapical branching cells failed to stain with the viable dye CFDA, but only 24% of subapical cells were unstained. Complementary results were seen with germlings from DiBAC-stained, caspofungin-treated cultures. Extended incubation of
A. fumigatus
with a single dose of caspofungin affected the same proportion of apical and subapical branching cells for up to 72 h. The dye-staining patterns illustrate that the cells at the active centers for new cell wall synthesis within
A. fumigatus
hyphae are killed when they are exposed to caspofungin.
Mutation in 23S rRNA Associated with Macrolide Resistance in
Neisseria gonorrhoeae
Authors: Ng Lai-King , Martin Irene , Liu Gary , Bryden Louis 
Published: October 2002

ABSTRACT

Fifty-six azithromycin-resistant (MICs, 2.0 to 4.0 μg/ml)
Neisseria gonorrhoeae
strains with cross-resistance to erythromycin (MICs, 2.0 to 64.0 μg/ml), isolated in Canada between 1997 and 1999, were characterized, and their mechanisms of azithromycin resistance were determined. Most (58.9%) of them belonged to auxotype-serotype class NR/IB-03, with a 2.6-mDa plasmid. Based on resistance to crystal violet (MICs ≥ 1 μg/ml), 96.4% of these macrolide-resistant strains appeared to have increased efflux. Nine of the eleven strains selected for further characterization were found to have a promoter region
mtrR
mutation, a single-base-pair (A) deletion in the 13-bp inverted repeat, which is believed to cause overexpression of the
mtrCDE
-encoded efflux pump. The two remaining macrolide-resistant strains (erythromycin MIC, 64.0 μg/ml; azithromycin MIC, 4.0 μg/ml), which did not have the mutation in the
mtrR
promoter region, were found to have a C2611T mutation (
Escherichia coli
numbering) in the peptidyltransferase loop in domain V of the 23S rRNA alleles. Although mutations in domain V of 23S rRNA alleles had been reported in other bacteria, including
E. coli
,
Streptococcus pneumoniae
, and
Helicobacter pylori
, this is the first observation of these mutations associated with macrolide resistance in
N. gonorrhoeae
.
In Vitro Interaction of Caspofungin Acetate with Voriconazole against Clinical Isolates of
Aspergillus
spp
Authors: Perea Sofia , Gonzalez Gloria , Fothergill Annette W. , Kirkpatrick William R. , Rinaldi Michael G. , Patterson Thomas F. 
Published: October 2002

ABSTRACT

The interaction between caspofungin acetate and voriconazole was studied in vitro by using 48 clinical
Aspergillus
spp. isolates obtained from patients with invasive aspergillosis. MICs were determined by the NCCLS broth microdilution method. Synergy, defined as a fractional inhibitory concentration (FIC) index of <1, was detected in 87.5% of the interactions; an additive effect, defined as an FIC index of 1.0, was observed in 4.2% of the interactions; and a subadditive effect, defined as an FIC index of 1.0 to 2.0, was found in 8.3% of the interactions. No antagonism was observed. Animal models are required to validate the in vivo significance of these in vitro data presented for the combination of caspofungin and voriconazole.
Incidence of High-Level Evernimicin Resistance in
Enterococcus faecium
among Food Animals and Humans
Authors: Aarestrup Frank Møller , McNicholas Paul M. 
Published: October 2002

ABSTRACT

Six high-level evernimicin-resistant
Enterococcus faecium
isolates were identified among 304 avilamycin-resistant
E
.
faecium
isolates from animals and 404 stool samples from humans with diarrhea. All four animal isolates, and one of the human isolates, were able to transfer resistance to a susceptible
E
.
faecium
strain. The resulting transconjugants all tested positive for the presence of
emtA
, a gene encoding a methyltransferase previously linked with high-level evernimicin resistance. The four transconjugants derived from animal isolates all carried the same plasmid, while a differently sized plasmid was found in the isolate from humans. This study demonstrated a low incidence of high-level evernimicin resistance mediated by the
emtA
gene in different
E
.
faecium
isolates of animal and human origin.
Inhibition of
Listeria innocua
in Cheddar Cheese by Addition of Nisin Z in Liposomes or by In Situ Production in Mixed Culture
Authors: Benech R.-O. , Kheadr E. E. , Laridi R. , Lacroix C. , Fliss I. 
Published: October 2002

ABSTRACT

The effect of addition of purified nisin Z in liposomes to cheese milk and of in situ production of nisin Z by
Lactococcus lactis
subsp.
lactis
biovar diacetylactis UL719 in the mixed starter on the inhibition of
Listeria innocua
in cheddar cheese was evaluated during 6 months of ripening. A cheese mixed starter culture containing
Lactococcus lactis
subsp.
lactis
biovar diacetylactis UL719 was selected for high-level nisin Z and acid production. Experimental cheddar cheeses were produced on a pilot scale, using the selected starter culture, from milk with added
L. innocua
(10
5
to 10
6
CFU/ml). Liposomes with purified nisin Z were prepared from proliposome H and added to cheese milk prior to renneting to give a final concentration of 300 IU/g of cheese. The nisin Z-producing strain and nisin Z-containing liposomes did not significantly affect cheese production and gross chemical composition of the cheeses. Immediately after cheese production, 3- and 1.5-log-unit reductions in viable counts of
L. innocua
were obtained in cheeses with encapsulated nisin and the nisinogenic starter, respectively. After 6 months, cheeses made with encapsulated nisin contained less than 10 CFU of
L. innocua
per g and 90% of the initial nisin activity, compared with 10
4
CFU/g and only 12% of initial activity in cheeses made with the nisinogenic starter. This study showed that encapsulation of nisin Z in liposomes can provide a powerful tool to improve nisin stability and inhibitory action in the cheese matrix while protecting the cheese starter from the detrimental action of nisin during cheese production.
Identification of the Bacterial Microflora in Dairy Products by Temporal Temperature Gradient Gel Electrophoresis
Authors: Ogier Jean-Claude , Son Olivier , Gruss Alexandra , Tailliez Patrick , Delacroix-Buchet Agnes 
Published: October 2002

ABSTRACT

Numerous microorganisms, including bacteria, yeasts, and molds, are present in cheeses, forming a complex ecosystem. Among these organisms, bacteria are responsible for most of the physicochemical and aromatic transformations that are intrinsic to the cheesemaking process. Identification of the bacteria that constitute the cheese ecosystem is essential for understanding their individual contributions to cheese production. We used temporal temperature gradient gel electrophoresis (TTGE) to identify different bacterial species present in several dairy products, including members of the genera
Lactobacillus
,
Lactococcus
,
Leuconostoc
,
Enterococcus
,
Pediococcus
,
Streptococcus
, and
Staphylococcus
. The TTGE technique is based on electrophoretic separation of 16S ribosomal DNA (rDNA) fragments by using a temperature gradient. It was optimized to reveal differences in the 16S rDNA V3 regions of bacteria with low-G+C-content genomes. Using multiple control strains, we first set up a species database in which each species (or group of species) was characterized by a specific TTGE fingerprint. TTGE was then applied to controlled dairy ecosystems with defined compositions, including liquid (starter), semisolid (home-made fermented milk), and solid (miniature cheese models) matrices. Finally, the potential of TTGE to describe the bacterial microflora of unknown ecosystems was tested with various commercial dairy products. Subspecies, species, or groups of species of lactic acid bacteria were distinguished in dairy samples. In conclusion, TTGE was shown to distinguish bacterial species in vitro, as well as in both liquid and solid dairy products.
Comparative Resistance of Phage Isolates of Four Genotypes of F-Specific RNA Bacteriophages to Various Inactivation Processes
Authors: Schaper M. , Durán A. E. , Jofre J. 
Published: October 2002

ABSTRACT
The effect of natural inactivation in freshwater, chlorination, ammonia, extreme pHs, temperature, and salt content on phage inactivation was evaluated on mixtures of F-specific RNA bacteriophage isolates belonging to genotypes I, II, III, and IV. The bacteriophages studied were previously but recently isolated from natural samples, characterized as F-specific RNA bacteriophages and genotyped by plaque hybridization with genotype-specific probes. Natural inactivation in river water was modeled by in situ incubation of bacteriophages inside submerged dialysis tubes. After several days bacteriophages of genotype I showed the highest persistence, which was significantly different from that of bacteriophages of genotype II, IV, or III. The pattern of resistance of phages belonging to the various genotypes to extreme pHs, ammonia, temperature, salt concentration, and chlorination was similar. In all cases, phages of genotype I showed the highest persistence, followed by the phages of genotypes II, III, and IV. The phages of genotypes III and IV were the least resistant to all treatments, and resistance of genotypes III and IV to the treatments was similar. Bacteriophages of genotype II showed intermediate resistance to some of the treatments. The resistance of four phages of genotype I to natural inactivation and chlorination did not differ significantly. These results indicate that genotypes III and IV are much more sensitive to environmental stresses and to treatments than the other genotypes, especially than genotype I. This should be taken into consideration in future studies aimed at using genotypes of F-specific RNA bacteriophages to fingerprint the origin of fecal pollution.
Plasmid-Borne Genes Code for an Angular Dioxygenase Involved in Dibenzofuran Degradation by
Terrabacter
sp. Strain YK3
Authors: Iida Toshiya , Mukouzaka Yuki , Nakamura Kaoru , Kudo Toshiaki 
Published: October 2002

ABSTRACT

The genes responsible for angular dioxygenation of dibenzofuran in actinomycetes were cloned by using a degenerate set of PCR primers designed by using conserved sequences of the dioxygenase alpha subunit genes. One sequence of alpha subunit genes was commonly amplified from four dibenzofuran-utilizing actinomycetes:
Terrabacter
sp. strains YK1 and YK3,
Rhodococcus
sp. strain YK2, and
Microbacterium
sp. strain YK18. A 5.2-kb
Pst
I fragment encoding the alpha and beta subunits of the terminal dioxygenase, ferredoxin, and ferredoxin reductase (designated
dfdA1
to
dfdA4
, respectively) was cloned from the large circular plasmid pYK3 isolated from
Terrabacter
sp. strain YK3. We confirmed that transcription of the
dfdA1
gene was induced by dibenzofuran in
Terrabacter
sp. strain YK3. Southern blot hybridization analysis revealed that this type of dioxygenase gene is distributed among diverse dibenzofuran-utilizing actinomycetes. However, genes homologous to
dfdA1
were not detected in dibenzofuran utilization-deficient mutants of
Terrabacter
,
Rhodococcus
, and
Microbacterium
species. When the
dfdA1
to
dfdA4
genes were introduced into a non-dibenzofuran-degrading mutant of
Rhodococcus
sp. strain YK2, strain YK2-RD2, which had spontaneously lost the gene homologous to
dfdA1
, the ability to degrade dibenzofuran was restored. Analysis of the breakdown products indicated that DfdA has angular dioxygenase activity. This
dfdA
transformant degraded several aromatic compounds, indicating that the novel angular dioxygenase possesses broad substrate specificity.
Biodiversity of Denitrifying and Dinitrogen-Fixing Bacteria in an Acid Forest Soil
Authors: Rösch Christopher , Mergel Alexander , Bothe Hermann 
Published: October 2002

ABSTRACT

Isolated soil DNA from an oak-hornbeam forest close to Cologne, Germany, was suitable for PCR amplification of gene segments coding for the 16S rRNA and nitrogenase reductase (NifH), nitrous oxide reductase (NosZ), cytochrome
cd
1
-containing nitrite reductase (NirS), and Cu-containing nitrite reductase (NirK) of denitrification. For each gene segment, diverse PCR products were characterized by cloning and sequencing. None of the 16S rRNA gene sequences was identical to any deposited in the data banks, and therefore each of them belonged to a noncharacterized bacterium. In contrast, the analyzed clones of
nifH
gave only a few different sequences, which occurred many times, indicating a low level of species richness in the N
2
-fixing bacterial population in this soil. Identical
nifH
sequences were also detected in PCR amplification products of DNA of a soil approximately 600 km distant from the Cologne area. Whereas biodiversity was high in the case of
nosZ
, only a few different sequences were obtained with
nirK
. With respect to
nirS
, cloning and sequencing of the PCR products revealed that many false gene segments had been amplified with DNA from soil but not from cultured bacteria. With the 16S rRNA gene data, many sequences of uncultured bacteria belonging to the
Acidobacterium
phylum and actinomycetes showed up in the PCR products when isolated DNA was used as the template, whereas sequences obtained for
nifH
and for the denitrification genes were closely related to those of the proteobacteria. Although in such an experimental approach one has to cope with the enormous biodiversity in soils and only a few PCR products can be selected at random, the data suggest that denitrification and N
2
fixation are not genetic traits of most of the uncultured bacteria.
Oxalobacter formigenes
and Its Potential Role in Human Health
Authors: Duncan Sylvia H. , Richardson Anthony J. , Kaul Poonam , Holmes Ross P. , Allison Milton J. , Stewart Colin S. 
Published: October 2002

ABSTRACT

Oxalate degradation by the anaerobic bacterium
Oxalobacter formigenes
is important for human health, helping to prevent hyperoxaluria and disorders such as the development of kidney stones. Oxalate-degrading activity cannot be detected in the gut flora of some individuals, possibly because
Oxalobacter
is susceptible to commonly used antimicrobials. Here, clarithromycin, doxycycline, and some other antibiotics inhibited oxalate degradation by two human strains of
O. formigenes
. These strains varied in their response to gut environmental factors, including exposure to gastric acidity and bile salts.
O. formigenes
strains established oxalate breakdown in fermentors which were preinoculated with fecal bacteria from individuals lacking oxalate-degrading activity. Reducing the concentration of oxalate in the medium reduced the numbers of
O. formigenes
bacteria. Oxalate degradation was established and maintained at dilution rates comparable to colonic transit times in healthy individuals. A single oral ingestion of
O. formigenes
by adult volunteers was, for the first time, shown to result in (i) reduced urinary oxalate excretion following administration of an oxalate load, (ii) the recovery of oxalate-degrading activity in feces, and (iii) prolonged retention of colonization.
Occurrence of Toxigenic
Aspergillus versicolor
Isolates and Sterigmatocystin in Carpet Dust from Damp Indoor Environments
Authors: Engelhart Steffen , Loock Annette , Skutlarek Dirk , Sagunski Helmut , Lommel Annette , Färber Harald , Exner Martin 
Published: October 2002

ABSTRACT

Over the past decade, there has been growing concern regarding the role of toxigenic fungi in damp indoor environments; however, there is still a lack of field investigations on exposure to mycotoxins. The goal of our pilot study was to quantify the proportion of toxigenic
Aspergillus versicolor
isolates in native carpet dust from damp dwellings with mold problems and to determine whether sterigmatocystin can be detected in this matrix. Carpet dust samples (
n
= 11) contained from <2.5 × 10
1
to 3.6 × 10
5
(median, 3.1 × 10
4
)
A. versicolor
CFU/g of dust, and the median proportion of
A. versicolor
from total culturable fungi was 18%. Based on thin-layer chromatography detection of sterigmatocystin, 49 of 50
A. versicolor
isolates (98%) were found to be toxigenic in vitro. By using high-performance liquid chromatography-electrospray ionization tandem mass spectrometry, sterigmatocystin could be detected in low concentrations (2 to 4 ng/g of dust) in 2 of 11 native carpet dust samples. From this preliminary study, we conclude that most strains of
A. versicolor
isolated from carpet dust are able to produce sterigmatocystin in vitro and that sterigmatocystin may occasionally occur in carpet dust from damp indoor environments. Further research and systematic field investigation are needed to confirm our results and to provide an understanding of the health implications of mycotoxins in indoor environments.