bluuebunny/crossref_metadata_2025_split huggingface dataset:
Amino Acid Repetitions in the Dihydropteroate Synthase of
Streptococcus pneumoniae
Lead to Sulfonamide Resistance with Limited Effects on Substrate

K
m
Authors: Haasum Ylva , Ström Katrin , Wehelie Rahma , Luna Vicki , Roberts Marilyn C. , Maskell Jeffrey P. , Hall Lucinda M. C. , Swedberg Göte 
Published: July 2002

ABSTRACT

Sulfonamide resistance in
Streptococcus pneumoniae
is due to changes in the chromosomal
folP
(
sulA
) gene coding for dihydropteroate synthase (DHPS). The first reported laboratory-selected sulfonamide-resistant
S. pneumoniae
isolate had a 6-bp repetition, the
sul-d
mutation, leading to a repetition of the amino acids Ile
66
and Glu
67
in the gene product DHPS. More recently, clinical isolates showing this and other repetitions have been reported. WA-5, a clinical isolate from Washington State, contains a 6-bp repetition in the
folP
gene, identical to the
sul-d
mutation. The repetition was deleted by site-directed mutagenesis. Enzyme kinetic measurements showed that the deletion was associated with a 35-fold difference in

K
i

for sulfathiazole but changed the

K
m

for
p
-aminobenzoic acid only 2.5-fold and did not significantly change the

K
m

for 2-amino-4-hydroxy-6-hydroxymethyl-7,8-dihydropteridine pyrophosphate. The enzyme characteristics of the deletion variant were identical to those of DHPS from a sulfonamide-susceptible strain. DHPS from clinical isolates with repetitions of Ser
61
had very similar enzyme characteristics to the DHPS from WA-5. The results confirm that the repetitions are sufficient for development of a resistant enzyme and suggest that the fitness cost to the organism of developing resistance may be very low.
Role of ATP-Binding-Cassette Transporter Genes in High-Frequency Acquisition of Resistance to Azole Antifungals in
Candida glabrata
Authors: Sanglard Dominique , Ischer Francoise , Bille Jacques 
Published: July 2002

ABSTRACT

Candida glabrata
has been often isolated from AIDS patients with oropharyngeal candidiasis treated with azole antifungal agents, especially fluconazole. We recently showed that the ATP-binding-cassette (ABC) transporter gene
CgCDR1
was upregulated in
C. glabrata
clinical isolates resistant to azole antifungal agents (D. Sanglard, F. Ischer, D. Calabrese, P. A. Majcherczyk, and J. Bille, Antimicrob. Agents Chemother. 43:2753–2765, 1999). Deletion of
CgCDR1
in
C. glabrata
rendered the null mutant hypersusceptible to azole derivatives and showed the importance of this gene in mediating azole resistance. We observed that wild-type
C. glabrata
exposed to fluconazole in a medium containing the drug at 50 μg/ml developed resistance to this agent and other azoles at a surprisingly high frequency (2 × 10
−4
to 4 × 10
−4
). We show here that this high-frequency azole resistance (HFAR) acquired in vitro was due, at least in part, to the upregulation of
CgCDR1
. The
CgCDR1
deletion mutant DSY1041 could still develop HFAR but in a medium containing fluconazole at 5 μg/ml. In the HFAR strain derived from DSY1041, a distinct ABC transporter gene similar to
CgCDR1
, called
CgCDR2
, was upregulated. This gene was slightly expressed in clinical isolates but was upregulated in strains with the HFAR phenotype. Deletion of both
CgCDR1
and
CgCDR2
suppressed the development of HFAR in a medium containing fluconazole at 5 μg/ml, showing that both genes are important mediators of resistance to azole derivatives in
C. glabrata
. We also show here that the HFAR phenomenon was linked to the loss of mitochondria in
C. glabrata
. Mitochondrial loss could be obtained by treatment with ethidium bromide and resulted in acquisition of resistance to azole derivatives without previous exposure to these agents. Azole resistance obtained in vitro by HFAR or by agents stimulating mitochondrial loss was at least linked to the upregulation of both
CgCDR1
and
CgCDR2
.
In Vitro Generation of Novel Pyrimethamine Resistance Mutations in theToxoplasma gondiiDihydrofolate Reductase
Authors: Reynolds Mary G. , Oh Jung , Roos David S. 
Published: July 2002

ABSTRACTPyrimethamine is a potent inhibitor of dihydrofolate reductase and is widely used in the treatment of opportunistic infections caused by the protozoan parasiteToxoplasma gondii. In order to assess the potential role ofdhfrsequence polymorphisms in drug treatment failures, we examined thedhfr-tsgenes of representative isolates forT. gondiivirulence types I, II, and III. These strains exhibit differences in their sensitivities to pyrimethamine but no differences in predicteddhfr-tsprotein sequences. To assess the potential for pyrimethamine-resistantdhfrmutants to emerge, three drug-sensitive variants of theT. gondii dhfr-tsgene (the wild-typeT. gondiisequence and two mutants engineered to reflect polymorphisms observed in drug-sensitivePlasmodium falciparum) were subjected to random mutagenesis and transfected into either wild-typeT. gondiiparasites ordhfr-deficientSaccharomyces cerevisiaeunder pyrimethamine selection. Three resistance mutations were identified, at amino acid residues 25 (Trp→Arg), 98 (Leu→Ser), and 134 (Leu→His).
Bactericidal Activities of Milk Lipids
Authors: Sprong R. Corinne , Hulstein Marco F. E. , Van der Meer Roelof 
Published: July 2002

ABSTRACTThe bactericidal capacity of digestion products of bovine milk triglycerides and membrane lipids was tested in vitro usingEscherichia coliO157:H7,Salmonella enteritidis, Campylobacter jejuni, Listeria monocytogenes, andClostridium perfringens. C10:0and C12:0fatty acids and digestion products of sphingolipids appeared to be effective bactericidal agents, whereas digestion products of phosphoglycerides were moderately bactericidal. Thus, milk fat sphingolipids and triglycerides, particularly those containing C10:0and C12:0fatty acids, may protect against food-borne gastroenteritis.
Multidrug-Resistant Urinary Tract Isolates of
Escherichia coli:
Prevalence and Patient Demographics in the United States in 2000
Authors: Sahm Daniel F. , Thornsberry Clyde , Mayfield David C. , Jones Mark E. , Karlowsky James A. 
Published: July 2002

ABSTRACT

Concurrent resistance to antimicrobials of different structural classes has arisen in a multitude of bacterial species and may complicate the therapeutic management of infections, including those of the urinary tract. To assess the current breadth of multidrug resistance among urinary isolates of
Escherichia coli,
the most prevalent pathogen contributing to these infections, all pertinent results in The Surveillance Network Database—USA from 1 January to 30 September 2000 were analyzed. Results were available for 38,835 urinary isolates of
E. coli
that had been tested against ampicillin, cephalothin, ciprofloxacin, nitrofurantoin, and trimethoprim-sulfamethoxazole. Of these isolates, 7.1% (2,763 of 38,835) were resistant to three or more agents and considered multidrug resistant. Among the multidrug-resistant isolates, 97.8% were resistant to ampicillin, 92.8% were resistant to trimethoprim-sulfamethoxazole, 86.6% were resistant to cephalothin, 38.8% were resistant to ciprofloxacin, and 7.7% were resistant to nitrofurantoin. The predominant phenotype among multidrug-resistant isolates (57.9%; 1,600 of 2,793) included resistance to ampicillin, cephalothin, and trimethoprim-sulfamethoxazole. This was the most common phenotype regardless of patient age, gender, or inpatient-outpatient status and in eight of the nine U.S. Bureau of the Census regions. Rates of multidrug resistance were demonstrated to be higher among males (10.4%) than females (6.6%), among patients >65 years of age (8.7%) than patients ≤17 (6.8%) and 18 to 65 (6.1%) years of age, and among inpatients (7.6%) than outpatients (6.9%). Regionally, the rates ranged from 4.3% in the West North Central region to 9.2% in the West South Central region. Given the current prevalence of multidrug resistance among urinary tract isolates of
E. coli
in the United States (7.1%), continued local, regional, and national surveillance is warranted.
Azithromycin Inhibits Quorum Sensing in
Pseudomonas aeruginosa
Authors: Tateda Kazuhiro , Comte Rachel , Pechere Jean-Claude , Köhler Thilo , Yamaguchi Keizo , Van Delden Christian 
Published: July 2002

ABSTRACT

We report that 2 μg of azithromycin/ml inhibits the quorum-sensing circuitry of
Pseudomonas aeruginosa
strain PAO1. Addition of synthetic autoinducers partially restored the expression of the trancriptional activator-encoding genes
lasR
and
rhlR
but not that of the autoinducer synthase-encoding gene
lasI
. We propose that azithromycin interferes with the synthesis of autoinducers, by an unknown mechanism, leading to a reduction of virulence factor production.
Continuous versus Intermittent Infusion of Vancomycin in Severe Staphylococcal Infections: Prospective Multicenter Randomized Study
Authors: Wysocki Marc , Delatour Frederique , Faurisson François , Rauss Alain , Pean Yves , Misset Benoit , Thomas Frank , Timsit Jean-François , Similowski Thomas , Mentec Herve , Mier Laurence , Dreyfuss Didier ,   The Study Group
Published: July 2002

ABSTRACT

A continuous infusion of vancomycin (CIV) may provide an alternative mode of infusion in severe hospital-acquired methicillin-resistant staphylococcal (MRS) infections. A multicenter, prospective, randomized study was designed to compare CIV (targeted plateau drug serum concentrations of 20 to 25 mg/liter) and intermittent infusions of vancomycin (IIV; targeted trough drug serum concentrations of 10 to 15 mg/liter) in 119 critically ill patients with MRS infections (bacteremic infections, 35%; pneumonia, 45%). Microbiological and clinical outcomes, safety, pharmacokinetics, ease of treatment adjustment, and cost were compared. Microbiological and clinical outcomes and safety were similar. CIV patients reached the targeted concentrations faster (36 ± 31 versus 51 ± 39 h,
P
= 0.029) and fewer samples were required for treatment monitoring than with IIV patients (7.7 ± 2.2 versus 11.8 ± 3.9 per treatment,
P
< 0.0001). The variability between patients in both the area under the serum concentration-time curve (AUC
24h
) and the daily dose given over 10 days of treatment was lower with CIV than with IIV (variances, 14,621 versus 53,975 mg
2
/liter
2
/h
2
[
P
= 0.026] and 414 versus 818 g
2
[
P
= 0.057], respectively). The 10-day treatment cost per patient was $454 ± 137 in the IIV group and was 23% lower in the CIV group ($321 ± 81:
P
< 0.0001). In summary, for comparable efficacy and tolerance, CIV may be a cost-effective alternative to IIV.
Integrons and Gene Cassettes in the
Enterobacteriaceae
Authors: White Peter A. , McIver Christopher J. , Rawlinson William D. 
Published: July 2002

ABSTRACT

Integrons were detected in 59 of 120 (49%) urinary isolates of
Enterobacteriaceae
by PCR using degenerate primers targeted to conserved regions of class 1, 2, and 3 integrase genes. PCR sequencing analysis of the cassette arrays revealed a predominance of cassettes that confer resistance to the aminoglycosides and trimethoprim.
Phosphorylation of β-d-Ribosylbenzimidazoles Is Not Required for Activity against Human Cytomegalovirus
Authors: Krosky Paula M. , Borysko Katherine Z. , Nassiri M. Reza , Devivar Rodrigo V. , Ptak Roger G. , Davis Michelle G. , Biron Karen K. , Townsend Leroy B. , Drach John C. 
Published: July 2002

ABSTRACTWe have previously reported that 2,5,6-trichloro-1-(β-d-ribofuranosyl)benzimidazole (TCRB) and its 2-bromo analog (2-bromo-5,6-dichloro-1-(β-d-ribofuranosy)benzimidazole [BDCRB]) are potent and selective inhibitors of human cytomegalovirus (HCMV) replication that block viral DNA maturation via HCMV gene products UL89 and UL56. To determine if phosphorylation is required for antiviral activity, the in vitro metabolism of BDCRB was examined and the antiviral activities of nonphosphorylatable 5′-deoxy analogs were determined. Reverse-phase high-performance liquid chromatography (HPLC) analysis of extracts from uninfected and HCMV-infected cells incubated with [3H]BDCRB revealed two major metabolites. Both were less polar than naturally occurring nucleoside monophosphates, but one peak coeluted with a BDCRB-5′-monophosphate (BDCRB-5′-MP) standard. Further analysis revealed, however, that neither metabolite partitioned with BDCRB-5′-MP on anion-exchange HPLC. Their retention patterns were not affected by incubation with alkaline phosphatase, thereby establishing that the compounds were not nucleoside 5′-monophosphates. Both compounds were detected in uninfected and HCMV-infected cells and in mouse live extracts, but neither has been identified. Like TCRB and BDCRB, the nonphosphorylatable 5′-deoxy analogs were potent and selective inhibitors of HCMV replication. The 5′-deoxy analogs maintained inhibition of HCMV replication upon removal of BDCRB, whereas an inhibitor of DNA synthesis did not. Similar to TCRB, its 5′-deoxy analog (5′-dTCRB) did not affect viral DNA synthesis, but 5′-dTCRB did inhibit viral DNA maturation to genome-length units. Additionally, virus isolates resistant to TCRB were also resistant to 5′-dTCRB and the 5′-deoxy analog of BDCRB. Taken together, these results confirm that TCRB, BDCRB, and their 5′-deoxy analogs have common mechanisms of action and establish that these benzimidazole ribonucleosides, unlike other antiviral nucleosides, do not require phosphorylation at the 5′ position for antiviral activity.
Antimicrobial Resistance among Clinical Isolates of
Streptococcus pneumoniae
in Canada during 2000
Authors: Low Donald E. , de Azavedo Joyce , Weiss Karl , Mazzulli Tony , Kuhn Magdalena , Church Deirdre , Forward Kevin , Zhanel George , Simor Andrew , McGeer A. 
Published: July 2002

ABSTRACT

A total of 2,245 clinical isolates of
Streptococcus pneumoniae
were collected from 63 microbiology laboratories from across Canada during 2000 and characterized at a central laboratory. Of these isolates, 12.4% were not susceptible to penicillin (penicillin MIC, ≥0.12 μg/ml) and 5.8% were resistant (MIC, ≥2 μg/ml). Resistance rates among non-β-lactam agents were the following: macrolides, 11.1%; clindamycin, 5.7%; chloramphenicol, 2.2%; levofloxacin, 0.9%; gatifloxacin, 0.8%; moxifloxacin, 0.4%; and trimethoprim-sulfamethoxazole, 11.3%. The MICs at which 90% of the isolates were inhibited (MIC
90
s) of the fluoroquinolones were the following: gemifloxacin, 0.03 μg/ml; BMS-284756, 0.06 μg/ml; moxifloxacin, 0.12 μg/ml; gatifloxacin, 0.25 μg/ml; levofloxacin, 1 μg/ml; and ciprofloxacin, 1 μg/ml. Of 578 isolates from the lower respiratory tract, 21 (3.6%) were inhibited at ciprofloxacin MICs of ≥4 μg/ml. None of the 768 isolates from children were inhibited at ciprofloxacin MICs of ≥4 μg/ml, compared to 3 of 731 (0.6%) from those ages 15 to 64 (all of these >60 years old), and 27 of 707 (3.8%) from those over 65. The MIC
90
s for ABT-773 and telithromycin were 0.015 μg/ml for macrolide-susceptible isolates and 0.12 and 0.5 μg/ml, respectively, for macrolide-resistant isolates. The MIC of linezolid was ≤2 μg/ml for all isolates. Many of the new antimicrobial agents tested in this study appear to have potential for the treatment of multidrug-resistant strains of pneumococci.
Accessory Gene Regulator (
agr
) Locus in Geographically Diverse
Staphylococcus aureus
Isolates with Reduced Susceptibility to Vancomycin
Authors: Sakoulas George , Eliopoulos George M. , Moellering Robert C. , Wennersten Christine , Venkataraman Lata , Novick Richard P. , Gold Howard S. 
Published: July 2002

ABSTRACT

The majority of infections with glycopeptide intermediate-level resistant
Staphylococcus aureus
(GISA) originate in biomedical devices, suggesting a possible increased ability of these strains to produce biofilm. Loss of function of the accessory gene regulator (
agr
) of
S. aureus
has been suggested to confer an enhanced ability to bind to polystyrene. We studied
agr
in GISA, hetero-GISA, and related glycopeptide-susceptible
S. aureus
isolates. All GISA strains from diverse geographic origins belong to
agr
group II. All GISA strains were defective in
agr
function, as demonstrated by their inability to produce delta-hemolysin. Hetero-GISA isolate A5940 demonstrated a nonsense mutation in
agrA
that was not present in a pulsed-field gel electrophoresis-indistinguishable vancomycin-susceptible isolate from the same patient. Various other
agr
point mutations were noted in several clinical GISA and hetero-GISA isolates. A laboratory-generated
agr
-null strain demonstrated a small but reproducible increase in vancomycin heteroresistance after growth in vitro in subinhibitory concentrations of vancomycin. This was not seen in the isogenic
agr
group II parent strain in which
agr
was intact. The in vitro bactericidal activity of vancomycin was attenuated in the
agr
-null strain compared to the parent strain. These findings imply that compromised
agr
function is advantageous to clinical isolates of
S. aureus
toward the development of vancomycin heteroresistance, perhaps through the development of vancomycin tolerance.
Long-Term Shifts in Patterns of Antibiotic Resistance in Enteric Bacteria
Authors: Houndt Tara , Ochman Howard 
Published: July 2002

ABSTRACT

Several mechanisms are responsible for the ability of microorganisms to tolerate antibiotics, and the incidence of resistance to these compounds within bacterial species has increased since the commercial use of antibiotics became widespread. To establish the extent of and changes in the diversity of antibiotic resistance patterns in natural populations, we determined the MICs of five antibiotics for collections of enteric bacteria isolated from diverse hosts and geographic locations and during periods before and after commercial application of antibiotics began. All of the pre-antibiotic era strains were susceptible to high levels of these antibiotics, whereas 20% of strains from contemporary populations of
Escherichia coli
and
Salmonella enterica
displayed high-level resistance to at least one of the antibiotics. In addition to the increase in the frequency of high-level resistance, background levels, conferred by genes providing nonspecific low-level resistance to multiple antibiotics, were significantly higher among contemporary strains. Changes in the incidence and levels of antibiotic resistance are not confined to particular segments of the bacterial population and reflect responses to the increased exposure of bacteria to antimicrobial compounds over the past several decades.
Glycine Betaine, Carnitine, and Choline Enhance Salinity Tolerance and Prevent the Accumulation of Sodium to a Level Inhibiting Growth of
Tetragenococcus halophila
Authors: Robert Hervé , Le Marrec Claire , Blanco Carlos , Jebbar Mohamed 
Published: July 2002

ABSTRACT

Natural-abundance
13
C-nuclear magnetic resonance was used to probe the intracellular organic solute content of the moderately halophilic bacterium
Tetragenococcus halophila
. When grown in complex growth media supplemented or not with NaCl,
T. halophila
accumulates glycine betaine and carnitine. Unlike other moderate halophiles,
T. halophila
was not able to produce potent osmoprotectants (such as ectoines and glycine betaine) through de novo synthesis when cultured in defined medium under hyperosmotic constraint. Addition of 2 mM carnitine, glycine betaine, or choline to defined medium improved growth parameters, not only at high salinity (up to 2.5 M NaCl) but also in media lacking NaCl. These compounds were taken up when available in the surrounding medium. The transport activity occurred at low and high salinities and seems to be constitutive. Glycine betaine and carnitine were accumulated by
T. halophila
in an unmodified form, while exogenously provided choline led to an intracellular accumulation of glycine betaine. This is the first evidence of the existence of a choline-glycine betaine pathway in a lactic acid bacterium. An assay showed that the compatible solutes strikingly repressed the accumulation of glutamate and slightly increased the intracellular potassium level only at high salinity. Interestingly, osmoprotectant-treated cells were able to maintain the intracellular sodium concentration at a relatively constant level (200 to 300 nmol/mg [dry weight]), independent of the NaCl concentration of the medium. In contrast, in the absence of osmoprotectant, the intracellular sodium content increased sharply from 200 to 2,060 nmol/mg (dry weight) when the salinity of the medium was raised from 1 to 2 M. Indeed, the imported compatible solutes play an actual role in regulating the intracellular Na
+
content and confer a much higher salt tolerance to
T. halophila.
Characterization and Role of the Branched-Chain Aminotransferase (BcaT) Isolated from
Lactococcus lactis
subsp.
cremoris
NCDO 763
Authors: Yvon Mireille , Chambellon Emilie , Bolotin Alexander , Roudot-Algaron Florence 
Published: July 2002

ABSTRACT

In
Lactococcus lactis
, which is widely used as a starter in the cheese industry, the first step of aromatic and branched-chain amino acid degradation is a transamination which is catalyzed by two major aminotransferases. We have previously purified and characterized biochemically and genetically the aromatic aminotransferase, AraT. In the present study, we purified and studied the second enzyme, the branched-chain aminotransferase, BcaT. We cloned and sequenced the corresponding gene and used a mutant, along with the luciferase gene as the reporter, to study the role of the enzyme in amino acid metabolism and to reveal the regulation of gene transcription. BcaT catalyzes transamination of the three branched-chain amino acids and methionine and belongs to class IV of the pyridoxal 5′-phosphate-dependent aminotransferases. In contrast to most of the previously described bacterial BcaTs, which are hexameric, this enzyme is homodimeric. It is responsible for 90% of the total isoleucine and valine aminotransferase activity of the cell and for 50 and 40% of the activity towards leucine and methionine, respectively. The original role of BcaT was probably biosynthetic since expression of its gene was repressed by free amino acids and especially by isoleucine. However, in dairy strains, which are auxotrophic for branched-chain amino acids, BcaT functions only as a catabolic enzyme that initiates the conversion of major aroma precursors. Since this enzyme is still active under cheese-ripening conditions, it certainly plays a major role in cheese flavor development.
Staphylococcal Surface Display of Metal-Binding Polyhistidyl Peptides
Authors: Samuelson Patrik , Wernérus Henrik , Svedberg Malin , Ståhl Stefan 
Published: July 2002

ABSTRACT

Recombinant
Staphylococcus xylosus
and
Staphylococcus carnosus
strains were generated with surface-exposed chimeric proteins containing polyhistidyl peptides designed for binding to divalent metal ions. Surface accessibility of the chimeric surface proteins was demonstrated and the chimeric surface proteins were found to be functional in terms of metal binding, since the recombinant staphylococcal cells were shown to have gained Ni
2+
- and Cd
2+
-binding capacity, suggesting that such bacteria could find use in bioremediation of heavy metals. This is, to our knowledge, the first time that recombinant, surface-exposed metal-binding peptides have been expressed on gram-positive bacteria. Potential environmental or biosensor applications for such recombinant staphylococci as biosorbents are discussed.