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J Verhoef

Publications and source records attributed to J Verhoef.

At least 145 records · Page 8Linked to original sources
PubMed1999

Molecular epidemiology of quinolone resistance and comparative in vitro activities of new quinolones against European Staphylococcus aureus isolates.

UNLABELLED: New fluoroquinolones (FQ) may possibly be used as alternative therapeutic options for Staphylococcus aureus infections. Our objectives were: (1) to define the in vitro activities of seven FQs in a collection of 434 methicillin-susceptible and 457 methicillin-resistant S. aureus from 23 European university hospitals; (2) to characterise the prevalence of mutations in the grlA and gyrA genes in all ciprofloxacin-resistant (n=433) isolates of S. aureus; (3) to determine the percentage of ciprofloxacin-resistant S. aureus strains with measurable quinolone efflux. METHODS: (1) The in vitro activities of different FQs were determined by microdilution tests. (2) PCR-amplified DNA was sequenced. (3) Ciprofloxacin minimum inhibitory concentrations (MIC) were determined in the presence and absence of reserpine, which inhibits efflux pumps. RESULTS: (1) Irrespective of the methicillin resistance of the isolates, sitafloxacin and clinafloxacin showed the best in vitro activities. (2) All ciprofloxacin-resistant isolates exhibited GrlA alterations, namely Ser-80-->Phe or Tyr or Glu-84-->Lys or Ala-116-->Glu or Pro or a combination of Ser-80-->Phe and Glu-84-->Val. These alterations in GrlA were combined with alterations in GyrA, namely Ser-84-->Leu or Lys or Glu-88-->Lys or Val. (3) Reserpine reduced ciprofloxacin MIC values in ca. 30% of the clinical isolates tested. CONCLUSIONS: (1) This current European overview of mutations involved in FQ resistance demonstrates that only a limited number of classical mutations in grlA and gyrA contributed to resistance in clinical isolates. (2) An efflux pump is involved in ca. 30% of ciprofloxacin-resistant S. aureus isolates. (3) Sitafloxacin and clinafloxacin are two very promising new FQs with good anti-staphylococcal activity. New FQs, perhaps in combination with efflux pump inhibitors, might play a role in the treatment of S. aureus infections.

Anti-Infective Agents↗
PubMed1999

Association of alterations in ParC and GyrA proteins with resistance of clinical isolates of Enterococcus faecium to nine different fluoroquinolones.

The parC and gyrA genes of 73 ciprofloxacin-resistant and 6 ciprofloxacin-susceptible Enterococcus faecium clinical isolates were partly sequenced. Alterations in ParC and GyrA, possibly in combination with other resistance mechanisms, severely restricted the in vitro activities of the nine quinolones tested. For all isolates, clinafloxacin and sitafloxacin showed the best activities.

Anti-Infective Agents↗
PubMed1999

Comparative activities of clinafloxacin, grepafloxacin, levofloxacin, moxifloxacin, ofloxacin, sparfloxacin, and trovafloxacin and nonquinolones linozelid, quinupristin-dalfopristin, gentamicin, and vancomycin against clinical isolates of ciprofloxacin-resistant and -susceptible Staphylococcus aureus strains.

The activities of eight fluoroquinolones and linezolid, quinupristin-dalfopristin (Synercid), gentamicin, and vancomycin were tested against 96 ciprofloxacin-susceptible and 205 ciprofloxacin-resistant Staphylococcus aureus strains. Overall, clinafloxacin, followed by moxifloxacin and trovafloxacin, was the most active quinolone tested. For all isolates, linezolid and quinupristin-dalfopristin showed activities that were at least comparable to vancomycin, with no cross-resistance to any other test compound.

Anti-Bacterial Agents↗
PubMed1999

Many class I integrons comprise distinct stable structures occurring in different species of Enterobacteriaceae isolated from widespread geographic regions in Europe.

Three sizes of inserted regions of DNA (800, 1,000, and 1,500 bp) were shown to be common among class I integrons in unrelated clinical isolates of Enterobacteriaceae from different European hospitals. Sequencing showed that 800-bp inserted regions comprised identical sequences including aacA4, that 1,000-bp inserted regions included aadA, and that 1,500-bp inserted regions included dfrI and aadA1, irrespective of host species and geographic origin. In addition promoter sequences were mostly identical for each size class. These data suggest that inserted gene cassettes and promoter regions of integrons are conserved and stable, with resistance genes transferred more often as part of the entire integron structure than as individual gene cassettes.

Base Sequence↗
PubMed1999

Comparative in vitro activities of ciprofloxacin, clinafloxacin, gatifloxacin, levofloxacin, moxifloxacin, and trovafloxacin against Klebsiella pneumoniae, Klebsiella oxytoca, Enterobacter cloacae, and Enterobacter aerogenes clinical isolates with alterations in GyrA and ParC proteins.

The in vitro activities of ciprofloxacin, clinafloxacin, gatifloxacin, levofloxacin, moxifloxacin, and trovafloxacin were tested against 72 ciprofloxacin-resistant and 28 ciprofloxacin-susceptible isolates of Klebsiella pneumoniae, Klebsiella oxytoca, Enterobacter cloacae, and Enterobacter aerogenes. Irrespective of the alterations in GyrA and ParC proteins, clinafloxacin exhibited greater activity than all other fluoroquinolones tested against K. pneumoniae and E. aerogenes.

Anti-Infective Agents↗
PubMed1999

Relative avidities of human immunoglobulin G antibodies for streptococcal pyrogenic exotoxins A and B.

In this pilot study, we investigated the relative avidities for streptococcal pyrogenic exotoxin A (SPE-A) and SPE-B of antibodies in sera from patients with fatal streptococcal toxic shock-like syndrome and from healthy individuals and in intravenous immunoglobulin (IVIG) preparations. We observed a great variation in the relative avidities of patient, control, and IVIG immunoglobulin G (IgG) (values estimated to be between 10(-7) and 10(-11) M), with mean values for patient IgG about 10-fold lower than those of control IgG.

Adult↗
PubMed1999

Lipopolysaccharide (LPS)-binding synthetic peptides derived from serum amyloid P component neutralize LPS.

Lipopolysaccharide (LPS) is the major mediator of gram-negative septic shock. Molecules that bind LPS and neutralize its toxic effects could have important clinical applications. We showed that serum amyloid P component (SAP) neutralizes LPS. A SAP-derived peptide, consisting of amino acids 27 to 39, inhibited LPS-mediated effects in the presence of human blood. In this study, we used a pepscan of overlapping 15-mer peptides and distinguished two additional LPS-binding regions within the SAP molecule, identified in the regions spanning amino acids 61 to 75 and 186 to 200. The corresponding SAP-derived peptides, pep61-75 and pep186-200, inhibited the binding of fluorescein isothiocyanate-labeled LPS to monocytes as efficiently as a bactericidal/permeability-increasing protein (BPI)-derived 15-mer peptide comprising amino acids 85 to 99. The same SAP-derived peptides very potently inhibited LPS-induced priming of phagocytes in human blood. Also, SAP-derived pep186-200 caused a prolonged survival of actinomycin D-sensitized mice treated with LPS to induce septic shock, indicating a potential use of this peptide in the defense against serious gram-negative sepsis in humans.

Amino Acid Sequence↗
PubMed1999

Lipopolysaccharide-induced tumor necrosis factor alpha production by human monocytes involves the raf-1/MEK1-MEK2/ERK1-ERK2 pathway.

During gram-negative sepsis, human monocytes are triggered to produce large quantities of proinflammatory cytokines such as tumor necrosis factor alpha (TNF-alpha) in response to endotoxin (lipopolysaccharide [LPS]). Several studies have identified signal transduction pathways that are activated by LPS, including activation of nuclear factor-kappaB (NF-kappaB) and activation of mitogen-activated protein kinases (MAPKs), including ERK1 and ERK2, c-Jun N-terminal kinase, and p38. In this study, the relevance of ERK1 and ERK2 activation for LPS-induced TNF-alpha production by primary human monocytes has been addressed with PD-098059, which specifically blocks activation of MAPK kinase (MEK) by Raf-1. TNF-alpha levels in the monocyte culture supernatant, induced by 10 ng of LPS/ml, were reduced by PD-098059 (50 microM). In addition, PD-098059 also reduced TNF-alpha mRNA expression when cells were stimulated for 1 h with LPS. On the other hand, LPS-induced interleukin-10 (IL-10) levels in the monocyte supernatant were only slightly inhibited by PD-098059. Ro 09-2210, a recently identified MEK inhibitor, completely abrogated TNF-alpha levels at nanomolar concentrations. IL-10 levels also were strongly reduced. To show the efficacy of PD-098059 and Ro 09-2210, ERK1 and -2 activation was monitored by Western blotting with an antiserum that recognizes the phosphorylated (i.e., activated) forms of ERK1 and ERK2. Addition of LPS to human monocytes resulted in activation of both ERK1 and ERK2 in a time- and concentration (50% effective concentration between 1 and 10 ng of LPS/ml)-dependent manner. Activation of ERK2 was blocked by PD-098059 (50 microM), whereas ERK1 seemed to be less affected. Ro 09-2210 completely prevented LPS-induced ERK1 and ERK2 activation. LPS-induced p38 activation also was prevented by Ro 09-2210. These data further support the view that the ERK signal transduction pathway is causally involved in the synthesis of TNF-alpha by human monocytes stimulated with LPS.

Calcium-Calmodulin-Dependent Protein Kinases↗
PubMed1999

Invasive and noninvasive group A streptococcal isolates with different speA alleles in The Netherlands: genetic relatedness and production of pyrogenic exotoxins A and B.

Streptococcal pyrogenic exotoxin A (SPE-A) and SPE-B have been implicated in the pathogenesis of severe group A streptococcal (GAS) disease. We studied 31 invasive GAS strains including 18 isolates from patients with toxic shock syndrome and 22 noninvasive strains isolated in The Netherlands between 1994 and 1998. These strains were associated with the different allelic variants of the gene encoding SPE-A. We selected endemic strains with speA-positive M and T serotypes: speA2-associated M1T1 and M22-60T12 strains, speA3-associated M3T3 strains, and speA4-associated M6T6 strains. Since speA1-positive isolates were not frequently encountered, we included speA1 strains of different serotypes. The GAS strains were compared genotypically by pulsed-field gel electrophoresis and phenotypically by the in vitro production of SPE-A and SPE-B. All strains within one M and T type appeared to be of clonal origin. Most strains produced SPE-A and SPE-B, but only a minority of the speA4-positive isolates did so. Among our isolates, speA1- and speA3-positive strains produced significantly more SPE-A than speA2- and speA4-carrying strains, while SPE-B production was most pronounced among speA1- and speA2-containing strains. There was a marked degree of variability in the amounts of exotoxins produced in vitro by strains that shared the same genetic profile. We conclude that the differences in the in vitro production of SPE-A and SPE-B between our selected strains with identical M and T types were not related to either genetic heterogeneity or the clinical course of GAS disease in the patient from whom they were isolated.

Alleles↗
PubMed1999

The prevalence of aminoglycoside resistance and corresponding resistance genes in clinical isolates of staphylococci from 19 European hospitals.

Aminoglycosides still play an important role in antistaphylococcal therapies, although emerging resistance amongst staphylococci is widespread. To further our understanding of the prevalence of aminoglycoside resistance in Europe, we tested 699 and 249 consecutive unrelated clinical isolates of Staphylococcus aureus and coagulase-negative staphylococci (CNS), respectively, from the SENTRY Antimicrobial Surveillance Program, for susceptibility to gentamicin, tobramycin, kanamycin and streptomycin, and examined the relationship between susceptibility to these antimicrobials and susceptibility to methicillin. Three hundred and sixty-three staphylococcal isolates demonstrated resistance to at least one of the aminoglycosides tested; all of these isolates were screened for the presence of aac(6')-Ie + aph(2"), ant(4')-Ia and aph(3')-IIIa, the genes encoding the most clinically relevant aminoglycoside-modifying enzymes. S. aureus isolates derived from hospital-acquired pneumonia tended to be more resistant to aminoglycosides and methicillin than isolates from blood or wound infections. In S. aureus, resistance to aminoglycosides was closely associated with methicillin resistance. Susceptibility of S. aureus to gentamicin has decreased by 9% from previous European studies to a current level of 77%, while susceptibility of CNS, currently at 67%, has increased by 21%. Geographical variation occurred, correlating with methicillin resistance, although intra-country variation was considerable. aac(6')-Ie + aph(2"), ant(4')-Ia and aph(3')-IIIa were found throughout Europe in 68%, 48% and 14% respectively of staphylococci resistant to at least one aminoglycoside. aph(3')-IIIa was considerably more common in methicillin-susceptible S. aureus and CNS isolates; the reverse was true for the other two resistance genes. The prevalence of ant(4')-Ia and aph(3')-IIIa genes in aminoglycoside-resistant staphylococci was significantly greater than that reported in previous European studies.

Acetyltransferases↗
PubMed1998

A synthetic lipopolysaccharide-binding peptide based on amino acids 27-39 of serum amyloid P component inhibits lipopolysaccharide-induced responses in human blood.

LPS-binding proteins in plasma play an important role in modifying LPS toxicity. Significant properties have already been attributed to the LPS-binding protein (LBP). It accelerates LPS toxicity as well as incorporation into high-density lipoproteins, leading to neutralization of LPS in serum. A search for other LPS-binding components in serum, using LPS-coated magnetic beads, revealed a new LPS-binding protein. N-terminal microsequencing identified this protein as serum amyloid P component (SAP). Purified SAP bound to smooth and rough types of LPS via the lipid A part. SAP inhibited the binding of FITC-labeled ReLPS (LPS from Salmonella minnesota strain R595) to human monocytes and the ReLPS-induced priming of the oxidative burst of human neutrophils only in the presence of low concentrations of LBP. In search for the LPS binding site of SAP, we found that pep27-39, a 13-mer peptide consisting of amino acids 27-39 of SAP, competitively inhibited the binding of LPS to SAP. In addition, pep27-39 significantly inhibited ReLPS-induced responses in phagocytes in the presence of serum, as well as in human whole blood. Carboxamidomethylated pep27-39 showed an even more pronounced reduction of the ReLPS-induced priming of phagocytes in human blood. Performing gel filtration of FITC-labeled ReLPS incubated with soluble CD14, we showed that SAP could not prevent binding of LPS to soluble CD14, in contrast to pep27-39. The ability of pep27-39 to antagonize specifically the effects of LPS in the complex environment of human blood suggests that pep27-39 may be a novel therapeutic agent in the treatment of gram-negative sepsis.

Acute-Phase Proteins↗
PubMed1998

Cloning and characterization of an accessory gene regulator (agr)-like locus from Staphylococcus epidermidis.

The presence of sequences related to the agr of Staphylococcus aureus was demonstrated in Staphylococcus epidermidis by agr-specific PCR, and Southern blot. The agr-like locus of S. epidermidis A086 was cloned and sequenced. An overall homology of 68% was found between the agr locus from S. epidermidis and S. aureus. The agr locus from S. epidermidis was organized similar to those from S. aureus and S. lugdunensis. The putative RNAII molecule contains four open reading frames, agr A, B, C and D. AgrA was a response regulator. AgrB showed homology with transducer and translocase molecules. AgrC is expected to act as a histidine protein kinase in which a leucine zipper is present. AgrD is presumably processed into an autoinducer peptide. The putative RNAIII molecule contained an open reading frame encoding a putative 26 amino acid (aa) polypeptide, which differed in 3 aa from the RNAIII encoded delta-toxin of S. aureus. Kinetic studies showed that the production of this RNAIII was elevated during the post-exponential phase. delta-Toxin activity was demonstrated for 21 of 23 tested S. epidermidis strains. Kinetic studies of the production of delta-toxin showed that the toxin was produced during the post-exponential phase. Sequencing of S. epidermidis A097, which showed a delayed agr-response, revealed a truncated AgrC lacking the histidine kinase domain. These data indicate that an agr-like locus is active in S. epidermidis during the post-exponential phase.

Amino Acid Sequence↗
PubMed1998

Detection of staphylococcal genes directly from cerebrospinal and peritoneal fluid samples using a multiplex polymerase chain reaction.

A multiplex polymerase chain reaction (PCR) that can simultaneously detect eubacterial isolates and the methicillin-susceptibility of staphylococcal isolates from cerebrospinal and peritoneal fluid samples was compared to conventional microbiological methods. Using conventional methods, bacteria were isolated from 8% (29/350) of the cerebrospinal fluid samples and from 5% (3/60) of the peritoneal fluid samples. All isolates except two Staphylococcus epidermidis isolates were also detected using the multiplex PCR. Coagulase-negative staphylococci and Staphylococcus aureus were correctly identified using both methods. The multiplex PCR can rapidly and simultaneously detect eubacteria, and the methicillin susceptibility of staphylococci from samples containing > or = 10(2) cfu/ml of bacteria.

Ascitic Fluid↗
PubMed1998

A double-blind, placebo-controlled, parallel group study of oral trovafloxacin on bowel microflora in healthy male volunteers.

BACKGROUND: Treatment with oral antibiotic drugs generally influences normal fecal flora. These changes can be both beneficial (eg, elimination of aerobic, gram-negative bacilli) and detrimental (eg, the appearance of resistant pathogenic micro-organisms). Trovafloxacin, a new fluoroquinolone with in vitro activity against anaerobes, and gram-negative, gram-positive, and atypical pathogens, is a potentially beneficial antimicrobial for bowel sterilization. This double-blind trial investigated the effect of trovafloxacin on the normal microbial bowel flora of healthy male subjects. METHODS: Subjects were randomized (in a 2:1 ratio) to receive either 200 mg trovafloxacin once daily for 10 days or a matching placebo. Fecal samples were collected at two baseline occasions, on visit days 4, 7, 10, and 17, and at follow-up. Bacterial species were identified and quantified in the fecal samples. RESULTS: Twelve subjects received the active drug and seven received placebo. No Enterobacteriaceae were found in samples from days 4 to 10 in subjects receiving trovafloxacin. No changes in Enterobacteriaceae were found throughout the study in subjects receiving placebo. Incidental Enterobacteriaceae were isolated from subjects in the trovafloxacin group at the end of the study. No clinically significant differences were found in either group with respect to prevalence, appearance, or disappearance of aerobic gram-positive cocci, anaerobic bacteria, or yeasts. All tested Enterobacteriaceae were highly susceptible to trovafloxacin. No increase in minimum inhibitory concentration values was seen in day 17 and follow-up samples for isolated Escherichia coli strains. No Clostridium difficile was found in day 17 or follow-up samples from subjects in the trovafloxacin group. All tests for clostridium toxin were negative. CONCLUSIONS: During the treatment period, E. coli could not be cultured from the feces of the 12 healthy subjects receiving 200 mg trovafloxacin daily during days 4 to 10. All isolated Enterobacteriaceae were susceptible to trovafloxacin and no changes in susceptibility were found after the treatment period. In subjects treated with trovafloxacin, the prevalence and number of gram-positive bacteria were rapidly reduced. Trovafloxacin is able to selectively and reversibly suppress bowel flora.

Administration, Oral↗
PubMed1998

Monocytes modulate enhancement of HIV-1 replication by Mycobacterium tuberculosis.

To investigate the effects of Mycobacterium tuberculosis on HIV-1 replication, peripheral blood mononuclear cells (PBMC) of bacille Calmette-Guerin (BCG)-vaccinated donors and non-BCG-vaccinated donors were infected in vitro with a lymphotropic isolate of HIV-1 and cultured in the presence of purified protein derivative (PPD). Addition of PPD resulted in enhanced HIV-1 replication and lymphoproliferation in BCG-vaccinated donor PBMC, while PPD had no such effects in control PBMC. HIV-1 replication increased even more when monocytes were removed from PBMC, while lymphoproliferation was decreased. High percentages of monocytes were associated with a decreased HIV-1 replication and proliferation that could not be reversed by addition of antibodies against the cytokines IL-1, transforming growth factor-beta (TGF-beta) or indomethacin. PPD stimulates PBMC to release IL-10, a cytokine known to down-regulate proliferation and HIV-1 replication. PPD-induced effects on proliferation as well as HIV-1 replication could be partially blocked by adding a monoclonal antibody against MHC class II molecules, suggesting that part of the mechanism of PPD-induced enhancement is T memory cell activation.

Antibodies, Monoclonal↗