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Jan Verhoef

Publications and source records attributed to Jan Verhoef.

49 records · Page 3Linked to original sources
PubMed2002

Evaluation of the Etest ESBL and the BD Phoenix, VITEK 1, and VITEK 2 automated instruments for detection of extended-spectrum beta-lactamases in multiresistant Escherichia coli and Klebsiella spp.

Seventy-four isolates of multiresistant Escherichia coli and Klebsiella spp. recovered during a 3-year period and 17 control strains with genotypically identified beta-lactamases were tested for the production of extended-spectrum beta-lactamases (ESBLs) by using the Etest and the VITEK 1, VITEK 2, and Phoenix automated instruments. The use of the Etest was evaluated by investigating its accuracy in detecting the ESBLs of the control strains and by comparing interpretation results of laboratory technicians and experts. The accuracy of the Etest was 94%. With the Etest as the reference for the clinical strains and the genotype as the reference for the control strains, the automated instruments detected the ESBLs with accuracies of 78% (VITEK 2), 83% (VITEK 1), and 89% (Phoenix). No significant difference between the systems with regard to the control strains was detected. The VITEK 2 did, however, perform less well than the Phoenix (P = 0.03) on the collection of clinical isolates, mainly because of its high percentage of indeterminate test results (11%). No significant difference between the performances of the VITEK 1 and either the VITEK 2 or the Phoenix was found. However, because of its associated BDXpert system the Phoenix showed the best performance. The Etest was found to be an accurate test but was limited by its indeterminate results (4%), its inability to differentiate between K1 hyperproduction and ESBLs, questionable guidelines concerning mutants inside the inhibition zones, and the inability of the technicians to recognize subtle zone deformations.

Anti-Bacterial Agents↗
PubMed2002

Production of BRO beta-lactamases and resistance to complement in European Moraxella catarrhalis isolates.

Of the 419 Moraxella catarrhalis isolates collected during the 1997-1999 European SENTRY surveillance study, 385 (92%) were beta-lactamase positive. Twenty-two (5.7%) produced BRO-2 beta-lactamase. Twenty-one new mutations were found in the putative promoter region of the bro genes. Nineteen percent of all isolates tested were complement sensitive. Resistance to beta-lactams is not linked to the phylogenetic lineages associated with susceptibility to complement.

Complement System Proteins↗
PubMed2002

Comparative evaluation of the BD Phoenix and VITEK 2 automated instruments for identification of isolates of the Burkholderia cepacia complex.

We evaluated two new automated identification systems, the BD Phoenix (Becton Dickinson) and the VITEK 2 (bioMérieux), for identification of isolates of the Burkholderia cepacia complex (BCC). The test sample included 42 isolates of the highly virulent and epidemic genomovar III, 45 isolates of B. multivorans, and 47 isolates of other members of the BCC. Rates of correct identification by the BD Phoenix and VITEK 2 were similar when all BCC isolates were considered (50 and 53%, respectively) but differed markedly for genomovar III (71 and 38%; P < 0.01) and for B. multivorans (58 and 89%; P < 0.001). For the BD Phoenix as well as the VITEK 2, taking all 134 isolates of the BCC together, rates of correct identification of clinical isolates (56 and 55%, respectively; n = 85) were higher than those of environmental isolates (21 and 39%, respectively; n = 28). Clinical isolates of genomovar III (n = 27) showed correct identification rates of 81% (BD Phoenix) and 48% (VITEK 2) (P < 0.01). Rates of misidentification for BD Phoenix and VITEK 2 were 9 and 17% for genomovar III, 22 and 7% for B. multivorans, and 36 and 13% for the other BCC members (P < 0.01), respectively. More than half of the isolates misidentified by each instrument were identified as Ralstonia pickettii, Ralstonia paucula (CDC IV C-2 group), Alcaligenes faecalis, Achromobacter spp., or, for the VITEK 2, "various nonfermenters." This study reemphasizes that confirmatory identification of BCC, preferably by molecular methods, is highly recommended.

Automation↗
PubMed2002

Automated ribotyping of vancomycin-resistant Enterococcus faecium isolates.

Vancomycin-resistant Enterococcus faecium (VREF) strains represent an important threat in hospital infections in the United States and are found at high frequencies in both the community and farm animals in Europe. We evaluated automated ribotyping for interlaboratory reproducibility by using the restriction enzymes EcoRI and BamHI and compared ribotyping to both amplification of fragment length polymorphism (AFLP) analysis and multilocus sequence typing (MLST) to assess its discriminatory power and capacity for the identification of epidemiologically important strains. Of 19 (EcoRI) and 16 (BamHI) isolates tested in duplicate in two laboratories, 18 (95%) and 16 (100%), respectively, showed reproducible ribotypes. These high reproducibility rates were obtained only after manual refinement of the automated fingerprint analysis. A group of 49 VREF strains initially selected to represent 32 distinct AFLP types were separated into 28 EcoRI ribotypes, 25 BamHI ribotypes, and 28 sequence types. Ribotyping with EcoRI and BamHI was able to discern the host-specific genogroups recently disclosed by AFLP typing and MLST and to distinguish most strains containing the esp gene, a marker specific for strains causing hospital outbreaks. An expandable ribotype identification library was created. We recommend EcoRI as the enzyme of choice for automated ribotyping of VREF strains. Given the high level of discrimination of VREF strains, the high rate of interlaboratory reproducibility, and the potential for the identification of epidemiologically important genotypes, automated ribotyping appears to be a very valuable approach for characterizing VREF strains.

Alleles↗
PubMed2002

Clinical evaluation of a NASBA-based assay for detection of Candida spp. in blood and blood cultures.

The number of life-threatening opportunistic fungal infections has shown a dramatic increase. However, the diagnosis of candidemia remains difficult. Nucleic acid amplification assays may improve the detection rate and decrease the time needed for detection and identification of Candida spp. Whole blood samples of patients suspected of having candidemia were analyzed using Nucleic Acid Sequence-Based Amplification (NASBA). Furthermore, aliquots of blood cultures of the patients after 2 days of culturing were tested. Eleven data sets from ten patients in two hospitals were generated. None of the whole blood samples was positive in the NASBA assay. Eight samples were positive in the NASBA assay after two days of culturing, whereas only two additional positive samples were found after longer incubation periods. Thus, a two-day culture step is sufficient to greatly improve the sensitivity of the NASBA assay. The NASBA assay detected Candida RNA in three patients. In one patient, the yeast was not detected by automated blood culturing, in another patient the NASBA assay detected the infection two days earlier than the blood culture system.

Candida↗
PubMed1999

Effect of glucose and pH on uropathogenic and non-uropathogenic Escherichia coli: studies with urine from diabetic and non-diabetic individuals.

It is generally assumed that one of the reasons why diabetics are more susceptible to urinary tract infections than non-diabetics is their 'sweet urine'. However, very little information is available on this subject. Therefore, the growth rates of different Escherichia coli strains were studied in human urine with and without added glucose and with and without a constant pH, and compared with their growth rates in Mueller-Hinton broth (MHB). Eight isolates were used (three from blood cultures from urosepsis patients, two urinary isolates, two faecal isolates and one laboratory strain K12). All isolates grew better in MHB than in urine, but with the exception of the laboratory strain, they had the same growth rate in urine. No significant difference was found between the growth rate in urine from diabetics without glucosuria and that in urine from non-diabetics. The addition of glucose (up to a concentration of 1000 mg/dl) to urine and MHB enhanced the growth rate of all isolates. However, very high concentrations of glucose (up to 10000 mg/dl) in urine and MHB caused a decrease in bacterial growth rate when the urinary pH was not kept constant. The stationary phase was reached later and the final bacterial yield was greater when the urine was made less acidic. As the uropathogenic strains did not grow better in urine than the other isolates, it may be concluded that better growth in urine is not one of the causes of the greater virulence of these strains.

Bacteriuria↗
PubMedDate not supplied

Discrimination of Klebsiella pneumoniae and Klebsiella oxytoca phylogenetic groups and other Klebsiella species by use of amplified fragment length polymorphism.

Bacteria of the genus Klebsiella are opportunistic pathogens responsible for an increasing number of multiresistant infections in hospitals. The two clinically and epidemiologically most important species, Klebsiella pneumoniae and K. oxytoca, have recently been shown to be subdivided into three and two phylogenetic groups, respectively. The aim of this study was an in depth evaluation of the amplified fragment length polymorphism (AFLP) genetic characterization method for epidemiological and phylogenic analyzes of Klebsiella isolates. First, we investigated the variability of AFLP patterns for Klebsiella strains within and between different outbreaks. Second, by use of carefully characterized phylogenetically representative strains, we examined whether different Klebsiella species and phylogenetic groups can be discriminated using AFLP. Twenty-four strains originating from seven presumed outbreaks and 31 non-associated strains were investigated. The AFLP fingerprints of all epidemiologically associated strains showed three or fewer fragment differences, whereas unrelated strains differed by at least four fragments. Cluster analysis of the AFLP data revealed a very high concordance with the phylogenetic assignation of strains based on the gyrA sequence and ribotyping data. The species K. pneumoniae, K. oxytoca, K. terrigena and the possibly synonymous pair K. planticola/K. ornithinolytica each formed a separate cluster. Similarly, strains of the phylogenetic groups of K. pneumoniae and K. oxytoca fell into their corresponding clusters, with only two exceptions. This study provides a preliminary cut-off value for distinguishing epidemiologically non-related Klebsiella isolates based on AFLP data; it confirms the sharp delineation of the recently identified phylogenetic groups, and demonstrates that AFLP is suitable for identification of Klebsiella species and phylogenetic groups.

Bacterial Proteins↗
PubMedDate not supplied

[Nasopharyngeal isolates of S. pneumoniae from healthy carriers and children with pneumonia: colonization rates and antimicrobial susceptibility].

OBJECTIVES: To compare colonization rates and antimicrobial resistance of nasopharyngeal pneumococci in healthy carriers and children with pneumonia. METHODS: A cross-sectional study. Healthy subjects of this study were selected from randomly chosen immunization centers and day-care centers, and those with pneumonia were selected in pediatric emergency rooms. Flexible perinasal alginate swabs were employed to collect nasopharyngeal pneumococci specimens. Isolation and identification were performed according to standard procedures. Minimum Inhibitory Concentrations were assessed by microdilution techniques. RESULTS: We studied 911 children, 429 healthy controls (60% of carriers, 72% attending day care centers and 49% recruited in immunization centers) and 482 children with pneumonia (50% of carriers) (P=0.02). The Minimum Inhibitory Concentration of penicillin to 441 isolates detected 198 (45%) of intermediate and 16 (4%) fully resistant pneumococci. Antimicrobial resistance rates of isolates from healthy carriers and children with pneumonia were, respectively: penicillin 48% (37% for immunization centers and 55% for day-care centers) and 50% (P>0.05), erythromycin 28% and 19% (P=0.05); cotrimoxazole 81% and 76% (P>0.05), chloramphenicol 6% and 7% (P>0.05), rifampin 5 and 3% (P>0.05) ceftriaxone 2 and 4% (P>0.05) and vancomycin 0% in both groups. An association among pneumococcal resistance to penicillin, erythromycin and cotrimoxazole was detected. CONCLUSIONS: Pneumococcal carriage rate was higher in healthy children than in children with pneumonia. Penicillin and cotrimoxazole resistance rates were high, especially among those attending day-care centers.

English Abstract↗