Novel fragments of clavulanate observed in the structure of the class A b-lactamase from Bacillus licheniformis BS3

in Journal of Antimicrobial Chemotherapy (2012), 67(10), 2379-2387

A Tripeptide Deletion in the Class C beta-Lactamase FOX-4 Enzyme Impairs Cefoxitin Hydrolysis and Slightly Increases Susceptibility to beta-Lactamase Inhibitors

in Journal of Antimicrobial Chemotherapy (2010), 65(6), 1187-94

OBJECTIVES: A natural variant of the AmpC enzyme from Escherichia coli HKY28 with a tripeptide deletion (Gly-286/Ser-287/Asp-288) was recently described. The isolate produced an inhibitor-sensitive AmpC ... [more ▼]

OBJECTIVES: A natural variant of the AmpC enzyme from Escherichia coli HKY28 with a tripeptide deletion (Gly-286/Ser-287/Asp-288) was recently described. The isolate produced an inhibitor-sensitive AmpC beta-lactamase variant that also conferred higher than usual levels of resistance to ceftazidime in the E. coli host. To demonstrate whether this is true in other class C beta-lactamase enzymes, we deleted the equivalent tripeptide in the FOX-4 plasmid-mediated class C beta-lactamase. METHODS: By site-directed mutagenesis, we deleted the tripeptide Gly-306/Asn-307/Ser-308 of FOX-4, thus generating FOX-4(DeltaGNS). The enzymes (FOX-4 wild-type and DeltaGNS) were purified and kinetic parameters (kcat, Km, kcat/Km) as well as IC50 values of several beta-lactams were assessed. Modelling studies were also performed. RESULTS: FOX-4(DeltaGNS) did not increase the catalytic efficiency towards ceftazidime, although it conferred a slight increase in the susceptibility to beta-lactamase inhibitors. There was also a noteworthy decrease in the cefoxitin MIC with the FOX-4(DeltaGNS) mutant (from 512 to 16 mg/L) as well as a 10-fold decrease in kcat/Km towards imipenem, which revealed specific structural features. CONCLUSIONS: Although deletions in the R2-loop are able to extend the substrate spectrum of class C enzymes, the present results do not confirm this hypothesis in FOX-4. The FOX-4 R2 site would already be wide enough to accommodate antibiotic molecules, and thus any amino acid replacement or deletion at this location would not affect the hydrolytic efficiency towards beta-lactams and would have a less drastic effect on the susceptibility to beta-lactamase inhibitors. [less ▲]

Third Belgian multicentre survey of antibiotic susceptibility of anaerobic bacteria

in Journal of Antimicrobial Chemotherapy (2007), 59(1), 132-139

Objectives: To collect recent data on the susceptibility of anaerobes and to compare them with results from previous studies. Methods: Four hundred and forty-three anaerobic clinical isolates from various ... [more ▼]

Objectives: To collect recent data on the susceptibility of anaerobes and to compare them with results from previous studies. Methods: Four hundred and forty-three anaerobic clinical isolates from various body sites were prospectively collected from October 2003 to February 2005 in nine Belgian hospitals. MICs were determined for nine anti-anaerobic and three recently developed antibiotics. Results: Most Gram-negative bacilli except Fusobacterium spp. were resistant to penicillin. Piperacillin/tazobactam, metronidazole, chloramphenicol, meropenem and amoxicillin/clavulanic acid were very active against all groups, but only 86% of Bacteroides fragilis group strains were susceptible to the latter. Cefoxitin, cefotetan and clindamycin were less active. In particular, only 62%, 52% and 48% of B. fragilis group strains were susceptible, respectively. Clindamycin shows a continuing decrease in activity, as 83% were still susceptible in 1987 and 66% in 1993-94. Anti-anaerobic activity of the new antibiotics is interesting, with MIC50 and MIC90 of 1 and > 32 mg/L for moxifloxacin, 2 and 4 mg/L for linezolid and 0.5 and 8 mg/L for tigecycline. Conclusions: The susceptibility of anaerobic bacteria remains stable in Belgium, except for clindamycin, which shows a continuous decrease in activity. However, for each of the tested antibiotics, at least a few resistant organisms were detected. Consequently, for severe infections involving anaerobic bacteria, it could be advisable to perform microbiological testing instead of relying on known susceptibility profiles. Periodically monitoring background susceptibility remains necessary to guide empirical therapy. [less ▲]

Is it necessary to change the classification of ß-lactamases?

in Journal of Antimicrobial Chemotherapy (2005), 55(6), 1051-1053

Antimicrobial susceptilities of Campylobacter strains isolated from food animals in Belgium.

in Journal of Antimicrobial Chemotherapy (2001), 48

Afin d’assurer une transparence tout le long de la chaîne de transformation de la viande, il faut disposer d’un système de traçabilité performant. La traçabilité administative montre des limites que ... [more ▼]

Afin d’assurer une transparence tout le long de la chaîne de transformation de la viande, il faut disposer d’un système de traçabilité performant. La traçabilité administative montre des limites que l’utilisation de marqueurs génétiques pourrait surmonter. Le génome de chaque individu possède des différences de séquences, à la base du polymorphisme génétique, dont les marqueurs génétiques sont les témoins. Parmi ceux-ci, deux classes semblent s’imposer en matière de traçabilité : les microsatellites et les polymorphismes simple nucléotide. Les microsatellites sont caractérisés par un degré de polymorphisme important avec de nombreux allèles pour un même locus. De plus, leur détection se fait directement par amplification itérative. Techniquement, le problème se pose lors de la détection simultanée de plusieurs microsatellites où le patron obtenu est difficile à interpréter. Les polymorphismes simple nucléotide sont répresentés par des mutations ponctuelles dans la séquence nucléotidique. Ils sont fréquents, stables, répartis de façon aléatoire et généralement bialléliques. La détection se fait soit par hybridation sur des biopuces, soit par spectrométrie de masse ou par d’autres techniques facilement automatisables. Cette automatisation est nécessaire pour pouvoir tester un grand nombre de polymorphismes simultanément sur un grand nombre d’échantillons, permettant ainsi de diminuer les coûts. L’avantage majeur des polymophismes simple nucléotide est le signal binaire obtenu, son désavantage est le caractère population- spécifique de ce type de marqueur. [less ▲]

How should zoster trials be conducted?

in Journal of Antimicrobial Chemotherapy (1995), 36(6), 1089-1101

In 1994, an international group of interested clinicians and biostatisticians met to discuss the design of clinical trials in herpes tester. They agreed that trials in herpes tester should have ... [more ▼]

In 1994, an international group of interested clinicians and biostatisticians met to discuss the design of clinical trials in herpes tester. They agreed that trials in herpes tester should have prospectively agreed definitions of all outcome measures and plans for data analysis. In immunocompetent individuals, in whom pain is the major outcome measure, trials should only include patients over the age of 50 years, and for those recruited within 72 fi of rash onset, should be designed to demonstrate superiority of any new therapy over existing antivirals. The primary endpoint should be time to cessation of pain for at least 4 weeks and, for the purposes of statistical analysis of its duration, the pain associated with herpes tester ought to be considered as a continuum. All other variables, including the incidence of post-herpetic neuralgia and effects upon quality of life should be considered as secondary end-points. Evaluation of treatment effects on primary endpoints should be based upon an intent-to-treat (ITT) analysis and subgroup analysis should be used only to support the findings of the ITT analysis. These elements of good study design should be borne in mind in the evaluation of current and future trails of antiviral drugs in herpes zoster. [less ▲]