The present study was aimed at simplifying procedures to delineate species and identify isolates based on DNA–DNA reassociation. DNA macro-arrays harbouring genomic DNA of reference strains of several Burkholderia species were produced. Labelled genomic DNA, hybridized to such an array, allowed multiple relative pairwise comparisons. Based on the relative DNA–DNA relatedness values, a complete data matrix was constructed and the ability of the method to discriminate strains belonging to different species was assessed. This simple approach led successfully to the discrimination of Burkholderia mallei from Burkholderia pseudomallei, but also discriminated Burkholderia cepacia genomovars I and III, Burkholderia multivorans, Burkholderia pyrrocinia, Burkholderia stabilis and Burkholderia vietnamiensis. Present data showed a sufficient degree of congruence with previous DNA–DNA reassociation techniques. As part of a polyphasic taxonomic scheme, this straightforward approach is proposed to improve species definition, especially for application in the rapid screening necessary for large numbers of clinical or environmental isolates.
Objectives: Fifty isolates of Burkholderia pseudomallei and 15 isolates of Burkholderia mallei were tested for their susceptibilities to 35 antimicrobial agents, including agents not previously tested against these bacteria.
Francisella tularensis subsp. holarctica strains are classified as biovars I and II, which are susceptible and naturally resistant to the macrolide erythromycin, respectively. The present study was aimed at both selecting biovar I strains with increased levels of erythromycin resistance and characterizing the underlying genetic mechanisms. Serial cultures in the presence of increasingly high erythromycin concentrations were performed to select independent high- and intermediate-level erythromycin-resistant mutants from each of three different biovar I strains. The mutants were characterized for cross-resistance to several antibiotics, presence of mutations in the genes encoding the 23S rRNA and the L4 and L22 ribosomal proteins, and overexpression of efflux pumps. Mutants displayed cross-resistance to all macrolide compounds tested but not to other classes of antibiotics. We found mutations in domain V of the 23S rRNA gene (G2057A, A2058G, A2058T and C2611T) and in the gene encoding L22, leading to either the G91D substitution or the M82K83R84 deletion. Analysis of mutants with intermediate resistance levels obtained over the course of the selection process revealed both a positive correlation between the number of mutated ribosomal operons and the resistance level, and an additional resistance mechanism in the early steps of selection. We showed that high-level resistance to macrolides can be easily obtained in vitro in F. tularensis subsp. holarctica biovar I strains, thereby suggesting that in vivo selection for resistance may explain reported failures of antibiotic treatment. Ketolides were the most effective macrolides tested, which may limit the risk of selection for resistance.
While expert vs. novice comparisons using fMRI revealed a link between executive function and expertise in scientific fields such as electricity and mechanics, it is still uncertain whether these functions are active components of the learning process, rather than its by-product.Using the Force Concept Inventory to track conceptual change, the aim of this study was to confirm that executive function is indeed relevant to this process.Data suggests that participants with higher executive function abilities, as approximated by the Wisconsin Card Sorting Test, are likely to make more progress toward conceptual changes in a 15-week physics course than participants with lesser abilities.This implies that executive function is solicited throughout the process of conceptual change, and not solely being used as a consequence of expertise.
ABSTRACT Burkholderia pseudomallei and B. mallei are two highly pathogenic bacteria, responsible for melioidosis and glanders, respectively. The two are closely related and can also be mistaken for B. thailandensis , a nonpathogenic species. To improve their differential identification, we describe a hydrolysis probe-based real-time PCR method using the uneven distribution of type III secretion system genes among these three species.
