A culture medium for screening 16S rRNA methylase-producing pan-aminoglycoside resistant Gram-negative bacteria.

The amikacin plus gentamicin-containing SuperAminoglycoside medium was developed for screening multiple-aminoglycoside resistance in Gram-negative bacteria (Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter baumannii). It was evaluated using aminoglycoside-susceptible (n=12) and aminoglycoside-resistant (n=59) Gram-negative isolates, including 16S rRNA methylase producers (n=20). Its sensitivity and specificity of detection were, respectively, of 95% and 96% for detecting multiple aminoglycoside-resistant methylase producers.

Rapid Polymyxin NP test for the detection of polymyxin resistance mediated by the mcr-1/mcr-2 genes.

The Rapid Polymyxin NP test has been recently developed to rapidly detect polymyxin resistance in Enterobacteriaceae. Here we evaluated this test for detecting MCR-1/MCR-2-producing Enterobacteriaceae using a collection of 70 non-redundant strains either recovered from the environment, animals, or humans. Sensitivity and specificity were found to be 100%.

Rapid Aminoglycoside NP Test for Rapid Detection of Multiple Aminoglycoside Resistance in Enterobacteriaceae.

The rapid aminoglycoside NP (Nordmann/Poirel) test was developed to rapidly identify multiple aminoglycoside (AG) resistance in Enterobacteriaceae It is based on the detection of the glucose metabolism related to enterobacterial growth in the presence of a defined concentration of amikacin plus gentamicin. Formation of acid metabolites was evidenced by a color change (orange to yellow) of the red phenol pH indicator. The rapid aminoglycoside NP test was evaluated by using bacterial colonies of 18 AG-resistant isolates producing 16S rRNA methylases, 20 AG-resistant isolates expressing AG-modifying enzymes (acetyl-, adenyl-, and phosphotransferases), and 10 isolates susceptible to AG. Its sensitivity and specificity were 100% and 97%, respectively, compared to the broth dilution method, which was taken as the gold standard for determining aminoglycoside resistance. The test is inexpensive, rapid (<2 h), and implementable worldwide.

Binding of silver nanoparticles to bacterial proteins depends on surface modifications and inhibits enzymatic activity.

Here we describe results from a proteomic study of protein-nanoparticle interactions to further the understanding of the ecotoxicological impact of silver nanoparticles (AgNPs) in the environment. We identified a number of proteins from Escherichia coli that bind specifically to bare or carbonate-coated AgNPs. Of these proteins, tryptophanase (TNase) was observed to have an especially high affinity for both surface modifications despite its low abundance in E. coli. Purified TNase loses enzymatic activity upon associating with AgNPs, suggesting that the active site may be in the vicinity of the binding site(s). TNase fragments with high affinities for both types of AgNPs were identified using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. Differences in peptide abundance/presence in mass spectra for the two types of AgNPs suggest preferential binding of some protein fragments based on surface coating. One high-binding protein fragment contained a residue (Arg103) that is part of the active site. Ag adducts were identified for some fragments and found to be characteristic of strong binding to AgNPs rather than association of the fragments with ionic silver. These results suggest a probable mechanism for adhesion of proteins to the most commonly used commercial nanoparticles and highlight the potential effect of nanoparticle surface coating on bioavailability.

Morphological and physiological traits of three major Arabidopsis thaliana accessions.

Arabidopsis is currently the most studied organism in plant biology. Its short life cycle and small genome size have rendered it one of the principal model systems. Additionally, numerous large T-DNA insertion mutant collections are available. The advent of molecular biology and the completion of the Arabidopsis genome sequence have contributed to helping researchers discover a large variety of mutants identified for their phenotypes. Yet, it is important to consider that natural phenotypic variations exist and appear in natural ecotypes, differing greatly in several traits. Although there are a vast number of ecotypes available, only a few have been extensively studied, and some have been created in laboratories. In order to identify new phenotypic differences, we chose to study the differences observed between three ecotypes: Columbia (Col-0), Landsberg erecta (Laer-0) and Wassilewskija (Ws-0). Our research focuses on observable morphological traits throughout plant growth and development along the entire plant life cycle. We then attempted to shed some light on phenotypic discrepancies through the study of the class III peroxidase protein family, which is involved in many aspects of plant growth and tissue differentiation. Both morphological and molecular aspects reveal that there are major variations between ecotypes, hence indicating a possibly interesting heterotic effect in the F1 from crosses between different Arabidopsis ecotypes.