Single-cell scattering and auto-fluorescence-based fast antibiotic susceptibility testing for gram-negative and gram-positive bacteria

In this study, we assess the scattering of light and auto-fluorescence from single bacterial cells to address the challenge of fast (<2 h), label-free phenotypic antimicrobial susceptibility testing (AST). Label-free flow cytometry is used for monitoring both the respiration-related auto-fluorescence in two different fluorescence channels corresponding to FAD and NADH, and the morphological and structural information contained in the light scattered by individual bacteria during incubation with or without antibiotic. Large multi-parameter data are analyzed using dimensionality reduction methods, based either on a combination of 2D binning and Principal Component Analysis, or with a one-class Support Vector Machine approach, with the objective to predict the Susceptible or Resistant phenotype of the strain. For the first time, both Escherichia coli (Gram-negative) and Staphylococcus epidermidis (Gram-positive) isolates were tested with a label-free approach, and, in the presence of two groups of bactericidal antibiotic molecules, aminoglycosides and beta-lactams. Our results support the feasibility of label-free AST in less than 2 h and suggest that single cell auto-fluorescence adds value to the Susceptible/Resistant phenotyping over single-cell scattering alone, in particular for the mecA+ Staphylococcus (i.e., resistant) strains treated with oxacillin

The surface protein HvgA mediates group B streptococcus hypervirulence and meningeal tropism in neonates

Lethal meningitis triggered by the hypervirulent group B streptococcus clone ST-17 is mediated by a novel surface protein called HvgA

b-lactamases à large spectre chez les flavobacteriaceae et résistance naturelle aux b-lactamines

CHATENAY M.-PARIS 11-BU Pharma. (920192101) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

Chromosome-Encoded β-Lactamases TUS-1 and MUS-1 from Myroides odoratus and Myroides odoratimimus (Formerly Flavobacterium odoratum), New Members of the Lineage of Molecular Subclass B1 Metalloenzymes

Myroides odoratus and Myroides odoratimimus (formerly designated in a single species as Flavobacterium odoratum) are gram-negative aerobes and sources of nosocomial infections in humans. They have variable susceptibility to β-lactams and a decreased susceptibility to carbapenems. Using genomic DNAs of M. odoratus CIP 103105 and M. odoratimimus CIP 103073 reference strains, shotgun cloning of β-lactamase genes was performed, followed by protein expression in Escherichia coli. The deduced amino acid sequences of these β-lactamase genes revealed that TUS-1 and MUS-1 from M. odoratus CIP 103105 and M. odoratimimus CIP 103073, respectively, shared 73% amino acid identity. Mature proteins TUS-1 and MUS-1, with pI values of 7.8 and 5.2, respectively, had relative molecular masses of ca. 26 kDa. These β-lactamases are members of the subclass B1 of metallo-β-lactamases and are distantly related to other metalloenzymes, being most closely related to IND-1 from Chryseobacterium indologenes (42% amino acid identity). However, phylogenic analysis showed that TUS-1 and MUS-1 belong to the same phylogenic lineage of subclass B1 enzymes that groups the subclass B1 β-lactamases of Flavobacterium species. Kinetic parameters of purified β-lactamases TUS-1 and MUS-1 detailed their hydrolysis spectra, which encompass most β-lactams except aztreonam. β-Lactamases TUS-1 and MUS-1 were classified in functional subgroup 3a of metalloenzymes. This work further characterizes chromosome-encoded metalloenzymes from Flavobacteriaceae species that explain at least part of their intrinsic resistance to β-lactams

EBR-1, a Novel Ambler Subclass B1 β-Lactamase from Empedobacter brevis

Empedobacter brevis (formerly designated Flavobacterium breve) is a gram-negative aerobe involved in nosocomial infections. The Ambler class B β-lactamase gene bla(EBR-1) was cloned and expressed in Escherichia coli from E. brevis clinical strain ASS-1, which had reduced susceptibility to expanded-spectrum cephalosporins and carbapenems. Purified β-lactamase EBR-1 hydrolyzed penicillins, cephalosporins, and carbapenems efficiently but not aztreonam. Kinetic parameters of EBR-1 were similar to those of class B enzymes such as BlaB, IND-2, and GOB-1 identified from other Flavobacteriaceae species, except for meropenem, which was more hydrolyzed by β-lactamase GOB-1. EBR-1, with a pI of 8.0 and a relative molecular mass of ca. 25 kDa, was classified in functional subgroup 3a, which includes most of the class B β-lactamases. EBR-1, which belongs to molecular subclass B1 of metalloenzymes, shares 58, 57, and 42% amino acid identity with the most closely related β-lactamases, IND-1/IND-2 from Chryseobacterium indologenes, CGB-1 from Chryseobacterium gleum, and BlaB from Chryseobacterium meningosepticum, respectively