3 research outputs found
Diversity of resistance mechanisms in carbapenem-resistant Enterobacteriaceae at a health care system in Northern California, from 2013 to 2016
The mechanism of resistance in carbapenem-resistant Enterobacteriaceae (CRE) has therapeutic implications. We comprehensively characterized emerging mechanisms of resistance in CRE between 2013 and 2016 at a health system in Northern California. A total of 38.7% (24/62) of CRE isolates were carbapenemase gene-positive, comprising 25.0% (6/24) blaOXA-48 like, 20.8% (5/24) blaKPC, 20.8% (5/24) blaNDM, 20.8% (5/24) blaSME, 8.3% (2/24) blaIMP, and 4.2% (1/24) blaVIM. Between carbapenemases and porin loss, the resistance mechanism was identified in 95.2% (59/62) of CRE isolates. Isolates expressing blaKPC were 100% susceptible to ceftazidime–avibactam, meropenem–vaborbactam, and imipenem–relebactam; blaOXA-48 like–positive isolates were 100% susceptible to ceftazidime–avibactam; and metallo β-lactamase–positive isolates were nearly all nonsusceptible to above antibiotics. Carbapenemase gene-negative CRE were 100% (38/38), 92.1% (35/38), 89.5% (34/38), and 31.6% (12/38) susceptible to ceftazidime–avibactam, meropenem–vaborbactam, imipenem–relebactam, and ceftolozane–tazobactam, respectively. None of the CRE strains were identical by whole genome sequencing. At this health system, CRE were mediated by diverse mechanisms with predictable susceptibility to newer β-lactamase inhibitors
Recommended from our members
Rapid, automated characterization of disulfide bond scrambling and IgG2 isoform determination
Human antibodies of the IgG2 subclass exhibit complex inter-chain disulfide bonding patterns that result in three structures, namely A, A/B, and B. In therapeutic applications, the distribution of disulfide isoforms is a critical product quality attribute because each configuration affects higher order structure, stability, isoelectric point, and antigen binding. The current standard for quantification of IgG2 disulfide isoform distribution is based on chromatographic or electrophoretic techniques that require additional characterization using mass spectrometry (MS)-based methods to confirm disulfide linkages. Detailed characterization of the IgG2 disulfide linkages often involve MS/MS approaches that include electrospray ionization or electron-transfer dissociation, and method optimization is often cumbersome due to the large size and heterogeneity of the disulfide-bonded peptides. As reported here, we developed a rapid LC-MALDI-TOF/TOF workflow that can both identify the IgG2 disulfide linkages and provide a semi-quantitative assessment of the distribution of the disulfide isoforms. We established signature disulfide-bonded IgG2 hinge peptides that correspond to the A, A/B, and B disulfide isoforms and can be applied to the fast classification of IgG2 isoforms in heterogeneous mixtures
Integrating Internal Fragments in the Interpretation of Top-Down Sequencing Data of Larger Oligonucleotides
In the context of direct top-down analysis or concerted
bottom-up
characterization of nucleic acid samples, the waning yield of terminal
fragments as a function of precursor ion size poses a significant
challenge to the gas-phase sequencing of progressively larger oligonucleotides.
In this report, we examined the behavior of oligoribonucleotide samples
ranging from 20 to 364 nt upon collision-induced dissociation (CID).
The experimental data showed a progressive shift from terminal to
internal fragments as a function of size. The systematic evaluation
of experimental factors, such as collision energy, precursor charge,
sample temperature, and the presence of chaotropic agents, showed
that this trend could be modestly alleviated but not suppressed. This
inexorable effect, which has been reported also for other activation
techniques, prompted a re-examination of the features that have traditionally
discouraged the utilization of internal fragments as a source of sequence
information in data interpretation procedures. Our simulations highlighted
the ability of internal fragments to produce self-consistent ladders
with either end corresponding to each nucleotide in the sequence,
which enables both proper alignment and correct recognition of intervening
nucleotides. In turn, contiguous ladders display extensive overlaps
with one another and with the ladders formed by terminal fragments,
which unambiguously constrain their mutual placement within the analyte
sequence. The experimental data borne out the predictions by showing
ladders with extensive overlaps, which translated into uninterrupted
“walks” covering the entire sequence with no gaps from
end to end. More significantly, the results showed that combining
the information afforded by internal and terminal ladders resulted
in much a greater sequence coverage and nucleotide coverage depth
than those achievable when either type of information was considered
separately. The examination of a series of 58-mer oligonucleotides
with high sequence homology showed that the assignment ambiguities
engendered by internal fragments did not significantly exceed those
afforded by the terminal ones. Therefore, the balance between potential
benefits and perils of including the former makes a compelling argument
for the development of integrated data interpretation strategies,
which are better equipped for dealing with the changing fragmentation
patterns obtained from progressively larger oligonucleotides