Tigecycline is regarded as a last-resort treatment for multidrug-resistant Acinetobacter baumannii. However, tigecycline resistance in A. baumannii has increased worldwide. In this study, we ...investigated tigecycline heteroresistance in A. baumannii isolates from South Korea. Antibiotic susceptibility testing was performed on 323 nonduplicated A. baumannii isolates. Among 260 and 37 tigecycline-susceptible and -intermediate-resistant A. baumannii isolates, 146 (56.2%) and 22 (59.5%) isolates were identified as heteroresistant to tigecycline through a disk diffusion assay and population analysis profiling. For selected isolates, an
time-kill assay was performed, and survival rates were measured after preincubation with diverse concentrations of tigecycline. Heteroresistant isolates showed regrowth after 12 h of 2× MIC of tigecycline treatment, and resistant subpopulations were selected by preexposure to tigecycline. Furthermore, genetic alterations in
, and
were assessed, and the relative mRNA expression levels of
and
were compared. The tigecycline resistance in subpopulations might be due to the insertion of IS
in
, leading to the overexpression of the AdeABC efflux pump. However, the tigecycline resistance of subpopulations was not stable during serial passages in antibiotic-free medium. The reversion of tigecycline susceptibility by antibiotic-free passages might occur by additional insertions of IS
in
and nucleotide alterations in
in some mutants. Tigecycline heteroresistance is prevalent in A. baumannii isolates, which results in treatment failure. Tigecycline resistance is mainly due to the overexpression of the AdeABC efflux pump, which is associated with genetic mutations, but this resistance could be reversed into susceptibility by additional mutations in antibiotic-free environments.
The evidence that antibiotic heteroresistance is responsible for treatment failure in clinical settings is increasing. Thus, detection and characterization of heteroresistance would be important for appropriate therapeutic guidance to treat bacterial infections. However, data on tigecycline heteroresistance in Gram-negative bacteria is currently limited, although tigecycline is regarded as a last-line antibiotic against infections caused by antibiotic-resistant pathogens. In this study, we investigated the tigecycline heteroresistance in Acinetobacter baumannii, which has been listed by the WHO as a priority for research and development of new antibiotics. We found very high prevalence of tigecycline-heteroresistant A. baumannii clinical isolates, which may result in treatment failure due to the selection of resistant subpopulations. We also identified the main resistance mechanism in tigecycline-resistant subpopulations, that is, upregulation of AdeABC efflux pumps due to IS
insertion in
In this study, we investigated the effects of colistin resistance on virulence and fitness in hypermucoviscous (HV) Klebsiella pneumoniae sequence type 23 (ST23) strains. Colistin-resistant mutants ...were developed from three colistin-susceptible HV K. pneumoniae ST23 strains. The lipid A structures of strains were analyzed by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry. Changes in HV were investigated using the string test, and extracellular polysaccharide production was quantified. The expression levels of the phoQ, pmrD, pmrB, pbgP, magA, and p-rmpA2 genes, serum resistance, and biofilm-forming activity were determined. The fitness of colistin-resistant mutants compared to that of the parental strains was examined by determining the competitive index (CI). The colistin-resistant mutants exhibited reduced HV, which was accompanied by decreased formation of capsular polysaccharides (CPS) and reduced expression of genes (magA and p-rmpA2). While there was enhanced expression of pmrD and pbgP in all colistin-resistant derivatives, there were differences in the expression levels of phoQ and pmrB between strains. MALDI-TOF analysis detected the addition of aminoarabinose or palmitate to the lipid A moiety of lipopolysaccharide in the colistin-resistant derivatives. In addition, survival rates in the presence of normal human serum were decreased in the mutant strains, and CI values (0.01 to 0.19) indicated significant fitness defects in the colistin-resistant derivatives compared to the respective parental strains. In hypervirulent HV K. pneumoniae strains, the acquisition of colistin resistance was accompanied by reduced CPS production, impaired virulence, and a significant fitness cost.
Abstract
Effective passivation of grain boundaries in perovskite solar cells is essential for achieving high device performance and stability. However, traditional polymer‐based passivation ...strategies can introduce challenges, including increased series resistance, disruption of charge transport, and insufficient passivation coverage. In this study, a novel approach is proposed that integrates a multifunctional ambipolar polymer into perovskite solar cells to address these issues. The ambipolar polymer is successfully incorporated into both the perovskite film and the hole transport layer (HTL), enabling comprehensive restoration of defect sites within the perovskite active layer. Moreover, this approach yields additional advantages for perovskite devices, such as enabling bidirectional charge transport, limiting pinhole formation at the HTL, reducing lithium‐ion migration from the HTL to the perovskite, and minimizing both the band offset and surface energy difference between the perovskite film and HTL interface. With these benefits, the ambipolar polymer integrated device achieves a power conversion efficiency (
PCE
) of 24.0%. Remarkably, it also exhibits enhanced long‐term stability, preserving 92% of its initial
PCE
after 2000 h under ambient conditions, and 80% of its initial
PCE
after 432 h under harsh conditions (at 85 °C and 85 ± 5% RH).
Antibiotic resistance is a global concern in public health. Antibiotic-resistant clones can spread nationally, internationally, and globally. This review considers representative antibiotic-resistant ...Gram-negative bacterial clones–CTX-M- 15-producing ST131 in
Escherichia coli
, extended-spectrum ß-lactamase-producing ST11 and KPC-producing ST258 in
Klebsiella pneumoniae
, IMP-6-producing, carbapenem-resistant ST235 in
Pseudomonas aeruginosa
, and OXA-23-producing global clone 2 in
Acinetobacter baumannii
–that have disseminated worldwide, including in Korea. The findings highlight the urgency for systematic monitoring and international cooperation to suppress the emergence and propagation of antibiotic resistance.
The development of tigecycline resistance in hypervirulent Klebsiella pneumoniae strains has resulted in decreased virulence that is associated with reduced production of capsular polysaccharides ...(CPS). In this study, we investigated the mechanisms that link tigecycline susceptibility to decreased virulence.
We compared transcriptomes from tigecycline-susceptible wild-type strains and tigecycline-resistant mutants using mRNA sequencing. ompR-overexpressed and ompR-deleted mutants were constructed from wild-type strains and tigecycline-resistant mutants, respectively. Antibiotic susceptibility tests were performed, and string tests and precipitation assays were conducted to identify phenotypic changes related to tigecycline susceptibility and ompR expression. Bacterial virulence was assessed by serum resistance and Galleria mellonella infection assays.
Transcriptomic analyses demonstrated a significant decrease in the expression of ompK35 in the tigecycline-resistant mutants. We observed that tigecycline-resistant mutants overexpressed ompR, and that the expression of ompK35 was regulated negatively by ompR. While tigecycline-resistant mutants and ompR-overexpressed mutants exhibited reduced hypermucoviscosity and virulence, deletion of ompR from tigecycline-resistant mutants restored their hypermucoviscosity and virulence.
In hypervirulent K. pneumoniae strains, ompR expression, which is regulated by exposure to tigecycline, may affect the production of CPS, leading to bacterial virulence.
Epidemiological studies of the naturally transformable bacterial pathogen Streptococcus pneumoniae have previously been confounded by high rates of recombination. Sequencing 240 isolates of the PMEN1 ...(Spain²³F-1) multidrug-resistant lineage enabled base substitutions to be distinguished from polymorphisms arising through horizontal sequence transfer. More than 700 recombinations were detected, with genes encoding major antigens frequently affected. Among these were 10 capsule-switching events, one of which accompanied a population shift as vaccine-escape serotype 19A isolates emerged in the USA after the introduction of the conjugate polysaccharide vaccine. The evolution of resistance to fluoroquinolones, rifampicin, and macrolides was observed to occur on multiple occasions. This study details how genomic plasticity within lineages of recombinogenic bacteria can permit adaptation to clinical interventions over remarkably short time scales.
Non-alcoholic fatty liver disease (NAFLD) is a dominant cause of chronic liver disease, but the exact mechanism of progression from simple steatosis to nonalcoholic steatohepatitis (NASH) remains ...unknown. Here, we investigated the role of exosomes in NAFLD progression. Exosomes were isolated from a human hepatoma cell line treated with palmitic acid (PA) and their miRNA profiles examined by microarray. The human hepatic stellate cell (HSC) line (LX-2) was then treated with exosome isolated from hepatocytes. Compared with controls, PA-treated hepatocytes displayed significantly increased CD36 and exosome production. The microarray analysis showed there to be distinctive miRNA expression patterns between exosomes from vehicle- and PA-treated hepatocytes. When LX-2 cells were cultured with exosomes from PA-treated hepatocytes, the expression of genes related to the development of fibrosis were significantly amplified compared to those treated with exosomes from vehicle-treated hepatocytes. In conclusion, PA treatment enhanced the production of exosomes in these hepatocytes and changed their exosomal miRNA profile. Moreover, exosomes derived from PA-treated hepatocytes caused an increase in the expression levels of fibrotic genes in HSCs. Therefore, exosomes may have important roles in the crosstalk between hepatocytes and HSCs in the progression from simple steatosis to NASH.
CrrAB two-component regulatory system is associated with colistin resistance in
Klebsiella pneumoniae
. Recently, some
K. pneumoniae
isolates lacking
crrAB
genes have been identified. In this study, ...we investigated the distribution and structural variation of the
crrBAC-kexD
cluster. To evaluate the structural variation of the
crrBAC-kexD
cluster, we explored 59 clinical
K. pneumoniae
isolates from Korea, and 508 whole genomes of
K. pneumoniae
and other strains of
Klebsiella
sp. Significant structural variations in
crrBAC-kexD
and its surrounding regions were identified among
K. pneumoniae
genomes. Within the genus
Klebsiella
, the cluster was identified only in
K. pneumoniae
,
K. variicola
, and
K. quasipneumoniae
, which form the
K. pneumoniae
complex. Among the 304 available
K. pneumoniae
genomes, an intact
crrBAC-kexD
cluster was identified in 178 isolates (58.6%), while the cluster was absent in 90 isolates (29.6%). Partial deletions within the cluster were identified in 22 genomes (7.2%). The most diverse structural patterns of the
crrBAC-kexD
cluster were observed in ST11 strains. Some clades lacked the
crrBAC-kexD
cluster. The
crrBAC-kexD
cluster was identified in the genomes of other bacterial species, including
Citrobacter freundii
and
Enterobacter ludwigii.
The
crrBAC-kexD
cluster is proposed to have been acquired by the ancestor of the
K. pneumoniae
complex from other bacterial species and the cluster may have been lost and re-acquired repeatedly in
K. pneumoniae
strains according to the phylogenetic analysis. The dynamic evolution of the
crrBAC-kexD
cluster suggests that it may have other roles, in addition to colistin resistance, in bacterial physiology.
Among 213 Pseudomonas aeruginosa isolates collected from 10 South Korean hospitals, 57 isolates (26.8%) were carbapenem-resistant. All but three of the isolates had a relevant decrease of oprD ...expression. However, decreased oprD expression was also detected in five of ten carbapenem-susceptible isolates. Outer membrane protein analysis confirmed porin loss in carbapenem-resistant P. aeruginosa isolates. Based on the mutations of oprD gene sequences, carbapenem-resistant P. aeruginosa isolates could be classified into five oprD mutational groups. However, there was no difference of OprD expression or carbapenem minimum inhibitory concentrations among the five mutational groups. Among the 57 carbapenem-resistant P. aeruginosa isolates, 41 (71.9%) overexpressed efflux systems or ampC. MexAB–OprM and AmpC overexpression (56.1% and 47.4%, respectively) was prevalent and was significantly associated with carbapenem resistance. However, no synergistic effect of efflux systems and AmpC on carbapenem resistance was evident. In conclusion, combination of several mutation-driven mechanisms leading to OprD inactivation and overexpression of efflux systems was the main carbapenem resistance mechanism, but acquisition of a transferable resistance determinant such as metallo-β-lactamase could be problematic in clinical settings in South Korea.
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