Variation in the formation of persister cells against meropenem in Klebsiella pneumoniae bacteremia and analysis of its clinical features

In vitro antibacterial and antibiofilm activities of isobavachalcone against Enterococcus faecalis clinical isolates from China

BACKGROUND

The pharmacological activities of the natural product isobavachalcone, such as antimicrobial activity, reverse transcriptase blockade, and antioxidant property have been extensively reported. Whereas, its antimicrobial and biofilm-inhibitory effects on clinical E. faecalis strains in China, along with its potential mechanisms, are still not fully clear. This research is intended to assess the in vitro antibacterial and anti-biofilm effects of isobavachalcone against clinical E. faecalis isolates sourced from China. Moreover, it further explores the potential target site of it within E. faecalis.

RESULTS

It was found that the minimum inhibitory concentrations (MICs) of isobavachalcone ranged from 6.25 to 12.5 µM against 220 E. faecalis clinical strains obtained from a tertiary hospital in China. The antibiofilm activity of it with sub-MIC concentration ( 1/2 × MIC ) against the biofilm formation of E. faecalis was demonstrated and Time -killing curve assay revealed the quick bactericidal effect of isobavachalcone against E. faecalis planktonic cells. However, no synergetic bactericidal activity of isobavachalcone co-administered with vancomycin, or ampicillin was observed for eradicating the biofilm. Moreover, isobavachalcone-resistant E. faecalis was isolated by in vitro induction of isobavachalcone, and whole genome sequencing was performed to determine the genetic mutations of ten functional proteins in isobavachalcone-resistant E. faecalis, including PurH and FlgJ, with the other eight proteins being related to cell wall or cell membrane biogenesis, DNA synthesis, and energy metabolism. In addition, molecular docking results indicate that there is a potential binding of isobavachalcone and PurH protein in E. faecalis.

CONCLUSION

This research highlights the potential of isobavachalcone as a potent antibacterial agent against E. faecalis clinical isolates, capable of significantly inhibiting biofilm formation at sub-MIC concentrations. PurH protein in E. faecalis might serve as a potential target of isobavachalcone and the specific action mechanism of isobavachalcone needs further study.

Klebsiella pneumoniae bacteremia mortality: a systematic review and meta-analysis

Objective

To analyze the mortality rate of patients with Klebsiella pneumoniae bacteremia (KPB) and the impact of extended spectrum beta-lactamase (ESBL) producing or carbapenem-resistance (CR) KP on the mortality rate among patients with bacteremia.

Methods

EMbase, Web of Science, PubMed, and The Cochrane Library were searched up to September 18th, 2022. Two reviewers independently extracted data and evaluated risk of bias of included studies by ROBINS-I tool. A meta-regression analysis was conducted using a mixed-effects model to explore possible sources of heterogeneity. A random-effects model was used for pooled analysis in case of significant heterogeneity (I2>50%). Otherwise, the fixed-effects model was performed.

Results

A total of 157 studies (37,915 enrolled patients) were included in the meta-analysis. The pooled death proportions of KPB were 17% (95% CI=0.14-0.20) at 7-day, 24% (95% CI=0.21-0.28) at 14-day, 29% (95% CI=0.26-0.31) at 30-day, 34% (95% CI=0.26-0.42) at 90-day, and 29% (95% CI=0.26-0.33) in hospital, respectively. Heterogeneity was found from the intensive care unit (ICU), hospital-acquired (HA), CRKP, and ESBL-KP in the meta-regression analysis. More than 50% of ICU, HA, CRKP, and ESBL-KP were associated with a significant higher 30-day mortality rates. The pooled mortality odds ratios (ORs) of CRKP vs. non-CRKP were 3.22 (95% CI 1.18-8.76) at 7-day, 5.66 (95% CI 4.31-7.42) at 14-day, 3.87 (95% CI 3.01-3.49) at 28- or 30-day, and 4.05 (95% CI 3.38-4.85) in hospital, respectively.

Conclusions

This meta-analysis indicated that patients with KPB in ICU, HA-KPB, CRKP, and ESBL-KP bacteremia were associated with a higher mortality rate. The high mortality rate caused by CRKP bacteremia has increased over time, challenging the public health.

In vitro activities of licochalcone A against planktonic cells and biofilm of Enterococcus faecalis

This study aims to evaluate the in vitro antibacterial and anti-biofilm activities of licochalcone A on Enterococcus faecalis and to investigate the possible target genes of licochalcone A in E. faecalis. This study found that licochalcone A had antibacterial activities against E. faecalis, with the MIC50 and MIC90 were 25 μM. Licochalcone A (at 4 × MIC) indicated a rapid bactericidal effect on E. faecalis planktonic cells, and killed more E. faecalis planktonic cells (at least 3-log10 cfu/ml) than vancomycin, linezolid, or ampicillin at the 2, 4, and 6 h of the time-killing test. Licochalcone A (at 10 × MIC) significantly reduced the production of E. faecalis persister cells (at least 2-log10 cfu/ml) than vancomycin, linezolid, or ampicillin at the 24, 48, 72, and 96 h of the time-killing test. Licochalcone A (at 1/4 × MIC) significantly inhibited the biofilm formation of E. faecalis. The RNA levels of biofilm formation-related genes, agg, esp, and srtA, markedly decreased when the E. faecalis isolates were treated with licochalcone A at 1/4 × MIC for 6 h. To explore the possible target genes of licochalcone A in E. faecalis, the licochalcone A non-sensitive E. faecalis clones were selected in vitro by induction of wildtype strains for about 140 days under the pressure of licochalcone A, and mutations in the possible target genes were detected by whole-genome sequencing. This study found that there were 11 nucleotide mutations leading to nonsynonymous mutations of 8 amino acids, and among these amino acid mutations, there were 3 mutations located in transcriptional regulator genes (MarR family transcriptional regulator, TetR family transcriptional regulator, and MerR family transcriptional regulator). In conclusion, this study found that licochalcone A had an antibacterial effect on E. faecalis, and significantly inhibited the biofilm formation of E. faecalis at subinhibitory concentrations.

Efficacy of Amikacin and Meropenem on Colistin-Induced Klebsiella pneumoniae Persisters

Colistin-based antibiotic therapies have been recommended for the treatment of multidrug-resistant Klebsiella pneumoniae infections. During colistin treatment, persister cells that tolerate antibiotics may arise. Here we designed an in vitro study to assess the killing activity of colistin, meropenem, and amikacin on colistin-induced K. pneumoniae persisters in comparison with starvation-induced persisters. Colistin-induced persisters were generated under exposure to 10 × minimum inhibitory concentration dose of colistin, whereas starvation-induced persisters were produced by limitation of nutrients. In colistin-induced persisters, amikacin totally inhibited cell growth in 6 hours, whereas 98% of the cell population was inhibited by meropenem, and total eradication with meropenem was observed after 24 hours. Both antibiotics also inhibited metabolic activity >88%. The lack of killing effect under colistin exposure suggested to us that these cells could protect themselves from further colistin stress. There was no significant permeabilization change in the cellular membrane with all antibiotics. There was no killing effect on starvation-induced persister cells with the exposure to all antibiotics. In 6 hours, the metabolic activity of the persisters with meropenem and colistin increased 99% and 40%, respectively, whereas there was no increase with amikacin. The sustained inhibition with amikacin was an important finding for antipersister effect of amikacin. Amikacin had rapid and sustained antipersister activity on colistin-induced persister cells. During the colistin treatment of K. pneumoniae infection, the addition of amikacin to the regimen seems to be an effective approach to prevent a recurrence.

Ecology and evolution of antibiotic persistence

Bacteria have at their disposal a battery of strategies to withstand antibiotic stress. Among these, resistance is a well-known mechanism, yet bacteria can also survive antibiotic attack by adopting a tolerant phenotype. In the case of persistence, only a small fraction within an isogenic population switches to this antibiotic-tolerant state. Persistence depends on the ecological niche and the genetic background of the strains involved. Furthermore, it has been shown to be under direct and indirect evolutionary pressure. Persister cells play a role in chronic infections and the development of resistance, and therefore a better understanding of this phenotype could contribute to the development of effective antibacterial therapies. In the current review, we discuss how ecological and evolutionary forces shape persistence.

Emergence of Multidrug Resistant Hypervirulent ST23 Klebsiella pneumoniae: Multidrug Resistant Plasmid Acquisition Drives Evolution

Background

In recent years, the emergence of multidrug resistant hypervirulent K. pneumoniae (MDR hvKp) isolates poses severe therapeutic challenge to global public health. The present study used the complete genome sequence of two MDR hvKp isolates belonging to ST23 to characterize the phylogenetic background and plasmid diversity.

Methods

Two hvKp isolates from patients with bacteremia were sequenced using Ion Torrent PGM and Oxford Nanopore MinION platforms and assembled by hybrid genome assembly approach. Comparative genomics approaches were used to investigate the population structure, evolution, virulence, and antimicrobial resistance of MDR hvKp strains.

Results

The study isolates exhibited typical features of hvKp phenotypes associated with ST23. The convergence of multidrug resistance and hypervirulence were attributed by the presence of multiple plasmids including a 216 kb virulence plasmid and MDR plasmids belonging to IncA/C₂, IncFIB, IncX3, and ColKP3 groups. The insertion of catA1 gene into virulence plasmid was observed along with genetic factors such as aerobactin, salmochelin, and rmpA2 that confer hvKp’s hypervirulent phenotype. The core genome single nucleotide polymorphism (SNP) phylogenetic analyses of the isolates showed the evolution of ST23 hvKp was predominantly driven by ICEKp acquisitions.

Conclusion

To the best of our knowledge, this is the first report of MDR hvKp isolates of ST23 with insertion of catA1 gene into the virulence plasmid which presents the possibility of hotspot integration sites on the plasmids to aid acquisition of AMR genes. ST23 is no longer confined to susceptible strains of hvKp. Our findings emphasize the need for more studies on recombinant events, plasmid transmission dynamics and evolutionary process involving hvKp.

A Quantitative Survey of Bacterial Persistence in the Presence of Antibiotics: Towards Antipersister Antimicrobial Discovery

Background: Bacterial persistence to antibiotics relates to the phenotypic ability to survive lethal concentrations of otherwise bactericidal antibiotics. The quantitative nature of the time-kill assay, which is the sector's standard for the study of antibiotic bacterial persistence, is an invaluable asset for global, unbiased, and cross-species analyses. Methods: We compiled the results of antibiotic persistence from antibiotic-sensitive bacteria during planktonic growth. The data were extracted from a sample of 187 publications over the last 50 years. The antibiotics used in this compilation were also compared in terms of structural similarity to fluorescent molecules known to accumulate in Escherichia coli. Results: We reviewed in detail data from 54 antibiotics and 36 bacterial species. Persistence varies widely as a function of the type of antibiotic (membrane-active antibiotics admit the fewest), the nature of the growth phase and medium (persistence is less common in exponential phase and rich media), and the Gram staining of the target organism (persistence is more common in Gram positives). Some antibiotics bear strong structural similarity to fluorophores known to be taken up by E. coli, potentially allowing competitive assays. Some antibiotics also, paradoxically, seem to allow more persisters at higher antibiotic concentrations. Conclusions: We consolidated an actionable knowledge base to support a rational development of antipersister antimicrobials. Persistence is seen as a step on the pathway to antimicrobial resistance, and we found no organisms that failed to exhibit it. Novel antibiotics need to have antipersister activity. Discovery strategies should include persister-specific approaches that could find antibiotics that preferably target the membrane structure and permeability of slow-growing cells.