Immunomodulatory effects of colistin on host responses against carbapenem-resistant Klebsiella pneumoniae biofilms

Supernatant of platelet-Klebsiella pneumoniae coculture induces apoptosis-like death in Klebsiella pneumoniae

Multidrug-resistant Klebsiella pneumoniae strains, especially carbapenem-resistant K. pneumoniae, have become a rapidly emerging crisis worldwide, greatly limiting current therapeutic options and posing new challenges to infection management. Therefore, it is imperative to develop novel and effective biological agents for the treatment of multidrug-resistant K. pneumoniae infections. Platelets play an important role in the development of inflammation and immune responses. The main component responsible for platelet antibacterial activity lies in the supernatant stimulated by gram-positive bacteria. However, little research has been conducted on the interaction of gram-negative bacteria with platelets. Therefore, we aimed to explore the bacteriostatic effect of the supernatant derived from platelet-K. pneumoniae coculture and the mechanism underlying this effect to further assess the potential of platelet-bacterial coculture supernatant. We conducted this study on the gram-negative bacteria K. pneumoniae and CRKP and detected turbidity changes in K. pneumoniae and CRKP cultures when grown with platelet-K. pneumoniae coculture supernatant added to the culture medium. We found that platelet-K. pneumoniae coculture supernatant significantly inhibited the growth of K. pneumoniae and CRKP in vitro. Furthermore, transfusion of platelet-K. pneumoniae coculture supernatant alleviated the symptoms of K. pneumoniae and CRKP infection in a murine model. Additionally, we observed apoptosis-like changes, such as phosphatidylserine exposure, chromosome condensation, DNA fragmentation, and overproduction of reactive oxygen species in K. pneumoniae following treatment with the supernatant. Our study demonstrates that the platelet-K. pneumoniae coculture supernatant can inhibit K. pneumoniae growth by inducing an apoptosis-like death, which is important for the antibacterial strategies development in the future.IMPORTANCEWith the widespread use of antibiotics, bacterial resistance is increasing, and a variety of multi-drug resistant Gram-negative bacteria have emerged, which brings great challenges to the treatment of infections caused by Gram-negative bacteria. Therefore, finding new strategies to inhibit Gram-negative bacteria and even multi-drug- resistant Gram-negative bacteria is crucial for treating infections caused by Gram-negative bacteria, improving the abuse of antibiotics, and maintaining the balance between bacteria and antibiotics. K. pneumoniae is a common clinical pathogen, and drug-resistant CRKP is increasingly difficult to cure, which brings great clinical challenges. In this study, we found that the platelet-K. pneumoniae coculture supernatant can inhibit K. pneumoniae growth by inducing an apoptosis-like death. This finding has inspired the development of future antimicrobial strategies, which are expected to improve the clinical treatment of Gram-negative bacteria and control the development of multidrug-resistant strains.

Diversity of Circulating NKT Cells in Defense against Carbapenem-Resistant Klebsiella Pneumoniae Infection

Nosocomial infection caused by carbapenem-resistant Klebsiella pneumonia (CRKP) infection has become a global public health problem. Human NK and NKT cells in peripheral immune responses are recognized as occupying a critical role in anti-bacterial immunity. Through performed scRNA-seq on serial peripheral blood samples from 3 patients with CRKP undergoing colonization, infection, and recovery conditions, we were able to described the immune responses of NK and NKT cells during CRKP infection and identified a mechanism that could contribute to CRKP clearance. The central player of CRKP infection process appears to be the NKT subset and CD56hiNKT subset which maintained immune competence during CRKP colonization. With time, CRKP leads to the loss of NK and CD160hiNKT cells in peripheral blood, resulting in suppressed immune responses and increased susceptibility to opportunistic infection. In summary, our study identified a possible mechanism for the CRKP invasion and to decipher the clues behind the host immune response that influences CRKP infection pathogenesis.

Biofilm of Klebsiella pneumoniae minimize phagocytosis and cytokine expression by macrophage cell line

Infectious bacteria in biofilm mode are involved in many persistent infections. Owing to its importance in clinical settings, many in vitro and in vivo studies are being conducted to study the structural and functional properties of biofilms, their drug resistant mechanism and the s urvival mechanism of planktonic and biofilm cells. In this regard, there is not sufficient information on the interaction between Klebsiella biofilm and macrophages. In this study, we have attempted to unravel the interaction between Klebsiella biofilm and macrophages in terms of phagocytic response and cytokine expression. In vitro phagocytosis assays were performed for heat inactivated and live biofilms of K. pneumoniae, together with the expression analysis of TLR2, iNOS, inflammatory cytokines such as IL-β1, IFN-γ, IL-6, IL-12, IL-4, TNF-α and anti-inflammatory cytokine, IL-10. A phagocytic rate of an average of 15% was observed against both heat inactivated and live biofilms when LPS + IFN-γ activated macrophages were used. This was significantly higher than non-activated macrophages when tested against heat inactivated and live biofilms (average 8%). Heat-inactivated and live biofilms induced similar phagocytic responses and up-regulation of pro-inflammatory genes in macrophages, indirectly conveying that macrophage responses are to some extent dependent on the biofilm matrix.

Daptomycin exerts differential immunomodulatory effects on host responses against methicillin-resistant Staphylococcus aureus biofilms

BACKGROUND

Daptomycin (DAP) is indicated for difficult-to-treat Gram-positive infections, especially those caused by methicillin-resistant S. aureus (MRSA). Exposure of S. aureus to sub-inhibitory concentrations (sub-MICs) of antibiotics have been shown to alter cell morphology or biofilm formation.

OBJECTIVES

To investigate the influence of DAP biofilm sub-MICs on the damage caused by human polymorphonuclear neutrophils (PMNs) against MRSA biofilms and the potential immunomodulatory activity of DAP on human monocytes (MNCs) exposed to MRSA biofilms.

METHODS

DAP activity against biofilms and the impact of DAP on the PMNs-induced biofilm damage were evaluated by the XTT reduction assay, whereas pathogen recognition, signal transduction and cytokine modulation of DAP on MNCs in response to MRSA biofilms were assessed by RT-PCR and ELISA methodology.

RESULTS

The MIC50 of DAP to MRSA biofilms was 16 to 32 mg/L. Pre-treatment of MRSA to 1, 2 or 4 mg/L DAP caused a synergistic effect on PMN-mediated biofilm damage, being dependent on the effector-to-target ratio. MNCs responded to MRSA biofilms and DAP through Toll like receptor 2 (TLR2) upregulation and increased NLRP3 inflammasome production. DAP caused 2.5-fold greater TLR2 mRNA levels than those caused by MRSA biofilms. A predominantly inflammatory response was induced by either component, causing the release of significantly increased IFN-γ, TNF-α, IL-8 and IL-6 levels by MNCs exposed to the combination treatment. MRSA biofilms alone or combined with DAP caused low amounts of IL-10 production, but increased IL-1β levels.

CONCLUSIONS

DAP may condition MNCs towards an inflammatory response through TLR2 engagement and NLRP3 inflammasome activation, possibly controlling biofilm-associated pathogenicity.

Risk Factors and Prognosis of Carbapenem-Resistant Klebsiella pneumoniae Infections in Respiratory Intensive Care Unit: A Retrospective Study

Purpose

Carbapenem-resistant Klebsiella pneumoniae (CRKP) infections have become a serious threat with high morbidity and mortality. Early identification of risk factors for CRKP infections is important, but these factors are still controversial. Therefore, we aimed to identify the risk factors and clinical outcomes of CRKP infections.

Patients and Methods

The retrospective, single-center study was carried out in the respiratory intensive care unit of the Chinese People’s Liberation Army General Hospital from 2017 to 2020. Patients infected with K. pneumoniae were included and categorized into the CRKP group and carbapenem-sensitive K. pneumoniae (CSKP) group based on the susceptibility to carbapenems. The independent risk factors were investigated by univariate analysis and multivariate logistic regression analysis. The clinical outcomes were also evaluated between the two groups.

Results

A total of 138 eligible patients were included in our study, with a median age of 80.5 years (interquartile range: 62.0–86.3), and 78.3% of them were males. Of the 138 patients, there were 97 patients in the CRKP group, and the other 41 were assigned into the CSKP group. Multivariate analysis showed that exposure to ≥three types of comorbidities (OR = 5.465, P = 0.003), previous hospitalization (OR = 4.279, P = 0.006), use of quinolones (OR = 5.872, P = 0.012), and indwelling urinary catheter (OR = 5.035, P = 0.000) were independent risk factors for CRKP infections. The in-hospital mortality rate of the CRKP group was 42.1%, which was higher compared with the CSKP group (17.5%, P = 0.006).

Conclusion

Exposure to ≥three types of comorbidities, previous hospitalization, use of quinolones, and indwelling urinary catheter were independent risk factors for CRKP infections, which had higher mortality compared with CSKP infections. Early detection of high-risk patients and timely control measures should be implemented to prevent the emergence of CRKP infections and thereby improve the clinical outcomes.

Metagenomic Sequencing Analysis of the Effects of Colistin Sulfate on the Pig Gut Microbiome

The gut microbiome plays important roles in maintaining host health, and inappropriate use of antibiotics can cause imbalance, which may contribute to serious disease. However, despite its promise, using metagenomic sequencing to explore the effects of colistin on gut microbiome composition in pig has not been reported. Herein, we evaluated the roles of colistin in gut microbiome modulation in pigs. Metagenomic analysis demonstrated that overall microbial diversity was higher in the colistin group compared with the control group. Antibiotic Resistance Genes Database analysis demonstrated that following colistin treatment, expression levels of tsnr, ant6ia, tetq, oleb, norm, ant3ia, and mexh were significantly upregulated, indicating that colistin may induce transformation of antibiotic resistance genes. Colistin also affected the microbiome distribution patterns at both genus and phylum levels. In addition, at the species level, colistin significantly reduced the abundance of Prevotella copri, Phascolarctobacterium succinatutens, and Prevotella stercorea and enhanced the abundance of Treponema succinifaciens and Acidaminococcus fermentans compared to the control group. Gene Ontology analysis demonstrated that following treatment with colistin, metabolic process, cellular process, and single-organism process were the dominant affected terms. Kyoto Encyclopedia of Genes and Genomes analysis showed that oxidative phosphorylation, protein processing in endoplasmic reticulum, various types of N-glycan biosynthesis, protein processing in endoplasmic reticulum, pathogenic Escherichia coli infection, and mitogen-activated protein kinase signaling pathway–yeast were the dominant signaling pathways in the colistin group. Overall, our results suggested that colistin affects microbial diversity and may modulate gut microbiome composition in pig, potentially providing novel strategy or antibiotic rationalization pertinent to human and animal health.