Host-pathogen interaction: Enterobacter cloacae exerts different adhesion and invasion capacities against different host cell types

Carbapenem-resistant Enterobacter hormaechei uses mucus metabolism to facilitate gastrointestinal colonization

The emergence and global spread of carbapenem-resistant Enterobacter cloacae complex species present a pressing public health challenge. Carbapenem-resistant Enterobacter spp. cause a wide variety of infections, including septic shock fatalities in newborns and immunocompromised adults. The intestine may be a major reservoir for these resistant strains, either by facilitating contamination of fomites and transfer to susceptible individuals, or through translocation from the gut to the bloodstream. For this reason, we sought to establish a neonatal mouse model to investigate the mechanisms underpinning gut colonization by carbapenem-resistant Enterobacter hormaechei. We describe a new mouse model to study gut colonization by Enterobacter spp., leading to vital insights into the adaptation of carbapenem-resistant E. hormaechei to the gut environment during the early stages of intestinal colonization. We observed successful colonization and proliferation of E. hormaechei in the 5-day-old infant mouse gut, with primary localization to the colon following oral inoculation. We also uncovered evidence that E. hormaechei uses mucus as a carbon source during colonization of the colon. Our findings underscore the importance of oxygen-dependent metabolic pathways, including the pyruvate dehydrogenase complex and N-acetyl-D-glucosamine metabolism, in gut colonization and proliferation, which aligns with previous human studies. These insights are essential for developing novel therapeutic strategies that can serve as decolonization therapies in at-risk populations.IMPORTANCEBloodstream infections caused by Enterobacter spp. pose a significant clinical threat. The intestine acts as the primary site for colonization and serves as a reservoir for infection. To combat this pathogen, it is crucial to understand how carbapenem-resistant Enterobacter spp. colonize the gut, as such knowledge can pave the way for alternative therapeutic targets. In this study, we developed a novel neonatal mouse model for gastrointestinal colonization by Enterobacter spp. and discovered that mucus plays a key role as a carbon source during colonization. Additionally, we identified two mucus catabolism pathways that contribute to intestinal colonization by carbapenem-resistant E. hormaechei. This new mouse model offers valuable insights into host-pathogen interactions and helps identify critical gastrointestinal fitness factors of Enterobacter, potentially guiding the development of vaccines and alternative therapeutic strategies to minimize intestinal carriage in patient populations at risk of infection with Enterobacter spp.

A fucose-binding superlectin from Enterobacter cloacae with high Lewis and ABO blood group antigen specificity

Bacteria frequently employ carbohydrate-binding proteins, so-called lectins, to colonize and persist in a host. Thus, bacterial lectins are attractive targets for the development of new anti-infectives. To find new potential targets for anti-infectives against pathogenic bacteria, we searched for homologs of Pseudomonas aeruginosa lectins and identified homologs of LecA in Enterobacter species. Here, we recombinantly produced and biophysically characterized a homolog that comprises one LecA domain and one additional, novel protein domain. This protein was termed Enterobacter cloacae lectin A (EclA) and found to bind l-fucose. Glycan array analysis revealed a high specificity for the LewisA antigen and the type II H-antigen (blood group O) for EclA, while related antigens LewisX, Y, and B, as well as blood group A or B were not bound. We developed a competitive binding assay to quantify blood group antigen-binding specificity in solution. Finally, the crystal structure of EclA could be solved in complex with methyl α-l-selenofucoside. It revealed the unexpected binding of the carbohydrate ligand to the second domain, which comprises a novel fold that dimerizes via strand-swapping resulting in an intertwined beta sheet.

The role of AbaI quorum sensing molecule synthase in host cell inflammation induced by Acinetobacter baumannii and its effect on zebrafish infection model

Acinetobacter baumannii is currently one of the most important opportunistic pathogens causing severe nosocomial infections worldwide. Quorum Sensing (QS) system is a widespread mechanism in bacteria to coordinate group behavior by sensing the density of bacterial populations and affect eukaryotic host cell. In Acinetobacter baumannii, AbaI protein is used as QS molecule synthetase to synthesize N- acyl homoserine lactones (AHLs). Currently, QS has made great progress in the study of drug resistance, but there is still a lack of complete understanding of its damage to host cells after adhesion and invasion. Thus, in this study, we examined the effects of abaI mutant (ΔabaI) on the functions of adhesion and invasion, cell viability, inflammation, apoptosis in A. baumannii infected A549 cells, to evaluate the effects of ΔabaI in a zebrafish model. We found the group infected with ΔabaI increased cell viability, reduced adhesion and invasion, cell injury, inflammatory cytokine production and apoptosis. By RNA-Seq, we explored the possibility that abaI stimulated A549 cells inflammation by A. baumannii infection via TLR4/MAPK signaling pathway. In addition, the ΔabaI significantly reduced pathogenicity and recruitment to neutrophils in zebrafish. These observations suggest that abaI plays a major role in A. baumannii infection.

Massive subcutaneous abscess: A case report of management and source control

INTRODUCTION AND IMPORTANCE

Postoperative peritoneal infection, a common complication, remains prevalent despite surgical advancements. Acute abdomen necessitates rapid treatment, often presenting with abdominal pain and systemic inflammation. Bladder injuries, potentially leading to sepsis, require immediate surgical intervention.

CASE PRESENTATION

We report a case of a 60-year-old man who came with the main complaint of feeling full in his stomach for 7 days, accompanied by non-radiating right lower abdominal pain since one day before hospital admission and a lethargy condition. There are complaints of seepage from the stitch marks on the right stomach, such as yellow urine. Laboratory and physical examination showed the patient in sepsis condition. CT Cystography showed a defect of 0.4 cm on the bladder dome, the contrast leakage into extraperitoneal and intraperitoneal, and tunneling to the right abdominal subcutaneous. The patient underwent subcutaneous abscess, bladder repair, and cystostomy. One month after surgery, the patient had normal micturition.

CLINICAL DISCUSSION

Acute abdominal pain is one sign of emergency surgery. It can be caused by infection, inflammation, vascular occlusion, or obstruction. Physical and laboratory examination of the patient showed a sepsis condition. CT Cystography showed the presence of bladder rupture and subcutaneous abscess. The only management is surgical exploration for infection source control.

CONCLUSIONS

This case underscores the importance of prompt diagnosis and comprehensive management, involving surgical intervention and targeted antibiotics, for sepsis-related complications post-TURP and bladder repair, necessitating a multidisciplinary approach for optimal outcomes and complication prevention.

High molecular/low acetylated chitosans reduce adhesion of Campylobacter jejuni to host cells by blocking JlpA

Infections caused by Campylobacter spp. are a major cause of severe enteritis worldwide. Multifactorial prevention strategies are necessary to reduce the prevalence of Campylobacter. In particular, antiadhesive strategies with specific inhibitors of early host-pathogen interaction are promising approaches to reduce the bacterial load. An in vitro flow cytometric adhesion assay was established to study the influence of carbohydrates on the adhesion of C. jejuni to Caco-2 cells. Chitosans with a high degree of polymerization and low degree of acetylation were identified as potent antiadhesive compounds, exerting significant reduction of C. jejuni adhesion to Caco-2 cells at non-toxic concentrations. Antiadhesive and also anti-invasive effects were verified by confocal laser scanning microscopy. For target identification, C. jejuni adhesins FlpA and JlpA were expressed in Escherichia coli ArcticExpress, and the influence of chitosan on binding to fibronectin and HSP90α, respectively, was investigated. While no effects on FlpA binding were found, a strong inhibition of JlpA-HSP90α binding was observed. To simulate real-life conditions, chicken meat was inoculated with C. jejuni, treated with antiadhesive chitosan, and the bacterial load was quantified. A strong reduction of C. jejuni load was observed. Atomic force microscopy revealed morphological changes of C. jejuni after 2 h of chitosan treatment, indicating disturbance of the cell wall and sacculi formation by electrostatic interaction of positively charged chitosan with the negatively charged cell surface. In conclusion, our data indicate promising antiadhesive and anti-invasive potential of high molecular weight, strongly de-acetylated chitosans for reducing C. jejuni load in livestock and food production. KEY POINTS: • Antiadhesive effects of chitosan with high DP/low DA against C. jejuni to host cells • Specific targeting of JlpA/Hsp90α interaction by chitosan • Meat treatment with chitosan reduces C. jejuni load.