Epithelial innate immune response to Acinetobacter baumannii challenge

Beta-defensin index: A functional biomarker for oral cancer detection

There is an unmet clinical need for a non-invasive and cost-effective test for oral squamous cell carcinoma (OSCC) that informs clinicians when a biopsy is warranted. Human beta-defensin 3 (hBD-3), an epithelial cell-derived anti-microbial peptide, is pro-tumorigenic and overexpressed in early-stage OSCC compared to hBD-2. We validate this expression dichotomy in carcinoma in situ and OSCC lesions using immunofluorescence microscopy and flow cytometry. The proportion of hBD-3/hBD-2 levels in non-invasively collected lesional cells compared to contralateral normal cells, obtained by ELISA, generates the beta-defensin index (BDI). Proof-of-principle and blinded discovery studies demonstrate that BDI discriminates OSCC from benign lesions. A multi-center validation study shows sensitivity and specificity values of 98.2% (95% confidence interval [CI] 90.3-99.9) and 82.6% (95% CI 68.6-92.2), respectively. A proof-of-principle study shows that BDI is adaptable to a point-of-care assay using microfluidics. We propose that BDI may fulfill a major unmet need in low-socioeconomic countries where pathology services are lacking.

Outer membrane protein A of Acinetobacter baumannii regulates pulmonary inflammation through the TLR2-NF-κB pathway

Acinetobacter baumannii (A. baumannii) is characterized by a high prevalence of drug resistance; how to effectively treat it is still a major clinical challenge. Our previous experiments confirmed that ompA, which is one of the most well-characterized virulence factors, may be dependent on the caspase-1 pathway-stimulated expression of NLRP3 inflammasome to enhance inflammation. TLRs (i.e., TLR2, etc.) is the initiating signal for NLRP3 inflammasome activation; how it relates to ompA in its underlying pathogenic mechanism is not clear. In this study, we proofed that ompA promoted NLRP3 inflammasome activation while the TLR2-NF-κB pathway was also activated after A. baumannii infection. Additionally, the expression of NLRP3 inflammasome-associated proteins and genes was inhibited by silencing TLR2 and NLRP3. This indicated that ompA might depend on the TLR2-NF-κB pathway to assemble and activate the NLRP3 inflammasome. OmpA promoted the assembly of the NLRP3 inflammasome through the TLR2-NF-κB pathway and inhibited the degradation of caspase-1 by the proteasome so that a large number of mature IL-1β/IL-18 and other proinflammatory factors were released extracellularly to enhance the body's inflammatory response. Taken together, the results of the joint pre-study confirmed a novel TLR2-NF-κB/NLRP3/caspase-1-modulated mechanism underpinning ompA activity, the NLRP3 inflammasome pathway may be as a potential immunomodulatory target against A. baumannii infections.

Designing of multi-epitope peptide vaccine against Acinetobacter baumannii through combined immunoinformatics and protein interaction-based approaches

Acinetobacter baumannii is one of the major pathogenic ESKAPE bacterium, which is responsible for about more than 722,000 cases in a year, globally. Despite the alarming increase in multidrug resistance, a safe and effective vaccine for Acinetobacter infections is still not available. Hence in the current study, a multiepitope vaccine construct was developed using linear B cell, cytotoxic T cell, and helper T cell epitopes from the antigenic and well-conserved lipopolysaccharide assembly proteins employing systematic immunoinformatics and structural vaccinology strategies. The multi-peptide vaccine was predicted to be highly antigenic, non-allergenic, non-toxic, and cover maximum population coverage worldwide. Further, the vaccine construct was modeled along with adjuvant and peptide linkers and validated to achieve a high-quality three-dimensional structure which was subsequently utilized for cytokine prediction, disulfide engineering, and docking analyses with Toll-like receptor (TLR4). Ramachandran plot showed 98.3% of the residues were located in the most favorable and permitted regions, thereby corroborating the feasibility of the modeled vaccine construct. Molecular dynamics simulation for a 100 ns timeframe further confirmed the stability of the binding vaccine-receptor complex. Finally, in silico cloning and codon adaptation were also performed with the pET28a (+) plasmid vector to determine the efficiency of expression and translation of the vaccine. Immune simulation studies demonstrated that the vaccine could trigger both B and T cell responses and can elicit strong primary, secondary, and tertiary immune responses. The designed multi-peptide subunit vaccine would certainly expedite the experimental approach for the development of a vaccine against A. baumannii infection.

Staphylococcus aureus and Acinetobacter sp. inhibit osseointegration of orthopaedic implants

Bacterial infections routinely cause inflammation and thereby impair osseointegration of orthopaedic implants. Acinetobacter spp., which causes osteomyelitis following trauma, on or off the battlefield, was however reported to cause neither osteomyelitis nor osteolysis in rodents. We therefore compared the effects of Acinetobacter strain M2 to those of Staphylococcus aureus in a murine implant infection model. Sterile implants and implants with adherent bacteria were inserted in the femur of mice. Bacterial burden, levels of pro-inflammatory cytokines, and osseointegration were measured. All infections were localized to the implant site. Infection with either S. aureus or Acinetobacter strain M2 increased the levels of pro-inflammatory cytokines and the chemokine CCL2 in the surrounding femurs, inhibited bone formation around the implant, and caused loss of the surrounding cortical bone leading to decreases in both histomorphometric and biomechanical measures of osseointegration. Genetic deletion of TLR2 and TLR4 from the mice partially reduced the effects of Acinetobacter strain M2 on osseointegration but did not alter the effects of S. aureus. This is the first report that Acinetobacter spp. impair osseointegration of orthopaedic implants in mice and the murine model developed for this study will be useful for future efforts to clarify the mechanism of implant failure due to Acinetobacter spp. and to assess novel diagnostic tools or therapeutic agents.

Acinetobacter baumannii: Virulence Strategies and Host Defense Mechanisms

Acinetobacter baumannii is a highly antibiotic-resistant bacterial pathogen known to cause severe life-threatening infections, including pneumonia, meningitis, and sepsis. Recent emergence of this bacterium as a serious nosocomial pathogen has led to categorization of A. baumannii as a "high-priority" pathogen by the World Health Organization (WHO), for which research efforts are urgently required to develop therapeutic interventions. Some of the properties that make A. baumannii a serious pathogen include its capacity to tolerate high levels of stress and enhanced expression of efflux pumps that enable high degrees of antibiotic resistance. Virulence mechanisms employed by A. baumannii to establish successful infection and host responses elicited against A. baumannii to counter the infection are discussed in detail in this article.

Proteomics Landscape of Host-Pathogen Interaction in Acinetobacter baumannii Infected Mouse Lung

Acinetobacter baumannii is an important pathogen of nosocomial infection worldwide, which can primarily cause pneumonia, bloodstream infection, and urinary tract infection. The increasing drug resistance rate of A. baumannii and the slow development of new antibacterial drugs brought great challenges for clinical treatment. Host immunity is crucial to the defense of A. baumannii infection, and understanding the mechanisms of immune response can facilitate the development of new therapeutic strategies. To characterize the system-level changes of host proteome in immune response, we used tandem mass tag (TMT) labeling quantitative proteomics to compare the proteome changes of lungs from A. baumannii infected mice with control mice 6 h after infection. A total of 6,218 proteins were identified in which 6,172 could be quantified. With threshold p < 0.05 and relative expression fold change > 1.2 or < 0.83, we found 120 differentially expressed proteins. Bioinformatics analysis showed that differentially expressed proteins after infection were associated with receptor recognition, NADPH oxidase (NOX) activation and antimicrobial peptides. These differentially expressed proteins were involved in the pathways including leukocyte transendothelial migration, phagocyte, neutrophil degranulation, and antimicrobial peptides. In conclusion, our study showed proteome changes in mouse lung tissue due to A. baumannii infection and suggested the important roles of NOX, neutrophils, and antimicrobial peptides in host response. Our results provide a potential list of protein candidates for the further study of host-bacteria interaction in A. baumannii infection. Data are available via ProteomeXchange with identifier PXD020640.

Microbiome dynamics and genomic determinants of bovine mastitis

The milk of lactating cows presents a complex ecosystem of interconnected microbial communities which can influence the pathophysiology of mastitis. We hypothesized possible dynamic shifts of microbiome composition and genomic features with different pathological conditions of mastitis (Clinical Mastitis; CM, Recurrent CM; RCM, Subclinical Mastitis; SCM). To evaluate this hypothesis, we employed whole metagenome sequencing (WMS) in 20 milk samples (CM, 5; RCM, 6; SCM, 4; H, 5) to unravel the microbiome dynamics, interrelation, and relevant metabolic functions. The WMS data mapped to 442 bacterial, 58 archaeal and 48 viral genomes with distinct variation in microbiome composition (CM > H > RCM > SCM). Furthermore, we identified a number of microbial genomic features, including 333, 304, 183 and 50 virulence factors-associated genes (VFGs) and 48, 31, 11 and 6 antibiotic resistance genes (ARGs) in CM, RCM, SCM, and H-microbiomes, respectively. We also detected different metabolic pathway and functional genes associated with mastitis pathogenesis. Therefore, profiling microbiome dynamics in different conditions of mastitis and associated microbial genomic features contributes to developing microbiome-based diagnostics and therapeutics for bovine mastitis.

Host Innate Immune Responses to Acinetobacter baumannii Infection

Acinetobacter baumannii has emerged as a major threat to global public health and is one of the key human pathogens in healthcare (nosocomial and community-acquired)-associated infections. Moreover, A. baumannii rapidly develops resistance to multiple antibiotics and is now globally regarded as a serious multidrug resistant pathogen. There is an urgent need to develop novel vaccines and immunotherapeutics as alternatives to antibiotics for clinical management of A. baumannii infection. However, our knowledge of host immune responses to A. baumannii infection and the identification of novel therapeutic targets are significantly lacking. This review highlights the recent advances and critical gaps in our understanding how A. baumannii interacts with the host innate pattern-recognition receptors, induces a cascade of inflammatory cytokine and chemokine responses, and recruits innate immune effectors (such as neutrophils and macrophages) to the site of infection for effective control of the infection. Such knowledge will facilitate the identification of new targets for the design and development of effective therapeutics and vaccines to fight this emerging threat.

Mechanisms Protecting Acinetobacter baumannii against Multiple Stresses Triggered by the Host Immune Response, Antibiotics and Outside-Host Environment

Acinetobacter baumannii is considered one of the most persistent pathogens responsible for nosocomial infections. Due to the emergence of multidrug resistant strains, as well as high morbidity and mortality caused by this pathogen, A. baumannii was placed on the World Health Organization (WHO) drug-resistant bacteria and antimicrobial resistance research priority list. This review summarizes current studies on mechanisms that protect A. baumannii against multiple stresses caused by the host immune response, outside host environment, and antibiotic treatment. We particularly focus on the ability of A. baumannii to survive long-term desiccation on abiotic surfaces and the population heterogeneity in A. baumannii biofilms. Insight into these protective mechanisms may provide clues for the development of new strategies to fight multidrug resistant strains of A. baumannii.

Innate Immune Responses to Acinetobacter baumannii in the Airway

Acinetobacter baumannii is an emerging opportunistic pathogen that has risen to become a serious global threat, prevalent in health care settings and the community, which results in high morbidity and mortality rates. Its alarming expansion of antibiotic resistance is one of the most problematic traits of A. baumannii and as so, this bacterium has been classified as a serious threat and high priority target by the CDC. The most common types of infections induced by this pathogen include pneumonia (both hospital and community acquired), bacteremia, skin and soft tissue, urinary tract infections, endocarditis, and meningitis. Nosocomial pneumonia is the most prevalent of these. This review summarizes the current state of the signaling and innate immune components activated in response to A. baumannii infection in the airway.

Biology of Hand-to-Hand Bacterial Transmission

Numerous studies have demonstrated that adequate hand hygiene among hospital staff is the best measure to prevent hand-to-hand bacterial transmission. The skin microbiome is conditioned by the individual physiological characteristics and anatomical microenvironments. Furthermore, it is important to separate the autochthonous resident microbiota from the transitory microbiota that we can acquire after interactions with contaminated surfaces. Two players participate in the hand-to-hand bacterial transmission process: the bacteria and the person. The particularities of the bacteria have been extensively studied, identifying some genera or species with higher transmission efficiency, particularly those linked to nosocomial infections and outbreaks. However, the human factor remains unstudied, and intrapersonal particularities in bacterial transmission have not been yet explored. Herein we summarize the current knowledge on hand-to-hand bacterial transmission, as well as unpublished results regarding interindividual and interindividual transmission efficiency differences. We designed a simple in vivo test based on four sequential steps of finger-to-finger contact in the same person artificially inoculated with a precise bacterial inoculum. Individuals can be grouped into one of three observed transmission categories: high, medium, and poor finger-to-finger transmitters. Categorization is relevant to predicting the ultimate success of a human transmission chain, particularly for the poor transmitters, who have the ability to cut the transmission chain. Our model allowed us to analyze transmission rate differences among five bacterial species and clones that cause nosocomial infections, from which we detected that Gram-positive microorganisms were more successfully transmitted than Gram-negative.

Dual oxidase: a novel therapeutic target in allergic disease

NADPH oxidases (NOXs) represent a family of enzymes that mediate regulated cellular production of reactive oxygen species (ROS) and play various functional roles in physiology. Among the NOX family, the dual oxidases DUOX1 and DUOX2 are prominently expressed in epithelial cell types at mucosal surfaces and have therefore been considered to have important roles in innate host defence pathways. Recent studies have revealed important insights into the host defence mechanisms of DUOX enzymes, which control innate immune response pathways in response to either microbial or allergic triggers. In this review, we discuss the current level of understanding with respect to the biological role(s) of DUOX enzymes and the unique role of DUOX1 in mediating innate immune responses to epithelial injury and allergens and in the development of allergic disease. These novel findings highlight DUOX1 as an attractive therapeutic target, and opportunities for the development of selective inhibitor strategies will be discussed.

Uncovering the mechanisms of Acinetobacter baumannii virulence

Acinetobacter baumannii is a nosocomial pathogen that causes ventilator-associated as well as bloodstream infections in critically ill patients, and the spread of multidrug-resistant Acinetobacter strains is cause for concern. Much of the success of A. baumannii can be directly attributed to its plastic genome, which rapidly mutates when faced with adversity and stress. However, fundamental virulence mechanisms beyond canonical drug resistance were recently uncovered that enable A. baumannii and, to a limited extent, other medically relevant Acinetobacter species to successfully thrive in the health-care environment. In this Review, we explore the molecular features that promote environmental persistence, including desiccation resistance, biofilm formation and motility, and we discuss the most recently identified virulence factors, such as secretion systems, surface glycoconjugates and micronutrient acquisition systems that collectively enable these pathogens to successfully infect their hosts.

Endogenous Antimicrobial Peptide Expression in Response to Bacterial Epidermal Colonization

Bacterial commensal colonization of human skin is vital for the training and maintenance of the skin’s innate and adaptive immune functions. In addition to its physical barrier against pathogen colonization, the skin expresses a variety of antimicrobial peptides (AMPs) which are expressed constitutively and induced in response to pathogenic microbial stimuli. These AMPs are differentially effective against a suite of microbial skin colonizers, including both bacterial and fungal residents of the skin. We review the breadth of microorganism-induced cutaneous AMP expression studies and their complementary findings on the efficacy of skin AMPs against different bacterial and fungal species. We suggest further directions for skin AMP research based on emerging skin microbiome knowledge in an effort to advance our understanding of the nuanced host–microbe balance on human skin. Such advances should enable the scientific community to bridge the gap between descriptive disease-state AMP studies and experimental single-species in vitro studies, thereby enabling research endeavors that more closely mimic the natural skin environs.

The Association of the Skin Microbiota With Health, Immunity, and Disease

The human skin is densely colonized by a highly diverse microbiota comprising all three domains of life. Long believed to represent mainly a source of infection, the human skin microbiota is nowadays well accepted as an important driver of human (skin) health and well-being. This microbiota is influenced by many host and environmental factors and interacts closely with the skin immune system. Although cause and effect are usually difficult to discriminate, changes in the skin microbiota clearly play a role in the pathobiology of many types of skin disease and cosmetic disorders. Consequently, treatment and prevention strategies have to respect this role, rendering pre- and probiotic and even transplantation therapies an additional option to the use of antibiotics.

The Immune Response against Acinetobacter baumannii, an Emerging Pathogen in Nosocomial Infections

Acinetobacter baumannii is the etiologic agent of a wide range of nosocomial infections, including pneumonia, bacteremia, and skin infections. Over the last 45 years, an alarming increase in the antibiotic resistance of this opportunistic microorganism has been reported, a situation that hinders effective treatments. In order to develop effective therapies against A. baumannii it is crucial to understand the basis of host–bacterium interactions, especially those concerning the immune response of the host. Different innate immune cells such as monocytes, macrophages, dendritic cells, and natural killer cells have been identified as important effectors in the defense against A. baumannii; among them, neutrophils represent a key immune cell indispensable for the control of the infection. Several immune strategies to combat A. baumannii have been identified such as recognition of the bacteria by immune cells through pattern recognition receptors, specifically toll-like receptors, which trigger bactericidal mechanisms including oxidative burst and cytokine and chemokine production to amplify the immune response against the pathogen. However, a complete picture of the protective immune strategies activated by this bacteria and its potential therapeutic use remains to be determined and explored.

Platelet-released growth factors induce the antimicrobial peptide human beta-defensin-2 in primary keratinocytes

Platelet-released growth factors (PRGF) and its related clinically used formulations [e.g. Vivostat platelet-rich fibrin (PRF(®) )] are thrombocyte concentrate lysates that support healing of chronic, hard-to-heal and infected wounds. Human beta-defensin-2 (hBD-2) is an antimicrobial peptide expressed in human keratinocytes exhibiting potent antimicrobial activity against wound-related bacteria. In this study, we analysed the influence of PRGF on hBD-2 expression in human primary keratinocytes and the influence of Vivostat PRF(®) on hBD-2 expression in experimentally generated skin wounds in vivo. Treatment of primary keratinocytes with PRGF caused a significant increase in hBD-2 gene and protein expressions in a concentration- and time-dependent manner. The use of blocking antibodies revealed that the PRGF-mediated hBD-2 induction was partially mediated by the epidermal growth factor receptor and the interleukin-6 receptor (IL-6R). Luciferase gene reporter assays indicated that the hBD-2 induction through PRGF required activation of the transcription factor activator protein 1 (AP-1), but not of NF-kappaB. In concordance with these cell culture data, Vivostat PRF(®) induced hBD-2 expression when applied to experimentally generated skin wounds. Together, our results indicate that the induction of hBD-2 by thrombocyte concentrate lysates can contribute to the observed beneficial effects in the treatment of chronic and infected wounds.

New molecules and adjuvants in the treatment of infections by Acinetobacter baumannii

INTRODUCTION

The current problems of the treatment of infections by Acinetobacter baumannii are linked with the increase of multidrug- and extensive-drug resistance and the lack of development of new antimicrobial drugs for Gram-negative bacilli. For these reasons, new alternatives for the treatment and control of severe infections by A. baumannii are necessary. Several studies have reported the effect of adjuvants to restore the efficacy of existing antimicrobial agents.

AREAS COVERED

In the present review, the authors describe the main results in the development of adjuvant drugs as well as new data on antimicrobial peptides, in monotherapy or in combination therapy with existing antimicrobial agents, which have shown promising preclinical results in vitro and in vivo.

EXPERT OPINION

The preclinical evaluation of adjuvants and antimicrobial peptides, in monotherapy or in combination therapy, for A. baumannii infections has shown promising results. However, caution is needed and further extensive in vivo studies and clinical trials have to be performed to confirm the potential use of these adjuvants as true therapeutic alternatives.

FAD-I, a Fusobacterium nucleatum Cell Wall-Associated Diacylated Lipoprotein That Mediates Human Beta Defensin 2 Induction through Toll-Like Receptor-1/2 (TLR-1/2) and TLR-2/6

We previously identified a cell wall-associated protein from Fusobacterium nucleatum, a Gram-negative bacterium of the oral cavity, that induces human beta defensin 2 (hBD-2) in primary human oral epithelial cells (HOECs) and designated it FAD-I (Fusobacterium-associated defensin inducer). Here, we report differential induction of hBD-2 by different strains of F. nucleatum; ATCC 25586 and ATCC 23726 induce significantly more hBD-2 mRNA than ATCC 10953. Heterologous expression of plasmid-borne fadI from the highly hBD-2-inducing strains in a ΔfadI mutant of ATCC 10953 resulted in hBD-2 induction to levels comparable to those of the highly inducing strains, indicating that FAD-I is the principal F. nucleatum agent for hBD-2 induction in HOECs. Moreover, anti-FAD-I antibodies blocked F. nucleatum induction of hBD-2 by more than 80%. Recombinant FAD-I (rFAD-I) expressed in Escherichia coli triggered levels of hBD-2 transcription and peptide release in HOECs similar to those of native FAD-I (nFAD-I) isolated from F. nucleatum ATCC 25586. Tandem mass spectrometry revealed a diacylglycerol modification at the cysteine residue in position 16 for both nFAD-I and rFAD-I. Cysteine-to-alanine substitution abrogated FAD-I's ability to induce hBD-2. Finally, FAD-I activation of hBD-2 expression was mediated via both Toll-like receptor-1/2 (TLR-1/2) and TLR-2/6 heterodimerization. Microbial molecules like FAD-I may be utilized in novel therapeutic ways to bolster the host innate immune response at mucosal surfaces.

Role of Aders and OXA23 Genes among Imipenem Resistant Acinetobacter baumannii Isolates from Two Hospitals of Tehran, Iran

BACKGROUND

This study aimed to evaluate the role of efflux pump regulator and OXA-23 genes in imipenem resistance Acinetobacter baumannii strains isolated from hospitalized patients in Tehran, Iran.

METHODS

This study was conducted on 60 A. baumannii isolates collected from patients admitted to the Shahid Motahari and Taleghani Hospitals in Tehran during 2013-14. Antibiotic susceptibility tests (AST) and minimal inhibitory concentration (MIC) was determined by broth micro dilution methods according to CLSI 2014 guidelines. The frequency of efflux pump adeRS and OXA-23 genes were detected by PCR and further sequencing.

RESULTS

The resistance of A. baumannii isolates to tested antibiotics was 100% to cefotaxime, ceftazidime, ceftriaxone, ciprofloxacin, cefepime, piperacillin, meropenem, co-trimoxazole and piperacillin/tazobactam, 97% to imipenem, 94% to gentamicin, 83% to amikacin, 76% to tetracycline, and 0.0% to colistin. The MIC of 58 (96.6%) strains to imipenem was highly decreased in the presence of efflux pump inhibitor (PaβN), by 4 to 64 folds. The adeR and adeS genes were detected in 36 (60%) and 59 (98.3%), respectively and the frequency of OXA-23 gene was 57 (95%) of isolates.

CONCLUSION

Existence of adeRS and OXA-23 genes in more than 50% of A. baumannii isolates in this study shows the presumptive role of efflux pump in simultaneous of carbapenemase production. Therefore, using new strategies are required in order to stop the vertical or horizontal exchanges mentioned genes from the resistant A. baumannii isolates to sensitive strains.

The potential protective role of the combination of IL-22 and TNF-α against genital tract Chlamydia trachomatis infection

Th22 cells are a novel class of lymphocytes characterized by the secretion of both IL-22 and TNF-α. In summary, Th22 cells have little or no direct impact on other immune cells, but exert selective effects on epithelia. It is not known, however, whether Th22 cells play a role in genital mucosal immunity. Here, we demonstrate that IL-22 and TNF-α synergistically induce several immunomodulatory molecules, such as the antimicrobial peptide mBD-2 (murine β-defensin 2) and the antimicrobial chemokines CXCL-9, -10, and -11 in primary murine oviduct epithelial cells (MOECs). The induction of innate immunity is relevant in an in vitro infection model, in which MOECs stimulated with Th22 cell supernatants or recombinant IL-22 and TNF-α effectively inhibit the growth of Chlamydia trachomatis and maintain the survival of the epithelia compared with IL-22 or TNF-α alone. In summary, we demonstrate that the Th22 cell cytokines IL-22 and TNF-α play important roles in genital tract infection. The potential for Th22 cell cytokines to modulate innate immune mediators may lead to the development of new topical agents to treat and/or prevent immune-mediated sexually transmitted diseases (STDs). In summary, we demonstrate that IL-22 and TNF-α represent a potent, synergistic cytokine combination for inducing genital mucosal immunity.