Code blue: Acinetobacter baumannii, a nosocomial pathogen with a role in the oral cavity

Acinetobacter baumannii as an oro-dental pathogen: a red alert!!

OBJECTIVES

This review highlights the existence and association of Acinetobacter baumannii with the oro-dental diseases, transforming this systemic pathogen into an oral pathogen. The review also hypothesizes possible reasons for the categorization of this pathogen as code blue due to its stealthy entry into the oral cavity.

METHODOLOGY

Study data were retrieved from various search engines reporting specifically on the association of A. baumannii in dental diseases and tray set-ups. Articles were also examined regarding obtained outcomes on A. baumannii biofilm formation, iron acquisitions, magnitude of antimicrobial resistance, and its role in the oral cancers.

RESULTS

A. baumannii is associated with the oro-dental diseases and various virulence factors attribute for the establishment and progression of oro-mucosal infections. Its presence in the oral cavity is frequent in oral microbiomes, conditions of impaired host immunity, age related illnesses, and hospitalized individuals. Many sources also contribute for its prevalence in the dental health care environment and the presence of drug resistant traits is also observed. Its association with oral cancers and oral squamous cell carcinoma is also evident.

CONCLUSIONS

The review calls for awareness on the emergence of A. baumannii in dental clinics and for the need for educational programs to monitor and control the sudden outbreaks of such virulent and resistant traits in the dental health care settings.

Upper respiratory tract microbiome profiles in SARS-CoV-2 Delta and Omicron infected patients exhibit variant specific patterns and robust prediction of disease groups

IMPORTANCE

The role of the upper respiratory tract (URT) microbiome in predicting lung health has been documented in several studies. The dysbiosis in COVID patients has been associated with disease outcomes by modulating the host immune system. However, although it has been known that different SARS-CoV-2 variants manifest distinct transmissibility and mortality rates in human populations, their effect on the composition and diversity of the URT microbiome has not been studied to date. Unlike the older variant (Delta), the newer variant (Omicron) have become more transmissible with lesser mortality and the symptoms have also changed significantly. Hence, in the present study, we have investigated the change in the URT microbiome associated with Delta and Omicron variants and identified variant-specific signatures that will be useful in the assessment of lung health and can be utilized for nasal probiotic therapy in the future.

Multidrug-resistant Acinetobacter spp. from hospital intensive care units in Brazilian Amazon

Acinetobacter spp. are one of the main pathogens responsible for healthcare-associated infections and are associated with high rates of morbidity and mortality globally, mainly because of their high capacity to present and develop resistance to antimicrobials. To identify species of the Acinetobacter and their resistance profiles from samples collected from hospitalized patients, health professionals and hospital environmental sources in the intensive care units of different public reference hospitals in Porto Velho City, Rondônia, Western Brazilian Amazon. Isolates were identified using microbiological and molecular techniques. The antimicrobial susceptibility profile was determined by disk diffusion. A total of 201 Acinetobacter spp. isolates were identified, of which 47.3% originated from hospital structures, 46.8% from patients and 6% from healthcare professionals. A. baumannii and A. nosocomialis were the most prevalent, with frequency of 58.7% and 31.8%, respectively. Regarding the susceptibility profile, it was observed that 56.3% were classified as multidrug-resistant and 76.2% of the samples belonging to A. baumannii were resistant to carbapenems. In contrast, 96.9% were susceptible to polymyxin B and 91.3% to doxycycline. The data presented here can be used to guide and strengthen the control of multidrug-resistant infections caused by Acinetobacter spp., in addition to improving providing information from a traditionally unassisted region of Brazil.

The effect of phage-antibiotic combination strategy on multidrug-resistant Acinetobacter baumannii biofilms

Acinetobacter baumannii (A. baumannii) is considered a critical human pathogen due to multi-drug resistance and increased infections. As a result of the resistance of A. baumannii biofilms to antimicrobial agents, it is necessary to develop new biofilm control strategies. In the present study, we evaluated the efficacy of two previously isolated bacteriophage C2 phage, K3 phage and phage cocktail (C2 + K3 phage) as a therapeutic agent in combination with antibiotic (colistin) against biofilm of multidrug-resistant A. baumannii strains (n = 24). The effects of phage and antibiotics on mature biofilm were investigated simultaneously and sequentially in 24 and 48 h. The combination protocol was more effective than antibiotics alone in 54.16% of the strains in 24 h. The sequential application was more effective than the simultaneous protocol compared with the 24 h single applications. When the application of antibiotics and phages alone was compared with their combined administration in 48 h. The sequential and simultaneous applications were more effective than single applications in all strains except two. We observed that combination of phage and antibiotics could increase biofilm eradication and provides new insights into the use of bacteriophages and antibiotics in the treatment of biofilm-associated infections caused by antibiotic-resistant bacteria.

The interactions of Candida albicans with gut bacteria: a new strategy to prevent and treat invasive intestinal candidiasis

BACKGROUND

The gut microbiota plays an important role in human health, as it can affect host immunity and susceptibility to infectious diseases. Invasive intestinal candidiasis is strongly associated with gut microbiota homeostasis. However, the nature of the interaction between Candida albicans and gut bacteria remains unclear.

OBJECTIVE

This review aimed to determine the nature of interaction and the effects of gut bacteria on C. albicans so as to comprehend an approach to reducing intestinal invasive infection by C. albicans.

METHODS

This review examined 11 common gut bacteria's interactions with C. albicans, including Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii, Enterococcus faecalis, Staphylococcus aureus, Salmonella spp., Helicobacter pylori, Lactobacillus spp., Bacteroides spp., Clostridium difficile, and Streptococcus spp.

RESULTS

Most of the studied bacteria demonstrated both synergistic and antagonistic effects with C. albicans, and just a few bacteria such as P. aeruginosa, Salmonella spp., and Lactobacillus spp. demonstrated only antagonism against C. albicans.

CONCLUSIONS

Based on the nature of interactions reported so far by the literature between gut bacteria and C. albicans, it is expected to provide new ideas for the prevention and treatment of invasive intestinal candidiasis.

Prediction of Putative Epitope Peptides against BaeR Associated with TCS Adaptation in Acinetobacter baumannii Using an In Silico Approach

Background and Objectives: The BaeR protein is involved in the adaptation system of A. baumannii and is associated with virulence factors responsible for systemic infections in hospitalized patients. This study was conducted to characterize putative epitope peptides for the design of vaccines against BaeR protein, using an immune-informatic approach. Materials and Methods: FASTA sequences of BaeR from five different strains of A. baumannii were retrieved from the UNIPROT database and evaluated for their antigenicity, allergenicity and vaccine properties using BepiPred, Vaxijen, AlgPred, AntigenPro and SolPro. Their physio-chemical properties were assessed using the Expasy Protparam server. Immuno-dominant B-cell and T-cell epitope peptides were predicted using the IEDB database and MHC cluster server with a final assessment of their interactions with TLR-2. Results: A final selection of two peptide sequences (36aa and 22aa) was made from the 38 antigenic peptides. E1 was considered a soluble, non-allergenic antigen, and possessed negative GRAVY values, substantiating the hydrophilic nature of the proteins. Further analysis on the T-cell epitopes, class I immunogenicity and HLA allele frequencies yielded T-cell immuno-dominant peptides. The protein-peptide interactions of the TLR-2 receptor showed good similarity scores in terms of the high number of hydrogen bonds compared to other protein-peptide interactions. Conclusions: The two epitopes predicted from BaeR in the present investigation are promising vaccine candidates for targeting the TCS of A. baumannii in systemic and nosocomial infections. This study also demonstrates an alternative strategy to tackling and mitigating MDR strains of A. baumannii and provides a useful reference for the design and construction of novel vaccine candidates against this bacteria.

P, Molina CA, Castillejo P. Beta-Lactam Antibiotic Resistance Genes in the Microbiome of the Public Transport System of Quito, Ecuador

Multidrug-resistant bacteria present resistance mechanisms against β-lactam antibiotics, such as Extended-Spectrum Beta-lactamases (ESBL) and Metallo-β-lactamases enzymes (MBLs) which are operon encoded in Gram-negative species. Likewise, Gram-positive bacteria have evolved other mechanisms through mec genes, which encode modified penicillin-binding proteins (PBP2). This study aimed to determine the presence and spread of β-lactam antibiotic resistance genes and the microbiome circulating in Quito's Public Transport (QTP). A total of 29 station turnstiles were swabbed to extract the surface environmental DNA. PCRs were performed to detect the presence of 13 antibiotic resistance genes and to identify and to amplify 16S rDNA for barcoding, followed by clone analysis, Sanger sequencing, and BLAST search. ESBL genes bla_TEM-1 and bla_CTX-M-1 and MBL genes bla_OXA-181 and mecA were detected along QPT stations, blaTEM being the most widely spread. Two subvariants were found for bla_TEM-1, bla_CTX-M-1, and bla_OXA-181. Almost half of the circulating bacteria found at QPT stations were common human microbiota species, including those classified by the WHO as pathogens of critical and high-priority surveillance. β-lactam antibiotic resistance genes are prevalent throughout QPT. This is the first report of bla_OXA-181 in environmental samples in Ecuador. Moreover, we detected a new putative variant of this gene. Some commensal coagulase-negative bacteria may have a role as mecA resistance reservoirs.

Taxonomic and functional profiling of Indian smokeless tobacco bacteriome uncovers several bacterial-derived risks to human health

Smokeless tobacco (ST) consumption keeps human oral health at high risk which is one of the major reasons for oral tumorigenesis. The chemical constituents of the ST products have been well discussed; however, the inhabitant microbial diversity of the ST products is less explored especially from south Asian regions. Therefore, the present investigation discusses the bacteriome-based analysis of indigenous tobacco products. The study relies on 16S amplicon-based bacteriome analysis of Indian smokeless tobacco (ST) products using a metagenomic approach. A total of 59,15,143 high-quality reads were assigned to 34 phyla, 82 classes, 176 orders, 256 families, 356 genera, and 154 species using the SILVA database. Of the phyla (> 1%), Firmicutes dominate among the Indian smokeless tobacco followed by Proteobacteria, Bacteroidetes, and Actinobacteria (> 1%). Whereas, at the genera level (> 1%), Lysinibacillus, Dickeya, Terribacillus, and Bacillus dominate. The comparative analysis between the loose tobacco (LT) and commercial tobacco (CT) groups showed no significant difference at the phyla level, however, only three genera (Bacillus, Aerococcus, and Halomonas) were identified as significantly different between the groups. It indicates that CT and LT tobacco share similar bacterial diversity and poses equal health risks to human oral health. The phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt 2.0) based analysis uncovered several genes involved in nitrate/nitrite reduction, biofilm formation, and pro-inflammation that find roles in oral pathogenesis including oral cancer. The strong correlation analysis of these genes with several pathogenic bacteria suggests that tobacco products pose a high bacterial-derived risk to human health. The study paves the way to understand the bacterial diversity of Indian smokeless tobacco products and their putative functions with respect to human oral health. The study grabs attention to the bacterial diversity of the smokeless tobacco products from a country where tobacco consumers are rampantly prevalent however oral health is of least concern.

Seasonal variability of the correlation network of antibiotics, antibiotic resistance determinants, and bacteria in a wastewater treatment plant and receiving water

Sewage treatment plants are an essential source of antibiotics, antibiotic resistance determinants, and bacteria in environmental waters. However, it is still unclear whether they can maintain a relatively stable relationship in wastewater and environmental waters. This study analyzed the removal capacity of the above three pollutants in the sewage treatment plant in summer and their impact on environmental waters, and then examines the relationship between the three contaminants in the wastewater and environmental waters in summer and winter based on our previous study. The results found that the removal capacity of bacteria in summer was poor, the concentration of fluoroquinolone in the effluent was higher than that in influent, and the abundance of intI1, tetW, qnrB, and ermB increased after wastewater treatment. Proteobacteria and Bacteroides were the main bacteria that constitute the correlation network between bacteria, and they existed stably in summer and winter. However, fluoroquinolones occupied a significant position in the determinant network of antibiotics and antibiotic resistance in summer and winter. There are fewer correlation between antibiotics and antibiotics resistance determinants in winter. Interestingly, the relationship between bacteria, antibiotics, and antibiotic resistance determinants was a mainly positive correlation in summer and negative correlation in winter. This study analyzed the relationship between bacteria, antibiotics, and antibiotic resistance determinants that were stable in the wastewater and environmental waters and pointed out the direction for subsequent targeted seasonal control of novel pollutants in wastewater and environmental waters.

Microcystin-leucine arginine induces skin barrier damage and reduces resistance to pathogenic bacteria in Lithobates catesbeianus tadpoles

Despite the importance of the skin mucosal barrier and commensal microbiota for the health of amphibians, the potential of environmental contaminants to disrupt the skin mucosal barrier and microbiota have rarely been studied in toxicology. In this study, tadpoles (Lithobates catesbeianus) were exposed to 0, 0.5, and 2 μg/L of microcystin-leucine arginine (MC-LR) for 30 days to explore the impacts of environmentally realistic MC-LR concentrations on the physical skin barrier, immune barrier, commensal microbiota, and skin resistance to pathogenic bacterial invasion. MC-LR exposure significantly reduced the collagen fibrils in the dermis of skin tissues and down-regulated tight junction and stratum corneum-related gene transcriptions, suggesting the damage caused by MC-LR to the physical barrier of the skin. Increased skin eosinophils and upregulated transcriptions of inflammation-related genes in the exposed tadpoles underline the development of skin inflammation resulting from MC-LR exposure even at environmentally realistic concentrations. Comparative transcriptome and immunobiochemical analyses found that antimicrobial peptides (Brevinin-1PLc, Brevinin-2GHc, and Ranatuerin-2PLa) and lysozyme were down-regulated in the exposed groups, while complement, pattern recognition receptor, and specific immune processes were up-regulated. However, the content of endotoxin lipopolysaccharide produced by bacteria increased in a dose-dependent pattern. The disc diffusion test showed a reduced ability of skin supernatant to inhibit pathogenic bacteria in the exposed groups. Analysis of microbial 16 S rRNA gene by high-throughput sequencing revealed that MC-LR interfered with the abundance, composition, and diversity of the skin commensal microbiota, which favored the growth of pathogen-containing genera Rhodococcus, Acinetobacter, and Gordonibacter. In summary, the current study provides the first clues about the impact of MC-LR on the integrity and function of skin barrier of amphibians. These new toxicological evidences can facilitate a more comprehensive evaluation of the ecological risk of MC-LR to amphibians.

Global Threat of Carbapenem-Resistant Gram-Negative Bacteria

Infections caused by multidrug-resistant (MDR) and extensively drug-resistant (XDR) Gram-negative bacteria (GNB), including carbapenem-resistant (CR) Enterobacterales (CRE; harboring mainly bla_KPC, bla_NDM, and bla_OXA-48-like genes), CR- or MDR/XDR-Pseudomonas aeruginosa (production of VIM, IMP, or NDM carbapenemases combined with porin alteration), and Acinetobacter baumannii complex (producing mainly OXA-23, OXA-58-like carbapenemases), have gradually worsened and become a major challenge to public health because of limited antibiotic choice and high case-fatality rates. Diverse MDR/XDR-GNB isolates have been predominantly cultured from inpatients and hospital equipment/settings, but CRE has also been identified in community settings and long-term care facilities. Several CRE outbreaks cost hospitals and healthcare institutions huge economic burdens for disinfection and containment of their disseminations. Parenteral polymyxin B/E has been observed to have a poor pharmacokinetic profile for the treatment of CR- and XDR-GNB. It has been determined that tigecycline is suitable for the treatment of bloodstream infections owing to GNB, with a minimum inhibitory concentration of ≤ 0.5 mg/L. Ceftazidime-avibactam is a last-resort antibiotic against GNB of Ambler class A/C/D enzyme-producers and a majority of CR-P. aeruginosa isolates. Furthermore, ceftolozane-tazobactam is shown to exhibit excellent in vitro activity against CR- and XDR-P. aeruginosa isolates. Several pharmaceuticals have devoted to exploring novel antibiotics to combat these troublesome XDR-GNBs. Nevertheless, only few antibiotics are shown to be effective in vitro against CR/XDR-A. baumannii complex isolates. In this era of antibiotic pipelines, strict implementation of antibiotic stewardship is as important as in-time isolation cohorts in limiting the spread of CR/XDR-GNB and alleviating the worsening trends of resistance.

[Application Progress of Dual RNA Sequencing in Microbial Research]

The human body is colonized by densely-populated and structurally complex communities of microorganisms. The microbiota interact not only with their host cells, but also with other microbiota. Dual RNA sequencing (Dual RNA-seq) can be used to conduct simultaneous analysis of the dynamic changes of gene expression of two (or more) interactive species, and to obtain thus, through the interaction model diagram, the inter-species regulatory relationship of genes of different species, and hence the interaction mechanism between species. We herein reviewed the application status and development prospects of Dual RNA-seq in the research of intestinal, respiratory, skin and oral microbes. Since the concept of Dual RNA-seq was first introduced, the technology has been applied to a range of infection models. Direct investigation into the dynamic interactions between species at the molecular level will contribute to the better understanding of the physiological changes of pathogens and hosts during the course of infection, and thus help reveal potential new targets or biomarkers. However, the Dual RNA-seq technology is still in its early stage of development, and there are some limitations in the experimental technology. For example, due to the dynamic nature of the interaction between species, there are urgent problems awaiting solutions, such as the optimal experimental conditions, the selection of sampling sites and how to achieve real-time observation. In addition, due to the large amount of bioinformatics data of Dual RNA-seq, further research is needed to explore for ways to process the interaction information quickly and flexibly.

Molecular epidemiology of carbapenem-resistant Acinetobacter baumannii isolated from three major hospitals in Jordan

BACKGROUND

In the last decade, incidences of carbapenem-resistant Acinetobacter baumannii have been increasingly reported worldwide. Consequently, A. baumannii was included in the World Health Organization's new list of critical pathogens, for which new drugs are desperately needed. The objective of this research was to study the molecular epidemiology and antimicrobial susceptibility of clinical carbapenem-resistant A. baumannii isolated from Jordanian hospitals.

METHODS

A total of 78 A. baumannii and 8 Acinetobacter spp. isolates were collected from three major hospitals in Jordan during 2018. Disc diffusion and microdilution methods were used to test their susceptibility against 19 antimicrobial agents. Multilocus sequence typing (MLST) was performed using the Pasteur scheme, followed by eBURST analysis for all isolates. PCR was used to detect β-lactam resistance genes, bla_OXA-23-like , bla_OXA-51-like , and bla_NDM-1 .

RESULTS

Of the 86 tested isolates, 78 (90.6%) exhibited resistance to carbapenems, whereas no resistance was recorded to tigecycline or polymyxins. Based on the resistance profiles, 10.4% and 84.8% of isolates were classified into multidrug resistant (MDR) or extensively drug resistant (XDR), respectively. The most prevalent carbapenems resistance genes amongst isolates were bla_OXA-51-Like (89.5%), followed by bla_OXA-23-Like (88.3%) and bla_NDM-1 (10.4%). MLST revealed the presence of 19 sequence types (STs), belonging to eight different international complexes. The most commonly detected clonal complex (CC) was CC2, representing 64% of all typed isolates.

CONCLUSIONS

This is the first study to report the clonal diversity of A. baumannii isolates in Jordan. A high incidence of carbapenem resistance was detected in the isolates investigated. In addition, our findings provided evidence for the widespread of bla_OXA-23-like harbouring carbapenem-resistant A. baumannii and belonging to CC2. The number of XDR isolates identified in this study is alarming. Thus, periodic surveillance and molecular epidemiological studies of resistance factors are important to improve treatment outcomes and prevent the spread of A. baumannii infections.

Characterization and Inhibition of 1-Deoxy-d-Xylulose 5-Phosphate Reductoisomerase: A Promising Drug Target in Acinetobacter baumannii and Klebsiella pneumoniae

The ESKAPE pathogens comprise a group of multidrug-resistant bacteria that are the leading cause of nosocomial infections worldwide. The prevalence of antibiotic resistant strains and the relative ease by which bacteria acquire resistance genes highlight the continual need for the development of novel antibiotics against new drug targets. The methylerythritol phosphate (MEP) pathway is an attractive target for the development of new antibiotics. The MEP pathway governs the synthesis of isoprenoids, which are key lipid precursors for vital cell components such as ubiquinone and bacterial hopanoids. Additionally, the MEP pathway is entirely distinct from the corresponding mammalian pathway, the mevalonic acid (MVA) pathway, making the first committed enzyme of the MEP pathway, 1-deoxy-d-xylulose 5-phosphate reductoisomerase (IspC), an attractive target for antibiotic development. To facilitate drug development against two of the ESKAPE pathogens, Acinetobacter baumannii and Klebsiella pneumoniae, we cloned, expressed, purified, and characterized IspC from these two Gram-negative bacteria. Enzyme inhibition assays using IspC from these two pathogens, and compounds fosmidomycin and FR900098, indicate IC₅₀ values ranging from 19.5–45.5 nM. Antimicrobial susceptibility tests with these inhibitors reveal that A. baumannii is susceptible to FR900098, whereas K. pneumoniae is susceptible to both compounds. Finally, to facilitate structure-based drug design of inhibitors targeting A. baumannii IspC, we determined the 2.5 Å crystal structure of IspC from A. baumannii in complex with inhibitor FR900098, and cofactors NADPH and magnesium.

Acinetobacter baumannii Biofilm Formation and Its Role in Disease Pathogenesis: A Review

Acinetobacter species, particularly Acinetobacter baumannii, is the first pathogen on the critical priority list of pathogens for novel antibiotics to become a "red-alert" human pathogen. Acinetobacter baumannii is an emerging global antibiotic-resistant gram-negative bacteria that most typically causes biofilm-associated infections such as ventilator-associated pneumonia and catheter-related infection, both of which are resistant to antibiotic therapy. A. baumannii's capacity to develop antibiotic resistance mechanisms allows the organism to thrive in hospital settings, facilitating the global spread of multidrug-resistant strains. Although Acinetobacter infections are quickly expanding throughout hospital environments around the world, the highest concentration of infections occurs in intensive care units (ICUs). Biofilms are populations of bacteria on biotic or abiotic surfaces that are encased in the extracellular matrix and play a crucial role in pathogenesis, making treatment options more difficult. Even though a variety of biological and environmental elements are involved in the production of A. baumannii biofilms, glucose is the most important component. Biofilm-mediated A. baumannii infections are the most common type of A. baumannii infection associated with medical equipment, and they are extremely difficult to treat. As a result, health care workers (HCWs) should focus on infection prevention and safety actions to avoid A. baumannii biofilm-related infections caused by medical devices, and they should be very selective when using treatments in combination with anti-biofilms. Therefore, this review discusses biofilm formation in A. baumannii, its role in disease pathogenesis, and its antimicrobial resistance mechanism.

Presence of non-oral bacteria in the oral cavity

A homeostatic balance exists between the resident microbiota in the oral cavity and the host. Perturbations of the oral microbiota under particular conditions can contribute to the growth of non-oral pathogens that are hard to kill because of their higher resistance to antimicrobials, raising the probability of treatment failure and reinfection. The presence of these bacteria in the oral cavity has been proven to be associated with several oral diseases such as periodontitis, caries, and gingivitis, and systemic diseases of importance in clinical medicine such as cystic fibrosis, HIV, and rheumatoid arthritis. However, it is still controversial whether these species are merely transient members or unique to the oral cavity. Mutualistic and antagonistic interactions between the oral microbiota and non-oral pathogens can also occur, though the mechanisms used by these bacteria are not clear. Therefore, this review presents an overview of the current knowledge about the presence of non-oral bacteria in the oral cavity, their relationship with systemic and oral diseases, and their interactions with oral bacteria.

Outer membrane protein A inhibits the degradation of caspase-1 to regulate NLRP3 inflammasome activation and exacerbate the Acinetobacter baumannii pulmonary inflammation

Acinetobacter baumannii (A. baumannii), one of the major pathogens that causes severe nosocomial infections, is characterised by a high prevalence of drug resistance. It has been reported that A. baumannii triggers the NOD-like receptor 3 (NLRP3) inflammasome, but the role of its virulence-related outer membrane protein A (ompA) remains unclear. Therefore, this study aimed to explore the effects of ompA on the NLRP3 inflammasome and its underlying molecular mechanisms. Results showed that ompA enhanced inflammatory damage, which was reduced as a result of knockout of the ompA gene. Additionally, ompA-stimulated expression of NLRP3 inflammasome was significantly blocked by silencing caspase-1, but activation of NLRP3 inflammasome was not altered after silencing ASC; this indicated that ompA was dependent on the caspase-1 pathway to activate the inflammatory response. Simultaneously, the wild-type (WT) strains triggered NLRP3 inflammasome after inhibition of caspase-1 degradation by proteasome inhibitor MG-132, aggravating tissue damage. These findings indicated that ompA may be dependent on the caspase-1 pathway to enhance inflammation and exacerbate tissue damage. Taken together, these results confirmed a novel capsase-1-modulated mechanism underpinning ompA activity, which further reveals the NLRP3 inflammasome pathway as a potential immunomodulatory target against A. baumannii infections.

Omics and interspecies interaction

Interspecies interactions are key determinants in biofilm behavior, ecology, and architecture. The cellular responses of microorganisms to each other at transcriptional, proteomic, and metabolomic levels ultimately determine the characteristics of biofilm and the corresponding implications for health and disease. Advances in omics technologies have revolutionized our understanding of microbial community composition and their activities as a whole. Large-scale analyses of the complex interaction between the many microbial species residing within a biofilm, however, are currently still hampered by technical and bioinformatics challenges. Thus, studies of interspecies interactions have largely focused on the transcriptional and proteomic changes that occur during the contact of a few prominent species, such as Porphyromonas gingivalis, Streptococcus mutans, Candida albicans, and a few others, with selected partner species. Expansion of available tools is necessary to grow the revealing, albeit limited, insight these studies have provided into a profound understanding of the nature of individual microbial responses to the presence of others. This will allow us to answer important questions including: Which intermicrobial interactions orchestrate the myriad of cooperative, synergistic, antagonistic, manipulative, and other types of relationships and activities in the complex biofilm environment, and what are the implications for oral health and disease?

Factors affecting simultaneous nitrification and denitrification (SND) in a moving bed sequencing batch reactor (MBSBR) system as revealed by microbial community structures

The effects of biological factors including dissolved oxygen (DO), pH, carbon/nitrogen (C/N) and hydraulic retention times (HRT) on the performance of simultaneous nitrification and denitrification (SND) in a moving bed sequencing batch reactor (MBSBR) were investigated. A low DO was found to be advantageous to the SND in that nitrification was not inhibited, while pH and C/N ratio were shown to have positive effects on SND, and HRT needed to be controlled in a suitable range. A desirable SND efficiency was obtained at a DO of 2.5 mg L^-1, pH of approximately 8.0, C/N ratio of 10 and HRT of 10 h in the MBSBR. High-throughput sequencing analysis showed that different operating conditions impacted microbial communities, resulting in different nitrogen removal mechanisms. Autotrophic and heterotrophic nitrification together contributed to the good nitrification performance, while denitrification was conducted by combined anoxic and aerobic processes. Furthermore, the results of principal component analyses (PCA) and the abundance of the predominant nitrification and denitrification genera both showed that DO and HRT might be regarded as the dominant variable factors influencing community structure analysis during SND, while the linear discriminant analysis (LDA) effect size (LEfSe) algorithm showed differences in abundance among the biofilm microbial communities with different DO. Overall, the results of this study improve our understanding of the bacterial community structure with different operating conditions in MBSBRs.

A Potential Role of Phospholipase 2 Group IIA (PLA2-IIA) in P. gingivalis-Induced Oral Dysbiosis

Porphyromonas gingivalis is an oral pathogen with the ability to induce oral dysbiosis and periodontal disease. Nevertheless, the mechanisms by which P. gingivalis could abrogate the host-microbe symbiotic relationship leading to oral dysbiosis remain unclear. We have recently demonstrated that P. gingivalis specifically increased the antimicrobial properties of oral epithelial cells, through a strong induction of the expression of PLA₂-IIA in a mechanism that involves activation of the Notch-1 receptor. Moreover, gingival expression of PLA₂-IIA was significantly increased during initiation and progression of periodontal disease in non-human primates and interestingly, those PLA₂-IIA expression changes were concurrent with oral dysbiosis. In this chapter, we present an innovative hypothesis of a potential mechanism involved in P. gingivalis-induced oral dysbiosis and inflammation based on our previous observations and a robust body of literature that supports the antimicrobial and proinflammatory properties of PLA₂-IIA as well as its role in other chronic inflammatory diseases.

Fungal-Bacterial Interactions in Health and Disease

Fungi and bacteria encounter each other in various niches of the human body. There, they interact directly with one another or indirectly via the host response. In both cases, interactions can affect host health and disease. In the present review, we summarized current knowledge on fungal-bacterial interactions during their commensal and pathogenic lifestyle. We focus on distinct mucosal niches: the oral cavity, lung, gut, and vagina. In addition, we describe interactions during bloodstream and wound infections and the possible consequences for the human host.

Multidrug-resistant Acinetobacter baumannii infection in lung transplant recipients: risk factors and prognosis

Backgrounds: Infectious complication is an important cause of poor outcome of lung transplantation (LT). Infections with Acinetobacter baumannii (A. baumannii) are problematic, because of limited therapeutic option due to increasing resistance to antibiotics. However, there are few studies on A. baumannii infection in lung transplant recipients. Thus, we aimed to investigate epidemiology and risk factors for infection with A. baumannii in lung transplant recipients. Methods: Lung transplant recipients ≥18 years of age in a university hospital were enrolled in this retrospective cohort study. Risk factors for infection with multidrug resistant A. baumannii and 90-day mortality were analysed. Results: Fifty-one of 96 lung transplant recipients experienced A. baumannii infection. Infected patients had a significantly higher 90-day mortality rate than uninfected (19.6% vs. 2.2%, p = .009). High blood urea nitrogen (BUN) before transplantation (odds ratio [OR] 1.16; p = .008), long duration of surgery (OR 1.16; p = .029) and hypoalbuminemia before transplantation (OR 4.01; p = .037) were independent risk factors for infection with multidrug resistant A. baumannii. On multivariate analysis, severe thrombocytopenia (OR 28.69; p = .005), high serum creatinine (OR 1.48; p = .042) and infection with multidrug resistant A. baumannii (OR 22.58; p = .031) were independent risk factors for 90-day mortality. Conclusions: Prolonged surgery, high BUN and hypoalbuminemia before LT were significant risk factors for infection with multidrug resistant A. baumannii. Severe thrombocytopenia, high serum creatinine and infection with multidrug resistant A. baumannii infection were independent risk factors for 90-day mortality.

An insight into the emergence of Acinetobacter baumannii as an oro-dental pathogen and its drug resistance gene profile - An in silico approach

Background

Acinetobacter baumannii, a potential nosocomial pathogen has stealthily gained entry into the oral cavity. Their association with other pathogens like Pseudomonas aeruginosa in chronic and aggressive periodontitis cases is well documented. The magnitude of problem caused by A . baumannii could be attributed to resistance genes acquired by the organism. Since the microbiome of oral cavity is heterogeneous and complex, the transfer of genes from multidrug resistant A . baumannii may be a serious threat in infection control and management. In view of this fact, the present study aims to categorize and characterize drug resistant genes present in each of the 19 genomes of Acinetobacter Sp. selected for the study.

Methods

About 19 genome sequences of Acinetobacter spp. with the predominance of different strains of A . baumannii was genotyped using in silico restriction digestion and pulse field gel electrophoresis (PFGE). Further, the prevalence of common drug resistant genes in the genome of various Acinetobacter spp. was recorded using in silico PCR analysis.

Results

Based on the PFGE pattern, phylogenetic tree was constructed and the genomes were clustered into 6 genotypes. Genotype 4 (n = 8; 42.10%) and 5 (n = 6; 31.57%) were predominant, followed by genotypes 2 (n = 2; 10.52%), 1, 3 and 6 (n = 1; 5.26%). Three species were excluded from the list since they were negative for most of the drug resistant genes tested. Prevalence of drug resistant genes in each of the 16 genomes analysed found oxa-51, ISAba 1 and ADC 1 to be the major genes found in A . baumannii. Acinetobacter spp. belonging to genotypes 4 and 5 were found to harbour 6-10 and 2-8 potential drug resistant genes respectively.

Conclusion

The present study showed cluster of multi-drug resistant genes in genomes analysed, thus, warranting the need for antibiotic surveillance, alternate therapeutic measures and development of novel antimicrobials. An extensive study on the genes conferring drug resistance in this pathogen will open new avenues for battling the entry and spread of this pathogen in vulnerable patient groups.

Treatment outcomes of patients with non-bacteremic pneumonia caused by extensively drug-resistant Acinetobacter calcoaceticus-Acinetobacter baumannii complex isolates: Is there any benefit of adding tigecycline to aerosolized colistimethate sodium?

Few therapeutic options exist for various infections caused by extensively drug-resistant Acinetobacter calcoaceticus-Acinetobacter baumannii (XDR-Acb) complex isolates, including pneumonia. This study investigated the clinical efficacy between aerosolized colistimethate sodium (AS-CMS, 2 million units thrice a day) treatment alone or in combination with standard-dose tigecycline (TGC) in patients with non-bacteremic pneumonia due to XDR-Acb, and explored the factors influencing patients' 30-day mortality.A 1:1 case (n = 106; receiving TGC plus AS-CMS) control (receiving AS-CMS alone with matching scores) observational study was conducted among adult patients with non-bacteremic XDR-Acb complex pneumonia in a Taiwanese medical center from January 2014 through December 2016. The clinically relevant data were retrospectively recorded. The primary endpoint was 30-day case fatality. Secondary endpoints investigated that if the co-morbidities, XDR-A. baumannii as a pneumonic pathogen, therapy-related factors, or airway colonization with colistin-resistant Acb negatively influenced the 14-day clinical condition of enrolled patients.A higher 30-day mortality rate was noted among the group receiving combination therapy (34.0% vs 22.6%; P = .17). The ≥7-day AS-CMS therapy successfully eradicated > 90% of airway XDR-Acb isolates. Nevertheless, follow-up sputum specimens from 10 (6.4% [10/156]) patients were colonized with colistin-resistant Acb isolates. After the conditional factors were adjusted by multivariate logistic analysis, the only factor independently predicting the 30-day case-fatality was the failure of treating XDR-Acb pneumonia at 14 days (adjusted odds ratio [aOR] = 38.2; 95% confidence interval [CI] = 9.96-142.29; P < .001). Cox proportional regression analysis found that chronic obstructive pulmonary disease (COPD) (adjusted hazard ratio [aHR] = 2.08; 95% CI = 1.05-4.10; P = .035), chronic renal failure (aHR = 3.00; 95% CI = 1.52-5.90; P = .002), non-invasive ventilation use (aHR = 2.68; 95% CI = 1.37-5.25; P = .004), and lack of TGC therapy (aHR = 0.52; 95% CI = 0.27-1.00; P = .049) adversely influenced the 14-day clinical outcomes. Conversely, the emergence of colistin-resistant Acb isolates in the follow-up sputum samples was not statistically significantly associated with curing or improving XDR-Acb pneumonia.In conclusion, aggressive pulmonary hygiene care, the addition of TGC, and corticosteroid dose tapering were beneficial in improving the 14-day patients' outcomes.

Transcriptome analysis of Porphyromonas gingivalis and Acinetobacter baumannii in polymicrobial communities

Acinetobacter baumannii is a nosocomial, opportunistic pathogen that causes several serious conditions including meningitis, septicemia, endocarditis, and pneumonia. It can be found in the oral biofilm, which may be a reservoir for pneumonia and chronic obstructive pulmonary disease. Subgingival colonization by A. baumannii is associated with chronic and aggressive periodontitis as well as refractory periodontal disease. Porphyromonas gingivalis, a keystone periodontal pathogen localized to subgingival plaque, is also implicated in several chronic conditions including aspiration pneumonia. Although both bacteria are found together in subgingival plaque and can cause multiple polymicrobial infections, nothing is known about the interactions between these two important human pathogens. In this study, we used RNA sequencing to understand the transcriptional response of both species as they adapt to heterotypic communities. Among the differentially regulated genes were those encoding a number of important virulence factors for both species including adhesion, biofilm formation, and protein secretion. Additionally, the presence of A. baumannii increased the abundance of P. gingivalis in model dual-species communities. Collectively these results suggest that both P. gingivalis and A. baumannii adapt to each other and have synergistic potential for increased pathogenicity. In identifying the mechanisms that promote pathogenicity and refractory disease, novel approaches to mitigate polymicrobial synergistic interactions may be developed to treat or prevent associated diseases.

In silico analysis of virulence genes in an emerging dental pathogen A. baumannii and related species

OBJECTIVES

Acinetobacter baumannii is an opportunistic pathogen which has recently been categorized as a high risk pathogen by World Health Organisation (WHO). The microbe has stealthily entered the oral cavity and has established itself as a potential pathogen by acquiring drug resistance and expression of several virulence genes. Surveillance on the type of virulence factors harboured by the organism will enable us to comprehend the mechanism of pathogenesis. The study was performed to screen for the presence of crucial virulence factors associated with Acinetobacter spp. as reviewed from the literature by employing computational tools.

DESIGN

Nineteen genome sequences of Acinetobacter spp. with the predominance of different strains of A. baumannii were classified phylogenetically into clusters using in silico restriction digestion and pulse field gel electrophoresis (PFGE). Further, the frequency of common virulence genes in the genome of various Acinetobacter spp. was recorded using in silico PCR analysis.

RESULTS

Based on PFGE pattern and phylogenetic tree the genomes of A. baumannii were clustered into 4 genotypes (G1-G4). Two species were excluded from the list since they were negative for almost all the virulence genes tested. Frequency of virulence genes in each of the 17 genomes analysed, found ompA and smpA to be the major virulence factors in A. baumannii and related species. Acinetobacter spp. belonging to genotypes 2 and 3 were found to harbour 1-15 and 6-10 potential genes encoding virulence factors respectively.

CONCLUSIONS

The present study showed numerous virulence genes in genomes analysed. In silico analysis of these virulence genes can be used as candidates to build novel therapeutic targets against the pathogen. An extensive study on the functional role of these genes could aid in stalling the propagation and dissemination of A. baumannii among susceptible individuals.

Pathogenic mechanisms of intracellular bacteria

PURPOSE OF REVIEW

We wished to overview recent data on a subset of epigenetic changes elicited by intracellular bacteria in human cells. Reprogramming the gene expression pattern of various host cells may facilitate bacterial growth, survival, and spread.

RECENT FINDINGS

DNA-(cytosine C5)-methyltransferases of Mycoplasma hyorhinis targeting cytosine-phosphate-guanine (CpG) dinucleotides and a Mycobacterium tuberculosis methyltransferase targeting non-CpG sites methylated the host cell DNA and altered the pattern of gene expression. Gene silencing by CpG methylation and histone deacetylation, mediated by cellular enzymes, also occurred in M. tuberculosis-infected macrophages. M. tuberculosis elicited cell type-specific epigenetic changes: it caused increased DNA methylation in macrophages, but induced demethylation, deposition of euchromatic histone marks and activation of immune-related genes in dendritic cells. A secreted transposase of Acinetobacter baumannii silenced a cellular gene, whereas Mycobacterium leprae altered the epigenotype, phenotype, and fate of infected Schwann cells. The 'keystone pathogen' oral bacterium Porphyromonas gingivalis induced local DNA methylation and increased the level of histone acetylation in host cells. These epigenetic changes at the biofilm-gingiva interface may contribute to the development of periodontitis.

SUMMARY

Epigenetic regulators produced by intracellular bacteria alter the epigenotype and gene expression pattern of host cells and play an important role in pathogenesis.

Candida-Bacteria Interactions: Their Impact on Human Disease

Candida species are the most common infectious fungal species in humans; out of the approximately 150 known species, Candida albicans is the leading pathogenic species, largely affecting immunocompromised individuals. Apart from its role as the primary etiology for various types of candidiasis, C. albicans is known to contribute to polymicrobial infections. Polymicrobial interactions, particularly between C. albicans and bacterial species, have gained recent interest in which polymicrobial biofilm virulence mechanisms have been studied including adhesion, invasion, quorum sensing, and development of antimicrobial resistance. These trans-kingdom interactions, either synergistic or antagonistic, may help modulate the virulence and pathogenicity of both Candida and bacteria while uniquely impacting the pathogen-host immune response. As antibiotic and antifungal resistance increases, there is a great need to explore the intermicrobial cross-talk with a focus on the treatment of Candida-associated polymicrobial infections. This article explores the current literature on the interactions between Candida and clinically important bacteria and evaluates these interactions in the context of pathogenesis, diagnosis, and disease management.

Analysis of bacterial community profiles of endodontically infected primary teeth using pyrosequencing

OBJECTIVE

The purpose of this study was to identify the endodontic microbiome in primary teeth with dental caries using high-throughput pyrosequencing and to establish data on the oral microbiome of primary teeth with endodontic infection.

METHODS

Ten primary teeth with dental caries and endodontic infection were included. Samples were collected from root canals using sterilized paper points and analyzed by pyrosequencing, based on the V1-V3 hypervariable region of the 16S rRNA gene. The data were analyzed using the CLcommunity software.

RESULTS

Analysis of the 10 samples yielded a total of 64,291 16S rRNA gene sequences. In total, 1586 OTUs (range, 91-235), six bacterial phyla, including unclassified, and 187 genera were assigned. At the genus level, Neisseria (group A), Acinetobacter (group B), and Fusobacterium (group C) were prominent. These predominant microorganisms were associated with the clinical condition and reflected the progression of endodontic infection in primary teeth.

CONCLUSIONS

This study revealed a relationship between the oral microbiome and endodontic infection in primary teeth. Additionally, anaerobic bacteria such as Fusobacterium species were dominant in the teeth with apical abscesses.

A practical guide to the oral microbiome and its relation to health and disease

The oral microbiome is incredibly complex with the average adult harboring about 50-100 billion bacteria in the oral cavity, which represent about 200 predominant bacterial species. Collectively, there are approximately 700 predominant taxa of which less than one-third still have not yet been grown in vitro. Compared to other body sites, the oral microbiome is unique and readily accessible. There is extensive literature available describing the oral microbiome and discussing the roles that bacteria may play in oral health and disease. However, the purpose of this review is not to rehash these detailed studies but rather to educate the reader with understanding the essence of the oral microbiome, namely that there are abundant bacteria in numbers and types, that there are molecular methods to rapidly determine bacterial associations, that there is site specificity for colonization of the host, that there are specific associations with oral health and disease, that oral bacteria may serve as biomarkers for non-oral diseases, and that oral microbial profiles may have potential use to assess disease risk.

Candida albicans Airway Colonization Facilitates Subsequent Acinetobacter baumannii Pneumonia in a Rat Model

The objective of the study was to determine the effects of Candida albicans respiratory tract colonization on Acinetobacter baumannii pneumonia in a rat model. Rats were colonized with C. albicans by instillation of 3 × 10(6) CFU into their airways, while sterile saline was instilled in the control group. The colonized rats were further divided into two groups: treated with amphotericin B or not. The rats were subsequently infected with A. baumannii (10(8) CFU by tracheobronchial instillation). A. baumannii lung CFU counts, cytokine lung levels, and rates of A. baumannii pneumonia were compared between groups. In vitro expression of A. baumannii virulence genes was measured by reverse transcription (RT)-PCR after 24-hour incubation with C. albicans or with Mueller-Hinton (MH) broth alone. Rats with Candida colonization developed A. baumannii pneumonia more frequently and had higher A. baumannii CFU burdens and heavier lungs than controls. After A. baumannii infection, lung interleukin 17 (IL-17) concentrations were lower and gamma interferon (IFN-γ) concentrations were higher in Candida-colonized rats than in controls. Candida-colonized rats treated with amphotericin B had a decreased rate of A. baumannii pneumonia and lower IFN-γ levels but higher IL-17 levels than untreated rats. Expression of basC, barB, bauA, ptk, plc2, and pld2 was induced while expression of ompA and abaI was suppressed in A. baumannii cultured in the presence of C. albicans C. albicans colonization facilitated the development of A. baumannii pneumonia in a rat model. Among Candida-colonized rats, antifungal treatment lowered the incidence of A. baumannii pneumonia. These findings could be due to modification of the host immune response and/or expression of A. baumannii virulence genes by Candida spp.

Intensive Periodontal Treatment Reduces Risk of Infection-Related Hospitalization in Hemodialysis Population: A Nationwide Population-Based Cohort Study

Periodontal disease (PD) is prevalent and correlated with malnutrition and inflammation in patients on hemodialysis (HD). Periodontal therapy improves systemic inflammatory and nutritional markers in HD population. The relationship between intensive PD therapy and clinical infectious outcomes in patients on HD remains unclear.In total, 4451 patients who underwent HD and intensive PD treatment between January 1, 1998 and December 31, 2010 were selected from the National Health Insurance Research Database as the case cohort. The comparison cohort was selected by matching a patient without PD with each PD treated patient at a 1:1 ratio according to a propensity score. The rates of hospitalizations for infectious diseases for both cohorts were analyzed and compared.Compared with the comparison cohort, the hazard ratio (HR) of hospitalization for overall infectious diseases was 0.72 (95% confidence interval [CI] = 0.66-0.78, P < 0.001) for the intensive PD treatment cohort. The intensive PD treated cohort had a significantly lower risk of acute and subacute infective endocarditis (HR = 0.54, 95% CI = 0.35-0.84, P < 0.01), pneumonia (HR = 0.71, 95% CI = 0.65-0.78, P < 0.001), and osteomyelitis (HR = 0.77, 95% CI = 0.62-0.96, P < 0.05) than did the comparison cohort.The intensive PD treatment of patients with HD was associated with reduced risks of overall infectious diseases, acute and subacute infective endocarditis, pneumonia, and osteomyelitis. Our study concurs the role of a conventional intervention in enhancing infectious diseases outcomes.