Evidence that Intraspecific Trait Variation among Nasal Bacteria Shapes the Distribution of Staphylococcus aureus

Nasal carriage of Staphylococcus aureus is a risk factor for infection, yet the bacterial determinants required for carriage are poorly defined. Interactions between S. aureus and other members of the bacterial flora may determine colonization and have been inferred in previous studies by using correlated species distributions. However, traits mediating species interactions are often polymorphic, suggesting that understanding how interactions structure communities requires a trait-based approach. We characterized S. aureus growth inhibition by the culturable bacterial aerobe consortia of 60 nasal microbiomes, and this revealed intraspecific variation in growth inhibition and that inhibitory isolates clustered within communities that were culture negative for S. aureus. Across microbiomes, the cumulative community-level growth inhibition was negatively associated with S. aureus incidence. To fully understand the ecological processes structuring microbiomes, it will be crucial to account for intraspecific variation in the traits that mediate species interactions.     

Methicillin-resistant Staphylococcus aureus in HIV patients: Risk factors associated with colonization and/or infection and methods for characterization of isolates – a systematic review

Staphylococcus aureus is an important cause of infections and HIV-infected individuals are frequently susceptible to this pathogen. The aim of this study was to perform a systematic review to identify both the risk factors associated with colonization/infection by methicillin-resistant S. aureus in HIV patients and the methods used for characterization of isolates. An electronic search of articles published between January 2001 and December 2013 was first conducted. Among 116 studies categorized as being at a quality level of A, B or C, only 9 studies were considered to have high methodological quality (level A). The majority of these studies were retrospective (4/9 studies). The risk factors associated with colonization/infection by S. aureus were use of antimicrobials (4/9 studies), previous hospitalization (4/9 studies) and low CD4+ T lymphocyte counts (<200 cells/μl) (3/9 studies). Culture in mannitol salt agar (3/9 studies) and the latex agglutination test (5/9 studies) were the main methods used for bacterial phenotypic identification. Genotypic profiles were accessed by pulsed-field gel electrophoresis (6/9 studies) and USA300 was the most prevalent lineage (5/9 studies). Most isolates were resistant to erythromycin (3/9 studies) and susceptible to vancomycin (4/9 studies). Ultimately, use of antimicrobials and previous hospitalization were the main risk factors for colonization/infection by methicillin-resistant S. aureus in HIV-infected individuals. However, the numbers of evaluated patients, the exclusion and inclusion criteria and the characterization of the S. aureus isolates were not uniform, which made it difficult to establish the characteristics associated with HIV patients who are colonized/infected by S. aureus.     

Mechanisms of folate metabolism-related substances affecting Staphylococcus aureus infection

Staphylococcus aureus (S. aureus) is one of the critical clinical pathogens which can cause multiple diseases ranging from skin infections to fatal sepsis. S. aureus is generally considered to be an extracellular pathogen. However, more and more evidence has shown that S. aureus can survive inside various cells. Folate plays an essential role in multiple life activities, including the conversion of serine and glycine, the remethylation of homocysteine to methionine, and the de novo synthesis of purine /dTMP, et al. More and more studies reported that S. aureus intracellular infection requires the involvement of folate metabolism. This review focused on the mechanisms of folate metabolism and related substances affecting S. aureus infection. Loss of tetrahydrofolic acid (THF)-dependent dTMP directly inhibits the nucleotide synthesis pathway of the S. aureus due to pabA deficiency. Besides, trimethoprim-sulfamethoxazole (TMP/SMX), a potent antibiotic that treats S. aureus infections, interferes in the process of the folate mechanism and leads to the production of thymidine-dependent small-colony variants (TD-SCVs). In addition, S. aureus is resistant to lysostaphin in the presence of serine hydroxymethyltransferase (SHMT). We provide new insights for understanding the molecular pathogenesis of S. aureus infection.     

Persistent Staphylococcus aureus Isolates from Two Independent Cases of Bacteremia Display Increased Bacterial Fitness and Novel Immune Evasion Phenotypes

Staphylococcus aureus bacteremia cases are complicated by bacterial persistence and treatment failure despite the confirmed in vitro susceptibility of the infecting strain to administered antibiotics. A high incidence of methicillin-resistant S. aureus (MRSA) bacteremia cases are classified as persistent and are associated with poorer patient outcomes. It is still unclear how S. aureus evades the host immune system and resists antibiotic treatment for the prolonged duration of a persistent infection. In this study, the genetic changes and associated phenotypic traits specific to S. aureus persistent bacteremia were identified by comparing temporally dispersed isolates from persistent infections (persistent isolates) originating from two independent persistent S. aureus bacteremia cases with the initial infection isolates and with three resolved S. aureus bacteremia isolates from the same genetic background. Several novel traits were associated specifically with both independent sets of persistent S. aureus isolates compared to both the initial isolates and the isolates from resolved infections (resolved isolates). These traits included (i) increased growth under nutrient-poor conditions; (ii) increased tolerance of iron toxicity; (iii) higher expression of cell surface proteins involved in immune evasion and stress responses; and (iv) attenuated virulence in a Galleria mellonella larva infection model that was not associated with small-colony variation or metabolic dormancy such as had been seen previously. Whole-genome sequence analysis identified different single nucleotide mutations within the mprF genes of all the isolates with the adaptive persistence traits from both independent cases. Overall, our data indicate a novel role for MprF function during development of S. aureus persistence by increasing bacterial fitness and immune evasion.     

A proteomic view of cell physiology and virulence of Staphylococcus aureus

Staphylococcus aureus is a human pathogen that has advanced to a main problem in hospital settings since effective treatment options for infections caused by this pathogen are limited. Thus, new strategies to prevent and treat S. aureus infections and rapid diagnostic tools are urgently needed. The course of an S. aureus infection largely depends on successful adaptation to the host environment and a very complex and poorly understood interplay of bacterial virulence factors with each other and with host components. Over the last years, genome sequences of different S. aureus strains have been published permitting a high-throughput proteomic analysis of this pathogen. This review summarizes the impact of 2D gel- and mass spectrometry-based proteomic approaches on a more comprehensive understanding of S. aureus pathophysiology and virulence. We show that only a combination of both techniques allows a proteomic view which adequately considers all subproteomic fractions of a bacterium, i.e. cytosolic, membrane, cell surface-associated, and extracellular proteins. By this means, the majority of proteins expressed in S. aureus can be identified and even quantified. In addition, posttranslational processes such as protein secretion, modification, processing, damages, and degradation can be adequately studied.     

Is there any rationale for treatment of Staphylococcus aureus infections with antimicrobials that are determined to be ineffective in vitro?

Antimicrobial drug resistance remains a leading problem in modern healthcare, impacting on treatment options, mortality, infection control and economic issues. The introduction of new antimicrobial drugs has consistently been followed by the emergence of resistant bacteria. This review aims to answer the question of whether clinical improvement is likely if treatment of Staphylococcus aureus infections is attempted with an antimicrobial drug against which resistance is expressed in vitro (RD). Over time, S. aureus has acquired a broad range of antimicrobial resistance mechanisms, and methicillin-resistant S. aureus (MRSA) strains have become the most common multidrug-resistant healthcare-related infection-causing bacteria in Europe. As intention-to-treat studies with an RD would be unethical, only observational studies to evaluate the impact of RD therapy have been performed. Most of these studies bolster the assumption that RD therapy offers no benefit to the patient, but some do not show a detrimental effect. Limited antimicrobial treatment options for severe, invasive infections caused by MRSA might tempt physicians to use antimicrobials to which in vitro resistance is reported by the microbiological laboratory. Reasons for this non-evidence-based approach might include better pharmacokinetic/pharmacodynamic parameters, lower toxicity and better bioavailability in specific compartments, and/or the assumption of increased in vivo susceptibility of those microorganisms reported as resistant in vitro. In vitro resistance of a bacterium to a drug implies that exposing this bacterium to that drug should result in a worse clinical outcome than would be obtained with a drug to which resistance has not been observed (SD). As a counterpoint to in vitro resistance breakpoints, the concept of clinical breakpoints is therefore briefly revisited in this review. In a nutshell, no evidence has been published that S. aureus infections can be reliably treated with RDs, either as a single administration or in combination therapy.     

Staphylococcus aureus colonization at ICU admission as a risk factor for developing S. aureus ICU pneumonia

ObjectiveTo quantify the incidence of intensive care unit (ICU)-acquired pneumonia caused by Staphylococcus aureus (S. aureus) and its association with S. aureus colonization at ICU admission.MethodsThis was a post-hoc analysis of two cohort studies in critically ill patients. The primary outcome was the incidence of microbiologically confirmed S. aureus ICU-acquired pneumonia. Incidences of S. aureus ICU pneumonia and associations with S. aureus colonization at ICU admission were determined using competing risks analyses. In all ICUs, patients were screened for respiratory tract S. aureus carriage on admission as part of infection control policies. Pooling of data was not deemed possible because of heterogeneity in baseline differences in patient population.ResultsThe two cohort studies contained data of 9156 ICU patients. The average carriage rate of S. aureus among screened patients was 12.7%. In total, 1185 (12.9%) patients developed ICU pneumonia. Incidences of S. aureus ICU pneumonia were 1.33% and 1.08% in cohorts 1 and 2, respectively. After accounting for competing events, the adjusted subdistribution hazard ratio (SHR) of S. aureus colonization at admission for developing S. aureus ICU pneumonia was 9.55 (95% CI 5.31-17.18) in cohort 1 and 14.54 (95% CI 7.24-29.21) in cohort 2.ConclusionThe overall cumulative incidence of S. aureus ICU pneumonia in these ICUs was low. Patients colonized with S. aureus at ICU admission had an up to 15 times increased risk for developing this outcome compared with non-colonized patients.     

Staphylococcus aureus induces expression of receptor activator of NF-kappaB ligand and prostaglandin E2 in infected murine osteoblasts

Osteomyelitis is an inflammatory disease of the bone that is characterized by the presence of necrotic bone tissue and increased osteoclast activity. Staphylococcus aureus is responsible for approximately 80% of all cases of human osteomyelitis. While the disease is especially difficult to treat, the pathogenesis of S. aureus-induced osteomyelitis is poorly understood. Elucidating the molecular mechanisms by which S. aureus induces osteomyelitis could lead to a better understanding of the disease and its progression and development of new treatments. Osteoblasts can produce several soluble factors that serve to modulate the activity or formation of osteoclasts. Receptor activator of NF-κB ligand (RANK-L) and prostaglandin E₂ (PGE₂) are two such molecules which can promote osteoclastogenesis and stimulate bone resorption. In addition, previous studies in our laboratory have shown that osteoblasts produce inflammatory cytokines, such as interleukin 6, following infection with S. aureus, which could induce COX-2 and in turn PGE₂, further modulating osteoclast recruitment and differentiation. Therefore, we hypothesized that following infection with S. aureus, osteoblasts will express increased levels of RANK-L and PGE₂. The results presented in this study provide evidence for the first time that RANK-L mRNA and protein and PGE₂ expression are upregulated in S. aureus-infected primary osteoblasts. In addition, through the use of the specific COX-2 inhibitor NS 398, we show that when PGE₂ production is inhibited, RANK-L production is decreased. These data suggest a mechanism whereby osteoblasts regulate the production of RANK-L during infection.     

Mechanisms of promoting the differentiation and bone resorption function of osteoclasts by Staphylococcus aureus infection

Bone infection is a common and serious complication in the field of orthopedics, which frequently leads to excessive bone destruction and fracture nonunion. Staphylococcus aureus (S. aureus) infection affects bone cell function which, in turn, causes bone destruction. Bone is mainly regulated by osteoblasts and osteoclasts. Osteoclasts are the only cell type with bone resorptive function. Their over-activation is closely associated with excessive bone loss. Understanding how S. aureus changes the functional state of osteoclasts is the key to effective treatment. By reviewing the literature, this paper summarizes several mechanisms of bone destruction caused by S. aureus influencing osteoclasts, thereby stimulating new ideas for the treatment of bone infection.     

Host airway proteins interact with Staphylococcus aureus during early pneumonia

Staphylococcus aureus is a major cause of hospital-acquired pneumonia and is emerging as an important etiological agent of community-acquired pneumonia. Little is known about the specific host-pathogen interactions that occur when S. aureus first enters the airway. A shotgun proteomics approach was utilized to identify the airway proteins associated with S. aureus during the first 6 h of infection. Host proteins eluted from bacteria recovered from the airways of mice 30 min or 6 h following intranasal inoculation under anesthesia were subjected to liquid chromatography and tandem mass spectrometry. A total of 513 host proteins were associated with S. aureus 30 min and/or 6 h postinoculation. A majority of the identified proteins were host cytosolic proteins, suggesting that S. aureus was rapidly internalized by phagocytes in the airway and that significant host cell lysis occurred during early infection. In addition, extracellular matrix and secreted proteins, including fibronectin, antimicrobial peptides, and complement components, were associated with S. aureus at both time points. The interaction of 12 host proteins shown to bind to S. aureus in vitro was demonstrated in vivo for the first time. The association of hemoglobin, which is thought to be the primary staphylococcal iron source during infection, with S. aureus in the airway was validated by immunoblotting. Thus, we used our recently developed S. aureus pneumonia model and shotgun proteomics to validate previous in vitro findings and to identify nearly 500 other proteins that interact with S. aureus in vivo. The data presented here provide novel insights into the host-pathogen interactions that occur when S. aureus enters the airway.     

Magnetic Nanoparticle Targeted Hyperthermia of Cutaneous Staphylococcus aureus Infection

The incidence of wound infections that do not adequately respond to standard-of-care antimicrobial treatment has been increasing. To address this challenge, a novel antimicrobial magnetic thermotherapy platform has been developed in which a high-amplitude, high-frequency, alternating magnetic field is used to rapidly heat magnetic nanoparticles that are bound to Staphylococcus aureus (S. aureus). The antimicrobial efficacy of this platform was evaluated in the treatment of both an in vitro culture model of S. aureus biofilm and a mouse model of cutaneous S. aureus infection. We demonstrated that an antibody-targeted magnetic nanoparticle bound to S. aureus was effective at thermally inactivating S. aureus and achieving accelerated wound healing without causing tissue injury.     

Bringing together what belongs together: Optimizing murine infection models by using mouse-adapted Staphylococcus aureus strains

Staphylococcus (S.) aureus is a leading cause of bacterial infection world-wide, and currently no vaccine is available for humans. Vaccine development relies heavily on clinically relevant infection models. However, the suitability of mice for S. aureus infection models has often been questioned, because experimental infection of mice with human-adapted S. aureus requires very high infection doses. Moreover, mice were not considered to be natural hosts of S. aureus. The latter has been disproven by our recent findings, showing that both laboratory mice, as well as wild small mammals including mice, voles, and shrews, are naturally colonized with S. aureus. Here, we investigated whether mouse-and vole-derived S. aureus strains show an enhanced virulence in mice as compared to the human-adapted strain Newman. Using a step-wise approach based on the bacterial genotype and in vitro assays for host adaptation, we selected the most promising candidates for murine infection models out of a total of 254 S. aureus isolates from laboratory mice as well as wild rodents and shrews. Four strains representing the clonal complexes (CC) 8, 49, and 88 (n?=?2) were selected and compared to the human-adapted S. aureus strain Newman (CC8) in murine pneumonia and bacteremia models. Notably, a bank vole-derived CC49 strain, named DIP, was highly virulent in BALB/c mice in pneumonia and bacteremia models, whereas the other murine and vole strains showed virulence similar to or lower than that of Newman. At one tenth of the standard infection dose DIP induced disease severity, bacterial load and host cytokine and chemokine responses in the murine bacteremia model similar to that of Newman. In the pneumonia model, DIP was also more virulent than Newman but the effect was less pronounced. Whole genome sequencing data analysis identified a pore-forming toxin gene, lukF-PV(P83)/lukM, in DIP but not in the other tested S. aureus isolates. To conclude, the mouse-adapted S. aureus strain DIP allows a significant reduction of the inoculation dose in mice and is hence a promising tool to develop clinically more relevant infection models.     

Farrerol regulates antimicrobial peptide expression and reduces Staphylococcus aureus internalization into bovine mammary epithelial cells

Mastitis, defined as inflammation of the mammary gland, is an infectious disease with a major economic influence on dairy industry. Staphylococcus aureus is a common gram-positive pathogen that frequently causes subclinical, chronic infection of the mammary gland in dairy cows. Farrerol, a traditional Chinese medicine isolated from rhododendron, has been shown to have anti-bacterial activity. However, the effect of farrerol on S. aureus infection in mammary epithelium has not been studied in detail. The aim of this study was to investigate the effect of farrerol on the invasion of bovine mammary epithelial cells (bMEC) by S. aureus. The expression of antimicrobial peptide genes by bMEC were assessed in the presence or absence of S. aureus infection. Our results demonstrated that farrerol (4–16 μg/ml) reduced > 55% the internalization of S. aureus into bMEC. We also found that farrerol was able to down-regulate the mRNA expression of tracheal antimicrobial peptide (TAP) and bovine neutrophil β-defensin 5 (BNBD5) in bMEC infected with S. aureus. The Nitric oxide (NO) production of bMEC after S. aureus stimulation was decreased by farrerol treatment. Furthermore, farrerol treatment suppressed S. aureus-induced NF-κB activation in bMEC. These results demonstrated that farrerol modulated TAP and BNBD5 gene expression in mammary gland, enhances bMEC defense against S. aureus infection and could be useful in protection against bovine mastitis.     

A systematic review of the global seasonality of infections caused by Acinetobacter species in hospitalized patients

BackgroundAcinetobacter is a leading multidrug resistant pathogen in hospitals worldwide that has been seen to exhibit periodic surges during summer months. However, winter peaks and lack of seasonality have also been noted.ObjectivesTo systematically collate and examine the evidence describing seasonal patterns in the incidence of Acinetobacter infection in hospitalized patients.Data sourcesMEDLINE/Ovid, EMBASE, Scopus and Web of Science.Study eligibility criteriaLongitudinal observational studies investigating seasonal variation in the incidence of Acinetobacter infection.ParticipantsPatients receiving hospital care.InterventionsRoutine hospital care.MethodsSystematic review with narrative evidence synthesis structured around clinical and methodological heterogeneity and internal validity of retrieved studies, seasonal patterns and risk factors detected, and stated hypotheses of mechanisms underlying seasonality. To examine consistency in reported seasonal patterns across different conditions, monthly incidence data were extracted, standardised, weighted and presented graphically.ResultsTwenty-five studies reporting 37006 cases of Acinetobacter infection or colonization during 1954 months of follow-up were reviewed. Standardised monthly incidence data pooled across studies exhibited a global seasonal pattern with an incidence peak in summer/warmer months and a trough in winter/colder months. This seasonal pattern remained consistent under different weighting schemes accounting for study size, length of follow-up and overall quality assessment rating. Seasonality persisted in different clinical settings and for different types and sources of infection. Nine studies provided consistent evidence of temperature-associated variation in Acinetobacter incidence, while there were controversial findings regarding other environmental variables. No study detected patient-related or clinical practice-related seasonal variation in Acinetobacter incidence.ConclusionsDespite substantial clinical and methodological heterogeneity in retrieved studies, a consistent global seasonal pattern in Acinetobacter infection incidence was evident in this review. This merits attention when designing or evaluating infection control interventions in hospitals. Future research should focus on elucidating driving mechanisms underlying the observed seasonality.     

Clinical comparison between exogenous and haematogenous periprosthetic joint infections caused by Staphylococcus aureus

Patient-related risk factors for invasive Staphylococcus aureus infection overlap with those for periprosthetic joint infections (PJIs). We compared these factors and clinical characteristics between 17 exogenous and 40 haematogenous PJIs caused by S. aureus. Exogenous cases presented significantly more often with damaged periprosthetic soft tissue, whereas haematogenous cases more often had systemic signs of infection, such as fever, chills, and sepsis syndrome. However, comorbid conditions associated with S. aureus infection and/or PJIs did not differ between the two groups. These findings imply that patient-related risk factors for S. aureus infection do not help to predict the mode of infection acquisition in prosthetic joints.     

Recombinant ESAT-6-Like Proteins Provoke Protective Immune Responses against Invasive Staphylococcus aureus Disease in a Murine Model

Staphylococcus aureus is a common pathogen found in the community and in hospitals. Most notably, methicillin-resistant S. aureus is resistant to many antibiotics, which is a growing public health concern. The emergence of drug-resistant strains has prompted the search for alternative treatments, such as immunotherapeutic approaches. To date, most clinical trials of vaccines or of passive immunization against S. aureus have ended in failure. In this study, we investigated two ESAT-6-like proteins secreted by S. aureus, S. aureus EsxA (SaEsxA) and SaEsxB, as possible targets for a vaccine. Mice vaccinated with these purified proteins elicited high titers of anti-SaEsxA and anti-SaEsxB antibodies, but these antibodies could not prevent S. aureus infection. On the other hand, recombinant SaEsxA (rSaEsxA) and rSaEsxB could induce Th1- and Th17-biased immune responses in mice. Mice immunized with rSaEsxA and rSaEsxB had significantly improved survival rates when challenged with S. aureus compared with the controls. These findings indicate that SaEsxA and SaEsxB are two promising Th1 and Th17 candidate antigens which could be developed into multivalent and serotype-independent vaccines against S. aureus infection.     

Gastrointestinal Dissemination and Transmission of Staphylococcus aureus following Bacteremia

Mutations that alter virulence and antibiotic susceptibility arise and persist during Staphylococcus aureus bacteremia. However, an experimental system demonstrating transmission following bacteremia has been lacking, and thus implications of within-host adaptation for between-host transmission are unknown. We report that S. aureus disseminates to the gastrointestinal tract of mice following intravenous injection and readily transmits to cohoused naive mice. Both intestinal dissemination and transmission were linked to the production of virulence factors based on gene deletion studies of the sae and agr two-component systems. Furthermore, antimicrobial selection for antibiotic-resistant S. aureus displaced susceptible S. aureus from the intestine of infected hosts, which led to the preferential transmission and dominance of antibiotic-resistant bacteria among cohoused untreated mice. These findings establish an animal model to investigate gastrointestinal dissemination and transmission of S. aureus and suggest that adaptation during the course of systemic infection has implications beyond the level of a single host.