Staphylococcus aureusIsolates Associated with Necrotizing Pneumonia Bind to Basement Membrane Type I and IV Collagens and Laminin

The role of human extracellular matrix proteins in defining Staphylococcus aureus biofilm infections

Twenty to forty one percent of the world's population is either transiently or permanently colonized by the Gram-positive bacterium, Staphylococcus aureus. In 2017, the CDC designated methicillin-resistant S. aureus (MRSA) as a serious threat, reporting ∼300 000 cases of MRSA-associated hospitalizations annually, resulting in over 19 000 deaths, surpassing that of HIV in the USA. S. aureus is a proficient biofilm-forming organism that rapidly acquires resistance to antibiotics, most commonly methicillin (MRSA). This review focuses on a large group of (>30) S. aureus adhesins, either surface-associated or secreted that are designed to specifically bind to 15 or more of the proteins that form key components of the human extracellular matrix (hECM). Importantly, this includes hECM proteins that are pivotal to the homeostasis of almost every tissue environment [collagen (skin), proteoglycans (lung), hemoglobin (blood), elastin, laminin, fibrinogen, fibronectin, and fibrin (multiple organs)]. These adhesins offer S. aureus the potential to establish an infection in every sterile tissue niche. These infections often endure repeated immune onslaught, developing into chronic, biofilm-associated conditions that are tolerant to ∼1000 times the clinically prescribed dose of antibiotics. Depending on the infection and the immune response, this allows S. aureus to seamlessly transition from colonizer to pathogen by subtly manipulating the host against itself while providing the time and stealth that it requires to establish and persist as a biofilm. This is a comprehensive discussion of the interaction between S. aureus biofilms and the hECM. We provide particular focus on the role of these interactions in pathogenesis and, consequently, the clinical implications for the prevention and treatment of S. aureus biofilm infections.

Pathogenicity and virulence of Aspergillus fumigatus

Pulmonary infections caused by the mould pathogen Aspergillus fumigatus are a major cause of morbidity and mortality globally. Compromised lung defences arising from immunosuppression, chronic respiratory conditions or more recently, concomitant viral or bacterial pulmonary infections are recognised risks factors for the development of pulmonary aspergillosis. In this review, we will summarise our current knowledge of the mechanistic basis of pulmonary aspergillosis with a focus on emerging at-risk populations.

Necrotizing pneumonia and purulent meningitis caused by bloodstream infection of CA-MRSA in a child: A rare case report

CASE PRESENTATION

We report the case of a girl aged 2 years and 10 months who had fever for 2 days, vomiting, poor mental status for 1 day, and one episode of convulsions.

SYMPTOMS AND SIGNS

The patient experienced a rapid onset of symptoms with fever, vomiting, and convulsions. Upon physical examination on admission, she presented with the following: temperature 38.6°C; pulse 185 beats/min; respiration 49 beats/min; blood pressure 89/51 mmHg; drowsiness; piebald skin all over her body; rice-grain-sized pustular rashes scattered on the front chest and both lower limbs, protruding from the surface of the skin; bilateral pupils that were equal in size and a circle with a diameter of about 3.0 mm, and slow light reflex; cyanotic lips; shortness of breath; positive for the three-concave sign; a small amount of phlegm that could be heard in both lungs; capillary refill time of 5 s; cold extremities; and a positive Babinski sign.

DIAGNOSTIC METHOD

A chest computed tomography scan showed multiple nodular and flake-like high-density shadows of varying sizes in each lobe in bilateral lungs, and a cavity with blurred edges could be seen in some nodules. A cranial magnetic resonance imaging examination demonstrated that the hyperintensity of diffusion-weighted imaging could be observed on the left cerebellar hemisphere and left parietal blade. Blood cultures, sputum, cerebrospinal fluid, and bronchoalveolar lavage fluid (BALF) by fiberoptic bronchoscopy all indicated the growth of methicillin-resistant Staphylococcus aureus (MRSA).

TREATMENT METHODS

After admission, the child was given meropenem combined with vancomycin, cefoperazone sulbactam combined with rifamycin, linezolid (oral) for anti-infection successively, and other adjuvant therapies.

CLINICAL OUTCOMES

The patient recovered clinically and was discharged from our hospital.

RECOMMENDED READERS

Neurology; Respiratory Medicine; Infectious Diseases Department.

Staphylococcus aureus Arsenal To Conquer the Lower Respiratory Tract

Staphylococcus aureus is both a commensal and a pathogenic bacterium for humans. Its ability to induce severe infections is based on a wide range of virulence factors. S. aureus community-acquired pneumonia (SA-CAP) is rare and severe, and the contribution of certain virulence factors in this disease has been recognized over the past 2 decades. First, the factors involved in metabolism adaptation are crucial for S. aureus survival in the lower respiratory tract, and toxins and enzymes are required for it to cross the pulmonary epithelial barrier. S. aureus subsequently faces host defense mechanisms, including the epithelial barrier, but most importantly the immune system. Here, again, S. aureus uses myriad virulence factors to successfully escape from the host’s defenses and takes advantage of them. The impact of S. aureus virulence, combined with the collateral damage caused by an overwhelming immune response, leads to severe tissue damage and adverse clinical outcomes. In this review, we summarize step by step all of the S. aureus factors implicated in CAP and described to date, and we provide an outlook for future research.

Complicated pneumonia in children

Complicated community-acquired pneumonia in a previously well child is a severe illness characterised by combinations of local complications (eg, parapneumonic effusion, empyema, necrotising pneumonia, and lung abscess) and systemic complications (eg, bacteraemia, metastatic infection, multiorgan failure, acute respiratory distress syndrome, disseminated intravascular coagulation, and, rarely, death). Complicated community-acquired pneumonia should be suspected in any child with pneumonia not responding to appropriate antibiotic treatment within 48-72 h. Common causative organisms are Streptococcus pneumoniae and Staphylococcus aureus. Patients have initial imaging with chest radiography and ultrasound, which can also be used to assess the lung parenchyma, to identify pleural fluid; CT scanning is not usually indicated. Complicated pneumonia is treated with a prolonged course of intravenous antibiotics, and then oral antibiotics. The initial choice of antibiotic is guided by local microbiological knowledge and by subsequent positive cultures and molecular testing, including on pleural fluid if a drainage procedure is done. Information from pleural space imaging and drainage should guide the decision on whether to administer intrapleural fibrinolytics. Most patients are treated by drainage and more extensive surgery is rarely needed; in any event, in low-income and middle-income countries, resources for extensive surgeries are scarce. The clinical course of complicated community-acquired pneumonia can be prolonged, especially when patients have necrotising pneumonia, but complete recovery is the usual outcome.

The Multivalent Role of Fibronectin-Binding Proteins A and B (FnBPA and FnBPB) of Staphylococcus aureus in Host Infections

Staphylococcus aureus, one of the most important human pathogens, is the causative agent of several infectious diseases including sepsis, pneumonia, osteomyelitis, endocarditis and soft tissue infections. This pathogenicity is due to a multitude of virulence factors including several cell wall-anchored proteins (CWA). CWA proteins have modular structures with distinct domains binding different ligands. The majority of S. aureus strains express two CWA fibronectin (Fn)-binding adhesins FnBPA and FnBPB (Fn-binding proteins A and B), which are encoded by closely related genes. The N-terminus of FnBPA and FnBPB comprises an A domain which binds ligands such as fibrinogen, elastin and plasminogen. The A domain of FnBPB also interacts with histones and this binding results in the neutralization of the antimicrobial activity of these molecules. The C-terminal moiety of these adhesins comprises a long, intrinsically disordered domain composed of 11/10 fibronectin-binding repeats. These repetitive motifs of FnBPs promote invasion of cells that are not usually phagocytic via a mechanism by which they interact with integrin α₅β₁ through a Fn mediated-bridge. The FnBPA and FnBPB A domains engage in homophilic cell-cell interactions and promote biofilm formation and enhance platelet aggregation. In this review we update the current understanding of the structure and functional properties of FnBPs and emphasize the role they may have in the staphylococcal infections.

Fulminant Staphylococcal Infections

Fulminant staphylococcal infection indicates an explosive, intense, and severe infection occurring in a patient whose previous condition and antecedent would never have caused any anticipation of life-threatening development. This includes necrotizing pneumonia, necrotizing fasciitis, and to some extent toxic shock syndrome and infective endocarditis. In the three former diseases, toxin production plays a major role whereas in the latter (fulminant presentation of infective endocarditis), association with any particular toxinic profile has never been demonstrated. This article reviews the clinical, pathophysiological, and therapeutic aspects of these diseases.

Genomic comparison between Staphylococcus aureus GN strains clinically isolated from a familial infection case: IS1272 transposition through a novel inverted repeat-replacing mechanism

A bacterial insertion sequence (IS) is a mobile DNA sequence carrying only the transposase gene (tnp) that acts as a mutator to disrupt genes, alter gene expressions, and cause genomic rearrangements. "Canonical" ISs have historically been characterized by their terminal inverted repeats (IRs), which may form a stem-loop structure, and duplications of a short (non-IR) target sequence at both ends, called target site duplications (TSDs). The IS distributions and virulence potentials of Staphylococcus aureus genomes in familial infection cases are unclear. Here, we determined the complete circular genome sequences of familial strains from a Panton-Valentine leukocidin (PVL)-positive ST50/agr4 S. aureus (GN) infection of a 4-year old boy with skin abscesses. The genomes of the patient strain (GN1) and parent strain (GN3) were rich for "canonical" IS1272 with terminal IRs, both having 13 commonly-existing copies (ce-IS1272). Moreover, GN1 had a newly-inserted IS1272 (ni-IS1272) on the PVL-converting prophage, while GN3 had two copies of ni-IS1272 within the DNA helicase gene and near rot. The GN3 genome also had a small deletion. The targets of ni-IS1272 transposition were IR structures, in contrast with previous "canonical" ISs. There were no TSDs. Based on a database search, the targets for ce-IS1272 were IRs or "non-IRs". IS1272 included a larger structure with tandem duplications of the left (IRL) side sequence; tnp included minor cases of a long fusion form and truncated form. One ce-IS1272 was associated with the segments responsible for immune evasion and drug resistance. Regarding virulence, GN1 expressed cytolytic peptides (phenol-soluble modulin α and δ-hemolysin) and PVL more strongly than some other familial strains. These results suggest that IS1272 transposes through an IR-replacing mechanism, with an irreversible process unlike that of "canonical" transpositions, resulting in genomic variations, and that, among the familial strains, the patient strain has strong virulence potential based on community-associated virulence factors.

Diagnosis and management of Panton-Valentine leukocidin toxin associated Staphylococcus aureus infection: an update

The incidence of invasive Staphylococcus aureus (SA) infection has increased in the past decade and is associated with poor outcomes and high mortality rates. Of all the virulence factors, Panton-Valentine Leukocidin (PVL) has received the greatest attention. PVL producing SA strains are more likely to produce severe skin and soft tissue infections (SSTIs) and necrotizing pneumonia. This review focuses on the current evidence on PVL-SA virulence, epidemiology, clinical disease and treatment with relevance to healthcare in India.

Emerging ST121/agr4 community-associated methicillin-resistant Staphylococcus aureus (MRSA) with strong adhesin and cytolytic activities: trigger for MRSA pneumonia and fatal aspiration pneumonia in an influenza-infected elderly

The pathogenesis of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) pneumonia in influenza-infected elderly individuals has not yet been elucidated in detail. In the present study, a 92-year-old man infected with influenza developed CA-MRSA pneumonia. His CA-MRSA was an emerging type, originated in ST121/agr4 S. aureus, with diversities of Panton–Valentine leucocidin (PVL)⁻/spat5110/SCCmecV⁺ versus PVL⁺/spat159^(etc.)/SCCmec⁻, but with common virulence potentials of strong adhesin and cytolytic activities. Resistance to erythromycin/clindamycin (inducible-type) and gentamicin was detected. Pneumonia improved with the administration of levofloxacin, but with the subsequent development of fatal aspiration pneumonia. Hence, characteristic CA-MRSA with strong adhesin and cytolytic activities triggered influenza-related sequential complications.

Staphylococcus aureus: the current state of disease, pathophysiology and strategies for prevention

Staphylococcus aureus is both a commensal organism and also an important opportunistic human pathogen, causing a variety of community and hospital-associated pathologies, such as bacteremia-sepsis, endocarditis, pneumonia, osteomyelitis, arthritis and skin diseases. The resurgence of S. aureus during the last decade in many settings has been facilitated not only by bacterial antibiotic resistance mechanisms but also by the emergence of new S. aureus clonal types with increased expression of virulence factors and the capacity to neutralize the host immune response. Prevention of the spread of S. aureus infection relies on the use of contact precautions and adequate procedures for infection control that so far have not been fully effective. Prevention using a prophylactic vaccine would complement these processes, having the potential to bring additional, significant progress toward decreasing invasive disease due to S. aureus.

Enterovirus D68 and Panton-Valentine Leukocidin-Positive Staphylococcus aureus Respiratory Coinfection with Fatal Outcome

A previously healthy 10-year-old girl with a 2-day history of upper respiratory illness and fever rapidly developed respiratory failure and sepsis with leukopenia, and expired despite attempts at resuscitation. Postmortem examination revealed bilateral necrotizing pneumonia and evidence of disseminated intravascular coagulation. Nasopharyngeal swabs and lung tissue submitted to the Centers for Disease Control and Prevention (CDC) were positive for Enterovirus D68 (EV-D68). Blood and lung cultures were positive for methicillin-resistant Staphylococcus aureus (MRSA). The isolates were submitted to the CDC and were found to be positive for the toxin Panton-Valentine leukocidin. We describe a fatality related to invasive toxin-mediated MRSA associated with EV-D68 coinfection, along with the clinical, laboratory, and autopsy findings, which provided important clues, prompting further investigation at the CDC to arrive at the correct diagnosis.

Healthcare- and Community-Associated Methicillin-Resistant Staphylococcus aureus (MRSA) and Fatal Pneumonia with Pediatric Deaths in Krasnoyarsk, Siberian Russia: Unique MRSA's Multiple Virulence Factors, Genome, and Stepwise Evolution

Methicillin-resistant Staphylococcus aureus (MRSA) is a common multidrug-resistant (MDR) pathogen. We herein discussed MRSA and its infections in Krasnoyarsk, Siberian Russia between 2007 and 2011. The incidence of MRSA in 3,662 subjects was 22.0% and 2.9% for healthcare- and community-associated MRSA (HA- and CA-MRSA), respectively. The 15-day mortality rates for MRSA hospital- and community-acquired pneumonia (HAP and CAP) were 6.5% and 50%, respectively. MRSA CAP cases included pediatric deaths; of the MRSA pneumonia episodes available, ≥27.3% were associated with bacteremia. Most cases of HA-MRSA examined exhibited ST239/spa3(t037)/SCCmecIII.1.1.2 (designated as ST239_Kras), while all CA-MRSA cases examined were ST8/spa1(t008)/SCCmecIV.3.1.1(IVc) (designated as ST8_Kras). ST239_Kras and ST8_Kras strongly expressed cytolytic peptide (phenol-soluble modulin α, PSMα; and δ-hemolysin, Hld) genes, similar to CA-MRSA. ST239_Kras pneumonia may have been attributed to a unique set of multiple virulence factors (MVFs): toxic shock syndrome toxin-1 (TSST-1), elevated PSMα/Hld expression, α-hemolysin, the staphylococcal enterotoxin SEK/SEQ, the immune evasion factor SCIN/SAK, and collagen adhesin. Regarding ST8_Kras, SEA was included in MVFs, some of which were common to ST239_Kras. The ST239_Kras (strain OC3) genome contained: a completely unique phage, φSa7-like (W), with no att repetition; S. aureus pathogenicity island SaPI2R, the first TSST-1 gene-positive (tst⁺) SaPI in the ST239 lineage; and a super copy of IS256 (≥22 copies/genome). ST239_Kras carried the Brazilian SCCmecIII.1.1.2 and United Kingdom-type tst. ST239_Kras and ST8_Kras were MDR, with the same levofloxacin resistance mutations; small, but transmissible chloramphenicol resistance plasmids spread widely enough to not be ignored. These results suggest that novel MDR and MVF⁺ HA- and CA-MRSA (ST239_Kras and ST8_Kras) emerged in Siberian Russia (Krasnoyarsk) associated with fatal pneumonia, and also with ST239_Kras, a new (Siberian Russian) clade of the ST239 lineage, which was created through stepwise evolution during its potential transmission route of Brazil-Europe-Russia/Krasnoyarsk, thereby selective advantages from unique MVFs and the MDR.

Guía de consenso para el abordaje de la neumonía adquirida en la comunidad en el paciente anciano

La incidencia de la neumonía adquirida en la comunidad se incrementa con la edad y se asocia a una elevada morbimortalidad debido a los cambios fisiológicos asociados al envejecimiento y a una mayor presencia de enfermedades crónicas. Debido a la importancia que tiene desde un punto de epidemiológico y pronóstico, y a la enorme heterogeneidad descrita en el manejo clínico, creemos que existía la necesidad de realizar un documento de consenso específico para este perfil de paciente. El propósito de este fue realizar una revisión de las evidencias en relación con los factores de riesgo para la etiología, la presentación clínica, el manejo y el tratamiento de la neumonía adquirida en la comunidad en los ancianos con el fin de elaborar una serie de recomendaciones específicas basadas en el análisis crítico de la literatura. Este documento es fruto de la colaboración de diferentes especialistas en representación de la Sociedad Española de Medicina de Urgencias y Emergencias (SEMES), Sociedad Española de Geriatría y Gerontología (SEGG), Sociedad Española de Quimioterapia (SEQ), Sociedad Española de Medicina Interna (SEMI), Sociedad Española de Neumología y Cirugía Torácica (SEPAR), Sociedad Española de Hospitalización a Domicilio (SEHAD) y Sociedad Española de Enfermedades Infecciosas y Microbiología Clínica (SEIMC).

Panton-Valentine Leukocidin-positive Staphylococcus aureus: a potentially significant pathogen in cystic fibrosis

Staphylococcus aureus is an important pathogen within the context of cystic fibrosis lung disease. Case reports have identified a strong association between the toxin Panton-Valentine Leukocidin (PVL) and lethal necrotizing pneumonia in healthy immunocompetent patients. PVL+ strains of Staphylococcus aureus have also been identified in patients with cystic fibrosis. We describe a further case of pneumonia in a patient with cystic fibrosis, and outline potential transmission of the organism from healthy family members to this patient. We review the evidence regarding the pathogenicity of PVL toxin with a special reference to patients with cystic fibrosis. We outline current concerns regarding the potential transmission of the organism and possible treatment strategies.

Triclosan promotes Staphylococcus aureus nasal colonization

The biocide triclosan is used in many personal care products, including toothpastes, soaps, clothing, and medical equipment. Consequently, it is present as a contaminant in the environment and has been detected in some human fluids, including serum, urine, and milk. Staphylococcus aureus is an opportunistic pathogen that colonizes the noses and throats of approximately 30% of the population. Colonization with S. aureus is known to be a risk factor for several types of infection. Here we demonstrate that triclosan is commonly found in the nasal secretions of healthy adults and the presence of triclosan trends positively with nasal colonization by S. aureus. We demonstrate that triclosan can promote the binding of S. aureus to host proteins such as collagen, fibronectin, and keratin, as well as inanimate surfaces such as plastic and glass. Lastly, triclosan-exposed rats are more susceptible to nasal colonization with S. aureus. These data reveal a novel factor that influences the ability of S. aureus to bind surfaces and alters S. aureus nasal colonization.

Triclosan has been used as a biocide for over 40 years, but the broader effects that it has on the human microbiome have not been investigated. We demonstrate that triclosan is present in nasal secretions of a large portion of a test population and its presence correlates with Staphylococcus aureus nasal colonization. Triclosan also promotes the binding of S. aureus to human proteins and increases the susceptibility of rats to nasal colonization by S. aureus. These findings are significant because S. aureus colonization is a known risk factor for the development of several types of infections. Our data demonstrate the unintended consequences of unregulated triclosan use and contribute to the growing body of research demonstrating inadvertent effects of triclosan on the environment and human health.

Severe leukopenia in Staphylococcus aureus-necrotizing, community-acquired pneumonia: risk factors and impact on survival

Background

Necrotizing pneumonia attributed to Panton-Valentine leukocidin-positive Staphylococcus aureus has mainly been reported in otherwise healthy children and young adults, with a high mortality rate. Erythroderma, airway bleeding, and leukopenia have been shown to be predictive of mortality. The objectives of this study were to define the characteristics of patients with severe leukopenia at 48-h hospitalization and to update our data regarding mortality predicting factors in a larger population than we had previously described.

Methods

It was designed as a case-case study nested in a cohort study. A total of 148 cases of community-acquired, necrotizing pneumonia were included. The following data were collected: basic demographic information, medical history, signs and symptoms, radiological findings and laboratory results during the first 48 h of hospitalization. The study population was divided into 2 groups: (1) with severe leukopenia (leukocyte count ≤3,000 leukocytes/mL, n=62) and (2) without severe leukopenia (>3,000 leukocytes/mL, n=86).

Results

Median age was 22 years, and the male-to-female gender ratio was 1.5. The overall in-hospital mortality rate was 41.2%. Death occurred in 75.8% of severe leukopenia cases with median survival time of 4 days, and in 16.3% of cases with leukocyte count >3,000/mL (P<0.001). Multivariate analysis indicated that the factors associated with severe leukopenia were influenza-like illness (adjusted odds ratio (aOR) 4.45, 95% CI (95% confidence interval) 1.67-11.88, P=0.003), airway bleeding (aOR 4.53, 95% CI 1.85-11.13, P=0.001) and age over 30 years (aOR 2.69, 95% CI 1.08-6.68, P=0.033). A personal history of furuncles appeared to be protective (OR 0.11, 95% CI 0.01-0.96, P=0.046).

Conclusion

S. aureus-necrotizing pneumonia is still an extremely severe disease in patients with severe leukopenia. Some factors could distinguish these patients, allowing better initial identification to initiate adapted, rapid administration of appropriate therapy.

Targeted protein engineering provides insights into binding mechanism and affinities of bacterial collagen adhesins

The collagen-binding bacterial proteins, Ace and Cna, are well characterized on the biochemical and structural level. Despite overall structural similarity, recombinant forms of the Ace and Cna ligand-binding domains exhibit significantly different affinities and binding kinetics for collagen type I (CI) in vitro. In this study, we sought to understand, in submolecular detail, the bases for these differences. Using a structure-based approach, we engineered Cna and Ace variants by altering specific structural elements within the ligand-binding domains. Surface plasmon resonance-based binding analysis demonstrated that mutations that are predicted to alter the orientation of the Ace and Cna N(1) and N(2) subdomains significantly affect the interaction between the MSCRAMM (microbial surface components recognizing adhesive matrix molecule) and CI in vitro, including affinity, association/dissociation rates and binding ratio. Moreover, we utilized this information to engineer an Ace variant with an 11,000-fold higher CI affinity than the parent protein. Finally, we noted that several engineered proteins that exhibited a weak interaction with CI recognized more sites on CI, suggesting an inverse correlation between affinity and specificity.

Herpes simplex virus type 1 infection facilitates invasion of Staphylococcus aureus into the nasal mucosa and nasal polyp tissue

BACKGROUND

Staphylococcus aureus (S. aureus) plays an important role in the pathogenesis of severe chronic airway disease, such as nasal polyps. However the mechanisms underlying the initiation of damage and/or invasion of the nasal mucosa by S. aureus are not clearly understood. The aim of this study was to investigate the interaction between S. aureus and herpes simplex virus type 1 (HSV1) in the invasion of the nasal mucosa and nasal polyp tissue.

METHODOLOGY/PRINCIPAL FINDINGS

Inferior turbinate and nasal polyp samples were cultured and infected with either HSV1 alone, S. aureus alone or a combination of both. Both in turbinate mucosa and nasal polyp tissue, HSV1, with or without S. aureus incubation, led to focal infection of outer epithelial cells within 48 h, and loss or damage of the epithelium and invasion of HSV1 into the lamina propria within 72 h. After pre-infection with HSV1 for 24 h or 48 h, S. aureus was able to pass the basement membrane and invade the mucosa. Epithelial damage scores were significantly higher for HSV1 and S. aureus co-infected explants compared with control explants or S. aureus only-infected explants, and significantly correlated with HSV1-invasion scores. The epithelial damage scores of nasal polyp tissues were significantly higher than those of inferior turbinate tissues upon HSV1 infection. Consequently, invasion scores of HSV1 of nasal polyp tissues were significantly higher than those of inferior turbinate mucosa in the HSV1 and co-infection groups, and invasion scores of S. aureus of nasal polyp tissues were significantly higher than those of inferior turbinate tissues in the co-infection group.

CONCLUSIONS/SIGNIFICANCE

HSV1 may lead to a significant damage of the nasal epithelium and consequently may facilitate invasion of S. aureus into the nasal mucosa. Nasal polyp tissue is more susceptible to the invasion of HSV1 and epithelial damage by HSV1 compared with inferior turbinate mucosa.

Host response signature to Staphylococcus aureus alpha-hemolysin implicates pulmonary Th17 response

Staphylococcus aureus pneumonia causes significant morbidity and mortality. Alpha-hemolysin (Hla), a pore-forming cytotoxin of S. aureus, has been identified through animal models of pneumonia as a critical virulence factor that induces lung injury. In spite of considerable molecular knowledge of how this cytotoxin injures the host, the precise host response to Hla in the context of infection remains poorly understood. We employed whole-genome expression profiling of infected lungs to define the host response to wild-type S. aureus compared with the response to an Hla-deficient isogenic mutant in experimental pneumonia. These data provide a complete expression profile at 4 and at 24 h postinfection, revealing a unique response to the toxin-expressing strain. Gene ontogeny analysis revealed significant differences in the extracellular matrix and cardiomyopathy pathways, both of which govern cellular interactions in the tissue microenvironment. Evaluation of individual transcript responses to Hla-secreting staphylococci was notable for upregulation of host cytokine and chemokine genes, including the p19 subunit of interleukin-23. Consistent with this observation, the cellular immune response to infection was characterized by a prominent Th17 response to the wild-type pathogen. These findings define specific host mRNA responses to Hla-producing S. aureus, coupling the pulmonary Th17 response to the secretion of this cytotoxin. Expression profiling to define the host response to a single virulence factor proved to be a valuable tool in identifying pathways for further investigation in S. aureus pneumonia. This approach may be broadly applicable to the study of bacterial toxins, defining host pathways that can be targeted to mitigate toxin-induced disease.

Pathogenic Naegleria fowleri and non-pathogenic Naegleria lovaniensis exhibit differential adhesion to, and invasion of, extracellular matrix proteins

Naegleria fowleri and Naegleria lovaniensis are closely related free-living amoebae found in the environment. N. fowleri causes primary amoebic meningoencephalitis (PAM), a rapidly fatal disease of the central nervous system, while N. lovaniensis is non-pathogenic. N. fowleri infection occurs when the amoebae access the nasal passages, attach to the nasal mucosa and its epithelial lining, and migrate to the brain. This process involves interaction with components of the host extracellular matrix (ECM). Since the ability to invade tissues can be a characteristic that distinguishes pathogenic from non-pathogenic amoebae, the objective of this study was to assess adhesion to, and invasion of, the ECM by these two related but distinct Naegleria species. N. fowleri exhibited a higher level of adhesion to the ECM components laminin-1, fibronectin and collagen I. Scanning electron microscopy revealed that N. fowleri attached on ECM substrata exhibited a spread-out appearance that included the presence of focal adhesion-like structures. Western immunoblotting revealed two integrin-like proteins for both species, but one of these, with a molecular mass of approximately 70 kDa, was detected at a higher level in N. fowleri. Confocal microscopy indicated that the integrin-like proteins co-localized to the focal adhesion-like structures. Furthermore, anti-integrin antibody decreased adhesion of N. fowleri to ECM components. Finally, N. fowleri disrupted 3D ECM scaffolds, while N. lovaniensis had a minimal effect. Collectively, these results indicate a distinction in adhesion to, and invasion of, ECM proteins between N. fowleri and N. lovaniensis.

Staphylococcus aureus hemolysins, bi-component leukocidins, and cytolytic peptides: a redundant arsenal of membrane-damaging virulence factors?

One key aspect of the virulence of Staphylococcus aureus lies in its ability to target the host cell membrane with a large number of membrane-damaging toxins and peptides. In this review, we describe the hemolysins, the bi-component leukocidins (which include the Panton Valentine leukocidin, LukAB/GH, and LukED), and the cytolytic peptides (phenol soluble modulins). While at first glance, all of these factors might appear redundant, it is now clear that some of these factors play specific roles in certain S. aureus life stages and diseases or target specific cell types or species. In this review, we present an update of the literature on toxin receptors and their cell type and species specificities. Furthermore, we review epidemiological studies and animal models illustrating the role of these membrane-damaging factors in various diseases. Finally, we emphasize the interplay of these factors with the host immune system and highlight all their non-lytic functions.

Comparative genomics and drug resistance of a geographic variant of ST239 methicillin-resistant Staphylococcus aureus emerged in Russia

Two distinct classes of methicillin-resistant Staphylococcus aureus (MRSA) are spreading in hospitals (as hospital-acquired MRSA, HA-MRSA) and in the community (as community-acquired MRSA, CA-MRSA). Multilocus sequence type (ST) 239 MRSA, one of the most worldwide-disseminated lineages, has been noted as a representative HA-MRSA. Here, we isolated ST239 MRSA (spa type 3 [t037] and staphylococcal cassette chromosome mec [SCCmec] type III.1.1.1) and its novel variant with ST239/spa351 (t030)/SCCmecIII.1.1.4 (SCCmecIII_R) not only from hospitals but also from patients with urethritis in the community in Russia. The Russian variant (strain 16K) possessed a hybrid genome consisting of CC8 and CC30, similar to the ST239/spa3/SCCmecIII.1.1.1 HA-MRSA (TW20) genome, but with marked diversity. The 16K′ CC30 section had SCCmecIII_R carrying the dcs-carrying unit (which corresponded to the SCCmecIVc J3 joining region of ST30 CA-MRSA), lacked SCCmercury, and possessed a novel mobile element structure (MES16K) carrying the ccrC-carrying unit (with the recombinase gene ccrC1 allele 3) and drug resistance tranposons. The Russian variant included strains with a high ability to transfer its multiple drug resistance by conjugation; e.g., for strain 16K, the transfer frequency of a chloramphenicol resistance plasmid (p16K-1 with 2.9 kb in size) reached 1.4×10⁻², followed by Tn554 conjugative transfer at 3.6×l0⁻⁴. The Russian variant, which has been increasing recently, included divergent strains with different plasmid patterns and pulsed field gel electrophoresis profiles. The data demonstrate the alternative nature of ST239 MRSA as CA-MRSA and also as a drug resistance disseminator, and its micro but dynamic evolution in Russia.

A Brazilian lineage of Staphylococcus lugdunensis presenting rough colony morphology may adhere to and invade lung epithelial cells

Staphylococcus lugdunensis is an unusually virulent coagulase-negative species, which causes serious infection similar to S. aureus. We evaluated the expression of virulence factors such as S. lugdunensis synergistic haemolysin (SLUSH), fibrinogen-binding protein (Fbl), biofilm production and biofilm-production-related genes in 23 S. lugdunensis clinical isolates and one type strain that had been previously characterized for their genotypes. In addition, the biofilm composition and the ability of isolates to adhere to and invade human epithelial lung cells were also investigated. The PCR method used detected the presence of slush and intercellular adhesin (ica) virulence genes in all isolates. All isolates produced the Fbl protein and, with the exception of the type strain, all isolates produced the SLUSH haemolysin. Fourteen (60.9 %) isolates produced biofilms. The detachment assay, using sodium metaperiodate or proteolytic enzymes to analyse the biofilm composition, showed protein-mediated biofilms in two representative isolates, one for each colony type (rough and smooth). All strongly biofilm-producing isolates, including three with rough colony morphology, had the same prevalent PFGE pattern. However, among the representative strains tested, only the S. lugdunensis isolate that formed rough colonies was able to adhere to and invade A549 cell monolayers in the same quantities as those observed with S. aureus isolates (P = 1.000). No significant adhesion or invasion was observed for the other isolates in comparison with the S. aureus isolate, independent of biofilm production or clonality. Our results could explain the incredible ability of this pathogen to cause infections that are as aggressive as S. aureus. In addition, the ability of S. lugdunensis to adhere to and invade eukaryotic cells was also noticed for isolates with rough colony morphology, reinforcing the increased virulence in this species.

Immunopathogenesis of Staphylococcus aureus pulmonary infection

Staphylococcus aureus is a common human pathogen highly evolved as both a component of the commensal flora and as a major cause of invasive infection. Severe respiratory infection due to staphylococci has been increasing due to the prevalence of more virulent USA300 CA-MRSA strains in the general population. The ability of S. aureus to adapt to the milieu of the respiratory tract has facilitated its emergence as a respiratory pathogen. Its metabolic versatility, the ability to scavenge iron, coordinate gene expression, and the horizontal acquisition of useful genetic elements have all contributed to its success as a component of the respiratory flora, in hospitalized patients, as a complication of influenza and in normal hosts. The expression of surface adhesins facilitates its persistence in the airways. In addition, the highly sophisticated interactions of the multiple S. aureus virulence factors, particularly the α-hemolysin and protein A, with diverse immune effectors in the lung such as ADAM10, TNFR1, EGFR, immunoglobulin, and complement all contribute to the pathogenesis of staphylococcal pneumonia.

Hemoglobin promotes Staphylococcus aureus nasal colonization

Staphylococcus aureus nasal colonization is an important risk factor for community and nosocomial infection. Despite the importance of S. aureus to human health, molecular mechanisms and host factors influencing nasal colonization are not well understood. To identify host factors contributing to nasal colonization, we collected human nasal secretions and analyzed their ability to promote S. aureus surface colonization. Some individuals produced secretions possessing the ability to significantly promote S. aureus surface colonization. Nasal secretions pretreated with protease no longer promoted S. aureus surface colonization, suggesting the involvement of protein factors. The major protein components of secretions were identified and subsequent analysis revealed that hemoglobin possessed the ability to promote S. aureus surface colonization. Immunoprecipitation of hemoglobin from nasal secretions resulted in reduced S. aureus surface colonization. Furthermore, exogenously added hemoglobin significantly decreased the inoculum necessary for nasal colonization in a rodent model. Finally, we found that hemoglobin prevented expression of the agr quorum sensing system and that aberrant constitutive expression of the agr effector molecule, RNAIII, resulted in reduced nasal colonization of S. aureus. Collectively our results suggest that the presence of hemoglobin in nasal secretions contributes to S. aureus nasal colonization.

Staphylococcus aureus is a medically important human pathogen that is found in the nasal passages of approximately 1/3 of the population. The nose serves as a reservoir for spread of this pathogen and predisposes the host to potential infection. Factors contributing to S. aureus nasal colonization are only beginning to be elucidated. The collection and analysis of human nasal secretions provided evidence that the presence of hemoglobin in nasal secretions can promote S. aureus nasal colonization. Hemoglobin reduced expression of the S. aureus agr quorum sensing regulatory system known to be involved in surface colonization, and it was found that induction of the agr system reduced nasal colonization. These findings suggest that individuals experiencing frequent nosebleeds would be prone to S. aureus colonization and epidemiological data supports these findings. By understanding host factors and bacterial molecular mechanisms involved in nasal colonization we may one day be able to design novel decolonization strategies.

DNA microarray-based characterisation of Panton-Valentine leukocidin-positive community-acquired methicillin-resistant Staphylococcus aureus from Italy

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) isolates are widespread in many countries, with varying distribution and epidemiology. The aim of this study was to collect and characterise the CA-MRSA isolates circulating in Italy, since only some case reports have been published. Eighteen Panton-Valentine-positive CA-MRSA isolates were collected from different Italian hospitals during the period 2005-2009 from severe infections (skin and soft tissue infections, n = 10; necrotising pneumonia, n = 7; and sepsis, n = 1). Accessory gene regulator (agr) typing, staphylococcal cassette chromosome (SCC) mec typing, spa typing, multi-locus sequence typing (MLST), pulsed-field gel electrophoresis (PFGE) and DNA microarray were applied to categorise isolates into clones and to compare the relevant genetic features of each clone. Six different clones were identified, the most common (7 out of 18 isolates, 38.8%) being agrI/ST8/SCCmecIV, corresponding to the USA300 clone. Six out of the seven USA300 isolates did not harbour the arginine catabolic mobile element (ACME). Four strains (22.2%) were agrIII/ST80/SCCmecIV, corresponding to the European clone. Two of the other clones, namely, agrIII/ST88/SCCmecV and agrIII/ST772/SCCmecV, corresponded to CA-MRSA clones rarely found in other countries and probably originating from Africa or the Indian subcontinent. The results of microarray hybridisations showed that the distribution of resistance genes and other virulence factors was specific to each clone. Some characteristics could be exploited as specific markers for a clone or a group of isolates, e.g. the mer operon, recovered only in ACME-negative USA300 strains. DNA microarray contributed to a more complete description of the variety of different CA-MRSA clones circulating in Italy.

Panton-Valentine leukocidin in the pathogenesis of community-associated methicillin-resistant Staphylococcus aureus infection

Methicillin-resistant Staphylococcus aureus (MRSA) is an important human pathogen that causes serious infectious diseases and was endemic in hospitals by the late 1960s. Beginning with its first report in the late 1990s, the rapid emergence of community-associated MRSA (CA-MRSA) worldwide responsible for a wide spectrum of diseases ranging from minor skin infections to fatal necrotizing pneumonia has been found in previously healthy individuals without established risk factors for MRSA acquisition. Recently, various virulence determinants unique to CA-MRSA have been uncovered, which explain how the pathogen spreads easily and causes severe CA-MRSA infections among humans. However, the role of Panton-Valentine leukocidin (PVL) in the pathogenesis of CA-MRSA infection is currently a matter of much debate because of conflicting data from epidemiologic studies of CA-MRSA infections and various murine disease models. Identifying specialized pathogenic traits of CA-MRSA and the concerted regulation of these factors remains a challenge that will foster development of vaccines and therapies designed to control CA-MRSA infections. This review focuses on the current status of molecular epidemiology associated with CA-MRSA in Taiwan and progresses toward understanding the enhanced virulence properties of CA-MRSA, with an emphasis on the role of Panton-Valentine leukocidin.

Staphylococcal scalded skin syndrome in an extremely low-birth-weight neonate: molecular characterization and rapid detection by multiplex and real-time PCR of methicillin-resistant Staphylococcus aureus

BACKGROUND

  Staphylococcal scalded skin syndrome (SSSS), caused by methicillin-resistant Staphylococcus aureus (MRSA) producing exfoliative toxin (ET), is a life-threatening infection for neonates in neonatal intensive care units (NICUs). SSSS in extremely low-birth-weight (ELBW) neonates is rare. A new class of MRSA (community-acquired MRSA, CA-MRSA) has been emerging in the community. The aim of this study was to characterize MRSA from an ELBW neonate with SSSS, and to develop rapid detection methods for SSSS-associated and emerging pediatric MRSA.

METHODS

  An ELBW infant in the NICU developed SSSS on day 16 after birth. Isolated MRSA was genetically characterized and compared with CA-MRSA from bullous impetigo (biCA-MRSA), which is positive for the ET and collagen-adhesin (CNA) genes in many cases, and the Panton-Valentine leucocidin (PVL) gene rarely. Specific primers and probes for five virulence genes (for ETA, ETB, ETD, PVL, CNA) were designed for multiplex polymerase chain reaction (PCR) and real-time PCR.

RESULTS

  MRSA strain H5 from SSSS exhibited the genotype (ST91, spa416[t375], agr3, SCCmecIVa, CoaI), and possessed the ETB and CNA genes, similar to ST91 biCA-MRSA (albeit with a divergence). Multiplex PCR detected the ETB and CNA genes of strain H5, and real-time PCR detected strain H5 at as low as 10(2)  CFU/mL. The assays were 100% specific and 100% sensitive, for the five virulence genes.

CONCLUSION

  ETB-positive ST91 MRSA, which was very similar to ST91 biCA-MRSA, was isolated from an ELBW infant with SSSS. The multiplex and real-time PCR assays specifically or quantitatively detected SSSS-associated and emerging pediatric MRSA.

A 24-year-old man with cough, rhabdomyolysis, and pneumomediastinum

BACKGROUND

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) frequently causes severe necrotizing pneumonia in young patients.

CASE

We present the case of a 24-year-old male, who was brought to the emergency department with persistent fevers, confusion, and severe cough. He was found to have necrotizing pneumonia, pneumomediastinum, and rhabdomyolysis with renal failure. Cultures were positive for influenza A and CA-MRSA. After a prolonged intensive care unit (ICU) stay, he made a complete recovery.

CONCLUSION

Community-acquired MRSA pneumonia is a growing health threat that typically presents in young adults after, or in conjunction with, a flu-like illness. It is characterized by a rapidly progressive deteriorating clinical course.

Molecular analysis of repeated methicillin-resistant Staphylococcus aureus infections in children

Background

Methicillin-resistant Staphylococcus aureus (MRSA) is a major pathogen that causes severe morbidity and mortality in hospitalized patients. It is unclear whether repeated MRSA infections in pediatric patients are caused by relapse of previous infecting strains or by acquiring new strains from extrinsic sources. The study aimed to define the genetic relatedness of MRSA isolates from children with repeated infections.

Methodology/Principal Findings

Children with multiple MRSA infections during 2004–2006 were identified in a teaching hospital. Repeated infections were confirmed by chart review and the responsible isolates were genotyped and screened for Panton-Valentine leukocidin (PVL) genes. Two consecutive episodes comprised an infection pair, and strain relatedness was defined for each pair as indistinguishable, highly related, or distinct if the isolates were of the same subtype, the same genotype, or different genotype, respectively. A total of 114 episodes comprising 66 infection pairs were identified in 48 children. The interval of infection pairs ranged from 15 days to 346 days, with a median duration of 57.5 days. Genotypings classified all isolates into 7 genotypes and 31 subtypes. Of 66 pairs, 46 (69.7%), 13 (19.7%) and 7 (10.6%) pairs were caused by indistinguishable, highly related and distinct strains, respectively. Subsequent infections caused by indistinguishable strains were more common for PVL-positive strains (17/18, 94.4%) than for PVL-negative strains (29/48, 60.4%, P = 0.007). The strain relatedness was not affected by the durations of interval between infections.

Conclusions/Significance

Most repeated MRSA infections in children are caused by indistinguishable strains even after a long period of interval, suggesting that persistent carriage and relapse of initial infecting strains were responsible for the majority of recurrent MRSA infections.

Factors associated with the outcome of life-threatening necrotizing pneumonia due to community-acquired Staphylococcus aureus in adult and adolescent patients

BACKGROUND

Although community-acquired Staphylococcus aureus pneumonia with highly virulent Panton-Valentine leukocidin (PVL)-positive strains, a severe disease with significant lethality, is rare, especially in adult and adolescent patients, recent reports highlight that these infections are on the rise.

OBJECTIVES

To describe the demographic and clinical features of reported cases of life-threatening community-acquired S. aureus pneumonia with usually PVL-positive strains in adult and adolescent patients, to evaluate the variables related to death, and to select a more appropriate antimicrobial treatment for this potentially deadly disease.

METHODS

We summarized all of the 92 reported cases and our case. The effect of 5 variables on mortality was measured using logistic regression.

RESULTS

S. aureus community-acquired pneumonia (CAP) with usually PVL-positive strains is a severe disease with significant lethality, i.e. 42.9%; a short duration of the time from the onset of symptoms to death, i.e. 5.5 ± 10.1 days, and prolonged hospital admissions, i.e. 33.2 ± 29.5 days. Seventy-three cases have been tested for the gene for PVL, and 71 strains have been found to carry the PVL gene. Logistic regression analysis showed that leucopenia (p = 0.002), influenza-like symptoms or laboratory-confirmed influenza (p = 0.011), and hemoptysis (p = 0.024) were the factors associated with death. Antibiotic therapies inhibiting toxin production were associated with an improved outcome in these cases (p = 0.007).

CONCLUSIONS

Physicians should pay special attention to those patients who acquired severe CAP during influenza season and have flu-like symptoms, hemoptysis, and leucopenia, and they should consider S. aureus more frequently among the possible pathogens of severe CAP. Empiric therapy for severe CAP with this distinct clinical picture should include coverage for S. aureus. Targeted treatment with antimicrobials inhibiting toxin production appears to be a more appropriate selection.

Community-acquired methicillin-resistant Staphylococcus aureus: community transmission, pathogenesis, and drug resistance

Methicillin-resistant Staphylococcus aureus (MRSA) is able to persist not only in hospitals (with a high level of antimicrobial agent use) but also in the community (with a low level of antimicrobial agent use). The former is called hospital-acquired MRSA (HA-MRSA) and the latter community-acquired MRSA (CA-MRSA). It is believed MRSA clones are generated from S. aureus through insertion of the staphylococcal cassette chromosome mec (SCCmec), and outbreaks occur as they spread. Several worldwide and regional clones have been identified, and their epidemiological, clinical, and genetic characteristics have been described. CA-MRSA is likely able to survive in the community because of suitable SCCmec types (type IV or V), a clone-specific colonization/infection nature, toxin profiles (including Pantone-Valentine leucocidin, PVL), and narrow drug resistance patterns. CA-MRSA infections are generally seen in healthy children or young athletes, with unexpected cases of diseases, and also in elderly inpatients, occasionally surprising clinicians used to HA-MRSA infections. CA-MRSA spreads within families and close-contact groups or even through public transport, demonstrating transmission cores. Re-infection (including multifocal infection) frequently occurs, if the cores are not sought out and properly eradicated. Recently, attention has been given to CA-MRSA (USA300), which originated in the US, and is growing as HA-MRSA and also as a worldwide clone. CA-MRSA infection in influenza season has increasingly been noted as well. MRSA is also found in farm and companion animals, and has occasionally transferred to humans. As such, the epidemiological, clinical, and genetic behavior of CA-MRSA, a growing threat, is focused on in this study.

Fatal cases of Staphylococcus aureus pleural empyema in infants

Community-associated infections and especially pleural empyema due to Staphylococcus aureus are increasing worldwide. The virulence of staphylococcal strains is notably determined by different toxin expressing-genes, such as the Panton-Valentine leukocidin (PVL) gene found in S. aureus isolates obtained from pediatric necrotizing pneumonia samples. We describe 2 similar cases of infants with severe respiratory distress and death after an upper respiratory tract infection, having occurred in the same urban area during the same winter time. Necropsies performed between November 2006 and March 2007 revealed bronchopneumonia and an important pleural empyema, justifying the review of clinical charts and laboratory exams. A methicillin-sensitive S. aureus (MSSA) isolate carrying the PVL gene was identified in both cases. We have subsequently cared for an additional case in the same time interval with sudden death and similar pathological findings. No positive microbiological results were obtained, a negative finding possibly related to a 5-day antibiotics regimen. This report describes the pathological features of these cases and stresses the need to recognize PVL-positive S. aureus infections in young children. Finally, we believe that all lethal infections due to PVL-positive S. aureus, independently of the methicillin resistance profile, deserve a mandatory report to the provincial public health authorities.

Pleuropulmonary complications of PVL-positive Staphylococcus aureus infection in children

It is increasingly recognized world-wide that Panton-Valentine leukocidin (PVL)-positive Staphylococcus aureus (PVL-SA) is associated with a highly aggressive and often fatal form of community-acquired pneumonia. We report four children who presented with severe pleuropulmonary complications due to infection by community-acquired methicillin-sensitive S. aureus (CA-MSSA), producing PVL toxin. The complications included bilateral multilobular infiltrates, pneumatocoeles, recurrent pneumothoraces, pleural effusion, empyema, lung abscess and diaphragmatic paralysis. This case series highlights the diverse pleuropulmonary manifestations of this potentially lethal infection and the importance of heightened awareness, early recognition and aggressive therapy.

CONCLUSION

Complicated pneumonia in a previously fit young patient with a history of preceding 'flu-like' illness or skin/soft tissue infection should raise the suspicion of infection by PVL-positive Staphylococcus aureus (PVL-SA). Severe pleuropulmonary complications are a feature of this disease.

Panton-Valentine leukocidin-producing Staphylococcus aureus infections: Report of 4 French cases

We report 4 cases of community-acquired infections due to Staphylococcus aureus producing Panton-Valentin leukocidin (SA-PVL) with uncommon multivisceral localizations. These cases highlight the need to screen for PVL in patients with serious staphylococcal infections. All patients were cured. Two of them received intravenous immunoglobulins in addition to antibiotics.

Cross-border dissemination of methicillin-resistant Staphylococcus aureus, Euregio Meuse-Rhin region

MRSA clones were associated with hospital-associated clonal complexes and with Panton-Valentine leukocidin–positive community-associated MRSA.

Because the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) differs among the 3 countries forming the Euregio Meuse-Rhin (EMR) region (Belgium, Germany, and the Netherlands), cross-border healthcare requires information about the spread of MRSA in the EMR. We investigated the emergence, dissemination, and diversity of MRSA clones in the EMR by using several typing methods. MRSA associated with clonal complexes 5, 8, 30, and 45 was disseminated throughout the EMR. Dutch isolates, mainly associated with sequence types (ST) ST5-MRSA-II, ST5-MRSA-IV, ST8-MRSA-IV, and ST45-MSRA-IV had a more diverse genetic background than the isolates from Belgium and Germany, associated with ST45-MRSA-IV and ST5-MRSA-II, respectively. MRSA associated with pigs (ST398-MRSA-IV/V) was found in the Dutch area of the EMR. Five percent of the MRSA isolates harbored Panton-Valentine leukocidin and were classified as community-associated MRSA associated with ST1, 8, 30, 80, and 89.

Comparison of Austrian, Hungarian and Macedonian methicillin-resistant and methicillin-sensitive Staphylococcus aureus strains in relation to prevalence of cytotoxin genes

Cytotoxin genes in 128 Austrian (AT) MSSA, 48 MRSA, 94 Hungarian (HU) MSSA, 110 MRSA and 67 Macedonian (MK) MSSA, 81 MRSA strains were examined. The presence of alfa-haemolysin gene (hla) was more common in HU MSSA strains compared to AT and MK (99%, 86%, 72%: p<0.001). AT and MK MRSA harboured hlb genes more frequently compared to HU (60%, 62%, 33%: p<0.001). HU and MK MRSA strains carried gamma-haemolysin gene (hlg) in higher percentage in contrast to AT (88%, 83%, 69%: p=0.01). Haemolysin gamma-variant gene (hlgv) was more prevalent in HU MSSA compared to AT and MK (84%, 56%, 69%: p<0.001). Panton-Valentine leukocidin genes were found only in AT, HU, MK MSSA and MK MRSA in 2.3%, 4%, 1.5% (p=0.53) and 1% (p=0.38), respectively. The 3-gene combination pattern comprising of hla, hlg and hld genes showed increased prevalence among AT MSSA compared to HU (27%, 11%: p<0.001). The 4-gene pattern composed of hla, hlg, hlgv and hld genes was significantly characteristic for HU MRSA in contrast to AT and MK MRSA (56%, 12.5%, 27%: p<0.001). Frequency of certain cytotoxin genes and combinations differed significantly in Staphylococcus aureus strains according to geographical origin and methicillin-resistance.

The signal peptide of Staphylococcus aureus panton valentine leukocidin LukS component mediates increased adhesion to heparan sulfates

Staphylococcus aureus necrotizing pneumonia is a severe disease caused by S. aureus strains carrying the Panton Valentine leukocidin (PVL) genes (lukS-PV & lukF-PV) encoded on various bacteriophages (such as phiSLT). Clinical PVL+ strains isolated from necrotizing pneumonia display an increased attachment to matrix molecules (type I and IV collagens and laminin), a phenotype that could play a role in bacterial adhesion to damaged airway epithelium during the early stages of necrotizing pneumonia (J Infect Dis 2004; 190: 1506–15). To investigate the basis of the observed adhesion of S. aureus PVL+ strains, we compared the ability of PVL+ and their isogenic PVL− strains to attach to various immobilized matrix molecules. The expression of recombinant fragments of the PVL subunits and the addition of synthetic peptides indicated that the processed LukS-PV signal peptide (LukS-PV SP) was sufficient to significantly enhance the ability of S. aureus to attach to extracellular matrix (ECM) components. Furthermore, we showed that adhesion to ECM components was inhibited by heparin and heparan sulfates (HS) suggesting that in vivo, HS could function as a molecular bridge between the matrix and S. aureus expressing the LukS-PV signal peptide. Site directed mutagenesis, biochemical and structural analyses of the LukS-PV signal peptide indicate that this peptide is present at the S. aureus surface, binds to HS in solid phase assay, and mediates the enhanced S. aureus matrix component adhesion. Our data suggests that after its cleavage by signal peptidase, the signal peptide is released from the membrane and associates to the cell wall through its unique C-terminus sequence, while its highly positively charged N-terminus is exposed on the bacterial surface, allowing its interaction with extracellular matrix-associated HS. This mechanism may provide a molecular bridge that enhances the attachment of the S. aureus PVL+ strains to ECM components exposed at damaged epithelial sites.