Purpura Fulminans Due toStaphylococcus aureus

Lung and pharyngeal abscess caused by enterotoxin G- and I-producing Staphylococcus aureus

We report a particularly serious case of extensive meticillin sensitive Staphylococcal lung and pharyngeal abscess. Our patient had no significant risk factors for severe infection. The detection of enterotoxin G and I here suggest that when present together, these toxins work synergistically to produce a more virulent strain of Staphylococcus aureus.

Treatment of MRSA soft tissue infections: an overview

MRSA is becoming increasingly common worldwide. With the emergence of new highly spreadable strains (community associated or CA-MRSA) novel presentation skin and soft tissue infections (SSTI) are being seen. Recurrent SSTI, including folliculitis, furunculosis and abscesses account for an increasing proportion of SSTI seen in the emergency department. Empirical antimicrobial management choices can be difficult, but clues to the nature of the MRSA may be gleaned from the history and clinical presentation. More severe SSTI due to necrotising fasciitis and purpura fulminans are emerging and warrant the broadest possible empirical Gram-positive cover, ideally with antimicrobials that stop exotoxin production, and sometimes intravenous immunoglobulin to neutralise exotoxins already produced.

Concentration-dependent effects of antimicrobials on Staphylococcus aureus toxin-mediated cytokine production from peripheral blood mononuclear cells

BACKGROUND

Toxins contribute to the pathogenicity of Staphylococcus aureus infections by inducing a dysregulated inflammatory response. This study evaluated the impact of anti-staphylococcal antibiotic exposures over an increasing concentration range on cytokine production from peripheral blood mononuclear cells (PBMCs) after S. aureus toxin exposures.

METHODS

Human PBMCs were suspended in complete Roswell Park Memorial Institute (RPMI) 1640 medium with 10% fetal bovine serum at 10(6) cells/mL with 100 ng/mL S. aureus toxic shock syndrome toxin-1 (TSST-1), staphylococcal enterotoxin A (SEA), α-toxin or Panton-Valentine leucocidin (PVL). Vancomycin, trimethoprim/sulfamethoxazole, tigecycline, daptomycin, linezolid, clindamycin and azithromycin were added at a concentration range of 0.5-100 mg/L. Cytokine [interleukin-1β (IL-1β), IL-6, IL-8, interferon-γ (IFN-γ) and tumour necrosis factor-α (TNF-α)] concentrations were measured in duplicate by ELISA following exposure and were compared with response with toxin alone.

RESULTS

At concentrations approximating serum C(max), tigecycline decreased IL-6 by 52%-57% and IFN-γ production by 43%-53% compared with toxin alone (P ≤ 0.05) and linezolid inhibited TNF-α by 12%-35% and IL-8 by 25%-42% (P ≤ 0.02). However, trimethoprim/sulfamethoxazole increased TNF-α and IL-8 production (P = 0.002). Clindamycin, daptomycin, vancomycin and azithromycin had no consistent significant effect at approximate serum C(max) concentrations. All antibiotics had a concentration-dependent effect on cytokine production, with tigecycline, clindamycin and trimethoprim/sulfamethoxazole being the most potent inhibitors of cytokine production at concentrations exceeding 25 mg/L.

CONCLUSIONS

S. aureus toxins stimulate production of inflammatory cytokines in PBMCs. Antimicrobials with high tissue penetration, including tigecycline, clindamycin, trimethoprim/sulfamethoxazole and linezolid, reduced cytokine production, which, along with their antimicrobial effects, may have importance in the therapeutic outcome of severe infections.

Heavy chain-only antibodies and tetravalent bispecific antibody neutralizing Staphylococcus aureus leukotoxins

Panton-Valentine leukocidin (PVL) is a pore-forming toxin associated with current outbreaks of community-associated methicillin-resistant strains and implicated directly in the pathophysiology of Staphylococcus aureus-related diseases. Humanized heavy chain-only antibodies (HCAb) were generated against S. aureus PVL from immunized transgenic mice to neutralize toxin activity. The active form of PVL consists of the two components, LukS-PV and LukF-PV, which induce osmotic lysis following pore formation in host defense cells. One anti-LukS-PV HCAb, three anti-LukF-PV HCAbs with affinities in the nanomolar range, and one engineered tetravalent bispecific HCAb were tested in vitro and in vivo, and all prevented toxin binding and pore formation. Anti-LukS-PV HCAb also binds to γ-hemolysin C (HlgC) and inhibits HlgC/HlgB pore formation. Experiments in vivo in a toxin-induced rabbit endophthalmitis model showed that these HCAbs inhibit inflammatory reactions and tissue destruction, with the tetravalent bispecific HCAb performing best. Our findings show the therapeutic potential of HCAbs, and in particular, bispecific antibodies.

Cutaneous community-acquired and hospital-acquired methicillin-resistant Staphylococcus aureus

The clinical presentation of methicillin-resistant Staphylococcus aureus (MRSA) infection ranges from asymptomatic colonization to cutaneous and invasive involvement. This review discusses the cutaneous presentations of community-acquired MRSA (CA-MRSA) and hospital-acquired MRSA (HA-MRSA) that one may encounter in the hospital or outpatient setting. Cutaneous CA-MRSA and HA-MRSA are often clinically indistinguishable, although they have different epidemiologic profiles and virulence factors. Bacterial culture is necessary for diagnosis and guides treatment, as infection with CA-MRSA and HA-MRSA require distinct clinical management. Guidelines for surgical interventions and antibiotic treatment of CA-MRSA and HA-MRSA will be discussed. Strategies for MRSA decolonization and prevention of further spread will also be reviewed.

An approach to the patient with retiform purpura

Retiform purpura consists of branching purpuric lesions caused by a complete blockage of blood flow in the dermal and subcutaneous vasculature. The differential diagnosis for retiform purpura is broad, including vasculitides of the small and medium vessels as well as microvascular occlusion due to thrombotic, infectious, and embolic phenomena. Determining the etiology of this important dermatologic sign can be a diagnostic challenge; however, an organized approach can improve the speed and accuracy of diagnosis and identify an effective treatment. This review focuses on early recognition, evaluation, and treatment of hospitalized patients with retiform purpura. Specifically, vasculitis, protein C and S deficiencies, heparin necrosis, warfarin necrosis, antiphospholipid antibody syndrome, disseminated intravascular coagulation, cryoglobulinemia, calciphylaxis, and cholesterol embolization syndrome will be discussed in detail. These conditions are commonly seen in consultative dermatology and can have multiorgan involvement, complicated laboratory evaluation, and long-term therapeutic implications.

Pragmatic management of Panton-Valentine leukocidin-associated staphylococcal diseases

Panton-Valentine leukocidin (PVL)-producing Staphylococcus aureus is associated with a broad spectrum of diseases, ranging from common uncomplicated soft tissue infections to severe diseases such as complicated soft tissue infections, extensive bone and joint infections, and necrotising pneumonia. Specialised management of infection based on the presence of PVL may not be required for mild infections, whereas it could be lifesaving in other settings. Moreover, most severe PVL diseases are recently identified entities and a 'gold standard' treatment from comparatives studies of different therapeutic options is lacking. Thus, recommendations are based on expert opinions, which are elaborated based on theory, in vitro data and analogies with other toxin-mediated diseases. In this review, we consider the potential need for specialised PVL-based management and, if required, which tools should be used to achieve optimal management.

Surgical management of acute infectious purpura fulminans

Purpura fulminans is a syndrome characterized by hemorrhagic infarction of the skin and underlying soft tissue as a result of disseminated intravascular coagulation and intravascular thrombosis. In this study, the authors report their experience with surgical intervention for acute infectious purpura fulminans (AIPF). A retrospective chart review was performed including all patients diagnosed with AIPF from January 1, 2006, to December 31, 2008, and treated at an academic medical center. Primary endpoints of interest were overall survival rate and the need for and level of eventual amputation. Improvement in limb perfusion was included as a secondary endpoint. Nine patients were diagnosed with AIPF at the authors' institution during a 3-year period, and seven of these diagnoses were made within 12 months. Overall mortality was 44% (5/9). Amputation was required in 80% of survivors (4/5). All patients explored within 24 hours of diagnosis had evidence for compartment syndrome with visible bulging muscle on fascial release. AIPF is a devastating disease with significant mortality and morbidity primarily related to the loss of multiple limbs. This study suggests that early diagnosis and surgical intervention in the form of compartment release and sympathectomy should be performed concurrently with the initial treatment of sepsis to minimize amputations in surviving patients.

Purpura fulminans caused by community-associated methicillin-resistant Staphylococcus aureus

Sepsis-induced purpura fulminans is a rare but life-threatening condition characterized by rapidly progressive hemorrhagic infarction of the skin due to dermal vascular thrombosis resulting in tissue loss and severe scarring. Although most commonly related to meningococcal or invasive group A streptococcal disease, it may also be caused by several other bacterial or viral pathogens including Pneumococcus and Varicella. Purpura fulminans associated with Staphylococcus aureus sepsis is rare but has been reported in adults. However, the syndrome is very unusual in children, and to our knowledge, only 2 cases of staphylococcal purpura fulminans have been reported in children, both due to methicillin-susceptible S aureus in the United Kingdom. We report the first well-described case of purpura fulminans due to community-associated methicillin-resistant S aureus in a child.

Gram-positive bacterial superantigen outside-in signaling causes toxic shock syndrome

Staphylococcus aureus and Streptococcus pyogenes (group A streptococci) are Gram-positive pathogens capable of producing a variety of bacterial exotoxins known as superantigens. Superantigens interact with antigen-presenting cells (APCs) and T cells to induce T cell proliferation and massive cytokine production, which leads to fever, rash, capillary leak and subsequent hypotension, the major symptoms of toxic shock syndrome. Both S. aureus and group A streptococci colonize mucosal surfaces, including the anterior nares and vagina for S. aureus, and the oropharynx and less commonly the vagina for group A streptococci. However, due to their abilities to secrete a variety of virulence factors, the organisms can also cause illnesses from the mucosa. This review provides an updated discussion of the biochemical and structural features of one group of secreted virulence factors, the staphylococcal and group A streptococcal superantigens, and their abilities to cause toxic shock syndrome from a mucosal surface. The main focus of this review, however, is the abilities of superantigens to induce cytokines and chemokines from epithelial cells, which has been linked to a dodecapeptide region that is relatively conserved among all superantigens and is distinct from the binding sites required for interactions with APCs and T cells. This phenomenon, termed outside-in signaling, acts to recruit adaptive immune cells to the submucosa, where the superantigens can then interact with those cells to initiate the final cytokine cascades that lead to toxic shock syndrome.

Clinical practice guidelines by the infectious diseases society of america for the treatment of methicillin-resistant Staphylococcus aureus infections in adults and children: executive summary

Evidence-based guidelines for the management of patients with methicillin-resistant Staphylococcus aureus (MRSA) infections were prepared by an Expert Panel of the Infectious Diseases Society of America (IDSA). The guidelines are intended for use by health care providers who care for adult and pediatric patients with MRSA infections. The guidelines discuss the management of a variety of clinical syndromes associated with MRSA disease, including skin and soft tissue infections (SSTI), bacteremia and endocarditis, pneumonia, bone and joint infections, and central nervous system (CNS) infections. Recommendations are provided regarding vancomycin dosing and monitoring, management of infections due to MRSA strains with reduced susceptibility to vancomycin, and vancomycin treatment failures.

Methicillin-resistant Staphylococcus aureus: a community health threat

Methicillin-resistant Staphylococcus aureus (MRSA), one of the most common causes of infections, has been traditionally recognized as a nosocomial pathogen. However, in recent years, its epidemiology has radically changed, being now observed even more frequently in the community, and accounting for > 50% of staphylococcal infections in the US outpatient setting. Community-acquired (CA)-MRSA strains typically cause infections among otherwise healthy individuals, with risk factors differing from those of nosocomial MRSA. The clinical manifestations may range from a furuncle to life-threatening infections, such as necrotizing fasciitis and pneumonia. The antibiotic treatment of these infections may also differ because CA-MRSA strains often retain susceptibility to antimicrobials other than glycopeptides and newer agents. Moreover, the production of toxins, such as the Panton-Valentine leukocidin (PVL), should influence the antibiotic choice because in these cases the use of a combination therapy with antimicrobial agents able to decrease toxin production is suggested. There are still many unanswered key questions regarding the epidemiology, prevention, and treatment of CA-MRSA infections. This article reviews current knowledge of CA-MRSA.

Clinical practice guidelines by the infectious diseases society of america for the treatment of methicillin-resistant Staphylococcus aureus infections in adults and children

Evidence-based guidelines for the management of patients with methicillin-resistant Staphylococcus aureus (MRSA) infections were prepared by an Expert Panel of the Infectious Diseases Society of America (IDSA). The guidelines are intended for use by health care providers who care for adult and pediatric patients with MRSA infections. The guidelines discuss the management of a variety of clinical syndromes associated with MRSA disease, including skin and soft tissue infections (SSTI), bacteremia and endocarditis, pneumonia, bone and joint infections, and central nervous system (CNS) infections. Recommendations are provided regarding vancomycin dosing and monitoring, management of infections due to MRSA strains with reduced susceptibility to vancomycin, and vancomycin treatment failures.

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.

Neonatal purpura fulminans secondary to group B streptococcal infection

Purpura fulminans is an acute and frequently fatal disorder characterized by sudden onset of progressive cutaneous hemorrhage and necrosis due to dermal vascular thrombosis and disseminated intravascular coagulation. The authors present a neonate with extensive purpura fulminans due to group B streptoccoccal septicemia and evaluated the attributable clinical mortality and morbidity of this potentially lethal syndrome. Clinicians especially neonatologists should be aware that early-onset sepsis of group B Streptococcus in the newborn infant with purpura fulminans could be a cause of maternal carriage due to colonization of this pathogen microorganism.

Virulence genes and genotypic associations in nasal carriage, community-associated methicillin-susceptible and methicillin-resistant USA400 Staphylococcus aureus isolates

It is not well understood why strains of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA), a major cause of skin and soft tissue infections, became successful so quickly, overtaking the place of methicillin-sensitive S. aureus (MSSA) in many communities. To evaluate the genetic basis of differences in their virulence traits, 293 S. aureus isolates consisting of three cohorts, genotypically defined clinical CA-MRSA (n = 77), clinical MSSA (n = 103), and nasal carriage MSSA (n = 113), collected over a 19-year period in two Midwestern states in the United States, were (i) extensively genotyped and (ii) screened for 40 known virulence genes which included those for enterotoxins, leukocidins, hemolysins, and surface proteins and several newly identified putative toxin genes from the USA400 lineage of CA-MRSA. Genotypically, nasal carriage and clinical MSSA isolates were much more diverse than was the CA-MRSA group, which was found to be of USA400 lineage only. Virulence gene profiles of the three groups showed that CA-MRSA strains harbored significantly higher percentages (≥95%; P value, <0.05) of the sea, sec, sec4, seg2, seh, sek, sel, sel2, ear, ssl1, lpl10, lukSF-PV, lukD, lukE, and clfA genes than did the carriage and the clinical MSSA group (range, 0% to 58%). Genes of the enterotoxin gene cluster, seg, sei, sem, sen, and seo, were present in the clinical and carriage isolates but not in the CA-MRSA group. These results suggest that the presence of additional virulence factors in USA400 CA-MRSA strains compared to the nasal carriage and clinical MSSA strains probably contributed to their enhanced virulence.

Community-associated methicillin-resistant Staphylococcus aureus: epidemiology and clinical consequences of an emerging epidemic

Staphylococcus aureus is an important cause of skin and soft-tissue infections (SSTIs), endovascular infections, pneumonia, septic arthritis, endocarditis, osteomyelitis, foreign-body infections, and sepsis. Methicillin-resistant S. aureus (MRSA) isolates were once confined largely to hospitals, other health care environments, and patients frequenting these facilities. Since the mid-1990s, however, there has been an explosion in the number of MRSA infections reported in populations lacking risk factors for exposure to the health care system. This increase in the incidence of MRSA infection has been associated with the recognition of new MRSA clones known as community-associated MRSA (CA-MRSA). CA-MRSA strains differ from the older, health care-associated MRSA strains; they infect a different group of patients, they cause different clinical syndromes, they differ in antimicrobial susceptibility patterns, they spread rapidly among healthy people in the community, and they frequently cause infections in health care environments as well. This review details what is known about the epidemiology of CA-MRSA strains and the clinical spectrum of infectious syndromes associated with them that ranges from a commensal state to severe, overwhelming infection. It also addresses the therapy of these infections and strategies for their prevention.

Community-associated meticillin-resistant Staphylococcus aureus

Meticillin-resistant Staphylococcus aureus (MRSA) is endemic in hospitals worldwide, and causes substantial morbidity and mortality. Health-care-associated MRSA infections arise in individuals with predisposing risk factors, such as surgery or presence of an indwelling medical device. By contrast, many community-associated MRSA (CA-MRSA) infections arise in otherwise healthy individuals who do not have such risk factors. Additionally, CA-MRSA infections are epidemic in some countries. These features suggest that CA-MRSA strains are more virulent and transmissible than are traditional hospital-associated MRSA strains. The restricted treatment options for CA-MRSA infections compound the effect of enhanced virulence and transmission. Although progress has been made towards understanding emergence of CA-MRSA, virulence, and treatment of infections, our knowledge remains incomplete. Here we review the most up-to-date knowledge and provide a perspective for the future prophylaxis or new treatments for CA-MRSA infections.

Panton-Valentine Leucocidin-related disease in England and Wales

Within the framework of the Health Protection Agency's programme of enhanced surveillance of Staphylococcus aureus with Panton-Valentine Leucocidin (PVL-SA) in England and Wales conducted during 2005-2006, we identified 720 PVL-SA, representing a two-fold increase between 2005 (n = 224) and 2006 (n = 496). The number of PVL-methicillin-resistant S. aureus rose from 119 to 159 in that period. Isolates were referred by 112 centres and included outbreaks of PVL-related disease in community and healthcare settings. One hundred individuals had systemic disease symptoms. Planned systematic surveillance-based studies aim to better address the question of whether these increases reflect an increasing prevalence of PVL-SA and/or improved case ascertainment of PVL-related syndromes.

SaeR binds a consensus sequence within virulence gene promoters to advance USA300 pathogenesis

This investigation examines the role of the SaeR/S 2-component system in USA300, a prominent circulating clone of community-associated methicillin-resistant Staphylococcus aureus. Using a saeR/S isogenic deletion mutant of USA300 (USA300DeltasaeR/S) in murine models of sepsis and soft-tissue infection revealed that this sensory system is critical to pathogenesis of USA300 during both superficial and invasive infection. Oligonucleotide microarray and real-time reverse-transcriptase polymerase chain reaction identified numerous extracellular virulence genes that are down-regulated in USA300DeltasaeR/S. Unexpectedly, an up-regulation of mecA and mecR1 corresponded to increased methicillin resistance in USA300DeltasaeR/S. 5'-RACE analysis defined transcript start sites for sbi, efb, mecA, lukS-PV, hlb, SAUSA300_1975, and hla, to underscore a conserved consensus sequence within promoter regions of genes under strong SaeR/S transcriptional regulation. Electrophoretic mobility shift assay experiments illustrated direct binding of SaeR(His) to promoter regions containing the conserved consensus sequence. Collectively, the findings of this investigation demonstrate that SaeR/S directly interacts with virulence gene promoters to significantly influence USA300 pathogenesis.

Diverse enterotoxin gene profiles among clonal complexes of Staphylococcus aureus isolates from the Bronx, New York

Staphylococcal enterotoxins (SE) can cause toxin-mediated disease, and those that function as superantigens are implicated in the pathogenesis of allergic diseases. The prevalence of 19 enterotoxin genes was determined by PCR in clinical S. aureus strains derived from wounds (108) and blood (99). We performed spa typing and multilocus sequence typing (MLST) to determine clonal origin, and for selected strains staphylococcal enterotoxin B (SEB) production was measured by enzyme-linked immunosorbent assay. Strains carried a median of five SE genes. For most SE genes, the prevalence rates among methicillin-resistant and methicillin-sensitive S. aureus isolates, as well as wound- and blood-derived isolates, did not differ. At least one SE gene was detected in all except two S. aureus isolates (>99%). Complete egc clusters were found in only 11% of S. aureus isolates, whereas the combination of sed, sej, and ser was detected in 24% of clinical strains. S. aureus strains exhibited distinct combinations of SE genes, even if their pulsed-field gel electrophoresis and MLST patterns demonstrated clonality. USA300 strains also showed considerable variability in SE content, although they contained a lower number of SE genes (mean, 3). By contrast, SE content was unchanged in five pairs of serial isolates. SEB production by individual strains varied up to 200-fold, and even up to 15-fold in a pair of serial isolates. In conclusion, our results illustrate the genetic diversity of S. aureus strains with respect to enterotoxin genes and suggest that horizontal transfer of mobile genetic elements encoding virulence genes occurs frequently.

Community-associated meticillin-resistant Staphylococcus aureus infections: epidemiology, recognition and management

Meticillin-resistant Staphylococcus aureus (MRSA) is an important cause of infection, particularly in hospitalized patients and those with significant healthcare exposure. In recent years, epidemic community-associated MRSA (CA-MRSA) infections occurring in patients without healthcare risk factors have become more frequent. The most common manifestation of CA-MRSA infection is skin and soft tissue infection, although necrotizing pneumonia, sepsis and osteoarticular infections can occur. CA-MRSA strains have become endemic in many communities and are genetically distinct from previously identified MRSA strains. CA-MRSA may be more capable colonizers of humans and more virulent than other S. aureus strains. Specific mechanisms of pathogenicity have not been elucidated, but several factors have been proposed as responsible for the virulence of CA-MRSA, including the Panton-Valentine leukocidin, phenol-soluble modulins and type I arginine catabolic mobile element. The movement of CA-MRSA strains into the nosocomial setting limits the utility of using clinical risk factors alone to designate community- or healthcare-associated status. Identification of unique genetic characteristics and genotyping are valuable tools for MRSA epidemiological studies. Although the optimum pharmacological therapy for CA-MRSA infections has not been determined, many CA-MRSA strains remain broadly susceptible to several non-beta-lactam antibacterial agents. Empirical antibacterial therapy should include an MRSA-active agent, particularly in areas where CA-MRSA is endemic.

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.

Reemergence of antibiotic-resistant Staphylococcus aureus in the genomics era

Staphylococcus aureus is the leading cause of bacterial infections in developed countries and produces a wide spectrum of diseases, ranging from minor skin infections to fatal necrotizing pneumonia. Although S. aureus infections were historically treatable with common antibiotics, emergence of drug-resistant organisms is now a major concern. Methicillin-resistant S. aureus (MRSA) was endemic in hospitals by the late 1960s, but it appeared rapidly and unexpectedly in communities in the 1990s and is now prevalent worldwide. This Review focuses on progress made toward understanding the success of community-associated MRSA as a human pathogen, with an emphasis on genome-wide approaches and virulence determinants.

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.

Staphylococcus aureus: a community pathogen

Staphylococcus aureus is a common human pathogen. S aureus infections most commonly clinically manifest as skin infections. There has been much interest in S aureus infections in the community over the past decade because of the rise of community-associated methicillin-resistant S aureus (CA-MRSA) infections, which have emerged globally over a relatively short period of time. In contrast to health care-associated methicillin resistant S aureus (HA-MRSA), circulating strains of CA-MRSA have characteristic pathogenesis, strain characteristics, epidemiology, and clinical manifestations that are distinct from HA-MRSA. In fact, CA-MRSA probably behaves more like community-associated methicillin-sensitive S aureus (MSSA). This article reviews current knowledge of the epidemiology and clinical manifestations of community-associated S aureus and CA-MRSA infections.

Cytolysins augment superantigen penetration of stratified mucosa

Staphylococcus aureus and Streptococcus pyogenes colonize mucosal surfaces of the human body to cause disease. A group of virulence factors known as superantigens are produced by both of these organisms that allows them to cause serious diseases from the vaginal (staphylococci) or oral mucosa (streptococci) of the body. Superantigens interact with T cells and APCs to cause massive cytokine release to mediate the symptoms collectively known as toxic shock syndrome. In this study we demonstrate that another group of virulence factors, cytolysins, aid in the penetration of superantigens across vaginal mucosa as a representative nonkeratinized stratified squamous epithelial surface. The staphylococcal cytolysin alpha-toxin and the streptococcal cytolysin streptolysin O enhanced penetration of toxic shock syndrome toxin-1 and streptococcal pyrogenic exotoxin A, respectively, across porcine vaginal mucosa in an ex vivo model of superantigen penetration. Upon histological examination, both cytolysins caused damage to the uppermost layers of the vaginal tissue. In vitro evidence using immortalized human vaginal epithelial cells demonstrated that although both superantigens were proinflammatory, only the staphylococcal cytolysin alpha-toxin induced a strong immune response from the cells. Streptolysin O damaged and killed the cells quickly, allowing only a small release of IL-1beta. Two separate models of superantigen penetration are proposed: staphylococcal alpha-toxin induces a strong proinflammatory response from epithelial cells to disrupt the mucosa enough to allow for enhanced penetration of toxic shock syndrome toxin-1, whereas streptolysin O directly damages the mucosa to allow for penetration of streptococcal pyrogenic exotoxin A and possibly viable streptococci.

Suppression of acute lung inflammation by intracellular peptide delivery of a nuclear import inhibitor

Acute lung inflammation is a potentially life-threatening complication of infections due to community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA), a worldwide emerging pathogen, which causes necrotizing pneumonia and acute respiratory distress syndrome (ARDS). MRSA virulence factors encompass immunotoxins termed superantigens that contribute to lung inflammation. In this study, we demonstrate that staphylococcal enterotoxin B (SEB)-induced lung inflammation is attenuated by a cell-penetrating peptide nuclear import inhibitor of nuclear factor (NF)-kappaB and other stress-responsive transcription factors (SRTFs). This inhibitor suppressed production of a wide spectrum of cytokines and chemokines induced by direct SEB airway exposure. Consequently, trafficking of neutrophils, monocytes/macrophages, and lymphocytes to the bronchoalveolar space was significantly reduced while vascular injury, manifested by increased permeability and protein leakage, was attenuated. Moreover, induction of systemic proinflammatory cytokines and chemokines in response to direct SEB airway exposure was reduced. Thus, intracellular delivery of a nuclear import inhibitory peptide suppresses respiratory and systemic expression of key mediators of lung inflammation evoked by SEB.

Spectrum of purpura fulminans

Purpura Fulminans is a severe disorder of acute onset with high morbidity and mortality. It is characterized by DIC with thrombocytopenia, hyofibrinogenemia, hypothrombinemia and anemia. It most often occurs in young with sudden appearance of symmetrical, tender, ecchymotic skin lesions usually involving the lower extremities. An infectious and noninfectious etiology has been proposed. Early recognition and early therapy with appropriate antibiotics and heparin is known to limit both morbidity and mortality. This article reports 5 cases of Purpura Fulminans treated at our centre with review of etiology, pathogenesis, clinical features and treatment.

Aetiology, diagnosis and management of infective causes of severe haemoptysis in intensive care units

PURPOSE OF THE REVIEW

Infective causes of severe haemoptysis have progressively shifted to causes related to chronic inflammatory lung diseases. Physicians should, however, recognize the most common of them, for example necrotizing parenchymal infections, tuberculosis and mycetoma.

RECENT FINDINGS

The recent increase in the incidence of a devastating Panton-Valentine leukocidin-associated staphylococcal pneumonia has reminded us of the crucial role of prompt diagnosis and management. General supportive care should be administered to prevent asphyxiation in addition to starting appropriate antibiotics as soon as possible. Once the bleeding has been controlled, the diagnostic strategy should integrate a detailed medical history, physical examination, Gram stain of the respiratory specimens and chest radiograph. Computed tomography scan has dramatically improved the diagnosis and the treatment of infective causes of severe haemoptysis by assessing the cause and mechanism(s) of haemoptysis. Although bronchial arteries are the major source of bleeding, nonbronchial systemic and pulmonary arteries' involvement should be feared, especially in haemoptysis related to tuberculosis and mycetoma.

SUMMARY

Endovascular therapy should be first attempted to control the bleeding and then elective surgery performed in case of localized lesion and adequate pulmonary function. Fibreoptic bronchoscopy with broncho-alveolar lavage remains the cornerstone of diagnosis in immunocompromised hosts with haemoptysis and in the rare cases of alveolar haemorrhage related to infectious diseases.

Skin and soft-tissue infections caused by community-acquired methicillin-resistant Staphylococcus aureus

Community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infection has become epidemic. Skin and soft-tissue infections (SSTIs) are the most frequent forms of the disease. Obtainment of culture specimens is important for documentation of the presence of MRSA and for susceptibility testing to guide therapy. Purulent lesions should be drained whenever possible. In areas where community-acquired MRSA isolates are prevalent, uncomplicated SSTI in healthy individuals may be treated empirically with clindamycin, trimethoprim-sulfamethoxazole, or long-acting tetracyclines, although specific data supporting the efficacy of these treatments are lacking. In healthy patients with small purulent lesions, drainage alone may be sufficient. In patients with complicated SSTI requiring hospitalization or intravenous therapy, vancomycin is the drug of choice because of the low cost, efficacy, and safety. Linezolid, daptomycin, and tigecycline are also effective, although published studies on the last 2 agents for the treatment of SSTI due to MRSA are more limited. Dalbavancin, telavancin, and ceftobiprole are investigational agents that may expand our therapeutic options for the treatment of SSTI caused by MRSA.

Pathogenesis of methicillin-resistant Staphylococcus aureus infection

Staphylococcus aureus is a versatile pathogen capable of causing a wide range of human diseases. However, the role of different virulence factors in the development of staphylococcal infections remains incompletely understood. Some clonal types are well equipped to cause disease across the globe, whereas others are facile at causing disease among community members. In this review, general aspects of staphylococcal pathogenesis are addressed, with emphasis on methicillin-resistant strains. Although methicillin-resistant S. aureus (MRSA) strains are not necessarily more virulent than methicillin-sensitive S. aureus strains, some MRSA strains contain factors or genetic backgrounds that may enhance their virulence or may enable them to cause particular clinical syndromes. We examine these pathogenic factors.

Necrotizing haemorrhagic pneumonia proves fatal in an immunocompetent child due to Panton-Valentine Leucocidin, toxic shock syndrome toxins 1 and 2 and enterotoxin C-producing Staphylococcus aureus

Panton-Valentine leucocidin (PVL) toxin-producing strains of Staphylococcus aureus (S. aureus) are associated with skin abscesses and furunculosis, with necrotizing pneumonia being a relatively rare problem. Here, we describe a fatal case of necrotizing pneumonia in a 14-year-old child who presented initially with sore throat and pyrexia. He deteriorated rapidly, developing hypotension, multiple organ failure and purpura fulminans. S. aureus was isolated from the tracheal aspirate, which was found to be positive for PVL, toxic shock syndrome toxins (TSST) 1 and 2 and staphylococcal enterotoxin C (SEC). It was postulated that purpura fulminans and toxic shock syndrome were a result of the abovementioned exotoxins.

CONCLUSION

This case highlights the emergence of PVL-positive community-acquired S. aureus infection and association of purpura fulminans with superantigens. Practitioners should be aware of this illness in order to initiate appropriate treatment.

Necrotising Pneumonia, Staphylococcus Aureus and Panton-Valentine Leukocidin

The Panton-Valentin leukocidin (PVL) strain of meticillin-resistant Staphylococcus aureus (MRSA) is producing a new pattern of MRSA-related disease in the UK and world-wide. PVL is one of several extracellular cytotoxins produced by Staphylococcus aureus, and is usually associated with skin and soft tissue infections. PVL MRSA is uncommon in hospitals, but in the US, and now in the UK, there have been reports of severe, rapidly progressive, community-acquired haemorrhagic, necrotising pneumonia occurring in previously healthy young adults, and associated with a mortality rate of up to 75%. We review features of the pathophysiology, diagnosis and treatment of this condition, whose incidence appears to be increasing in the UK.

Superantigen profile of Staphylococcus aureus isolates from patients with steroid-resistant atopic dermatitis

BACKGROUND

Superantigens induce skin inflammatory responses in atopic dermatitis, which is commonly associated with Staphylococcus aureus infection. T cells activated in vitro by superantigens become steroid resistant. The objective was to assess the superantigen profiles of S. aureus isolates from patients with steroid-resistant atopic dermatitis.

METHODS

We compared the superantigen-production capability of S. aureus isolates from 78 patients with steroid-resistant atopic dermatitis (group 1) with that of 30 vaginal isolates from healthy women (group 2) and 22 isolates from a general population of patients with atopic dermatitis (group 3). Polymerase chain reaction with primers for superantigens, combined with selected antibody testing, was used to analyze the presence of toxic shock syndrome toxin 1, staphylococcal enterotoxins, and enterotoxin-like superantigens.

RESULTS

S. aureus isolates from group 1 had a statistically significant difference in superantigen profile, compared with the profiles of group 2 and group 3 isolates. Group 2 isolates were similar in profile to group 3 isolates, with 4 and 5 superantigens per isolate, respectively. In contrast, group 1 isolates produced a mean of 8 superantigens each (P<<.001, for comparison with group 2 or group 3). These group 1 isolates were more likely to produce the 3 major toxic shock syndrome-associated superantigens (toxic shock syndrome toxin 1, staphylococcal enterotoxin B, and staphylococcal enterotoxin C) and to produce unusual combinations of superantigens (e.g., toxic shock syndrome toxin 1 and staphylococcal enterotoxin B).

CONCLUSIONS

S. aureus isolates from patients with steroid-resistant atopic dermatitis appear to be selected on the basis of greater production of superantigens, compared with that of isolates from control groups. Superantigens may offer selective advantages for colonization of patients.

Increased surface toll-like receptor 2 expression in superantigen shock

OBJECTIVE

Examination of the interaction between gram-positive bacterial superantigens and toll-like receptor 2 (TLR2) in health and critical illness.

DESIGN

Laboratory ex vivo model and prospective clinical, cohort study.

SETTING

Two research laboratories in university hospitals and two intensive care units.

SUBJECTS/PATIENTS

Laboratory study was performed in transfected HeLa cells and primary human monocytes from healthy volunteers. Clinical study used cells from 20 healthy controls and 45 critically ill patients with circulatory shock.

INTERVENTIONS

HeLa cells and purified monocytes were exposed to purified superantigens or isogenic bacterial supernatants and readout obtained by cytokine enzyme-linked immunosorbent assay, flow cytometry, and quantitative real-time polymerase chain reaction. Peripheral blood mononuclear cells from patients with circulatory shock were compared with controls using flow cytometry and measurement of cytokines after ligand exposure.

MEASUREMENTS AND MAIN RESULTS

Superantigens were unable to signal through ligation by TLR2. However, TLR2 was up-regulated on the surface of primary human monocytes, without detectable TLR2 messenger RNA neosynthesis, by a range of superantigens and superantigen-containing Streptococcus pyogenes supernatants, although not by isogenic superantigen-negative strains. Superantigen mutant constructs with disrupted major histocompatibility complex class II-binding sites did not support TLR2 up-regulation. TLR2 up-regulation was associated with an increase in the proinflammatory response to TLR2 ligands only at high ligand concentrations. TLR2 was up-regulated in a small subset of patients with severe S. pyogenes sepsis but not in patients with any other category of septic or circulatory shock; responses to TLR2 ligands were reduced in all categories of critically ill patient, however.

CONCLUSIONS

Superantigens up-regulate monocyte surface TLR2 expression through major histocompatibility complex class II signaling. Enhanced surface TLR2 expression may be a specific feature of patients with S. pyogenes-induced shock. Importantly, intensity of TLR2 signaling is not necessarily coupled to TLR2 expression when ligand concentrations are low or after onset of critical illness.

Occult methicillin-resistant Staphylococcus aureus abscesses in 2 pediatric patients

Methicillin-resistant Staphylococcus aureus (MRSA) infections have become more common over the last decade. Recently, severe MRSA infections including necrotizing pneumonia, purpura fulminans, and rapidly progressive skin abscesses have been reported. These severe infections frequently have been associated with the virulence factor Panton-Valentine leukocidin (PVL). Two unusual cases of occult deep tissue abscesses in children who had family members with a history of severe MRSA skin abscesses are presented in this article. Both children initially presented with fever without a focus. Deep tissue MRSA (PVL positive) abscesses evolved. Empiric antibiotic therapy for MRSA should be considered for infants and children who are hospitalized with occult fever and who have a family member with a history of MRSA infection.

Molecular analysis of staphylococcal superantigens

Staphylococcal superantigens (SAgs) comprise a large family of exotoxins produced by Staphylococcus aureus strains. These exotoxins are important in a variety of serious human diseases, including menstrual and nonmenstrual toxic shock syndrome (TSS), staphylococcal pneumonias, and a recently described staphylococcal purpura fulminans. In addition, these SAg exotoxins are being increasingly recognized for their possible roles in many other human diseases, such as atopic dermatitis, Kawasaki syndrome, nasal polyposis, and certain autoimmune disorders. To clarify the full spectrum of human diseases caused by staphylococcal SAgs, it is necessary to have assays for them. At present there are 17 well-characterized, serologically distinct SAgs made by S. aureus: TSS toxin-1; staphylococcal enterotoxins (SEs) A, B, C (multiple minor variant forms exist), D, E, and I; and SE-like G, H, J, K, L, M, N, O, P, and Q. In addition, SE-like proteins R, S, T, and U have been identified but remain poorly characterized. The most straightforward way to analyze S. aureus strains for the well-characterized SAgs is through polymerase chain reaction for their genes; we provide here our method for this analysis. Although it would be ideal to confirm that all of the same SAgs are produced by S. aureus strains that have the genes, antibody reagents for SAg detection are only available for TSS toxin-1; SEs A-E; and enterotoxin-like proteins G, H, and Q. We provide a Western immunoblot procedure that allows in vitro quantification of these SAgs.

HLA class II transgenic mice mimic human inflammatory diseases

Population studies have shown that among all the genetic factors linked with autoimmune disease development, MHC class II genes on chromosome 6 accounts for majority of familial clustering in the common autoimmune diseases. Despite the highly polymorphic nature of HLA class II genes, majority of autoimmune diseases are linked to a limited set of class II-DR or -DQ alleles. Thus a more detailed study of these HLA-DR and -DQ alleles were needed to understand their role in genetic predisposition and pathogenesis of autoimmune diseases. Although in vitro studies using class-II restricted CD4 T cells and purified class II molecules have helped us in understanding some aspects of HLA class-II association with disease, it is difficult to study the role of class II genes in vivo because of heterogeneity of human population, complexity of MHC, and strong linkage disequilibrium among different class II genes. To overcome this problem, we pioneered the generation of HLA-class II transgenic mice to study role of these molecule in inflammatory disease. These HLA class II transgenic mice were used to develop novel in vivo disease model for common autoimmune diseases such as rheumatoid arthritis, multiple sclerosis, insulin-dependent diabetes mellitus, myasthenia gravis, celiac disease, autoimmune relapsing polychondritis, autoimmune myocarditis, thyroiditis, uveitis, as well as other inflammatory disease such as allergy, tuberculosis and toxic shock syndrome. As the T-cell repertoire in these humanized HLA transgenic mice are shaped by human class II molecules, they show the same HLA restriction as humans, implicate potential triggering mechanism and autoantigens, and identify similar antigenic epitopes seen in human. This review describes the value of these humanized transgenic mice in deciphering role of HLA class II molecules in immunopathogenesis of inflammatory diseases.

A review of community-associated methicillin-resistant Staphylococcus aureus skin and soft tissue infections

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a cause of infection among otherwise healthy children and adults in the community. Skin and soft tissue infections are most common, but invasive manifestations also occur. A limited number of strains that may possess unique virulence or transmissibility factors have accounted for the majority of these infections. These strains emerged in the community but now are being transmitted in both community and healthcare settings. Incision and drainage remains the primary treatment for skin abscesses. Strains of MRSA circulating in the community generally are susceptible to a number of nonbeta-lactam antimicrobial agents, although resistance patterns may vary temporally and geographically. Educating patients on strategies to prevent further transmission is a critical component of case management. More data are needed to determine optimal strategies for management and prevention of MRSA skin infections in the community.