Correlation of histopathologic findings with clinical outcome in necrotizing fasciitis

Emerging infection: streptococcal toxic shock-like syndrome caused by group B Streptococcus (GBS), Streptococcus agalactiae

Streptococcus agalactiae or Group B Streptococcus (GBS) infections are commonly associated with infections in neonates and pregnant women. However, there has been a rising incidence in nonpregnant adults. The risk of GBS infection in nonpregnant adults is increased for patients of advanced age and those with underlying medical conditions such as diabetes mellitus and cancer. We present a 77-year-old female with type-2 diabetes mellitus, hypertension, and bilateral foot ulcers that presented in probable septic shock with necrotic foot ulcers and necrotizing fasciitis and underwent bilateral lower limb amputations. The patient fulfilled the Streptococcal Toxic Shock Syndrome (STSS) criteria as defined by The Working Group on Severe Streptococcal Infections. These criteria were created for group A Streptococcus (Streptococcus pyogenes). Our patient fulfilled the Working Group's criteria, except that the blood culture was positive for group B Streptococcus (Streptococcus agalactiae). Numerous studies demonstrate the importance of early detection and antibiotic treatment for GBS infections in general and early surgical management for necrotizing soft tissue infections (NSTIs) such as necrotizing fasciitis.

Necrotizing fasciitis and fatal septic shock associated with Streptococcus constellatus

Streptococcus constellatus is usually a benign, commensal bacteria but has increased incidence in blood cultures and abscesses. This pathogenic involvement is most prevalent in individuals with underlying medical conditions, such as solid tumors and type 2 diabetes mellitus, as well as in cases of community-acquired infections. We report a 43-year-old male with a right medial thigh ulcer and necrotic scrotal skin. The wound culture from surgical debridement grew Streptococcus constellatus, and histology was consistent with stage III necrotizing fasciitis. Regardless of etiology, the mortality rate of patients with necrotizing fasciitis is greatly decreased with early intervention and thorough surgical debridement.

Necrotising soft-tissue infections

The incidence of necrotising soft-tissue infections has increased during recent decades such that most physicians might see at least one case of these potentially life-threatening infections in their career. Despite advances in care, necrotising soft-tissue infections are still associated with high morbidity and mortality, underlining a need for continued education of the medical community. In particular, failure to suspect necrotising soft-tissue infections, fuelled by poor awareness of the disease, promotes delays to first surgical debridement, amplifying disease severity and adverse outcomes. This Review will focus on practical approaches to management of necrotising soft-tissue infections including prompt recognition, initiation of specific management, exploratory surgery, and aftercare. Increased alertness and awareness for these infections should improve time to diagnosis and early referral to specialised centres, with improvement in the prognosis of necrotising soft-tissue infections.

Necrotizing fasciitis of the face: current concepts in cause, diagnosis and management

PURPOSE OF REVIEW

Necrotizing fasciitis of the face is uncommon but potentially life threatening. With adequate multidisciplinary treatment, mortality and has significantly improved. This article highlights current concepts and supporting literature in the management of facial necrotizing fasciitis.

RECENT FINDINGS

Management of necrotizing fasciitis involving the face requires a multisciplinary team approach, including early medical and surgical intervention. With early haemodynamic support, broad spectrum antibiotics and aggressive surgical debridement, mortality has reduced significantly. Soft-tissue reconstruction can be effectively utilized once the infection has been adequately treated. Although some adjunctive treatment such as vacuum assisted closure dressing has shown to be of benefit, other treatments such as hyperbaric oxygen remains controversial.

SUMMARY

Necrotizing fasciitis is an aggressive soft tissue involving that rapidly spreads along fascial planes. Necrotizing fasciitis involving the face is rare owing to its rich blood supply but is also difficult to manage due to the complex regional anatomy. Common sources are odontogenic, sinugenic, peritonsillar or salivary gland infections and often polymicrobial. The principles of treatment include early and aggressive haemodynamic support, broad spectrum antibiotics and aggressive surgical debridement. Often times repeat debridements following close monitoring is required. Reconstructive options are viable only after the infection has been adequately treated. Although mortality has significantly improved, mediastinal involvement, multiple comorbidities and delayed treatment confers a worse prognosis.

Regional Variations in Microbiology and Outcomes of Necrotizing Soft Tissue Infections: A Systematic Review and Meta-Analysis

Background: Frequency, microbiology, and outcomes of necrotizing soft tissue infections (NSTIs) could vary across the United States because of differences in locoregional and environmental factors. We synthesized the literature from across the regions of the United States on NSTIs in a systematic review/meta-analysis. Methods: PubMed, ProQuest, Scopus, and Web of Science databases were systematically searched and screened. DerSimonian-Laird random-effects meta-analyses were performed using 'meta' package in R to determine pooled prevalences. Meta-regression analyses examined moderator effects of risk factors. Results: Twenty-seven studies (2,242 total patients) were included. Pooled prevalences of polymicrobial and monomicrobial infections were 52.2% and 39.9%, respectively. The prevalence of monomicrobial NSTIs increased over the last two decades (p = 0.018), whereas polymicrobial infections declined (p = 0.003). Meta-regression analysis showed that most polymicrobial NSTIs were Fournier gangrene (p < 0.001), whereas monomicrobial NSTIs mostly affected extremities (p < 0.001). Staphylococcus aureus was the most common organism isolated (predominantly in the South), followed by Bacteroides spp. (predominately in the East) and Streptococcus pyogenes. Methicillin-resistant Staphylococcus aureus (MRSA) accounted for 11.9% of NSTIs, mainly in the South. The overall mortality rate was 17.8% and declined over last two decades (p < 0.001), with the lowest rate reported in the last decade at 13% without any regional differences. Conclusions: Advancement in the management of NSTIs may have contributed to the observed decline in NSTI-related mortality in the United States. However, the proportion of monomicrobial NSTIs seems to be increasing, possibly because of increased comorbidities affecting extremities. Causative organisms varied by region. Multi-center observational studies are warranted to confirm our observations.

Early Diagnosis and Surgical Management of Necrotizing Fasciitis of the Lower Extremities: Risk Factors for Mortality and Amputation

Objective: In this study, we seek to identify patient characteristics associated with limb loss and mortality while exploring the potential impact a multidisciplinary care team may have. Approach: This was a 10-year retrospective review of patients presenting to our tertiary care center for limb salvage with a diagnosis of lower extremity (LE) necrotizing fasciitis (NF). Patient demographics, clinical history, and outcomes were compared between survivors and nonsurvivors and between those who underwent LE amputation and those who did not. The article adheres to the strengthening the reporting of observational studies in epidemiology statement. Results: Sixty-two patients presented to our tertiary care center for limb salvage with LE NF. Forty-two patients underwent LE amputation: 27 (43.5%) underwent below-knee amputation, 1 (1.6%) underwent above-knee amputation, 8 (12.9%) underwent transmetatarsal amputation and 2 (3.2%) underwent calcanectomy. The overall mortality rate was 16.1% (n = 10). Risk factors for mortality included increased age (p = 0.034), higher Charlson Comorbidity Index (p = 0.011), thrombocytopenia (p = 0.002), hypotension (p = 0.015), erythema (p = 0.010), pain (p = 0.027), diabetes mellitus (p = 0.012), and malignancy (p < 0.001). Risk factors for LE amputation included DM (p = 0.017), peripheral vascular disease (p = 0.033), and an elevated laboratory risk indicator for necrotizing fasciitis (LRINC) (p = 0.033). Innovation: To identify outcomes after admission to a tertiary hospital with a dedicated limb salvage team with LE NF and to analyze risk factors for mortality and amputation. Conclusions: This is a comprehensive analysis of risk factors for mortality and amputation after LE NF. Our institution's experience highlights the importance of a multidisciplinary approach in the care of these patients.

Necrotizing fasciitis a review

Necrotizing fasciitis is an uncommon, rapidly progressive, often aggressive bacterial infection that causes extensive necrosis of the subcutaneous tissue and fascia, relatively sparing the muscle and skin tissues. Rapid diagnosis of the disease is mandatory because the delay in initiation of aggressive treatment negatively influences the outcome. Specific clinical signs may not be always present, which makes an accurate and timely diagnosis difficult. Based on the literature, this article presents a review of the historical background, etiology, pathophysiology, clinical findings, diagnostic strategies, treatment and prognosis of the disease.

Murine Soft Tissue Infection Model to Study Group A Streptococcus (GAS) Pathogenesis in Necrotizing Fasciitis

Group A streptococcus (GAS) necrotizing fasciitis (NF) causes high morbidity and mortality despite prompt intravenous administration of antibiotics, surgical soft-tissue debridement, and supportive treatment in the intensive care unit. Since there is no effective vaccine against GAS infections, a comprehensive understanding of NF pathogenesis is required to design more efficient treatments. To increase our understanding of NF pathogenesis, we need a reliable animal model that mirrors, at least in part, the infectious process in humans. This chapter describes a reliable murine model of human NF that mimics the histopathology observed in humans, namely the destruction of soft tissue, a paucity of infiltrating neutrophils, and the presence of many gram-positive cocci at the center of the infection.

A case of necrotizing fasciitis following intra-articular injections - Iatrogenic or spontaneous?

Here, we report a case of necrotizing fasciitis following intra-articular injection of hyaluronic acid. A 73-year-old female received intra-articular injections of hyaluronic acid due to arthralgia at the left shoulder and knee, and was found dead in her living room at one day. At the forensic autopsy, injection marks with bullae and erythema were found at the left shoulder and knee and liquefactive necrosis of muscle tissues was observed in the left but not right extremities. Histopathological examinations of the left upper arm and thigh revealed severe rhabdomyolysis with lots of bacterial clusters. Bacteriological examinations detected group A Streptococcus from intracardiac blood and affected muscle tissues. Postmortem biochemical analysis of blood showed escalated blood urea nitrogen (133.8 mg/dL), creatinine (4.57 mg/dL) and C-reactive protein (45.0 mg/dL). The cause of her death was diagnosed as streptococcal toxic shock syndrome (STSS). Moreover, it was suggested that the injection was inappropriately conducted and served as a portal of bacterial entry.

Necrotising fasciitis: a narrative review of the literature

Necrotising fasciitis is a severe, life-threatening and rapidly progressive soft tissue infection that often requires aggressive surgical management, with an estimated incidence of about 0.24-0.40 per 100 000 in the UK. Necrotising fasciitis can be classified based on its microbiology or the anatomy or body region affected. Initial signs of necrotising fasciitis can be minimal and non-specific but a patient often presents with pain out of proportion to clinical signs on examination, as well as erythema and oedema, in addition to systemic symptoms associated with sepsis. Diagnosis is often based on high clinical suspicion with biochemical and clinical imaging used as adjuncts. To aid with early diagnosis of necrotising fasciitis, a scoring system known as the Laboratory Risk Indicator for necrotising fasciitis was developed which has a positive predictive value of 92%. Once diagnosed, appropriate resuscitation and antibiotics, along with prompt and aggressive surgical debridement, is the mainstay of treatment.

Streptococcal toxic shock syndrome with fatal outcome: Report on four forensic autopsy cases

Streptococcal toxic shock syndrome (STSS) is a severe infection most commonly caused by group A streptococcus. It is clinically characterized by rapidly progressive multiple organ failure and septic shock. This report presents four fatal cases associated with STSS. In two cases (cases 2 and 3), the portals of entry may be ulcer and mucosa at the surgical site; the initial symptoms in these cases included fever. In the other cases, the portal of entry was unknown; the initial symptom was pain. In two cases (cases 1 and 3), malpractice was suspected before autopsy. At autopsy, blood culture was positive for group A streptococcus in all of the present cases. Although C-reactive protein levels were increased, procalcitonin levels were not markedly elevated. This is the first report of autopsy cases associated with STSS in which postmortem computed tomography was performed; the swelling of muscles and increased concentrations of peripheral subcutaneous tissue without gas may be characteristic findings. Histology revealed extensive bacterial colonies and necrosis with mild neutrophilic reaction in two cases (cases 3 and 4), and hemophagocytosis in two cases (cases 1 and 4). It is essential to perform appropriate examinations and make a proper diagnosis because STSS still has a high fatality rate and medical malpractice is often suspected. In addition, it is important to evaluate STSS again for the reduction of the fatal cases associated with STSS.

Necrotizing Soft-Tissue Infections: Clinical Features and Diagnostic Aspects

The term necrotizing soft-tissue infection (NSTI) encompasses a heterogenous group of patients with necrotizing infections, involving any body part. NSTI is diagnosed by surgical exploration, where necrosis of the subcutaneous tissue and/or muscle tissue, undermining of the skin, thrombosis of the superficial veins, and deliquescent tissue can be seen. Patients can present with vague symptoms, and approximately half of patients experience severe pain. The clinical presentation and microbiological etiology vary according to affected body site, with NSTI located to the extremities being dominated by monomicrobial group A streptococcal infections, and NSTI located to the anogenital area dominated by polymicrobial infections. No set of diagnostic criteria exists, and suspicion of the diagnosis should come from careful clinical examination and signs of local or systemic severity. Laboratory blood values show no distinct pattern but resemble those of sepsis. Imaging can aid the diagnostic process but must not delay surgical intervention.

Pathogenic Mechanisms of Streptococcal Necrotizing Soft Tissue Infections

Necrotizing skin and soft tissue infections (NSTIs) are severe life-threatening and rapidly progressing infections. Beta-hemolytic streptococci, particularly S. pyogenes (group A streptococci (GAS)) but also S. dysgalactiae subsp. equisimilis (SDSE, most group G and C streptococcus), are the main causative agents of monomicrobial NSTIs and certain types, such as emm1 and emm3, are over-represented in NSTI cases. An arsenal of bacterial virulence factors contribute to disease pathogenesis, which is a complex and multifactorial process. In this chapter, we summarize data that have provided mechanistic and immuno-pathologic insight into host-pathogens interactions that contribute to tissue pathology in streptococcal NSTIs. The role of streptococcal surface associated and secreted factors contributing to the hyper-inflammatory state and immune evasion, bacterial load in the tissue and persistence strategies, including intracellular survival and biofilm formation, as well as strategies to mimic NSTIs in vitro are discussed.

Different types of bullae of limbs with necrotizing fasciitis predict different outcome: a prospective study

Study objective

Necrotizing fasciitis (NF) is an uncommon life-threatening necrotizing skin and soft tissue infection. Bullae are special skin manifestations of NF. This study was conducted to analyze the differences between different types of bullae of limbs with NF for providing the information to emergency treatment.

Methods

From April 2015 to August 2018, patients were initially enrolled based on surgical confirmation of limbs with NF. According to the presence of different bullae types, patients were divided into no bullae group (Group N), serous-filled bullae group (Group S), and hemorrhagic bullae group (Group H). Data such as demographics, clinical outcomes, microbiological results, presenting symptoms/signs, and laboratory findings were compared among these groups.

Results

In total, 187 patients were collected, with 111 (59.4%) patients in Group N, 35 (18.7%) in Group S, and 41 (21.9%) in Group H. Group H had the highest incidence of amputation, required intensive care unit care, and most patients infected with Vibrio species. In Group N, more patients were infected with Staphylococcus spp. than Group H. In Group S, more patients were infected with β-hemolytic Streptococcus than Group H. Patients with bacteremia, shock, skin necrosis, anemia, and longer prothrombin time constituted higher proportions in Group H and S than in Group N.

Conclusions

In southern Taiwan, patients with NF accompanied by hemorrhagic bullae appear to have more bacteremia, Vibrio infection, septic shock, and risk for amputation. If the physicians at the emergency department can detect for the early signs of NF as soon as possible, and more patient’s life and limbs may be saved.

Surgical Strategies: Necrotizing Fasciitis of the Foot and Ankle Treated With Dermal Regeneration Matrix for Limb Salvage

Although necrotizing fasciitis is a life-threatening entity that needs expeditious treatment, cases involving the lower extremity are less commonly encountered than in the upper extremity. Surgical intervention is often required and likely lead to amputation (below-knee or above-knee) vs debridement in the lower extremity.Coverage options in the foot and ankle after serial debridements can present many challenges for limb salvage. Patients are often left with large soft tissue defects requiring coverage with a subsequent increase in relative morbidity. Treatment options for coverage in these cases include negative-pressure wound therapy, split-thickness skin grafting, free flap coverage, or higher-level amputation. In the diabetic population, who present with a lower extremity necrotizing infection, limb salvage is often a challenge given the multiple comorbidities associated with these patients including peripheral vascular disease, immunocompromised state, and neuropathy. Optimal treatment strategies for these necrotizing infections in the foot and ankle remain uncertain.We offer a technique tip for utilization of a dermal regeneration matrix to allow coverage of large soft tissue defect with exposed tendon and/or bone without the need for free flap coverage or higher-level amputation, thus allowing for an additional limb salvage option.Level of Evidence: Level V, expert opinion.

Penile Necrosis as a Presenting Sign of Purpura Fulminans Mimicking Fournier's Gangrene

ABSTRACT

We report the case of a 63-year-old white man who, 3 days after stent removal of endoscopic drainage of pancreatic cysts, developed a penile necrosis due to purpura fulminans (PF) that has been misdiagnosed as Fournier's gangrene. Penile necrosis was rapidly followed by a lethal multiorgan failure due to disseminated intravascular coagulopathy (DIC), triggered by the subsequent development of a severe acute pancreatitis. PF describes a rare syndrome involving intravascular thrombosis and hemorrhagic infarction of the skin. Although reports of penile necrosis secondary to various causes are documented in the literature, penile necrosis secondary to PF in the setting of acute pancreatitis is a rare event. Histopathologic studies of the skin showing an occlusive nonvasculitic vasculopathy are the first step to achieve an accurate diagnosis.

Necrotizing fasciitis of the upper back presenting with left shoulder pain

Necrotizing fasciitis is a severe and progressive infection of deep soft tissues which results in destruction of the fascia and overlying subcutaneous fat. We report a case of a 45-year-old diabetic gentleman who initially presented with left shoulder pain, which was treated symptomatically. Upon representation, he had fever and the pain extended to his left upper back. There was a warm, firm and mildly tender purplish swelling on his mid to the left upper back. Blood tests revealed significantly elevated white cell counts and C-reactive protein. A CT thorax showed extensive soft tissue gas within the deep and superficial fascial layers of his left upper back. Necrotizing fasciitis was confirmed intraoperatively. The diagnosis of this condition is often difficult as early symptoms can be mild and nonspecific. A high Laboratory Risk Indicator for NECrotizing fasciitis (LRINEC) score may be helpful to rule in this diagnosis and guide further management.

Predictors for gram-negative monomicrobial necrotizing fasciitis in southern Taiwan

BACKGROUND

Necrotizing fasciitis (NF) is a rare and life-threatening necrotizing skin and soft-tissue infection. Infectious pathogens of NF must be detected early and treated rapidly to prevent loss of limb or a fatal outcome. This study aimed to detect more reliable predictors between gram-negative and gram-positive monomicrobial NF of limbs.

METHODS

A total of 100 patients with limb monomicrobial NF were diagnosed prospectively from April 2015 to July 2018. These monomicrobial NF pathogens can be divided into gram-negative and gram-positive groups according to the result of Gram staining and final bacterial reports. Data such as demographics, seawater or seafood contact history, infectious location, comorbidities, presenting signs and symptoms, and laboratory findings were recorded and compared.

RESULTS

A total of 55 patients were infected with gram-negative organisms and 45 patients with gram-positive organisms. Among the 55 cases of monomicrobial gram-negative NF, 48 (87.3%) were caused mainly by Vibrio spp. (38, 69.1%) and Aeromonas spp. (10, 18.2%). A higher incidence of chronic kidney disease, cerebrovascular accident, tachypnea, and septic shock; a higher rate of band forms of leukocytes of more than 3%, serum lactate of more than 20 mg/dL, and C-reactive protein level of less than 150 mg/dL; prolonged prothrombin time; and a lower fibrinogen level were observed in patients with gram-negative infection. In a multivariate analysis, a higher incidence of seawater or seafood contact history (odds ratio [OR]: 66.301; 95% confidence interval [CI]: 7.467-588.702), a higher rate of hyperlactatemia (OR: 7.904; 95% CI: 1.231-50.744), and a low fibrinogen level (OR: 1.013; 95% CI: 1.004-1.023) indicated gram-negative infection.

CONCLUSIONS

In southern Taiwan, NF of limbs mainly affected the lower limbs, exhibited monomicrobial infection, and was predominated by gram-negative bacteria. Gram-negative monomicrobial NF of limbs often occurred in individuals with the more seawater or seafood contact history, hyperlactatemia, and low fibrinogen levels.

The Role of Streptococcal and Staphylococcal Exotoxins and Proteases in Human Necrotizing Soft Tissue Infections

Necrotizing soft tissue infections (NSTIs) are critical clinical conditions characterized by extensive necrosis of any layer of the soft tissue and systemic toxicity. Group A streptococci (GAS) and Staphylococcus aureus are two major pathogens associated with monomicrobial NSTIs. In the tissue environment, both Gram-positive bacteria secrete a variety of molecules, including pore-forming exotoxins, superantigens, and proteases with cytolytic and immunomodulatory functions. The present review summarizes the current knowledge about streptococcal and staphylococcal toxins in NSTIs with a special focus on their contribution to disease progression, tissue pathology, and immune evasion strategies.

Pathogenesis of Hypervirulent Group A Streptococcus

Group A Streptococcus (GAS) causes common pharyngitis and skin infections and occasional severe invasive infections. This review describes the recent progress on the pathogenesis of hypervirulent GAS. CovRS mutations are frequent among invasive GAS isolates and lead to hypervirulence. GAS CovRS mutants can be selected in vivo by neutrophils. The role of protease SpeB in source-sink dynamics of wild-type GAS and hypervirulent variants is discussed. Streptolysin S and PAF acetylhydrolase Sse critically and synergistically contribute to the inhibition of neutrophil recruitment by GAS CovS mutants. CovS mutations in emm3 GAS lead to the vascular invasion and enhance systemic GAS dissemination.

Fulminant group A streptococcal infection without gangrene in the extremities: Analysis of five autopsy cases

Five autopsy cases of fulminant group A streptococcal infection without gangrene in the extremities are presented. Clinical course of the fulminant illness was short (2-4 days). One pathological autopsy case was aged (86-years-old), and hemorrhagic cystitis was observed. The other four forensic autopsy cases were young (24-38 years-old) with the mean age of 32, and the primary infective lesions were located in the postpartum endometrium, tonsil and bronchus (2 cases). Systemic coccal dissemination with poor neutrophilic reaction was seen in two of five cases. Bilateral renal cortical necrosis was noted in three cases (including two with bacterial embolism). Hemophagocytosis, probably resulting from hypercytokinemia, was characteristic in three cases without bacterial embolism. Gram-positive cocci colonizing the hemorrhagic and necrotizing lesions were consistently immunoreactive for streptococcal antigens and Strep A (a carbohydrate antigen on group A streptococci). Neutrophilic reaction was mild in the primary infected foci. Clinicians should note that fulminant streptococcal infection (streptococcal toxic shock syndrome) in young and immunocompetent patients may not be associated with gangrene in the extremities. Autopsy prosecutors (diagnostic and forensic pathologists) must recognize the difficulty in making an appropriate autopsy diagnosis, particularly when bacterial embolism is not associated.

Necrotizing fasciitis of the lower extremity: imaging pearls and pitfalls

OBJECTIVE

The purpose of this article is to review the imaging findings of necrotizing fasciitis as seen on radiograph, ultrasound, CT, and MRI, and to recognize the early findings in this potentially fatal disease.

CONCLUSION

Although classically a clinical diagnosis, imaging is a powerful adjunct to facilitate early diagnosis in equivocal cases. Compared to plain radiography, ultrasound, CT and MR provide higher sensitivity and specificity for the diagnosis of necrotizing fasciitis. Cross-sectional imaging findings include asymmetric thickening of fascia, soft tissue air, blurring of fascial planes, inflammatory fat stranding, reactive lymphadenopathy, and nonenhancement of muscular fascia.

Fatal necrotizing myositis from fulminant Streptococcus dysgalactiae subspecies equisimilis (SDSE) infection: A case report of autopsy images

Over the past few decades, Streptococcus dysgalactiae subspecies equisimilis (SDSE) have been considered as weak pathogenicity compared with S. pyogenes (GAS). Some recent reports argue that SDSE may bring severe soft tissue infection as same as GAS. No reports have been tried to reveal the clinical characteristics and autopsy images of fulminant SDSE infection. In this case report, we aimed to present a case of fatal necrotizing myositis from fulminant SDSE infection at iliopsoas, including autopsy appearance.

Requirement and Synergistic Contribution of Platelet-Activating Factor Acetylhydrolase Sse and Streptolysin S to Inhibition of Neutrophil Recruitment and Systemic Infection by Hypervirulent emm3 Group A Streptococcus in Subcutaneous Infection of Mice

Hypervirulent group A streptococcus (GAS) can inhibit neutrophil recruitment and cause systemic infection in a mouse model of skin infection. The purpose of this study was to determine whether platelet-activating factor acetylhydrolase Sse and streptolysin S (SLS) have synergistic contributions to inhibition of neutrophil recruitment and systemic infection in subcutaneous infection of mice by MGAS315, a hypervirulent genotype emm3 GAS strain. Deletion of sse and sagA in MGAS315 synergistically reduced the skin lesion size and GAS burden in the liver and spleen. However, the mutants were persistent at skin sites and had similar growth factors in nonimmune blood. Thus, the low numbers of Δsse ΔsagA mutants in the liver and spleen were likely due to their reduction in the systemic dissemination. Few intact and necrotic neutrophils were detected at MGAS315 infection sites. In contrast, many neutrophils and necrotic cells were present at the edge of Δsse mutant infection sites on day 1 and at the edge of and inside Δsse mutant infection sites on day 2. ΔsagA mutant infection sites had massive numbers of and few intact neutrophils at the edge and center of the infection sites, respectively, on day 1 and were full of intact neutrophils or necrotic cells on day 2. Δsse ΔsagA mutant infection sites had massive numbers of intact neutrophils throughout the whole infection site. These sse and sagA deletion-caused changes in the histological pattern at skin infection sites could be complemented. Thus, the sse and sagA deletions synergistically enhance neutrophil recruitment. These findings indicate that both Sse and SLS are required but that neither is sufficient for inhibition of neutrophil recruitment and systemic infection by hypervirulent GAS.

Prognostic factors in necrotizing soft-tissue infections (NSTI): A cohort study

BACKGROUND

Necrotizing soft-tissue infection (NSTI) is uncommon but life-threatening. A recent meta-analysis estimated the overall mortality at 23.5%.

OBJECTIVE

We sought to identify risk factors associated with mortality in a cohort of patients with NSTI in a tertiary care center.

METHODS

We identified 512 patients with NSTI between 1996 and 2012 in the national hospital database Program for Medicalization of Information Systems and examined risk factors of mortality with NSTI by univariate and multivariate analysis.

RESULTS

We included 109 patients with a confirmed diagnosis of NSTI; 31 (28%) died at a median follow-up of 274 days (range 2-6135 days). On multivariate analysis, independent risk factors of mortality were age older than 75 years (hazard ratio [HR] 4.4, 95% confidence interval [CI] 1.8-10.3), multifocal NSTI (HR 5.9, 95% CI 1.9-18.5), severe peripheral vascular disease (HR 5.1, 95% CI 1.5-17.0), hospital-acquired infection (HR 3.9, 95% CI 1.4-10.7), severe sepsis (HR 7.4, 95% CI 1.7-33.1), and septic shock on hospital admission (HR 13.9, 95% CI 3.8-50.4).

LIMITATIONS

This was a retrospective cohort, which disallows a precise record of the delay between diagnosis and surgery.

CONCLUSION

Our findings for this robust cohort of patients with a definite diagnosis of NSTI could help clinicians stratify NSTI severity at clinical course onset.

Acute abdomen due to group A streptococcus bacteremia caused by an isolate with a mutation in the csrS gene

Streptococcus pyogenes (group A streptococcus) is an aerobic gram-positive coccus that causes infections ranging from non-invasive pharyngitis to severely invasive necrotizing fasciitis. Mutations in csrS/csrR and rgg, negative regulator genes of group A streptococcus, are crucial factors in the pathogenesis of streptococcal toxic shock syndrome, which is a severe, invasive infection characterized by sudden onset of shock and multiorgan failure, resulting in a high mortality rate. Here we present a case of group A streptococcal bacteremia in a 28-year-old Japanese woman with no relevant previous medical history. The patient developed progressive abdominal symptoms that may have been due to spontaneous bacterial peritonitis, followed by a state of shock, which did not fulfill the proposed criteria for streptococcal toxic shock. The isolate was found to harbor a mutation in the negative regulator csrS gene, whereas the csrR and rgg genes were intact. It was noteworthy that this strain carrying a csrS mutation had caused group A streptococcal bacteremia characterized by acute abdomen as the presenting symptom in a young individual who had been previously healthy. This case indicates that group A streptococcus with csrS mutations has potential virulence factors that are associated with the onset of group A streptococcal bacteremia that does not meet the diagnostic criteria for streptococcal toxic shock syndrome.

Necrotizing fasciitis and its mimics: what radiologists need to know

OBJECTIVE

The purpose of this article is to review the imaging features of necrotizing fasciitis and its potential mimics. Key imaging features are emphasized to enable accurate and efficient interpretation of variables that are essential in appropriate management.

CONCLUSION

Necrotizing fasciitis is a medical emergency with potential lethal outcome. Dissecting gas along fascial planes in the absence of penetrating trauma (including iatrogenic) is essentially pathognomonic. However, the lack of soft-tissue emphysema does not exclude the diagnosis. Mimics of necrotizing fasciitis include nonnecrotizing fasciitis (eosinophilic, paraneoplastic, inflammatory (lupus myofasciitis, Churg-Strauss, nodular, or proliferative), myositis, neoplasm, myonecrosis, inflammatory myopathy, and compartment syndrome. Necrotizing fasciitis is a clinical diagnosis, and imaging can reveal nonspecific or negative findings (particularly during the early course of disease). One should be familiar with salient clinical and imaging findings of necrotizing fasciitis to facilitate a more rapid and accurate diagnosis and be aware that its diagnosis necessitates immediate discussion with the referring physician.

Current concepts in the management of necrotizing fasciitis

Necrotizing fasciitis (NF) is a severe, rare, potentially lethal soft tissue infection that develops in the scrotum and perineum, the abdominal wall, or the extremities. The infection progresses rapidly, and septic shock may ensue; hence, the mortality rate is high (median mortality 32.2%). Prognosis becomes poorer in the presence of co-morbidities, such as diabetes mellitus, immunosuppression, chronic alcohol disease, chronic renal failure, and liver cirrhosis. NF is classified into four types, depending on microbiological findings. Most cases are polymicrobial, classed as type I. The clinical status of the patient varies from erythema, swelling, and tenderness in the early stage to skin ischemia with blisters and bullae in the advanced stage of infection. In its fulminant form, the patient is critically ill with signs and symptoms of severe septic shock and multiple organ dysfunction. The clinical condition is the most important clue for diagnosis. However, in equivocal cases, the diagnosis and severity of the infection can be secured with laboratory-based scoring systems, such as the laboratory risk indicator for necrotizing fasciitis score or Fournier's gangrene severity index score, especially in regard to Fournier's gangrene. Computed tomography or ultrasonography can be helpful, but definitive diagnosis is attained by exploratory surgery at the infected sites. Management of the infection begins with broad-spectrum antibiotics, but early and aggressive drainage and meticulous debridement constitute the mainstay of treatment. Postoperative management of the surgical wound is also important for the patient's survival, along with proper nutrition. The vacuum-assisted closure system has proved to be helpful in wound management, with its combined benefits of continuous cleansing of the wound and the formation of granulation tissue.

Characterization of streptococcal platelet-activating factor acetylhydrolase variants that are involved in innate immune evasion

Human pathogen group A streptococcus (GAS) has developed mechanisms to subvert innate immunity. We recently reported that the secreted esterase produced by serotype M1 GAS (SsE(M1)) reduces neutrophil recruitment by targeting platelet-activating factor (PAF). SsE(M1) and SsE produced by serotype M28 GAS (SsE(M28)) have a 37% sequence difference. This study aims at determining whether SsE(M28) is also a PAF acetylhydrolase and participates in innate immune evasion. We also examined whether SsE evolved to target PAF by characterizing the PAF acetylhydrolase (PAF-AH) activity and substrate specificity of SsE(M1), SsE(M28), SeE, the SsE homologue in Streptococcus equi, and human plasma PAF-AH (hpPAF-AH). PAF incubated with SsE(M28) or SeE was converted into lyso-PAF. SsE(M1) and SsE(M28) had kcat values of 373 s(-1) and 467 s(-1), respectively, that were ≥ 30-fold greater than that of hpPAF-AH (12 s(-1)). The comparison of SsE(M1), SsE(M28), and hpPAF-AH in kcat and Km in hydrolyzing triglycerides, acetyl esters, and PAF indicates that the SsE proteins are more potent hydrolases against PAF and have high affinity for PAF. SsE(M28) possesses much lower esterase activities against triglycerides and other esters than SsE(M1) but have similar potency with SsE(M1) in PAF hydrolysis. Deletion of sse(M28) in a covS deletion mutant of GAS increased neutrophil recruitment and reduced skin infection, whereas in trans expression of SsE(M28) in GAS reduced neutrophil infiltration and increased skin invasion in subcutaneous infection of mice. These results suggest that the SsE proteins evolved to target PAF for enhancing innate immune evasion and skin invasion.

Regulation of inhibition of neutrophil infiltration by the two-component regulatory system CovRS in subcutaneous murine infection with group A streptococcus

Hypervirulent invasive group A streptococcus (GAS) isolates inhibit neutrophil infiltration more than pharyngitis isolates do, and the molecular basis of this difference is not well understood. This study was designed to first determine whether natural null mutation of the two-component regulatory system CovRS is responsible for the enhancement of the inhibition of neutrophil recruitment seen in hypervirulent GAS. Next, we examined the role of CovRS-regulated interleukin-8/CXC chemokine peptidase (SpyCEP), C5a peptidase (ScpA), and platelet-activating factor acetylhydrolase (SsE) in the enhanced innate immune evasion. Invasive isolate MGAS5005 induces less neutrophil infiltration and produced a greater lesion area than pharyngitis isolate MGAS2221 in subcutaneous infections of mice. It is known that MGAS5005, but not MGAS2221, has a natural 1-bp deletion in the covS gene. Replacement of covS(Δ1bp) in MGAS5005 with wild-type covS resulted in the MGAS2221 phenotype. Deletion of covS from MGAS2221 resulted in the MGAS5005 phenotype. Tests of single, double, and triple deletion mutants of the MGAS5005 sse, spyCEP, and scpA genes found that SsE plays a more important role than SpyCEP and ScpA in the inhibition of neutrophil recruitment and that SsE, SpyCEP, and ScpA do not have synergistic effects on innate immune evasion by MGAS5005. Deletion of sse, but not spyCEP or scpA, of MGAS2221 enhances neutrophil recruitment. Thus, covS null mutations can cause substantial inhibition of neutrophil recruitment by enhancing the expression of the chemoattractant-degrading virulence factors, and SsE, but not SpyCEP or ScpA, is required for CovRS-regulated GAS inhibition of neutrophil infiltration.

[Necrotizing soft tissue infection of the upper limb]

Necrotizing soft tissue infections and necrotizing fasciitis are life-threatening infections affecting the hypodermis, muscular fascia, and dermis secondarily. Mortality is high, with an average of 30%. The early diagnosis of necrotizing soft tissue infection is challenging, but is key to successful management of these patients. The mainstay of therapy includes early and wide surgical debridement, antibiotics and supportive care. Adjunctive therapies may have a role, but their effectiveness remains unproven. A review of the literature allows us to highlight this multidisciplinary management.

Group A Streptococcus secreted esterase hydrolyzes platelet-activating factor to impede neutrophil recruitment and facilitate innate immune evasion

The innate immune system is the first line of host defense against invading organisms. Thus, pathogens have developed virulence mechanisms to evade the innate immune system. Here, we report a novel means for inhibition of neutrophil recruitment by Group A Streptococcus (GAS). Deletion of the secreted esterase gene (designated sse) in M1T1 GAS strains with (MGAS5005) and without (MGAS2221) a null covS mutation enhances neutrophil ingress to infection sites in the skin of mice. In trans expression of SsE in MGAS2221 reduces neutrophil recruitment and enhances skin invasion. The sse deletion mutant of MGAS5005 (Δsse^MGAS5005) is more efficiently cleared from skin than the parent strain. SsE hydrolyzes the sn-2 ester bond of platelet-activating factor (PAF), converting biologically active PAF into inactive lyso-PAF. K_M and k_cat of SsE for hydrolysis of 2-thio-PAF were similar to those of the human plasma PAF acetylhydrolase. Treatment of PAF with SsE abolishes the capacity of PAF to induce activation and chemotaxis of human neutrophils. More importantly, PAF receptor-deficient mice significantly reduce neutrophil infiltration to the site of Δsse^MGAS5005 infection. These findings identify the first secreted PAF acetylhydrolase of bacterial pathogens and support a novel GAS evasion mechanism that reduces phagocyte recruitment to sites of infection by inactivating PAF, providing a new paradigm for bacterial evasion of neutrophil responses.

GAS is a major human pathogen causing a variety of infections, including pharyngitis and necrotizing fasciitis. GAS pathogenesis is mediated by a large array of secreted and cell-surface virulence factors. However, the functions of many GAS virulence factors are poorly understood. Recently, we reported that the esterase secreted by GAS (SsE) is a CovRS (the control of virulence two component regulatory system)-regulated protective antigen and is critical for spreading in the skin and systemic dissemination of GAS in a mouse model of necrotizing fasciitis. This report presents three major findings regarding the function and functional mechanism of SsE: 1) SsE contributes to GAS inhibition of neutrophil recruitment; 2) SsE is a potent PAF acetylhydrolase and the first secreted bacterial PAF acetylhydrolase identified so far; and 3) the PAF receptor significantly contributes to neutrophil recruitment in skin GAS infection. These findings support a novel mechanism for evasion of the innate immune system by GAS that may be relevant to other infections.

Recent advances in the treatment of necrotizing fasciitis

With four types of necrotizing fasciitis (NF) now recognized, the diagnosis and management of NF becomes more challenging as physicians face more unusual pathogenic and atypical presentations. With few published guidelines and little evidence base to justify therapies, much of the literature is pragmatic or provides limited evidence with small underpowered studies and disparate case reports.

[Necrotizing fasciitis. 2011 update]

Necrotizing fasciitis belongs to a group of complicated soft tissue infections that can be even life threatening. Despite growing knowledge about its etiology, predictors, and the clinical progression, the mortality remains at a high level with 20%. A relevant reduction can be achieved only by an early diagnosis followed by consistent therapy. The clinical findings in about 75% of the cases are pain out of proportion, edema and tenderness, blisters, and erythema. It is elementary to differentiate a necrotizing or a non-necrotizing soft tissue infection early. In uncertain cases it can be necessary to perform a surgical exploration to confirm the diagnosis. The histopathologic characteristics are the fascial necrosis, vasculitis, thrombosis of perforating veins, the presence of the disease-causing bacteria as well as inflammatory cells like macrophages and polymorphonuclear granulocytes. Secondly, both the cutis and the muscle can be affected. In many cases there is a disproportion of the degree of local and systemic symptoms. Depending on the infectious agents there are two main types: type I is a polymicrobial infection and type II is a more invasive, serious, and fulminant monomicrobial infection mostly caused by group A Streptococcus pyogenes.Invasive, severe forms of streptococcal infections seem to occur more often in recent years. Multimodal and interdisciplinary therapy should be based on radical surgical débridement, systemic antibiotic therapy as well as enhanced intensive care therapy, which is sometimes combined with immunoglobulins (in streptococcal or staphylococcal infections) or hyperbaric oxygen therapy (HBOT, in clostridial infections). For wound care of extensive soft tissue defects vacuum-assisted closure has shown its benefit.

Streptolysin S-like virulence factors: the continuing sagA

Streptolysin S (SLS) is a potent cytolytic toxin and virulence factor that is produced by nearly all Streptococcus pyogenes strains. Despite a 100-year history of research on this toxin, it has only recently been established that SLS is just one of an extended family of post-translationally modified virulence factors (the SLS-like peptides) that are produced by some streptococci and other Gram-positive pathogens, such as Listeria monocytogenes and Clostridium botulinum. In this Review, we describe the identification, genetics, biochemistry and various functions of SLS. We also discuss the shared features of the virulence-associated SLS-like peptides, as well as their place within the rapidly expanding family of thiazole/oxazole-modified microcins (TOMMs).

Streptolysin S inhibits neutrophil recruitment during the early stages of Streptococcus pyogenes infection

In contrast to infection of superficial tissues, Streptococcus pyogenes infection of deeper tissue can be associated with a significantly diminished inflammatory response, suggesting that this bacterium has the ability to both promote and suppress inflammation. To examine this, we analyzed the behavior of an S. pyogenes mutant deficient in expression of the cytolytic toxin streptolysin S (SLS-) and evaluated events that occur during the first few hours of infection by using several models including injection of zebrafish (adults, larvae, and embryos), a transepithelial polymorphonuclear leukocyte (PMN) migration assay, and two-photon microscopy of mice in vivo. In contrast to wild-type S. pyogenes, the SLS- mutant was associated with the robust recruitment of neutrophils and significantly reduced lethal myositis in adult zebrafish. Similarly, the mutant was attenuated in embryos in its ability to cause lethality. Infection of larva muscle allowed an analysis of inflammation in real time, which revealed that the mutant had recruited PMNs to the infection site. Analysis of transepithelial migration in vitro suggested that SLS inhibited the host cells' production of signals chemotactic for neutrophils, which contrasted with the proinflammatory effect of an unrelated cytolytic toxin, streptolysin O. Using two-photon microscopy of mice in vivo, we showed that the extravasation of neutrophils during infection with SLS- mutant bacteria was significantly accelerated compared to infection with wild-type S. pyogenes. Taken together, these data support a role for SLS in the inhibition of neutrophil recruitment during the early stages of S. pyogenes infection.

Skin and soft tissue infections

Skin and soft tissue infections are a common cause of hospitalization and use of antibiotic therapy, and may result in significant disability. Infections managed by surgeons may vary from simple, noncomplicated cellulitis to severe necrotizing soft tissue infections. The differentiation of necrotizing infections from nonnecrotizing infections is critical to achieving adequate surgical therapy. An understanding of the changing epidemiology of all complicated skin and soft tissue infections is required for selection of appropriate empiric antibiotic therapy.

Necrotizing fasciitis: microbiological characteristics and predictors of postoperative outcome

OBJECTIVE

Necrotizing fasciitis is a life threatening soft-tissue infection with a high morbidity and mortality. Prompt treatment based on extensive surgical debridement and antibiotic therapies are the therapeutic principles.

METHODS

The medical records of patients with necrotizing fasciitis (n = 26) from 1996 to 2005 were retrospectively analyzed.

RESULTS

The localization of necrotizing fasciitis was most commonly the trunk (42.3 %). Type I polymicrobial infection was the dominating infection. The involvement of anaerobic bacteria was associated with an increase in the number of surgical revisions (p = 0.005). Length of postoperative intensive care unit stay, duration of postoperative ventilation and mortality were significantly increased in the ASA IV-V group. Computed tomography displayed only a limited significance as diagnostic tool for initial diagnosis.

CONCLUSIONS

In severe cases the combination of necrotic skin and soft tissue gas facilitates the correct diagnosis, which should than be followed by immediate - and most often - repeated debridement. If anaerobes are isolated an early and aggressive second look is necessary.

First Streptococcus pyogenes signature-tagged mutagenesis screen identifies novel virulence determinants

The virulence of bacterial pathogens is a complex process that requires the dynamic expression of many genes for the pathogens to invade and circumvent host defenses, as well as to proliferate in vivo. In this study, we employed a large-scale screen, signature-tagged mutagenesis (STM), to identify Streptococcus pyogenes virulence genes important for pathogenesis within the host. Approximately 1,200 STM mutants were created and screened using the zebrafish infectious disease model. The transposon insertion site was identified for 29 of the 150 mutants that were considered attenuated for virulence. Previously reported streptococcal virulence genes, such as mga, hasA, amrA, smeZ, and two genes in the sil locus, were identified, confirming the utility of the model for revealing genes important for virulence. Multiple genes not previously implicated in virulence were also identified, including genes encoding putative transporters, hypothetical cytosolic proteins, and macrolide efflux pumps. The STM mutant strains display various levels of attenuation, and multiple separate insertions were identified in either the same gene or the same locus, suggesting that these factors are important for this type of acute, invasive infection. We further examined two such genes, silB and silC of a putative quorum-sensing regulon, and determined that they are significant virulence factors in our model of necrotizing fasciitis. sil locus promoter expression was examined under various in vitro conditions, as well as in zebrafish tissues, and was found to be differentially induced. This study was a unique investigation of S. pyogenes factors required for successful invasive infection.

Five cases of necrotizing fasciitis: lack of skin inflammatory signs as a clinical clue for the fulminant type

Herein, we describe five patients with necrotizing fasciitis (NF) who had variable outcomes and clinical manifestations. At the onset, all patients exhibited purpura with or without blister and ulceration accompanied by severe pain and tenderness in the affected skin. Out of five patients, three lacked inflammatory signs such as redness and heat, and two of the three patients showed fulminant progression and died despite intensive treatments including surgical debridement, antimicrobial therapy, close monitoring and physiological support. Tissue specimens from the patients without skin inflammatory signs showed mild neutrophil infiltration in addition to necrosis from the epidermis to subcutaneous fat, and variable amounts of thrombi. Furthermore, numerous bacteria were detected by Gram stain. By contrast, the remaining two patients with skin inflammatory signs revealed slower progression, and tissue specimens from both patients showed heavy neutrophil infiltration, but bacteria were hardly detected. Therefore, these cases suggest the possibility that the paucity of skin inflammatory signs, such as redness and heat, in NF may be a clinical clue to predict the fulminant type.

Incompetence of neutrophils to invasive group A streptococcus is attributed to induction of plural virulence factors by dysfunction of a regulator

Group A streptococcus (GAS) causes variety of diseases ranging from common pharyngitis to life-threatening severe invasive diseases, including necrotizing fasciitis and streptococcal toxic shock-like syndrome. The characteristic of invasive GAS infections has been thought to attribute to genetic changes in bacteria, however, no clear evidence has shown due to lack of an intriguingly study using serotype-matched isolates from clinical severe invasive GAS infections. In addition, rare outbreaks of invasive infections and their distinctive pathology in which infectious foci without neutrophil infiltration hypothesized us invasive GAS could evade host defense, especially neutrophil functions. Herein we report that a panel of serotype-matched GAS, which were clinically isolated from severe invasive but not from non-invaive infections, could abrogate functions of human polymorphnuclear neutrophils (PMN) in at least two independent ways; due to inducing necrosis to PMN by enhanced production of a pore-forming toxin streptolysin O (SLO) and due to impairment of PMN migration via digesting interleukin-8, a PMN attracting chemokine, by increased production of a serine protease ScpC. Expression of genes was upregulated by a loss of repressive function with the mutation of csrS gene in the all emm49 severe invasive GAS isolates. The csrS mutants from clinical severe invasive GAS isolates exhibited high mortality and disseminated infection with paucity of neutrophils, a characteristic pathology seen in human invasive GAS infection, in a mouse model. However, GAS which lack either SLO or ScpC exhibit much less mortality than the csrS-mutated parent invasive GAS isolate to the infected mice. These results suggest that the abilities of GAS to abrogate PMN functions can determine the onset and severity of invasive GAS infection.

Staging of necrotizing fasciitis based on the evolving cutaneous features

BACKGROUND

Necrotizing fasciitis is a severe soft-tissue infection characterized by a fulminant course and high mortality. Early recognition is difficult as the disease is often clinically indistinguishable from cellulitis and other soft-tissue infections early in its evolution. Our aim was to study the manifestations of the cutaneous signs of necrotizing fasciitis as the disease evolves.

METHODS

This was a retrospective study on patients with necrotizing fasciitis at a single institution. Their charts were reviewed to document the daily cutaneous changes from the time of presentation (day 0) through to day 4 from presentation.

RESULTS

Twenty-two patients were identified. At initial assessment (day 0), almost all patients presented with erythema, tenderness, warm skin, and swelling. Blistering occurred in 41% of patients at presentation whereas late signs such as skin crepitus, necrosis, and anesthesia were infrequently seen (0-5%). As time elapsed, more patients had blistering (77% had blisters at day 4) and eventually the late signs of necrotizing fasciitis characterized by skin crepitus, necrosis, and anesthesia (9-36%) were seen. A clinical staging system was developed based on our observations. Stage migration from early to late stage necrotizing fasciitis was evident with majority of patients in stage 1 at day 0 (59%), whereas by day 4, majority had developed into stage 3 (68%).

CONCLUSION

This study has demonstrated the continuum of cutaneous manifestations as necrotizing fasciitis evolves. This will help in the early recognition and intervention of this devastating condition.

SalY of the Streptococcus pyogenes lantibiotic locus is required for full virulence and intracellular survival in macrophages

Streptococcus pyogenes utilizes numerous mechanisms for evading the host immune response but has only recently been found to survive in the intracellular environment. In this study, we demonstrate the requirement of a putative ABC transporter permease for intracellular survival in macrophages. The highly attenuated S. pyogenes mutant, SalY, was identified from a transposon mutagenesis screen, with over 200-fold attenuation in virulence in a zebrafish invasive-disease model. Sequencing of the region surrounding the insertion identified a locus that is highly conserved in other S. pyogenes genomes and is homologous to an operon involved in lantibiotic production. In vitro analysis demonstrated that the SalY mutant is deficient in intracellular survival in murine macrophages, a phenotype also observed in zebrafish macrophages in vivo. Macrophage crude cell lysates added to bacterial cultures resulted in the death of the SalY mutant but only growth inhibition of the wild-type strain. Specific depletion of zebrafish macrophages in vivo restored the ability of the SalY mutant to cause disease to wild-type levels. The SalY-infected, macrophage-depleted zebrafish exhibit large lesions and invasive dissemination at a rate and level similar to those of the wild type. In contrast, an M protein mutant with a degree of attenuation similar to that of the SalY mutant did not regain full virulence by in vivo depletion of macrophages. The putative SalY ABC transporter may be an example of the ability of S. pyogenes to adapt and evolve new survival strategies that allow dissemination and growth in previously uninhabitable sites.