Influences of linezolid, penicillin, and clindamycin, alone and in combination, on streptococcal pyrogenic exotoxin a release

Epidemiology and treatment of community-associated methicillin-resistantStaphylococcus aureusin children

Similar to the epidemiology of methicillin-sensitive Staphylococcus aureus, community-associated methicillin-resistant S. aureus infections occur in children in different regions of the USA and throughout the world. Although minor skin and soft-tissue infections predominate, life-threatening invasive disease and death can result. The novel genetic elements, staphylococcal cassette chromosome mec IV and V, explain the narrow antibiotic resistance pattern, and suggest the mechanism of spread among staphylococci. Panton-Valentine leukocidin apparently plays a role in its pathogenesis. Clindamycin therapy is often effective for treatment, but inducible resistance can develop if the isolate exhibits macrolide resistance due to the erm mechanism. Other drugs displaying in vitro activity against community-associated methicillin-resistant S. aureus include trimethoprim-sulfamethoxazole, tetracyclines, quinolones, linezolid and vancomycin. While experience in pediatric patients is limited, daptomycin, ketolides, glycylcyclines, newer glycopeptides and beta-lactamase-stable cephalosporins may be useful in the future. Further research could include well-designed studies of mechanisms of virulence, continued surveillance of changes in pathogenicity and susceptibility, as well as treatment effectiveness.

Serious group a streptococcal infections

The spectrum of illnesses caused by group A streptococcus (GAS) includes invasive infections, noninvasive infections, and noninfectious complications. Increasingly virulent infections associated with high morbidity and mortality have been observed since the late 1980s and continue to be prevalent in North America and worldwide. Penicillin remains the therapy of choice, with the addition of clindamycin recommended in high risk cases. Early recognition of GAS as the cause of these serious clinical syndromes is critical for timely administration of appropriate therapy. In this review, the pathophysiology, clinical manifestations, and treatment of invasive GAS infections are discussed.

Host gene expression profiling and in vivo cytokine studies to characterize the role of linezolid and vancomycin in methicillin-resistant Staphylococcus aureus (MRSA) murine sepsis model

Linezolid (L), a potent antibiotic for Methicillin Resistant Staphylococcus aureus (MRSA), inhibits bacterial protein synthesis. By contrast, vancomycin (V) is a cell wall active agent. Here, we used a murine sepsis model to test the hypothesis that L treatment is associated with differences in bacterial and host characteristics as compared to V. Mice were injected with S. aureus USA300, and then intravenously treated with 25 mg/kg of either L or V at 2 hours post infection (hpi). In vivo alpha-hemolysin production was reduced in both L and V-treated mice compared to untreated mice but the reduction did not reach the statistical significance [P = 0.12 for L; P = 0.70 for V). PVL was significantly reduced in L-treated mice compared to untreated mice (P = 0.02). However the reduction of in vivo PVL did not reach the statistical significance in V- treated mice compared to untreated mice (P = 0.27). Both antibiotics significantly reduced IL-1β production [P = 0.001 for L; P = 0.006 for V]. IL-6 was significantly reduced with L but not V antibiotic treatment [P<0.001 for L; P = 0.11 for V]. Neither treatment significantly reduced production of TNF-α. Whole-blood gene expression profiling showed no significant effect of L and V on uninfected mice. In S. aureus-infected mice, L altered the expression of a greater number of genes than V (95 vs. 42; P = 0.001). Pathway analysis for the differentially expressed genes identified toll-like receptor signaling pathway to be common to each S. aureus-infected comparison. Expression of immunomodulatory genes like Cxcl9, Cxcl10, Il1r2, Cd14 and Nfkbia was different among the treatment groups. Glycerolipid metabolism pathway was uniquely associated with L treatment in S. aureus infection. This study demonstrates that, as compared to V, treatment with L is associated with reduced levels of toxin production, differences in host inflammatory response, and distinct host gene expression characteristics in MRSA sepsis.

Streptococcus agalactiae toxic shock-like syndrome: two case reports and review of the literature

We present 2 patients with Streptococcus agalactiae toxic shock-like syndrome and review another 11 well-reported cases from the literature. Streptococcal toxic shock-like syndrome is a devastating illness with a high mortality rate, therefore we stress the importance of early supportive management, antimicrobial therapy, and surgical intervention. Toxic shock-like syndrome is likely to be underestimated in patients with invasive Streptococcus agalactiae infection who present with shock. Early diagnosis requires high suspicion of the illness, along with a thorough mucocutaneous examination. Streptococcus agalactiae produces uncharacterized pyrogenic toxins, which explains the ability of the organism to cause toxic shock-like syndrome.

Streptococcus pyogenes and re-emergence of scarlet fever as a public health problem

Explosive outbreaks of infectious diseases occasionally occur without immediately obvious epidemiological or microbiological explanations. Plague, cholera and Streptococcus pyogenes infection are some of the epidemic-prone bacterial infections. Besides epidemiological and conventional microbiological methods, the next-generation gene sequencing technology permits prompt detection of genomic and transcriptomic profiles associated with invasive phenotypes. Horizontal gene transfer due to mobile genetic elements carrying virulence factors and antimicrobial resistance, or mutations associated with the two component CovRS operon are important bacterial factors conferring survival advantage or invasiveness. The high incidence of scarlet fever in children less than 10 years old suggests that the lack of protective immunity is an important host factor. A high population density, overcrowded living environment and a low yearly rainfall are environmental factors contributing to outbreak development. Inappropriate antibiotic use is not only ineffective for treatment, but may actually drive an epidemic caused by drug-resistant strains and worsen patient outcomes by increasing the bacterial density at the site of infection and inducing toxin production. Surveillance of severe S. pyogenes infection is important because it can complicate concurrent chickenpox and influenza. Concomitant outbreaks of these two latter infections with a highly virulent and drug-resistant S. pyogenes strain can be disastrous.

Virulence-suppressing effects of linezolid on methicillin-resistant Staphylococcus aureus: possible contribution to early defervescence

In the present study, immunomodulatory effects of linezolid (LZD) on methicillin-resistance Staphylococcus aureus (MRSA) infections were evaluated. We have retrospectively reviewed treatment effects of LZD on 52 patients with severe MRSA infections. Sixty-four percent of the febrile patients demonstrated significant defervescence within 3 days, despite the presence of positive culture results. We speculated that this finding might be due to early anti-inflammatory effects of LZD, and to investigate this further we initiated in vivo experiments using mice MRSA pneumonia models. Mice were treated with either LZD or vancomycin (VCM) immediately after intranasal administration of MRSA. Bacterial numbers and levels of inflammatory cytokines in the lungs were determined. Although the bacterial burden in the lungs was not apparently different between the two groups, LZD but not VCM treatment significantly reduced induction of inflammatory cytokines in the lungs (P < 0.05). To evaluate whether this anti-inflammatory response was due to suppression of virulence factor expression, filter-sterilized supernatants of MRSA incubated in broth overnight with sub-MICs of LZD were subcutaneously administered to mice. To clarify whether LZD possesses direct host-modulating activity, cytokine responses to the supernatants were examined in mice pretreated with LZD. Interestingly, MRSA solutions prepared in the presence of sub-MICs of LZD revealed significant suppression of interleukin 6 (IL-6) in a dose-dependent manner (P < 0.05), but pretreatment of mice with LZD revealed no changes in cytokines. These findings suggest that sub-MICs of LZD might suppress virulence factors of MRSA, which may be associated with a reduction in endogenous pyrogens. These data may explain at least in part early defervescence observed in LZD-treated individuals.

The Streptococcus pyogenes proteome: maps, virulence factors and vaccine candidates

Streptococcus pyogenes is an important cause of human morbidity and mortality worldwide. A wealth of genomic information related to this pathogen has facilitated exploration of the proteome, particularly in response to environmental conditions thought to mimic various aspects of pathogenesis. Proteomic approaches are also used to identify immunoreactive proteins for vaccine development and to identify proteins that may induce autoimmunity. These studies have revealed new mechanisms involved in regulating the S. pyogenes proteome, which has opened up new avenues in the study of S. pyogenes pathogenesis. This article describes the methods used, and progress being made towards characterizing the S. pyogenes proteome, including studies seeking to identify potential vaccine candidates.

Invasive group A streptococcal infection: an update on the epidemiology and orthopaedic management

Invasive group A streptococcus (iGAS) is the most common cause of monomicrobial necrotising fasciitis. Necrotising infections of the extremities may present directly to orthopaedic surgeons or by reference from another admitting specialty. Recent epidemiological data from the Health Protection Agency suggest an increasing incidence of iGAS infection in England. Almost 40% of those affected had no predisposing illnesses or risk factors, and the proportion of children presenting with infections has risen. These observations have prompted the Chief Medical Officer for the Central Alerting System in England to write to general practitioners and hospitals, highlighting the need for clinical vigilance, early diagnosis and rapid initiation of treatment in suspected cases. The purpose of this annotation is to summarise the recent epidemiological trends, describe the presenting features and outline the current investigations and treatment of this rare but life-threatening condition.

Clindamycin-induced CovS-mediated regulation of the production of virulent exoproteins streptolysin O, NAD glycohydrolase, and streptokinase in Streptococcus pyogenes

The administration of high-dose clindamycin (CLI) along with penicillin is recommended for the treatment of streptococcal toxic shock syndrome. However, the prevalence of CLI-resistant Streptococcus pyogenes strains is increasing worldwide, and the effect of CLI on CLI-resistant S. pyogenes strains remains unknown. We aimed to evaluate the effect of CLI on the in vitro production of three major virulent exoproteins, namely, streptolysin O (Slo), NAD glycohydrolase (Nga), and streptokinase (Ska), by CLI-resistant S. pyogenes strains. After the incubation of M1 serotype CLI-resistant S. pyogenes D2TY in the presence of 1 microg/ml CLI, the amounts of Slo, Nga, and Ska and the levels of slo, nga, and ska mRNA in the supernatant were analyzed by Northern blotting and Western blotting, respectively. The results of both assays showed that the production of Slo, Nga, and Ska was higher with CLI treatment than without CLI treatment. We evaluated the role of the sensor kinase CovS, which is involved in the two-component system of S. pyogenes, in the CLI-induced production of these three exoproteins. Northern blotting analysis revealed that CLI induced the expression of covS mRNA in wild-type strain D2TY. Furthermore, both Northern blotting and Western blotting analyses showed that CLI decreased the levels of expression of Slo, Nga, and Ska in isogenic covS mutant D2TYcovS. These results suggest that CLI increases the production of three virulent exoproteins in CLI-resistant S. pyogenes strains via the action of CovS.

Release of SpeA from Streptococcus pyogenes after exposure to penicillin: Dependency on dose and inhibition by clindamycin

The amount and time course of SpeA release from group A streptococci (GAS) was studied at different starting inoculate after exposure to different doses of penicillin, clindamycin or a combination of the 2. The release was related to the bacterial concentration and killing rate. A clinical GAS strain was exposed to benzylpenicillin, 2 and 1000 x MIC, clindamycin, 2 and 32 x MIC, or combinations of the 2. Samples for viable counts and SpeA analyses were drawn before and after the addition of antibiotics and at 3, 6 and 24 h. The SpeA release was higher at low than at high concentrations of penicillin and the combination (both, p<0.05). The addition of clindamycin to penicillin reduced SpeA production at both concentrations (p<0.01). Most SpeA was released before 3 h, and for penicillin and the combination, the amount correlated to the number of killed bacteria during this period (r=0.50; p<0.05). A positive correlation was found between the inoculum size and the SpeA concentration at time zero (r=0.54; p<0.05). The SpeA concentration was dependent on the initial number of bacteria, the class of antibiotic, the dose of penicillin and the killing rate.

Gram-positive toxic shock syndromes

Toxic shock syndrome (TSS) is an acute, multi-system, toxin-mediated illness, often resulting in multi-organ failure. It represents the most fulminant expression of a spectrum of diseases caused by toxin-producing strains of Staphylococcus aureus and Streptococcus pyogenes (group A streptococcus). The importance of Gram-positive organisms as pathogens is increasing, and TSS is likely to be underdiagnosed in patients with staphylococcal or group A streptococcal infection who present with shock. TSS results from the ability of bacterial toxins to act as superantigens, stimulating immune-cell expansion and rampant cytokine expression in a manner that bypasses normal MHC-restricted antigen processing. A repetitive cycle of cell stimulation and cytokine release results in a cytokine avalanche that causes tissue damage, disseminated intravascular coagulation, and organ dysfunction. Specific therapy focuses on early identification of the illness, source control, and administration on antimicrobial agents including drugs capable of suppressing toxin production (eg, clindamycin, linezolid). Intravenous immunoglobulin has the potential to neutralise superantigen and to mitigate subsequent tissue damage.

Cell surface hydrophobicity and adherence of a strain of group B streptococci during the post-antibiotic effect of penicillin

The minimum inhibitory concentration and post-antibiotic effects of an antimicrobial agent are parameters to be taken into consideration when determining its dosage schedules. The in vitro post-antibiotic effects on cell surface hydrophobicity and bacterial adherence were examined in one strain of group B streptococci. Exposure of the microorganism for 2 h at 37 °C to 1 x MIC of penicillin induced a PAE of 1.1 h. The cell surface charge of the Streptococcus was altered significantly during the post-antibiotic phase as shown by its ability to bind to xylene: hydrophobicity was decreased. Bacterial adherence to human buccal epithelial cells was also reduced. The results of the present investigation indicate that studies designed to determine therapeutic regimens should evaluate the clinical significance of aspects of bacterial physiology during the post-antibiotic period.

Activities of clindamycin, daptomycin, doxycycline, linezolid, trimethoprim-sulfamethoxazole, and vancomycin against community-associated methicillin-resistant Staphylococcus aureus with inducible clindamycin resistance in murine thigh infection and in vitro pharmacodynamic models

Controversy exists about the most effective treatment options for community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) and about the ability of these strains to develop inducible resistance to clindamycin during therapy. Using both in vitro pharmacodynamic and murine thigh infection models, we evaluated and compared several antimicrobial compounds against CA-MRSA. Strains with inducible macrolide lincosamide-streptogramin type B (iMLS(B)) resistance and strains in which resistance was noninducible were evaluated. Two levels of inocula (10(5) and 10(7)) were evaluated for clindamycin activity in the in vivo model. In both models, the antimicrobial evaluation was performed in triplicate, and bacterial quantification occurred over 72 h, with drug doses that were designed to simulate the free drug area-under-the-concentration-time curve values (fAUCs) obtained from human samples. When the activity of clindamycin against the iMLS(B) strains was evaluated, constitutive resistance was noted at 24 h (MIC of >256), and failure was noted at an inoculum of > or =10(6) in the in vivo models. However, at a low inoculum (10(5)) in the murine thigh-infection model, clindamycin demonstrated modest activity, reducing the CFU/thigh count for clindamycin resistance-inducible strains at 72 h (0.45 to 1.3 logs). Overall, administration of daptomycin followed by vancomycin demonstrated the most significant kill against all strains in both models. Against the clindamycin noninducible strain, clindamycin and doxycycline demonstrated significant kill. Doxycycline, linezolid, and trimethoprim-sulfamethoxazide (not run in the murine model) demonstrated bacteriostatic activity against clindamycin resistance-inducible isolates. This study demonstrates that clindamycin's activity against the iMLS(B) strains tested is partially impacted by inoculum size. At present, there are several alternatives that appear promising for treating clindamycin resistance-inducible strains of CA-MRSA.

[Lethal streptococcal toxic shock syndrome in pediatrics. Presentation of 3 cases]

Three cases of children admitted to the Pediatric Intensive Medicine Unit in the months of February to March 2004 with the diagnosis of streptococcal toxic shock syndrome are presented. Two were under 2 years of age and the initial symptoms suggested viriasis. They evolved towards septic shock with early multiorganic failure and then death due to massive hemoptysis, ventricular fibrillation due to hyperkaliemia. Streptococcus pyogenes with serotypes M1T1 was isolated in all the cases and the patients had the clinical criteria of streptococcal toxic shock syndrome. Their course was unfavorable in spite of the resuscitation steps, early antibiotic treatment and artificial support of the different organic failures. We stress the rareness of the cases, early age, its appearance in a short period of time, its sudden onset and the null response to treatment initiated.

Effect of antibiotics on Staphylococcus aureus producing Panton-Valentine leukocidin

We examined the capacity of Staphylococcus aureus strains to release Panton-Valentine leukocidin (PVL) in the presence of antibiotics. No PVL was detected when S. aureus was incubated at inhibitory concentrations, while subinhibitory concentrations of oxacillin enhanced the PVL level; clindamycin, linezolid, and fusidic acid were inhibitory; and vancomycin had roughly no effect.

Growth phase-dependent effect of clindamycin on production of exoproteins by Streptococcus pyogenes

The administration of high-dose clindamycin plus benzylpenicillin has been recommended for the treatment of streptococcal toxic shock-like syndrome caused by Streptococcus pyogenes, and clindamycin has been found to be more effective than beta-lactams in retrospective analyses of human cases. Although therapeutic doses of clindamycin have also been shown to be effective against experimental infections and clindamycin has great efficacy against the production of bacterial exoproteins, we recently reported that the level of production of some exoproteins was unchanged or even increased by a subinhibitory dose of clindamycin when it is added upon the initiation of bacterial culture and the treated cultures were analyzed by two-dimensional gel electrophoresis. In this study we further examined the effect of clindamycin on the production of exoproteins by adding it to Streptococcus pyogenes cultures during various growth phases. We found that the levels of production of some proteins, NAD+ glycohydrolase, streptolysin O, and streptococcal inhibitor of complement, were increased when clindamycin was added at early-log-phase growth, which was the result that was seen when clindamycin was added at the beginning of culture. However, clindamycin inhibited the production of most types of proteins when it was administered to Streptococcus pyogenes cultures at mid-log-phase growth. In csrS- or mga-knockout bacterial strains, the increase in exoproteins seen in parental strains was considerably inhibited. Our study indicates that the in vitro effect of clindamycin on the production of exoproteins greatly depends on the growth phase of bacteria and some regulatory factors of Streptococcus pyogenes that are involved in this phenomenon.

Therapies for necrotising fasciitis

Necrotising fasciitis is a rare but life-threatening infectious disease emergency. Delays in diagnosis and treatment are common, and mortality rates often exceed 30%. Successful management of this disease requires high clinical suspicion and aggressive action. The mainstays of therapy include early and wide surgical debridement, antibiotics and supportive care, with prompt surgical intervention. Adjunctive modalities, such as protein synthesis inhibitors, hyperbaric oxygen and intravenous immunoglobulin, may have a role, but their effectiveness remains unproven. New rapid diagnostic tools are emerging that promise to revolutionize early detection of necrotising fasciitis. Research into the molecular microbiology, especially regarding group A streptococcus, are providing novel insights into the pathogenesis of necrotising soft tissue infections and identifying future targets for rationally designed interventions.

Streptococcal pyomyositis of the psoas: case reports and review

We present two unusual cases of pyomyositis of the psoas muscle caused by Group A beta-hemolytic streptococcus (GABHS) in children presenting with fever, emesis and leg pain. Pyomyositis secondary to GABHS is rare in children and cases involving the psoas muscle have not been previously reported. In our discussion, we review the epidemiology, presentation, diagnosis and treatment of GABHS psoas myositis in comparison with staphylococcal pyomyositis. Prompt recognition of the signs and symptoms of GABHS psoas pyomyositis is essential for treatment of this life-threatening infection.

Necrotizing fasciitis: pathogenesis and treatment

Necrotizing fasciitis is a rapidly progressive, life-threatening infection and a true infectious disease emergency. Despite much clinical experience, the management of this disease remains suboptimal, with mortality rates remaining approximately 30%. Necrotizing fasciitis rarely presents with obvious signs and symptoms and delays in diagnosis enhance mortality. Therefore, successful patient care depends on the physician's acumen and index of suspicion. Prompt surgical debridement, intravenous antibiotics, fluid and electrolyte management, and analgesia are mainstays of therapy. Adjunctive clindamycin, hyperbaric oxygen therapy and intravenous immunoglobulin are frequently employed in the treatment of necrotizing fasciitis, but their efficacy has not been rigorously established. Improved understanding of the pathogenesis of necrotizing fasciitis has revealed new targets for rationally designed therapies to improve morbidity and mortality.

Reducing the global burden of sepsis in infants and children: a clinical practice research agenda

OBJECTIVE

Sepsis remains a predominant cause of mortality and morbidity in children in the developing and industrialized world. This review discusses a clinical practice research agenda to reduce this global burden.

DESIGN

Summary of the literature with analysis by experts.

RESULTS

Many interventions have been proven effective in decreasing sepsis. Heterologous immunization with attenuated Bacillus Camille Guerin vaccine reduces all-cause mortality, and specific immunizations further reduce morbidity and mortality from many specific microbes. Antepartum antibiotics reduce the prevalence of cerebral palsy and mortality in infants. Administration of antibiotics to neonates with signs of sepsis reduces all-cause mortality five-fold and can also reduce mortality in the big four killers of children: severe pneumonia, diarrhea, malaria, or measles. Immunonutrition with zinc and vitamin A can further reduce morbidity in diarrhea and pneumonia and reduce mortality in measles. First-hour rapid intravenous fluid resuscitation achieves 100% survival in dengue shock, and time-sensitive fluid resuscitation and inotropic support reduces mortality ten-fold in meningococcal septic shock. Multiple organ failure occurs when late or inadequate resuscitation results in systemic thrombosis or when infection is not eradicated because of immunosuppression or inadequate source control.

CONCLUSIONS

The global burden of sepsis can be reduced by 1) prevention with improved heterologous or specific vaccines and vitamin or mineral supplement programs; 2) early recognition and treatment with appropriate antibiotics, intravenous fluid resuscitation, and inotropic support in organized healthcare-delivery systems; and 3) development of new diagnostics and therapeutics that reduce systemic thrombosis, improve immune function, and kill resistant organisms.

Effect of antibiotics on group A Streptococcus exoprotein production analyzed by two-dimensional gel electrophoresis

High-dose clindamycin (CLDM) and benzylpenicillin (PCG) are the recommended chemotherapeutic remedies for toxic shock-like syndrome caused by group A streptococci. One reason for this is that it has been shown that CLDM suppresses the expression of some exoproteins, e.g., SpeB, SpeA, and streptolysin O (Slo). We analyzed the effects of antibiotics on the production of whole exoproteins by two-dimensional gel electrophoresis. Unexpectedly, we found that the levels of several exoproteins, Slo, NAD(+)-glycohydrolase (Nga), M protein, and Sic, were increased by CLDM treatment, although we also confirmed previous findings that the levels of various exoproteins, including SpeB, were decreased. The increases in exoprotein levels were also detected by using other protein synthesis inhibitor antibiotics: erythromycin, kanamycin, tetracycline, chloramphenicol, and linezolid. Peptidoglycan synthesis inhibitors (such as PCG, cefazolin, and imipenem), DNA replication inhibitors (such as gatifloxacin), and an RNA polymerase inhibitor (rifampin) did not have significant effects on exoprotein production. The combination of CLDM and PCG had no advantageous effects with regard to exoprotein production compared to the effect achieved with CLDM alone. We also analyzed the transcriptional levels of slo and nga by reverse transcription-PCR and found that this change was also detected at the transcriptional level. Furthermore, the phenomenon was seen not only in strains of the M1 serotype but also in strains of the other M serotypes. Our study suggests that the clinical effectiveness of CLDM might be due to the inhibition of the production of a limited number of exoproteins.