Structure of the Streptococcus pyogenes NAD+ Glycohydrolase Translocation Domain and Its Essential Role in Toxin Binding to Oropharyngeal Keratinocytes.

The emergence and continued dominance of a Streptococcus pyogenes (group A Streptococcus, GAS) M1T1 clonal group is temporally correlated with acquisition of genomic sequences that confer high level expression of cotoxins streptolysin O (SLO) and NAD+-glycohydrolase (NADase). Experimental infection models have provided evidence that both toxins are important contributors to GAS virulence. SLO is a cholesterol-dependent pore-forming toxin capable of lysing virtually all types of mammalian cells. NADase, which is composed of an N-terminal translocation domain and C-terminal glycohydrolase domain, acts as an intracellular toxin that depletes host cell energy stores. NADase is dependent on SLO for internalization into epithelial cells, but its mechanism of interaction with the cell surface and details of its translocation mechanism remain unclear. In this study we found that NADase can bind oropharyngeal epithelial cells independently of SLO. This interaction is mediated by both domains of the toxin. We determined by NMR the structure of the translocation domain to be a ß-sandwich with a disordered N-terminal region. The folded region of the domain has structural homology to carbohydrate binding modules. We show that excess NADase inhibits SLO-mediated hemolysis and binding to epithelial cells in vitro, suggesting NADase and SLO have shared surface receptors. This effect is abrogated by disruption of a putative carbohydrate binding site on the NADase translocation domain. Our data are consistent with a model whereby interactions of the NADase glycohydrolase domain and translocation domain with SLO and the cell surface increase avidity of NADase binding and facilitate toxin-toxin and toxin-cell surface interactions. IMPORTANCE NADase and streptolysin O (SLO) are secreted toxins important for pathogenesis of group A Streptococcus, the agent of strep throat and severe invasive infections. The two toxins interact in solution and mutually enhance cytotoxic activity. We now find that NADase is capable of binding to the surface of human cells independently of SLO. Structural analysis of the previously uncharacterized translocation domain of NADase suggests that it contains a carbohydrate binding module. The NADase translocation domain and SLO appear to recognize similar glycan structures on the cell surface, which may be one mechanism through which NADase enhances SLO pore-forming activity during infection. Our findings provide new insight into the NADase toxin and its functional interactions with SLO during streptococcal infection.

NAD+-Glycohydrolase Promotes Intracellular Survival of Group A Streptococcus.

A global increase in invasive infections due to group A Streptococcus (S. pyogenes or GAS) has been observed since the 1980s, associated with emergence of a clonal group of strains of the M1T1 serotype. Among other virulence attributes, the M1T1 clone secretes NAD+-glycohydrolase (NADase). When GAS binds to epithelial cells in vitro, NADase is translocated into the cytosol in a process mediated by streptolysin O (SLO), and expression of these two toxins is associated with enhanced GAS intracellular survival. Because SLO is required for NADase translocation, it has been difficult to distinguish pathogenic effects of NADase from those of SLO. To resolve the effects of the two proteins, we made use of anthrax toxin as an alternative means to deliver NADase to host cells, independently of SLO. We developed a novel method for purification of enzymatically active NADase fused to an amino-terminal fragment of anthrax toxin lethal factor (LFn-NADase) that exploits the avid, reversible binding of NADase to its endogenous inhibitor. LFn-NADase was translocated across a synthetic lipid bilayer in vitro in the presence of anthrax toxin protective antigen in a pH-dependent manner. Exposure of human oropharyngeal keratinocytes to LFn-NADase in the presence of protective antigen resulted in cytosolic delivery of NADase activity, inhibition of protein synthesis, and cell death, whereas a similar construct of an enzymatically inactive point mutant had no effect. Anthrax toxin-mediated delivery of NADase in an amount comparable to that observed during in vitro infection with live GAS rescued the defective intracellular survival of NADase-deficient GAS and increased the survival of SLO-deficient GAS. Confocal microscopy demonstrated that delivery of LFn-NADase prevented intracellular trafficking of NADase-deficient GAS to lysosomes. We conclude that NADase mediates cytotoxicity and promotes intracellular survival of GAS in host cells.

The human antimicrobial peptide LL-37 binds directly to CsrS, a sensor histidine kinase of group A Streptococcus, to activate expression of virulence factors.

Group A Streptococcus (GAS) responds to subinhibitory concentrations of LL-37 by up-regulation of virulence factors through the CsrRS (CovRS) two-component system. The signaling mechanism, however, is unclear. To determine whether LL-37 signaling reflects specific binding to CsrS or rather a nonspecific response to LL-37-mediated membrane damage, we tested LL-37 fragments for CsrRS signaling and for GAS antimicrobial activity. We identified a 10-residue fragment (RI-10) of LL-37 as the minimal peptide that retains the ability to signal increased expression of GAS virulence factors, yet it has no detectable antimicrobial activity against GAS. Substitution of individual key amino acids in RI-10 reduced or abrogated signaling. These data do not support the hypothesis that CsrS detects LL-37-induced damage to the bacterial cell membrane but rather suggest that LL-37 signaling is mediated by a direct interaction with CsrS. To test whether LL-37 binds to CsrS, we used the purified CsrS extracellular domain to pull down LL-37 in vitro, a result that provides further evidence that LL-37 binds to CsrS. The dissociation of CsrS-mediated signaling from membrane damage by LL-37 fragments together with in vitro evidence for a direct LL-37-CsrS binding interaction constitute compelling evidence that signal transduction by LL-37 through CsrS reflects a direct ligand/receptor interaction.

Effects of temperature and nutrients on growth and toxicity of Alexandrium affine from southeastern Gulf of California.

An Alexandrium affine strain (AAJQ-1) from San José Island, Gulf of California was characterized for growth and toxicology. Fivefold of f/2 + Se cultures were incubated for 34 days in a temperature gradient (21-29 °C). Aliquots were collected every third day for cell counting, toxin determination, and nutrient analyses. In this study ELISA method was used to evaluate the PSP toxin production due to the lower detection limit than the HPLC method. The highest cell density (6724 cells mL-1) and growth rate (0.22 day-1) were obtained at 27 °C and they were related to temperature in all treatments. Cell density showed negative correlation with nitrate at temperatures ≥23 °C, and with orthophosphate 27 °C, furthermore, these correlations promote the toxin production (0.05-0.45 fmol STX cell-1); beyond that nitrite at high temperature seems to promote toxin production, which has not been sufficiently documented.

Growth and paralytic shellfish poisoning toxin production by a Mexican dinoflagellate strain of Alexandrium tamiyavanichii Balech (1994) under different nutrient conditions.

Alexandrium tamiyavanichii is a marine dinoflagellate known to produce Paralytic Shellfish Poisoning (PSP) toxin. Thus, a strain was isolated from La Paz Bay, Baja California Sur, Mexico and used to explore whether stress conditions, such as phosphorus limitation (PL) and nitrogen enrichment (NE) modulate population growth and PSP toxin production in the GSe medium. Growth kinetics showed that the PL treatment produced a 3.4-fold increase in cell density versus control at day 30 of the culture cycle. The highest PSP concentration was found in the control culture (309 fmol cell-1) on day 21. Saxitoxin (STX) was the main analog in all the treatments (> 40 % mol). In conclusion, PL and NE treatments promoted growth kinetics in the species studied but did not affect the PSP toxin production. For the first time, the present research describes A. tamiyavanichii high toxicity strain isolated from Mexican coasts relative to the South-Atlantic strains.

Interplay between human STING genotype and bacterial NADase activity regulates inter-individual disease variability.

Variability in disease severity caused by a microbial pathogen is impacted by each infection representing a unique combination of host and pathogen genomes. Here, we show that the outcome of invasive Streptococcus pyogenes infection is regulated by an interplay between human STING genotype and bacterial NADase activity. S. pyogenes-derived c-di-AMP diffuses via streptolysin O pores into macrophages where it activates STING and the ensuing type I IFN response. However, the enzymatic activity of the NADase variants expressed by invasive strains suppresses STING-mediated type I IFN production. Analysis of patients with necrotizing S. pyogenes soft tissue infection indicates that a STING genotype associated with reduced c-di-AMP-binding capacity combined with high bacterial NADase activity promotes a 'perfect storm' manifested in poor outcome, whereas proficient and uninhibited STING-mediated type I IFN production correlates with protection against host-detrimental inflammation. These results reveal an immune-regulating function for bacterial NADase and provide insight regarding the host-pathogen genotype interplay underlying invasive infection and interindividual disease variability.

Is there a trend towards semi-extended knee positioning during intramedullary tibial nailing in Latin America? A survey among 990 orthopaedic surgeons.

OBJECTIVE: The aim of this study was to evaluate the Latin American orthopaedic trauma surgeons preference regarding knee positioning and entry portals for IM nailing and identify the reasons of these preferences. METHODS: Using the AO Trauma database, 22.285 surveys were distributed by email to Latin American orthopaedic surgeons. Demographic data and practice patterns, especially regarding knee positioning and approach for tibial nailing, were then evaluated and statistically treated. RESULTS: amongst one thousand five hundred fourteen responses, 990 orthopaedic surgeons (4.4% of response rate) fully responded to the survey. Transpatellar tendon approach (613 / 61.9%,) with the knee in flexion (518 / 52.3%) on a radiolucent table remains the standard practice for intramedullary tibial nailing. Even for proximal and distal tibial nailing, the transpatellar tendon approach (455 / 46%) with the knee in flexion (562 / 56.8%) hold on the most used method. Only 55 (9.36%) orthopaedic surgeons reported that they have migrated to the supra-patellar tibial nailing in the recent years. The main reasons for a low rate of migration were lack of knowledge about the technique and unavailability of specific gigs and cartilage protectors for a safe suprapatellar nailing. CONCLUSION: Even with the potential benefits of the semi-extended knee positioning for tibial nailing, the Latin American orthopaedic community remains using the transpatellar tendon approach with the knee in flexion as the standard technique. Lack of surgical training for suprapatellar and parapatellar approaches with the knee in semi-extension, added by the unavailability of suprapatellar jigs and soft outer protection sleeves contribute to counter the trend towards the semi-extended techniques.

Availability and use of resources for emergency fracture care of pelvic trauma associated with haemorrhagic shock in Latin America: A cross-sectional study.

Determining the true availability of resources and understanding the level of training of surgeons involved in the treatment of patients with pelvic fractures and haemorrhagic shock is critical. In the herein study, the availability of technical, technological, and human resources for the care of this injury in Latin America region was analysed, and the preferences of orthopaedic trauma surgeons when performing interventions for the diagnosis and treatment of patients with pelvic trauma and associated haemorrhagic shock was described. A cross sectional web-based survey containing questions on knowledge, attitudes, and practices with respect to imaging resources, emergency pelvic stabilization methods, and interventions used for bleeding control was sent to 948 Latin America orthopaedic trauma surgeons treating pelvic fractures in the emergency department. Differences between regional clusters, level of training, type of hospital, and pelvic surgery volume were assessed. 368 responses were obtained, with 37.5% of respondents reporting formal training in pelvic surgery and 36.0% having available protocol for managing these patients. The most frequently used interventions were the supra-acetabular pelvic external fixator and pelvic packing. Limited hospital and imaging resources are available for the care of patients with pelvic trauma and associated haemorrhagic shock throughout Latin America. In addition, the training of orthopaedic trauma surgeons dealing with this type of injury and the volume of pelvic surgeries per year is heterogeneous. It should be urgently considered to develop management protocols adapted to Latin America according to the availability of resources, as well as to promote training in this severe life-threatening traumatic condition.

Treatment of fracture-related infection in Latin America (FRILA). Proposal for a multicentre regional registry.

Postoperative bone infection is a severe complication in the treatment of fractures. The management of this pathology is challenging, but recent advances have been made to achieve standardization that can help diagnosis and decision-making. However, we are unaware of studies validating these models in Latin America. Therefore, this study aims to collect data from patients with fracture-related infections treated in different institutions in Latin America to create a registry that will assist in future clinical decision-making regarding the diagnostic process and the surgical and medical treatment of these patients.

Streptococcus pyogenes can support or inhibit growth of Haemophilus influenzae by supplying or restricting extracellular NAD.

Nicotinamide adenine dinucleotide (NAD+) is an essential co-factor for cellular metabolism and serves as a substrate in enzymatic processes. NAD+ is produced by de novo synthesis or salvage pathways in nearly all bacterial species. Haemophilus influenzae lacks the capacity for de novo synthesis, so it is dependent on import of NAD+ from the external environment or salvage biosynthetic pathways for recycling of NAD+ precursors and breakdown products. However, the actual sources of NAD+ utilized by H. influenzae in the respiratory tract are not well defined. In this study, we found that a variety of bacteria, including species found in the upper airway of humans, released NAD+ that was readily detectable in extracellular culture fluid, and which supported growth of H. influenzae in vitro. By contrast, certain strains of Streptococcus pyogenes (group A streptococcus or GAS) inhibited growth of H. influenzae in vitro by secreting NAD+-glycohydrolase (NADase), which degraded extracellular NAD+. Conversely, GAS strains that lacked enzymatically active NADase released extracellular NAD+, which could support H. influenzae growth. Our results suggest that many bacterial species, including normal flora of the upper airway, release NAD+ into the environment. GAS is distinctive in its ability to both release and degrade NAD+. Thus, colonization of the airway with H. influenzae may be promoted or restricted by co-colonization with GAS in a strain-specific manner that depends, respectively, on release of NAD+ or secretion of active NADase. We suggest that, in addition to its role as a cytotoxin for host cells, NADase may serve a separate function by restricting growth of H. influenzae in the human respiratory tract.

RocA Binds CsrS To Modulate CsrRS-Mediated Gene Regulation in Group A Streptococcus.

The orphan regulator RocA plays a critical role in the colonization and pathogenesis of the obligate human pathogen group A Streptococcus Despite multiple lines of evidence supporting a role for RocA as an auxiliary regulator of the control of virulence two-component regulatory system CsrRS (or CovRS), the mechanism of action of RocA remains unknown. Using a combination of in vitro and in vivo techniques, we now find that RocA interacts with CsrS in the streptococcal membrane via its N-terminal region, which contains seven transmembrane domains. This interaction is essential for RocA-mediated regulation of CsrRS function. Furthermore, we demonstrate that RocA forms homodimers via its cytoplasmic domain. The serotype-specific RocA truncation in M3 isolates alters this homotypic interaction, resulting in protein aggregation and impairment of RocA-mediated regulation. Taken together, our findings provide insight into the molecular requirements for functional interaction of RocA with CsrS to modulate CsrRS-mediated gene regulation.IMPORTANCE Bacterial two-component regulatory systems, comprising a membrane-bound sensor kinase and cytosolic response regulator, are critical in coordinating the bacterial response to changing environmental conditions. More recently, auxiliary regulators which act to modulate the activity of two-component systems, allowing integration of multiple signals and fine-tuning of bacterial responses, have been identified. RocA is a regulatory protein encoded by all serotypes of the important human pathogen group A Streptococcus Although RocA is known to exert its regulatory activity via the streptococcal two-component regulatory system CsrRS, the mechanism by which it functions was unknown. Based on new experimental evidence, we propose a model whereby RocA interacts with CsrS in the streptococcal cell membrane to enhance CsrS autokinase activity and subsequent phosphotransfer to the response regulator CsrR, which mediates transcriptional repression of target genes.

Multisystem Analysis of Mycobacterium tuberculosis Reveals Kinase-Dependent Remodeling of the Pathogen-Environment Interface.

Tuberculosis is the leading killer among infectious diseases worldwide. Increasing multidrug resistance has prompted new approaches for tuberculosis drug development, including targeted inhibition of virulence determinants and of signaling cascades that control many downstream pathways. We used a multisystem approach to determine the effects of a potent small-molecule inhibitor of the essential Mycobacterium tuberculosis Ser/Thr protein kinases PknA and PknB. We observed differential levels of phosphorylation of many proteins and extensive changes in levels of gene expression, protein abundance, cell wall lipids, and intracellular metabolites. The patterns of these changes indicate regulation by PknA and PknB of several pathways required for cell growth, including ATP synthesis, DNA synthesis, and translation. These data also highlight effects on pathways for remodeling of the mycobacterial cell envelope via control of peptidoglycan turnover, lipid content, a SigE-mediated envelope stress response, transmembrane transport systems, and protein secretion systems. Integrated analysis of phosphoproteins, transcripts, proteins, and lipids identified an unexpected pathway whereby threonine phosphorylation of the essential response regulator MtrA decreases its DNA binding activity. Inhibition of this phosphorylation is linked to decreased expression of genes for peptidoglycan turnover, and of genes for mycolyl transferases, with concomitant changes in mycolates and glycolipids in the cell envelope. These findings reveal novel roles for PknA and PknB in regulating multiple essential cell functions and confirm that these kinases are potentially valuable targets for new antituberculosis drugs. In addition, the data from these linked multisystems provide a valuable resource for future targeted investigations into the pathways regulated by these kinases in the M. tuberculosis cell.IMPORTANCE Tuberculosis is the leading killer among infectious diseases worldwide. Increasing drug resistance threatens efforts to control this epidemic; thus, new antitubercular drugs are urgently needed. We performed an integrated, multisystem analysis of Mycobacterium tuberculosis responses to inhibition of its two essential serine/threonine protein kinases. These kinases allow the bacterium to adapt to its environment by phosphorylating cellular proteins in response to extracellular signals. We identified differentially phosphorylated proteins, downstream changes in levels of specific mRNA and protein abundance, and alterations in the metabolite and lipid content of the cell. These results include changes previously linked to growth arrest and also reveal new roles for these kinases in regulating essential processes, including growth, stress responses, transport of proteins and other molecules, and the structure of the mycobacterial cell envelope. Our multisystem data identify PknA and PknB as promising targets for drug development and provide a valuable resource for future investigation of their functions.

Binding of NAD+-Glycohydrolase to Streptolysin O Stabilizes Both Toxins and Promotes Virulence of Group A Streptococcus.

The globally dominant, invasive M1T1 strain of group A Streptococcus (GAS) harbors polymorphisms in the promoter region of an operon that contains the genes encoding streptolysin O (SLO) and NAD+-glycohydrolase (NADase), resulting in high-level expression of these toxins. While both toxins have been shown experimentally to contribute to pathogenesis, many GAS isolates lack detectable NADase activity. DNA sequencing of such strains has revealed that reduced or absent enzymatic activity can be associated with a variety of point mutations in nga, the gene encoding NADase; a commonly observed polymorphism associated with near-complete abrogation of activity is a substitution of aspartic acid for glycine at position 330 (G330D). However, nga has not been observed to contain early termination codons or mutations that would result in a truncated protein, even when the gene product contains missense mutations that abrogate enzymatic activity. It has been suggested that NADase that lacks NAD-glycohydrolase activity retains an as-yet-unidentified inherent cytotoxicity to mammalian cells and thus is still a potent virulence factor. We now show that expression of NADase, either enzymatically active or inactive, augments SLO-mediated toxicity for keratinocytes. In culture supernatants, SLO and NADase are mutually interdependent for protein stability. We demonstrate that the two proteins interact in solution and that both the translocation domain and catalytic domain of NADase are required for maximal binding between the two toxins. We conclude that binding of NADase to SLO stabilizes both toxins, thereby enhancing GAS virulence.IMPORTANCE The global increase in invasive GAS infections in the 1980s was associated with the emergence of an M1T1 clone that harbors a 36-kb pathogenicity island, which codes for increased expression of toxins SLO and NADase. Polymorphisms in NADase that render it catalytically inactive can be detected in clinical isolates, including invasive strains. However, such isolates continue to produce full-length NADase. The rationale for this observation is not completely understood. This study characterizes the binding interaction between NADase and SLO and reports that the expression of each toxin is crucial for maximal expression and stability of the other. By this mechanism, the presence of both toxins increases toxicity to keratinocytes and is predicted to enhance GAS survival in the human host. These observations provide an explanation for conservation of full-length NADase expression even when it lacks enzymatic activity and suggest a critical role for binding of NADase to SLO in GAS pathogenesis.

First report of an intraerythrocytic small piroplasm in wild Iberian lynx (Lynx pardinus).

A wild injured Iberian lynx (Lynx pardinus) was taken from the Sierra Morena population. During the health check small intraerythrocytic piroplasms, morphologically indistinguishable from other feline piroplasms, were observed in Wright-Giemsa-stained blood films. Amplification by polymerase chain reaction of a portion of the 18S nuclear small subunit (NSS) rRNA gene and sequencing revealed similarity of the unknown organism with sequences obtained from Pallas's cat from Mongolia and from a domestic cat in Spain. In a retrospective (1993-2003) study of 50 Iberian lynx tissue samples, no amplifications of the 18S NSS rRNA gene of the organism were obtained. This is the first report of a naturally occurring erythroparasitemia in the Iberian lynx and the first documented case of naturally occurring piroplasm infection in a free-ranging felid from Europe.

Neumotórax espontáneo en pediatría. Reporte de un caso y revisión de la literatura / Spontaneous pneumothorax in pediatrics. Case report and a review of the literature

El neumotórax consiste en la acumulación de aire en el espacio pleural tras un defecto en una de las pleuras. Puede ser de origen traumático o espontáneo, dividiéndose este último en primario o secundario según ausencia o presencia de enfermedad pulmonar subyacente. En pediatría tiene incidencia variable, pero es más frecuente en varones, adolescentes, de fenotipo asténico y fumadores. Se sospecha ante un cuadro de disnea de inicio súbito asociado o no a dolor torácico y se certifica el diagnóstico y extensión mediante radiografía de tórax. Suelen seguirse las recomendaciones de tratamiento establecidas en pacientes adultos debido a que no existen guías específicas para esta edad.Dependiendo de sumagnitud, las opciones terapéuticas para un primer episodio de neumotórax espontáneo varían entre el manejo conservador con observación y oxigenoterapia, la pleurotomía mínima con instalación de tubo o el manejo quirúrgico primario mediante apicectomía y pleurodesis, que se plantea especialmente ante fuga de aire persistente o recidiva. Si el manejo es conservador, existe un riesgo de recurrencia de alrededor de un 40%. Se presenta el caso de un adolescente de sexomasculino que presenta un neumotórax espontáneo primario extenso con fuga de aire persistente, por lo que semaneja con apicectomía y pleurodesis por videotoracoscopia (VATS).

A pneumothorax is an accumulation of air in the pleural space caused by a defect in the pleura. It can be traumatic or spontaneous; the latter being primary or secondary if there is underlying lung disease. Its incidence in pediatrics is variable, but it ismore common in thin, adolescent,male smokers. It is to be suspected in sudden dyspnea,with orwithout chest pain, and the diagnosis is confirmed and quantified by chest X-ray. Pediatric patients are treated in the same way as adults, there being no specific guidelines for the pathology in pediatrics. Depending on the extent of the pneumothorax, treatment may be conservative, administering oxygen and monitoring; removing the air with a chest tube through a minimal pleurotomy; or apicectomy and pleurodesis if other methods are unsuccessful. With conservative treatment there is a 40% chance of recurrence. We present the case of a male adolescent who presented with an extensive primary pneumothorax which did not resolve with conservative treatment and so was treated by video-assisted thorascopic apicoectomy and pleurodesis.

Apendicolitiasis: revisión y serie clínica / Appendicolithiasis: Review and case series report

La presencia de cálculos (coprolitos, fecalitos o apendicolitos) en el lumen del apéndice cecal se denomina apendicolitiasis. Es un hallazgo frecuente, especialmente en niños, sometidos a apendicectomía por apendicitis aguda. También puede ser un hallazgo imagenológico en el estudio de un paciente por otro motivo. Históricamente se ha postulado la relación causal con apendicitis, pero la literatura reciente postula que el factor obstructivo adjudicado al apendicolito pareciera asociarse solo a la presencia de complicaciones y no ser un elemento causal de apendicitis aguda. Hasta el momento, no existe evidencia suficiente para plantear un manejo estandarizado ante el hallazgo de apendicolitiasis en pacientes asintomáticos. Presentamos cuatro casos clínicos de pacientes con apendicolitiasis, todos los cuales consultaron por dolor abdominal, descartándose cuadro agudo y fueron sometidos a cirugía diferida. El examen histopatológico de nuestros pacientes demostró en todos, algún grado de inflamación apendicular, reafirmando la necesidad de someter a cirugía los pacientes con apendicolitiasis sintomática. Se realiza una revisión bibliográfica del tema y las diferentes opciones ante al hallazgo de un coprolito apendicular.

The presence of calculi (coproliths, fecaliths or appendicoliths) in the appendiceal lumen is refered to as appendicolithiasis. It is a common finding, especially in pediatric patients undergoing surgery for acute appendicitis. Appendicolithiasis can also be a finding in patients undergoing diagnostic imaging tests for other conditions. Historically a casual relation has been considered between appendicolithiasis and appendicitis, but recent literature shows that the presence of an appendicolith is associated with complications but it is not the cause of appendicitis. So far, there is not enough evidence supporting a standarized treatment for patients with asymptomatic appendicolithiasis. We present four clinical cases and a review of relevant literature.

Solution structure of the novel dispersin protein of enteroaggregative Escherichia coli.

Enteroaggregative Escherichia coli (EAEC), increasingly recognized as an important cause of infant and travelers' diarrhoea, exhibits an aggregative, stacked-brick pattern of adherence to epithelial cells. Adherence is mediated by aggregative adherence fimbriae (AAFs), which are encoded on the pAA virulence plasmid. We recently described a highly prevalent pAA plasmid-borne gene, aap, which encodes a protein (nicknamed dispersin) that is secreted to the bacterial cell surface. Dispersin-null mutants display a unique hyper-aggregating phenotype, accompanied by collapse of AAF pili onto the bacterial cell surface. To study the mechanism of this effect, we solved the structure of dispersin from EAEC strain 042 using solution NMR, revealing a stable beta-sandwich with a conserved net positive surface charge of +3 to +4 among 23 dispersin alleles. Experimental data suggest that dispersin binds non-covalently to lipopolysaccharide on the surface of the bacterium. We also show that the AAF organelles contribute positive charge to the bacterial surface, suggesting that dispersin's role in fimbrial function is to overcome electrostatic attraction between AAF and the bacterial surface.

Mal de Pott: a propósito de un caso

La tuberculosis continúa siendo un problema de salud pública a pesar de los múltiples esfuerzos realizados para su control. En Panamá, aunque con menor incidencia que en el adulto, se siguen presentando casos de tuberculosis infantil. Los datos son inespecíficos y existe baja probabilidad de recuperar el bacilo , por lo que el diagnóstico resulta difícil y debe basarse en una alta sospecha diagnóstica y nexo epidemiológico.

Tuberculosis remains a public health problem despite many efforts to control it. In Panama, although to a lesser extend than in adults, there continue to be cases of childhood tuberculosis. Clinical data are nonspecific and there is low probability of recovering the bacillus, so diagnosis is difficult and based on high diagnostic suspicion and epidemiological link.