Relación entre ausencia de células endocervicales y citología Papanicolaou negativa en portadoras de lesiones escamosas premalignas de cuello uterino

Objetivo : Determinar la relación entre la ausencia de células endocervicales y resultados citológicos Papanicolaou falsos negativos. Material y métodos : Estudio observacional, de enfoque cuantitativo, transversal, relacional y retrospectivo realizado en el Servicio de Anatomía Patológica del Hospital General de Huacho. Se realizó la búsqueda de resultados de biopsias de cuello uterino positivos para lesiones intraepiteliales escamosas y sus respectivos resultados citológicos Papanicolaou previos durante los años 2016 al 2018. Se seleccionó los resultados negativos con ausencia de células endocervicales. Resultados : De los 158 resultados citológicos, 23 mostraron ausencia de células endocervicales y de éstos, sólo dos (8,7%) fueron reportados como negativos. En total 11 (7%) citologías fueron negativas. Conclusiones : No se encontró relación entre la ausencia de células endocervicales y resultados citológicos falsos negativos; por tanto, no influyó de manera significativa en la detección de lesiones escamosas premalignas de cuello uterino.

SUMMARY Objective : To determine the relationship between absence of endocervical cells and false negative Pap smears in patients with squamous premalignant cervix lesions. Methods : A cross sectional study was carried out at Servicio de Anatomía Patológica del Hospital General de Huacho. A search for positive cervix biopsies for squamous intraepithelial lesions and their Pap smears from 2016 to 2018 was done. Negative Pap smears with absence of endocervical cells were investigated. Results : 23 out of 158 cytology results showed absence of endocervical cells, only two (8.7%) were reported negative. Eleven cytologies were negative (7%). Conclusions : No relationship was found between absence of endocervical cells and false negative results at Pap smears. Therefore, no influence in the detection of squamous pre-malignant cells was found.

Mafosfamide, a cyclophosphamide analog, causes a proinflammatory response and increased permeability on endothelial cells in vitro.

Post-transplantation cyclophosphamide (PTCy) has decreased GVHD incidence. Endothelial damage in allo-HCT is caused by multiple factors, including conditioning treatments and some immunosupressants, and underlies HCT-complications as GVHD. Nevertheless, the specific impact of PTCy on the endothelium remains unclear. We evaluated the effect of mafosfamide (MAF), an active Cy analog, on endothelial cells (ECs) vs. cyclosporine A (CSA), with known damaging endothelial effect. ECs were exposed to MAF and CSA to explore changes in endothelial damage markers: (i) surface VCAM-1, (ii) leukocyte adhesion on ECs, (iii) VE-cadherin expression, (iv) production of VWF, and (v) activation of intracellular signaling proteins (p38MAPK, Akt). Results obtained (expressed in folds vs. controls) indicate that both compounds increased VCAM-1 expression (3.1 ± 0.3 and 2.8 ± 0.6, respectively, p < 0.01), with higher leukocyte adhesion (5.5 ± 0.6, p < 0.05, and 2.8 ± 0.4, respectively). VE-cadherin decreased with MAF (0.8 ± 0.1, p < 0.01), whereas no effect was observed with CSA. Production of VWF augmented with CSA (1.4 ± 0.1, p < 0.01), but diminished with MAF (0.9 ± 0.1, p < 0.05). p38MAPK activation occurred with both compounds, being more intense and faster with CSA. Both drugs activated Akt, with superior MAF effect at longer exposure. Therefore, the cyclophosphamide analog MAF is not exempt from a proinflammatory effect on the endothelium, though without modifying the subendothelial characteristics.

Acute Abdomen and Appendicitis in 1010 Pediatric Patients With COVID-19 or MIS-C: A Multinational Experience from Latin America.

BACKGROUND: To date, there are only sporadic reports of acute abdomen and appendicitis in children with coronavirus disease 2019 (COVID-19) and multisystem inflammatory syndrome in children (MIS-C). METHODS: Children 17 years of age or younger assessed in 5 Latin American countries with a diagnosis of microbiologically confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and children fulfilling MIS-C definition were included. For children with acute abdomen, we investigate main radiologic patterns, surgical treatment and intraoperative findings, outcomes. FINDINGS: One-thousand ten children were enrolled. Forty-two children (4.2%) had a clinical diagnosis of acute abdomen. Four (9.5%) were diagnosed with MIS-C and did not undergo surgery. The remaining 38 children (3.8%) underwent abdominal surgery due to suspected appendicitis, 34 of them (89.7%) had an intraoperative diagnosis of acute appendicitis (AA), while 4 of them had nonsurgical findings. Eight children died (0.8%), none of them being diagnosed with appendicitis. Children with AA were significantly older than those without (P < 0.0001). Children with complicated appendicitis had more frequently fever (85.7% vs. 60%), intestinal distension on the abdominal radiograph (7.1% vs. none), leukocytosis (85.7% vs. 40%) and high levels of C-reactive protein (35.7% vs. 5%), although differences were not statistically significant. CONCLUSIONS: Our study showed that children may present with acute abdomen during COVID-19 or MIS-C, which is not always associated with intraoperative findings of appendicitis, particularly in case of MIS-C. Further studies are needed to better characterize children with acute abdomen during COVID-19 or MIS-C, to avoid delay in diagnosis of surgical conditions and at the same time, minimize unnecessary surgical approaches.

Paediatric snakebite envenoming: recognition and management of cases.

Snakebite in children can often be severe or potentially fatal, owing to the lower volume of distribution relative to the amount of venom injected, and there is potential for long-term sequelae. In the second of a two paper series, we describe the pathophysiology of snakebite envenoming including the local and systemic effects. We also describe the diagnosis and management of snakebite envenoming including prehospital first aid and definitive medical and surgical care.

Intervalos de referencia para 25-hidroxivitamina D en población autóctona y aparentemente sana de Yucatán / Reference values for 25-hydroxy-vitamin D in a native and apparently healthy population from Yucatan, Mexico

Introducción: La 25-hidroxivitamina D [25(OH)D] se considera un marcador del estado general de salud y su deficiencia es un problema a nivel mundial. En la actualidad no existe un consenso para definir sus niveles óptimos, siendo necesario establecerlos para cada población de acuerdo con sus características étnicas y factores ambientales a los que está expuesta. Objetivo: Determinar los intervalos de referencia para 25(OH)D en población autóctona y aparentemente sana de Yucatán. Métodos: Se estudiaron 71 voluntarios aparentemente sanos, de uno u otro sexo, de uno a 65 años, originarios y residentes en Yucatán. Se determinaron los niveles séricos de 25(OH)D, así como los de calcio, fósforo y paratohormona por su relación con el metabolismo de la vitamina D. Los intervalos de referencia se calcularon con los métodos paramétrico y consistente. Se registró el fototipo de piel y se aplicó el test de Garabédian para determinar el consumo diario de calcio y vitamina D. Resultados: El valor medio de 25(OH)D fue de 23,49±5,60ng/mL. Los límites de referencia para 25(OH)D total y por sexos fueron más estrechos y significativamente diferentes a los propuestos por el fabricante. Se encontró correlación directa entre los niveles de 25(OH)D y el calcio sérico (r=0,36; p=0,003) e inversa con la paratohormona intacta (r=−0,44; p<0,001). Una dieta rica en calcio y vitamina D no es suficiente para mantener los requerimientos normales de 25(OH)D en esta población. Conclusiones: Los intervalos de referencia propuestos están adecuados a las peculiaridades de la población de Yucatán, y pudieran mejorar la exactitud de la medición del estado de salud con base en los niveles séricos de vitamina D

Introduction: 25-hydroxyvitamin D [25(OH)D] is considered a marker of general health and its deficiency is a problem worldwide. There is still no consensus to define their optimal levels, with it being necessary to establish them for each population according to their ethnic characteristics and environmental factors to which they are exposed. Objective: To determine the reference intervals for 25(OH)D in the native and apparently healthy population of Yucatan. Methods:The study included 71 apparently healthy volunteers, female and male, between one and 65 years old, and originally from Yucatan. Serum levels of 25(OH)D were measured along with the determination of calcium, phosphorus, and parathormone levels due to their relationship with vitamin D metabolism. Reference intervals were calculated using parametric and robust methods. The skin phototype was recorded and the Garabedian test was applied to determine the daily intake of calcium and vitamin D. Results: The mean value of 25(OH)D was 23.49±5.60ng/mL. The reference limits for total and gender-related 25(OH)D, and by gender were narrower and significantly different from those proposed by the manufacturer. A direct correlation was found between 25(OH)D levels and serum calcium (r=0.36; P=.003) and an inverse one with intact parathormone (r=−0.44; P<.001). A diet rich in calcium and vitamin D is not sufficient to maintain the normal requirements of 25(OH)D in this population. Conclusions: The proposed reference intervals are adequate to the peculiarities of the population of Yucatan and could improve the accuracy of health status measurement based on serum levels of vitamin D

Análisis de epistasia de polimorfismos de genes metabólicos asociados a cardiopatía isquémica en Yucatán / Epistasis analysis of metabolic genes polymorphisms associated with ischemic heart disease in Yucatan

Objetivo: La epistasia es un tipo de interacción genética que podría explicar gran parte de la variabilidad fenotípica que muestran las enfermedades complejas. En este trabajo se determinó el efecto de la epistasia de genes metabólicos y los factores de riesgo cardiovascular en la susceptibilidad al desarrollo de cardiopatía isquémica en Yucatán. Métodos: Estudio de casos y controles en 79 pacientes yucatecos con cardiopatía isquémica y 101 controles sanos pareados por edad y origen con los casos. Se genotipificaron los polimorfismos -108CT, Q192R, L55M (paraoxonasa 1, PON1), C677T, A1298C (5,10 metilentetrahidrofolato reductasa, MTHFR) y la presencia/ausencia del gen glutatión S-transferasa T1 (GSTT1). El análisis de epistasia se realizó con el método de reducción dimensional multifactorial (MDR). El mejor modelo de predicción de riesgo se seleccionó con base en la precisión (%), la significación estadística (p < 0,05) y la consistencia de la validación cruzada. Resultados: Se encontró asociación independiente del genotipo nulo GSTT1*0/0 (OR = 3,39; IC: 1,29-8,87; p = 0,017) y el alelo nulo (OR = 1,86; IC: 1,19-2,91; p = 0,007) con la cardiopatía isquémica. La deleción GSTT1*0 y el genotipo 677TT (MTHFR) se identificaron de alto riesgo cardiovascular, mientras que el genotipo silvestre GSTT1*1 y la variante CC677 se clasificaron de bajo riesgo. La interacción gen-ambiente identificó al gen GSTT1, al polimorfismo C677T (MTHFR) y a la hipertensión arterial como los factores que mejor explican la cardiopatía isquémica en la población estudiada. Conclusiones: La interacción de los genes GSTT1 y MTHFR conjuntamente con la hipertensión arterial puede constituir un modelo de predicción de riesgo para el inicio temprano de cardiopatía isquémica en la población de Yucatán

Objective: Epistasis is a type of genetic interaction that could explain much of the phenotypic variability of complex diseases. In this work, the effect of epistasis of metabolic genes and cardiovascular risk on the susceptibility to the development of ischemic heart disease in Yucatan was determined. Methods: Case-control study in 79 Yucatecan patients with ischemic heart disease and 101 healthy controls matched by age and origin with cases. The polymorphisms -108CT, Q192R, L55M (paraoxonase 1; PON1), C677T, A1298C (methylenetetrahydrofolate reductase; MTHFR), and the presence/absence of the glutathione S-transferase T1 (GSTT1) gene were genotyped. Epistasis analysis was performed using the multifactorial dimensional reduction method. The best risk prediction model was selected based on precision (%), statistical significance (P<0.05), and cross-validation consistency. Results: We found an independent association of the null genotype GSTT1*0/0 (OR=3.39, CI: 1.29-8.87, P=0.017) and the null allele (OR=1.86, CI: 1.19-2.91, P=0.007) with ischemic heart disease. The GSTT1*0 deletion and the 677TT genotype (MTHFR) were identified as being at a high cardiovascular risk, whereas the GSTT1*1 wild type genotype and the CC677 variant were at low risk. The gene-environment interaction identified the GSTT1 gene, C677T polymorphism (MTHFR), and hypertension as the factors that best explain ischemic heart disease in the study population. Conclusions: The interaction of the MTHFR, GSTT1 and hypertension may constitute a predictive model of risk for early onset ischemic heart disease in the population of Yucatan

Epistasis analysis of metabolic genes polymorphisms associated with ischemic heart disease in Yucatan. / Análisis de epistasia de polimorfismos de genes metabólicos asociados a cardiopatía isquémica en Yucatán.

OBJECTIVE: Epistasis is a type of genetic interaction that could explain much of the phenotypic variability of complex diseases. In this work, the effect of epistasis of metabolic genes and cardiovascular risk on the susceptibility to the development of ischemic heart disease in Yucatan was determined. METHODS: Case-control study in 79 Yucatecan patients with ischemic heart disease and 101 healthy controls matched by age and origin with cases. The polymorphisms -108CT, Q192R, L55M (paraoxonase 1; PON1), C677T, A1298C (methylenetetrahydrofolate reductase; MTHFR), and the presence/absence of the glutathione S-transferase T1 (GSTT1) gene were genotyped. Epistasis analysis was performed using the multifactorial dimensional reduction method. The best risk prediction model was selected based on precision (%), statistical significance (P<0.05), and cross-validation consistency. RESULTS: We found an independent association of the null genotype GSTT1*0/0 (OR=3.39, CI: 1.29-8.87, P=0.017) and the null allele (OR=1.86, CI: 1.19-2.91, P=0.007) with ischemic heart disease. The GSTT1*0 deletion and the 677TT genotype (MTHFR) were identified as being at a high cardiovascular risk, whereas the GSTT1*1 wild type genotype and the CC677 variant were at low risk. The gene-environment interaction identified the GSTT1 gene, C677T polymorphism (MTHFR), and hypertension as the factors that best explain ischemic heart disease in the study population. CONCLUSIONS: The interaction of the MTHFR, GSTT1 and hypertension may constitute a predictive model of risk for early onset ischemic heart disease in the population of Yucatan.

Prevalencia de infecciones de transmisión sexual en pacientes sintomáticos y asintomáticos de Yucatán / Prevalence of sexually transmitted infections in symptomatic and asymptomatic patients from Yucatan

Introducción. Los datos epidemiológicos sobre infecciones de transmisión sexual (ITS) no virales en Yucatán son limitados y provienen de pruebas serológicas. Material y métodos. Estudio retrospectivo para estimar la prevalencia de ITS no virales en pacientes de Yucatán utilizando un método molecular. Se tomaron muestras urogenitales en 147 pacientes (53 hombres y 94 mujeres) para la extracción de los ácidos nucleicos. Se utilizó la reacción en cadena de la polimerasa en tiempo real para la detección simultánea de Chlamydia trachomatis, Neisseria gonorrhoeae, Mycoplasma genitalium, Mycoplasma hominis, Ureaplasma urealyticum, Ureaplasma parvum y Trichomonas vaginalis. El análisis estadístico se realizó con el test exacto de Fisher. Resultados. La prevalencia de ITS fue de 45,6%. Ureaplasma spp. fue el patógeno más frecuente y el sexo femenino el más afectado (p=0,022). Se detectó un 12,2% de coinfecciones con mayor frecuencia en mujeres (16,0 vs. 3,7%, p=0,035). No se encontraron diferencias significativas entre los pacientes sintomáticos (n=138) con reacción en cadena de la polimerasa positivo (n=64) y negativo (n=74). Las mujeres entre 21-40 años fueron las más expuestas a ITS (p <0,05). Conclusiones. Estos datos confirman la alta prevalencia de ITS no virales en Yucatán, siendo el primer reporte epidemiológico aplicando un método molecular (AU)

Introduction. Epidemiological data about non-viral sexually transmitted infections (STI) in Yucatan are limited and come from serological methods. Material and methods. Retrospective study to estimate the prevalence of STI in symptomatic and asymptomatic patients from Yucatan based on a molecular method. The urogenital samples were taken from 147 patients (53 men and 94 women) to extracted nucleic acids. Real-time polymerase chain reaction was used to simultaneous detection of Chlamydia trachomatis, Neisseria gonorrhoeae, Mycoplasma genitalium, Mycoplasma hominis, Ureaplasma urealyticum, Ureaplasma parvum y Trichomonas vaginalis. Statistical analysis was performed with the Fisher's exact test. Results. The prevalence of STIs was 45.6%. Ureaplasma spp. was the pathogen most frequent and the females the most affected (p=.022). It was detected 12.2% of coinfections being more frequent in women (16.0 vs. 3.7%, p=.035). No significant differences were found between symptomatic patients (n=138) with positive polymerase chain reaction (n=64) and negative (n=74). Women 21-40 years were the most exposed to STIs (p<.05). Conclusions. These data confirm the high prevalence of non-viral STIs in Yucatán, being the first epidemiological report based on a molecular method (AU)

Toxocariosis humana en el Perú: aspectos epidemiológicos, clínicos y de laboratorio / Human toxocariasis: epidemiology, clinical and laboratory aspects

Toxocariosis es una infección causada por larvas de nemátodos del género Toxocara siendo T. canis o Toxocara cati, nemátodos del perro y gato respectivamente, los más importantes para el ser humano. Las especies del Género Toxocara pertenecen a la orden Ascaridida, superfamilia Ascaridiodea, familia Toxocaridae. La enfermedad es ocasionada principalmente por T. canis. La toxocariosis humana fue descrita por primera vez por Wilder en 1950, quien identificó un nemátodo de especie desconocida en un granuloma de retina de un niño. En 1952, Beaver reportó casos de una enfermedad multisistémica, crónica y severa, asociada a hipereosinofilia . En el Perú, en 1991, Maguiña y col reportaron los primeros casos de Larva migrans visceral y en 1999, Miranda y col, reportaron los primeros casos de Larva migrans ocular.

Toxocariasis is an infection caused by nematode larvae from Toxocara genus, and the most important infective agents for humans are Toxocara canis and Toxocara cati, parasites from dogs and cats, respectively. Toxocara species belong to Ascaridida order, Ascaridodea super-family, Toxocaridae family. The disease in humans is mainly caused by T. canis. Human toxocariasis was described for the .rst time by Wilder in 1950, who identi.ed a then-unknown nematode in a child presenting with a granulomatous lesion in one of his eyes. In 1952, Beaver reported cases of a multi-systemic, chronic, and sever disease, associated to hypereosinophilia. In Peru, in 1991, Maguiña et al. reported the very. rst cases of visceral larva migrans, and in 1999, Miranda et al. reported the very .rst cases of ocular larva migrans.

Validez del tacto materno en el reconocimiento de fiebre en niños menores de 36 meses / Validity of maternal palpation in the detection of fever in children under 36 months

Objetivo: Determinar la validez del tacto materno como método de detección de la presencia o no de fiebre en los niños. Material y métodos: Se seleccionaron por conveniencia a 269 madres y sus respectivos niños menores de 36 meses que acudieron al Servicio de Emergencias Pediátricas del Hospital Nacional Cayetano Heredia por cualquier molestia. Se preguntó a las madres si su niño presentaba fiebre o no (detectado por tacto), y luego se procedió con la medición de la temperatura rectal de cada niño. Resultados: Se incluyeron 269 participantes. El tacto materno para la detección de fiebre tuvo una sensibilidad de 79,3% (69,6% a 86,5%), especificidad 91,8% (86,8% a 94,9%), VPP 82,1% (72,6% a 88,9%) y VPN 90,3% (85,1% a 93,8%); el likelihood ratio positivo fue 9,62 (5,86 a 15,81) y el likelihood ratio negativo fue 0,23 (0,15 a 0,34). La correlación (índice Kappa) de fiebre o no fiebre determinada por la madre y la medida por termómetro fue de 0,72 (p:0,0000). Conclusiones: Las madres tienen una buena capacidad discriminativa en la determinación de la presencia o ausencia de fiebre mediante la palpación, por lo que la detección de fiebre por tacto materno es un eficiente método de despistaje.

Objective: To determine how valid is the maternal palpation as a screening method to determine the presence or absence of fever in children. Material and methods: We selected for convenience 269 mothers and their children under 36 months, who attended the Pediatric Emergency Service of Hospital Nacional Cayetano Heredia for any complaint. Then, we asked the mothers if their child had fever or not (detected by palpation), and then we proceeded with the rectal temperature measurement of each child. Results: We included 269 participants. The maternal palpation for the detection of fever had a sensitivity of 79% (69.6% to 86.5%), specificity 91.7% (86.8% to 94.9%), PPV 82.1% (72.6% to 88.9%) and NPV 90.3% (85.1% to 93.8%); the positive likelihood ratio was 9.62 (5.86 to 15.81) and the negative likelihood ratio was 0.23 (0.15 to 0.34). The correlation (Kappa index) of fever or absence of fever determinated for the mother and thermometer was 0.72 (p:0.0000). Conclusions: Mothers have a well accuracy in determining the presence or absence of fever by palpation, therefore detection of fever by palpation is an efficient screening method.

Los consultores en línea con relación a su situación laboral

Menciona que a partir del año 2005, dentro de los servidores públicos se crea una figura híbrida, se trata de trabajadores que realizan exactamente las mismas funciones de servidores públicos en un cargo de línea, sin embargo estos son contratados bajo la modalidad de consultores estando la prestación de los servicios que presta sujeta únicamente a un contrato administrativo eventual

Sensibilidad antibiótica de Streptococcus pneumoniae en portadores nasofaríngeos en niños sanos menores de un año en Lima, Perú / Antibiotic susceptibility of Streptococcus pneumoniae in nasopharyngeal carriers in healthy children younger than one year of age in Lima, Peru

Introducción: el neumococo es causa importante de morbi-mortalidad en niños en países en vías de desarrollo. En los últimos años han aparecido a nivel mundial cepas de neumococo resistentes a penicilina y a otros antibióticos utilizados frecuentemente en pediatría. A nivel local hay pocos estudios recientes que describen este problema. Objetivo: el objetivo principal del estudio fue determinar el porcentaje de resistencia antibiótica del neumococo en portadores nasofaríngeos en niños sanos entre dos meses y un año en los Consultorios de Crecimiento y Desarrollo y/o Vacunación de los hospitales Cayetano Heredia, Edgardo Rebagliati, San Bartolomé e Instituto Nacional de Salud del Niño en Lima, Perú. Materiales y métodos: se tomaron muestras de hisopado nasofaríngeoen 400 niños (noviembre 2007-junio 2008) para cultivo de neumococo y determinación de su sensibilidad a la penicilina y a otros antibióticos con la prueba de sensibilidad en disco. Resultados: se encontró 28 por ciento (111/400) de portadores nasofaríngeos de neumococo. De las 111 cepas aisladas, 60 (55 por ciento) fueron resistentes a cotrimoxazol, 52 (47 por ciento) a penicilina y 30 (35 por ciento) a azitromicina. No se encontró ninguna asociación entre los factores estudiados y la condición de portador y/o resistencia antibiótica. Conclusión: la resistencia del neumococo al cotrimoxazol y a la penicilina fue alta. Sin embargo, se necesita completar el estudio con la determinación de la concentración inhibitoria mínima para poder usar los nuevos puntos de corte para penicilina para cepas no-meníngeas. Con estos nuevos criterios es muy probable que la penicilina continúe siendo la droga de elección para infecciones no severas fuera del sistema nervioso central.

Introducction: Pneumococcus is a major cause of morbidity and mortality in children in developing countries. Over the last few years, pneumococcal strains resistant to penicillin and other antibiotics commonly used in pediatrics have emerged. There are few recent local studies that describe this problem. Objectives: The main purpose of the study was to determine the pneumococcal resistance rates in healthy nasopharyngeal carriers 2 to12 months of age, who attended the outpatient clinic for a routine well child and/or vaccination visit at Cayetano Heredia, Edgardo Rebagliati, San Bartolomé Hospitals and Instituto Nacional de Salud del Niño in Lima-Peru. Methods: Nasopharyngeal samples were obtained from 400 children (November 2007-June 2008) for S. pneumoniae culture and determination of the susceptibility to penicillin and other antibiotics by disk diffusion. Results: The pneumococcal carriage rate was 28 per cent (111/400). From the 111 strains isolated, 60 (55 per cent) were resistant to cotrimoxazole, 52 (47 per cent) to penicillin and 30 (35 per cent) to azythromycin. We did not find any association between the factors analyzed and the carrier state and/or antibiotic resistance. Conlusions: We found high resistance rates of pneumococcus to cotrimoxazole and penicillin. However, this study needs to be complemented with minimal inhibitory concentrations in order to use the new penicillin breakpoints for non-meningeal strains. With the new breakpoints, it is likely that penicillin will continue to be the drug of choice for non-severe infections outside the central nervous system.

Regulation of Aggregatibacter (Actinobacillus) actinomycetemcomitans leukotoxin secretion by iron.

The gram-negative oral and systemic pathogen Aggregatibacter (Actinobacillus) actinomycetemcomitans produces a leukotoxin (LtxA) that is a member of the RTX (repeats in toxin) family of secreted bacterial toxins. We have recently shown that LtxA has the ability to lyse erythrocytes, which results in a beta-hemolytic phenotype on Columbia blood agar. To determine if LtxA is regulated by iron, we examined beta-hemolysis under iron-rich and iron-limiting conditions. Beta-hemolysis was suppressed in the presence of FeCl3. In contrast, strong beta-hemolysis occurred in the presence of the iron chelator deferoxamine. We found that secretion of LtxA was completely inhibited by free iron, but expression of ltxA was not regulated by iron. Free chromium, cobalt, and magnesium did not affect LtxA secretion. Other LtxA-associated genes were not regulated by iron. Thus, iron appears to play an important role in the regulation of LtxA secretion in A. actinomycetemcomitans in a manner independent of gene regulation.

Characterization of leukotoxin from a clinical strain of Actinobacillus actinomycetemcomitans.

Actinobacillus actinomycetemcomitans is a Gram negative pathogen that is the etiologic agent of localized aggressive periodontitis (LAP), a rapidly progressing and severe disease of the oral cavity that affects predominantly adolescents. A. actinomycetemcomitans is also found in extraoral infections including infective endocarditis. As one of its many virulence determinants, A. actinomycetemcomitans produces the RTX (repeats in toxin) exotoxin, leukotoxin (LtxA). LtxA specifically kills leukocytes of humans and Old World Monkeys. All of our current knowledge of A. actinomycetemcomitans LtxA is based on the protein from strain JP2, a nonadherent laboratory isolate. Because laboratory isolates can lose virulence properties, we wished to examine LtxA from a clinical isolate, NJ4500. We show that localization patterns of LtxA do not differ between the strains. Subcellular localization studies with NJ4500 revealed that LtxA localizes to the outer membrane and that the interaction between LtxA and the surface of cells is specific. Surface localized LtxA was not removed with NaCl treatment and protease protection experiments revealed that approximately 10 kDa of LtxA is exposed. We purified secreted LtxA from NJ4500 and found that the specific activity of this toxin was greater than that of secreted LtxA from JP2. For other RTX toxins, fatty acid modification affects toxin activity, and A. actinomycetemcomitans LtxA is predicted to be modified. We show by two-dimensional gel electrophoresis that NJ4500 LtxA is more highly modified than JP2 LtxA, suggesting that the difference in activities could be due to differential modification. Studies of A. actinomycetemcomitans pathogenesis should therefore consider LtxA from clinical isolates.