Role of PumB antitoxin as a transcriptional regulator of the PumAB type-II toxin-antitoxin system and its endoribonuclease activity on the PumA (toxin) transcript.

The PumAB type-II toxin-antitoxin (TA) system is encoded by pumAB genes that are organized into an operon. This system is encoded by the pUM505 plasmid, isolated from a Pseudomonas aeruginosa clinical strain. The pumA gene encodes a putative RelE toxin protein (toxic component), whereas the pumB gene encodes a putative HTH antitoxin protein. The expression of the PumAB system in Escherichia coli confers plasmid stability. In addition, PumA toxin overexpression in P. aeruginosa possesses the capability to increase bacterial virulence, an effect that is neutralized by the PumB antitoxin. The aim of this study was to establish the mechanism of regulation of the PumAB toxin-antitoxin system from pUM505. By an in silico analysis of the putative regulatory elements, we identified two putative internal promoters, PpumB and PpumB-AlgU (in addition to the already reported PpumAB), located upstream of pumB. By RT-qPCR assays, we determined that the pumAB genes are transcribed differentially, in that the mRNA of pumB is more abundant than the pumA transcript. We also observed that pumB could be expressed individually and that its mRNA levels decreased under oxidative stress, during individual expression as well as co-expression of pumAB. However, under stressful conditions, the pumA mRNA levels were not affected. This suggests the negative regulation of pumB by stressful conditions. The PumB purified protein was found to bind to a DNA region located between the PpumAB and the pumA coding region, and PumA participates in PumB binding, suggesting that a PumA-PumB complex co-regulates the transcription of the pumAB operon. Interestingly, the pumA mRNA levels decreased after incubation in vitro with PumB protein. This effect was repressed by ribonuclease inhibitors, suggesting that PumB could function as an RNAse toward the mRNA of the toxin. Taken together, we conclude that the PumAB TA system possesses multiple mechanisms to regulate its expression, as well as that the PumB antitoxin generates a decrease in the mRNA toxin levels, suggesting an RNase function. Our analysis provides new insights into the understanding of the control of TA systems from mobile plasmid-encoded genes from a human pathogen.

Water consumption practices in university campuses. The experience of the National Autonomous University of Mexico.

The Water Network of the National Autonomous University of Mexico (Red del Agua UNAM) and the Program for the Management, Use, and Reuse of Water in UNAM (PUMAGUA) carried out a survey with the aim of knowing the water consumption practices of the university community in its campuses located in the Metropolitan Area of the Valley of Mexico. A sample of 2,095 students, academics, administrative and support staff participated in this survey. The results show that 74% of the sample consume bottled water and that their average spending is between 0.50 and 1 dollar per day (11 to 20 Mexican pesos). The rates of bottled water consumption contrasts with the perception about water quality, since only 13% consider water quality distributed in the water fountains located within university campuses as 'poor' or 'very poor'. The rates of bottled water consumption among university community are similar to the ones reported by studies in Mexico City and in Mexico as a whole, even though UNAM has a Water Observatory that allows people to know in real time water quantity and quality in university campuses.

Influence of the technique and comorbidities in hypofractionated radiotherapy for prostate cancer.

PURPOSE: To analyze the differences in toxicity and biochemical relapse-free survival with hypofractionated radiotherapy with three-dimensional radiotherapy (3D-CRT) or volumetric arc therapy (VMAT) for prostate cancer taking into account comorbidity measured using the Charlson Comorbidity Index (CCI). METHODS: From January 2011 to June 2016, 451 patients with prostate cancer were treated with 60 Gy (20 daily fractions). VMAT or 3D-CRT was used. Distribution by stage: 17% low-risk, 27.2% intermediate-risk; 39.2% high-risk, 16.6% very high-risk. Mean CCI was 3.4. RESULTS: With a median follow up of 51 months, most patients did not experience any degree of acute GI toxicity (80.9%) compared to 19.1%, who experienced some degree, mainly G-I /II. In the multivariate analysis, only technique was associated with acute GI toxicity ≥ G2. Patients treated with VMAT had greater acute GI toxicity compared with those who received 3D-CRT (23.9% vs. 13.5%, p = 0.005). With respect to acute GU toxicity, 72.7% of patients experienced some degree, fundamentally G-I/II. Neither age, CCI, nor androgen deprivation therapy (ADT) were associated with greater toxicity. Overall survival at 2, 5 and 7 years was 97%, 88% and 83% respectively. The only factor with statistical significance was CCI, with a greater number of events in individuals with a CCI ≥ 4 (p < 0.03). CONCLUSIONS: Hypofractionated radiotherapy for prostate cancer is an effective, well-tolerated treatment even for elderly patients with no associated comorbidity. Longer follow up is needed in order to report data on late toxicity.

[Residual ankle instability in patients with syndesmosis lesions without fracture treated with situational screws]. / Inestabilidad residual de tobillo en pacientes con lesión de la sindesmosis sin fractura tratados con tornillos situacionales.

INTRODUCTION: The lesion of the distal tibiofibular syndesmosis is commonly accompanied by the fracture of the maleollus either medial or lateral, rarely, the syndesmosis can be injured without there being a fracture of any of the bone structures that make up the ankle, accounting for about 1% of all injuries. Being very rare, they are not diagnosed at the acute event, and are usually treated as a simple sprained ankle. MATERIAL AND METHODS: Series of cases with ankle fractureless syndesmosis lesion, treated with situational double screw placement, deferred support and implant removal at two months. After six months of initial surgery, the Cumberland ankle instability (CAIT) test is applied which measures the degree of ankle instability. RESULTS: For one year, 4 cases of fractureless synosmosis lesions were found out of a total of 349 surgical cases treated in the hospital, exclusively in male patients, all under the age of 40. Six months after surgery, CAIT was applied, encountering residual instability in 100% of treated cases. DISCUSSION: This result is unencouraging and makes us reconsider the treatment established to improve the final stability of the ankle.

INTRODUCCIÓN: La lesión de la sindesmosis tibioperonea se presenta por lo regular acompañada de la fractura de los maléolos ya sea medial o lateral, muy rara vez la sindesmosis puede lesionarse sin que exista una fractura de alguna de las estructuras óseas que conforman el tobillo, representa alrededor de 1% de todas las lesiones. Al ser muy raras, no se diagnostican en el evento agudo y suelen tratarse como un simple esguince de tobillo. MATERIAL Y MÉTODOS: Serie de casos con lesión de la sindesmosis sin fractura de tobillo, tratadas con colocación de doble tornillo situacional, apoyo diferido y retiro de los implantes a los dos meses. Posteriormente, a los seis meses de la cirugía inicial se aplica el test de inestabilidad de tobillo de Cumberland (CAIT), el cual cuenta con nueve reactivos donde se mide el grado de inestabilidad del tobillo. RESULTADOS: Durante un año se detectaron cuatro casos de lesión de la sindesmosis sin fractura de un total de 349 casos quirúrgicos tratados en el hospital, exclusivamente en pacientes masculinos, todos ellos menores de 40 años. Seis meses después de la cirugía se aplicó el CAIT encontrando una inestabilidad residual en 100% de los casos tratados, algunos en mayor medida que los demás. DISCUSIÓN: Este resultado es poco alentador y nos hace reconsiderar el tratamiento establecido para mejorar la estabilidad final del tobillo.

[Prevalence of complications related to the removal of the syndesmotic screw]. / Prevalencia de las complicaciones relacionadas con el retiro del tornillo de situación.

BACKGROUND: Removal of the syndesmotic screw is a currently-disputed procedure. Most of the publications that promote avoid this procedure considered that the rate of complications is high. The aim of this work was to determine the rate of complications related to the removal of the syndesmotic screw to learn about the safety and compare the results with the international literature. MATERIAL AND METHODS: A descriptive, observational, retrospective and cross-sectional study in which took a sample of all cases operated of removal of the syndesmotic screw at our hospital from February 2015 January 2016 for the prevalence of the complications associated with this procedure. The statistical analysis was descriptive. RESULTS: A total of 207 patients were studied. Five patients with complications were observed (2.41%). Two cases with wound dehiscence, two cases with superficial infection (1.92%), and a case with subsequent diastasis of the syndesmosis, with pain associated to instability (0.48%) which required revision surgery. CONCLUSIONS: In the sample of our hospital, the prevalence of complications related to the syndesmotic screw removal was less than that reported in the literature so far; Thus we could say that is a safe procedure, with low risk for infection and post-traumatic instability of the ankle.

ANTECEDENTES: El retiro del tornillo de situación es un procedimiento actualmente cuestionado. La mayoría de las publicaciones que exhortan a evitar este procedimiento consideran que la tasa de complicaciones es elevada. El objetivo de este trabajo fue conocer la tasa de complicaciones relacionadas con el retiro del tornillo de situación para comprobar la seguridad del procedimiento y comparar los resultados con la literatura internacional. MATERIAL Y MÉTODOS: Se realizó un estudio descriptivo, observacional, retrospectivo y transversal en el cual se tomó una muestra de todos los casos operados de retiro de tornillo de situación en nuestro hospital de Febrero de 2015 a Enero de 2016 para obtener la prevalencia de las complicaciones relacionadas con este procedimiento. El análisis estadístico fue descriptivo. RESULTADOS: Se estudió un total de 207 pacientes. Se observaron cinco pacientes con complicaciones (2.41%). Dos casos con dehiscencia de la herida, dos casos con infección superficial (1.92%) y un caso con diástasis subsecuente de la sindesmosis con dolor asociado a inestabilidad (0.48%), el cual requirió de cirugía de revisión. CONCLUSIONES: En la muestra estudiada de nuestro hospital, la prevalencia de complicaciones relacionadas con el retiro del tornillo situacional fue menor que la reportada en la literatura hasta el momento; por ende, podríamos afirmar que es un procedimiento seguro, con una baja tasa de infección e inestabilidad postraumática del tobillo.

Análisis, por Simulación, de los Esfuerzos Cortantes en la Superficie del Iris, en Presencia de Lentes Fáquicos Intraoculares / Analysis, by Simulation, of shear stresses on the Surface of Iris, in Presence of Intraocular Factor Lenses

Resumen: En este estudio, se presenta una metodología para evaluar lentes fáquicos intraoculares, cuando el flujo del humor acuoso es asimétrico, debido a modificaciones en el área de salida del fluido. El objetivo es determinar el efecto que tienen las asimetrías del flujo del humor acuoso en el esfuerzo cortante sobre el iris y la córnea en presencia de un lente fáquico intraocular. Se considera la geometría del ojo propuesta por Repetto et al.,7 y se resuelve el flujo del humor acuso con y sin lente empleando simulaciones mediante el método de elemento finito. Para validar el método, se compara la solución numérica obtenida con los resultados de Tychsen et al.8 obteniendo valores del mismo orden. Los resultados obtenidos son perfiles de velocidad, líneas de corriente y esfuerzos cortantes en las superficies del iris y la córnea. El modelo no toma en cuenta las variaciones de la temperatura, por lo que no se consideran los efectos de flotación. Los resultados muestran que las asimetrías tienen un gran impacto en la dinámica del humor acuoso e incrementan los esfuerzos cortantes; sin embargo no son suficientes como para causar desprendimiento de las céluas del iris o de la córnea.

Abstract: The study presents a methodology to evaluate intraocular phakic lenses, considering asymmetric aqueous humor flow due to modified conditions of the fluid outlet area. The main objective is to determine the effect of asymmetries on shear stresses with and without phakik lenses. A finite element numerical simulation was developed using the eye geometry proposed by Repetto et al.6 The numerical method was tested with the results obtained by Tychsen et al.8, giving results of the same order of magnitude. Velocity profiles, pressure distribution and shear stress at the solid boundaries are shown. The model does not take into account temperature variations. Therefore no buoyancy effects were considered. The results show that the induced asymmetries have a significant impact on aqueous humor velocity and on shear forces; however the shear stresses are not sufficient to cause cell detachment so the lens can be considered as harmless.

Radiotherapy in soft-tissue sarcoma of the extremities.

Sarcomas are an infrequent and heterogeneous group of neoplasia. Surgery with or without associated radiotherapy (RT) is the basic treatment for this type of tumour. To increase the therapeutic ratio (the index between cytotoxic effects in tumours and normal tissue complications with a certain dose of radiation), new advances are being investigated to increase local and distant control and to decrease the morbidity of the treatment. The aim of this review was to analyse the different strategies, based on technology and biology, which are being investigated to increase the therapeutic ratio of this disease.

[Undetected traumatic posterior glenohumeral dislocation]. / Luxación glenohumeral posterior traumática no detectada.

INTRODUCTION: Glenohumeral dislocation (GHD) is frequent, but traumatic posterior glenohumeral dislocation (TPGHD) is rare, with an incidence of 1-4% of all GHD. The diagnosis is a challenge: sometimes, it can be omitted due to incorrect diagnosis, absence of consideration in the differential diagnosis, suboptimal radiographic evaluation and an absence of characteristic signs and symptoms; missed diagnosis reaches 60-79% and the diagnosis can delay from 24 hours to a year. OBJECTIVE: To transmit previous experiences to provide support for better diagnosing TPGHD, favoring appropriate attention. CASE REPORTS: Case 1. 34-year-old male. Delayed diagnosis of left TPGHD in the 4th week. Reverse Hill-Sachs < 25%. Closed reduction, immobilization for four weeks. Follow-up at week 20, good functional recovery (UCLA = 32). Case 2. 32-year-old male. Eight months with undiagnosed left TPGHD. Reverse Hill-Sachs 25%. Open reduction, immobilization for four weeks. Eight-month post-surgical follow-up. Good functional recovery (UCLA = 29). DISCUSSION: The diagnosis of TPGHD is difficult because of its lack of frequency. Even with delayed diagnosis-treatment, evolution can be favorable provided that the reverse Hill-Sachs injury is 25% or minor. To avoid a delayed diagnosis and inadequate attention, we must always consider the injury mechanism, physical examination with the arm fixed in internal rotation, clinical suspicion in functional deficit for external rotation, flexion and abduction, radiographic studies including true AP and scapula lateral (Y view).

INTRODUCCIÓN: La luxación glenohumeral (LGH) es frecuente, pero la luxación glenohumeral posterior traumática (LGHPT) es rara. Su diagnóstico es un reto, puede omitirse o pasar inadvertida; en ello influye un sinnúmero de factores, como una evaluación radiológica inadecuada y ausencia de signos-síntomas característicos. Se reporta una omisión diagnóstica de 60-79% y confirmación diagnóstica con una demora desde 24 horas hasta un año. OBJETIVO: Transmitir experiencia previa para proporcionar herramientas que ayuden a evitar omisión diagnóstica en la LGHPT. REPORTE DE CASOS: Caso 1. Masculino, 34 años. Diagnóstico tardío de LGHPT izquierda en la cuarta semana. Hill-Sachs inversa < 25%. Reducción cerrada (DePalma), inmovilización por cuatro semanas. Seguimiento a la semana 20. Recuperación funcional buena (UCLA = 32). Caso 2. Masculino, 32 años. Diagnóstico tardío de LGHPT izquierda en el octavo mes. Hill-Sachs inversa de 25%. Reducción abierta (McLaughlin-Neer), inmovilización por cuatro semanas. Seguimiento postquirúrgico a ocho meses. Recuperación funcional buena (UCLA = 29). DISCUSIÓN: El diagnóstico de LGHPT es difícil por su poca frecuencia. Para evitar retraso en el diagnóstico e inadecuada atención, debe considerarse siempre una evaluación inicial que tome en cuenta la posición del brazo, el mecanismo de lesión; en la exploración física, el brazo en rotacion interna y poco dolor, déficit funcional para la rotación externa, flexión y abducción.

Plasmid pUM505 encodes a Toxin-Antitoxin system conferring plasmid stability and increased Pseudomonas aeruginosa virulence.

Pseudomonas aeruginosa plasmid pUM505 possesses a pathogenicity island that contains the pumAB genes that encode products with sequence similarity to Toxin-Antitoxin (TA) modules. RT-PCR assays on the overlapping regions of the pumAB genes generated a bicistronic messenger RNA, suggesting that they form an operon. When the pumAB genes were cloned into the pJET vector, recombinant plasmid pJET-pumAB was maintained under nonselective conditions in Escherichia coli cells after six daily subcultures, whereas pJET without pumAB genes was lost. These data indicate that pumAB genes confer post-segregational plasmid stability. In addition, overexpression of the PumA protein in the E. coli BL21 strain resulted in a significant growth inhibition, while BL21 co-expressing the PumA and PumB proteins did not show growth inhibition. These results indicate that pumAB genes encode a TA system where the PumB protein counters the toxic effects of the PumA toxin. Furthermore, P. aeruginosa PAO1 transformants with the pumA gene increased Caenorhabditis elegans and mouse mortality rate and improved mouse organ invasion, effects neutralized by the PumB protein. Moreover, purified recombinant His-PumA protein decreased the viability of C. elegans, indicating that the PumA protein could acts as a toxin. These results indicate that PumA has the potential to promoter the PAO1 virulence against C. elegans and mice when is expressed in absence of PumB. This is the first description, to our knowledge, of a plasmid-encoded TA system that confers plasmid stability and encoded a toxin with the possible ability to increase the P. aeruginosa virulence.

Improving efficacy and efficiency through the implementation of a new organisational model in a Radiation Oncology Department.

BACKGROUND: To evaluate a new organisational model, "process management" (PM), implemented in the Hospital Universitario Virgen de la Victoria (HUVV) compared with traditional models used in other Radiation Oncology Departments (RODs), in terms of efficacy and efficiency. METHODS: The study period ranged from September 2011 to August 2012. Efficacy was assessed, comparing the number of patients attended in first consultation and treated per month, average waiting time from referral to first visit and average waiting time from first visit to treatment. Data were collected from two public hospitals in Andalusia: the HUVV and another Public Hospital in Andalusia (PHA1). Efficiency was assessed comparing the costs per patient attended in first visit and treated at HUVV in 2012 compared with those of a second Public Hospital in Andalusia (PHA2) for 2008. The number of sessions saved using hypofractionation versus classical schemes during the year 2012 in HUVV was estimated, and the money saved was calculated. RESULTS: In the efficacy analysis, we found significant differences in the average waiting time for first visit, start of treatment, and the number of patients seen and treated annually. After calculating the total cost generated in the ROD, the efficiency analysis showed a lower cost per patient attended in first visit (EUR 599.17) and per patient treated (EUR 783.50), with a saving of 6035 sessions using hypofractionated schemes. CONCLUSIONS: Process management in an ROD reduces time, both to first medical visit and to treatment initiation, allowing an optimisation of linear accelerator (LINAC) capacity.

Isolation of a conjugative F-like plasmid from a multidrug-resistant Escherichia coli strain CM6 using tandem shock wave-mediated transformation.

Genetic characterization of plasmids from bacterial strains provides insight about multidrug resistance. Ten wild type Escherichia coli (E. coli) strains isolated from cow fecal samples were characterized by their antibiotic resistance profile, plasmid patterns and three different identification methods. From one of the strains, a fertility factor-like plasmid was replicated using tandem shock wave-mediated transformation. Underwater shock waves with a positive pressure peak of up to approximately 40 MPa, followed by a pressure trough of approximately -19 MPa were generated using an experimental piezoelectric shock wave source. Three different shock wave energies and a fixed delay of 750 µs were used to study the relationship between energy and transformation efficiency (TE), as well as the influence of shock wave energy on the integrity of the plasmid. Our results showed that the mean shock wave-mediated TE and the integrity of the large plasmid (~70 kb) were reduced significantly at the energy levels tested. The sequencing analysis of the plasmid revealed a high identity to the pHK17a plasmid, including the replication system, which was similar to the plasmid incompatibility group FII. It also showed that it carried an extended spectrum beta-lactamase gene, ctx-m-14. Furthermore, diverse genes for the conjugative mechanism were identified. Our results may be helpful in improving methodologies for conjugative plasmid transfer and directly selecting the most interesting plasmids from environmental samples.

Concurrent radiotherapy plus epidermal growth factor receptor inhibitors in patients with human papillomavirus-related head and neck cancer.

PURPOSE: Concurrent radio-chemotherapy (RT-CT) is the standard treatment for locally advanced head and neck squamous cell carcinoma (LA-HNSCC), but RT plus epidermal growth factor receptor (EGFR) inhibitors is an effective option when CT is not appropriate. Human papillomavirus (HPV) is associated with an improved prognosis in LA-HNSCC; however, it has not been fully studied as a prognostic factor after RT + EGFR inhibitors. EXPERIMENTAL DESIGN: Immunohistochemical expression of p16INK4A and PCR of HPV16 DNA were retrospectively analyzed in tumor blocks from 52 stage III/IV LA-HNSCC patients treated with RT + EGFR inhibitors. Disease-free survival (DFS) and overall survival (OS) were analyzed by the Kaplan-Meier method. RESULTS: DNA of HPV16 was found in six of 52 tumors (12 %) and p16 positivity in eight tumors (15 %). After a median follow-up time of 45 months (6-110), p16-positive patients treated with RT + EGFR inhibitors showed an improved DFS (2-year DFS 75 vs. 44 %, HR 0.25, 95 % CI 0.06-0.99, p = 0.047) compared with p16-negative patients. These differences were outperformed when compared by HPV16 status (2-year OS rates of 83 vs. 58 %, HR 0.17, 95 % CI 0.02-0.99, p = 0.049 and 2-year DFS rates of 83 vs. 45 %, HR 0.17, 95 % CI 0.02-0.99, p = 0.049). In the Cox regression analysis with OS as the end point, ECOG 0-1 was the only prognostic factor independently associated with a good prognosis in the multivariable analysis. CONCLUSION: In this study, p16/HPV16-positive patients with LA-HNSCC treated with RT + EGFR inhibitors showed a better survival, not confirmed in multivariate analysis.

Immunohistochemical expression of cyclooxygenase-2 in patients with advanced cancer of the larynx who have undergone induction chemotherapy with the intention of preserving phonation.

INTRODUCTION: Cyclooxygenase-2 (COX2) is an enzyme that plays a role in different stages of the carcinogenic process and has prognostic and predictive values that have not yet been established. The objective of this study was to evaluate the role of COX2 overexpression in advanced squamous cell carcinoma of the larynx that has been treated with a phonation conservation protocol. MATERIALS AND METHODS: This study included a retrospective analysis of 59 patients with resectable tumours that were treated with chemotherapy (CT) and/or radiation therapy (RT). The expression levels of COX2, epidermal growth factor receptor (EGFR), vascular endothelial growth factor (VEGF), and vascular endothelial growth factor receptor (VEGFR-2) in collected biopsy specimens were determined via immunohistochemistry. RESULTS: Forty-four percent of the included samples demonstrated overexpression of COX2. In the statistical analysis, COX2 overexpression did not correlate with other clinical or treatment efficacy prognostic factors; however, the median global survival (OS) of patients whose tumours expressed COX2 was 79 months, whereas COX2-negative patients had a median OS of only 38 months, although this finding did not reach statistical significance. The other analysed biological parameters did not demonstrate a significant relationship with COX2. CONCLUSIONS: COX2 overexpression was a common finding in our study. The results obtained did not reveal relationships with established prognostic categories; however, the difference in survival between patients with and without COX2 expression justifies the need for future prospective studies that utilise a larger patient sample size.

Genetic Diversity and Geographical Distribution of Phytoplasmas Associated with Potato Purple Top Disease in Mexico.

Potato purple top (PPT) disease has caused severe economic losses in some potato (Solanum tuberosum) growing areas of Mexico. Two distinct phytoplasma strains belonging to the aster yellows and peanut witches'-broom groups (16SrI and 16SrII groups) have been associated with PPT disease in several regions of Mexico. However, there has been no previous large-scale survey in the main potato growing areas in Mexico to analyze the diversity and geographical distribution of phytoplasmas. Potato samples were collected between 2003 and 2006 and were analyzed by nested polymerase chain reaction assays. On the basis of results from nucleotide sequence comparisons and virtual restriction fragment length polymorphism analysis of 16S rDNA, four different phytoplasma groups were detected in potato growing areas in Mexico. The aster yellows group (16SrI) 'Candidatus Phytoplasma asteris' was distributed in all potato growing areas, whereas peanut witches'-broom group (16SrII) 'Candidatus Phytoplasma aurantifolia' was detected in Guanajuato and Sinaloa, X-disease group (16SrIII) was detected in Coahuila and Guanajuato, and the Mexican periwinkle virescence (16SrXIII) was only detected in Sinaloa. Phytoplasmas from X-disease and Mexican periwinkle virescence groups were detected in potato samples for the first time in Mexico.

Detection and Molecular Characterization of Two Little Leaf Phytoplasma Strains Associated with Pepper and Tomato Diseases in Guanajuato and Sinaloa, Mexico.

Pepper (Capsicum annuum) and tomato (Lycopersicon esculentum) are important vegetable crops in Mexico. Recently, symptoms associated with phytoplasma diseases such as witches'-broom (shoot proliferation) and little leaf were observed in pepper and tomato fields in central and northwestern Mexico. DNA extracted from symptomatic and asymptomatic plants was used in nested polymerase chain reaction (PCR) assays with primers amplifying 16S rDNA sequences for phytoplasmas. Twenty-four percent of pepper and 49% of tomato samples yielded a nested rDNA product of 1.25 kb. Restriction fragment length polymorphism profiles and sequencing of PCR products allowed classification of the detected phytoplasmas with the aster yellows group (16SrI). Both phytoplasmas, pepper little leaf (PeLL) and tomato little leaf (ToLL), could be included as new members of the aster yellows group because HaeIII and TaqI restriction enzymes discriminated among these phytoplasmas and members of other 16SrI subgroups. PeLL and ToLL phytoplasma sequences were deposited and compared with those in GenBank, and the maximum identity was found with several isolates of 'Candidatus Phytoplasma asteris'. The highest identity (99%) has been observed with tomatillo little leaf phytoplasma and ash witches'-broom phytoplasma. This is the first report of 'Ca. Phytoplasma asteris' associated with pepper and tomato diseases in the Mexican states of Guanajuato and Sinaloa.