Thymine adsorption on two-dimensional boron nitride structures: first-principles studies.

First-principles total-energy calculations were performed to investigate the structural and electronic properties of thymine (T) adsorption on pristine and Al-doped two-dimensional hexagonal boron nitride (2D-hBN) surfaces. Periodic density functional theory, as developed in the PWscf code of the quantum espresso package, was applied. The pseudopotential theory was used to deal with electron-ion interactions. The generalized gradient approximation was applied to treat the exchange-correlation energies. Van der Waals interactions were incorporated in the calculations. Considering T as an elongated molecule and the interactions through one oxygen atom of the molecule ring, two geometries were explored in pristine and Al-doped systems: in (1) the ring side O interacts with B, and (2) the O at the molecule end interacting with the B. The pristine case yields (4 × 4-a), (5 × 5-b) and (6 × 6-b) as the ground states, , while the doped system shows (4 × 4-a), (5 × 5-a) and (6 × 6-a) as the ground states. Calculations of the adsorption energies indicate chemisorption. Doping enhances the surface reactivity, inducing larger binding energies. The total density of states (DOS) was calculated and interpreted with the aid of the projected DOS. Below the Fermi energy, the DOS graphs indicate that p orbitals make the largest contributions. Above the Fermi level, the DOS is formed mainly by -s and H-s orbitals. The DOS graphs indicate that the structures have non-semiconductor behavior.

Levels and enterotoxigenicity of Clostridium perfringens in pozole, tamales, and birria.

A quantitative survey of Clostridium perfringens in typical foods served at local restaurants was conducted for 18 months in Guadalajara, Mexico. A total of 151 samples, including goat's birria (50), pozole (50), and beef tamales (51), were collected from small restaurants in Guadalajara. Samples were tested for C. perfringens by the most probable number (MPN) method and for mesophilic aerobic plate counts (MAPCs) and coliform, yeast, and mold counts by plate count methods. Isolates confirmed as C. perfringens were further sporulated and tested for cytotoxic or cytotonic effect against Vero cells as an indication of enterotoxin production. C. perfringens was detected in 78 (52%) of all samples at concentrations that ranged from 2.3 to 5.4 log MPN/g. Average MAPCs were 1.3 to 2.7 log CFU/g, depending on the type of dish. Coliform counts ranged from less than 1.0 to 1.5 CFU/g, and yeast and mold counts were less than 1.0 log CFU/g in all cases. A total of 118 isolates of C. perfringens were tested for enterotoxic effect on Vero cells; 82 (70%) showed activity against Vero cells. Of them, 31 isolates induced cell lysis, indicating cytotoxic effect; 41 induced cell elongation, indicating cytotonic effect; and 10 produced both cytotoxic and cytotonic effect. Dilution of the bacterial filtrates that were still producing an effect on Vero cells ranged from 1:80 to 1:5,120. These results underscore the importance of determining enterotoxigenicity when testing for C. perfringens in foods.

Laparoscopic Heller myotomy for classic achalasia: results of our initial series of 20 patients.

BACKGROUND: The aim of this study was to review our results in the surgical management of achalasia by laparoscopic esophageal cardiomyotomy and partial fundoplication. METHODS: The patient population was comprised of a consecutive series of 20 patients with classic achalasia who underwent laparoscopic cardiomyotomy and partial fundoplication. Clinical, radiological, and physiological characteristics were analyzed prospectively, with an emphasis on the outcome and complications. RESULTS: There were 12 women and eight men; their mean age was 37 years. Four intraoperative complications occurred-two mucosal perforations that were resolved laparoscopically and two cases of pneumothorax. The median hospital stay was 4 days (range, 2-14) and the median time to start oral feeding was 3 days (range, 1-7). After a median follow-up of 14 months (range, 2-83), 16 patients were asymptomatic and four had mild heartburn and/or dysphagia. All patients gained weight (median, 8.0 kg; range, 1-23). We observed a median postoperative decrease in esophageal diameter of 1.6 cm (range, 0.2-2.9). Fifteen patients were subjected to physiological esophageal studies; the results showed that power esophageal sphincter pressure had decreased from 32 (range, 15-60) to 12 mmHg (range, 6-25). The median DeMeester score was 14.5 (range, 0.9-194). The median esophageal acid exposure was 3% (range 0-34.6). CONCLUSIONS: Our initial experience with the laparoscopic management of classic achalasia yielded satisfactory clinical, radiological, and physiological results.

Isolation of Arcobacter spp. from retail meats and cytotoxic effects of isolates against vero cells.

A survey of Arcobacter spp. was conducted over a 12-month period in Guadalajara, Mexico. A total of 135 samples (45 lean ground beef samples, 45 lean ground pork samples, and 45 chicken samples, including drumsticks, gizzards, and ground or chopped breast) were collected from local butcheries. The samples were enriched in Johnson-Murano enrichment medium and then streaked onto Johnson-Murano agar plates. Typical colonies were subjected to microscopic and biochemical identification followed by polymerase chain reaction confirmation of the genus Arcobacter. All isolates confirmed to be Arcobacter isolates were then inoculated into Eagle's minimum essential medium to determine their cytotoxicity against Vero cells. Arcobacter spp. were detected in 28.8, 51.1, and 40.0% of beef, pork, and chicken samples, respectively. From these samples, 101 isolates were confirmed to be Arcobacter spp. by polymerase chain reaction. Overall, the species most frequently identified was A. butzleri, followed by A. skirrowii. A. cryaerophilus was isolated only from pork meat. Ninety-five (95%) of the Arcobacter isolates produced a virulence mechanism against Vero cells, and 38 of them induced cell elongation, indicating enterotoxin production. Eighteen isolates produced the formation of vacuoles, and 39 produced both vacuolization and elongation. The vacuolization effect may be related to a vacuolizing toxin. The production of a vacuolizing toxin by Arcobacter spp. has not previously been reported. Results obtained in this study indicate that Arcobacter spp. may show cytotoxic effects other than the recognized enterotoxin production.

Spread of bacterial pathogens during preparation of freshly squeezed orange juice.

To study the potential of three bacterial pathogens to cross-contaminate orange juice during extraction, normal operation conditions during juice preparation at food service establishments were simulated. The spread of Salmonella enterica serovar Typhimurium, Escherichia coli O157:H7, and Listeria monocytogenes from inoculated oranges to work surfaces and to the final product was determined. The transference of these three bacterial pathogens to orange juice made from uninoculated oranges with the use of contaminated utensils was also studied. Fresh oranges were inoculated with a marker strain of rifampicin-resistant Salmonella Typhimurium, E. coli O157:H7, or L. monocytogenes. Final pathogen levels in juice were compared as a function of the use of electric or mechanical juice extractors to squeeze orange juice from inoculated oranges. Pathogen populations on different contact surfaces during orange juice extraction were determined on sulfite-phenol red-rifampicin plates for Salmonella Typhimurium and E. coli O157:H7 and on tryptic soy agar supplemented with 0.1 g of rifampicin per liter for L. monocytogenes. After inoculation, the average pathogen counts for the orange rind surface were 2.3 log10 CFU/cm2 for Salmonella Typhimurium, 3.6 log10 CFU/cm2 for E. coli O157:H7, and 4.4 log10 CFU/cm2 for L. monocytogenes. This contamination was spread over all utensils used in orange juice squeezing. Mean pathogen counts for the cutting board, the knife, and the extractor ranged from -0.3 to 2.1 log10 CFU/cm2, and the juice contained 1.0 log10 CFU of Salmonella Typhimurium per ml, 2.3 log10 CFU of E. coli O157:H7 per ml, and 2.7 log10 CFU of L. monocytogenes per ml. Contact with contaminated surfaces resulted in the presence of all pathogens in orange juice made from uninoculated oranges. These results give emphasis to the importance of fresh oranges as a source of pathogens in orange juice.

Photoswitched singlet energy transfer in a porphyrin-spiropyran dyad.

A photochromic nitrospiropyran moiety (Sp) has been covalently linked to a zinc (PZn) and to a free-base (P(H2)) porphyrin. In the resulting dyads (P(Zn)-Sp(c) and P(H2)-Sp(c)), the porphyrin first excited singlet states are unperturbed by the closed form of the attached spiropyran. Excitation of the spiropyran moiety of either dyad in the near-UV region results in ring opening to a merocyanine form (P-Sp(o)) that absorbs at 600 nm. The open form re-closes thermally in 2-methyltetrahydrofuran with a time constant of 20 s, or following irradiation into the 600 nm band. Excitation of the zinc porphyrin moiety in the merocyanine form of the dyad yields 1PZn-Sp(o). The lifetime of the zinc porphyrin excited state is reduced from its usual value of 1.8 ns to 130 ps by singlet-singlet energy transfer to the merocyanine moiety to give PZn-1Sp(o). The quantum yield of energy transfer is 0.93. Quenching is also observed in the free base dyad, where 1P(H2)-Sp(o) and P(H2)-1Sp(o) exchange singlet excitation energy. This photoswitchable quenching phenomenon provides light-activated control of the porphyrin excited states, and consequently control of any subsequent energy or electron-transfer processes that might be initiated by these excited states in more complex molecular photonic or optoelectronic devices.

Biliary duct injury: partial segment IV resection for intrahepatic reconstruction of biliary lesions.

A technique for intrahepatic reconstruction of the biliary tree after complex high injuries is described. The fundament of the procedure is the removal of a wedge of segment IV at the level of the hilar plate. When the hilar plate is reached and no adequate exposure of the ducts can be obtained, removing a 1 x 1-in wedge of segment IV between the gallbladder bed and the round ligament exposes the left and right ducts. An anteroposterior view of the plate is obtained instead of a caudocephalic dissection, exposing healthy, nonscarred ducts for reconstruction. We have used this approach in 22 patients, and adequate exposure of the ducts has been obtained, with a high success rate of patency of the anastomosis at a mean follow-up of 3 years. Twenty patients have a patent anastomosis, with a good quality of life and no restenosis.

Behavior of enterotoxigenic strains of Staphylococcus aureus in milk fermented with a yogurt starter culture.

The ability of a yogurt starter culture formed by Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp bulgaricus to inhibit the growth of four enterotoxin type A and B producers Staphylococcus aureus strains (ATCC 6538, S6, FRI-100 and a strain isolated from milk) during fermentation of milk and subsequent storage was investigated. Sterile skim milk was inoculated with about 10(6) CFU/ml of S. aureus and with about 10(6) CFU of starter culture, and incubated at 42 degrees C during 8 h, followed by refrigeration at 4 degrees C. Samples were taken every 2 h during fermentation and every 2 days during storage. Viable count of lactic acid bacteria and S. aureus as well as pH, acidity, thermostable deoxyribonuclease (TNase) and staphylococcal enterotoxin A (SEA) production were evaluated. Behavior of four strains was similar; S. aureus survived the 8 h fermentation with LAB, and its population began to decrease from the first day of storage, being completely inhibited at 9-10 days. TNase and SEA production were positive in all samples taken along the study. It was demonstrated that enterotoxigenic strains of S. aureus were able to survive the fermentation of milk with a yogurt starter culture and they were inhibited after several days during storage of the fermented product, contrary to the general belief which considered it very difficult due to the low pH. Even though S. aureus was inhibited, TNase and SEA were demonstrable along the storage. Therefore, fermented milks may play an important role in the transmission of this organism.

[External version in pelvic presentation]. / Versión externa en presentación pélvica.

We made a prospective, population-based study of external version attempt in the department of obstetrics at Hospital, Clínica y Maternidad Conchita A.C. at Monterrey, N.L. 45 patients were enrolled with diagnosis of breech presentation. We tested the hypothesis to determined the average of success and how this procedure can reduce the primary C section rate. Of the 45 patients, 48.9% were primiparous, we had success in the external version in 27 patients (60%), 81.4% had vaginal delivery and 18.6% C section. During the study the incidence of primary C section in breech presentation shown low rates from 15.3% to 9.3%. We did'nt have complications in the procedure. With these results, we concluded that the attempt of external version is more safety and had less risks for the mother and fetus that breech delivery, and we can reduced the primary C section rate for this indication.

[Esophagocardiomyotomy or modified Heller technique, through the thorax, for the treatment of achalasia]. / Esofagocardiomiotomía o Heller moldificado por vía torácica, para el tratamiento de la acalasia.

BACKGROUND: Since 1913 surgical myotomy has been an effective method for patients with esophageal achalasia and until today there is controversy between pneumatic dilatation or surgery and between the abdominal or thoracic approach for Heller's procedure. AIMS: To find out the long-term results with thoracic short esophagomyotomy without an antireflux procedure for esophageal achalasia. METHODS: The charts of 31 patients with achalasia operated of thoracic Heller's myotomy between 1986 and 1995 were reviewed in retrospective fashion. RESULTS: Demographic and clinical data were similar to those reported in the English literature. Twenty five patients received medical or endoscopic treatment with poor results. Prior abdominal Heller's myotomy was performed in 5 patients, 25 per cent of patients developed postoperative complications, there was no operative mortality. The mean follow-up period was 4 years and 93.6 per cent of patients showed good to excellent results; in this group 3 patients (9.7 per cent) reported sporadic dysphagia. Two patients (6.4 per cent) had gastroesophageal reflux. CONCLUSIONS: The thoracic esophagomyotomy is a safe procedure for esophageal achalasia, it is easy to perform, there are several technical advantages over the abdominal approach, an antireflux procedure is not necessary and in the long-term follow-up a large number of good-to-excellent results may be obtained with both surgical approaches.

[Incidence of fetal macrosomia: maternal and fetal morbidity]. / Incidencia de macrosomía fetal. Morbilidad materna y fetal.

The macrosomia is an obstetric eventuality associated to high maternal-fetal morbidity-mortality. This assay was planned in order to know the incidence of macrosomia in our institution, the relation between vaginal and abdominal deliveries and the fetal-maternal morbidity we reviewed 3590 records and we found 5.6% incidence of macrosomia in the global obstetric population. There was 58% of vaginal deliveries, 68% of the newborn were male. The main complications were in the C. sections, 2 laceration of the hysterectomy, and 2 peroperative atonias. In the vaginal deliveries, the lacerations of III and IV grade were 9 of each grade. The main fetal complications were 5 slight to severe asphyxia and 4 shoulder dystocias. This assay concludes that the macrosomia in our service is similar to the already published ones, a 42% were C. section and the maternal-fetal morbidity was low.

[Pancreatoduodenectomy in the treatment of carcinoma of Vater's ampulla]. / Pancreatoduodenectomía en el tratamiento de carcinoma del ámpula de Vater.

OBJECTIVE: To analyze clinical characteristics, diagnostic methods, intraoperative findings, morbidity & mortality and outcome of a series of patients with ampullary adenocarcinoma. DESIGN: Retrospective analysis. SETTING: Tertiary-care medical center. PATIENTS: Thirty four consecutive patients who underwent radical resection between 1960 and 1992. RESULTS: The most frequent findings were jaundice (91%), weight loss (44%) and palpable gallbladder (42%). Thirty-three patients (97%) underwent Whipple resection and one total pancreatectomy (3%). The postoperative mortality was 15%. Overall survival at 1, 5, 10 and 14 years was 67, 36, 25 and 17% respectively. Fourteen patients died of tumor recurrence developed more than five years after the resection. CONCLUSION: Radical resection for ampullary carcinoma remains the procedure of first choice in these patients.

Clinical behavior and prognostic factors of periampullary adenocarcinoma.

OBJECTIVE: The authors evaluated the outcome and potential prognostic factors of 60 patients with surgically resected periampullary tumors. SUMMARY BACKGROUND DATA: Periampullary carcinomas exhibit different clinical behaviors according to their site of origin. There are no prognostic factors for deciding the type of surgery to be used or for choosing patients with tumors that have a poor prognosis for adjuvant treatment. METHODS: A retrospective review was performed of 15 clinical and pathologic variables encountered among 60 patients with periampullary tumors. Tumors were divided into four groups according to their site of origin. Kaplan-Meier survival curves of the four groups were plotted and differences were evaluated with the log-rank test. Cox's proportional hazards model was used to test for separate and combined independent predictors of disease-free survival. RESULTS: Twenty-nine ampullary carcinomas, 20 ductal pancreatic carcinomas, 7 distal common bile duct carcinomas, and 4 carcinomas of the periampullary duodenum were found. Five-year disease-free survival was 43%, 0%, 0%, and 75%, respectively. According to the Cox analysis, absence of neural invasion and use of adjuvant chemotherapy were significant factors for longer survival of patients with ampullary tumors. Lymphatic invasion was related to a shorter survival in patients with pancreatic carcinoma. CONCLUSIONS: Five-year disease-free survival of patients with periampullary tumors is related to tumor type. Prognosis was better for ampullary tumors if neural invasion was absent and if adjuvant chemotherapy was used. Lymphatic invasion was associated with a shorter recurrence-free survival among patients with pancreatic carcinoma.

Comparison of outcomes and complications for open and laparoscopic cholecystectomy in Mexico.

A retrospective analysis of the outcome and surgical complications of two groups of patients undergoing cholecystectomy was performed. Group I consisted of 253 patients who underwent laparoscopic cholecystectomy between 1991 and 1994, and group II was formed by 292 patients who met the same preoperative criteria than patients of group I and underwent open cholecystectomy between 1986 and 1990, prior to the introduction of laparoscopic cholecystectomy in our hospital. General characteristics and associated clinical conditions were similar for both groups. Intraoperative cholangiography was used more frequently in group II whereas preoperative ERCP was performed more frequently in group I patients. There was no operative mortality in any of the groups. There were no statistically significant differences between both groups in terms of type and number of complications.

[7 cases of carcinoma of the distal choledochus]. / Siete casos de carcinoma del colédoco distal.

Seven patients with carcinoma of the lower third of the extrahepatic bile duct over a twenty year period, were analyzed with emphasis to the presentation, laboratory, surgical findings, histology and outcome. There were four males and three females. The mean age was 59 years (range 53 to 68). All patients presented jaundice, abdominal pain and weight loss. Serum bilirubin levels were over 5 mg/dL in six patients (86%). The most useful diagnostic studies were endoscopic cholangiography, percutaneous cholangiography and computed tomography. All patients underwent a Whipple procedure. There was no operative mortality. In the long term follow-up, three patients were free of disease, and four had died. Tumor recurrence was high (43%) in spite of the curative resection.

[Survival of Listeria monocytogenes in milk fermented with a starter culture for making yogurt]. / Sobrevivencia de Listeria monocytogenes en leche fermentada con un cultivo iniciador para elaborar yogur.

The purpose of this research was to determine the survival of Listeria monocytogenes in sterile skim milk during the fermentation with a yogurt starter culture and during storage at refrigeration temperature. Sterile skim milk was inoculated with 10(3), 10(5) and 10(7) cfu/ml of L. monocytogenes and with 10(6) cfu of lactic acid bacteria. Inoculated milks were fermented for 8 h at 42 degrees C, followed by refrigeration at 4 degrees C. Samples were taken at 2 h intervals during fermentation and at 2 days intervals during storage. Acidity and pH were measured, as well as viable count of lactic acid bacteria and pathogen. L. monocytogenes survived 8h, 10 days and 32 days in the fermented milk, when the inocula were 10(3), 10(5) and 10(7) cfu/ml, respectively. Inhibition of the pathogen was associated with a decrease of pH below 4.0 and increase in acidity. It was demonstrated that this pathogen is able to survive several weeks in milk fermented with a starter culture, contrary to the general belief which considered it very difficult due to the low pH. Therefore fermented milks may play an important role in the transmission of these bacteria.

[Duodenal cancer]. / Cáncer de duodeno.

UNLABELLED: To analyze the general characteristics and outcome of a cohort of 6 patients with malignant duodenal tumors who underwent surgical radical resection. DESIGN: Longitudinal retrolective study. SETTING: A third level medical center. RESULTS: Mean age was 48 years. M/F ratio was 2:1. The most frequent symptom was duodenal obstruction. Mean time between the beginning of the symptoms and the correct diagnosis was 15 months. Five of six patients demonstrated abnormalities on gastrointestinal X rays. All patients underwent Whipple resection, this was curative in 2, palliative in 2 more and not evaluated in two cases due to operative mortality. Five tumors were adenocarcinomas and one a carcinoid tumor. The long-term mortality occurred in 2 patients. CONCLUSIONS: The diagnosis of primary duodenal carcinoma needs a deep clinical suspicion, some patients when treated by radical resection may experience long-term survival.

[The surgical possibilities in patients with adenocarcinoma of the pancreas]. / Posibilidades quirúrgicas en los pacientes con adenocarcinoma del páncreas.

OBJECTIVE: To analyze the types of surgical procedures which can be performed in patients with pancreatic adenocarcinoma and its results. SUMMARY BACKGROUND DATA: Until the 80's the incidence of resection for pancreatic adenocarcinoma was low with a high morbidity and mortality rates, and the 5-year survival rate below 8 per cent. During the last decade many reports in the international literature are showing very low morbidity and mortality rates and much better long-term survival rates (35-40 per cent). The palliative procedures had not change. METHODS: The retrospective analysis of charts of patients with any surgical procedures and diagnosis of pancreatic adenocarcinoma, between 1962 and 1991, was performed, such analysis included demographic data, surgical procedures, operative morbidity and mortality, and long-term results. RESULTS: There were 410 patients, 52 per cent were males and 48 per cent were females. Tumor resection was possible in only 20 per cent of the patients (pancreatoduodenectomy 69 per cent, distal pancreatectomy 17 per cent and total pancreatectomy 14 per cent). The remaining 80 per cent were candidates for palliative procedures (73 per cent) and diagnostic procedures (27 per cent). The resected group showed a high operative morbidity and mortality rates in particular total pancreatectomy, and the 5-year survival rate was 8 per cent. This figure was 4 per cent with the Whipple's procedure. When palliative or diagnostic procedures were performed, 97 per cent were dead during the first 12 months, and there were no survivors after 20 months. CONCLUSIONS: Our results are equal to those reported in the world literature until 1985, after that date better results are increasingly reported, but we shall wait at least the next decade in order to know if there are some changes in our results. There has been no changes with palliative procedures.

Risk factors for operative morbidity in patients with systemic lupus erythematosus: an analysis of 63 surgical procedures.

The surgical morbidity rate of patients with Systemic Lupus Erythematosus is considered very high; however, the experience in the literature is small. This study will determine the rate of surgical morbidity and the existence of predictive factors in patients with such a disease. The medical records of 53 patients with Systemic Lupus Erythematosus who underwent 63 major operations were analyzed retrospectively. The rate and causes of operative morbidity were registered. Univariate and multivariate statistical analysis was performed to ascertain the existence of predictive factors for morbidity. The overall morbidity and mortality were 16% and 6% respectively. Lymphopenia, hypoalbuminemia, increased SGOT and SGPT, urgent indication of operation, the physical status of the American Society of Anesthesiology, as well as a shorter duration of Systemic Lupus Erythematosus showed a significant correlation with operative morbidity in the univariate analysis; high blood urea nitrogen showed marginal significance. Physical status, urgent indication, and blood urea nitrogen remained as significant variables with the multivariate logistic regression analysis. The surgical morbidity rate of these patients may be lower than previously estimated. The physical status, urgency of operation, and level of blood urea nitrogen seemed to be the most useful independent predictors for surgical morbidity risk in patients with Systemic Lupus Erythematosus.

[Syringomyelia and pregnancy. A case report]. / Siringomielia y embarazo. Informe de un caso.

This report refers to the case of a 39-year-old woman, fourth gestation, who during her first pregnancy developed neurologic deficit of the left hand, which slowly progressed getting to affect during seven years, all the left upper extremity and the right hand. During this time, she had two abortions, and between the third and fourth pregnancies, because of the clinical suspicion, laboratory tests were done, finding by electromyography, lesion of anterior process of spinal chord at cervical level. During this fourth pregnancy, neurologic deficit increased and it was decided to interrupt pregnancy by cesarean section under epidural block at 38 weeks of gestation. According to our knowledge this syringomyelia case and pregnancy, is the first one reported in our country.