Nature of bonding in the cyclization reactions of (2-Ethynylphenyl)triazene and 2-Ethynylstyrene.

The topological analysis of the electron localization function (ELF) has been applied to explore the nature of bonding in thermal cyclizations of (2-ethynylphenyl)triazene and 2-ethynylstyrene. These processes have been proposed to occur through both five- (i.e., coarctate) and six-membered (i.e., pericyclic) transition states. The analysis of electron delocalization, as measured from an irreducible ELF f-localization domain reduction diagram, allows us to characterize these cyclizations of 2-ethynylstyrene in terms of a more pronounced pericyclic or coarctate character than those associated with (2-ethynylphenyl)triazene. The latter evolve through pseudopericyclic and pseudocoarctate pathways. It is found that ELF results are also in good agreement with recent magnetic evidence data obtained from the anisotropy of induced current density (ACID) calculations.

[Distribution of capsular types and antimicrobial susceptibility of Streptococcus agalactiae causing infections in Argentina]. / Distribución de tipo capsular y sensibilidad antimicrobiana de Streptococcus agalactiae productores de infecciones en Argentina.

Streptococcus agalactiae is an endogenous bacterium that has emerged in the last 20 years as an etiological agent in both neonatal and perinatal infections, and in immunocompromised patients. The differentiation of the capsular polysaccharide, the presence of surface proteins c, X, R, and molecular methods allow classification in serotypes and genotypes. This identification is a useful tool for epidemiological purposes and virulence studies in this bacterium. The objective of this work was to study the serotypes and the antimicrobial susceptibility of isolates recovered from invasive diseases in different areas of Argentina. In the analyzed sample a fair predominance of Ia and III serotypes was recovered, followed by II and IV serotypes. All the isolates were found to be sensitive to penicillin. A 6% of resistance to erythromycin and a 4.5% to clindamycin were detected. In three of the isolates, constitutive MLS phenotype (resistance to macrolides, lincosamins and streptogramins) was founded, while in the remaining one, inducible MLS phenotype was detected. These results stress the importance of conducting a surveillance of the prevalent serotypes in our country with the goal of future prevention of this disease with an effective vaccine. The knowledge of the antimicrobial susceptibility profile will be also important to obtain therapeutic success in the treatment.

Distribución de tipo capsular y sensibilidad antimicrobiana de Streptococcusagalactiae productores de infecciones en Argentina / Distribution of capsular types and antimicrobial susceptibility of Streptococcus agalactiae causing infections in Argentina

Streptococcus agalactiae es una bacteria colonizante que ha emergido en los últimos años como causante de infecciones neonatales, perinatales y en pacientes con compromiso inmunológico. La caracterización del polisacárido capsular, de las proteínas de superficie (c, X, R), así como el análisis de marcadores moleculares, permiten su clasificación en serotipos y genotipos. Esto resulta de utilidad para fines epidemiológicos y para estudios de virulencia de la bacteria. El objetivo de este trabajo fue conocer los serotipos prevalentes y la sensibilidad antimicrobiana de aislamientos provenientes de procesos infecciosos en pacientes de distintas zonas de Argentina. En la muestra analizada se obtuvo predominio de los serotipos Ia y III, seguido de II y IV. Todas las cepas resultaron sensibles a penicilina. Se observó 6% de resistencia a eritromicina y 4,5% a clindamicina. En 3 de las cepas se detectó fenotipo MLS (resistencia a macrólidos, lincosaminas y estreptograminas) constitutiva y en una cepa, resistencia MLS inducible. Los resultados logrados en este estudio destacan la importancia de efectuar un relevamiento de los serotipos más frecuentes en nuestro país en vistas a la prevención de esta infección con una vacuna que realmente sea eficaz, como así también el conocimiento de la sensibilidad antimicrobiana para lograr éxito terapéutico en los tratamientos.

Streptococcus agalactiae is an endogenous bacterium that has emerged in the last 20 years as an etiological agent in both neonatal and perinatal infections, and in immunocompromised patients. The differentiation of the capsular polysaccharide, the presence of surface proteins c, X, R, and molecular methods allow classification in serotypes and genotypes. This identification is a useful tool for epidemiological purposes and virulence studies in this bacterium. The objective of this work was to study the serotypes and the antimicrobial susceptibility of isolates recovered from invasive diseases in different areas of Argentina. In the analyzed sample a fair predominance of Ia and III serotypes was recovered, followed by II and IV serotypes. All the isolates were found to be sensitive to penicillin. A 6% of resistance to erythromycin and a 4.5% to clindamycin were detected. In three of the isolates, constitutive MLS phenotype (resistance to macrolides, lincosamins and streptogramins) was founded, while in the remaining one, inducible MLS phenotype was detected. These results stress the importance of conducting a surveillance of the prevalent serotypes in our country with the goal of future prevention of this disease with an effective vaccine. The knowledge of the antimicrobial susceptibility profile will be also important to obtain therapeutic success in the treatment.

[Bacteremia in 2 hospitals in Rosario, Argentina]. / Bacteriemias en dos hospitales de Rosario, Argentina.

Bacteremia is associated with high morbidity and mortality. Nosocomial bacteremia is associated with an attributable mortality of 35%. In order to characterize the etiological agent of bacteremia cases during two time periods, 6605 patients were studied as follows: 1) from 1980 to 1982 (n = 2401) and 2) from 1988 to 2000 (n = 4204). A total of 596 cases of bacteremia were detected. The most frequent agents were Staphylococcus aureus, negative coagulase (CNS) Staphylococcus, Klebsiella pneumoniae and Escherichia coli. In the second period, an increase in the frequency of bacteremia caused by gram positive bacteria, particularly gram-positive cocci, was noted. Conversely, gram negative bacteria diminished significantly in the second period, specially enterobacterial species. Methicillin-resistant S. aureus and CNS were significantly more frequently isolated in the second period. Infrequent agents of endocarditis, such as Actinobacillus actinomycetemcomitans, Haemophilus aphrophilus, and Corynebacterium urealyticum, were isolated.

[Hepatic abscess and bacteremia due to Lactobacillus rhamnosus]. / Absceso hepático y bacteriemia debida a Lactobacillus rhamnosus.

The incidence of severe infections caused by Lactobacillus spp. is very low. This paper reports a case of a liver abscess and bacteremia due to Lactobacillus rhamnosus. The patient is a 73 year-old woman with antecedent of diabetes mellitus. She has undergone surgery and received antimicrobial therapy (ampicillin plus gentamicin). The clinical outcome was favorable.

Absceso hepático y bacteriemia debida a Lactobacillus rhamnosus / Liver abscess and bacteremia due to Lactobacillus rhamnosus

Las infecciones severas por Lactobacillus spp. son infrecuentes. En una paciente de 73 años, de sexo femenino, diabética descompensada, se presenta un caso de absceso hepático y bacteriemia causado por Lactobacillus rhamnosus. La misma fue sometida a laparotomía con drenaje de absceso del lóbulo derecho y tratada con ampicilina y gentamicina con una evolución favorable.

Bacteriemias en dos hospitales de Rosario, Argentina / [Bacteremia in 2 hospitals in Rosario, Argentina]

Bacteremia is associated with high morbidity and mortality. Nosocomial bacteremia is associated with an attributable mortality of 35

. In order to characterize the etiological agent of bacteremia cases during two time periods, 6605 patients were studied as follows: 1) from 1980 to 1982 (n = 2401) and 2) from 1988 to 2000 (n = 4204). A total of 596 cases of bacteremia were detected. The most frequent agents were Staphylococcus aureus, negative coagulase (CNS) Staphylococcus, Klebsiella pneumoniae and Escherichia coli. In the second period, an increase in the frequency of bacteremia caused by gram positive bacteria, particularly gram-positive cocci, was noted. Conversely, gram negative bacteria diminished significantly in the second period, specially enterobacterial species. Methicillin-resistant S. aureus and CNS were significantly more frequently isolated in the second period. Infrequent agents of endocarditis, such as Actinobacillus actinomycetemcomitans, Haemophilus aphrophilus, and Corynebacterium urealyticum, were isolated.

Calorimetric and computational study of 1,3,5-trithiane.

To understand the differences in conformational behavior and reactivity of oxygen- and sulfur-containing 1,3,5-heterocyclohexanes, the enthalpies of formation and sublimation of 1,3,5-trithiane, 1, have been measured. The numerical value of the enthalpy of formation for this compound in the solid state is -8.6 +/- 2.6 kJ mol(-1), while the corresponding value in the gaseous state is 84.6 +/- 2.6 kJ mol(-1). The value for the enthalpy of sublimation is 93.2 +/- 0.2 kJ mol(-1). Standard ab initio molecular orbital calculations at the G2(MP2), G2, and G3 levels were performed, and the calculated enthalpies of formation are compared with the experimental data. These experimental and theoretical studies support the relevance of through-space lone pair-lone pair electronic repulsion in the sulfur heterocycle.

Importance of hand germ contamination in health-care workers as possible carriers of nosocomial infections.

The importance of hands in the transmission of nosocomial infection has been world wide admitted. However, it is difficult to induce this behavior in health-care workers. The aim of the present work was to point out the importance of hand bacteria colonization, the influence of hand washing and of patient physical examination. One hundred health-care workers were randomly divided in two groups: Group A without hand washing previous to patient physical examination or handling (PPE); group B with hand washing previous to PPE. Direct fingerprint samples in Columbia agar before and after PPE were obtained. The colonies were counted and identified by conventional techniques, and antibiograms according to NCCLS were performed. Before PPE group A participants showed a high number of bacteria regarding group B participants (73.9 Vs 20.7; p < 0.001); 44 out of 50 participants were carriers of potentially pathogen bacteria. No group B participants were carriers of potential pathogen bacteria before PPE. The latter group showed an increase in number of bacteria after PPE (20.7 CFU (before) Vs 115.9 CFU (after); p < 0.001). Sixteen group B participants were contaminated after PPE with potential pathogens such as S. aureus (50% of them methicillin resistant); Escherichia coli, Pseudomonas aeruginosa and Enterococcus faecalis, half of them multiresistant. We can conclude on the importance of these results to implement educational programs and to provide the health-care workers with the proper commodities to fulfill this practice.

Influence of alkyl substitution on the gas-phase stability of 1-adamantyl cation and on the solvent effects in the solvolysis of 1-bromoadamantane.

1-Adamantyl cations having three methyl groups or one, two, or three isopropyl groups on the 3-, 5-, and 7-positions were found by FT ICR to be more stable than the 1-adamantyl cation and that the stability increases with the number of isopropyl group. The relative stabilities calculated by PM3 were in good agreement with the experimental results. In contrast, the sequence of the rates for the solvolysis in nonaqueous solvents are 3,5,7-(Me)(3)-1-AdBr < 1-bromoadamantane (1-AdBr) < 3,5,7-(n-Pr)(3)-1-AdBr < 3,5,7-(i-Pr)(3)-1-AdBr. The rates of solvolysis of 3,5,7-(i-Pr)(3)-1-AdBr and 3,5,7-(n-Pr)(3)-1-AdBr relative to 1-AdBr at 25 degrees C are 15 and 3.8 in EtOH, respectively, but markedly decreases with the increase in the amount of added water, reaching 0.84 and 0.15, respectively, in 60% EtOH. Reflecting these effects of water, the Grunwald-Winstein (GW) relationship for 3,5,7-(i-Pr)(3)-1-AdBr and 3,5,7-(n-Pr)(3)-1-AdBr against Y(Br) is linear for nonaqueous alcohols (EtOH, MeOH, TFE-EtOH, TFE, 97% HFIP), but marked downward deviations are observed for aqueous organic solvents, in particular, aqueous ethanol and aqueous acetone. The effect of the alkyl substituents to diminish relative solvolytic reactivity in EtOH-H(2)O mixtures may be ascribed to a blend of steric hindrance to Betarphinsted base-type hydration to the beta-hydrogens and hydrophobic interaction of the alkyl groups with ethanol to make the primary solvation shell less ionizing. The introduction of one nonyl group to the 3-position showed much smaller deviations in the GW relationship than the case of 3,5,7-(n-Pr)(3)-1-AdBr. The markedly decelerated solvolysis of alkylated 1-bromoadamantanes in aqueous organic solvents is a kinetic version of anomalously diminished dissociation of alkylbenzoic acids in aqueous ethanol and aqueous tert-butyl alcohol that was demonstrated by Wepster and co-workers a decade ago and ascribed to hydrophobic effects.

An experimental and theoretical study of the basicity of tetra-tert-butyltetrahedrane.

The gas-phase basicity (GB) of tetra-tert-butyltetrahedrane (tBu4THD) was determined by FT-ICR mass spectrometry and comparison with reference compounds of known basicity. Its GB, 1035+/-10 kJ x mol(-1), makes tetra-tert-butyltetrahedrane one of the strongest bases reported so far. Ab initio calculations [B3LYP/6-31G(d) and B3LYP/6-311 + G(d,p)//6-31G(d)] have been carried out in order to compare the high experimental basicity of tBu4THD with that estimated theoretically. Both B3LYP/6-31G(d) and QCISD(T) calculations were used to determine the reaction path which connects the initial tetrahedrane-ammonium complex with the final products, protonated cyclobutadiene (CBDH+) and ammonia.

[Arcanobacterium haemolyticum sinusitis]. / Sinusitis debida a Arcanobacterium haemolyticum.

Arcanobacterium haemolyticum is a bacterial pharyngeal pathogen that predominantly infects adolescents and young adults. It rarely causes severe infection. A case of sinusitis in an 18-year-old female patient with a skin rash is presented. The strain was susceptible to erythromicin, ampicilin, vancomicin, cephalotin, clindamicin, rifampicin and penicillin. Erythromicin has been proposed as first-line therapy.

Organic Thermochemistry at High ab Initio Levels. 3. A G3 Study of Cyclic Saturated and Unsaturated Hydrocarbons (Including Aromatics).

With the purpose of exploring the reliability of the enthalpies of formation calculated using the G3 method, we have examined a series of saturated and unsaturated alicyclic hydrocarbons varying the size and the number of formal double bonds in the molecule. Heats of formation have been calculated at the G3 level through both atomization reactions and bond separation isodesmic reactions, and comparisons with experimental values and with values previously calculated at the G2(MP2) and G2 levels have been made. The quality of the G3-calculated enthalpies of formation using atomization reactions is comparable to that obtained at the G2 level using bond separation reactions, whereas G3 calculations are two to three times faster than G2 calculations.

[Prevalence of enterohemorrhagic Escherichia coli in a cattle area of Argentina. Genotypic characterization of the strains of animal origin]. / Prevalencia de Escherichia coli enterohemorrágico en una zona ganadera de Argentina. Caracterización genotípica de las cepas de origen animal.

BACKGROUND: There is a high prevalence of infection by Enterohemorrhagic Escherichia coli (EHEC) and patients with hemolytic uremic syndrome (HUS) in Argentina. AIM: To study cattle and pigs as a possible reservoir of EHEC in Argentina. MATERIAL AND METHODS: One hundred two healthy animals (68 cattles and 31 pigs) from a livestock in Argentina, were studied. Stool samples were obtained with a rectal swab. The strains were identified by DNA hybridization with specific gene probes detecting Shiga-like toxin 1 and 2 (Stx1, Stx2), and hly gen related to fimbrial adhesin-associated plasmid. EHEC strains were serogrouped using commercial antisera. RESULTS: EHEC was isolated from 30 out of 68 bovines cultures (44.1%) and from 25 out of 31 pigs (58.1%). Isolates carrying genes codifying both Stx1 and Sxt2, were observed in 50% of cattle and 63.9% of pigs. The gene which codifies for hemolysin (associated to fimbrial adhesin) was observed in about 41% of EHEC isolates. Strains belonging to serogroups O26, O111, and O157 were isolated from cattle, and O111, and O157 from pigs. CONCLUSIONS: The high percentage of EHEC in both cattle and pigs and the presence of human infection-associated serogroups, suggests that these animals are a reservoir of EHEC associated with disease in humans.

[Antimicrobial resistance among species of Salmonella, Shigella, Escherichia, and aeromonas isolated from children with diarrhea in 7 Argentinian centers]. / Resistencia a los antimicrobianos de especies de Salmonella, Shigella, Escherichia y Aeromonas aisladas de niños diarreicos en siete centros de Argentina.

The increasing levels of resistance of enteropathogenic bacteria against antimicrobial agents present geographic variations. We have analysed the antimicrobial susceptibility of isolates obtained from 4,364 children under 5 years of age with acute diarrhea, in 7 cities of Argentina. Diarrheagenic E. coli exhibited 74.5% of resistance against ampicillin, 64.2% against sulfametoxazole-trimethoprim, and Shigella spp., 62% and 75.6% respectively. Salmonella sp. showed 35%, 14%, 41.8%, 65.4%, 14.5%, and 13.6% of resistance against ampicillin, chloranfenicol, sulfametoxazole-trimetoprim, sulfadiazin, gentamycin, and fosfomycin respectively. These values are higher than the ones observed in developed countries. Aeromonas showed significantly lower resistance percentage. Important differences in our country were observed, consequently, local trials should be carried out in order to apply corrective measures.

Role of Chelation and Resonance on the Intrinsic Acidity and Basicity of Tropolone.

The gas-phase basicity and acidity of tropolone have been determined by Fourier transform ion cyclotron resonance mass spectrometry (FT ICR) techniques. Ab initio calculations at the MP2/-6311+G(d,p) level were carried out to describe the effects that protonation and deprotonation have on the aromaticity and hence on the stability of the system. Experimental and calculated energetics of protonation and deprotonation are in excellent agreement. Our analysis shows that both the protonated and the deprotonated species are stabilized by resonance. As a consequence the acidity of tropolone (341.3 kcal/mol) is enhanced, and this compound is found to be surprisingly as acidic as benzoic acid. This is in good agreement with the results reported in the literature and obtained in DMSO solutions. The intramolecular hydrogen bond becomes significantly weaker upon protonation, and this effect tends to counterbalance the resonance stabilization of the cation. As a consequence, tropolone is found to be slightly less basic than tropone.