Coupled-channel study of the Rydberg-valence interaction in HBr.

We report an ab initio study of the low-lying valence and Rydberg states of HBr. The calculations are carried out employing the multireference single- and double-excitation configuration interaction method including the spin-orbit interaction. The first excited adiabatic potential of 1Σ+ symmetry presents two minima which correspond to the Rydberg E1Σ+ and valence V1Σ+ observed states. We calculate the vibrational levels of these two states using a coupled-channel treatment based on the two diabatic potentials deduced from the ab initio adiabatic potentials and the Rydberg-valence interaction. The chaotic energy separations between the observed levels are well reproduced in the calculations. We have also obtained for the first time theoretical data for numerous Rydberg states of HBr lying in the (66-79) × 103 cm-1 excitation energy interval. The calculated spectroscopic parameters are found to be in good agreement with experiment and provide a basis for future studies of radiative and non-radiative processes in the HBr molecule.

Rydberg, valence, and ion-pair quintet states of O2.

We report an ab initio study of the quintet states of molecular oxygen. The calculations are carried out employing the multireference single and double excitation configuration interaction package. Potential energy curves of the six quintet valence states dissociating into ground state atoms and of the four quintet states dissociating to ion-pair atoms were computed. A number of bound quintet Rydberg series converging to the a(4)Πu and b(4)Σg(-) states of the O2(+) cation have been identified.

Interpretation of the accidental predissociation of the E(1) Π state of CO.

A special case of predissociation, known as indirect or accidental predissociation observed in the Rydberg E(1)Π bound state of CO is discussed. We resort to ab initio potentials in order to determine the plausible mechanism for this predissociation. Values of the predissociation width for the valence k(3)Π state of CO, as obtained from Fermi's golden rule, are also reported. The predissociation width obtained for the mixed E(1)Π (v = 1, J = 7) state is 0.033 cm(-1) compared to the experimental value of 0.034 cm(-1). The mixed E - E(') state with J = 28, v = 0 is found to be in near resonance condition with the k(3)Π (v = 4, J = 28) state, thus providing the means to indirect predissociation.

Two novel class I integron arrays containing IMP-18 metallo-ß-lactamase gene in Pseudomonas aeruginosa clinical isolates from Puerto Rico.

During a ß-lactam resistance surveillance study, 12 IMP-18-positive Pseudomonas aeruginosa isolates belonging to 9 different pulsed-field gel electrophoresis groups were identified. In nine isolates, a class I integron with a novel gene array was identified that contained bla(IMP-18) and bla(OXA-224), while in two isolates the class I integron contained bla(IMP-18) and bla(OXA-2) but in a new arrangement. Our findings show the dissemination of two novel class I integrons in P. aeruginosa from different regions of Puerto Rico.

Adiabatic versus diabatic descriptions of the lowest Rydberg and valence 1Σ+ states of HCl.

In this contribution we first report new ab initio self-consistent field configuration interaction calculations of the first excited adiabatic potential of (1)Σ(+) symmetry, the 2(1)Σ(+) or B(1)Σ(+) state, which presents two minima and can thus be seen as made up of the Rydberg E(1)Σ(+) and the valence V(1)Σ(+) states. Based on the computed 2(1)Σ(+) potential, we devised a theoretical procedure to compute the vibronic structure in order to try to explain the energy levels observed in the region above 76 254.4 cm(-1) which display an irregular vibrational structure, indicative of spectral perturbations. We try to find out which representation of the electronic states, the diabatic or the adiabatic one, is best suited to replicate the lowest observed vibronic levels of the E and V states. To this end, we deduce, from the 2(1)Σ(+) potential and its complementary adiabatic potential, two diabatic potentials. We then carry out a coupled equation treatment based on these diabatic potentials. The results of this treatment indicate that, in the present case, the adiabatic representation is better than the diabatic one to describe the observed vibronic levels. This is due, as expected, to the existence of a strong electrostatic interaction between the two diabatic potentials.

An interpretation of the anomalous (1)Pi vibronic structure in the far-UV spectrum of CO.

The far-UV spectrum of carbon monoxide presents numerous abnormal (1)Pi rovibronic levels in the region 92,000-105,000 cm(-1) which have been observed by several experimentalists. Yet, and in spite of various attribution attempts carried out over the past two decades, the nature of these levels is poorly understood and they still lack a definitive assignment. The absorption lines in this energy region are characterized by irregular energy level positions and spacings, and odd, smaller than expected, rotational constants. In the current contribution we address this puzzle by relying on recent ab initio calculations of several Rydberg and valence states of CO [G. J. Vazquez, J. M. Amero, H. P. Liebermann, and H. Lefebvre-Brion, J. Phys. Chem. A 113, 13395 (2009)], and on further new calculations in which we compute electronic transition moments between the ground state and several excited (1)Pi states. We focus on the perturbations between the adiabatic (1)Pi states, specifically on the interaction between the second and third potential energy curves, reported in our previous paper. The second adiabatic potential energy curve, which we refer to as E-E('), displays a distorted shape with two minima as a result of an avoided crossing with the third one. We report here the computation of the lowest vibronic levels of a system of two electronic states which undergo a strong Rydberg-valence interaction. Our vibronic calculations proceed as follows: from the second and third computed adiabatic curves we first obtain approximate diabatic curves for the (X (2)Sigma(+))3ppi E (1)Pi Rydberg state and for the valence E(') (1)Pi state. Then we solve a system of 2x2 coupled equations in order to obtain the perturbed vibronic energy levels and wave functions for the interacting E and E(') states. The computed vibronic levels obtained from the coupled equation treatment are compared to the first six observed (1)Pi levels. A good agreement is found with experiment for the four lowest vibronic levels and a reasonable accord for two higher levels.

Potential energy curves for the (1)Sigma(+) and (1,3)Pi states of CO.

Ab initio potential energy curves of CO are calculated to address a number of problems remaining in the interpretation of the experimental VUV absorption spectra. The calculations are of the type SCF MRSD-CI. We employed the aug-cc-pVQZ basis set for both carbon and oxygen, augmented with twelve diffuse functions, of s-, p-, and d-type, located on both atomic centers. We focus on the energy region 85,000 cm(-1) < E < 110,000 cm(-1) characterized by strong interactions between Rydberg and valence states. In this work we deal specifically with the (1)Sigma(+), (1)Pi, and (3)Pi states lying in this region. Some of the relevant findings are as follows: The minimum of the C'(1)Sigma(+) valence state is found 1920 cm(-1) above the value inferred from an extrapolation of experimental data. A new (1)Pi valence state, labeled E', is found to perturb strongly the (X(2)Sigma(+))3ppi E(1)Pi Rydberg state. The electrostatic perturbation of the (X(2)Sigma(+))3ppi c(3)Pi Rydberg state by the k(3)Pi valence state is confirmed. The energy position of the (A(2)Pi)3ssigma (3)Pi state, the triplet companion of the W(1)Pi Rydberg state, is predicted.

Insight into the Rydberg states of CH.

Ab initio electronic structure calculations of a relatively large number of Rydberg states of the CH radical were carried out employing the multireference single and double excitation configuration interaction (MRD-CI) method. A Gaussian basis set of cc-pV5Z quality augmented with 12 diffuse functions was used together with an extensive treatment of electron correlation. The main focus of this contribution is to investigate the 3d Rydberg complex assigned by Watson [Astrophys. J. 555, 472 (2001)] to three unidentified interstellar bands. The authors' calculations reproduce quite well the absolute excitation energies of the three components of the 3d complex, i.e., 2Sigma+(3dsigma), 2Pi(3dpi), and 2Delta(3ddelta), but not the energy ordering inferred from a rotational assignment of the 3d<--X 2Pi laboratory spectrum. The computation of the 4d complex is reported for the first time along with a number of other higher lying Rydberg species with an X 1Sigma+ core. The lowest Rydberg states belonging to series converging to the a 3Pi and A 1Pi excited states of CH+ are also calculated.

The microbial etiologies of diarrhea in hospitalized patients from the Puerto Rico Medical Center Hospitals

The development of diarrhea in hospitalized patients is a frequently encountered clinical problem, which may be due to infectious or non-infectious causes. The purpose of this study was to identify which common community enteric pathogens, if any, are responsible for diarrheal episodes in hospitalized patients. Stool samples from 76 consecutive, hospitalized patients were analyzed utilizing routine bacterial cultures, smears for identification of ova and parasites and Enzyme-Link Immunoadsorbent Assay (ELISA) for enteric bacteria, parasites and viruses. The results obtained demonstrated that the usual community enteric pathogens were not identified as a major cause of nosocomial diarrhea. In hospital-acquired diarrhea, Clostridium difficile toxins assay was the only clinically significant test in the evaluation of these patients. As a result of this study a guideline for the management of this condition in hospitalized patients is presented.

A comparison of the antimicrobial resistance patterns of gram-negative bacilli isolated from community-private and university-affiliated hospitals from Puerto Rico

Few studies have been performed in Puerto Rico concerning the antimicrobial resistance pattern of clinically significant Gram-negative bacilli. The antimicrobial resistance patterns of 5,590 Gram-negative bacteria obtained from three Community-Private Hospitals (CPH) and three University-Affiliated Hospitals (UAH) were evaluated utilizing the institutions' antimicrobial susceptibility reports for the year 2000. The objectives of this study were: to retrospectively evaluate the reported in vitro resistance of clinical isolates of E. coli, K. pneumoniae, E. cloacae, S. marcescens, P. aeruginosa and A. baumannii to selected standard antibiotics and to compare the antimicrobial resistance patterns between Community-Private (CPH) and University Affiliated hospitals (UAH). E. coli was the most common Gram-negative enteric bacilli in both CPH and UAH. In UAH, E. coli demonstrated a statistically significant higher resistance to the selected beta lactams and amikacin antibiotics but not to ciprofloxacin or gentamicin. For K. pneumoniae, the antimicrobial resistant pattern showed that UAH isolates were significantly more resistant to the tested antibiotics with the exception of ceftriaxone. In CPH, E. cloacae isolates were significantly more resistant to piperacillin-tazobactam, ciprofloxacin and gentamicin, while in UAH this organism was more resistant to amikacin. In UAH, S. marcescens isolates demonstrated a statistically significant higher resistance to all tested antibiotics with the exception of imipenem, which was similar in both hospitals group. Pseudomonas aeruginosa demonstrated a statistically significant higher resistance in UAH to all selected antibiotics with the exception of ciprofloxacin and gentamicin, which was similar in both hospitals group. Acinetobacter baumannii was the most resistant organisms in both hospitals group. UAH isolates were significantly more resistant than CPH isolates for all tested antibiotics. When compare with other large-scale antimicrobial resistance studies, the present study results suggest an apparent higher resistance in the Puerto Rican isolates. The high numbers of antimicrobial resistant Gram-negative bacilli in our study strongly suggest multiple mechanisms of antimicrobial resistance including the presence of extended spectrum and chromosomally derepressed beta-lactamases.

A comparison of the antimicrobial resistance patterns of gram-positive cocci isolated from community-private and university-affiliated hospitals from Puerto Rico

The antimicrobial resistance patterns of 2,462 selected Gram-positive cocci obtained from three Community-Private Hospitals (CPH) and three University-Affiliated Hospitals (UAH) were evaluated utilizing the institutions' antimicrobial susceptibility reports for the year 2000. The objectives of this study were: 1) to evaluate the in vitro resistance to selected standard antibiotics of Staphylococcus aureus, Enterococcus faecalis, Enterococcus faecium and Streptococcus pneumoniae clinical isolates, and 2) to compare the antimicrobial resistance patterns between community-private (CPH) and university-affiliated hospitals (UAH). Staphylococcus aureus was the most common Gram-positive isolated organism in CPH (63.3 per cent) followed by E. faecalis (31.0 per cent). In UAH, the most prevalent cocci were E. faecalis (51.7 per cent) followed by S. aureus (43.9 per cent). Enterococcus faecium represented 2.3 per cent and 4.4 per cent of CPH and UAH isolates, respectively. Streptococcus pneumoniae represented 3.4 per cent of the total Gram-positive isolates from CPH, no S. pneumoniae was reported in UAH. The antimicrobial susceptibility results showed that for Staphylococcus aureus there was a statistically significant higher resistance to methicillin and thrimethoprim sulfamethoxazole in UAH, while resistance to erythromycin was significantly higher in CPH. There was no difference in the resistance of S. aureus to other antimicrobial agents between hospitals groups. A statistically significant resistant to vancomycin was found between enterococcal isolates from UAH (43 per cent) and CPH (12.7 per cent). High-level aminoglycoside resistance (HLAR) was observed among UAH enterococcal isolates with E. faecium showing a higher resistance than E. faecalis, no data for HLAR in CPH could be obtained. For pneumococci 46 per cent of CPH isolates were resistant to penicillin. In summary, there are important differences in the prevalence and antimicrobial resistance between the Gram-positive bacteria isolated from community and teaching hospitals.

Prospective study using standardized methodology for antimicrobial susceptibility of gram-positive cocci isolated from the Puerto Rico Medical Center

The Gram-positive cocci (GPC), Staphylococcus aureus, Streptococcus pneumoniae, Enterococcus faecalis and Enterococcus faecium, have become important causes of community and nosocomial-acquired infections. The prevalence of multiple resistant isolates to standard antimicrobial drugs has significantly increased over the past decades. Few prospective studies have been performed in Puerto Rico (PR) concerning the GPC antimicrobial susceptibilities pattern. The purpose of this study was to evaluate the in vitro susceptibility of GPC clinical isolates from PR to selected standard antibiotics and to the new antimicrobial agents, linezolid (LZ), quinupristin/dalfopristin (Q/D) and gemifloxacin (GM). The in vitro susceptibility utilizing disk diffusion and Etest methods to selected antibiotics was determined for a total of 429 isolates obtained during a period of 5 months from the Puerto Rico Medical Center Bacteriology Laboratory. The distribution of GPC collected was as follows: 213 S. aureus isolates, 162 E. faecalis, 16 E. faecium and 38 S. pneumoniae. The results of the susceptibility test demonstrated: 1) that in S. aureus, 100 per cent of the isolates were susceptible to vancomycin (VAN), LZ and Q/D; 93 per cent to GM; and 61 per cent to methicillin/oxacillin; 2) in S. pneumoniae, 100 per cent were susceptible to LN and GM; 87 per cent to Q/D; and 53 per cent to penicillin; 3) in E. faecalis, 99 per cent were susceptible to ampicillin; 93 per cent to LZ; 79 per cent to GM; 78.6 per cent to VAN; and 0 per cent to Q/D. Sixty eight and 66 per cent of the E. faecalis isolates were susceptible to gentamicin and streptomycin respectively; and 4) in E. faecium, 100 per cent were susceptible to LZ; 94 per cent to Q/D; 69 per cent to GM; 37.5 per cent to VAN and 20 per cent to ampicillin. In E. faecium isolates, 50 per cent and 31 per cent were susceptible to gentamicin and streptomycin, respectively. Of the vancomycin resistant enterococci, 88.9 per cent and 21 per cent of E. faecium and faecalis showed VanA phenotypic resistance, respectively...

Poly(3-hydroxybutyrate) synthesis genes in Azotobacter sp. strain FA8.

Genes responsible for the synthesis of poly(3-hydroxybutyrate) (PHB) in Azotobacter sp. FA8 were cloned and analyzed. A PHB polymerase gene (phbC) was found downstream from genes coding for beta-ketothiolase (phbA) and acetoacetyl-coenzyme A reductase (phbB). A PHB synthase mutant was obtained by gene inactivation and used for genetic studies. The phbC gene from this strain was introduced into Ralstonia eutropha PHB-4 (phbC-negative mutant), and the recombinant accumulated PHB when either glucose or octanoate was used as a source of carbon, indicating that this PHB synthase cannot incorporate medium-chain-length hydroxyalkanoates into PHB.

Phosphotransbutyrylase expression in Bacillus megaterium.

The molecular analysis of a genomic region of B. megaterium revealed the presence of a gene coding for the enzyme phosphotransbutyrylase (Ptb). The enzyme activity was measured throughout the different phases of growth in B. megaterium, and its activity was found to be maximal in the late exponential growth phase. The branched amino acids isoleucine and valine activated Ptb expression. PtbBm was capable of using butyryl-CoA and 2-methyl-propionyl CoA as substrates. ActBm, a final sigma54 regulator from B. megaterium whose gene is situated upstream from the ptb gene, activated its expression.

Paromomycin: no more effective than placebo for treatment of cryptosporidiosis in patients with advanced human immunodeficiency virus infection. AIDS Clinical Trial Group.

To evaluate the efficacy of paromomycin for the treatment of symptomatic cryptosporidial enteritis in human immunodeficiency virus-infected adults, we conducted a prospective, randomized, double-blind, placebo-controlled trial before the widespread introduction of highly active antiretroviral therapy (HAART). Seven units under the auspices of the AIDS Clinical Trials Group enrolled 35 adults with CD4 cell counts of < or = 150/mm(3). Initially, 17 patients received paromomycin (500 mg 4 times daily) and 18 received matching placebo for 21 days. Then all patients received paromomycin (500 mg q.i.d.) for an additional 21 days. Clinical definitions of response were measured by an average number of bowel movements per day in association with concurrent need for antidiarrheal agents that was lower than that before study entry. There was no treatment response during the placebo-controlled phase of the study according to protocol-defined criteria (P=.88). Three paromomycin recipients (17.6%) versus 2 placebo recipients (14.3%) responded completely. Rates of combined partial and complete responses in the paromomycin arm (8 out of 17, 47.1%) and the placebo arm (5 out of 14, 35.7%) of the study were also similar (P=.72). The clinical course of cryptosporidiosis was quite variable. Paromomycin was not shown to be more effective than placebo for the treatment of symptomatic cryptosporidial enteritis. However, inadequate statistical power prevents definitive rejection of the usefulness of paromomycin as therapy for this infection.

Diagnosis of malaria by polymerase chain reaction.

Malaria is no longer endemic in Puerto Rico, however, imported cases of the disease are occasionally reported to the Health Department of the Island. This is a report of a 45-year-old female patient who traveled to Kenya and Niger and was admitted to a San Juan area hospital with an 8 day history of daily chills and fever, myalgia, nausea and vomiting. Upon admission, peripheral blood displayed multiple intra-erythrocytic ring-shape trophozoites, highly suggestive of Plasmodium falciparum. The polymerase chain reaction was used as a complementary method for the detection of malaria parasites and confirmation of post-treatment parasite clearance. This report presents an imported case of malaria in Puerto Rico and showed the use of a molecular technique to diagnose Plasmodium.

Trans activation of the Escherichia coli ato structural genes by a regulatory protein from Bacillus megaterium: potential use in polyhydroxyalkanoate production.

A Bacillus megaterium genomic fragment, which encoded an activator homologous to sigma 54 regulators and which was capable of activating Escherichia coli ato genes in trans, was detected in a gene library of B. megaterium screened for beta-ketothiolase activity. The fragment presented only one complete open reading frame (ORF1), which encoded a protein of 398 amino acids. The recombinant plasmid complemented mutations in the Escherichia coli atoC regulatory gene. The constitutive expression of the E. coli ato operon mediated by ORF1 could be useful for the synthesis of polyhydroxyalkanoates with different flexibility properties by recombinant E. coli strains.

[Poly-(3-hydroxybutyrate) granules in Bacillus megaterium. Isolation and analysis of associated proteins]. / Gránulos de poli(3-hidroxibutirato) en Bacillus megaterium. Aislamiento y análisis de las proteínas asociadas.

Bacillus megaterium accumulates poly-(3-hydroxybutyrate) (PHB) as a reserve material in intracellular granules. In this work we described a method for the preparation of PHB granules from B. megaterium PV447 and the analysis by polyacrylamide gel electrophoresis of the associated proteins. By comparison with another species a function is proposed for some of these proteins.

Efficacy of antibiotic combinations including rifampin against methicillin-resistant Staphylococcus epidermidis: in vitro and in vivo studies.

Rifampin in combination with other antibiotics has been used successfully in the treatment of serious infections due to Staphylococcus epidermidis. The authors evaluated the efficacy of rifampin in combination with either cephalothin, nafcillin, gentamicin, or vancomycin to determine in vitro synergistic or antagonistic interactions of the combinations and to determine the role of the second antibiotic in preventing the emergence of rifampin-resistant mutants. The authors found that among 10 isolates of methicillin-resistant S. epidermidis, synergy was found in checkerboard studies (inoculum, 10(5) colony-forming units/ml) for only two isolates and only with nafcillin and rifampin; antagonism was present with one combination for each of four different isolates. Time-kill studies showed each antibiotic capable of preventing the emergence of rifampin-resistant mutants for all 10 isolates, but no synergy or antagonism was present. In experimental endocarditis, however, the addition of cephalothin did not prevent the emergence of rifampin-resistant mutants, and rifampin-resistant mutants were as capable of causing endocarditis as were their rifampin-sensitive parents. Thus, rifampin was a bactericidal antibiotic against methicillin-resistant S. epidermidis. The benefit of a second antibiotic in vitro was the prevention of the emergence of rifampin-resistant mutants. However, in vivo results with a beta-lactam antibiotic did not confirm in vitro observations. More animal and human studies should be performed with antibiotic combinations including rifampin against methicillin-resistant S. epidermidis.