Antimicrobial and antiviral activities of an actinomycete (Streptomyces sp.) isolated from a Brazilian tropical forest soil

A promising producer of bioactive compounds isolated from a Brazilian tropical soil was tested for its range of antimicrobial activities. Strain 606, classified as Streptomyces sp., could not be identified up to species level, suggesting a possible new taxon. The supernatant and 10 extracts and fractions, obtained by extraction and chromatographic techniques, presented antimicrobial activity using antibiograms. The methanolic fraction was highly active against pathogenic bacteria, phytopathogenic fungi and the human pathogenic yeast Candida albicans. It also possessed high antiviral activity inhibiting the propagation of an acyclovir-resistant herpes simplex virus type 1 strain on HEp-2 cells at non-cytotoxic concentration. The strong cytotoxic effect suggests an antitumour action. This revised version was published online in August 2006 with corrections to the Cover Date.     

An unsupervised neural network model for the development of reflex co-ordination

In this paper, we present a model for the development of connections between muscle afferents and motoneurones in the human spinal cord. The model consists of a limb with six muscles, one motoneurone pool, one pooled (Ia-like) afferent for each muscle and a central programme generator. The weights of the connections between the afferents and the motoneurone pools are adapted during centrally induced movements of the limb. The connections between the afferents and the motoneurone pools adapt in a hebbian way, using only local information present at the synapses. This neural network is tested in two examples of a limb with two degrees of freedom and six muscles. Despite the simplifications, the model predicts the pattern of autogenic and heterogenic monosynaptic reflexes quite realistically.     

Evaluation of Probiotic Properties of Novel Brazilian Lactiplantibacillus plantarum Strains

Probiotics and Antimicrobial Proteins - Beneficial effects of Lactiplantibacillus plantarum strains have been widely reported. Knowing that the effects of probiotic bacteria are strain-dependent,...     

Trypanosoma cruzi: strain selection by different schedules of mouse passage of an initially mixed infection

From an initial double infection in mice, established by simultaneous and equivalent inocula of bloodstream forms of strains Y and F of Trypanosoma cruzi, two lines were derived by subinoculations: one (W) passaged every week, the other (M) every month. Through biological and biochemical methods only the Y strain was identified at the end of the 10th and 16th passages of line W and only the F strain at the 2nd and 4th passages of line M. The results illustrate strain selection through laboratory manipulation of initially mixed populations of T. cruzi.     

Candidemia by Species of the Candida parapsilosis Complex in Children’s Hospital: Prevalence, Biofilm Production and Antifungal Susceptibility

Opportunistic infections are an increasingly common problem in hospitals, and the yeast Candida parapsilosis has emerged as an important nosocomial pathogen. The aims of this study were to determine and compare (i) the prevalence rate among C. parapsilosis complex organisms isolated from blood in a public children’s hospital in São Paulo state, (ii) the ability of the complex C. parapsilosis species identified to produce biofilm and (iii) the antifungal susceptibility profiles. Forty-nine (49) specimens of isolated blood yeast were analyzed, previously identified as C. parapsilosis by conventional methods. After the molecular analysis, the isolates were characterized as C. parapsilosis sensu stricto (83.7 %), C. orthopsilosis (10.2 %) and C. metapsilosis (6.1 %). All species were able to form biofilm. The species with the highest biofilm production was C. parapsilosis sensu stricto, followed by C. orthopsilosis and further by C. metapsilosis. All of the strains have demonstrated similar susceptibility to fluconazole, caspofungin, voriconazole, cetoconazole and 5-flucytosine. Only one strain of C. parapsilosis was resistant to amphotericin B. Regarding itraconazole, 66.6 and 43.9 % isolates of C. metapsilosis and C. parapsilosis, respectively, have demonstrated to be susceptible dose-dependent, with one isolate of the latter species resistant to the drug. Candida parapsilosis sensu stricto has demonstrated to be the less susceptible, mainly to amphotericin B, caspofungin and “azoles” such as fluconazole. Therefore, C. metapsilosis and C. orthopsilosis are still involved in a restricted number of infections, but these data have become essential for there are very few studies of these species in Latin America.     

Antimicrobial resistance and class I integrons in Salmonella enterica isolates from wild boars and Bísaro pigs

The antibiotic resistance phenotype and genotype and the integron type were characterized in 58 Salmonella enterica isolates recovered from Bísaro pigs and wild boars (20 S. Typhimurium, 17 S. Rissen, 14 S. Enteritidis and 7 S. Havana). Most S. Typhimurium isolates (15/20 of Bísaro pigs and wild boars) showed ampicillin, chloramphenicol, streptomycin, tetracycline, sulfonamide, and amoxicillin-clavulanic acid resistances. Of the 17 S. Rissen isolates of both origins, 13 were resistant to ampicillin, tetracycline and trimethoprim-sulfamethoxazole. Among the S. Enteritidis isolates of Bísaro pigs, eight were nalidixic acid-resistant and three were sulfonamide-resistant. The tet(A) or tet(G) genes were detected in most tetracycline-resistant isolates. The intI1 gene was identified in 72.5% of S. enterica isolates in which the conserved region 3' of class 1 integrons (qacEΔ1+sul1) was also amplified, whereas none had the intI2 gene. The dfrA12+orfF+aadA2 gene cassette arrangement was found in the variable region of class 1 integrons in 14 S. Rissen isolates. Fifteen S. Typhimurium isolates had two integrons with variable regions of 1000 and 1200 bp that harbored the aadA2 and blaPSE-1 gene cassettes, respectively. In these isolates the floR and tet(G) genes were also amplified, indicative of the genomic island 1 (SGI1). Salmonella Typhimurium and S. Rissen of animal origin frequently show a multi-antimicrobial resistant phenotype, which may have implications in public health.     

Structure-activity relationship of 5'-substituted fluoro-neplanocin a analogues as potent inhibitors of S-adenosylhomocysteine hydrolase

Four 5'-substituted fluoro-neplanocin A analogues la-d were designed and synthesized, and the inhibitory activity against SAH was in the following order: NH2 > SH > F, N3, indicating a hydrogen bonding donor is essential for inhibitory activity.     

High-resolution structure of shikimate dehydrogenase from Thermotoga maritima reveals a tightly closed conformation

Shikimate dehydrogenase (SDH), which catalyses the NADPH-dependent reduction of 3-dehydroshikimate to shikimate in the shikimate pathway, is an attractive target for the development of herbicides and antimicrobial agents. Structural analysis of a SDH from Thermotoga maritima encoded by the Tm0346 gene was performed to facilitate further structural comparisons between the various shikimate dehydrogenases. The crystal structure of SDH from T. maritima was determined at 1.45 Å by molecular replacement. SDH from T. maritima showed a monomeric architecture. The overall structure of SDH from T. maritima comprises the N-terminal α/β sandwich domain for substrate binding and the C-terminal domain for NADP binding. When the T. maritima SDH structure was compared with those of the SDHs from other species, the SDH from T. maritima was in a tightly closed conformation, which should be open for catalysis. Notably, α7 moves toward the active site (∼5 Å), which forces the SDH of T. maritima in a more closed form. Four ammonium sulfate (AMS) ions were identified in the structure. They were located in the active site and appeared to mimic the role of the substrate in terms of the enzyme activity and stability. The new high resolution structural information reported in this study, including the AMS binding sites as a potent inhibitor binding site of SDHs, is expected to supplement the existing structural data and will be useful for structure-based antibacterial discovery against SDHs.