1,720,975 research outputs found
MUTANTI pnc IN ESCHERICHIA COLI K-12
No full textMutans of E. coli K12 deficient in the recycling pathway of NAD were isolated. Nutritional properties of
mutants provide elucidations regarding NAD turnover and utilization of exogenous NAD
Transformation of Streptococcus sanguis Challis with a plasmid of Streptococcus pneumoniae
No full textThe present work is concerned with plasmid transformation of Streptococcus sanguis strain Challis with derivatives of pDP1/pSMB1, the only plasmid found to occur naturally in Streptococcus pneumoniae. Two recombinant plasmids derived from the cryptic pSMB1 were used: pDP27 (4.5 kb) conferring resistance to chloramphenicol (Cm), and pDP28 (7.8 kb), a shuttle plasmid, conferring resistance to Cm in Escherichia coli, and resistance to erythromycin (Em) in pneumococcus. It could be shown that pSMB1 can replicate in S. sanguis; in fact, Challis strain V288 was transformed to Cm-resistance and to Em-resistance by pDP27 and pDP28 respectively.
Shuttle plasmid pDP28 can transform S. sanguis both when isolated from pneumococcus and from E. coli, albeit with a different efficiency. The low frequency of transformation observed when pDP28 was isolated from E. coli DH1 (recA) was shown to be due to lack of multimeric forms of the plasmid in the DNA preparations obtained from this strain. When pDP28 was isolated from E. coli C600 (RecA+), multimeric forms were present, and transformations of S. sanguis was more efficiency Using pDP28 as vector in cloning experiments, where S. sanguis was the host of the recombinant DNA molecules, treatment of the vector with alkaline phosphatase inhibited the recovery of recombinant clones
Gene exchange in streptococci: the conjugative chromosomal element 6001 as vector of recombinant DNA molecules
No full textProperties of an E. coli O26 mutant with modified cell wall and improved efficiency as recipient in conjugation for an FII plasmid.
No full textAmong populations of an E. coli O26 strain two types of mutants have been found to be present which act as better recipients in conjugation for an FII plasmid. Some properties of one of these mutants, O26SMB9, are here described. They indicate that a defect in the cell-wall structure has occurred which corresponds to a smooth-semirough transition
Antimicrobial activity of Inga fendleriana extracts and isolated flavonoids
No full textThe EtOAc and n-BuOH extracts of Inga fendleriana inhibited Gram-positive, but not Gram-negative bacteria; a narrow
spectrum of activity against Staphylococcus epidermidis was detected. The MIC values of the extracts ranged from 125 to 850
μg/mL. Quercetin 3-methylether, myricetin 3-O-rhamnoside and tricetin showed antibacterial activity against the same
bacterial strains with MICs in the range from 31 to 250 μg/mL. In time-kill kinetic studies, the flavonoids showed bactericidal
effects at the concentrations corresponding to four times the MICs
Unusual species of campylobacters isolated in the Siena Tuscany area, Italy
No full textFrom January 1989 to December 1990, stool samples from 288 children with enteritis were examined for the presence of unusual campylobacters which represented about 20% of all campylobacteria isolated when the filtration technique was used. The isolation percentage was the following: C. jejuni ss. jejuni 6.9%; C. coli 2%; C. jejuni ss. doylei, C. upsaliensis and C. concisus each 0.7%. The atypical Campylobacter isolates were examined for their virulence characteristics. Toxin profiles based on cytotonic, cytotoxic and cytolethal distending factors were determined after analysis responses in Vero, CHO and HeLa cells. Adhesivity and invasivity tests were performed on Intestine 407 cells. No strain was cytotoxic. C. jejuni ss. doylei and C. concisus induced an elongation of CHO cells (a cytotonic-like effect). C. upsaliensis strains provoked a cytolethal distending effect. No strain adhered to cells in vitro. Our results suggest that the filtration technique is excellent for the isolation of atypical campylobacters and indicate that the unusual Campylobacter isolates could be potentially virulent
Two different types of conjugation prone recipients for an FII plasmid in populations of an E. coli O26 strain
No full textIn populations of an E. coli O26 strain three types of cells can be found which show different degrees of recipient ability in conjugation for an FII plasmid. In this paper the characterization of the plasmid used, pSMB35, is described and the conjugation-proficient mutants, O26SMB9 and O26SMB11, are compared for some of their properties
Host-vector system for integration of recombinant DNA into chromosomes of transformable and nontransformable streptococci
No full textWe describe a genetic system in which transformation of Streptococcus pneumoniae and Streptococcus sanguis was used to insert recombinant DNA into the conjugative chromosomal element Ω(cat tetM) 6001 (Ω6001). The element containing the recombinant DNA was then transferred by conjugation to the chromosome of transformable and nontransformable streptococci. When Escherichia coli plasmid pDP36 was used as donor in transformation, it was capable of inserting 5.9 kilobases of heterologous DNA into the chromosome of competent streptococcal strains carrying Ω6001; the transformants were scored for erythromycin resistance. Genetic analysis showed that in a fraction of the erythromycin-resistant transformants the integration via flanking homology of the heterologous DNA caused inactivation of the tetM gene of Ω6001. By analyzing the stability of the resistance markers, we found that stable integration of heterologous DNA was achieved only in the erythromycin-resistant, tetracycline-sensitive transformants. It was possible to detect conjugal transfer of the heterologous sequences from stable transformants to strains of S. pneumoniae, S. sanguis, Streptococcus pyogenes, and Streptococcus faecalis. The Ω6001-pDP36 host-vector system opens new possibilities for gene transfer in streptococci. By this method cloned streptococcal DNA (possibly mutagenized in vitro) can be returned to the orginal host, greatly facilitating complementation tests and fine physiological studies
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