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M F Vicente

Publications and source records attributed to M F Vicente.

24 records · Page 2Linked to original sources
PubMed1988

Expression in Escherichia coli and sequence analysis of the listeriolysin O determinant of Listeria monocytogenes.

To evaluate the role of hemolysin production in the virulence of Listeria monocytogenes, we have undertaken the analysis of the chromosomal region containing hlyA, the gene coding for listeriolysin O. A recombinant cosmid, conferring a hemolytic phenotype to Escherichia coli, was shown to express listeriolysin O, by immunoblotting with a specific antiserum against listeriolysin O. The presence of hlyA on the cosmid was demonstrated by DNA hybridization with a probe previously shown to contain part of hlyA. The complete nucleotide sequence of hlyA has been determined. The deduced protein sequence reveals the presence of a putative 25-amino-acid signal sequence: the secreted form of listeriolysin O would have 504 amino acids, in agreement with the molecular weight of purified listeriolysin O (58,000). The protein sequence is highly homologous to those of streptolysin O and pneumolysin. A peptide of 11 amino acids conserved in the three proteins contains the unique cysteine known to be essential for lytic activity. By DNA-DNA hybridization, the listeriolysin O gene was detected in all L. monocytogenes strains tested, even in the nonhemolytic type strain. The gene was absent in other species of the genus Listeria.

Amino Acid Sequence↗
PubMed1987

A protoplast transformation system for Listeria sp.

We describe protoplast transformation of members of the genus Listeria with plasmid DNA. Shuttle vectors able to replicate in both Escherichia coli and Listeria have been constructed by fusing the E. coli plasmid pUC8 with the Bacillus subtilis plasmids pBD9 and pBD10.

DNA Replication↗
PubMed1986

Postantibiotic effect of imipenem on gram-positive and gram-negative micro-organisms.

The bactericidal effect (BE) of an antibiotic reduces the infective population, and its postantibiotic effect (PAE) assures a persistent inhibition of bacterial cells after a short exposure to the antimicrobial agent. Both effects prevent the early regrowth of the infecting organisms when the antibiotic tissue levels decrease to below the MIC value. The BE and the PAE of imipenem, cefotaxime, ceftazidime, piperacillin, gentamicin and ampicillin on Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Pseudomonas aeruginosa, Acinetobacter calcoaceticus, Staphylococcus aureus and Streptococcus faecalis were investigated with viable counts and continuous impedance monitoring of broth cultures. Imipenem and gentamicin gave similar high BE and PAE values at low concentrations and with short drug exposures in most strains tested. PAE is low or non-existent for Gram-negative strains with other beta-lactam antibiotics. These results suggest the possibility of future clinical studies with new experimental dosage schedules for imipenem.

Anti-Bacterial Agents↗
PubMed1985

beta-Lactam coselection of sensitive and TEM-1 beta-lactamase-producing subpopulations in heterogeneous Escherichia coli colonies.

We tested the effect of different concentrations of cefamandole, cefotaxime, cefoxitin and imipenem on homogeneous and heterogeneous bacterial stationary colonies. A reduction of not more than 100-fold in the bacterial colony population was obtained with sensitive Escherichia coli K12 strains. When an E. coli strain producing high levels of TEM-1 beta-lactamase constituted 6% or more of the population, the whole colony was resistant to cefamandole, but still sensitive to cefotaxime, cefoxitin or imipenem. Thus in the case of cefamandole the sensitive subpopulation is co-selected by the resistant one. It is suggested that the occurrence of resistant subpopulations, as a small part of an apparently sensitive E. coli population, can lead to therapeutic failures with beta-lactamase-sensitive agents.

Anti-Bacterial Agents↗