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J P Gratia

Publications and source records attributed to J P Gratia.

At least 19 recordsLinked to original sources
PubMed1998

Effects of Ca2+ ions on survival, growth, and cell size in Serratia marcescens SMG40 exposed to mecillinam.

Serratia marcescens strain SMG40 is sensitive to mecillinam killing at concentrations approaching those required for rod-to-sphere conversion. After a 1 h exposure to mecillinam, the type of response was found to depend on the conditions of post-incubation. Whereas they lysed soon after transfer to a tenfold-diluted broth, treated cells stopped dividing and enlarged impressively without immediate lysis when they were transferred to a complete low-agar medium and incubated at 30 degrees C. More remarkably, the presence of Ca2+ cations in any post-incubation medium definitely protected treated cells from lysis, enabled them to divide as spheres, and prevented enlargement. These survival-promoting and size-limiting effects were reversible upon elimination of Ca2+ from the medium. They were observable at far lower ionic concentrations than those required for osmotic stabilization. The growth rate depended on the Ca2+ concentration (from 10 microM) and on the presence of other supplements. Na+ cations also exerted a protective effect but acted differently from Ca2+ ions; the effects of Na+ and Ca2+ ions appeared as synergistic. A physiological activity of calcium is suggested for this bacterial strain, resulting in a RodA-like mecillinam resistant phenotype.

Amdinocillin↗
PubMed1994

Ufr/s variation in Escherichia coli K12: a reversible double-mutation or alternate chromosome expression in non-complementing diploids?

A novel form of bacterial variation found in an FhuA- mutant of Escherichia coli K12 was characterized by the alternation of (1) simultaneous resistance to lipopolysaccharide-specific phage U3 and to FhuA-specific agents (Ufr phenotype); and (2) a return to the sensitivity pattern of the initial strain (Ufs). In Ufr cells, loss of the U3 receptor permitted C21 adsorption without modifying the sensitivity to other tested phages or colicins. Genetic analysis revealed that Ufr variants were altered at two distinct loci. Ufr bacteria, though derived from a strain F- devoid of classical gene transfer mechanisms, were transiently able to promote mating between themselves and, to some extent, with other bacteria, including Rec-. Heterogenic matings resulted in the formation of persistent heterozygotes segregating Ufr- and Ufs-like bacteria. Pedigree analysis and subcloning of heterozygotic isolates indicate that they were diploids, as was the initial Ufr strain. Functional genetic complementation between these two genomes was only transient and the alternative forms were likely to result from the expression of a single chromosome of the heterozygotes. Mutation occurred in either form without causing any change in the alternative form.

Bacteriophages↗
PubMed1992

Differential activity of bacteriocins and cefotaxime against Serratia marcescens clinical isolate SMG40 and its pigmented variant.

Strain Serratia marcescens SMG40 was nonpigmented but yielded pigmented variants at low frequency. Of 15 tested bacteriocins, 10 were active against the original strain, but only 7 were active against the pigmented variant Pdg+. Moreover, active cephalosporins, e.g., cefotaxime, were more active against the Pdg+ variant than against strain SMG40. These reciprocal differences in susceptibility to some bacteriocins and to cefotaxime were maintained in subclones derived from Pdg+/- sectored colonies. However, mutants of pigmentation isolated from the Pdg+ variant were not modified with regard to bacteriocins and cefotaxime. Other clinical isolates of Serratia were examined for comparison, but strain SMG40 appeared to be unique.

Amoxicillin↗
PubMed1989

Products of defective lysogeny in Serratia marcescens SMG 38 and their activity against Escherichia coli and other Enterobacteria.

From a series of Serratia marcescens clinical isolates analysed with respect to bacteriocin production, one strain (SMG 38) was exceptional in that it produced two distinct phage-tail-like bacteriocins differing in morphology, sedimentation, heat sensitivity, and host range. The more active component (bc25) was effective against Serratia, while the other component (McG) inhibited growth of Escherichia coli, Salmonella typhimurium and Shigella sonnei, but not Serratia. Plaque formation on tested strains was negative except in the single case of the lysate of a subclone of SMG 38 which caused the production of a virulent phage, phi epsilon, in E. coli K12 RH 5108. This seems to be a rare event. Like the bacteriocin McG, phage phi epsilon used the same receptor protein, coded at about 30 min (locus fig) on the E. coli chromosome, as does the temperate and serologically unrelated phage phi gamma. Both McG and UV-irradiated phi epsilon killed sensitive bacteria. The survival rate depended on the input multiplicity and also on the indicator strain, and was increased by the presence of prophage phi 80 in the cell. When survivors were allowed to resume their growth under normal conditions, they showed cell elongation whatever their RecA phenotype. No difference was observed between the two agents with respect to these observations, except that McG, unlike irradiated phi epsilon, was inactive against Klebsiella pneumoniae UNF 5023, which possessed the Fig receptor.

Bacteriocins↗
PubMed1980

Studies on the mechanism of transduction by bacteriophage phi gamma. II. Formation of transducing elements.

The formation of the transducing elements (TE) of bacteriophage phi gamma, analyzed in lysogens of the thermo-inducible derivative phi gamma hyI, has been found to parallel the formation of plaque-forming particles with a frequency of 2 X 10(-2) TE/PFU, but is mor sensitive to temperature and ti UV. Deletion of one of the prophage termini (attR) prevents normal excision and formation of plaque-forming particles, but does not affect the formation of transducing elements, which arise at a rate of nearly 10(-1) TE per induced bacterium. Transducing elements, would be formed by in situ encapsulation of a hybrid segment from a specidic point in the induced prophage, possibly the presumed packaging initiation site of the normal phage genome, before excision of the latter has occurred. Analysis of the mechanism of transduction to partly heterologous lysogens has revealed the participation of a co-infecting genome arranged in a linear fashion and has given evidence for a permutation in the sequence of transducing and nontransducing genomes. The data re consistent with a mechanism of encapsidation distinct from the Ter system even for hybrids inheriting part of the phi 80 genome, but endowed with the property to form transducing elements like those of phi gamma. Upon infection, transducing elements are formed after one cycle of lytic development with the same characteristics as those resulting from induction, but with a frequency 50 to 100 times lower. This process is dependent on the efficiency of Int promoted recombination. Superinfection experiments performed under conditions preventing Int promoted recombination reveal that any superinfecting phi gamma can promote the formation of transducing particles, depending on the presence within the host prophage of a site from which transducing genome packaging initiates.

Chromosome Mapping↗
PubMed1976

Studies on the mechanism of transduction by bacteriophage phi gamma. I. Genetic characterization of the transducing segment.

The bacteriophage phi gamma, though related to the lambdoid phage phi80, has unusual features in its specialized transduction and is being investigated to determine the mechanism of the transduction process. Genetic analysis of the transducing element gives evidence for a relatively long and uniform linear segment, up to about 1% of the E. coli chromosome, extending in either direction from the prophage attachment site, e.g., on the right side: att80-tonB-trpABCDE-cysB-pryF. The att end includes a variable amount of phage genome, probably very short in most particles. In a small fraction of the transducing particles the phage segment may be more extensive and, conversely, the bacterial segment is shorter, ending around cysB. The transducing segment from modificationless bacteria carries a site susceptible to the K-restriction system which affects the efficiency of transduction.

Arginine↗