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R Fontana

Publications and source records attributed to R Fontana.

At least 127 records · Page 7Linked to original sources
PubMed1987

Changes in penicillin-binding proteins during the life cycle of Micromonospora.

The penicillin-binding proteins (PBPs) of Micromonospora were studied. Only one PBP (48,000 mol weight) was found in membranes isolated from primary mycelia, whereas three PBPs were observed in secondary mycelia and designated PBP 1 (89,000 mol weight), PBP2 (69,000) and PBP3 (48,000). Both the unique PBP produced by primary mycelia and PBP3 of secondary mycelia had the same affinity for penicillin which was higher than that of PBP2 and 3. The role of these proteins in the cell life cycle of Micromonospora is discussed.

Bacterial Proteins↗
PubMed1986

In Streptococcus faecium penicillin-binding protein 5 alone is sufficient for growth at sub-maximal but not at maximal rate.

In Streptococcus faecium inhibition by both benzylpenicillin and cefotaxime of cells growing at maximal and at reduced rates was associated with saturation of different penicillin-binding proteins. Cells growing at reduced rates were not inhibited by benzylpenicillin concentrations that saturated all penicillin-binding proteins except penicillin-binding protein 5, but did stop growing when this protein was saturated.

Bacterial Proteins↗
PubMed1986

Comparison of effects of penicillin minimal inhibitory and sub-inhibitory concentration on Staphylococcus aureus and Streptococcus faecium does not support the view that antibiotic sub-inhibitory concentrations can specifically interfere with bacterial virulence.

The effect of minimal (MIC) and sub-minimal (sub-MIC) inhibitory concentrations of penicillin on Staphylococcus aureus and Streptococcus faecium were compared. It was found that similar alterations in both cell shape and ultrastructure were found in the presence of penicillin MIC and sub-MICs, the only difference being that while in the presence of penicillin MIC all individual cells were altered, in the presence of sub-MICs the damaged portion was smaller the lower the penicillin concentration and the longer the incubation time. By testing the effect of inoculum size on the penicillin MIC, it was found that penicillin concentrations, which were sub-MICs for rather dense population, turned out to be the MICs for lower density populations. These findings do not support the view that sub-MICs of antibiotics can cause specific damage to bacterial cells which, although not leading to growth inhibition, lowers their virulence. On the contrary, it is suggested that penicillin sub-MICs have no specific effect on Staphylococcus aureus and Streptococcus faecium cells, but simply differ from MIC in that they do not inhibit all cells.

Microbial Sensitivity Tests↗
PubMed1986

Purification of Streptococcus faecium penicillin binding protein 5, a multifunctional penicillin-binding protein.

Penicillin-binding protein 5 of Streptococcus faecium has been solubilized and partially separated from other membrane proteins by covalent affinity chromatography. PBP 5 was successively purified to homogeneity by resolution on SDS-polyacrylamide gel, elution and renaturation of penicillin-binding activity. The purification procedure does not alter the properties that the protein exhibits in the membranous environment.

Bacterial Proteins↗
PubMed1985

Hematin-catalyzed epoxidation of 7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene by polyunsaturated fatty acid hydroperoxides.

Hematin catalyzes the epoxidation of 7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (BP-7,8-diol) by 13-hydroperoxy-9-cis,11-trans-octadecadienoic acid and other fatty acid hydroperoxides in the presence of detergent. The major oxidation product is the anti-dihydrodiolepoxide and the minor product is the syn-dihydrodiolepoxide. (+)-BP-7,8-diol is oxidized to (-)-anti-diolepoxide and (+)-syn-diolepoxide whereas (-)-BP-7,8-diol is oxidized to (+)-anti-diolepoxide and (-)-syn-diolepoxide. Oxygen labeling studies indicate that the source of the epoxide oxygen is O2. The phenolic antioxidants butylated hydroxyanisole and butylated hydroxytoluene inhibit epoxidation by 100 and 93%, respectively. These observations suggest that hematin-catalyzed epoxidation proceeds by a free radical mechanism. Incubation of hematin, BP-7,8-diol, and a series of fatty acid hydroperoxides containing two, one, or zero double bonds alpha to the carbon bearing the hydroperoxide indicates that at least one double bond is essential for generation of the epoxidizing agent. Taken with results of the study of the metabolism of 13-hydroperoxy-9-cis,11-trans-octadecadienoic acid by hematin described in the accompanying paper (Dix, T. A., and Marnett, L. J. (1985) J. Biol. Chem. 260, 5351-5357), these results indicate that the epoxidizing agent is a peroxyl radical generated by coupling of O2 to a carbon-centered radical derived from the double bonds adjacent to the hydroperoxide group. The detergents Tween 20, Triton X-100, and Triton X-405 dramatically enhance epoxidation above but not below their critical micellar concentrations. The intensity and lambda max of the ultraviolet absorption spectrum of BP-7,8-diol increase in the presence of detergent, indicating that an important role of detergent is solubilization of the hydrophobic substrate. However, detergent also stimulates the hematin-catalyzed oxidation of a water-soluble polycyclic hydrocarbon, bis-(carboxyethyl)-anthracene, suggesting that detergent has an effect on the peroxidase activity of hematin. A detailed mechanism for epoxidation of BP-7,8-diol by hematin and fatty acid hydroperoxides is presented and its relevance to other hydroperoxide-dependent epoxidizing systems is discussed.

Benzopyrenes↗
PubMed1985

Regulation of penicillin-binding protein activity: description of a methicillin-inducible penicillin-binding protein in Staphylococcus aureus.

The penicillin-binding proteins (PBPs) of two methicillin-resistant strains of Staphylococcus aureus (R2 and R1) were analyzed in cells grown in the absence and in the presence of methicillin. Under the former condition, strain R2 showed the typical PBP pattern of beta-lactam-susceptible strains, while strain R1 showed a markedly increased amount of PBP-3. Under the latter condition, on the other hand, a novel PBP (PBP-2a) located between PBP-2 and -3 was detected in strain R2, while strain R1 appeared to synthesize an even greater amount of PBP-3, in respect to untreated cells. Both R2 PBP-2a and R1 PBP-3 showed a very low affinity for methicillin, which was consistent with the MICs for the respective strains.

Bacterial Proteins↗
PubMed1985

Transition from resistance to hypersusceptibility to beta-lactam antibiotics associated with loss of a low-affinity penicillin-binding protein in a Streptococcus faecium mutant highly resistant to penicillin.

Penicillin-binding protein (PBP) 5 of Streptococcus faecium has been shown to have a very low affinity for penicillin, and this PBP was suggested to be responsible for both the natural low susceptibility and high resistance to the antibiotic in this species (R. Fontana, R. Cerini, P. Longoni, A. Grossato, and P. Canepari, J. Bacteriol. 155:1343-1350, 1983). In this study, an S. faecium mutant (Rev 14) hypersusceptible to penicillin was derived from the highly resistant S. faecium R40 treated with novobiocin, and its properties were compared with those of the parent and S. faecium PS, a relatively susceptible strain from which R40 was isolated. The hypersusceptible strain did not synthesize PBP 5, but it did resemble the parent in cell morphology, growth rate, and autolytic activity. In addition, it was highly susceptible to other beta-lactams but remained as susceptible as R40 and PS to antibiotics of a different mechanisms of action. The affinity of individual PBPs for the beta-lactams tested was the same in all the strains. This finding suggested that Rev 14 hypersusceptibility was due to the lack of PBP 5 and strongly supported the role of this protein in the mechanism of both natural low susceptibility and high-level resistance to beta-lactams in S. faecium.

Anti-Bacterial Agents↗
PubMed1985

Different staphylococcal species contain various numbers of penicillin-binding proteins ranging from four (Staphylococcus aureus) to only one (Staphylococcus hyicus).

The penicillin-binding proteins of a total of 25 staphylococcal strains belonging to five different species were analyzed. All strains of the same species showed an identical penicillin-binding protein pattern which clearly differed from that of strains of the other species. Staphylococcus aureus, Staphylococcus intermedius, Staphylococcus simulans, and the dolphin strains were found to contain two to four penicillin-binding proteins. Strains of Staphylococcus hyicus exhibited only one penicillin-binding protein.

Bacterial Proteins↗
PubMed1984

Division of temperature-sensitive Streptococcus faecium mutants after return to the permissive temperature.

The regrowth of 27 temperature-sensitive division mutants of Streptococcus faecium ATCC 9790 was examined after various periods of incubation at the nonpermissive temperature. Several of the mutants blocked at various stages of septum formation or of daughter-cell separation divided in a partially or completely synchronous way after a short incubation at the nonpermissive temperature. All four lytic mutants blocked early in the cell division cycle divided at a normal rate after a brief lag.

Cell Division↗
PubMed1983

Streptococcus faecium ATCC 9790 penicillin-binding proteins and penicillin sensitivity are heavily influenced by growth conditions: proposal for an indirect mechanism of growth inhibition by beta-lactams.

The effects of variations in growth conditions on the penicillin response of Streptococcus faecium ATCC 9790 were studied. Changes in the growth temperature and medium composition were found to cause striking changes in the bacterial generation time, cellular penicillin sensitivity (minimum inhibitory concentration), sensitivity of peptidoglycan synthesis to inhibition by penicillin, rate of autolysis, and labeling pattern of penicillin-binding proteins. However, no constant relationship between these parameters and the minimum inhibitory concentration could be observed. Similar electrophoretic patterns for penicillin-binding proteins were observed in cells grown in different media at the optimal growth temperature. Inhibition of cell division by penicillin in cells grown at this temperature (but not at higher or lower temperatures) caused filamentation of the bacteria. In cells grown in a chemically defined medium at the optimal temperature (but not at temperatures above or below), complete inhibition of cell division was associated with only partial inhibition (34% after 150 min) of peptidoglycan synthesis. It is suggested that the status and physiological importance of individual penicillin-binding proteins in S. faecium are heavily influenced by growth conditions. Depending on the growth conditions, different penicillin-binding proteins may perform the cellular function, indispensible for bacterial growth.

Bacterial Proteins↗