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Biomedical subjects

R Fontana

Publications and source records attributed to R Fontana.

At least 19 recordsLinked to original sources
PubMed1992

Spontaneous haematoma as unusual complication of silastic dural substitute. Report of 2 cases.

Two cases of an unusual complication of synthetic duraplasty are reported. In both cases, patients had been operated on because of meningiomas and dural defects had been repaired with Silastic. Some years later they developed severe graft-related haematomas and were ultimately successfully treated only by the removal of the synthetic grafts. On the basis of this and other clinical experiences, biological dural grafts seem to be preferable to synthetic ones.

Dura Mater↗
PubMed1992

In vitro activity of cefpirome (HR 810) against enterococci and staphylococci.

The inhibitory activity of cefpirome (HR 810), a new cephalosporin derivative for parenteral use, was tested by agar dilution methods against Enterococcus faecalis (100 strains), Staphylococcus aureus (40 strains) and coagulase-negative staphylococcal species (60 strains) in comparison with other beta-lactam antibiotics. For E. faecalis, the cefpirome minimum inhibitory concentration (MIC) range was 2-128 micrograms/ml, with an MIC50 of 8 micrograms/ml, and an MIC90 of 64 micrograms/ml. The optimal bactericidal activity against strains with MICs of < or = 8 micrograms/ml occurred at 2-4 times the MIC, and the reduction in the initial inoculum was 99.9-99.7% after 24 h incubation at these concentrations. Mec gene-negative staphylococci (both S. aureus and coagulase-negative species) had cefpirome MICs of 0.25-2 micrograms/ml (MIC50 0.5 microgram/ml, MIC90 1 microgram/ml). Mec gene-positive strains had MICs of 0.5-128 micrograms/ml (MIC50 2 micrograms/ml, MIC90 32 micrograms/ml). Strains with borderline resistance to oxacillin which did not harbor the mec gene and which were susceptible to cefpirome maintained their susceptibility even when high-density inocula were used and after several passages in media containing the antibiotic. These studies present some potential advantages of cefpirome over other cephalosporins in the inhibitory activity against Gram-positive cocci.

Anti-Bacterial Agents↗
PubMed1992

Mechanisms of resistance to growth inhibition and killing by beta-lactam antibiotics in enterococci.

Enterococci are characterized by an intrinsic resistance to growth inhibition by beta-lactam antibiotics. The low susceptibility of enterococci to beta-lactam antibiotics is associated with the synthesis of a particular penicillin-binding protein (PBP) that has a low affinity for beta-lactam agents. This protein appears to be capable of taking over the function of the other PBPs when they are saturated with beta-lactam molecules or inactivated by mutations. A quantitative correlation can be established between the binding of several beta-lactam molecules to the low-affinity PBP and the minimal inhibitory concentration for enterococcal strains. In contrast, the mechanism of enterococcal resistance to the bactericidal activity of beta-lactam agents that inhibit growth at relatively low concentrations appears to be associated with an alteration in the pattern of autolytic enzyme activity. In particular, lack of or poor activity of an autolytic enzyme appears to be responsible for the paradoxical bactericidal response often exhibited by clinical isolates of Enterococcus faecalis in the presence of penicillin.

Anti-Bacterial Agents↗
PubMed1992

Diffusion of meropenem and imipenem through the outer membrane of Escherichia coli K-12 and correlation with their antibacterial activities.

The outer membrane permeability to meropenem and imipenem in Escherichia coli K-12 was investigated, and its porin-deficient mutants were transformed with a constructed vector carrying the carbapenem-hydrolyzing CphA metallo-beta-lactamase gene. By using the method of Zimmermann and Rosselet, meropenem was shown to penetrate through the outer membrane of E. coli K-12 five times faster than cephaloridine but twice as slowly as imipenem. Lack of one or both porins significantly reduced the penetration of both carbapenems. No evidence of specific porin pathways of the type described in Pseudomonas aeruginosa was found. Despite its slower penetration, meropenem was two to eight times more active than imipenem against both parent and porin-defective mutants, whether harbouring CphA beta-lactamase or not. Meropenem was also more active than imipenem against E. coli DC2, a strain with a breakdown in the outer membrane permeability which made periplasmic concentrations of beta-lactams similar to the external concentrations. In this strain, meropenem caused a more than 50% reduction in cell number increase at a concentration very close to the 50% inhibitory concentration for penicillin-binding protein type 2 (PBP 2), whereas imipenem, at the same concentration, did not significantly inhibit cell growth. This result was explained by the higher affinity of meropenem for PBP 3 compared with imipenem and supports the conclusion that synergistic inhibition of both PBPs was the main mechanism in the better antibacterial activity of meropenem.

Bacteria↗
PubMed1991

Detection of penicillin-binding proteins immunologically related to penicillin-binding protein 5 of Enterococcus hirae ATCC 9790 in Enterococcus faecium and Enterococcus faecalis.

Penicillin-binding protein (PBP) 5 of Enterococcus hirae ATCC 9790 belongs to the class of the high-molecular mass, low-affinity PBPs which have been correlated with penicillin resistance in most Enterococcus species. Polyclonal antibodies were raised against PBP 5 and used to detect immunologically related membrane proteins in E. faecium and E. faecalis strains. Several strains of both species were found to have a membrane protein of similar molecular mass to E. hirae PBP 5 which reacted with the antibodies. Some E. faecium strains did not react with antibodies but their derivatives with increased penicillin minimal inhibitory concentrations did. In some E. faecalis strains the lack of a PBP 5-related protein was associated with failure to select stable penicillin-resistant derivatives.

Bacterial Proteins↗
PubMed1991

Effect of non-beta-lactam antibiotics on penicillin-binding protein synthesis of Enterococcus hirae ATCC 9790.

Fosfomycin, bacitracin and vancomycin in combination with penicillin exhibit a synergic effect against Enterococcus hirae ATCC 9790. This strain, when incubated in presence of the MIC of non-beta-lactam antibiotics, showed an alternated pattern of PBPs. Bacitracin and vancomycin caused a decrease in the density of all PBPs while fosfomycin only reduced that of PBP 6. It is suggested that the observed synergy is a consequence of the inhibition of PBP synthesis by antibiotics which act on the early stages of peptidoglycan synthesis prior to the formation of cross-links.

Bacitracin↗
PubMed1991

Danazol: in vitro effects on human hemopoiesis and in vivo activity in hypoplastic and myelodysplastic disorders.

We examined the effects of danazol on in vitro growth of human bone marrow and peripheral blood progenitor cells from 15 normal donors and 5 myelodysplastic patients, and on in vivo hemopoiesis in 30 patients with hypoplastic or myelodysplastic disorders. At concentrations similar to that reported as the plasma level after oral administration, danazol significantly increased CFU-GM colony growth in all normal donors, while the influence on CFU-E, BFU-E, CFU-MK and CFU-GEMM colony growth was less evident. The stimulatory effect on CFU-GM was observed even after accessory cell depletion. Np stimulatory effect either in vitro on the growth of all hemopoietic progenitors or in vivo was observed in 15 myelodysplastic patients, while 7 complete and 3 partial hematological responses occurred in 15 patients with hypoplastic disorders. In conclusion, our results suggest that danazol exerts a direct stimulatory activity in vitro at least on CFU-GM, and a hemopoietic stimulatory effect in vivo in hypoplastic but not in myelodysplastic disorders.

Adult↗
PubMed1991

Genotypic identification of methicillin-resistant coagulase-negative staphylococci by polymerase chain reaction.

A rapid method for the detection of methicillin resistance in staphylococci was developed. The method was based on the polymerase chain reaction (PCR) and primers that targeted the internal region of the coding frame of the mec gene. The amplification reaction was carried out with crude cell lysates as a source of target DNA and provided data in less than 5 h. Seventy-four isolates of coagulase-negative staphylococci were tested by PCR, DNA hybridization with a probe derived from the mec gene, and an agar dilution susceptibility assay. PCR results showed a 100% correlation with the susceptibility assay carried out with high inocula (10(8) CFU) and incubation at 32 degrees C for 48 h. PCR was more sensitive and specific than DNA hybridization in detecting methicillin resistance in coagulase-negative staphylococci. The former technique identified the mec gene in all the strains which were phenotypically resistant but which did not hybridize with the probe. Identification of methicillin-resistant strains by PCR offers a very specific, sensitive, and rapid alternative to traditional susceptibility tests and DNA hybridization as a guide for the treatment of infections caused by staphylococci.

Coagulase↗
PubMed1991

Nonradioactive DNA probe for detection of gene for methicillin resistance in Staphylococcus aureus.

A DNA probe was developed by inserting, in the SmaI site of pBluescript sK, a 528-bp fragment of the gene responsible for intrinsic resistance to beta-lactam antibiotics in Staphylococcus aureus (mec determinant). The mec probe provided a useful tool for the rapid identification of the intrinsic resistance trait and for establishing guidelines for testing the in vitro susceptibility of S. aureus to beta-lactams.

DNA Probes↗
PubMed1991

Mechanism of action of BAY v 3522, a new cephalosporin with unusually good activity against enterococci.

The in vitro activity of BAY v 3522, a new cephalosporin with unusually good activity against enterococci, was tested on 100 clinical isolates of Enterococcus faecalis. The MIC for 86.3% of the strains was 4 micrograms/ml, whereas the MIC for 13.7% ranged from 8 to 16 micrograms/ml. No differences were found between MICs determined with low- or high-density inocula. The bactericidal activity of BAY v 3522 was tested on eight clinical strains; most strains showed a ca. 3-log decrease of the original inoculum at two to eight times the MIC. The interaction of BAY v 3522 and of other beta-lactams with penicillin-binding proteins (PBPs) was studied with a laboratory strain, E. hirae ATCC 9790, producing a discernible amount of PBP 5, a protein belonging to the family of low-affinity PBPs, responsible for the low susceptibility of enterococci to beta-lactams. PBPs 3 and 5 of ATCC 9790 showed the highest affinity for the new cephalosporin. Bay V 3522 at the MIC (8 micrograms/ml) saturated these two PBPs without any significant binding to the other PBPs. This result may explain the good antienterococcal activity of BAY v 3522.

Ampicillin↗
PubMed1990

Mechanisms of resistance of enterococci to beta-lactam antibiotics.

Two mechanisms are responsible for resistance of enterococci to beta-lactam antibiotics: alterations of penicillin-binding proteins and production of a beta-lactamase. The latter has been found in a few clinical isolates of Enterococcus faecalis, whereas the former appears to account for resistance in most strains. A correlation has been established between the amount of a particular penicillin-binding protein which has a low affinity for penicillin and the level of resistance. The higher activity of some penicillins, as compared to cephalosporins, has been related to the relatively higher affinity for these penicillins of the penicillin-binding protein involved in the mechanism of resistance. Alterations in the autolytic enzyme pattern have been associated with the paradoxical response to bactericidal activity of penicillin often exhibited by Enterococcus faecalis clinical isolates.

Anti-Bacterial Agents↗
PubMed1990

A method for detection of human papillomavirus DNA in stored slides of stained cervical smears.

A simple method was developed for extraction of DNA from stored slides of Papanicolaou stained cervical smears. HPV type 16 DNA was detected by DNA hybridization in 7/10 samples from known HPV-16 positive patients, whereas the 10 samples from negative patients were also negative with our assay. Using our method for obtaining data from stained cervical smears, it will be possible to design and perform historical cohort studies on stored material.

DNA, Viral↗
PubMed1990

Small bowel obstruction associated with a leiomyomatous uterus. A case report and review of the literature.

A 38-year-old woman developed small bowel obstruction shortly after a cholecystectomy because of a massively enlarged leiomyomatous uterus. Small bowel obstruction is a relatively rare complication from fibroid tumors and results from entrapment of the bowel between serosal pedunculated fibroids (as in this patient), adhesions to infarcted leiomyomas, or from compression of the small bowel by the large mass. Large uterine leiomyomas clearly must be considered in the etiology of intestinal obstruction.

Adult↗
PubMed1990

Paradoxical response of Enterococcus faecalis to the bactericidal activity of penicillin is associated with reduced activity of one autolysin.

Ten clinical isolates of Enterococcus faecalis were examined for susceptibility to the bactericidal activity of penicillin. Four of these had MBCs of penicillin equal to 2 to 4 x the MIC, and six exhibited a paradoxical response to penicillin, i.e., the bactericidal activity of the antibiotic had a concentration optimum at 2 to 4 x the MIC and decreased significantly at concentrations above this. We found that the paradoxical response to penicillin was an intrinsic and stable property of a strain, but that its phenotypic expression was not homogeneous; only a fraction of the cell population that died at low concentrations was able to survive at high penicillin concentrations. The size of this fraction increased with increasing antibiotic concentration and reached a maximum in the late-log phase of growth. All 10 strains produced a lytic enzyme that was active on Micrococcus luteus heat-killed cells, whereas only some strains lysed E. faecalis heat-killed cells. Strains producing large amounts of the latter enzyme did not show the paradoxical response to penicillin, whereas mutants of these strains that lacked this enzymatic activity paradoxically responded to the antibiotic activity. In addition, from strains that showed paradoxical response to penicillin and produced only the enzyme that was active on M. luteus, it was possible to isolate mutants that were also capable of lysing E. faecalis cells and that were killed with similar efficiency by all concentrations above the MBC. On the basis of these findings, the paradoxical response to penicillin is explained as a property of certain strains of E. faecalis; this property is genetically characterized by alterations in synthesis or activity of one autolysin but phenotypically expressed only by a few cells that are in a particular physiological condition when exposed to high concentrations of antibiotics.

Bacterial Proteins↗
PubMed1990

In vitro response to bactericidal activity of cell wall-active antibiotics does not support the general opinion that enterococci are naturally tolerant to these antibiotics.

The incidence of tolerance and paradoxical response to bactericidal activity of penicillin was investigated in 50 clinical isolates of Enterococcus faecalis. Of the isolates tested, 86% exhibited the paradoxical phenomenon whereby there were more survivors at high than at low concentrations above the MIC. Low penicillin concentrations caused decreases equal to or higher than 99.9% in 11 strains, from 99.9 to 99.5% in 23 strains, and lower than 99.5% in 9 strains. Of the total strains, 14% were killed to the same extent by all concentrations above the MIC. The bactericidal activities of other beta-lactams (ampicillin and piperacillin) and other cell wall inhibitors (vancomycin and daptomycin) were also tested against some of these strains. In general, beta-lactams exhibited the best bactericidal activity at 2 x MIC. Piperacillin was the most active, as at 2 x MIC it reduced the original inoculum by 99.9% or more in most of the strains. No concentration of vancomycin above the MIC caused 99.9% killing of the strains, whereas daptomycin was bactericidal at 8 x MIC in most cases. Paradoxical response to bactericidal activity of beta-lactams was abolished by incubation of the inoculum with 2 x MIC before exposure to higher antibiotic concentrations. These findings suggest that enterococci are not always tolerant to cell wall-active antibiotics and that accurate in vitro bactericidal tests may be useful for the choice of appropriate therapy for infections caused by these microorganisms.

Ampicillin↗
PubMed1990

In vitro activity of sulbactam/ampicillin against ampicillin-resistant, beta-lactamase-producing bacteria isolated in Italian hospitals.

A multicenter study aimed at assessing the in vitro activity of sulbactam/ampicillin against a wide range of bacterial pathogens was performed using 2,209 clinical strains, all recently collected from inpatients in seven Italian centers and preliminarily screened as being ampicillin-resistant and beta-lactamase producers. In comparative disk diffusion trials using 8 large-spectrum antimicrobials, the percentage of resistance to sulbactam/ampicillin in staphylococci was similar to the percentage of resistance to netilmicin and lower than to the other antibiotics; with gram-negative bacteria, only netilmicin, ofloxacin, and, less consistently, cefotetan showed lower incidences of resistance. The minimal inhibitory concentrations (MICs) of ampicillin alone and sulbactam/ampicillin together were determined using the agar dilution method. The Enterobacteriaceae strains which shifted to ampicillin susceptibility in the presence of sulbactam averaged 68%, but values significantly above or below average were observed in some genera of this family. The percentage of strains which the presence of sulbactam rendered ampicillin-susceptible in vitro reached 97% in Haemophilus strains and 100% in branhamellae and gonococci. High percentages were also recorded in staphylococci, with a peak of 100% in oxacillin-susceptible Staphylococcus aureus strains. In general, center-to-center differences were relatively limited.

Ampicillin↗
PubMed1989

In vitro activity of lomefloxacin (SC-47111) against enterobacteriaceae, enterococci and staphylococci.

The activity of lomefloxacin, a new difluorinated quinolone, was tested against 190 Enterobacteriaceae strains (belonging to 23 different species), 70 enterococci and 70 staphylococci. As regards Enterobacteriaceae, the activity of lomefloxacin was the same as that of norfloxacin in 9 out of the 23 species tested, and only slightly lower in further 8 species. Minimum inhibitory concentrations (MIC) values for 90% of strains were 0.5 microgram/ml in 2 species, 0.25 microgram/ml in 6, 0.125 microgram/ml in 4, and lower than 0.125 microgram/ml in 8. Slightly higher values were obtained for Serratia marcescens (2 micrograms/ml), whilst, as already reported for the other new quinolones, the susceptibility of the Providencia genus was very poor, with MIC values up to 128 micrograms/ml for the vast majority of strains. Lomefloxacin proved bactericidal at the MIC in all the Enterobacteriaceae strains tested but 20. In the latter strains, however, bactericidal activity could be appreciated at values slightly exceeding MIC. As regards enterococci, the MIC for 90% of strains was 32 micrograms/ml. Minimum bactericidal concentration (MBC) was the same as the MIC for 78% of the strains tested and was only twofold higher in all the others. The new drug was also active against staphylococci having an MIC50 and MIC90 of 0.5 and 2 micrograms/ml, respectively. It was bactericidal at the MIC for 62% of the strains and at twofold the MIC for all the others.

4-Quinolones↗