Search PubMed⌕ Search

Biomedical subjects

H Hof

Publications and source records attributed to H Hof.

At least 55 records · Page 3Linked to original sources
PubMed1998

Reduced intracellular activity of antibiotics against Listeria monocytogenes in multidrug resistant cells.

Multidrug resistance is expressed not only by bacteria, but also by tumor cells and by some normal cells of the body. It enables eukaryotic cells to exclude not only cytostatic drugs but also non-cytostatic antibiotics. This was demonstrated in genetically engineered multidrug resistant (MDR) cells infected with the facultative intracellular bacterium Listeria monocytogenes for all macrolide antibiotics tested (azithromycin, clarithromycin, erythromycin, josamycin, roxithromycin and spiramycin). In these cells and in conventionally selected MDR cells higher concentrations of the macrolides were necessary to inhibit the growth of L. monocytogenes than in the respective parental cells. This effect was due to a reduced intracellular accumulation, which was shown with a biological assay for all macrolides tested. For azithromycin, the results of this test were confirmed by measurement of the intracellular concentrations with high-performance liquid chromatography (HPLC). Besides the macrolides, MDR cells excluded also antibiotics of other chemical groups which was shown for ciprofloxacin, clindamycin, rifampicin and the streptogramin derivative RP 59500. In addition, in conventionally selected cells higher concentrations of chloramphenicol, doxycyclin, ofloxacin and trimethoprim than in the respective parental cells were necessary to inhibit the growth of L. monocytogenes. In contrast, when using genetically engineered cells, no significant differences were found for these antibiotics. These differences might be due to a higher expression of multidrug resistance in the conventionally selected cells because these cells were also more effective in excluding rhodamine 123 in a flow cytometric assay. In conclusion, expression of multidrug resistance by eukaryotic cells leads to a reduced concentration of macrolides and other antibiotics in these cells and to an impairment of activity against intracellular bacteria.

Animals↗
PubMed1998

Phosphatidylcholine-specific phospholipase C from Listeria monocytogenes is an important virulence factor in murine cerebral listeriosis.

Meningoencephalitis is a serious and often fatal complication of Listeria monocytogenes infection. The aim of the present study was to analyze the role of internalin A (InlA) and B, which are involved in the invasion of L. monocytogenes into cultivated host tissue cells, and that of phosphatidylcholine-specific phospholipase C (PlcB), which mainly promotes the direct cell-to-cell spread of L. monocytogenes, in murine cerebral listeriosis by use of an InlA/B (DeltainlAB2)- and a PlcB (DeltaplcB2)-deficient isogenic deletion mutant strain and the wild-type (WT) L. monocytogenes EGD. Listeria strains were directly applied to the brain, a technique which has been employed previously to study the pathogenesis of cerebral listeriosis (D. Schlüter, S. B. Oprisiu, S. Chahoud, D. Weiner, O. D. Wiestler, H. Hof, and M. Deckert-Schlüter, Eur. J. Immunol. 25:2384-2391, 1995). We demonstrated that PlcB, but not InlA or InlB, is an important virulence factor in cerebral listeriosis. Nonimmunized mice infected intracerebrally with the DeltaplcB2 strain survived significantly longer and had a reduced intracerebral bacterial load compared to mice infected with the DeltainlAB2 strain or WT bacteria. In addition, immunization with the WT prior to intracerebral infection significantly increased the survival rate of mice challenged intracerebrally with the DeltaplcB2 strain compared to that of mice infected with the WT or DeltainlAB2 strain. Histopathology revealed that the major difference between the various experimental groups was a significantly delayed intracerebral spread of the DeltaplcB2 mutant strain, indicating that cell-to-cell spread is an important pathogenic feature of cerebral listeriosis. Interestingly, irrespective of the Listeria mutant used, the apoptosis of hippocampal and cerebellar neurons and an internal hydrocephalus developed in surviving mice, indicating that these complications are not dependent on the virulence factors InlA/B and PlcB. In conclusion, this study points to PlcB as a virulence factor important for the intracerebral pathogenesis of murine L. monocytogenes meningoencephalitis.

Animals↗
PubMed1998

Successful treatment of murine listeriosis and salmonellosis with levofloxacin.

Levofloxacin (L-ofloxacin) is a fluoroquinolone derivative. It is the active substance contained in ofloxacin with a broad spectrum of antibacterial activity against both Gram-negative and Gram-positive bacteria. In this work we examined the activity of levofloxacin against the facultative intracellular bacteria Listeria monocytogenes and Salmonella typhimurium in vitro, in tissue culture and in animal models of infection. The minimum inhibitory concentrations (MICs) MIC90 for Salmonella enterica and L. monocytogenes were 0.078 mg/l and 4 mg/l, respectively. Levofloxacin was bactericidal against L. monocytogenes and S. typhimurium because 8 x MIC killed 90% of the initial inoculum of L. monocytogenes EGD and S. typhimurium LT2 within 4 hours and 3 hours, respectively. Levofloxacin was more effective than ampicillin against L. monocytogenes EGD infecting tissue culture cells. Also in tissue culture cells infected with S. typhimurium LT2, levofloxacin was slightly more effective than ciprofloxacin. In animal models of infection, levofloxacin was as potent as the reference substances. In conclusion, levofloxacin is a candidate for the treatment of infections caused by facultative intracellular Gram-positive and Gram-negative bacteria.

Animals↗
PubMed1997

Interleukin-10 downregulates the intracerebral immune response in chronic Toxoplasma encephalitis.

The expression of the immunosuppressive cytokine interleukin (IL)-10 in the normal and Toxoplasma gondii-infected murine brain was analysed. Microglia/macrophages expressed IL-10 at the mRNA and protein level in the normal brain. In Toxoplasma encephalitis (TE), CD4+ and CD8+ T-cells also contributed to the upregulated IL-10 production. Neutralization of endogenous IL-10 in chronic TE reduced the intracerebral parasitic load and increased the number of immune cells and the production of protective cytokines. These findings indicate that intracerebral expression of IL-10 interferes with the immune response in TE and may contribute to parasite persistence in the brain.

Animals↗
PubMed1997

Excellent activity of newer quinolones on Legionella pneumophila in J774 macrophages.

The activity of six antibiotics directed against intracellularly multiplying Legionella pneumophilia was examined in tissue cultures with J774 macrophages. The drugs tested were the new quinolones, BAY Y 3118 and clinafloxacin, and ciprofloxacin, erythromycin, gentamicin and ampicillin served as reference drugs. Additionally, the MICs of these drugs against L. pneumophila were determined in vitro by broth microdilution. Despite their low MIC values, ampicillin and gentamicin did not inhibit intracellular multiplication of L. pneumophila in J774 macrophages. In contrast, an inhibition of intracellular growth could be demonstrated for the four other antibiotics. The new quinolones BAY Y 3118 and clinafloxacin showed the highest activity against intracellular L. pneumophila. At a concentration of 0.00078 mg/L already, a marked reduction in bacterial counts was seen for both drugs in comparison to the growth control without antibiotics. The corresponding effective concentrations were 0.0125 mg/L for ciprofloxacin and 0.2 mg/L for erythromycin. It may be concluded that new quinolone derivatives might become an alternative to erythromycin and rifampicin which at present are the drugs of primary choice for the treatment of legionnaires' disease.

Ampicillin↗
PubMed1997

Clinafloxacin (CL 960) is superior to standard therapeutics in the treatment of murine listeriosis and salmonellosis.

Clinafloxacin is a novel fluoroquinolone with a broad spectrum of antibacterial activity against both gramnegative and grampositive bacteria. In this work, the activity against the facultatively intracellular bacteria Listeria monocytogenes and Salmonella typhimurium was examined in vitro, in tissue culture and in animal models of infection. All strains of L. monocytogenes and S. enterica were highly susceptible against clinafloxacin, with minimal inhibitory concentrations (MICs) that were consistently lower than those for ampicillin and ciprofloxacin, respectively. Clinafloxacin was rapidly bactericidal against L. monocytogenes and S. typhimurium since 8 times the MIC killed the bacteria within 2 hours. In contrast to ampicillin and ciprofloxacin, there was a postantibiotic effect (PAE) of 2 hours with 8 x MIC on L. monocytogenes. Clinafloxacin was more effective than ampicillin and ciprofloxacin in tissue culture cells infected with S. typhimurium or L. monocytogenes. In animal models of infection, clinafloxacin was also more potent than the reference substances. In conclusion, clinafloxacin is an excellent candidate substance for the treatment of infections caused by facultatively intracellular grampositive and gramnegative bacteria.

Ampicillin↗
PubMed1997

Management of listeriosis.

Determination of the MIC in vitro is often used as the basis for predicting the clinical efficacy of antibiotics. Listeriae are uniformly susceptible in vitro to most common antibiotics except cephalosporins and fosfomycin. However, the clinical outcome is poor. This is partially because listeriae are refractory to the bactericidal mechanisms of many antibiotics, especially to ampicillin-amoxicillin, which still is regarded as the drug of choice. A true synergism can be achieved by adding gentamicin. Another point is that listeriae are able to reside and multiply within host cells, e.g., macrophages, hepatocytes, and neurons, where they are protected from antibiotics in the extracellular fluid. Only a few agents penetrate, accumulate, and reach the cytosol of host cells, where the listeriae are found. Furthermore, certain host cells may exclude antibiotics from any intracellular compartment. Thus, determination of the antibacterial efficacy of a drug against listeriae in cell cultures may be a better approximation of potential therapeutic value. Certain host cells may have acquired the property of excluding certain antibiotics, for example macrolides, from intracellular spaces, which might explain therapeutic failures of antibiotic therapy in spite of low MICs. Animal models do not completely imitate human listeriosis, which is characterized by meningitis, encephalitis, soft tissue and parenchymal infections, and bacteremia. Meningitis produced in rabbits is a hyperacute disease, whereby most listeriae lie extracellularly, fairly accessible to antibiotics that can cross the blood-cerebrospinal fluid barrier. In the murine model of systemic infection, Listeria monocytogenes is located mainly within macrophages and parenchymal cells of the spleen and liver, hardly accessible to certain drugs, such as ampicillin and gentimicin. The therapeutic efficacy of drugs clearly depends on the model used. Thus, for example, the combination of ampicillin with gentamicin acts synergistically in the rabbit meningitis model but not in the mouse model. Since conventional antimicrobial therapy with antibiotics is not satisfactory, particularly in the immunocompromised host (about 30% of patients with listeriosis die in spite of a rational choice of antibiotics), other possibilities must be considered for therapy as well as prevention. Indeed, listeriae are highly susceptible to several endogenous antibiotics, such as defensins. Bacteriocins produced by related bacterial species, e.g., lactobacilli and enterococci, are rapidly bactericidal. However, unfortunately, the use of such alternative measures along with immunization and immunmodulation is not yet feasible.

Animals↗
PubMed1997

Detection and identification of Candida species in experimentally infected tissue and human blood by rRNA-specific fluorescent in situ hybridization.

Two 18S rRNA-targeted oligonucleotide probes specific for Candida albicans and Candida parapsilosis were used to detect and identify by fluorescent in situ hybridization these medically important Candida species in deep organs of mice after experimental systemic infection. The C. albicans-specific probe detected fungal cells in kidney, spleen, and brain sections of a mouse infected with C. albicans but not in a mouse infected with the closely related species C. parapsilosis. Conversely, the C. parapsilosis-specific probe detected fungal cells in the deep organs of a mouse infected with C. parapsilosis but not in the deep organs of a C. albicans-infected mouse. In addition, the C. albicans-specific probe was used to detect this species in human blood spiked with yeast cells by a lysis-filtration assay and subsequent fluorescent in situ hybridization. By this assay, as few as three yeast cells per 0.5 ml of blood were consistently detected. Our results demonstrate that fluorescent in situ hybridization with species-specific rRNA-targeted oligonucleotide probes provides a novel, culture-independent method for the sensitive detection and identification of Candida species in clinically relevant material.

Animals↗
PubMed1997

Expression pattern and cellular origin of cytokines in the normal and Toxoplasma gondii-infected murine brain.

In the normal brain, low levels of cytokines are observed, whereas inflammatory disorders of the central nervous system are characterized by an up-regulation of cytokine production. The cellular sources for cytokines in the central nervous system are largely undefined. In the present study, we have analyzed intracerebral cytokine production in normal and Toxoplasma gondii-infected mice using immunohistochemistry, in situ hybridization, flow cytometry of brain-derived leukocytes, and reverse transcriptase polymerase chain reaction detection in various subpopulations of inflammatory cells. In the normal brain, neurons and choroid plexus epithelia expressed interleukin (IL)-1 beta and IL-10. Microglia/macrophages produced IL-1 beta, IL-10, and tumor necrosis factor-alpha In Toxoplasma encephalitis, these cell types exhibited increased levels of the respective cytokines. In addition, microglia/macrophages showed a de novo expression of inducible nitric oxide synthase. CD4+ and CD8+ T cells, which were recruited to the brain, produced IL-2, IL-10, tumor necrosis factor-alpha, and interferon-gamma. IL-4 was exclusively detectable in CD4+ T cells, whereas CD8+ T cells showed expression of IL-1 beta. As chronic Toxoplasma encephalitis was not associated with neuronal degeneration and an up-regulation of neurotrophic factors, some cytokines may also exert neurotrophic and/or neuroprotective properties.

Animals↗
PubMed1996

Rapid detection of susceptibility to fluconazole in Candida species by a bioluminescence assay of intracellular ATP.

Infections with Candida albicans and Candida species and antifungal resistance are increasingly recognized. The detection of fluconazole resistance is indispensable. We, therefore, compared two rapid methods that use commercially available test kits with the proposed standard of the NCCLS for fluconazole testing. When strains of Candida albicans and Candida species susceptible or resistant to fluconazole were used, measurement of ATP content was superior to the other test because an excellent correlation was obtained already after 5 hours of incubation. The measurement of the metabolic reduction of XTT yielded comparable results, but 24 hours of incubation were necessary.

Adenosine Triphosphate↗
PubMed1996

Intracerebral targets and immunomodulation of murine Listeria monocytogenes meningoencephalitis.

In humans, infection with Listeria monocytogenes (L. monocytogenes) can severely affect the central nervous system (CNS). In the present study we have employed a murine model of CNS listeriosis to characterize the intracerebral distribution of L. monocytogenes. Following intracerebral application of a low dose of L. monocytogenes (serovar 1/2a, EGD strain) a severe fatal leptomeningitis, ventriculitis, and encephalitis developed. Listeria were detectable both intracellularly in different cell types of the CNS and extracellularly in the cerebrospinal fluid. Ultrastructural analysis revealed macrophages, granulocytes, plexus epithelial cells, ependymal cells, and neurons as target cells. An inflammatory reaction with macrophages and granulocytes developed in the brains of these animals but was not sufficient to prevent the fatal outcome of the disease. However, active immunization of mice prior to an intracerebral challenge infection significantly reduced the mortality. Immunized animals showed an early recruitment of a significant number of CD8+ and, to a lesser degree, CD4+ T cells within 24 hours p.i. as well as a strong activation of microglial cells and macrophages. These findings may provide an interesting model for studies on the pathogenesis of cerebral listeriosis.

Adjuvants, Immunologic↗
PubMed1996

RP 59500, a streptogramin derivative, is effective in murine listeriosis.

RP 59500 (Synercid) a streptogramin derivative, is a mixture of two water-soluble substances, RP 57669 (quinupristin), and RP 54476 (dalfopristin). It was tested in vitro and in vivo against Listeria strains. All strains were sensitive in vitro. The MICs of 60 strains of Listeria monocytogenes, L. seeligeri, L. ivanovii, and L. innocua were between 0.156 and 0.625 mg/l. Strains of L. grayi were inhibited by 1.25 mg/l of RP 59500. In contrast to its bactericidal effect against other gram-positive bacteria, RP 59500 was bacteriostatic against L. monocytogenes in all concentrations tested (up to 16 x MIC). However, it exerted a pronounced postantibiotic effect. RP 59500 was ineffective against intracellular L. monocytogenes multiplying in L929 mouse fibroblast cells. When it was included in the supernatant of the cells in nontoxic concentrations of below 12.5mg/l alone or in combination with gentamicin (50mg/l) it was not able to inhibit the growth of the listeriae in the cells. However, when tested in peritoneal exudate cells, it was bacteriostatic against L. monocytogenes. In spite of its relatively poor effects on listeriae in vitro, RP 59500 was as active as erythromycin in a mouse model of listeriosis. When mice iv infected with L. monocytogenes were treated ip with 2mg/animal every 12 hours with either erythromycin or RP 59500, both substances prevented growth of the bacteria in the organs, but were unable to eradicate the listeriae. We conclude that RP 59500 is a candidate substance for the treatment of human listeriosis which might be used when therapy with ampicillin is not feasible.

Animals↗
PubMed1996

Effects of FK-506 on the course of murine salmonellosis.

Bacterial infections are a major threat to immunocompromised patients. Therefore, the effect of immunosuppression with cyclosporin A and FK-506 on the course of murine salmonellosis was tested. Treatment of mice with both substances reduced the amount of circulating CD4+ T-cells and CD8+ T-cells in uninfected and infected mice. The substances effectively suppressed the proliferation of spleen cells of treated mice upon activation with concanavalin A (ConA) and upon activation by mouse peritoneal macrophages infected with live salmonellae, but left the response to lipopolysaccharide (LPS) unaltered. In particular, treatment of mice with nontoxic doses led to an increase in Salmonella typhimurium counts in the organs of primarily infected mice from day 14 onward, but not in the early phase of infection. In mice treated during secondary infection with S. typhimurium the bacterial counts in the organs were increased from day 3 of infection onward. We conclude that both substances aggravate murine salmonellosis, most likely by inhibition of T-cell function. Patients receiving FK-506 might also be, therefore, at risk of salmonella infection.

Animals↗
PubMed1996

Effects of amphotericin B incorporated into liposomes and in lipid suspensions in the treatment of murine candidiasis.

The effects of similar amounts of amphotericin B (CAS 1397-89-3, AmB) in different preparations either as conventional amphotericin B (des-AmB), or liposomal AmB (lipos-AmB), or des-AmB dissolved in a lipid emulsion (lipid-AmB) on Candida albicans and other Candida species were compared in several in vitro and in vivo models. The minimal inhibitory concentration (MIC) of des-AmB was equal to the MIC of lipid-AmB when determined after 24 h. In contrast, the MIC of lipos-AmB was 4-8 times the MIC of des-AmB. When tested at 4 times the MIC of the respective preparations suspension of lipid-AmB led to a reduced ability to kill the fungi whereas des-AmB reduced the inoculum by 99% within 6 h. Four times the MIC of lipos-AmB failed completely to kill the fungi in the same time, but was only fungistatic. At 24 h all preparations had killed the yeasts at concentrations 4 times the MIC. In contrast to the in vitro data, lipos-AmB was more active in the treatment of murine candidiasis than lipid-AmB and des-AmB. Lipos-AmB but not lipid-AmB or des-AmB was able to significantly reduce the amount of Candida albicans in the liver when given in the same dosage. Concomitantly, AmB measured by HPLC was highly concentrated in the livers of the mice treated with lipos-AmB. It is concluded that even when given in the same dosage as des-AmB and lipid-AmB, lipos-AmB is more effective in the treatment of murine candidiasis, although it is less effective in vitro. Lipid-AmB is no alternative to lipos-AmB in this model of systemic infection of mice with Candida albicans.

Amphotericin B↗
PubMed1996

Interferon-gamma receptor-deficiency renders mice highly susceptible to toxoplasmosis by decreased macrophage activation.

Toxoplasma gondii may cause severe infections in immunocompromised patients including fetuses and those with AIDS. Among the factors mediating protection against T. gondii, IFN-gamma has gained special attention. To analyze the role of IFN-gamma in the early phase of toxoplasmosis, IFN-gamma receptor-deficient (IFN-gamma R0/0) mice were orally infected with low-virulent toxoplasms. IFN-gamma R0/0 mice died of the disease up to day 10 postinfection, whereas immunocompetent wild-type (WT) mice developed a chronic toxoplasmosis. Histopathology revealed that in IFN-gamma R0/0 mice, the parasite multiplied unrestrictedly in the small intestine, the intestinal lymphatic tissue, the liver, and the spleen. Ultimately, animals died of a necrotizing hepatitis. In WT mice, the same organs were effected, but multiplication of the parasite was effectively limited. Compared with WT mice, immunohistochemistry and flow cytometry demonstrated that in IFN-gamma R0/0 mice, macrophages were only marginally activated in response to the infection, as evidenced by a reduced expression of major histocompatability complex class II antigens. In addition, immunohistochemistry and RT-PCR showed a reduced production of the macrophage-derived cytokines tumor necrosis factor-alpha, inducible nitric oxide synthase, and IL-1 beta in the liver of IFN-gamma R0/0 mice. In contrast, activation of T cells, recruitment of immune cells to inflammatory foci, and anti-T. gondii IgM antibody production were unaffected by the mutation of the IFN-gamma R. Moreover, induction of IL-2, IL-4, and IL-10 mRNA transcripts in the liver was normal in IFN-gamma R0/0 mice. Adoptive transfer experiments revealed that the immune T cells of WT animals did not protect IFN-gamma R0/0 mice from lethal infection with highly virulent toxoplasms, whereas WT mice were significantly protected by the adoptive transfer. Based on these studies, we conclude that IFN-gamma is absolutely required for an efficient activation of macrophages. Macrophages are of critical importance in toxoplasmosis, and insufficient macrophage activation cannot be compensated by other immune mechanisms.

Adoptive Transfer↗