Vancomycin in meningitis caused by penicillin G resistant Streptococcus pneumoniae

We report two cases of penicillin G-resistant pneumococcal meningitis in adults, with clinical and bacteriological failure of amoxicillin and negative or incomplete response to third generation cephalosporins. Meningitis occurred in a man treated for myeloma and in an elderly woman under prolonged intermittent amoxicillin therapy for chronic otitis. Such situations are known as exposing to pneumococcal meningitis and to resistance of the strain involved to penicillin G. Both patients were cured by vancomycin in continuous infusion associated with rifampicin or fosfomycin. Contrary to third generation cephalosporins, which have higher minimal inhibitory concentrations, vancomycin and rifampicin are still fully active against penicillin G-resistant pneumococcal strains. Thus, vancomycin administered in continuous infusion and associated with rifampicin and fosfomycin deserves to be tried as first-line treatment of pneumococcal meningitis in patients at risk of resistance to penicillin G.     

Identification of Streptococcus mutans antigen D as the HPr component of the sugar-phosphotransferase transport system

Fosfomycin tromethamine is an orally administered fosfomycin that may be used for single-dose therapy of uncomplicated urinary tract infections. At breakpoint concentrations [< or = 128 micrograms/ml plus 25 micrograms/ml glucose-6-phosphate (G-6-P)], fosfomycin tromethamine inhibited > 90% of the 350 bacterial isolates tested. When testing Escherichia coli, Klebsiella spp., and Enterobacter spp., we note that the performance of fosfomycin disks improved when G-6-P was added to the disks. The interpretive error rates were minimized when 200-micrograms fosfomycin disks were supplemented with either 50 or 100 micrograms G-6-P. Using < or = 128 and > or = 256 micrograms/ml as the susceptible and resistant MIC breakpoints, respectively, the regression-analysis-derived disk diffusion zone diameter breakpoints for the 200-micrograms fosfomycin disk supplemented with 50 micrograms of G-6-P are as follows: susceptible, > or = 16 mm; intermediate, 13-15 mm; and resistant, < or = 12 mm.     

Severe methicillin-resistant Staphylococcus aureus infections. Emergence of resistance to fusidic acid or fosfomycin during treatment with continuous infusion of vancomycin

OBJECTIVES: To evaluate the development of resistance to fosfomycin or fucidic acid in severe infections caused by methicillin-resistant Staphylococcus aureus (MRSA) and to assess the relationship with serum levels of vancomycin METHODS: A retrospective study was performed in patients hospitalized in our intensive care unit during a 3-year period (1993-1995) who were treated for severe MRSA infection with continuous infusion vacomycin and fosfomycin or fucidic acid. We analyzed the development of resistance and serum levels of vancomycin. RESULTS: During this period, only 20 patients received continuous infusion vancomycin plus fucidic acid or fosfomycin. MSRA resistant to fucidic or fosfomycin developed in 9. Vancomycin serum levels were significantly lower in patients who developed resistance to focidic acid or fosfomycin, both during the first 5 days of treatment (16.68 +/- 1.07 micrograms/ml vs. 22.64 +/- 1.05 mg/ml, p < 0.01) and throughout treatment duration (17.29 +/- 1.07 micrograms/ml vs. 21.85 +/- 0.78 microgram/ml, p < 0.01). CONCLUSIONS: Our findings confirm that in spite of continuous vancomycin infusion at an initial rate of 2 g/24 h, Staphylococcus aureus resistance to fosfomycin or fucidic acid an develop during ongoing treatment. Vancomycin levels of at least 20 micrograms/ml should be obtained as rapidly as possible.     

Effects of fosfomycin and imipenem/cilastatin on nephrotoxicity and renal excretion of vancomycin in rats

PURPOSE: The effects of fosfomycin and imipenem/cilastatin on the nephrotoxicity of vancomycin were studied in rats, and those on the renal handling of vancomycin were also investigated in perfused kidneys. METHODS: The protective effects of fosfomycin and imipenem/cilastatin on vancomycin nephrotoxicity were evaluated by increases in plasma concentration of creatinine and urea nitrogen in rats. The urinary excretion of vancomycin was measured and analyzed kinetically in the perfused rat kidney. RESULTS: The nephrotoxicity induced by vancomycin (500 mg/kg, i.v.) was inhibited almost completely by co-administration of fosfomycin or imipenem/cilastatin. In the perfused rat kidney, the excretion ratio of vancomycin was less than those of p-aminohippurate and cimetidine, and greater than that of arbekacin, suggesting the secretion and reabsorption of vancomycin in renal tubules. The tissue/perfusate ratios of unbound vancomycin were not significantly changed by co-treatment with fosfomycin or imipenem/cilastatin. Imipenem/cilastatin significantly decreased the excretion ratio of vancomycin. Fosfomycin also decreased vancomycin excretion ratio, although this effect was not significant. CONCLUSIONS: The renal handling of vancomycin was different from those of organic anions and cations and an aminoglycoside antibiotic. The protective effects of fosfomycin and imipenem/cilastatin against the nephrotoxicity of vancomycin might be partly due to the change in renal handling of vancomycin, probably in its tubular secretion/ reabsorption, in rats.     

The spatial dynamics of prion disease

An important component of the latency period of the transmissible spongiform encephalopathies (prion diseases) can be attributed to delays during the propagation of the infectious prion isoform, PrPSc, through peripheral nervous tissues. A growing body of data report that the host prion protein, PrPC, is required in both peripheral and central nervous tissues for susceptibility to infection. We introduce a mathematical model, which treats the PrPSc as a mobile infectious pathogen, and show how peripheral delays can be understood in terms of the intercellular dispersal properties of the PrPSc strain, its decay rate, and its efficiency at transforming the PrPC. It has been observed that when two pathogenic strains co-infect a host, the presence of the first inoculated strain can slow down, or stop completely, the spread of the second strain. This is thought to result from a reduced concentration of host protein available for conversion by the second strain. Our model can explain the mechanisms of such interstrain competition and the time-course of the increased delay. The model provides a link between those data suggesting a role for a continuous chain of PrP-expressing tissue linking peripheral sites to the brain, and data on prion strain competition.     

Bovine spongiform encephalopathy and natural scrapie

Scrapie in sheep and Bovine Spongiform Encephalopathy in cattle are neurodegenerative diseases. They belong to the group of transmissible spongiform encephalopathies (prion diseases). Scrapie is a worldwide enzootic disease, first described two centuries ago. It is due to more than 20 different strains of agent and strongly influenced by genetic factors of the host. There is no evidence of a link between this disease and human transmissible spongiform encephalopathies. Bovine Spongiform Encephalopathy is a consequence of oral infection of cattle by meat and bone meal produced in the United Kingdom and contaminated by the agent. The strain is unique and has been selected and massively amplified in the alimentary chain. It is probably linked to a new variant of Creutzfeldt-Jakob disease in man. It is expected that the ban on the incorporation of animal proteins in the alimentation of ruminants will soon eradicate it, although the risk of potential mutants of the disease and its possible transmission to sheep and goats exists.     

The focus on women veterans who use Veterans Administration health care: the Veterans Administration Women''s Health Project

There is no consensus regarding the benefit versus harm of antibiotic therapy for treatment of disease due to enterohemorrhagic Escherichia coli O157. The effects in vitro of subinhibitory concentrations of 13 antimicrobial agents on the release of Shiga toxin (Stx) by three different Escherichia coli O157 strains expressing Stx 1 or Stx 2 either alone or in combination were investigated. The Stx-induced cell death of Vero cells was determined using a colorimetric assay based on the measurement of lactate dehydrogenase (LDH) released into the supernatant from the cytosol of damaged cells. Growth of all O157 strains in broth cultures containing subinhibitory concentrations of cotrimoxazole, trimethoprim, azithromycin, or gentamicin was accompanied by a marked increase in the release of Stx. Exposure to cefixime, ceftriaxone, or erythromycin caused a marked increase in the release of Stx by the O157 strain producing Stx 2 alone, but decreased toxin production was observed with the Stx 1 producer and the strain producing Stx 1 and Stx 2. Exposure to ampicillin caused increased Stx release in the Stx 2-producing strain but had no effect on Stx production in the other two test isolates. Exposure to penicillin G, streptomycin, ciprofloxacin, fosfomycin, or sulfamethoxazole caused an increase in toxin production in two of the three test strains in each case, while decreases were observed for the other isolates. The response of Escherichia coli O157 isolates to subinhibitory concentrations of antibiotics seems to be highly dependent on the nature of the strain involved.     

Evolution of rhizobia by acquisition of a 500-kb symbiosis island that integrates into a phe-tRNA gene

Nodulation and nitrogen fixation genes of Mesorhizobium loti are encoded on the chromosome of the bacterium. Nevertheless, there is strong evidence that these genes can be transferred from an inoculant strain to nonsymbiotic mesorhizobia in the field environment. Here we report that the chromosomal symbiotic element of M. loti strain ICMP3153 is transmissible in laboratory matings to at least three genomic species of nonsymbiotic mesorhizobia. The element is 500 kb in size, integrates into a phe-tRNA gene, and encodes an integrase of the phage P4 family just within its left end. The entire phe-tRNA gene is reconstructed at the left end of the element upon integration, whereas the 3' 17 nucleotides of the tRNA gene are present as a direct repeat at the right end. We termed the element a symbiosis island on the basis of its many similarities to pathogenicity islands. It may represent a class of genetic element that contributes to microbial evolution by acquisition.     

Analysis of an outbreak of non-phage-typeable methicillin-resistant Staphylococcus aureus by using a randomly amplified polymorphic DNA assay

A cluster of methicillin-resistant Staphylococcus aureus (MRSA) infections among patients on an intensive care unit (ICU) was detected by routine infection control surveillance. In the period from 5 January to 22 June 1995, 10 patients on the ICU and a further 6 patients (5 on one ward that had received colonized patients transferred from the ICU) were affected by MRSA strains with the same antibiotic susceptibility patterns. Seven (44%) of these 16 colonized patients developed MRSA bacteremia. MRSA isolates with the same characteristics were also found on the hands of one member of the ICU staff. The isolates were untypeable by phage typing, but 15 of 17 outbreak strains analyzed genetically had identical randomly amplified polymorphic DNA (RAPD) and pulsed-field gel electrophoresis (PFGE) profiles. A single strain of MRSA that was nontypeable by phage typing and that was isolated on the ICU on 1 January and six nontypeable and epidemiologically unrelated MRSA isolates all had RAPD profiles distinct from that of the outbreak strain. Implementation of strict infection control measures stopped the further spread of MRSA on the ICU, the affected general ward, and seven other wards that received MRSA carriers from the ICU. Although nontypeable by phage typing and not previously recognized as an epidemic strain, this strain of MRSA was readily transmissible and highly virulent. RAPD typing was found to be a simple, rapid, and effective method for the epidemiological investigation of this outbreak, and performance of typing by this method was simpler and less time-consuming than that of typing by PFGE. RAPD typing may have more general application for the study of S. aureus infections in hospitals.     

The 139H scrapie agent produces hypothalamic neurotoxicity and pancreatic islet histopathology: electron microscopic studies

Neuronal degeneration, along with astrocytosis, spongiform vacuolation, and amyloid (PrPSc) formation, have long been regarded as neuropathological hallmarks of transmissible spongiform encephalopathies (TSEs). In animals, these diseases include; scrapie, transmissible mink encephalopathy, chronic wasting disease, bovine and feline spongiform encephalopathies, and in humans; kuru, Creutzfeldt-Jakob disease (CJD), and Gerstmann-Str?ussler-Scheinker syndrome (GSS). The abnormal amyloid protein, (PrPSc) is toxic to neurons. Our previous studies showed that hamsters treated with 139H scrapie strain developed obesity, and generalized endocrinopathy, including lesions in hypothalamus, pituitary and pancreas. Histochemical and immunocytochemical studies revealed extensive pathological changes in the islets of Langerhans in 139H-infected hamsters, but not in hamsters infected with 263K scrapie strain. Using routine electron microscopy (EM), we have observed more details of lesions in the beta cells of islets of Langerhans in these animals. Cytoplasmic vacuolation occurred, cytoplasmic organelles were found damaged and disrupted, and membranes were occasionally ruptured. The width of endoplasmic reticulum (ER) lumina were 50-150 nm in controls, whereas in 139H-infected hamsters, they wee occasionally increased up to 4000 nm in diameter. Most beta cells showed degranulation. These EM observations suggest that the cellular death seen in the islets of Langerhans in 139H-infected hamsters is due to necrosis, not apoptosis. Since there were no amyloid deposits found in the islet of Langerhans at the EM level, and there were extremely low scrapie infectivity levels and PrPSc levels in pancreas, it is suggested that the changes noted in pancreas were not a direct toxic effect of PrPSc. Instead, our study suggests that scrapie prion protein PrPSc, acting as a neurotoxicant, alters the hypothalamic neuroendocrine regulation of the pancreas.     

Monoclonal antibody F89/160.1.5 defines a conserved epitope on the ruminant prion protein

The transmissible spongiform encephalopathies are a heterogeneous group of fatal neurodegenerative disorders occurring in humans, mink, cats, and ruminant herbivores. The occurrence of novel transmissible spongiform encephalopathies in cattle in the United Kingdom and Europe and in mule deer and elk in parts of the United States has emphasized the need for reliable diagnostic tests with standardized reagents. Postmortem diagnosis is performed by histologic examination of brain sections from affected animals. The histopathological criteria for transmissible spongiform encephalopathies include gliosis, astrocytosis, neuronal degeneration, and spongiform change. These lesions vary in intensity and anatomic location depending on the host species and genetics, stage of disease, and infectious agent source. Diagnosis by histopathology alone may be ambiguous in hosts with early cases of disease and impossible if the tissue is autolyzed. Deposition of the prion protein (an abnormal isoform of a native cellular sialoglycoprotein) in the central nervous system is a reliable marker for infection, and immunohistochemical detection of this marker is a useful adjunct to histopathology. In the present paper we describe monoclonal antibody (MAb) F89/160.1.5, which reacts with prion protein in tissues from sheep, cattle, mule deer, and elk with naturally occurring transmissible spongiform encephalopathies. This MAb recognizes a conserved epitope on the prion protein in formalin-fixed, paraffin-embedded sections after hydrated autoclaving. MAb F89/160.1.5 will be useful in diagnostic and pathogenesis studies of the transmissible spongiform encephalopathies in these ruminant species.     

Analysis of genome-type, serovar and antibiotic susceptibility of Pseudomonas aeruginosa isolated in Beijing Hospital China in 1991 to 1993]

We analyzed the in vitro antibiotic susceptibility pattern and serovar for 192 strains of Pseudomonas aeruginosa isolated at Beijing Hospital(China) from October 1991 to October 1993. The frequency of resistant strains was high, more than 15%, for ceftazidime, cefsulodin, cefoperazone, aztreonam, gentamicin, tobramycin, tosufloxacin, ofloxacin and fosfomycin. The incidence of resistants against piperacillin and imipenem was significantly low. Among the 192 strains, 16 were designated as being multi-drug resistant strains(i.e.; resistant to more than 8 drugs out of 11 drugs), and all of the multi-drug resistant strains were isolated from inpatients. Predominant serovar of 192 strains were 60(31.3%) for G, 28(14.7%) for E, and 24(12.5%) for I. Multi-drug resistant strains have no characteristic serovar. Restriction enzyme SpeI digestion analysis(using pulse field electrophoresis) of P. aeruginosa-genome yielded several common patterns, and was shown to be useful for tracing the route of nosocomial infection. Further, isolates with closely related genome type, in which the size of one digested band was different, showed a different minimum inhibitory concentration of fosfomycin in one genome type or new quinolones in the other genome type. Analysis of genome type and antibiotic susceptibility pattern may exhibit the antibiotic resistant gene.     

Analysis of the nucleotide sequence of the treehopper-transmitted geminivirus, tomato pseudo-curly top virus, suggests a recombinant origin

The genome of tomato pseudo-curly top virus (TPCTV), originating from Florida, has been cloned and sequenced. TPCTV is the only geminivirus identified with a vector specificity which falls outside the Cicadellidae (leafhoppers) and Aleyrodidae (whiteflies). Infectivity of the cloned viral genome was demonstrated by Agrobacterium-mediated inoculation of several host species. Progeny virus was transmissible by the treehopper vector of TPCTV, Micrutalis malleifera (Fowler). The genome of TPCTV shows features typical of both subgroups I and III genera of the family Geminiviridae. The coat protein of TPCTV, although distinct from all previously characterized geminiviruses, exhibits features more akin to the leafhopper-transmitted geminiviruses than those transmissible by the whitefly Bemisia tabaci Genn. The relationship of TPCTV to other geminiviruses, particularly beet curly top virus, is discussed in relation to the possible evolutionary origins of this virus.     

Physical and genetic map of the mitochondrial genome of Cryphonectria parasitica Ep155

In the chestnut-blight fungus, Cryphonectria parasitica, a cytoplasmically transmissible (infectious) form of hypovirulence is associated with mitochondrial DNA (mtDNA) mutations that cause respiratory deficiencies. To facilitate the characterization of such mutations, a restriction map including the probable location of 13 genes was constructed for a relatively well-characterized virulent strain of the fungus, Ep155. The physical map is based on the order of all fragments generated by cleavage of the mtDNA by the PstI restriction endonuclease and includes some of the cleavage sites for HindIII, EcoRI, and XbaI. It was constructed from hybridization patterns of cloned mtDNA fragments with Southern blots of mtDNA digested with the four restriction enzymes. On this map, the probable locations of genes commonly found in the mitochondrial genomes of ascomycetes were determined by low-stringency hybridization of cloned Neurospora crassa mitochondrial gene probes to Southern blots of C. parasitica mtDNA. The data indicate that the mtDNA of strain Ep155 is a circular molecule of approximately 157 kbp and ranks among the largest mitochondrial chromosomes observed so far in fungi. The mtDNAs of 11 different C. parasitica isolates range in size from 135 to 157 kbp and in relatedness from 68 to 100 percent, as estimated from restriction-fragment polymorphisms. In addition to the typical mtDNA, the mitochondria of some isolates of the fungus contain double-stranded DNA plasmids consisting of nucleotide sequences not represented in the mtDNA of Ep155.     

Middle fossa cyst presenting as a delayed complication of temporal lobectomy: case report

The antibiotic susceptibilities of 43 strains of Escherichia coli O157:H7 identified in the summer of 1996 in Japan were investigated. Growth of 90% of O157 strains was inhibited at a concentration of < or = 0.5 micro/ml by several agents including fosfomycin with glucose-6-phosphate.     

Antimicrobial potentiality of a new beta-lactum antibiotic fosfomycin

Antimicrobial action of penicillin and some of its derivatives including fosfomycin was studied with respect to 225 strains of Gram-positive and Gram negative bacteria. Fosfomycin was found to possess somewhat less activity against Staphylococcus aureus compared with other penicillins; however, it showed powerful activity towards Escherichia coli, Klebsiella spp. and Proteus mirabilis.     

Antibiotic susceptibility testing (agar disk diffusion and agar dilution) of clinical isolates of Enterococcus faecalis and E. faecium: comparison of Mueller-Hinton, Iso-Sensitest, and Wilkins-Chalgren agar media

Forty-two isolates of Enterococcus faecalis and 56 isolates of Enterococcus faecium, including 8 vancomycin-resistant strains, were examined for comparative susceptibility to 27 antimicrobial drugs with the agar dilution method, employing Mueller-Hinton (MHA), Iso-Sensitest (ISTA), and Wilkins-Chalgren (WCA) agar. The Bauer-Kirby agar disk diffusion method was used to comparatively test 24 of the agents in parallel. The enterococci yielded better growth on ISTA and WCA. However, WCA completely antagonized co-trimoxazole and, though less, fosfomycin. Importantly, WCA slightly reduced the activities of teicoplanin (minimal inhibitory concentrations, MICs, raised up to twofold) and vancomycin (MICs raised two- to fourfold) against enterococci and staphylococcal quality control strains. Therefore, WCA was judged unsuitable for susceptibility testing of enterococci. For E. faecalis no discrepancies between agar dilution MICs and inhibition zone diameters were encountered with augmentin, ampicillin, ampicillin-sulbactam, chloramphenicol, mupirocin, oxacillin, teicoplanin, and co-trimoxazole. Overall, MHA yielded fewer very major (category I) and major (category II) discrepancies than ISTA. However, numerous minor (category III), slight (category IV), minimal (category V), and/or negligible (category VI) discrepancies were encountered with ciprofloxacin, doxycycline, erythromycin, fosfomycin, fusidic acid, meropenem, ofloxacin and rifampin. With respect to E. faecium, only cefotaxime, mupirocin, oxacillin, and teicoplanin yielded nondiscrepant results. Several very major (I) and major (II) discrepancies were observed with augmentin, ampicillin, ampicillin-sulbactam, doxycycline, fusidic acid, imipenem, and penicillin G. Minor discrepancies (categories III-VI) were particularly numerous with augmentin, chloramphenicol, ciprofloxacin, doxycycline, and piperacillin. The largest numbers of negligible (VI) discrepancies were noted with fosfomycin, fusidic acid, and ofloxacin. It is recommended to test one cephalosporin (cefuroxime or the like) in parallel for educational purposes and to exclude fosfomycin, fusidic acid, and rifampin from test batteries because of the wide scatter of test results. The large number of minimal (V) discrepancies of ciprofloxacin against E. faecalis, the numerous minor (III) and slight (IV) discrepancies of chloramphenicol against E. faecium, and the not insignificant number of very major (I) and minor (III) discrepancies observed with meropenem against isolates of E. faecalis necessitated proposals for new disk intermediate susceptibility criteria.     

Algodystrophies of the limbs

1. We studied intestinal glucose transport in pigs during the acute and convalescent phases of an invasive viral enteritis, transmissible gastroenteritis. 2. When diarhoea was severe 40 h after experimental infection, net absorption of glucose, Na+ and water, measured by marker perfusion in the jejunum, was reduced; the enhancement of Na+ and water absorption in response to increasing perfusate glucose concentrations up to 120 mmol/l was diminished compared with the response observed in control and convalescent pigs. 3. Measured in vitro, 40 h after infection, unidirectional fluxes of 3-O-methyl-D-glucose across the jejunal epithelium were reduced and net absorption of the sugar was obliterated. Phlorizin (0.05 mmol/l), which completely inhibited net 3-O-methyl-D-glucose absorption in control tissue, had no significant effect on transmissible gastroenteritis jejunum. 4. Our data suggest that in this invasive viral enteritis, which closely resembles human rotavirus enteritis, glucose absorption is impaired as a result of defects in both active and passive glucose flux. 5. Differences between the mechanisms of viral diarrhoea, demonstrated by our study and those of the enterotoxigenic diarrhoeas, should be taken into consideration in formulating active therapeutic measures for children with acute viral diarrhoea.     

Prionoses--neurodegenerative diseases caused by prions, offectious proteinaceous molecules

Prionoses are a group of human and animal neurodegenerative diseases caused by prions, infectious pathogens that differ from bacteria, fungi, parasites, viroids, and viruses. Despite intensive searches over the past three decades, no nucleic acid has been found within prions and considerable experimental data argue that prions are composed exclusively of proteins (glycoproteins). Normal prion protein (PrPC) is encoded by a gene present in all nuclear cells of humans and other mammals but is constitutively expressed mainly in neurons. PrPC is protease sensitive and nonpathogenic but it can be modified to the pathological and protease resistant form designated PrPSC which is essential for infectivity. Prion diseases are manifested as infectious, genetic, or sporadic disorders and are also named as transmissible spongiform encephalopathies (TSE). TSE culminate with a progressive and fatal degeneration of the CNS. The human prionoses include Creutzfeldt-Jakob disease (CJD), kuru, Gerstman-Str?ussler-Scheinker syndrome (GSS), and fatal familial insomnia (FFI). In mammals, more than 15 different species have been described to suffer from prion disorders till now. Scrapie of sheep and goats is the oldest and the most studied of the prion diseases. Bovine spongiform encephalopathy (BSE) and transmissible mink encephalopathy are thought to result from the feeding of scrapie-infected animal products, whereas BSE has been identified in transmission to mice, domestic cats, two exotic species of ruminant, and monkey. More than 20 cases of clinically and pathologically atypical form of CJD, referred to as "new variant" CJD (vCJD) have been recognized in unusually young people in the United Kingdom. There is a strong evidence that the same prion strain is involved in both BSE and vCJD. It suggest the breaking of species barrier which results by spreading of BSE to humans, putatively by dietary exposure. Understanding the function of prion proteins and their modification to the pathological form may give new insight into the etiologic and pathogenic mechanisms also other diseases caused by aberrant proteins, including Alzheimer' disease, amyotrophic lateral sclerosis, and Parkinson's disease. (Tab. 4, Fig. 3, Ref. 76.)     

Scrapie-associated PrP accumulation and agent replication: effects of sulphated glycosaminoglycan analogues

An abnormally protease-resistant and apparently neuropathogenic form of PrP accumulates in the brains of hosts with scrapie and related transmissible spongiform encephalopathies. Studies with scrapie-infected neuroblastoma cells have highlighted dramatic differences in the metabolism of the normal (protease-sensitive) and scrapie-associated (protease-resistant) isoforms of PrP. Furthermore, this model has been useful in identifying inhibitors of protease-resistant PrP accumulation and scrapie agent replication which are valuable as potential therapeutic agents and as probes of the mechanism of protease-resistant PrP formation. These inhibitors include the amyloid stain Congo red and certain sulphated glycans which are glycosaminoglycans themselves or glycosaminoglycan analogues. The relative potencies of various sulphated glycans correlate with their previously determined anti-scrapie activities in vivo, suggesting that the prophylactic effects of sulphated polyanions is due to inhibition of protease-resistant PrP accumulation. These and other observations suggest that an interaction of PrP with endogenous sulphated glycosaminoglycans or proteoglycans is important in protease-resistant PrP accumulation, and raise the possibility that therapies for transmissible spongiform encephalopathies and other amyloidoses could be based on blocking (pre)amyloid-glycosaminoglycan interactions.