- Volume 47, Issue 9, 1998
Volume 47, Issue 9, 1998
- Editorial
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- Review Article
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Resistance to antimicrobial agents: a personal view
More LessProblems of antimicrobial drug resistance are presently serious, but not yet desperate. The principal areas of concern are two-fold: multiresistant opportunist bacteria that affect vulnerable patients in high dependency areas of hospitals (the most pressing problem for developed countries); and multidrug resistance among classic pathogens like Mycobacterium tuberculosis, Salmonella typhi, Shigella spp., Neisseria gonorrhoeae and Plasmodium falciparum (mainly, although not exclusively, a problem for developing countries). The first type can be contained to a large extent by good infection control practices and careful prescribing based on agreed policies of antimicrobial drug use. The input of infection control nurses and laboratory-based clinical microbiologists is crucial and these services deserve full support. The second type additionally requires coordinated action to regulate more effectively the manufacture, availability, promotion and use of antimicrobial drugs. In this case the input of governments, international agencies and pharmaceutical companies is essential. Prescription-only status for antimicrobial drugs used in man and animals should be the norm. The number of drugs available for the treatment of viral, fungal and parasitic infections is comparatively small and much less is known about resistance. More research in these areas would be welcome. Teaching good prescribing habits to medical students is presently haphazard and needs to be formalised. Surveillance needs to be improved. The second half of the 20th century has been a golden age of antibiotics, but the outlook is uncertain. If antimicrobial chemotherapy is to have a secure future, prescribers must learn to use these powerful tools with greater discretion and their use worldwide must be regulated effectively.
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- Host Response To Infection
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Synergic antistaphylococcal properties of lactoferrin and lysozyme
More LessStaphylococcus epidermidis colonises a wide range of implanted prosthetic devices, but rarely contact lenses – despite a similarity in material composition. A conceivable explanation for this anomaly is the action of the tear defences, including the constitutive proteins lactoferrin and lysozyme. Therefore this study investigated the effect of lactoferrin, lysozyme and serum on the growth of S. epidermidis isolates in artificial tear fluid. Whether supplemented with serum alone or serum with either apolactoferrin or lysozyme, this medium induced a similar, strain-variable effect. However, simultaneous addition of these proteins induced a greater bactericidal or bacteristatic effect. Of those strains killed by the concerted action of apolactoferrin and lysozyme, the absence of serum led to a further increase in the bactericidal effect, whereas strains displaying bacteriostasis were unaffected by serum. Iron saturation of lactoferrin reversed the antimicrobial synergy of apolactoferrin and lysozyme. These results show synergy between lactoferrin and lysozyme which is dependent on the iron limitation of lactoferrin. As a bactericidal mechanism, this synergy is augmented by serum, but bacteriostasis remains unaffected by serum supplemention. Thus, the combination of lysozyme and lactoferrin may partly explain the low level of contact lens colonisation by S. epidermidis in vivo.
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- Diagnostic Microbiology
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Clinical evaluation of the Mycobacteria Growth Indicator Tube (MGIT) compared with radiometric (Bactec) and solid media for isolation of Mycobacterium species
More LessThe aim of this study was to evaluate the clinical use of a new culture system for the isolation of mycobacteria. Routine clinical specimens were cultured in the Mycobacteria Growth Indicator Tube, the radiometric Bactec 460 TB system and on Lowenstein Jensen (LJ) medium to compare recovery rates and times for detection of mycobacteria and contamination rates. MGIT was tested for its ability to support the growth of a wide range of mycobacterial species. Acid-fast bacilli (AFB) were detected on direct smears of 76 of 603 clinical specimens and mycobacteria were isolated by at least one method from 109 specimens; 93% of these were detected in the MGIT, 95% in the Bactec 460 TB system and 87% on LJ medium. The MGIT, Bactec and LJ media detected 92%, 97% and 95%, respectively, of 61 M. tuberculosis isolates and 94%, 94% and 77% of the 48 isolates belonging to the M. avium complex (MAC). The mean detection times in MGIT, Bactec and LJ media for M. tuberculosis were 22, 14 and 27 days respectively, and for MAC were 14, 12, and 29 days, respectively. Growth of M. tuberculosis was detected in Bactec, within 4 weeks, in 93% of the 61 culture-positive specimens, compared with only 61% in MGIT and 66% on LJ. The number of MAC detected within 4 weeks was similar in Bactec and MGIT, but less in LJ medium. Differences in sensitivity and time to detection of growth between media were greater for specimens in which AFB were not detected on direct smear than those on which AFB were seen. Contamination rates were similar in the three systems (3-4%). MGIT supported the growth of all 28 Mycobacterium spp. inoculated. MGIT has significant safety advantages and is less labour intensive than other methods, but the time to detection of M. tuberculosis, especially in smear-negative specimens, was longer in MGIT than in Bactec.
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- Antimicrobial Resistance
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Heterogeneous location of the mupA high-level mupirocin resistance gene in Staphylococcus aureus
More LessEpidemiologically unrelated clinical isolates of Staphylococcus aureus with high-level resistance to mupirocin (MIC ≥ 512 mg/L) were studied to determine the location of the mupA resistance gene. The gene was carried on plasmids of variable size, some of which were transferable in vitro. DNA hybridisation of genomic DNA from 85 isolates showed that mupA was located on EcoRI fragments of seven different sizes; the most frequently observed fragments were 7 kb (46 isolates) or 4.1 kb (21 isolates). All isolates retained a 1.6-kb NcoI fragment that hybridised with mupA probes, but showed heterogeneous hybridisation patterns after digestion with HincII. These data suggested that mupA may be conserved, but that variation occurs in the flanking DNA proximal to it. Amplification of spacer regions between mupA and closest proximal copy of IS257 yielded products of variable size and was consistent with the presence of IS257 in either orientation. It is proposed that IS257-mediated events are responsible for the heterogeneity observed. The location of mupA varied between epidemiologically unrelated isolates of the same strain, including isolates of EMRSA-16 – one of the two predominant methicillin-resistant strains in UK hospitals at the present time – and this correlated with variations in the digestion patterns of the mupirocin resistance plasmids. The variable location of mupA should be evaluated further as a potential epidemiological tool with which to monitor the spread of high-level mupirocin resistance in EMRSA-16 or other strains of S. aureus.
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- Bacterial Pathogenicity And Characterisation
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Analysis of TbpA and TbpB functionality in defective mutants of Neisseria meningitidis
More LessIron uptake analysis suggested that the Neisseria meningitidis transferrin (Tf) binding proteins, TbpA and TbpB, form only one type of receptor complex. Mutants defective in the synthesis of either TbpA or TbpB, but not defective in both proteins, can bind Tf, suggesting that both proteins are surface exposed and function in Tf binding. Also, iron uptake from Tf into the meningococci did not require the presence of both Tbps. The TbpB-defective mutant incorporated c. 37% of the iron taken up by the wild-type strain, but this was insufficient for bacterial growth. The TbpA-defective mutant incorporated c. 50% of the iron taken up by the wild-type strain and was able to grow with Tf as the only iron source. Mouse antibodies specific for TbpA were able to block c. 70% of the iron uptake from Tf in the wild-type strain, whereas they blocked only 22% of iron uptake in the TbpB-defective mutant and did not block uptake in the TbpA-defective strain. These results emphasise that TbpA should be considered in future vaccine trials in which iron-restricted proteins are to be included in the vaccine formulation.
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Carbon source utilisation by Bordetella bronchiseptica
More LessBordetella bronchiseptica isolates utilised tricarboxylic acid cycle intermediates – succinate, citrate, α-ketoglutarate, fumarate, lactate and oxalo-acetate; the organic acids pyruvate, acetate and lactate; and the amino acids proline, glutamate, glutamine and tyrosine – as sole sources of carbon and energy. The inability of B. bronchiseptica isolates, representing the three phase types and from different animal hosts, to utilise carbohydrates and sugar alcohols as sole carbon and energy sources was confirmed and extended. The influence of the carbon substrate on doubling time, piliation, flagellation, motility, capsule production and adherence to mammalian cells was also measured.
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Inhibition of enhanced toxin production by Clostridium difficile in biotin-limited conditions
More LessProduction of toxins A and B by Clostridium difficile is enhanced in a defined medium with biotin-limited conditions. In the present study compounds inhibitory to enhanced toxin production by a C. difficile strain were examined. Increases in biotin concentration from 0.05 nM to 50 nM accelerated growth and inhibited enhanced toxin production. Asparagine, glutamic acid and glutamine (10 mM) showed an effect on growth and toxin production similar to that of biotin. Lysine (10 mM) suppressed growth and inhibited toxin production. Addition of these toxin-inhibitory compounds within an incubation period of 2 days inhibited the enhanced toxin production, but later addition showed only slight inhibition of toxin production. Amino acids contained in the defined medium under the biotin-limited conditions were actively utilised in the presence of the three toxin-inhibitory amino acids, but in the presence of lysine, amino-acid utilisation was suppressed. Different mechanisms of action of these toxin-inhibitory molecules, which may be divided into excess biotin, asparagine-glutamic acid-glutamine group, and lysine, are discussed.
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Differential efficacy of passive immunisation against infection by Lyme disease spirochaetes transmitted by partially fed vector ticks
More LessThe efficacy of passive immunisation against tick-transmitted Lyme disease spirochaetal infection was determined in relation to the duration of previous feeding of infected vector ticks. Thus, mice challenged with spirochaete-infected unfed or partially fed nymphal ticks were passively immunised with monoclonal and polyclonal antibodies against the Lyme disease spirochaete (Borrelia burgdorferi) at various intervals after tick attachment. Spirochaetal infection in challenged mice and engorged ticks was verified by xenodiagnosis and indirect immunofluorescent antibody assay, respectively. Although tick-transmitted spirochaetal infection could be aborted by anti-OspA antibodies and hyperimmune antiserum, nearly all immunised mice challenged with infected ticks that had previous 36-h attachment became infected. More than 72% of the nymphal ticks used in this challenge retained their B. burgdorferi infection after engorgement on mice immunised with anti-spirochaete antibodies, and their subsequent infectivity to mice remained effective. It is concluded that a higher efficiency of transmission by partially fed infected nymphs and a lower efficacy of passive immunisation against infection result from an effect of previous feeding of infected ticks that activates antigenic change and enables the spirochaetes to circumvent OspA-based humoral immunity.
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Enteropathogenicity markers in Escherichia coli isolated from infants with acute diarrhoea and healthy controls in Rio de Janeiro, Brazil
More LessFaeces from urban children > 2 years old with acute diarrhoeal illness and from non-diarrhoeal infants (controls) were examined for Escherichia coli and other enteropathogens. A total of 990 E. coli isolates from 100 patients and 50 controls was tested for enteropathogenic E. coli (EPEC) serotype (O:H), adherence to HEp-2 cells after incubation for 3 and 6 h, fluorescent actin staining (FAS), DNA hybridisation with EAF, eaeA, STh, STp and EAggEC probes and production of heat-labile enterotoxin (LT) and verocytotoxin (VT) with Y1 and Vero cells. EPEC were the most prevalent enteropathogens in patients (32.7%; and 14% in controls). Enteroinvasive E. coli (EIEC) and Vero cytotoxin-producing E. coli (VTEC) were not detected. The rate of isolation of enterotoxigenic E. coli (ETEC) was identical in both groups. Among the EPEC isolates the prevalent serotypes were O111:H2, O55:NM and O119:H6. Localised adherence (LA) was found significantly more frequently in isolates from patients (19.6%) than controls (2.1%). All LA-positive EPEC isolates were FAS+ and eaeA+, but only 75.2% of them hybridised with the EAF probe. Diffusely adhering E. coli (DAEC) and enteroaggregative E. coli (EAggEC) were found with equal frequency in patients and controls. Twenty-seven E. coli isolates were negative for EAF but positive for eaeA and FAS and produced LA in 6-h adherence tests. These EAF-/eaeA+ strains were the only putative enteropathogen identified in seven patients and were not found in controls. The ability of these strains to elicit ultrastructural cell alterations and cell-signalling events was evaluated in Caco-2 cells (human colon carcinoma cell line) by the gentamicin invasion assay and by transmission electron microscopy. The numbers of intracellular bacteria in cell invasion tests varied from 0.4% to 1.6% of the cell-associated bacteria after a 6-h incubation period. Tyrosine phosphorylation of host cell proteins was assessed in HEp-2 cells by immunofluorescence microscopy and all strains gave positive results. EAF-/eaeA+ E. coli strains express most of the virulence properties found among true EPEC strains and can be a relevant cause of infant diarrhoea in developing countries.
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Distribution of insertion sequence IS200 among different clonal lines of the related Salmonella serotypes Livingstone and Eimsbuettel
More LessThe copy number and genetic location of IS200 have provided evidence of strain relatedness in many serotypes of Salmonella. In this study, 100 isolates of the related serotypes Livingstone (6,7:d:l, w) and Eimsbuettel (6,7,14:d:l, w), representing 10 ribotype/biotype (RT/BT) groups isolated from human and non-human sources in seven countries over a 26-year period, were examined for their IS200 profiles. The distribution of IS200 in strains of these serotypes was limited, being present in all 53 isolates of ribotype 1 (RT1) and its variant type RT6, in one of five isolates of RT5 but in none of 42 isolates of RTs 2, 3 or 4. Although the seven IS200 profiles identified in RT1 isolates were of little value for further discrimination within different biotype groups, they were extremely valuable for confirming serotype: isolates of RT1/BT8/IS200 profile A (or its variants) and those of RT1/BT3/IS200 profile B (or its variants) were almost invariably associated with serotypes Livingstone and Eimsbuettel, respectively.
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Experimental campylobacter infection and diarrhoea in immunodeficient mice
More LessThe responses of previously untested immunodeficient mouse strains to campylobacter infection are described. Three strains of adult immunodeficient mice (SCID-Beige, C.B-17-SCID-Beige and RAG-2) were inoculated intragastrically with Campylobacter jejuni NCTC 11168. All mice became heavily colonised, but none developed clinical signs of disease. Immunocompetent BALB/c mice inoculated similarly had much lower colonisation levels. The co-administration of iron dextran had no effect on colonisation levels nor the development of clinical signs of disease. In contrast, C.B-17-SCID-Beige mice, when inoculated with one of a series of 10 clinical isolates of C. jejuni, were more heavily colonised for extended periods (up to 5 months) and approximately 10–20% of the mice became ill with diarrhoea. C. jejuni was detected in mouse faeces throughout at levels of 107–109 cfu/g. All mice killed whilst ill with diarrhoea displayed histopathological lesions typical of human campylobacteriosis. Severe pathology was limited to the large intestine and was suggestive of an acute, bacteria-induced inflammation. Although blood was detected in the diarrhoeal stools, no evidence of mucosal epithelial cell invasion was found by immunohistology. No pathology was detected in tissue sections from any of the animals that had not developed signs of disease following C. jejuni inoculation. These immunodeficient mouse strains are readily, and heavily, colonised as adults by C. jejuni. The diarrhoea, although sporadic, was reproducibly produced, and could provide the basis for pathogenicity studies.
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- Molecular Mycology
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Molecular probes for the detection of pathogenic fungi in the presence of human tissue
More LessFour primer systems, amplifying fragments of the gene coding for the small ribosomal subunit (18S rRNA) were characterised with pure cultures of 65 medically relevant fungal species plus two mushrooms. A primer cocktail (TR1/CA1-TR2/AF2) amplified 59 of 67 fungal species; the universal fungal primer 1 (UF1) in combination with the eukaryotic primers S3 or EU1 amplified 64 and 65 of 67 fungal species, respectively. The design of an additional primer (RZY1) enabled the amplification of the missing members of the zygomycetes. The primer systems amplified all the medically relevant fungi tested. These included eight Candida spp. and seven other yeast species, 13 dermatophytes, 32 moulds (including six zygomycetes and five dimorphic fungi) and two mushrooms. Eleven controls including DNA from Schistosoma mansoni, Escherichia coli, Mycobacterium tuberculosis and man were not amplified. The oligonucleotide CA hybridised with C. albicans, C. tropicalis and C. parapsilosis; the oligonucleotide TR hybridised with the 13 dermatophytes; the oligonucleotide AF hybridised with Aspergillus fumigatus, A. flavus, A. terreus, A. nidulans, A. versicolor, A. tamarii, A. clavatus, A. fischeri, but not with A. niger or A. versicolor; and the oligonucleotide HC hybridised with three varieties of Histoplasma capsulatum. These oligonucleotides did not hybridise with the other fungi nor the controls. The specificity of the newly designed primer systems was confirmed by selective amplification of fungal DNA from human lung tissue spiked with fungal biomass and from vitrectomy fluid of a patient with candida endophthalmitis.
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- Book Reviews
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Volumes and issues
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Volume 73 (2024)
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Volume 72 (2023 - 2024)
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Volume 71 (2022)
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Volume 70 (2021)
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Volume 69 (2020)
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Volume 68 (2019)
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Volume 67 (2018)
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Volume 66 (2017)
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Volume 65 (2016)
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Volume 64 (2015)
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Volume 47 (1998)
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