- Volume 49, Issue 12, 2000
Volume 49, Issue 12, 2000
- Editorial
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- Review Article
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Pathogenesis of pneumococcal infection
More LessThe pathogenesis of pneumococcal infection is a complex interplay between pneumococcal virulence determinants and the host immune response. Molecular studies have considerably advanced our knowledge and understanding of the precise structures and functions of the different determinants and their pathogenic roles. This review describes the mechanisms by which pneumococci attach, invade, evade lung defences and cause severe disease. Better understanding of the critical steps in this complex process will enable more effective clinical intervention to be developed to reduce the mortality exacted by this versatile pathogen.
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- Antimicrobial Resistance
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Characterisation of drug resistance gene cassettes associated with class 1 integrons in clinical isolates of Escherichia coli from Taiwan, ROC
More LessThe presence of class 1 integrons in clinical isolates of Escherichia coli was detected by PCR. Of 104 E. coli isolates from Kaohsiung, 54 (52%) carried class 1 integrons, with inserted DNA regions of 1–3 kb. These integrons were located on plasmids, as demonstrated by Southern hybridisation. DNA sequencing was used to identify the genetic content of the integron-variable regions. Different class 1 integrons contained various numbers, kinds and combinations of gene cassettes within their variable regions. These gene cassettes included those encoding resistance to trimethoprim (dfrIa, dfrV, dfr12 and dfr17), aminoglycosides (aadA1a, aadA2, aadA4 and aadB), chloramphenicol (cmlA), erythromycin (ereA2) and β-lactams (blaP1). An integron carrying three inserted cassettes – dfr12-orfF-aadA2 – was present in 33 (61%) of the 54 isolates with class 1 integrons. Gene cassettes encoding resistance were expressed phenotypically. The results indicate that class 1 integrons are widespread in clinical E. coli isolates in Taiwan. The types, combinations and frequency of the gene cassettes in integrons may reflect the specific selective pressures to which the isolates were exposed and could provide useful surveillance data for relation to antibiotic usage information.
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Co-transfer of plasmids in association with conjugative transfer of mupirocin or mupirocin and penicillin resistance in methicillin-resistant Staphylococcus aureus
A. PAWA, W.C. NOBLE and S.A. HOWELLTwo distinct strains of methicillin-resistant Staphylococcus aureus (MRSA) isolated from patients in a dermatology ward were also resistant to mupirocin. The mupirocin resistance plasmids from both strains were indistinguishable by EcoRI and HindIII restriction digest analysis, except for the presence of genes apparently mediating penicillinase production in some transconjugants. Conjugative transfer of the plasmid mediating mupirocin resistance from one of these strains to a recipient S. aureus was accompanied in some cases by co-transfer of plasmids mediating resistance to tetracycline or erythromycin; in some instances a plasmid which possessed no apparent resistance markers was also transferred. The second strain demonstrated conjugative transfer of penicillin and mupirocin resistance as well as transfer of a plasmid mediating gentamicin resistance, but transfer of erythromycin resistance was not apparently plasmid-mediated.
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- Clinical Microbiology
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Contamination of expressed human breast milk with an epidemic multiresistant Staphylococcus aureus clone
More LessNosocomial infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are a major cause of outbreaks in intensive care units. Infants make up a sector of the population that presents a high risk for MRSA infections. Mother-to-infant transmission has been indicated as a possible cause of MRSA infections in neonates. The occurrence and characteristics of MRSA in samples of banked human milk were investigated by selective culture, antibiogram and pulsed-field gel electrophoresis. MRSA contamination was found in 11% of 500 samples of expressed, fresh-frozen milk from 500 different donors at five Brazilian milk banks. The great majority of the contaminated samples passed breast milk quality control criteria for dispensing as raw milk under Brazilian and American guidelines. Most of the MRSA isolates belonged to the Brazilian epidemic clone, which is reported to be widespread in several Brazilian states, in Argentina and in Portugal. It is concluded that expressed breast milk can be a reservoir of multiresistant S. aureus epidemic clones. Studies are necessary to assess the source of contamination and potential role of MRSA-contaminated milk in the transmission of MRSA to neonates.
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- Correspondence
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- Identification Of Bacteria
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PCR for detection and identification of Streptococcus sobrinus
More LessOligonucleotide primers were designed based upon a comparison of the dextranase gene (dex) sequences from Streptococcus sobrinus and S. mutans. The primers amplified a 1610-bp long DNA fragment on the dex gene by a PCR. The pair of primers was specific to S. sobrinus as the other members of the mutans streptococci – S. mutans, S. downei, S. cricetus, S. rattus, S. macacae and S. ferus – gave no PCR products. Other gram-positive oral bacteria (15 strains of 10 species of cocci and 18 strains of 12 species of rods) and gram-negative oral bacteria (3 strains of 3 species of cocci and 31 strains of 22 species of rods) also gave negative results in the PCR. The PCR procedure was able to detect as little as 100 fg of purified chromosomal DNA or as few as 9 cfu of S. sobrinus NIDR6715. Seven clinical isolates of S. sobrinus were also positive in the dex PCR. This laboratory developed the S. mutans-specific PCR (dexA PCR) method with the primers specific for a portion of the dextranase gene of S. mutans Ingbritt. Primers for the dex and dexA PCR methods detected two species exclusively from the mutans streptococci. Furthermore, these two species were effectively differentiated by the species-specific amplicons with different lengths. The application of the PCR method to human dental plaque showed that the prevalence of S. sobrinus (83%) in oral cavities was higher than currently supposed (0–50%). These results suggest that the described PCR method is suitable for the specific detection and identification of human cariogenic bacteria, S. sobrinus and S. mutans.
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Monoclonal antibody-based rapid identification of Burkholderia pseudomallei in blood culture fluid from patients with community-acquired septicaemia
More LessA monoclonal antibody-based latex agglutination (MAb-LA) test was employed for the rapid identification of Burkholderia pseudomallei in blood culture fluid from patients with community-acquired septicaemia. These patients were admitted to 12 hospitals in the northeastern part of Thailand which is a region known to be endemic for melioidosis. Blood samples were collected and immediately added to the blood culture bottles which were incubated in either automated (five hospitals) or manual (seven hospitals) culture systems. Of a total of 1369 culture-positive specimens, 204 specimens were culture-positive for B. pseudomallei. Of those, 194 (95%) were positive by MAb-LA and the type of blood culture system did not affect positivity rates. The performance of the MAb-LA test on these specimens was highly satisfactory compared with culture detection and confirmation by biochemical test, with 95.1% sensitivity, 99.7% specificity and 98.8% and 99.2% for positive and negative predictive values, respectively. The method described is highly reproducible, simple to perform even by inexperienced laboratory personnel and does not require expensive or elaborate equipment.
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- Molecular Epidemiology
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Investigation for a more virulent variant among the C:2b:P1.2,5 Spanish meningococcal epidemic strains by molecular epidemiology
More LessA rise in the incidence of meningococcal disease has occurred in Spain in recent years, especially in some regions in the north-west of the country. Most cases have been caused by meningococci characterised as Neisseria meningitidis C:2b:P1.2,5. A total of 107 C:2b:P1.2,5 meningococcal isolates (60 from patients and 47 from carriers) and 12 isolates showing related antigenic combinations (C:2b:NST, C:2b:P1.2, C:2b:P1.5, C:NT:P1.2,5) was analysed by pulsed-field gel electrophoresis to determine the genetic variability of the epidemic and related strains. Endonucleases BglII and NheI were used to cut chromosomal DNA. When BglII was used, most of the C:2b:P1.2,5 isolates showed the same pulsotype regardless of whether they were from clinical cases or carriers. Isolates showing the principal profile after digestion with endonuclease BglII were analysed with NheI. Four pulsotypes were identified, of which two were found in only one isolate each. The major profiles (1 and 2) showed differential distribution among clinical and carrier isolates; pulsotype 1 was the most frequent among clinical isolates. However, the proportions of isolates showing profiles 1 and 2 were similar among carrier isolates. This could indicate that there are two variants of the C:2b:P1.2,5 strain with differing pathogenicity.
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Molecular epidemiological study of Vibrio cholerae isolates from infected patients in Teheran, Iran
More LessA total of 110 clinical isolates of Vibrio cholerae O1 biotype El Tor serotype Ogawa isolated in a recent outbreak from different districts of Teheran, Iran, was subjected to 99 carbon source utilisation tests, ribotyping and toxinogenotyping. PCR showed that the genes encoding cholera toxin (ctxA), toxin co-regulated pilus (tcp), accessory cholera enterotoxin (ace) and zonula occludens toxin (zot) were present in 100%, 100%, 97.3% and 99.1% of the isolates, respectively. Restriction fragment length polymorphism (RFLP) study of the BglI-digested DNA probed with five oligonucleotides targeting the conserved regions of 16S and 23S rRNA genes revealed a similar ribotype pattern for 109 isolates. All but one isolate showed ribotype pattern B21a, containing seven bands with molecular sizes ranging from 11 to 3.9 kb. The toxin gene restriction pattern (toxinogenotype) showed that the isolates carried either three or two copies of the toxin genes (ace, zot, ctx) which were recognised as TB41a and TB69 patterns, respectively. Overall, the ribotyping data showed that, despite biochemical differences in 12 of the 99 carbon sources, most of the isolates studied belonged to a single clone.
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Molecular typing of Mycobacterium avium isolates by sequencing of the 16S–23S rDNA internal transcribed spacer and comparison with IS1245-based fingerprinting
More LessThe nucleotide sequence of the variable 16S–23S rDNA internal transcribed spacer (ITS) was determined in 32 strains of Mycobacterium avium, including 29 clinical isolates, two environmental isolates and the reference strain M. avium ATCC 35712. The results were compared with those obtained by the IS1245-based restriction fragment length polymorphism (RFLP) assay. The strains belonged to three distinct ITS sequevars, Mav-A, Mav-B and Mav-C. Sixteen of 17 isolates of the Mav-B sequevar were from HIV-positive patients; the Mav-A sequevar included six and five isolates from HIV-positive and HIV-negative individuals, respectively, as well as the two environmental isolates and the M. avium reference strain ATCC 35712; only one isolate, from a HIV-infected patient, belonged to the Mav-C sequevar. IS1245-RFLP analysis of M. avium isolates of sequevars Mav-A and Mav-B showed that isolates occurring in clusters of identical or highly related RFLP patterns generally belong to the same sequevar, and that M. avium strains belonging to the same sequevar may present distinct and unrelated IS1245-RFLP patterns. The question of the molecular markers specific for M. avium clones pathogenic for man is discussed.
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- Virology
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Temperature-sensitive acetylesterase activity of haemagglutinin-esterase specified by respiratory bovine coronaviruses
More LessNumerous respiratory bovine coronaviruses (RBCV) were isolated recently from nasal swab samples and lung tissues of feedlot cattle with acute respiratory tract disease. These newly emerging RBCV isolates exhibited distinct phenotypic features that differentiated them from enteropathogenic bovine coronaviruses (EBCV). The RBCV strains had a receptor-destroying enzyme function mediated by acetylesterase (AE) activity of the haemagglutinin-esterase (HE) glycoprotein. The HE genes of wild-type EBCV strain LY138 and RBCV strains OK-0514 (OK) and LSU-94LSS-051 (LSU) were cloned, sequenced and transiently expressed in COS-7 cells. The enzymic properties of HE proteins in COS-7 cellular extracts and in purified virus preparations were assayed at room temperature, 37°C and 39°C by two different assays. One assay used ρ-nitrophenyl acetate (PNPA) as substrate and detected serine-esterase activity; the second assay monitored AE function with bovine submaxillary mucin (BSM) as substrate. The PNPA tests confirmed that HE proteins of EBCV and RBCV were functionally expressed in transfected COS-7 cells. Time-dependent determination of the AE activity of purified RBCV OK and LSU particles showed lower AE activity at 39°C than at 37°C, whereas the purified EBCV LY particles retained full AE activity at both 37°C and 39°C. Transiently expressed RBCV HE exhibited a marked reduction of AE activity after 40 min of assay time at 37°C. In contrast, the AE activity of the transiently expressed EBCV HE remained stable beyond 40 min. The deduced amino-acid sequences of the HE proteins specified by the RBCV strains OK and LSU contained specific amino-acid changes in comparison with the EBCV LY strain, which may be responsible for the observed enzymic differences. These results are consistent with the hypothesis that RBCV strains have evolved to selectively replicate in respiratory tissues and that HE may play a role in this tissue tropism.
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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 63 (2014)
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Volume 62 (2013)
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Volume 61 (2012)
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Volume 60 (2011)
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Volume 58 (2009)
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Volume 56 (2007)
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Volume 53 (2004)
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Volume 50 (2001)
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Volume 49 (2000)
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Volume 48 (1999)
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Volume 47 (1998)
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Volume 46 (1997)
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Volume 45 (1996)
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Volume 44 (1996)
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Volume 43 (1995)
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Volume 42 (1995)
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Volume 41 (1994)
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Volume 40 (1994)
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Volume 39 (1993)
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Volume 38 (1993)
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Volume 37 (1992)
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Volume 36 (1992)
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Volume 35 (1991)
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Volume 34 (1991)
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Volume 33 (1990)
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Volume 32 (1990)
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Volume 31 (1990)
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Volume 30 (1989)
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Volume 29 (1989)
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Volume 28 (1989)
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Volume 27 (1988)
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Volume 26 (1988)
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Volume 25 (1988)
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Volume 24 (1987)
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Volume 23 (1987)
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Volume 22 (1986)
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Volume 21 (1986)
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Volume 20 (1985)
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Volume 19 (1985)
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Volume 18 (1984)
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Volume 17 (1984)
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Volume 16 (1983)
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Volume 15 (1982)
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Volume 14 (1981)
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Volume 13 (1980)
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Volume 12 (1979)
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Volume 11 (1978)
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Volume 10 (1977)
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Volume 9 (1976)
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Volume 8 (1975)
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Volume 7 (1974)
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Volume 6 (1973)
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Volume 5 (1972)
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Volume 4 (1971)
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Volume 3 (1970)
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Volume 2 (1969)
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Volume 1 (1968)