- Volume 33, Issue 2, 1990
Volume 33, Issue 2, 1990
- Articles
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Virulence of ten serogroups of Clostridium difficile in hamsters
M. Delmée and V. AvesaniSummaryA slide agglutination technique identifying 10 serogroups of Clostridium difficile (A,B,C,D,F,G,H,I,K and X) has been described previously. In this study, we have used the hamster to compare the ability of the 10 serogroup reference strains to colonise and produce disease. Groups of four hamsters were each given a single intraperitoneal injection of either clindamycin or cefoxitin, and an oral challenge dose of C. difficile. The time taken to establish faecal colonisation and the length of survival after colonisation were monitored. All hamsters treated with cefoxitin became colonised by day 3 and those challenged with the cytotoxigenic strains of serogroups A,C,H and K developed colitis and died. Among those challenged with the non-toxigenic strains of groups B,D,I and X and the toxigenic strains of groups F and G, faecal colonisation was established without signs of disease. This demonstrates that there are differences in virulence even among toxigenic strains of C. difficile. The same phenomenon was observed after treatment with clindamycin but the pattern of colonisation was quite different with some strains. In the hamsters challenged with toxigenic strains of groups C and K and non-toxigenic strains of groups D and I, which are highly resistant to clindamycin, the response was the same as with cefoxitin. The results were different with strains which were susceptible to clindamycin. Some animals became colonised much later than those treated with cefoxitin but the mortality was similar. The remaining animals became colonised by day 3, not by the challenge organism but by another strain which always belonged to serogroup D or C; the source of these organisms was thought to be either previously undetected faecal carriage or the environment. Four animals infected by a toxigenic serogroup-C strain died. Another five, colonised by a non-toxigenic serogroup-D strain survived even though they had been challenged with a strain of a virulent serogroup. This protective effect and the differences in the potential to colonise after clindamycin therapy may warrant further investigation in man.
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Application of small fragment restriction endonuclease analysis (SF-REA) to the epidemiological fingerprinting of Staphylococcus aureus
R. Haertl and G. BandlowSummaryTotal cell DNA of 14 isolates of Staphylococcus aureus from patients of an intensive care unit (ICU) and 180 unrelated strains was examined by restriction endonuclease analysis (REA). EcoRI-generated DNA fragments were either subjected to conventional REA on agarose gels and stained with ethidium bromide or separated by polyacrylamide gel electrophoresis and visualised by silver staining (SF-REA). Both methods were compared for inter-strain discriminatory ability, reproducibility and handling. All DNA-cleavage patterns of unrelated strains clearly differed from each other when subjected to SF-REA. In contrast, all S. aureus isolates from the ICU gave identical restriction fragment patterns. These findings supported the suspicion of nosocomial infection in these patients. Conventional REA proved the identity of the ICU isolates, but it failed to differentiate between some of the unrelated strains. Therefore SF-REA of total cell DNA seemed to be superior. It has proved to be a very useful technique for studying the epidemiology of S. aureus in hospitals.
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Diversity of staphylococci exhibiting high-level resistance to mupirocin
More LessSummaryPlasmids mediating high-level resistance to mupirocin (MIC > 1000 mg/L) in staphylococci from various sources were studied by restriction endonuclease cleavage. Several patterns were obtained but six plasmids isolated from various Staphylococcus aureus and S. epidermidis strains were indistinguishable. The diversity and spread of these plasmids is illustrated.
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Plasmid profiles of Shigella dysenteriae type 1 isolates from Ethiopia with special reference to R-plasmids
More LessSummaryPlasmid profiles of 80 Shigella dysenteriae type 1 (Shiga’s bacillus) strains, collected between 1974 and 1985 in Ethiopia, were examined. Strains with the dominant antibiotic-resistance (R-) type—resistance to ampicillin (A), chloramphenicol (C), streptomycin (S), sulphadiazine (Su) and tetracycline (T)—showed two distinct plasmid profiles (PP). Six plasmid bands were demonstrated in “Ethiopian strains” with PP-1A isolated between 1974 and 1982. In mating experiments with these strains, Escherichia coli K12 recipients showed plasmids pYH 10a (72 Mda, atypical Inc FIme, coding for ACSSuT resistance). Eight plasmid bands were demonstrated in strains with PP-2A. These strains were first isolated in 1980 and carried plasmid pYH 11a (40 Mda, Inc X, coding for ACT resistance). Strains with PP-2A were identical with a “Zairian strain” described elsewhere. Strains with R-type ACT were “Zairian strains” lacking the 5.1-and 4.2-Mda plasmids. Those with R-type CSSuT were temporally clustered in 1978—1980 and carried plasmid pYH12 (58 Mda, Inc B, coding for the same R-type). A trimethoprim-resistant strain (Gimira strain) had a pattern of small plasmids similar to those of the “Zairian strain” and is probably a subclone of the latter. The fact that a limited number of plasmid profiles have remained constant over many years shows the limitation of plasmid profile analysis as an epidemiological tool. However, when the usual profile is known for a given area, identification of a distinctly different pattern becomes easy and epidemiologically useful.
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Plasmids and factors associated with virulence in environmental isolates of Vibrio cholerae non-O1 in Bangladesh
More LessSummaryPlasmid profiles and factors associated with toxigenicity in 51 strains of Vibrio cholerae non-O1 isolated from water samples collected in Bangladesh were analysed. Eleven (21.5%) strains were found to harbour at least one plasmid of 1.7-115 Mda; seven of these strains shared a 115-Mda plasmid. Six of 13 strains tested gave positive cytotoxic and enterotoxic responses. However, two non-cytotoxic strains were enterotoxigenic. Only three of the six cytotoxic and enterotoxic strains caused haemagglutination of human erythrocytes which indicated that toxin production and haemagglutinating activity were unrelated in these V. cholerae non-O1 strains. Conjugal transfer assays demonstrated that the 115-Mda plasmid harboured by some of the toxigenic V. cholerae non-O1 strains carried genes coding for antibiotic resistance and cytotoxin production but not for enterotoxin production. However, this plasmid was also carried by non-toxigenic strains. Some other strains carrying no plasmids or only small-mol.-wt plasmids, were found to be toxigenic. Therefore, toxin production is not plasmid-mediated in all V. cholerae non-O1 strains. Regardless of their pathogenic potential, V. cholerae non-O1 strains possessed the capacity to grow in conditions of iron limitation and, under these conditions, synthesis of at least two new outer-membrane proteins was induced.
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Pathogenic factors of Pseudomonas cepacia isolates from patients with cystic fibrosis
More LessSummaryOne hundred and nineteen isolates of Pseudomonas cepacia, 98 of which were from cystic fibrosis (CF) patients and 21 from environmental and other human sources, were examined for biochemical and exo-enzymatic properties that may contribute to the pathogenicity of this bacterium. The following characteristics were demonstrated significantly more frequently in isolates from CF patients than in control isolates: production of catalase, ornithine decarboxylase, valine aminopeptidase, C14 lipase, alginase and trypsin; reduction of nitrate to nitrite; hydrolysis of urea and xanthine; complete haemolysis on bovine red blood cells; cold-sensitive haemolysis on human red blood cells; greening of horse and rabbit red blood cells. The role of these factors in the pulmonary disease associated with cystic fibrosis is not clear. However, several factors which have been reported previously as being associated with pathogenic processes with other bacteria have now been described in P. cepacia. Additional factors not previously reported as “pathogenicity factors” are also described.
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The use of selective media for the isolation of Pseudomonas pseudomallei in clinical practice
More LessSummaryAshdown’s selective-differential agar medium, with or without preenrichment in selective broth, was evaluated for the isolation of Pseudomonas pseudomallei from 1972 clinical specimens obtained from 643 subjects in Northeast Thailand; 226 patients proved to have melioidosis. The use of Ashdown’s medium significantly increased the frequency of recovery of P. pseudomallei from sites or specimens with an extensive normal flora (throat, rectum, wounds and sputum) as compared to the recovery on blood and MacConkey agars (p<0.01). The isolation frequency from throat, rectal and wound swabs was further increased by the use of the broth pre-enrichment. The colonial morphology of P. pseudomallei on Ashdown’s medium was sufficiently characteristic to allow presumptive identification. With the use of these selective media it was possible to culture P. pseudomallei from throat swabs taken from 87% of the patients from whom the organism could also be isolated from corresponding tracheal aspirates or sputum specimens. P. pseudomallei was isolated from rectal swabs taken from 51 patients, the first time that faecal excretion of the organism has been demonstrated in man. The diagnosis of melioidosis would not have been confirmed bacteriologically in eight patients (3.5%) without the use of the selective media. It is suggested that, in areas endemic for melioidosis, all sputum specimens should be cultured on selective media, such as Ashdown’s. For the investigation of clinically suspected cases of melioidosis, and for follow-up during treatment of the disease, the use of broth pre-enrichment is recommended for specimens obtained from sites with an extensive normal flora.
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Antibacterial activity of fluoroquinolones in combination with zidovudine
More LessSummarySince patients with AIDS may receive fluoroquinolones concurrently with zidovudine, the antibacterial interaction of these drugs was investigated. No evidence was found of antagonism between zidovudine and ciprofloxacin, DR-3355, enoxacin, lomefloxacin or ofloxacin against enterobacteria, staphylococci or Pseudomonas aeruginosa. Furthermore, the bactericidal activity of the fluoroquinolones against selected enterobacteria in nutrient broth was not affected by a clinically achievable concentration of zidovudine. It seems unlikely that zidovudine will have an adverse effect on the antibacterial activity of the fluoroquinolones in patients with AIDS.
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