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M Rivas

Publications and source records attributed to M Rivas.

63 records · Page 4Linked to original sources

[Identification, biotypification and characterization of Pasteurella multocida strains isolated in Argentina].

Thirty Pasteurella multocida strains isolated in Argentina from human and animal samples were identified, biotypified and characterized. Twenty-two (73%) strains were identified as P. multocida subsp. multocida, 5 (17%) as P. multocida subsp. gallicida, and 3 (10%) as P. multocida subsp. septica. All strains were grouped in 8 biotypes, and 70% of the strains presented capsular type A. The most frequent somatic serotypes were 1 (n:11) and 3 (n:9). P. multocida strains from swine source were resistant to tiamulin, streptomycin and tetracycline. Characterization of P. multocida strains isolated in Argentina is the first step to conduct future studies intended for the prevention and treatment of pasteurellosis in human and veterinary medicine.

Animals↗

An evaluation of the pooling culture method for the detection of Escherichia coli enterotoxins.

The efficiency of the pooling method for the detection of enterotoxigenic Escherichia coli (ETEC) strains associated with children acute diarrhea, was evaluated. This study involved the analysis of 6989 E. coli strains corresponding to 1485 cases, coming from 7 hospitals at different geographic locations. Three to five strains from each case were inoculated in pool in Casamino-acids-yeast extract-salts medium plus lincomycin (30 micrograms/ml) and incubated at 37 degrees C during 18 hours with shaking. Polymyxin sulphate B (2200 U/ml) was added to the cultures, and incubation with shaking continued for additional 30 minutes. The culture was then centrifuged and the supernatant tested by a) the enzyme-linked immunosorbent assay to detect heat-labile enterotoxin (LT) and b) the suckling mouse assay for the detection of heat-stable enterotoxin (ST). Strains from a pool were individually studied in all positive cases as shown by the pooling methodology. Also, in 1 out of every 15 negative cases by the pool method, their component strains were individually analyzed, to confirm that there were no false negatives. Fifty seven LT-ETEC, 61 ST-ETEC and 15 LT-ST cases were detected. From the 89 negatives selected by the pool method, 2 cases were positive when the component strains were individually tested (p1 = 2.25%, 95% confidence interval from 0.27 to 7.88%). In both cases one of the non ETEC strains inhibited the ETEC strain. In other 5 negative cases (p2 = 5.62%, 95% confidence interval from 1.85% to 12.63%), ETEC strains were detected when analyzed individually, and gave a positive result when the pooling method was repeated.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteriological Techniques↗

[Production of thermolabile exotoxin by strains of Escherichia coli isolated in Argentina].

The production of heat-labile enterotoxin (LT) by E. coli strains was studied. Four strains isolated from acute infant diarrhea cases in Argentina and one reference strain, all of them producers of different levels of LT, were employed. GM1-ELISA was used as titration method. The production was assayed in two culture media; Evans (Ev) and Trypticase Soy Broth (CTS) with or without glucose and with different concentrations of lincomycin (0; 30; 45 y 90/micrograms/ml). The effects of pH and inoculum concentration were also examined. Higher levels of LT were found to be produced in Ev (mean production value X = 233.1 ng/ml) than in CTS (X = 133.8 ng/ml), although the difference was statistically not significant (P = 0.22). Lincomycin addition stimulated toxin synthesis and release in both media, and these effects were found to increase with the concentration of the antibiotic (P less than 0.01). Glucose increased the LT levels of low-producing strains and also the growth rate, cellular yield and LT levels of 40T and CC2e strains. Levels of LT released were found to be independent of inoculum concentration. In CTS without pH control, the LT production was one half the levels attained with regulated pH. This was not an effect on the release of the toxin as the determination included both the extracellular LT and the intracellular toxin accumulated in the periplasmic space, which is released by polymyxin B treatment. A pH-dependent inactivation of the synthetized and release toxin was demonstrated.

Argentina↗

[Numerical taxonomy of gram-positive anaerobic bacilli].

Numerical Taxonomy's techniques were employed on twenty one anaerobic Gram positive bacilli strains taking account of eighty morphologic and biochemical features. Two methods of coding (weighted and non weighted) and four clustering methods (unweighted pair-group method using arithmetic averages; weighted pair-group method using arithmetic averages; single linkage and complete linkage) were used. Eight dendrograms were obtained and they showed that C. haemolyticum (strains 1, 2, 4, 7); C. subterminale (strains 8, 19); C. botulinum (strain 14) and C. sporogenes (strain 15) belong to a different group than the other strains. Another group would be formed with C. perfringens (strains 3, 5, 6, 12, 16, 21) and C. paraperfringens (strains 9, 10, 11). Of the remaining strains the two classified as Propionibacterium acnes (strains 17, 18) have a very high degree of agreement. C. histolyticum (strain 20) adjoins at a very low level, while C. butyricum (strain 13) shows a unfixed behaviour. The dendrograms display a disposition according with Classical Taxonomy.

Bacteriological Techniques↗

[Cases of gastroenteritis associated to Vibrio cholerae no 01 in Oran, Salta].

Forty-one sporadic cases of non-O group 1 Vibrio cholerae gastroenteritis were detected in Orán, Salta, between February 1992 and February 1995. The frequency of isolation was 0.9% of the diarrhea cases. Out of 41 patients, 21 (51.2%) were older than 15 years and 25 (60.9%) were male. All the patients had diarrhea, 24 (58.5%) had watery stools and 6 (14.6%) cholera-like diarrhea; 10 (24.4%) presented vomiting and 12 (29%) mild dehydration. Six malnourished children who suffered from diarrhea with moderate dehydration for more than a week, were hospitalized. V. cholerae non O1 and Shigella flexneri were isolated from one patient, during the first outbreak and V. cholerae non O1 and Salmonella IV 50:b:- were recovered simultaneously from another patient during the fourth outbreak. A 72 year old woman died during the second cholera outbreak. The symptoms were: watery diarrhea, vomiting, fever and mild dehydration. A strain of V. cholerae O5, that did not produce cholera toxin, heat-stable enterotoxin, Kanagawa-like hemolysin or verocitotoxin was detected. It was positive for El Tor hemolysin and D-mannose and L-fucose resistant cells-associated hemagglutinins. Among the 41 isolates studied, all were oxidase and indole positive, fermented glucose, saccharose and mannitol. They were all motile, produced lysine and ornithine decarboxylases but not arginine dihydrolase or hydrogen sulfide. They were sensitive to O129 vibriostatic compound. None of them belonged to O1 or O139 serogroup and they did not produce cholera troxin. Among the V. cholerae non O1 strains isolated, 9.5% were resistant to ampicillin and 4.9% to trimethoprim-sulfamethoxazole. Active surveillance had shown that V. cholerae non-O1 is not an important agent of diarrhea in Orán, Salta.

Adolescent↗

Differential kinetic patterns for Shiga toxin production by Escherichia coli.

We studied the differential kinetic patterns for Shiga toxin (Stx) production (i.e. Stx1, Stx2 and Stx2c) in different reference Escherichia coli strains and in those isolated from hemolytic uremic syndrome (HUS) patients. These results were correlated with those obtained by specific cytotoxic activity assays on Vero cells and hybridization tests with DNA probes for Stx1 and Stx2. Strains cultured in Penassay broth were sampled at 1.5; 3; 5; 9 and 24 hours to determine bacterial growth and its association with cell-bound and free cytotoxicity. Stx1 showed an intracellular/extracellular concentration ratio (ic/ec) between 32 and 200 times after 3 h-growth. At 24 h both Stx1 concentrations were equal or, in some strains, the ec resulted 2-fold higher that the ic. The ic-Stx1 was equal or just 2-fold higher that ec after 3 h-growth. However, at 24 h the released toxin level was 16 to 32 times higher that cell-bound toxin. The ec-Stx2c increased logarithmically, with maximal yields at 5 h, remaining constant up to 24 h. At that time ic-toxin was 2-fold higher than the released one. When the same experiments were performed on strains isolated from HUS patients they showed that the kinetic patterns obtained corresponded to Stx2. These results were confirmed by hybridization assays. In this study we have shown that Stx1 production decreases dramatically during stationary phase while Stx2 is detected at high level at that time. This could explain the higher frequency of association of Stx2-producing E. coli strains and HUS in some countries, including Argentina.

Animals↗