[Detection of verotoxin-producing Escherichia coli O157 in patients with hemolytic uremic syndrome].
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Bacterial Toxins↗
Biomedical subjects
M Rivas
Publications and source records attributed to M Rivas.
[Proposal for microbiological criteria for the control of cheese spreads].
Eighteen lots of processed cheese and processed cheese spread were analyzed. Results obtained for the yeasts and molds count (RHL) and the total coliforms count (RCT) were 88.9% inferior to 100 per gram, in the 90 subsamples studied. The fecal coliforms count (RCF) and the S. aureus count were, respectively, 96.6% and 94.4% inferior to 10 per gram, for the same subsamples. Taking into account the format presented by the International Commission on Microbiological Specifications for Foods and the results of our survey, a three class plan is proposed for the following microbiological tests: RHL (n = 5, c = 2, m = 100, M = 1000); RCT (n = 5, c = 2, m = 100, M = 1000); RCF (n = 5, c = 2, m = 10, M = 100); and S. aureus count (n = 5, c = 1, m = 100, M = 1000). Therefore, applying these microbiological specifications, 4 lots (22.2%) would be rejected.
Argentina↗
[Microbiological quality of dehydrated and instant products for infants and children ].
A total of 23 lots of dehydrated and instant products for babies and children were analyzed. Neither Salmonella, C. perfringens, B. cereus, St. aureus, Group A beta-hemolytic streptococci, fecal coliforms, E. coli nor aflatoxins could be detected in the 115 samples studied. With the exception of the cereals, results obtained for the Aerobic Plate Count (RAP), the Moulds and Yeast Count (RHL) and the Total Coliforms Count (RCT) were, respectively, 91% equal of lower then 3 per gram, and 92% lower than 100 per gram. The results obtained justify the proposition of consultants of FAO/WHO, to limit determination to RAP, RCT, and investigation of Salmonella. According to specifications of FAO/WHO, 10,5% of the lots examined would be considered non acceptable. With regard to the cereals, the lower sensitivity of the used techniques, due to the physical sample characteristics, makes it advisable to adopt RHL here, too.
Argentina↗
[Enterotoxigenicity and biochemical features of strains of Staphylococcus aureus of different origins ].
A total of 118 Staphylococcus aureus strains isolated from routine sampling, samples from food poisoning outbreaks and human clinical specimens were examined for the production of enterotoxins A, B, C, D and E. The toxic properties of strains were compared with other biochemical characteristics and with the sensitivity to antibiotics. Of the total strains examined, 17.8% (21 strains) produced enterotoxins, and of the toxigenic strains, 81% (17 strains) produced just one type of enterotoxin and 19% (4 strains) two types. Enterotoxin A production was found in 52.4% strains, the other enterotoxins detected in decreasing order of frequency were: C; B; AD; D; AB and BD. All the strains examined produced catalases, coagulases, thermonuclease and fermented glucose; 81 and 89.7% for toxigenic and non-toxigenic strains, respectively, fermented mannitol; 47.6 and 54.6% hydrolyzed casein and 47.6 and 52.6% gelatin; 85.7 and 92.8% produced yellow or orange pigment. Mixed acid fermentation was carried out in 100% and in 96.9%; acetoin was produced by 57.1 and 47.4%; one or more hemolysins were released by 85.7 and 92.8% of the toxigenic and non-toxigenic strains, respectively. Sensitivity to antibiotics was widespread among all the strains. No relation was found between enterotoxin B production and methicillin and tetracycline resistance. Neither the biochemical properties nor the sensitivity to antibiotics has been shown to correlate reliably with toxin production.
Anti-Bacterial Agents↗
[Infection of a cerebrospinal fluid shunt system by Bacillus circulans and Bacillus larvae].
A two episodes case of CSF ventriculo-atrial shunt infection due to B. circulans and B. larvae is presented. B. circulans was first isolated from 4 blood cultures and CSF (shunt valve tap). The patient showed a brain damage syndrome reversible with antibiotic treatment. Lethal toxin production was demonstrated for the B. circulans strain in a mouse model. This strain was found to be a variant of Gordon's description as it produced urease and was tolerant to 7% NaCl. The patient recovered after cefotaxime, cotrimoxazole and rifampicin treatment. A second infection due to B. larvae was detected two months later. The shunt system was removed due to obstruction and a scanning electron microscopy study was performed. Confluent masses of white blood cells and rods were observed on the inner surface of the catheter. As for as we know, this is the first case of human infection due to B. larvae.
Adolescent↗
[Numerical taxonomy of the genus Bacillus].
Eighty-one morphologic and biochemical features of seventy Bacillus strains were studied. Techniques of Numerical Taxonomy were used for this purpose. One method of coding and four others of clustering methods were used. Clustering methods were: weighted an unweighted pair-groups methods using arithmetic averages (WPGMA and UPGMA, respectively) and those of simple and complete linkage. With this methodology four dendrograms were obtained. The highest cophenetic correlation coefficient (0,718) was obtained from UPGMA. With UPGMA a classification in eleven groups and fourteen subgroups was obtained. Group was defined as the cluster of strains linked with similarity coefficients greater than 0.700 and subgroup as the cluster of strains linked with similarity coefficients greater than 0.800. It is important to take into account that in WPGMA dendrogram a very similar distribution was observed. As in classical taxonomy, the characteristic morphologic and physiological variabilities of the genus Bacillus were observed.
Algorithms↗
[Ice cream of industrial manufacture. Incidence of Staphylococcus aureus and enterotoxigenicity].
A total of 70 samples of ice-creams, milk, milk cream and water or fruit based were obtained from 7 different industrial producers. Of these samples, 14.3% were positive for Staphylococcus aureus in 1 g: 97.2% showed less than 10 St. aureus in 1 g, 1.4% between 101-1,000 and 1.4% between 1,001-10,000. In 21 strains enterotoxigenicity, was investigated, as well as the response to different biochemical tests and the susceptibility to antibiotics: 9.5% of the strains were toxigenic (2 strains), 1 produced enterotoxin A and 1 enterotoxin B. There was no difference between toxigenic and nontoxigenic strains when the biochemical tests were performed (catalase test, coagulase test, thermostable nuclease production, anaerobic utilization of glucose and mannitol, gelatin and casein hydrolysis, production of hemolysins and pigments). All the strains showed a wide susceptibility when they were tested with different antibiotics. Our results confirm the limit introduced to the article 1078 of the Argentine Food Code for ice-creams of industrial production (100 per g) but there is no specification of the count method to be used.
Argentina↗
[The determination of glycosylated hemoglobin levels (I): methods].
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Adolescent↗
[Cottage-industry and semi-industrial ice-creams. Incidence of Staphylococcus aureus and enterotoxigenicity].
Sixty seven samples of ice-creams were taken from seven different semi-industrial and small-scale shops. 43.3% of the samples were positive for the investigation of Staphylococcus aureus in 1 g; 88% showed less than 10 St. aureus in 1 g; 10.5% between 10 and 100 and 1.5% between 101 and 1,000. In 29 strains was investigated enterotoxigenicity, as well as the response to different biochemical tests and the susceptibility to antibiotics: 21% of the strains were toxigenic (4 produced enterotoxin A, 1 enterotoxin B and 1 enterotoxins A and D). There was no difference between the toxigenic and non-toxigenic strains when biochemical tests were performed (catalase test, coagulase test, thermostable nuclease production, anaerobic utilization of glucose and mannitol, gelatin and casein hydrolysis, production of hemolysins and pigments). All the strains showed susceptibility to different antibiotics. On the basis of the present study it is proposed to incorporate in article 1075 of the Argentine Food Code the limit of 100 Staphylococcus aureus in 1 g of ice creams.
Enterotoxins↗
[Simplified preliminary identification of some species of Clostridium].
A dichotomous key is proposed for the identification of eight species of Clostridium: Clostridium botulinum, C. butyricum, C. haemolyticum, C. histolyticum, C. paraperfringens, C. perfringens, C. sporogenes y C. subterminale, on the basis of the Gram staining, catalase production, growth on nutrient agar, glucose utilization, motility test, gelatin hydrolysis, lecithinase production, human blood hemolysis and the test of mice toxicity.
Animals↗
Prospective study of enteropathogens in two communities of Misiones, Argentina.
Children under five years of age, from two communities of different socio-economic strata (97 from Zaiman and 55 from Las Dolores) were examined epidemiologically during 2 years, by means of quarterly visits of the working team, who carried out the collection of faecal samples. During the study, one or more enteropathogens were identified in 73.9% of samples in children from Zaiman and in 58.3% of the samples from Las Dolores, being associated to diarrhoea in 70.5% and to asymptomatic infections in 65.7%. The number of diarrheic episodes was higher in Zaiman (15.45%) than in Las Dolores (12.35%), being more frequent in the spring-summer seasons. In Zaiman, the bacterial enteropathogen proportion was relevantly higher (p < 0.005) in children with diarrhoea, whereas the presence of parasites was more frequent in asymptomatic children (p < 0.01). Rotavirus had an even distribution within diarrheic and asymptomatic children. In Las Dolores, no relevant differences were found in the detection of enteroparasites between diarrheic and asymptomatic children. Mixed infections were detected; enterotoxigenic Escherichia coli (ETEC)-rotavirus and ETEC-parasites being the most frequent ones. ETEC was involved in 85% of these infections. These data, together with the high enteropathogen carriage, suggest an elevated level of environmental contamination. The latter plays an important role in diarrheic diseases, and added to the most extreme poverty, it affects children's lives.
Argentina↗
Asymptomatic infections by diarrheagenic Escherichia coli in children from Misiones, Argentina, during the first twenty months of their lives.
Diarrheagenics Escherichia coli are the major agents involved in diarrheal disease in developing countries. The aim of this study was to evaluate the time of appearance of the first asymptomatic infection by the different categories of diarrheagenic E. coli in 44 children since their birth and during the first 20 months of their lives. In all of the children studied, we detected at least one category of diarrheagenic E. coli through the 20 months of the study. 510 diarrheagenic E. coli (33.5%) were obtained from the 1,524 samples collected from the 44 children during the time of the study (31.4% EAggEC, 28.8% EPEC, 27.1% DAEC, and 12.7% ETEC). Neither EHEC nor EIEC were identified. The median age for diarrheagenic E. coli colonization was 7.5 months. The mean weaning period was 12.8 months and the mean age for introduction of mixed feeding (breast fed supplemented) was 3.8 months. A significantly lower incidence of diarrheal disease and asymptomatic infections was recorded among the exclusively breast-fed rather than in the supplemented and non breast-fed infants. For ETEC, EPEC and EAggEC the introduction of weaning foods and complete termination of breast-feeding were associated with an increase of asymptomatic infections.
Argentina↗
[Antimicrobial resistance among species of Salmonella, Shigella, Escherichia, and aeromonas isolated from children with diarrhea in 7 Argentinian centers].
The increasing levels of resistance of enteropathogenic bacteria against antimicrobial agents present geographic variations. We have analysed the antimicrobial susceptibility of isolates obtained from 4,364 children under 5 years of age with acute diarrhea, in 7 cities of Argentina. Diarrheagenic E. coli exhibited 74.5% of resistance against ampicillin, 64.2% against sulfametoxazole-trimethoprim, and Shigella spp., 62% and 75.6% respectively. Salmonella sp. showed 35%, 14%, 41.8%, 65.4%, 14.5%, and 13.6% of resistance against ampicillin, chloranfenicol, sulfametoxazole-trimetoprim, sulfadiazin, gentamycin, and fosfomycin respectively. These values are higher than the ones observed in developed countries. Aeromonas showed significantly lower resistance percentage. Important differences in our country were observed, consequently, local trials should be carried out in order to apply corrective measures.
Acute Disease↗
[Isolation of Escherichia coli O157:H7 in storm drains in the city of Mar del Plata with bacterial contamination of fecal origin].
The present study was focused on the isolation and characterization of Escherichia coli, particularly the serotype O157:H7, from five combined-sewer outflows waters, which drain into the beaches of Mar del Plata. Seventeen hemolytic uremic syndrome cases were reported in Mar del Plata during the sampling period (May 1995-April 1996) in children between 9 month- and 5 year-old, and 3 deaths were recorded. E. coli identification was carried out by biochemical tests. E. coli was detected in 75% of the samples and a total of 98 strains were selected, with 11 sorbol non-fermenting strains. The strains belonged to the O1, O6, O44, O86a, O119 and O168 serogroups. As none of the known virulence factors was detected, strains could not be grouped within any of the diarrheagenic E. coli categories. None of the E. coli strains belonged to the O157:H7 serotype, but E. coli isolation showed fecal contamination in the combined-sewer outflows. Since their waters drain into beaches for recreational use, it is necessary to emphasize the detection of E. coli that would cause severe human illness. Bacterial pollution in combined-sewer outflows draining into Mar del Plata coasts might represent a high risk for human health.
Argentina↗
[Isolation and characterization of Shiga-toxin-producing Escherichia coli from frozen hamburgers and soft cheeses].
Shiga toxin producing-Escherichia coli (STEC), an important emerging foodborne pathogen, has been associated with bloody and non-bloody diarrhea, hemorrhagic colitis, hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura. The cattle have been shown to be a major reservoir of STEC and raw foods such as ground beef and milk are the most common vehicles of infection. In the present study, the prevalence of STEC in 95 samples of frozen hamburgers and in 114 samples of soft cheese was established in 8.4% and 0.9%, respectively. The genotypic and phenotypic characteristics of the strains were determined. The virulence genes stx1, stx2, eaeA and EHEC-hlyA were identified by PCR and by colony blot hybridization assays. Serotyping, antimicrobial susceptibility and production of Stx using specific cytotoxicity assays on Vero cells were also determined. All STEC strains were characterized as eaeA-/EHEC-hlyA+. The stx2 genotype was prevalent (77.8%), and four different O:H serotypes were found, comprising: O8:H19 (5 strains), O113:H21 (1), O8:H16 (1), and O39:H49 (1). One STEC strain was nontypable. Although soft cheese complimented the microbiological quality controls for the coliform counts, the detection of STEC in one sample raises doubts concerning the effectiveness of the current quality controls. These data contribute to the implementation of strategies for the prevention and control of HUS.
Adhesins, Bacterial↗
[Development and application of a method for isolating Escherichia coli O157:H7 in the city of Gualeguaychú].
Culture media, reagents, and commercial kits were compared on artificially contaminated food samples. The objective was to find an isolation method for Escherichia coli O157:H7 sensitive, specific and accessible in terms of cost, requirements of equipments and qualification of the analyst. The adopted scheme consisted in a selective enrichment at 42 degrees C during 18 to 24 h, using an appropriate medium, in accordance with the nature of the sample, followed by a step of immunomagnetic separation and simultaneous isolation on a chromogenic agar and MacConkey sorbitol agar with potassium tellurite and cefixime, during 18-24 h at 37 degrees C. The presumptive colonies were confirmed as E. coli O157 by serological and biochemical tests. Secondly, this methodology was applied to food samples, water, bovine gastric content and manure. A total of 410 samples were studied: 279 from meat, 54 milk and dairy products, 6 from vegetables, 27 water samples and 44 bovine gastric content and manure. The frequency of isolation of E. coli O157:H7 was of 3.9%. The phenotypic and genotypic characterization of the isolates was performed. A simple isolation methodology for E. coli O157 was developed, which proved accessible to food laboratories of lower complexity. This methodology allowed the detection of this pathogen in food and environmental samples in Gualeguaychú City. The role of water as vehicle of infection was also established. The strains harbored the same virulence factors as those recovered from human disease.
Animals↗
[Validation of a multiplex PCR for detection of Shiga toxin-producing Escherichia coli].
Shiga toxin-producing Escherichia coli (STEC) cause non-bloody or bloody diarrhea, hemorrhagic colitis and hemolytic uremic syndrome (HUS) in humans. The aim of the present study was to validate a multiplex PCR for the STEC diagnosis based on the detection of stx1, stx2 and rfbO157 genes. The multiplex PCR validation was carried out in two independent laboratories in a parallel way. Work range, selectivity and robustness were established. The PCR performance was evaluated using different concentrations of two STEC strains harboring different target genes. The work range depended on the strain analyzed, the maximum and the minimum values were 6.6 x 10(7) and 1.0 x 10(4) CFU/50 microl. The detection limit was 1.0 x 10(4) CFU/50 microl and the cut limit 1.0 x 10(5) CFU/50 ml. A good robustness was observed when different variables were introduced. Inclusivity, exclusivity, positive predictivity, negative predictivity and analytical accuracy were of 100%. Interference was not shown when different concentrations of STEC strains, carrying different genes, were used. The validated technique is an appropriate alternative for detection and confirmation of STEC O157 and non-O157 strains from bacterial cultures.
Cell Fractionation↗
[Isolation of Shiga-toxin-producing Escherichia coli strains during a gastrointestinal outbreak at a day care center in Mar del Plata City].
From October 15 to November 8, 2003, a gastrointestinal outbreak occurred at a day care center in a Hospital in Mar del Plata City. Fourteen out of 80 (17.5%) children, mean age 23.6 +/- 13.9 months, and the mother of one of them had diarrhea. One case developed hemolytic uremic syndrome. No conclusive evidence of the origin of the outbreak was found, but the epidemic curve suggested person-to-person spread. The usual practices at the place where infant milk formula was prepared at the day care center, together with the inadequate infrastructure conditions and hygiene practices at the kitchen of the hospital, were considered risk factors. One case had Shiga toxin-producing Escherichia coli (STEC) O103:H2 infection and other STEC O26:H11. The duration of shedding for the child with O26:H11 infection was 37 days. In the other symptomatic children, the pathogen was not recovered from fecal samples collected 6 or more days after the onset of the illness. This emphasizes that the collection of early samples is necessary to recover STEC strains. In order to prevent and control enteric diseases in day care facilities the following measures are necessary: optimal hygiene standards, early case reporting, and exclusion of those who remain culture-positive.
Adult↗