Revista latinoamericana de microbiologia最新文献

Aflatoxins are potent mutagenic and carcinogenic compounds produced by some strains of Aspergillus flavus, A. nomius, and A. parasiticus that are commonly present in the environment. Human populations, particularly those whose basic diet includes grains, are in risk to exposure to aflatoxins. It is thus necessary to monitor and control the contamination of food and feed by aflatoxins in both domestic and international trade. As large amounts of corn are imported into Mexico from the United States, this paper stresses the need to develop legislation and enforce standards to ensure trade of corn with the minimal amount of aflatoxin.

Most molecular protocols for Dengue virus detection described so far are time consuming and cumbersome with mosquito samples. In order to count with a sensitive and specific molecular detection system for monitoring possible Dengue outbreaks and circulating viral serotypes in field-caught Aedes aegypti populations from Northeastern Argentina, a RT-PCR and RFLP assay was developed. The original RT-PCR assay proposed by Sudiro et al. for human serum was optimized for mosquito samples. Modifications were done at the RNA extraction-purification and at the thermal profile steps. The generic 230 bp amplicon was validated by RFLP assay and cycle sequencing. Results showed that, due to the generic characteristic of the primers used, certain mosquito genome regions could be co-amplified, making confirmation of the Dengue specific amplicon by RFLP assay a required step. Under these conditions, the proposed method can be employed as a Dengue viral generic screening procedure in Aedes aegypti mosquito samples, giving in our hands an estimated 99.52% of confirmed negatives (207/208 tested samples).

Nitrogen fixation an ancient process that may is have originated in the archaean Eon under the primitive atmosphere anoxygenic conditions. Diazotrophy is an exclusive process of prokaryotes, only Euryarchaeota and 6 of 54 Bacteria phyla have diazotrophs lineages. Some of them coevolved with flowering plants for the establishment of molecular bases of a mutualistic symbiosis relationship. In rhizobia, the nitrogen fixation occurs inside the nodules, special structures on the roots or stems of legumes. Nodule organogenesis starts with the bacterial nodulation factors (Nod factors) codified in large plasmids or symbiotic islands in the bacterial genomes. Nodulation genes had more recent origin than the nitrogen fixation ones because the origin of the nod gene is associated with the origin of the hosts. The 16S rRNA phylogeny groups rhizobia in 7 genuses of the alpha-Proteobacteria: Bradyrhizobium, Mesorhizobium, Rhizobium, Sinorhizobium, Methylobacterium and Devosia, and two genuses recently described in f-Proteobacteria: Burkholderia and Wautersia. The phylogenies obtained with other chromosomal genes are similar at the genus level, but it is incongruent with the symbiotic gene (nif & nod) phylogeny, because horizontal gene transfer has allowed their evolution in function to the legume host fitness.

Salmonella is a Gram negative bacillus that behaves like a facultative intracellular pathogen. Its environment is the human and animal gastrointestinal tracts, it is never found like a normal microbiota. It is associated with gastrointestinal problems, septicaemic disease and abortion, due to its cellular invasion capacity and its intraphagocytic survival. Nowadays, it is known that Salmonella contains five pathogenicity islands. Several genes involved in the cellular invasion of nonphagocytic cells such as epithelial cells, apoptosis of macrophages, activation of routes of MAP kinases and transcription factors are located in centisome 63, constituting the pathogenicity island 1 (SPI-1). The SPI-2 and SPI-3 islands control the intracellular survival and replication. The SPI-4 island encodes a putative type I secretion system and its believed that it participates in the intracellular survival. Finally, the SPI-5 island encodes for factors involved in the fluid secretion and inflammatory reaction in the intestinal mucosa. Due to a coordinated and precise regulation of the Salmonella genes, it allows for adaptation to environmental changes that occur during an inflammatory process.

A prospective study of the clinical and epidemiological aspects of Candida spp. sepsis was performed to assess the frequency, etiology, and risk factors in the neonatology service of the Pediatrics Hospital "Dr. Elías Toro" (2002-2003). Forty four out of 128 neonatal intensive care patients, with clinical sepsis and suspected fungal etiology, were chosen randomly for this study. Infant blood, urine, gastrointestinal tract, oral and skin samples were cultured. Samples were also taken from health care worker hands and the environment. The antifungal susceptibility patterns of the isolates were evaluated. The prevalence of Candida spp. from the clinical samples was: C. albicans (72.06%), C. parapsilosis (13.24%), C. tropicalis (10.29 %), C. guilliermondii (2.94%), and C. glabrata (1.47%). Due to the similarity of the susceptibility pattern of some isolates from infants and health care workers, we speculate a horizontal nosocomial infection. Statistical analysis revealed the following significant risk factors associated with Candida spp. isolation: prolonged hospitalization (p < 0.05), missing prenatal birth control (p < 0.05), and parenteral nutrition (p < 0.05). Blood cultures were all negative for bacteria and only 2.90% were positive for Candida spp. All 44 neonates receiving empirical therapy with amphotericin B (0.5-1.0 mg/k/day) evolved satisfactorily.

Background: Group B Streptococcus (GBS) remains as a leading cause of neonatal sepsis and meningitis in developed countries, where type III is the most common serotype. Although GBS is considered an uncommon cause of perinatal pathology in Mexico, a vaginal colonization rate of 14% in pregnant women and a neonatal infection rate of 1/1500 live births have been reported. The aim of this study was to determine the serotype distribution in a collection of 286 GBS strains isolated in Mexico from asymptomatic carriers and in adult and neonatal invasive disease cases.

Methods: The collection included GBS strains isolated between January 1988 and April 1998 at the Instituto Nacional de Perinatologia and Hospital de Pediatria in Mexico City. GBS and serotype were confirmed by latex agglutination.

Results: Most strains were isolated from asymptomatic carriers (66%). 30% were invasive isolates, and 10% of them were from neonates. 48.6% were type I, 32.9% type III, 14% type II, and 4% were non-typeable.

Conclusion: Serotype I is predominant in Mexico but participation of serotype III is increasing, and a decrease of non-typeable isolates was detected.

A dinoflagellate bloom ("red tide" event) dominated by the toxic Gymnodinium catenatum Graham (Gymnodiniales, Dinophyceae; 99.7%) and the noxious Noctiluca scintillans (Mcartney) Kofoid (Noctilucaceae, Dinophyceae; 0.3%) was observed in Bahia de Mazatlán Bay, México, on 24-26 January 2000. Photographic and microscopic analysis of samples during such an event, allowed us to collect evidence of a marked The particularity of grazing of G. catrenatum by by N. scintillans cells, suggesting a mechanism of "biocontrol" between these species that may contribute to attenuate a potentially toxic phenomenon under natural conditions.

The use of the DIRAMIC system for the detection of urinary tract infections (UTI) and the possibility to identify Escherichia coli in the same culture media was evaluated. The results from DIRAMIC detection system were compared to counts of colony forming units per milliliter (CFU/ml) of urine inoculated in CLED Medium; 884 urine specimens were processed taking > or =10(4) CFU/ml as criteria of positive urine culture counts. For E. coli identification, substrates for the determination of beta-glucuronidase and tryptophanase were incorporated to the culture medium and named DETID-Ec. Outputs were compared to those from API RAPIDEC-ur strips. The DIRAMIC system can detect UTI, with a sensitivity and specificity of 82.25 and 94.49%, respectively. It was possible to identify E. coli during detection with 87.50% of sensitivity and 95.96% of specificity. The small volumes of culture medium used in the DIRAMIC system as well as the short times for the detection make the system a rapid and economical method for screening UTI. Furthermore, by using DETID-Ec culture medium the time and the number of biochemical tests necessary for the E. coli identification are lowered.

Laguna de Pozuelos is an extensive wetland in Morthwestern Argentina at 3,600 m above sea level in the Argentinean Andes. The principal lake, placed in the central depression of endorheic basin, is rich in minerals like Cu, As, Fe, etc. It collects water from underground courses and from two main tributaries, namely Santa Catalina River to the north and Cincel River to the south. Following the dry and rainy seasons, the surface of the lake is subject to an annual contraction-expansion cycle, with increasing of salinity during evaporation period. Prokaryotes inhabitants these particular environments have been not described and a few of such places have been surveyed for microbial diversity studies. To systematically explore the underlying communities of Bacteria from the water lake of Laguna de Pozuelos wetland and Cincel River, bacterial 16S rRNA genes (rDNAs) were PCR amplified and analyzed by terminal restriction fragment length polymorphism (T-RFLP) analysis. Analysis of the microbial community with T-RFLP identified a minimum of 19 operational taxonomic units (OTU). T-RF patterns derived from multiple-enzyme digestion with RsaI, HaeIII and HhaI were analyzed in order to provide a preliminary picture of the relative diversity of this complex microbial community. By the combined use of the three restriction endonucleases bacterial populations of this particular place were identified.

Microwave irradiation (MWI) has been applied to the development of rapid methods to process biological samples for scanning electron microscopy (SEM). In this paper we propose two simple and quick techniques for processing bacteria (Proteus mirabilis and Vibrio mimicus) for SEM using MWI. In the simplest methodology, the bacteria were placed on a cover-glass, air-dried, and submitted to conductivity stain. The reagent used for the conductivity stain was the mordant of a light microscopy staining method (10 ml of 5% carbolic acid solution, 2 g of tannic acid, and 10 ml of saturated aluminum sulfate 12-H2O). In the second method the samples were double fixed (glutaraldehyde and then osmium), submitted to conductivity stain, dehydrated through a series of ethanol solutions of increasing concentration, treated with hexamethyldisilazine (HMDS), and dried at 35 degrees C for 5 minutes. In both methods the steps from fixation to treatment with HMDS were done under MWI for 2 minutes in an ice-water bath, in order to dissipate the heat generated by the MWI. Although both techniques preserve bacterial morphology adequately, the latter, technique showed the best preservation, including the appearance of flagella, and that process was completed in less than 2 hours at temperatures of MWI between 4 to 5 degrees C.