Papers by Alejandro Cravioto
Critical Reviews in Microbiology, 2002
Enteroaggregative Escherichia coli heat-stable enterotoxin 1 (EAST1) is a small protein that was ... more Enteroaggregative Escherichia coli heat-stable enterotoxin 1 (EAST1) is a small protein that was first detected more than a decade ago in an enteroaggregative E. coli (EAEC) strain isolated from the stools of a diarrheic child. The EAST1 gene, astA, is not solely present in EAEC, but also in other categories of diarrheagenic E. coli. Strains expressing EAST1 have been shown to induce diarrhea principally in humans, although they have also been associated with piglets and calves. EAST1 toxin has been proposed as a virulence factor implicated in the mechanism of pathogenesis of EAEC and could play a role in the pathogenicity of other enteropathogens as well. This toxin is often compared to E. coli STa enterotoxin because they share some physical and mechanistic similarities. This review summarizes the various observations on EAST1 since its discovery.
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Boletín médico del Hospital Infantil de México, 1991
The household acceptance of oral rehydration solution salts was studied in a cohort of 75 rural m... more The household acceptance of oral rehydration solution salts was studied in a cohort of 75 rural mothers over a two year period. The study was carried out in a rural Mexican village between August 1985 and February 1988. There were 636 episodes of diarrhea, with an average of four episodes per child per year. There were no deaths due to diarrhea or its complications and only 2% of these episodes required the use of parenteral solutions. Acceptance of oral rehydration remained around 50% during subsequent bouts of diarrhea. Variables such as a medium high socioeconomic level of the family, and the reading of journals and newspapers by the mother and the presence of water supply in the home were significantly associated with the acceptance of oral rehydration treatment. On the other hand, families classified as traditional rejected the procedure with significantly higher frequency. The data presented indicates the need for redesigning oral rehydration, treatment programs to increase th...
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Applied and Environmental Microbiology, 2007
Manure samples were collected from 16 organic (ORG) and 9 low-input conventional (LIC) Dutch dair... more Manure samples were collected from 16 organic (ORG) and 9 low-input conventional (LIC) Dutch dairy farms during August and September 2004 to determine the prevalence of the STEC virulence genes stx 1 (encoding Shiga toxin 1), stx 2 (encoding Shiga toxin 2), and eaeA (encoding intimin), as well as the rfbE gene, which is specific for Escherichia coli O157. The rfbE gene was present at 52% of the farms. The prevalence of rfbE was higher at ORG farms (61%) than at LIC farms (36%), but this was not significant. Relatively more LIC farms were positive for all Shiga toxin-producing E. coli (STEC) virulence genes eaeA , stx 1 , and stx 2 , which form a potentially highly virulent combination. Species richness of Enterobacteriaceae , as determined by DGGE, was significantly lower in manure positive for rfbE . Survival of a green fluorescent protein-expressing E. coli O157:H7 strain was studied in the manure from all farms from which samples were obtained and was modeled by a biphasic declin...
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Vibrio choleraeO1 classical (CL) biotype caused the fifth and sixth pandemics, and probably the e... more Vibrio choleraeO1 classical (CL) biotype caused the fifth and sixth pandemics, and probably the earlier cholera pandemics, be-fore the El Tor (ET) biotype initiated the seventh pandemic in Asia in the 1970s by completely displacing the CL biotype. Al-though the CL biotype was thought to be extinct in Asia and although it had never been reported from Latin America, V. chol-erae CL and ET biotypes, including a hybrid ET, were found associated with areas of cholera endemicity inMexico between 1991 and 1997. In this study, CL biotype strains isolated from areas of cholera endemicity inMexico between 1983 and 1997 were characterized in terms of major phenotypic and genetic traits and compared with CL biotype strains isolated in Bangladesh be-tween 1962 and 1989. According to sero- and biotyping data, all V. cholerae strains tested had the major phenotypic and geno-typic characteristics specific for the CL biotype. Antibiograms revealed the majority of the Bangladeshi strains to be resist...
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Genes & genomics, 2021
BACKGROUND Pseudomonas aeruginosa is an important opportunistic pathogen especially in nosocomial... more BACKGROUND Pseudomonas aeruginosa is an important opportunistic pathogen especially in nosocomial infections due to its easy adaptation to different environments; this characteristic is due to the great genetic diversity that presents its genome. In addition, it is considered a pathogen of critical priority due to the high antimicrobial resistance. OBJECTIVES The aim of this study was to characterize the mobile genetic elements present in the chromosome of six Mexican P. aeruginosa strains isolated from adults with pneumonia and children with bacteremia. METHODS The genomic DNA of six P. aeruginosa strains were isolated and sequenced using PacBio RS-II platform. They were annotated using Prokaryotic Genome Annotation Pipeline and manually curated and analyzed for the presence of mobile genetic elements, antibiotic resistances genes, efflux pumps and virulence factors using several bioinformatics programs and databases. RESULTS The global analysis of the strains chromosomes showed a ...
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New England Journal of Medicine
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Infection and Immunity
An enterotoxigenic strain of Escherichia coli O25:H42 (strain E8775), isolated from a patient in ... more An enterotoxigenic strain of Escherichia coli O25:H42 (strain E8775), isolated from a patient in Bangladesh with diarrhea, caused mannose-resistant hemagglutination (MRHA) of human and bovine erythrocytes. The strain did not show slide agglutination or immunodiffusion precipitin lines with antiserum specific for the colonization factor antigen CFA/I or CFA/II. A variant E. coli strain, E8775-B, did not cause MRHA or produce enterotoxin. Electron microscopy revealed the presence of fimbriae on the surface of strain E8775 but not strain E8775-B. When strain E8775 was grown at 22 degrees C, it became MRHA negative and fimbriae were absent. An antiserum prepared against strain E8775 was absorbed with strain E8775-B to make an antiserum specific for the fimbrial antigen. Using this absorbed antiserum, we found the fimbrial antigen in 48 of 742 enterotoxigenic E. coli strains. The 48 strains belonged to serogroups O25, O115, and O167. It is suggested by analogy to the properties of previo...
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Journal of clinical microbiology
Samples (1,318) of enterotoxigenic Escherichia coli (ETEC) isolated in 1994-1995 from children wi... more Samples (1,318) of enterotoxigenic Escherichia coli (ETEC) isolated in 1994-1995 from children with diarrhea from Nepal, Indonesia, Peru, and Thailand were examined for colonization factor antigen (CFA) and coli surface (CS) antigens. Fifty-five percent of 361 heat-labile and heat-stable (LT-ST), 14% of 620 LT-only, and 48% of 337 ST-only ETEC had CFA/CS antigens. LT-ST ETEC strains were predominantly in the CFA II group, and ST only strains were in the CFA IV group. Additional studies are needed to identify ETEC strains that do not have CFA/CS antigens.
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Journal of clinical microbiology
Sequence variation was studied in several target genes in 54 strains of group A Streptococcus (GA... more Sequence variation was studied in several target genes in 54 strains of group A Streptococcus (GAS) cultured from children with pharyngitis in Mexico City. Although 16 distinct emm alleles were identified, only 4 had not been previously described. Virtually all bacteria (31 of 33 [94%] with the streptococcal pyrogenic exotoxin gene (speA) had emm1-related, emm3, or emm6 alleles. The gene (sic) encoding an extracellular GAS protein that inhibits complement function was unusually variable among isolates with the emm1 family of alleles, with a total of seven variants identified. The data suggest that many GAS strains infecting Mexican children are genetically similar to organisms commonly encountered in the United States and western Europe. Sequence variation in the sic gene is useful for rapid differentiation among GAS isolates with the emm1 family of alleles.
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Infection and Immunity
We examined 205 enterotoxigenic strains of Escherichia coli for colonization factor antigens (CFA... more We examined 205 enterotoxigenic strains of Escherichia coli for colonization factor antigens (CFA) I and II, using an immunodiffusion technique with specific antisera. A total of 36 strains of serogroups O63, O78, O114, O128, and O153 and 1 rough strain possessed CFA/I and gave a single precipitin line; 47 strains of serogroups O6, O8, O80, and O115 possessed CFA/II. The latter strains gave a major precipitin line (component 3) when tested with specific antisera prepared against strain E1392 or PB-176 (both E. coli O6.H16; biotype A). However, all 16 strains of E. coli O6.H16 belonging to biotype A gave a second precipitin line (component 1) when tested with both antisera. When CFA/II-positive strains were tested with a specific antiserum prepared against E. coli O6.H16 strains of biotype B or C, all strains gave component 3, but 16 of 17 strains of E. coli O6.H16 belonging to biotype B, C, or F gave a second precipitin line (component 2) not given by strains of biotype A. CFA/II-po...
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Applied and environmental microbiology
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Infection and Immunity
Enteroaggregative Escherichia coli (EAEC) is an emerging cause of diarrheal illness. Clinical dat... more Enteroaggregative Escherichia coli (EAEC) is an emerging cause of diarrheal illness. Clinical data suggest that diarrhea caused by EAEC is predominantly secretory in nature, but the responsible enterotoxin has not been described. Work from our laboratories has implicated a ca. 108-kDa protein as a heat-labile enterotoxin and cytotoxin, as evidenced by rises in short-circuit current and falls in tissue resistance in rat jejunal tissue mounted in an Ussing chamber. Here we report the genetic cloning, sequencing, and characterization of this high-molecular-weight heat-labile toxin. The toxin (designated the plasmid-encoded toxin [Pet]) is encoded on the 65-MDa adherence-related plasmid of EAEC strain 042. Nucleotide sequence analysis suggests that the toxin is a member of the autotransporter class of proteins, characterized by the presence of a conserved C-terminal domain which forms a β-barrel pore in the bacterial outer membrane and through which the mature protein is transported. Th...
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Journal of Clinical Microbiology
Genomic fingerprints from 92 capsulated and noncapsulated strains of Haemophilus influenzae from ... more Genomic fingerprints from 92 capsulated and noncapsulated strains of Haemophilus influenzae from Mexican children with different diseases and healthy carriers were generated by PCR using the enterobacterial repetitive intergenic consensus (ERIC) sequences. A cluster analysis by the unweighted pair-group method with arithmetic averages based on the overall similarity as estimated from the characteristics of the genomic fingerprints, was conducted to group the strains. A total of 69 fingerprint patterns were detected in theH. influenzae strains. Isolates from patients with different diseases were represented by a variety of patterns, which clustered into two major groups. Of the 37 strains isolated from cases of meningitis, 24 shared patterns and were clustered into five groups within a similarity level of 1.0. One fragment of 1.25 kb was common to all meningitis strains. H. influenzae strains from healthy carriers presented fingerprint patterns different from those found in strains f...
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Infection and Immunity
The pathogenic mechanisms of enteroaggregative Escherichia coli (EAggEC) infection are not fully ... more The pathogenic mechanisms of enteroaggregative Escherichia coli (EAggEC) infection are not fully elucidated. In this work we show that an ammonium sulfate precipitate of culture supernatant of EAggEC strain 049766 increased the potential difference (PD) and the short-circuit current (Isc) in rat jejunal preparations mounted in Ussing chambers. The precipitate contained two major proteins of 108 and 116 kDa, which were partially copurified by chromatography in DEAE-cellulose. This chromatographic fraction (peak I) increased jejunal PD and Isc in a dose-dependent manner, accompanied by a decrease in tissue electrical resistance. These effects were inhibited by incubation of peak I at 75°C for 15 min or for 1 h with proteinase K at 37°C. Rabbit polyclonal antibodies against peak I containing both the 108- and 116-kDa proteins inhibited the enterotoxic effect. Specific polyclonal antibodies raised against the 108-kDa but not against the 116-kDa protein inhibited the enterotoxic effect, ...
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Journal of Clinical Microbiology
Helicobacter pylori virulence determinants have not previously been studied in detail in Latin Am... more Helicobacter pylori virulence determinants have not previously been studied in detail in Latin Americans with H. pylori infections. We characterized the vacA(vacuolating cytotoxin gene A) and cagA(cytotoxin-associated gene A) types of more than 400 single-colony isolates from 20 patients in Mexico City. For 17 patients H. pylori strains of two or more different vacAgenotypes were isolated from gastric biopsy specimens, indicating infection with two or more strains of H. pylori. The most frequent vacA genotype was s1b/m1. vacAdiversity was more marked than that described previously, in that isolates from seven patients had untypeable vacA midregions and isolates from nine patients had type s1 signal sequence coding regions which could not be further subtyped. Previously undescribedvacA type s2/m1 strains were found in five patients. All patients were infected with cagA-positive strains, but occasionally, these coexisted with small numbers ofcagA-negative strains. In conclusion, coinf...
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The American Journal of Tropical Medicine and Hygiene
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The American Journal of Tropical Medicine and Hygiene
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Frontiers in microbiology, 2018
Intestinal infections represent an important public health concern worldwide. is one of the main ... more Intestinal infections represent an important public health concern worldwide. is one of the main bacterial agents involved in the pathogenesis of different diseases. In 2011, an outbreak of hemorrhagic colitis (HC) and hemolytic uremic syndrome (HUS) in Germany was related to a non-O157 STEC strain of O104:H4 serotype. The difficulty in identifying the origin of the bacteria related to the outbreak showed the importance of having epidemiological information from different parts of the world. The aim of this study was to perform a retrospective analysis to determine if strains isolated from cattle from different locations in Mexico have similar characteristics to those isolated in other countries. Samples obtained in different years from 252 cows belonging to 5 herds were analyzed. A total of 1,260 colonies were selected from the 252 samples, 841 (67%) of which corresponded to and 419 (33%) to other enterobacteria. In total, 78% (656) of the strains could be serotyped, of which 393 (...
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Papers by Alejandro Cravioto