Patricio Valenzuela

Genes Related to Long Polar Fimbriae of Pathogenic Escherichia coli Strains as Reliable Markers To Identify Virulent Isolates

ABSTRACT Lpf (stands for long polar fimbriae) is one of the few adhesive factors of enterohemorrhagic Escherichia coli O157:H7 associated with colonization of the intestine. E. coli O157:H7 strains possess two lpf loci encoding highly regulated fimbrial structures. Database analysis of the genes encoding the major fimbrial subunits demonstrated that they are present in commensal as well as pathogenic (both intestinal and extraintestinal) E. coli strains and in Salmonella strains and that the lpfA1 and lpfA2 genes are highly prevalent among LEE (locus of enterocyte effacement)-positive E. coli strains associated with severe and/or epidemic disease. Further DNA sequence analysis of the lpfA1 and lpfA2 genes from different attaching-and-effacing E. coli strains has led us to the identification of several polymorphisms and the classification of the major fimbrial subunits into distinct variants. Using collections of pathogenic E. coli isolates from Europe and Latin America, we demonstrated that the different lpfA types are associated with the presence of specific intimin (eae) adhesin variants and, most importantly, that they are found in specific E. coli pathotypes. Our results showed that the use of these fimbrial genes as markers, in combination with the different intimin types, resulted in a specific test for the identification of E. coli O157:H7, distinguishing it from other pathogenic E. coli strains.

Distribution of Classical and Nonclassical Virulence Genes in Enterotoxigenic Escherichia coli Isolates from Chilean Children and tRNA Gene Screening for Putative Insertion Sites for Genomic Islands

ABSTRACT Enterotoxigenic Escherichia coli (ETEC) is an important cause of diarrhea. Three adhesins (Tia, TibA, EtpA), an iron acquisition system (Irp1, Irp2, and FyuA), a GTPase (LeoA), and an autotransporter (EatA) are ETEC virulence-related proteins that, in contrast to the classical virulence factors (enterotoxins and fimbrial colonization factors) have not heretofore been targets in characterizing isolates from epidemiological studies. Here, we determined the occurrence of these nonclassical virulence genes in 103 ETEC isolates from Chilean children with diarrhea and described their association with O serogroups and classical virulence determinants. Because tia, leoA, irp2, and fyuA are harbored by pathogenicity islands inserted into the selC and asnT tRNA genes (tDNAs), we analyzed the regions flanking these loci. Ten additional tDNAs were also screened to identify hot spots for genetic insertions. Associations between the most frequent serogroups and classical colonization factor (CF)-toxin profiles included O6/LT-STh/CS1-CS3-CS21 (i.e., O6 serogroup, heat-labile [LT] and human heat-stable [STh] enterotoxins, and CFs CS1, -3 and -21), O6/LT-STh/CS2-CS3-CS21, and O104-O127/STh/CFAI-CS21. The eatA and etpA genes were detected in more than 70% of the collection, including diverse serogroups and virulence profiles. Sixteen percent of the ETEC strains were negative for classical and nonclassical adhesins, suggesting the presence of unknown determinants of adhesion. The leuX, thrW, and asnT tDNAs were disrupted in more than 65% of strains, suggesting they are hot spots for the insertion of mobile elements. Sequences similar to integrase genes were identified next to the thrW, asnT, pheV, and selC tDNAs. We propose that the eatA and etpA genes should be included in characterizations of ETEC isolates in future epidemiological studies to determine their prevalence in other geographical regions. Sequencing of tDNA-associated genetic insertions might identify new ETEC virulence determinants.

Debt Sustainability Under Catastrophic Risk: The Case for Government Budget Insurance

Natural disasters are an important source of vulnerability in the Caribbean region. Despite being one of the more disaster-prone areas of the world, it has the lowest levels of insurance coverage. This paper examines the vulnerability of Belize’s public finance to the occurrence of hurricanes and the potential impact of insurance instruments in reducing that vulnerability. The paper finds that catastrophic risk insurance significantly improves Belize’s debt sustainability. In addition, the methodology employed makes it possible to estimate the appropriate level of insurance, which for the case of Belize is a maximum coverage of US

Resolving the African Financial Development Gap: Cross-Country Comparisons and a Within-Country Study of Kenya

120 million per year. International organizations can play a role in assisting countries to overcome distortions in insurance markets, as well as in helping to relax internal political resistance to the purchase of insurance policies.

Identification of Coli Surface Antigen 23, a Novel Adhesin of Enterotoxigenic Escherichia coli

With extensive country and firm-level data sets, this paper first documents that the financial sectors of most Sub-Saharan African countries remain significantly underdeveloped by the standards of other developing countries. The paper also finds that population density appears to be considerably more important for banking sector development in Africa than elsewhere. To better understand how countries can overcome the high costs of developing viable banking sectors outside large metropolitan areas, the analysis focuses on Kenya, which has made significant strides in financial inclusion and development in recent years. The paper finds a positive and significant impact of Equity Bank, a leading private commercial bank, on financial access, especially for underprivileged households. Equity Banks business model -- providing financial services to population segments typically ignored by traditional commercial banks and generating sustainable profits in the process -- can be a potential solution to the financial access problem that has hindered the development of inclusive financial sectors in many other African countries.

A tRNAGlu that uncouples protein and tetrapyrrole biosynthesis

ABSTRACT Enterotoxigenic Escherichia coli (ETEC) is an important cause of diarrhea, mainly in developing countries. Although there are 25 different ETEC adhesins described in strains affecting humans, between 15% and 50% of the clinical isolates from different geographical regions are negative for these adhesins, suggesting that additional unidentified adhesion determinants might be present. Here, we report the discovery of Coli Surface Antigen 23 (CS23), a novel adhesin expressed by an ETEC serogroup O4 strain (ETEC 1766a), which was negative for the previously known ETEC adhesins, albeit it has the ability to adhere to Caco-2 cells. CS23 is encoded by an 8.8-kb locus which contains 9 open reading frames (ORFs), 7 of them sharing significant identity with genes required for assembly of K88-related fimbriae. This gene locus, named aal (adhesion-associated locus), is required for the adhesion ability of ETEC 1766a and was able to confer this adhesive phenotype to a nonadherent E. coli HB101 strain. The CS23 major structural subunit, AalE, shares limited identity with known pilin proteins, and it is more closely related to the CS13 pilin protein CshE, carried by human ETEC strains. Our data indicate that CS23 is a new member of the diverse adhesin repertoire used by ETEC strains.

Financial Intermediation, Markets, and Alternative Financial Sectors

Glu‐tRNA is either bound to elongation factor Tu to enter protein synthesis or is reduced by glutamyl‐tRNA reductase (GluTR) in the first step of tetrapyrrole biosynthesis in most bacteria, archaea and in chloroplasts. Acidithiobacillus ferrooxidans, a bacterium that synthesizes a vast amount of heme, contains three genes encoding tRNAGlu. All tRNAGlu species are substrates in vitro of GluRS1 from A. ferrooxidans. Glu ‐ tRNA 3 Glu , that fulfills the requirements for protein synthesis, is not substrate of GluTR. Therefore, aminoacylation of tRNA 3 Glu might contribute to ensure protein synthesis upon high heme demand by an uncoupling of protein and heme biosynthesis.

Characterization of the most prevalent colonization factor antigens present in Chilean clinical enterotoxigenic Escherichia coli strains using a new multiplex polymerase chain reaction.

We provide a comprehensive review of firms’ financing channels (internal and external, domestic and international) around the globe, with the focus on alternative finance—financing from all the nonmarket, non-bank external sources. We argue that while traditional financing channels, including financial markets and banks, provide significant sources of funds for firms in developed countries, alternative financing channels provide an equally important source of funds in both developed and developing countries. Alternative finance is often the dominant source of funds for firms in fastgrowing economies. We compare market- and bank-finance with alternative finance, along with the supporting mechanisms such as legal and institutional structures. Much more research is needed to better understand alternative finance and its role in corporate financing. We suggest ways to obtain firm-level data on various forms of alternative finance and thus overcome the main obstacle in the field.

Characterization of Genomic Island 3 and Genetic Variability of Chilean Field Strains of Brucella abortus

Current methods to detect the colonization factor antigens (CFAs) associated with enterotoxigenic Escherichia coli (ETEC) strains are cumbersome, with some methods requiring antibodies that are not readily available. To achieve a gene-based method, we designed 2 multiplex polymerase chain reaction reactions to detect genes encoding the most common ETEC fimbrial colonization factors, including CFA/I and coli surface (CS) antigens CS1, CS2, CS3, CS4, CS5, and CS6. Analysis of 183 clinical ETEC strains shows that the most prevalent colonization factors were CFA/I only, CS1 and CS3, CS2 and CS3, and CS6 only. Interestingly, we identified 3 clinical isolates expressing CS1 only without its regulator rns. The method described here proved to be rapid and robust and correlates well with phenotypic expression of the CFAs, becoming a novel molecular diagnostic and research tool for future epidemiologic studies.

Gone with the wind: Demographic transitions and domestic saving

ABSTRACT One of the capabilities developed by bacteria is the ability to gain large fragments of DNA from other bacteria or to lose portions of their own genomes. Among these exchangeable fragments are the genomic islands (GIs). Nine GIs have been identified in Brucella, and genomic island 3 (GI-3) is shared by two pathogenic species, B. melitensis and B. abortus. GI-3 encodes mostly unknown proteins. One of the aims of this study was to perform pulsed-field gel electrophoresis (PFGE) on field isolates of B. abortus from Chile to determine whether these isolates are clonally related. Furthermore, we focused on the characterization of GI-3, studying its organization and the genetic conservation of the GI-3 sequence using techniques such as tiling-path PCR (TP-PCR) and restriction fragment length polymorphism-PCR (RFLP-PCR). Our results, after PFGE was performed on 69 field isolates of B. abortus from Chile, showed that the strains were genetically homogeneous. To increase the power of genetic discrimination among these strains, we used multiple locus variable-number tandem-repeat (VNTR) analysis with 16 loci (MLVA-16). The results obtained by MLVA-16 showed that the strains of B. abortus were genetically heterogeneous and that most of them clustered according to their geographic origin. Of the genetic loci studied, panel 2B was the one describing the highest diversity in the analysis, as well as locus Bruce19 in panel 2A. In relation to the study of GI-3, our experimental analysis by TP-PCR identified and confirmed that GI-3 is present in all wild strains of B. abortus, demonstrating the high stability of gene cluster GI-3 in Chilean field strains.