Showing papers in "International Microbiology in 1998"

Human enteric viruses in the water environment: a minireview.

Abstract: Summary Water virology started around half a century ago, with scientists attempting to detect poliovirus in water samples. Since that time, other enteric viruses responsible for gastroenteritis and hepatitis, among a great variety of virus strains, have replaced enteroviruses as the main target for detection in the water environment. Technical molecular developments, polymerase-chain reaction (PCR) amplification being the method of choice, enable the detection of fastidious health-significant viruses. However, shortcomings of molecular procedures include their potential incompatibility with concentration methods, indispensable to reduce the water sample volume to assay for viruses, and the inability to discern between infectious and non infectious material. On the other hand, these procedures are restrained to sophisticated laboratories and detection of alternative indicator organisms has been proposed. Bacterial indicators fail to give a reliable clue of the virological quality of water. Selected bacteriophage groups appear as a better choice for their use as virus indicators.

Bacterial evolution and the cost of antibiotic resistance

Abstract: Bacteria clearly benefit from the possession of an antibiotic resistance gene when the corresponding antibiotic is present. But do resistant bacteria suffer a cost of resistance (i.e., a reduction in fitness) when the antibiotic is absent? If so, then one strategy to control the spread of resistance would be to suspend the use of a particular antibiotic until resistant genotypes declined to low frequency. Numerous studies have indeed shown that resistant genotypes are less fit than their sensitive counterparts in the absence of antibiotic, indicating a cost of resistance. But there is an important caveat: these studies have put resistance genes into naive bacteria, which have no evolutionary history of association with the resistance genes. An important question, therefore, is whether bacteria can overcome the cost of resistance by evolving adaptations that counteract the harmful side-effects of resistance genes. In fact, several experiments (in vitro and in vivo) show that the cost of antibiotic resistance can be substantially diminished, even eliminated, by evolutionary changes in bacteria over rather short periods of time. As a consequence, it becomes increasingly difficult to eliminate resistant genotypes simply by suspending the use of antibiotics.

Candida albicans: genetics, dimorphism and pathogenicity.

Abstract: Candida albicans is a dimorphic fungus that causes severe opportunistic infections in humans. Recent advances in molecular biology techniques applied to this organism (transformation systems, gene disruption strategies, new reporter systems, regulatable promoters) allow a better knowledge of both the molecular basis of dimorphism and the role of specific genes in Candida morphogenesis. These same molecular approaches together with the development of appropriate experimental animal models to analyze the virulence of particular mutants, may help to understand the molecular basis of Candida virulence.

Induction of microbial secondary metabolism.

Abstract: Precursors often stimulate production of secondary metabolites either by increasing the amount of a limiting precursor, by inducing a biosynthetic enzyme (synthase) or both. These are usually amino acids but other small molecules also function as inducers. The most well-known are the auto-inducers which include gamma-butyrolactones (butanolides) of the actinomycetes, N-acylhomoserine lactones of Gram-negative bacteria, oligopeptides of Gram-positive bacteria, and B-factor (3'-[1-butylphosphoryl] adenosine) of Amycolatopsis mediterranei. The actinomycete butanolides exert their effects via receptor proteins which normally repress chemical and morphological differentiation (secondary metabolism and differentiation into aerial mycelia and spores respectively) but, when complexed with the butanolide, can no longer function. Homoserine lactones of Gram-negative bacteria function at high cell density and are structurally related to the butanolides. They turn on plant and animal virulence, light emission, plasmid transfer, and production of pigments, cyanide and beta-lactam antibiotics. They are made by enzymes homologous to Lux1, excreted by the cell, enter other cells at high density, bind to a LuxR homologue, the complex then binding to DNA upstream of genes controlled by "quorum sensing" and turning on their expression. Quorum sensing also operates in the case of the peptide pheromones of the Gram-positive bacteria. Here, secretion is accomplished by an ATP binding casette (ABC transporter), the secreted pheromone being recognized by a sensor component of a two-component signal transduction system. The pheromone often induces its own synthesis as well as those proteins involved in protein/peptide antibiotic (including bacteriocins and lantibiotics) production, virulence and genetic competence. The B-factor of A. mediterranei is an inducer of ansamycin (rifamycin) formation.

The role of non- Saccharomyces yeasts in industrial winemaking

Abstract: The fermentation of grape juice into wine is a complex microbiological process, in which yeasts play a central role. Traditionally, identification and characterization of yeast species have been based on morphological and physiological characteristics. However, the application of molecular biology techniques represents an alternative to the traditional methods of yeast identification and are becoming an important tool in solving industrial problems. Although Saccharomyces cerevisiae is responsible for the alcoholic fermentation, the presence of non-Saccharomyces species could be important since they produce secondary metabolites, which can contribute to the final taste and flavor of wines.

Non-conventional yeasts as hosts for heterologous protein production.

Abstract: Yeasts are an attractive group of lower eukaryotic microorganisms, some of which are used in several industrial processes that include brewing, baking and the production of a variety of biochemical compounds. More recently, yeasts have been developed as host organisms for the production of foreign (heterologous) proteins. Saccharomyces cerevisiae has usually been the yeast of choice, but an increasing number of alternative non-Saccharomyces yeasts has now become accessible for modern molecular genetics techniques. Some of them exhibit certain favourable traits such as high-level secretion or very strong and tightly regulated promoters, offering significant advantages over traditional bakers' yeast. In the present work, the current status of Kluyveromyces lactis, Yarrowia lipolytica, Hansenula polymorpha and Pichia pastoris (the best-known alternative yeast systems) is reviewed. The advantages and limitations of these systems are discussed in relation to S. cerevisiae.

Mitochondrial DNA: a tool for populational genetics studies.

Abstract: Mitochondria are cellular organelles that have the function of the oxidative phosphorilation and the formation of ATP. In humans, the mtDNA is a double-stranded, circular, covalent closed molecule of 16.5 kb. The mtDNA is inherited as a haploid from the mother and heteroplasmy has been found rarely. From a populational perspective, it could be considered as a system of small, sexually isolated demes, or clonal lineages, with an evolutionary rate 5 to 10 times faster than the nuclear genome. All these characteristics make this molecule ideal for evolutionary studies. We present two applications of this molecule in genetical studies. One of these is referred to the Balearic Islands populations, Majorca, Minorca, Ibiza, and Chuetas. The other example is the populational dynamics of the different mitochondrial haplotypes in Drosophila subobscura. We also discuss the importance of nuclear markers to complete these studies as well as the study of the Y chromosome to compensate the bias produced by the study of only the mtDNA.

Structure and properties of the outer membranes of Brucella abortus and Brucella melitensis.

Abstract: The brucellae are Gram-negative bacteria characteristically able to multiply facultatively within phagocytic cells and which cause a zoonosis of world-wide importance. This article reviews the structure and topology of the main components (lipopolysaccharide, native hapten polysaccharide, free lipids and proteins) of the outer membranes of Brucella abortus and B. melitensis, as well as some distinctive properties (permeability and interactions with cationic peptides) of these membranes. On these data, an outer membrane model is proposed in which, as compared to other Gram-negatives, there is a stronger hydrophobic anchorage for the lipopolysaccharide, free lipids, porin proteins and lipoproteins, and a reduced surface density of anionic groups, which could be partially or totally neutralized by ornithine lipids. This model accounts for the permeability of Brucella to hydrophobic permeants and for its resistance to the bactericidal oxygen-independent systems of phagocytes.

Yeast communities associated with sugarcane in Campos, Rio de Janeiro, Brazil.

Abstract: Yeast communities associated with sugarcane leaves, stems and rhizosphere during different phases of plant development were studied near Campos, in Rio de Janeiro, Brazil Atmospheric temperature, soil granulometry and pH, and sugar cane juice degree Brix and pH were determined Yeast communities associated with sugarcane were obtained after cellular extraction by shaking, blending and shaking plus sonication, and cultured on Yeast Nitrogen Base Agar plus glucose (05%) and Yeast Extract-Malt Extract Agar No significant differences in yeast counts were found among the cellular extraction treatments and culture media 230 yeast cultures were identified according to standard methods, and distinct yeast communities were found for each substrate studied The prevalent species isolated from sugarcane were Cryptococcus laurentii, Cryptococcus albidus, Rhodotorula mucilaginosa and Debaryomyces hansenii

Yarrowia lipolytica: a model organism for protein secretion studies.

Abstract: This paper reviews the advantages of the yeast Yarrowia lipolytica as a tool in the study of protein secretion. Work has been focused on the early steps leading the polypeptide, from the cytoplasmic ribosomes where it is synthesized, to the lumen of the endoplasmic reticulum. Using a thermosensitive allele of the 7SL RNA, the first in vivo evidence for a co-translational translocation was shown. Genetic screens allowed the identification of several new components of the translocation apparatus: Sls1p, an ER lumenal component involved in both translocation and lumenal transit; Tsr1p, involved in SRP-ribosome targeting; Tsr3p. Major translocation partners were also identified by reverse genetics (Sec61p, Sec62p, Kar2p, Srp54p, Sec65p).

Evolution of bacterial resistance to antibiotics during the last three decades.

Abstract: Bacterial resistance to antibiotics is often plasmid-mediated and the associated genes encoded by transposable elements. These elements play a central role in evolution by providing mechanisms for the generation of diversity and, in conjunction with DNA transfer systems, for the dissemination of resistances to other bacteria. At the University Hospital of Zaragoza, extensive efforts have been made to define both the dissemination and evolution of antibiotic resistance by studying the transferable R plasmids and transposable elements. Here we describe the research on bacterial resistance to antibiotics in which many authors listed in the references have participated. The aspects of bacterial resistance dealt with are: (i) transferable resistance mediated by R plasmids in Gramnegative bacteria, (ii) R plasmid-mediated resistance to apramycin and hygromycin in clinical strains, (iii) the transposon Tn 1696 and the integron Ini>4 , (iv) expression of Escherichia coli resistance genes in Haemophilus influenzae , (v) aminoglycosidemodifying- enzymes in the genus Mycobacterium with no relation to resistance, and (vi) macrolide-resistance and new mechanisms developed by Gram-positive bacteria.

Morphogenesis by symbiogenesis.

Abstract: Here we review cases where initiation of morphogenesis, including the differentiation of specialized cells and tissues, has clearly evolved due to cyclical symbiont integration. For reasons of space, our examples are drawn chiefly from the plant, fungal and bacterial kingdoms. Partners live in symbioses and show unique morphological specializations that result when they directly and cyclically interact. We include here brief citations to relevant literature where plant, bacterial or fungal partners alternate independent with entirely integrated living. The independent, or at least physically unassociated stages, are correlated with the appearance of distinctive morphologies that can be traced to the simultaneous presence and strong interaction of the plant with individuals that represent different taxa.

The fungus Ustilago maydis , from the aztec cuisine to the research laboratory

Abstract: Ustilago maydis is a plant pathogen fungus responsible for corn smut. It has a complex life cycle. In its saprophitic stage, it grows as haploid yeast cells, while in the invasive stage it grows as a mycelium formed by diploid cells. Thus, a correlation exists between genetic ploidy, pathogenicity and morphogenesis. Dimorphism can be modulated in vitro by changing environmental parameters such as pH. Studies with auxotrophic mutants have shown that polyamines play a central role in regulating dimorphism. Molecular biology approaches are being employed for the analysis of fundamental aspects of the biology of this fungus, such as mating type regulation, dimorphism or cell wall biogenesis.

Molecular mechanisms of Salmonella invasion: the type III secretion system of the pathogenicity island 1

Abstract: Salmonella spp. are facultative intracellular pathogens which are able to enter into non-phagocytic cells as an essential step in their pathogenic life cycle. The majority of the molecular determinants involved in this entry process are encoded in a pathogenicity island located at the centisome 63 of the bacterial chromosome, and belong to a specialized protein secretion system termed "type III" or "contact-dependent". This secretion system is used by Salmonella spp. and several other bacterial pathogens to translocate bacterial effector proteins into the eukaryotic cell. Thus, a bidirectional biochemical cross-talk with the host cell is initiated, which leads to several responses such as membrane ruffling, bacterial internalization and the activation of various transcription factors.

Candida adherence phenomena, from commensalism to pathogenicity.

Abstract: Summary Molecules present in the most external layers of Candida cells are essential for the adherence to host surfaces, playing a pivotal role in the pathophysiology of candidiasis. Receptors for fibrinogen, fibronectin and other components of the extracellular matrix have been described in Candida surfaces. Their expression may be influenced by particular host conditions, and these changes may be important in the transition from commensalism to pathogenicity. Surface proteins are also essential in the interactions of the fungal cell with the various constitutive, inducible defense host mechanisms that act during candidiasis.

Evolution of the clusters of genes for β-lactam antibiotics: a model for evolutive combinatorial assembly of new β-lactams

Abstract: β-Lactam antibiotics are produced by prokaryotic and eukaryotic organisms. The genes for β-lactam biosynthesis are organized in clusters but the location of the different genes is not identical. Biosynthesis genes are clustered with genes for resistance ( bla , pbp ) and for the efflux of the antibiotic ( cmc T) in prokaryotes. Comparison of proteins reveals much larger differences for primary metabolism enzymes than for β-lactam biosynthesis enzymes in producing organisms. This suggests a horizontal transfer of the β-lactam antibiotic biosynthesis genes.

Multicolonization of human nasopharynx due to Neisseria spp.

Abstract: The colonization due to Neisseria spp. in the nasopharynx of forty healthy adults was studied by using a selective medium that allows the differentiation of Neisseria species and inhibits the rest of pharyngeal microbiota. The medium detected a variety of colonial morphology types and some metabolic characteristics of the isolates. We demonstrated the multicolonization by several Neisseria spp. in the same individual, and we isolated several strains of the same species, after analysis by pulsed-field gel electrophoresis (PFGE) patterns obtained from the different colonial types previously identified as the same species. The forty adults studied were colonized by 112 forms of Neisseria spp., and twelve colonization patterns were obtained: one species (45%), two (45%), three (7.5%) and four (2.5%). N. perflava-N. sicca, either alone or in combination with other species was the most frequent isolate (92.5%). The analysis of PFGE patterns obtained from different colonial types revealed the multicolonization by several strains of the same species in some individuals. This fact was found in N. perflava-N. sicca (50%) and N. mucosa (2.5%).

Prions: an evolutionary perspective.

Abstract: Studies in both prion-due diseases in mammals and some non-Mendelian hereditary processes in yeasts have demonstrated that certain proteins are able to transmit structural information and self-replication. This induces the corresponding conformational changes in other proteins with identical or similar sequences. This ability of proteins may have been very useful during prebiotic chemical evolution, prior to the establishment of the genetic code. During this stage, proteins (proteinoids) must have molded and selected their structural folding units through direct interaction with the environment. The proteinoids that acquired the ability to propagate their conformations (which we refer to as conformons) would have acted as reservoirs and transmitters of a given structural information and hence could have acted as selectors for conformational changes. Despite the great advantage that arose from the establishment of the genetic code, the ability to propagate conformational changes did not necessarily disappear. Depending on the degree of involvement of this capacity in biological evolution, we propose two not mutually exclusive hypotheses: (i) extant prions could be an atavism of ancestral conformons, which would have co-evolved with cells, and (ii) the evolution of conformons would have produced cellular proteins, able to transmit structural information, and, in some cases, participating in certain processes of regulation and epigenesis. Therefore, prions could also be seen as conformons of a conventional infectious agent (or one that co-evolved with it independently) that, after a longer or shorter adaptive period, would have interacted with conformons from the host cells.

Selection of very small differences in bacterial evolution.

Abstract: As the Science of Biology is constantly changing due to new discoveries and advanced techniques it is essential that a systematic study of the environmental causes of natural selection on microorganisms be conducted. Very small phenotypic differences among individuals within bacterial populations arise as a result of spontaneous genetic variation, but the evolutionary importance of these small changes is frequently considered to be non-significant. Recent in vitro experiments indicate that efficient selection of these very small differences may take place in environmental compartments where a particular intensity of the selective agent is exerted. Model studies based on competition between bacterial populations only differing in one or two amino acid changes of a detoxifying antibiotic enzyme (e.g. beta-lactamase) have shown that at a narrow range of antibiotic concentrations the variant population is strongly selected over the original type, despite the extremely low phenotypic differences in antibiotic susceptibility. These selective concentrations are expected to occur in precise environmental compartments (selective compartments). Due to the high frequency of structured habitats in natural environments, the intensity of selective agents is commonly exerted along certain gradients. Each one of the points forming these gradients (or intersection among gradients) may have a particular selective ability for a specific genetic variant. Considering the environment as a composition of an extremely high number of specific selective compartments may help to understand the existence of high levels of genetic variability in natural bacterial populations. This may be one of the clues towards the unraveling of bacterial evolution.

Crucial crises in biology: life in the deep biosphere.

Abstract: The origin and evolution of life on Earth are the result of a series of crises that have taken place on the planet over about 4500 millions of years since it originated. Biopoiesis (origin of life), ecopoiesis (origin of ecosystems) and the first ecosystems (stromatolites and microbial mats), as well as eukaryopoiesis (origin of nucleated cells) are revised. The paper then focuses on the study of the deep biosphere, describing ecosystems never found before, which are independent of solar radiation and have changed previous assumptions about the requirements of life; even the concept of biosphere, as Vernadsky defined it, has increased its scope. Since the discovery, in 1987, of bacteria growing in the crevices of rocks at 500 m deep, in boreholes drilled near the Savanna River, Aiken, South Carolina, other bacteria have been found in the deep subsurface reaching depths of about 3 km (e.g., in the Columbia River Basalt Group, near Richland, Washington state), in an anaerobic, hot, high-pressure environment. Some kinds of microorganisms can thrive at such depths, living in many cases a geochemical existence, by using very specialized metabolisms, which depend on the local environments. The existence of organisms independent from photosynthetic production is the most outstanding, novel feature of the deep biosphere. Living beings might not need other energy and chemical sources than those which occur in the development of all planetary bodies. Life, therefore, could even be an ineluctable outcome of planetary evolution and, as a corollary, a natural continuation of the usual development of physical phenomena in the universe.

Numerical taxonomy of heavy metal-tolerant nonhalophilic bacteria isolated from hypersaline environments.

Abstract: Summary A total of 232 metal-tolerant bacterial strains were isolated from water and sediment samples collected in different hypersaline environments located in Cadiz, Huelva and Moron de la Frontera (Spain). They were isolated on a medium containing mercury, chromium, cadmium, copper or zinc. These halotolerant isolates were analyzed by numerical taxonomy techniques by using the simple matching (S SM ) and Jaccard (S J ) coefficients; clustering was achieved using the unweighted pair group method with averages (UPGMA) algorithm. At the 81% and 83% similarity level, different numbers of phenons were obtained for Gram-negative and Grampositive halotolerant microorganisms. Most of the 48 Gram-negative metal-tolerant strains studied were grouped into nine phenons, representing the genera Pseudoalteromonas, Alteromonas, Xanthomonas, Pseudomonas, Alcaligenes and Enterobacteria. The 72 Gram-positive metal-tolerant strains grouped into eight phenons, with only 15 strains left unassigned. Most of the isolates were assigned to the genus Bacillus (seven phenons), and one phenon comprised microorganisms with phenotypic characteristics similar to those of the genus Celullomonas.

Ciencia y producción científica en América Latina. El proyecto Latíndex

Abstract: No es la primera vez que me refiero a este subcontinente nuestro como un rompecabezas. Su complejidad atane de manera evidente a su geografia politica, pero tambien a su historia, y a los avatares internos y externos que unas veces han empujado y otras han actuado como freno en su desarrollo economico, social y, por supuesto, cientifico. Los paises de America Latina presentan una historia comun en la que comparten lenguas, raices y tradiciones, y que ha marcado su singular via de progreso. En ese progreso, hay que reconocerlo, la ciencia ha desempenado un papel secundario, de manera que, hasta ya entrado el siglo XX, las aportaciones a la ciencia fueron igualmente contadas. Los interrogantes que nos hemos planteado para explicarnos

A protocol for PCR in situ hybridization of hyphomycetes.

Abstract: Summary A protocol for application of Polymerase Chain Reaction (PCR) in situ hybridization for the detection of hyphomycetes is presented. The experiments are exemplary carried out with strains of the genera Penicillium and Cladosporium. The small ribosomal subunit is amplified in situ by PCR using fungal specific primers. The amplicon is used as target region for a fluorescein-marked probe. The permeability of the fungal cell wall for the primers and the probe can be successfully achieved by enzymatic treatment with β-glucanase. The protocol can be used as a basis for further development of in situ hybridization with taxon specific probes.

The cell wall structure: developments in diagnosis and treatment of candidiasis

Abstract: Candidiasis are among the fungal infections the most difficult to diagnose and treat. Research focused on specific fungal components which are absent in the host, such as the cell wall has lead to a better understanding of Candida albicans pathogenicity and clinical impact. The cell wall is responsible for antigenic expression and primary interaction with the host. It is composed mainly of β-glucans, chitin and mannoproteins, which account for the rigidity of the wall and for the fungal morphology. Of these components, mannoproteins might carry a “morphogenetic code” which might modulate the molecular architecture of the cell wall. The features of specific cell wall proteins as part of building blocks to form this structure is revised, and the usefulness of monoclonal antibodies obtained against cell wall components to study those processes, together with their clinical applicability, is discussed.

Cosmopolitan distribution of the large composite microbial mat spirochete, Spirosymplokos deltaeiberi

Abstract: Inocula from organic-rich black muds immediately underlying intertidal laminated microbial mats dominated by Microcoleus chthonoplastes yielded large, variable diameter spirochetes. These unusual spirochetes, previously reported only from the Alfacs Peninsula at the delta of the Ebro river in northeast Spain, contain striking arrays of cytoplasmic granules packed into their protoplasmic cylinders. On several occasions, both in summer and winter, the huge spirochetes were recognized in samples from mats growing in the Sippewissett salt marsh at Woods Hole Massachusetts. They were also seen in similar samples from microbial mats at North Pond, Laguna Figueroa, Baja California Norte, Mexico. The identity of these spirochetes was confirmed by electron microscopy: number and disposition of flagella, composite structure, measurements of their distinctive cytoplasmic granules. The granules, larger, more conspicuous and present in addition to ribosomes, are hypothesized to contain ATPases. As culture conditions worsen, these spirochetes retract into membrane-bounded round bodies in which they form refractile inclusions. From morphology and behavior we conclude the North American spirochetes from both Atlantic and Pacific intertidal microbial mats are indistinguishable from those at the delta of the Ebro river. We conclude a cosmopolitan distribution for Spirosymplokos deltaeiberi.

Candida albicans fibrinogen binding mannoprotein: expression in clinical strains and immunogenicity in patients with candidiasis.

Abstract: Summary A 58 kDa cell wall-associated fibrinogen binding mannoprotein (mp58), previously characterized by our group in a Candida albicanslaboratory strain (ATCC 26555), was found to be also present in the cell wall of clinical isolates of this fungus. Most strains examined appear to have functional mp58 species, as detected by their ability to bind fibrinogen. Western immunoblot analysis, with a monovalent polyclonal antibody generated against the mp58 species from strain ATCC 26555, revealed differences in recognition patterns depending on the strain tested and the culture conditions used. Serum samples from normal and Candida infected individuals were examined for the presence of antibodies against mp58 by Western immunoblotting. None of the sera from control individuals and patients suffering from superficial candidiasis contained antibodies against mp58. However, positive reactivity with this antigen and other cell wall constituents was detected for all sera from patients with confirmed systemic candidiasis. Together, these results suggest that mp58 could play an active role during infection and may be useful as a specific antigenic marker for candidiasis.

Cloning, characterization and chromosomal localization of a repeated sequence in Crypthecodinium cohnii, a marine dinoflagellate.

Abstract: Genomic DNA of Crypthecodinium cohnii has been extracted in the presence of cetylmethylammonium bromide and hydrolysed by 13 restriction enzymes. No typical ladder-like pattern or isolated band of satellite sequences were found with any of these enzymes. A “mini” genomic DNA library had been made and screened by reverse hybridization to isolate highly repeated sequences. Seven such DNA fragments were sequenced. The copy number of one of them (Cc18), 226 bp long, was estimated at around 25,000, representing 0.06% of the total genome. Cc18 was found to be included in a higher fragment of 3.0 kb by Southern blot analysis after cleavage by PstI. This higher molecular weight fragment could be composed either of tandemly repeated Cc18 sequences, or by only one or a very low copy number of Cc18. In this latter case, these fragments, also repeated 25,000 times would represent 1 to 2% of the total genome. Genomic localization of Cc18 by in situ hybridization on squashed C. cohnii cells showed that it was widely distributed on the different chromosomes. All the chromosomes observed displayed Cc18 labeling, which appeared homogeneously distributed. The ability of Cc18 to be a specific molecular marker to distinguish sibling C. cohnii species is discussed.

Colimetry of marine waters off Fortaleza (Ceará State, Brazil) and detection of enteropathogenic Escherichia coli strains.

Abstract: Bacteriological analyses of seawater from three main beaches in Fortaleza, Brazil were performed during 1997. Thirty-six samples per beach were collected for a total of 108 samples. For Meireles Beach, 44% of the samples had MPN total coliforms values of at least 1100 or over 2400/100 ml, followed by Formosa and Diarios beaches showing lower counts. For fecal coliforms the highest numbers were demonstrated for Formosa, followed by Meireles and Diarios beaches in this descending order: 13.0%, 11.1% and 8.3%, respectively. Escherichia coli strains were identified in 76.8% of the 108 samples. Among 295 strains of E. coli, 21 belonged to serogroups O25, O26, O91, O112, O119, O158 and O164. Strains from serogroup O26 were tested using PCR, ELISA and Vero cells to detect Verotoxins VT1 and VT2 and all strains were negative. No LT and ST, as determined by ELISA and suckling mice assays, were detected among the 295 strains. All strains of E. coli were sensitive to ampicillin, cephalothin, gentamicin, tetracycline, sulfametox-trimethoprim, chloramphenicol and ciprofloxacin. Although the E. coli strains were not toxigenic, their presence in high numbers could be of public health significance.