RESUMO
We have used amplified fragment length polymorphism (AFLP), multilocus sequence analysis (MLSA) and DNA-DNA hybridization for genotypic classification of Xanthomonas pathovars associated with the plant family Anacardiaceae. AFLP and MLSA results showed congruent phylogenetic relationships of the pathovar mangiferaeindicae (responsible for mango bacterial canker) with strains of Xanthomonas axonopodis subgroup 9.5. This subgroup includes X. axonopodis pv. citri (synonym Xanthomonas citri). Similarly, the pathovar anacardii, which causes cashew bacterial spot in Brazil, was included in X. axonopodis subgroup 9.6 (synonym Xanthomonas fuscans). Based on the thermal stability of DNA reassociation, consistent with the AFLP and MLSA data, the two pathovars share a level of similarity consistent with their being members of the same species. The recent proposal to elevate X. axonopodis pv. citri to species level as X. citri is supported by our data. Therefore, the causal agents of mango bacterial canker and cashew bacterial spot should be classified as pathovars of X. citri, namely X. citri pv. mangiferaeindicae (pathotype strain CFBP 1716) and X. citri pv. anacardii (pathotype strain CFBP 2913), respectively. Xanthomonas fuscans should be considered to be a later heterotypic synonym of Xanthomonas citri.
Assuntos
Anacardiaceae/microbiologia , Xanthomonas/classificação , Análise do Polimorfismo de Comprimento de Fragmentos Amplificados , Variação Genética , Dados de Sequência Molecular , Filogenia , RNA Ribossômico 16S/genética , Análise de Sequência de DNA , Xanthomonas/genéticaRESUMO
AIMS: In order to evaluate the part played in biocorrosion by microbial groups other than sulfate-reducing bacteria (SRB), we characterized the phylogenetic diversity of a corrosive marine biofilm attached to a harbour pile structure as well as to carbon steel surfaces (coupons) immersed in seawater for increasing time periods (1 and 8 months). We thus experimentally checked corroding abilities of defined species mixtures. METHODS AND RESULTS: Microbial community analysis was performed using both traditional cultivation techniques and polymerase chain reaction cloning-sequencing of 16S rRNA genes. Community structure of biofilms developing with time on immersed coupons tended to reach after 8 months, a steady state similar to the one observed on a harbour pile structure. Phylogenetic affiliations of isolates and cloned 16S rRNA genes (rrs) indicated that native biofilms (developing after 1-month immersion) were mainly colonized by gamma-proteobacteria. Among these, Vibrio species were detected in majority with molecular methods while cultivation techniques revealed dominance of Enterobacteriaceae such as Citrobacter, Klebsiella and Proteus species. Conversely, in mature biofilms (8-month immersion and pile structure), SRB, and to a lesser extent, spirochaetes were dominant. CONCLUSIONS: Corroding activity detection assays confirmed that Enterobacteriaceae (members of the gamma-proteobacteria) were involved in biocorrosion of metallic material in marine conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: In marine biofilms, metal corrosion may be initiated by Enterobacteriaceae.
Assuntos
Biofilmes , Carbono , Enterobacteriaceae/fisiologia , Aço , Sequência de Bases , Biodiversidade , Clonagem Molecular/métodos , Corrosão , Enterobacteriaceae/genética , Imersão , Microscopia Eletrônica de Varredura/métodos , Filogenia , RNA Bacteriano/genética , RNA Ribossômico 16S/genética , Água do Mar/microbiologia , Microbiologia da ÁguaRESUMO
Eighty Vibrio cholerae O1 strains selected to represent the 1998-to-1999 history of the largest cholera epidemic in Kenya were characterized by ribotyping, antimicrobial susceptibility, and random amplified polymorphic DNA patterns. Except for 19 strains from 4 local outbreaks in North Eastern Province along the Somalia border, the other 61 strains from 25 outbreaks occurring in districts scattered around the country were all ribotype B27 and resistant to chloramphenicol, spectinomycin, streptomycin, sulfamethoxazole, and trimethoprim. The 61 strains showed similar and specific amplified DNA patterns. These findings indicate that the predominant strains that caused the Kenyan epidemic had a clonal origin and suggest that ribotype B27 strains, which first appeared in West Africa in 1994, have had a rapid spread to eastern Africa.
Assuntos
Cólera/epidemiologia , Surtos de Doenças , Vibrio cholerae O1/classificação , Vibrio cholerae O1/genética , Antibacterianos/farmacologia , Proteínas de Bactérias/genética , Técnicas de Tipagem Bacteriana , Cólera/microbiologia , Farmacorresistência Bacteriana Múltipla , Humanos , Quênia/epidemiologia , Testes de Sensibilidade Microbiana , Técnica de Amplificação ao Acaso de DNA Polimórfico , Ribotipagem , Vibrio cholerae O1/efeitos dos fármacosRESUMO
Phylogenetic relationships within the genus Pseudomonas were examined by comparing partial (about 1000 nucleotides) rpoB gene sequences. A total of 186 strains belonging to 75 species of Pseudomonas sensu stricto and related species were studied. The phylogenetic resolution of the rpoB tree was approximately three times higher than that of the rrs tree. Ribogroups published earlier correlated well with rpoB sequence clusters. The rpoB sequence database generated by this study was used for identification. A total of 89 isolates (79.5%) were identified to a named species, while 16 isolates (14.3%) corresponded to unnamed species, and 7 isolates (6.2%) had uncertain affiliation. rpoB sequencing is now being used for routine identification of Pseudomonas isolates in our laboratory.
Assuntos
RNA Polimerases Dirigidas por DNA/genética , Filogenia , Pseudomonas/classificação , Pseudomonas/genética , DNA Bacteriano/química , DNA Bacteriano/genética , Dados de Sequência Molecular , Pseudomonas/enzimologia , Análise de Sequência de DNARESUMO
The nomenclature of the genus Salmonella has reached an unsatisfactory state of affairs, with two systems of nomenclature in circulation. One system, proposed in the 1980s by Le Minor and Popoff, has received wide acceptance, although it does not conform to the rules of the Bacteriological Code. The other system, which conforms to the rules of the Bacteriological Code, is being used by an ever-decreasing minority. As a result of a number of recent Requests for an Opinion, the Judicial Commission of the International Committee on the Systematics of Prokaryotes has issued an Opinion (Opinion 80) with the intention that it should solve these discrepancies. However, like all Opinions, it is limited to matters of nomenclature and does not help to interpret the taxonomic consequences. The Judicial Commission has therefore asked experts in the field of nomenclature and taxonomy to write a commentary on the nomenclatural and taxonomic consequences of Opinion 80. The present article explains the nomenclatural consequences of Opinion 80, together with a clear presentation of the taxonomy that results when applying the currently widely accepted interpretation that the genus Salmonella currently includes only two species.
Assuntos
Salmonella/classificação , Terminologia como AssuntoRESUMO
A new Vibrio species, Vibrio ponticus, is proposed to accommodate four marine bacteria isolated from sea water, mussels and diseased sea bream (Sparus aurata), at the Mediterranean coast of Spain. Strains are Gram negative, slightly halophilic bacteria that require Na+ ion for growth, oxidase and catalase positive, negative for arginine dihydrolase and ornithine decarboxylase but positive for lysine decarboxylase and indole, and utilize beta-hydroxybutyrate as a sole carbon source. Phylogenetic analysis locate these marine bacteria in the vicinity of the V. fluvialis-V. furnissii clade, sharing with these two species 16S rDNA sequence similarities slightly above 97% (97.1 and 97.3%, respectively). DNA-DNA hybridisation values confirm that the four strains form a genospecies and represent a new species in the genus Vibrio. We propose strain 369T (CECT 5869T, DSM 16217T) as the type strain.
Assuntos
Bivalves/microbiologia , Dourada/microbiologia , Água do Mar/microbiologia , Vibrio/classificação , Vibrio/isolamento & purificação , Ácido 3-Hidroxibutírico/metabolismo , Animais , Carboxiliases/análise , Catalase/análise , DNA Bacteriano/química , DNA Bacteriano/isolamento & purificação , DNA Ribossômico/química , DNA Ribossômico/isolamento & purificação , Ácidos Graxos/análise , Violeta Genciana , Hidrolases/análise , Indóis/análise , Mar Mediterrâneo , Dados de Sequência Molecular , Hibridização de Ácido Nucleico , Ornitina Descarboxilase/análise , Oxirredutases/análise , Fenazinas , Filogenia , RNA Ribossômico 16S/genética , Análise de Sequência de DNA , Homologia de Sequência do Ácido Nucleico , Espanha , Vibrio/química , Vibrio/fisiologia , Vibrioses/veterináriaRESUMO
During the period of 9-27 March 2001, Pseudomonas putida strains were recovered from 10 neonates hospitalized in the neonatal intensive care unit of Farhat Hached Hospital, Sousse (Tunisia). Seven neonates developed bacteraemia, and three had an umbilical catheter-related infection (without bacteraemia). A total of 18 isolates were cultured from blood (N = 11) and catheters (N = 7). These isolates were identified as P. putida by routine biochemical methods (API 20 NE, bioMérieux, Lyon, France). Restriction endonuclease DNA profiles were determined by pulsed-field gel electrophoresis using two endonucleases XbaI and SpeI. They yielded the same patterns showing that the outbreak was caused by a single clone of P. putida. Although the antiseptic solutions used to clean the umbilicus were implicated circumstantially as probable sources, they were not sampled and so this could not be confirmed.
Assuntos
Bacteriemia/epidemiologia , Infecção Hospitalar/epidemiologia , Surtos de Doenças , Unidades de Terapia Intensiva Neonatal , Pseudomonas putida/isolamento & purificação , Bacteriemia/sangue , Bacteriemia/microbiologia , Cateteres de Demora/microbiologia , Infecção Hospitalar/microbiologia , Eletroforese em Gel de Campo Pulsado , Humanos , Recém-Nascido , Tunísia/epidemiologia , Umbigo/microbiologiaRESUMO
A Gram-negative rod was isolated from the blood cultures of an 84-year-old man with foot cellulitis. The bacterium was first identified as Sphingobacterium spiritivorum on the basis of standard assimilation tests. However, sequencing analysis of its 16S rRNA genes and whole genome hybridization studies with other related bacteria showed that this isolate belongs to a so far undescribed species of Sphingobacterium, close to S. mizutae. This bacterium was susceptible to most of the antibiotics tested, including glycopeptides, but was resistant to aminoglycosides and polymyxins. Treatment with amoxicillin-clavulanate cured the infection.
Assuntos
Bacteriemia/microbiologia , Celulite (Flegmão)/microbiologia , Infecções por Bactérias Gram-Negativas/microbiologia , Sphingobacterium/crescimento & desenvolvimento , Idoso , Idoso de 80 Anos ou mais , Combinação Amoxicilina e Clavulanato de Potássio/uso terapêutico , Bacteriemia/tratamento farmacológico , Celulite (Flegmão)/tratamento farmacológico , Quimioterapia Combinada , Infecções por Bactérias Gram-Negativas/tratamento farmacológico , Humanos , Masculino , Testes de Sensibilidade MicrobianaRESUMO
Culturable cells and non-culturable cells of fecal coliforms, obtained by irradiation at 312 nm were submitted to the combined stress conditions of salinity and starvation. After 14 days, beta-galactosidase activity of UV-irradiated cells was at least twice the value of non-irradiated cells. UV-irradiated cells thus contribute more than non-irradiated cells to the enzyme assay after incubation in saline water. This finding is essential for the interpretation of quantitative investigations into the environment using enzymatic methods.
Assuntos
Contagem de Colônia Microbiana/métodos , Monitoramento Ambiental/métodos , Escherichia coli/enzimologia , Escherichia coli/crescimento & desenvolvimento , Fezes/microbiologia , Água do Mar/microbiologia , beta-Galactosidase/metabolismo , Relação Dose-Resposta à Radiação , Enterobacteriaceae/classificação , Enterobacteriaceae/enzimologia , Enterobacteriaceae/crescimento & desenvolvimento , Enterobacteriaceae/efeitos da radiação , Ativação Enzimática , Escherichia coli/isolamento & purificação , Escherichia coli/efeitos da radiação , Glucose/metabolismo , Estatística como Assunto , Raios Ultravioleta , Poluentes da Água/análise , beta-Galactosidase/análiseRESUMO
AIMS: To isolate, identify, and characterize heterotrophic bacteria in acid-mine drainage that mediate oxidation of As(III). METHODS AND RESULTS: Samples of acid-mine drainage were collected over a period of 14 months. Heterotrophic and non-obligatory acidophilic bacteria in the samples were cultured on a solid medium (pH 7.0-7.2), and three strains were isolated. The three different strains belong to the genus Thiomonas, and have more than 99% homology with the group Ynys1. Culturing in mineral media demonstrated that the isolated strains used thiosulphate as an energy source, and oxidized iron in the presence of thiosulphate. However, none of the strains were able to oxidize arsenic in the presence of thiosulphate, nor could they use iron or arsenic alone as an energy source. In vitro experiments demonstrated that two of the Thiomonas strains were able to oxidize more than 90% of the As(III) present in the acid-mine drainage, whereas no abiotic oxidation of arsenic occurred. CONCLUSIONS: Two strains of newly identified Thiomonas sp. found in acid-mine drainage are capable of oxidizing arsenic. SIGNIFICANCE AND IMPACT OF STUDY: These results represent the first reported oxidation of arsenic by Thiomonas sp. Biologically mediated oxidation and subsequent immobilization of arsenic is of great interest for the remediation of contaminated mine sites.
Assuntos
Arsênio/metabolismo , Resíduos Industriais/análise , Mineração , Thiobacillus/metabolismo , Poluentes Químicos da Água/metabolismo , Biodegradação Ambiental , Meios de Cultura , Concentração de Íons de Hidrogênio , Oxirredução , Filogenia , Thiobacillus/classificação , Thiobacillus/isolamento & purificaçãoRESUMO
Corynebacterium macginleyi was isolated from conjunctival swabs of a farmer suffering from purulent conjunctivitis. This species has only recently been reported in Switzerland and Germany to be exclusively isolated from ocular surfaces. This represents the first isolation of C. macginleyi in Italy indicating that its circulation is not geographically limited.
Assuntos
Túnica Conjuntiva/microbiologia , Conjuntivite/microbiologia , Infecções por Corynebacterium/diagnóstico , Infecções por Corynebacterium/microbiologia , Corynebacterium/isolamento & purificação , Idoso , Antibacterianos , Corynebacterium/classificação , Infecções por Corynebacterium/tratamento farmacológico , Quimioterapia Combinada/administração & dosagem , Seguimentos , Humanos , Itália , Masculino , RNA Bacteriano , Análise de Sequência de RNA , Resultado do TratamentoRESUMO
Vibrio cholerae is again the subject of attention on account of the current increase in the world-wide incidence of cholera. In this study, 200 clinical isolates of V. cholerae serotypes O1 and non-O1, non-O139, were collected from different provinces in Iran. The isolates were subjected to biochemical analysis, antibiogram, PCR of toxin genes, plasmid profile, ribotyping and pulsed-field gel electrophoresis (PFGE). The analysis of plasmid content showed that 33-96% of V. cholerae isolated from different provinces carry a large plasmid. PCR analysis of V. cholerae O1 showed that the genes encoding cholera toxin (ctx), toxin co-regulated pilus (tcp), accessory cholera enterotoxin (ace) and zonula occludens toxin (zot) were present in 55-97% of isolates in different provinces. Restriction fragment length polymorphism (RFLP) of BglI-digested DNA probed with five oligonucleotides revealed three different ribotype patterns in isolates of V. cholerae O1. The ribotype pattern B21 of V. cholerae O1 El Tor was found to be the predominant pattern in the isolates studied. V. cholerae non-O1, non-O139 isolates showed a single ribotype pattern. PFGE analysis also showed 10 different patterns amongst the isolates, 9 of which were in V. cholerae O1. Overall, the analysis of polymorphism of ribotypes and PFGE patterns of the isolates showed that the provinces in Iran were affected by a limited number of clones of V. cholerae O1 and non-O1, non-O139 strains.
Assuntos
Vibrio cholerae/classificação , Vibrio cholerae/genética , Cólera/microbiologia , Toxina da Cólera/genética , Conjugação Genética , DNA Bacteriano/análise , Farmacorresistência Bacteriana Múltipla , Eletroforese em Gel de Campo Pulsado , Genótipo , Humanos , Irã (Geográfico) , Fenótipo , Plasmídeos/análise , Reação em Cadeia da Polimerase , Ribotipagem , Sorotipagem , Vibrio cholerae/efeitos dos fármacosRESUMO
Twelve phenotypically similar marine bacteria have been studied by means of ribotyping, DNA-DNA hybridization and cultural and physiological characterization. Phylogenetic analysis has been performed of the 16S and 23S rRNA genes of two representative strains. Phylogenetically, they belong to the Vibrio/Photobacterium branch of the gamma-Proteobacteria and they share all of the properties that define the genus Vibrio. The strains represent a new Vibrio species that is phenotypically similar to Vibrio splendidus. However, resistance to the vibriostatic agent 0129 and production of acid from several carbohydrates allow differentiation between V. splendidus and the proposed new species. The DNA G+C content of the proposed type strain is 44.0 mol %. The name Vibrio lentus sp. nov. is proposed for the new species and strain 40M4T (= CECT 5110T = DSM 13757T) is the type strain.
Assuntos
Ostreidae/microbiologia , Vibrio/classificação , Vibrio/genética , Animais , Composição de Bases , Sequência de Bases , DNA Bacteriano/química , DNA Bacteriano/genética , DNA Ribossômico/genética , Mar Mediterrâneo , Dados de Sequência Molecular , Hibridização de Ácido Nucleico , Fenótipo , Filogenia , RNA Bacteriano/genética , RNA Ribossômico 16S/genética , RNA Ribossômico 23S/genética , Ribotipagem , Especificidade da Espécie , Vibrio/isolamento & purificaçãoRESUMO
We screened the La Plata drinking water distribution network for fecal and total coliform bacterial indicator by purification procedures, cultivating 66 membrane-filtered samples from the two networks on m-T7 agar. Subterranean and river-derived water yielded 13 and 18 confirmed gram-negative bacillus isolates, with 54% and 72% representing total coliforms, respectively. Those from the former source were Klebsiella oxytoca, Enterobacter agglomerans, and Enterobacter aerogenes and from the latter Klebsiella oxytoca, Enterobacter agglomerans, and Enterobacter cloacae, genomic group 3. Since 58% of the samples were positive using m-T7 medium it is suggested that the inclusion in standard quality control protocols should be implemented.
Assuntos
Enterobacteriaceae/isolamento & purificação , Microbiologia da Água , Poluição da Água/análise , Abastecimento de Água/análise , Algoritmos , Argentina , Técnicas de Tipagem Bacteriana , Técnicas Bacteriológicas , Meios de Cultura/farmacologia , Enterobacter/classificação , Enterobacter/isolamento & purificação , Enterobacteriaceae/efeitos dos fármacos , Enterobacteriaceae/crescimento & desenvolvimento , Klebsiella/isolamento & purificação , Saúde da População Urbana , Purificação da Água/métodosRESUMO
Nonculturable segmented filamentous bacteria (SFB) have been described in the gut of rats, mice and chickens, and 16S rRNA sequences for these organisms are available. These organisms, peripherically related to Clostridium phylogenetic group I, have been provisionally named 'Candidatus Arthromitus'. This work reports the observation of similar bacteria in the intestinal content of the distal intestine, preferentially, in the adult rainbow trout (Oncorhynchus mykiss) that exhibited episodic acute diarrhea, usually during the summer. Abdominal distension, intestinal fluid-mucus content and epithelium detachment were observed in trout. The demonstration that the observed microorganisms are bacteria and belong in the 'Candidatus Arthromitus' group was achieved by in situ hybridization with, respectively, a eubacterial probe and an oligonucleotide probe designed to react specifically with SFB 16S rRNA (encoded by the rrs gene) sequences. The sequenced rrs gene was compared with published sequences and found to be closely related to (although distinct from) other SFB sequences. Implication of these bacteria in trout diarrheic illness remains hypothetical.
Assuntos
Diarreia/veterinária , Doenças dos Peixes/microbiologia , Bactérias Gram-Positivas Formadoras de Endosporo/classificação , Hibridização in Situ Fluorescente , Oncorhynchus mykiss , Animais , DNA Ribossômico/análise , Diarreia/microbiologia , Infecções por Bactérias Gram-Positivas/microbiologia , Infecções por Bactérias Gram-Positivas/veterinária , Bactérias Gram-Positivas Formadoras de Endosporo/genética , Bactérias Gram-Positivas Formadoras de Endosporo/isolamento & purificação , Intestinos/microbiologia , RNA Ribossômico 16S/genéticaRESUMO
We describe a MluI ribotyping scheme for Shigella which approaches correlation with serotyping. One hundred and seventeen reference strains and previously serotyped clinical isolates representing the 57 Shigella serotypes and biotypes were included in this study. A total of 51 distinct ribotypes were obtained and a database was built with them. The number of bands composing each ribotype varied from 9 to 15. The fragments ranged in size from 1.6 to 18.8 kbp. One hundred and eleven clinical isolates were successfully identified in a double blind study with standard biochemical/serologic methods, by automatic comparison of their ribotypes with our database using the software Taxotron.
Assuntos
Proteínas de Bactérias , Bases de Dados Factuais , Disenteria Bacilar/microbiologia , Genes de RNAr , Ribotipagem , Shigella/classificação , Desoxirribonucleases de Sítio Específico do Tipo II/metabolismo , Disenteria Bacilar/epidemiologia , Escherichia coli/classificação , Escherichia coli/genética , Humanos , Sorotipagem , Shigella/genética , SoftwareRESUMO
We screened the La Plata drinking water distribution network for fecal and total coliform bacterial indicator by purification procedures, cultivating 66 membrane-filtered samples from the two networks on m-T7 agar. Subterranean and river-derived water yielded 13 and 18 confirmed gram-negative bacillus isolates, with 54 and 72 representing total coliforms, respectively. Those from the former source were Klebsiella oxytoca, Enterobacter agglomerans, and Enterobacter aerogenes and from the latter Klebsiella oxytoca, Enterobacter agglomerans, and Enterobacter cloacae, genomic group 3. Since 58 of the samples were positive using m-T7 medium it is suggested that the inclusion in standard quality control protocols should be implemented.
Assuntos
Abastecimento de Água/análise , Enterobacteriaceae , Poluição da Água/análise , Microbiologia da Água , Algoritmos , Argentina , Técnicas de Tipagem Bacteriana , Técnicas Bacteriológicas , Meios de Cultura , Enterobacter , Enterobacteriaceae , Klebsiella , Purificação da Água/métodos , Saúde da População UrbanaRESUMO
We screened the La Plata drinking water distribution network for fecal and total coliform bacterial indicator by purification procedures, cultivating 66 membrane-filtered samples from the two networks on m-T7 agar. Subterranean and river-derived water yielded 13 and 18 confirmed gram-negative bacillus isolates, with 54 and 72 representing total coliforms, respectively. Those from the former source were Klebsiella oxytoca, Enterobacter agglomerans, and Enterobacter aerogenes and from the latter Klebsiella oxytoca, Enterobacter agglomerans, and Enterobacter cloacae, genomic group 3. Since 58 of the samples were positive using m-T7 medium it is suggested that the inclusion in standard quality control protocols should be implemented.(AU)
Assuntos
Estudo Comparativo , Enterobacteriaceae/isolamento & purificação , Microbiologia da Água , Poluição da Água/análise , Abastecimento de Água/análise , Algoritmos , Argentina , Técnicas de Tipagem Bacteriana , Técnicas Bacteriológicas , Meios de Cultura/farmacologia , Enterobacter/classificação , Enterobacter/isolamento & purificação , Enterobacteriaceae/efeitos dos fármacos , Enterobacteriaceae/crescimento & desenvolvimento , Klebsiella/isolamento & purificação , Saúde da População Urbana , Purificação da Água/métodosRESUMO
From September 1997 to November 1998, the French National Center for Salmonella and Shigella received 22 Shigella isolates recovered from 22 different patients suffering from dysentery. None of these isolates reacted with any of the antisera used to identify established Shigella serotypes, but all of them agglutinated in the presence of antisera to a previously described potentially new Shigella dysenteriae serotype (represented by strain 96-204) primarily isolated from stool cultures of imported diarrheal cases in Japan. All French isolates, as well as strain 96-204, showed biochemical reactions typical of S. dysenteriae and gave positive results in a PCR assay for detection of the plasmid ipaH gene coding for invasiveness. No Shiga toxin gene was detected by PCR. These isolates were indistinguishable by molecular analysis of ribosomal DNA (ribotyping) and seemed to be related to S. dysenteriae serotypes 3 and 12. However, further characterization by restriction of the amplified O-antigen gene cluster clearly distinguished this new serotype from all other Shigella or Escherichia coli serotypes.