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Diarrheagenic Escherichia Coli b r a z i l i a n j o u r n a l o f m i c r o b i o l o g y 4 7 S (2 0 1 6) 3–30 ht tp://www.bjmicrobiol.com.br/ Medical Microbiology Diarrheagenic Escherichia coli a,∗ b a a Tânia A.T. Gomes , Waldir P. Elias , Isabel C.A. Scaletsky , Beatriz E.C. Guth , c b c d Juliana F. Rodrigues , Roxane M.F. Piazza , Luís C.S. Ferreira , Marina B. Martinez a Universidade Federal de São Paulo, Escola Paulista de Medicina, Departamento de Microbiologia, Imunologia e Parasitologia, São Paulo, SP, Brazil b Instituto Butantan, Laboratório de Bacterologia, São Paulo, SP, Brazil c Universidade de São Paulo, Instituto de Ciências Biomédicas, Departamento de Microbiologia, São Paulo, SP, Brazil d Universidade de São Paulo, Faculdade de Ciências Farmacêuticas, Departamento de Análises Clínicas e Toxicológicas, São Paulo, SP, Brazil a r t i c l e i n f o a b s t r a c t Article history: Most Escherichia coli strains live harmlessly in the intestines and rarely cause disease in Received 8 October 2016 healthy individuals. Nonetheless, a number of pathogenic strains can cause diarrhea or Accepted 27 October 2016 extraintestinal diseases both in healthy and immunocompromised individuals. Diarrheal Available online 5 November 2016 illnesses are a severe public health problem and a major cause of morbidity and mortal- ity in infants and young children, especially in developing countries. E. coli strains that Keywords: cause diarrhea have evolved by acquiring, through horizontal gene transfer, a particular set of characteristics that have successfully persisted in the host. According to the group of Escherichia coli Diarrhea virulence determinants acquired, specific combinations were formed determining the cur- Pathogenic mechanisms rently known E. coli pathotypes, which are collectively known as diarrheagenic E. coli. In this Virulence factor review, we have gathered information on current definitions, serotypes, lineages, virulence Epidemiology mechanisms, epidemiology, and diagnosis of the major diarrheagenic E. coli pathotypes. © 2016 Sociedade Brasileira de Microbiologia. Published by Elsevier Editora Ltda. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/). The genus Escherichia, which was named after the Ger- a number of pathogenic strains can cause intestinal and man pediatrician Theodor Escherich, consists of facultative extraintestinal diseases both in healthy and immunocompro- 3 anaerobic Gram-negative bacilli that belong to the family mised individuals. 1 Enterobacteriaceae. The genus type species Escherichia coli is Diarrheal illnesses are a severe public health problem and widely distributed, where it is the major facultative anaerobe a major cause of morbidity and mortality in infants and young 4 inhabiting the large intestine of humans and warm-blooded children. Low- and middle-income countries in Africa, Asia 2 animals. Although most E. coli strains live harmlessly in and Latin America are the most affected regions with diarrheal the colon and seldom cause disease in healthy individuals, diseases occurring more often with lethal outcomes mainly ∗ Corresponding author. E-mail: [email protected] (T.A. Gomes). http://dx.doi.org/10.1016/j.bjm.2016.10.015 1517-8382/© 2016 Sociedade Brasileira de Microbiologia. Published by Elsevier Editora Ltda. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 4 b r a z i l i a n j o u r n a l o f m i c r o b i o l o g y 4 7 S (2 0 1 6) 3–30 due to poor living conditions (inadequate water supplies, Improvements in techniques allowing a better understand- poor environmental hygiene and sanitation, and insufficient ing of the genome and virulence mechanisms among EPEC 5 education). strains over the years have led to the sub-classification of EPEC 3,12 E. coli strains involved in diarrheal diseases are one of the into typical EPEC (tEPEC) and atypical EPEC (aEPEC). Typi- most important of the various etiological agents of diarrhea, cal EPEC strains causing human infectious diarrhea possess where strains have evolved by the acquisition, through hori- a large virulence plasmid known as the EPEC adherence fac- zontal gene transfer, of a particular set of characteristics that tor (EAF) plasmid (pEAF), which encodes the type IV fimbriae 3,5,6 have successfully persisted in the host. According to the called the bundle-forming pilus (BFP), while aEPEC do not 6,12 group of virulence determinants acquired, specific combina- possess this plasmid. tions were formed determining the currently known E. coli The majority of tEPEC strains fall into well-recognized O pathotypes, which are collectively known as diarrheagenic serotypes. Classical EPEC O serogroups include O55, O86, O111, 6 E. coli (DEC). The DEC pathotypes differ regarding their prefer- O114, O119, O127, and O142. The most common H antigens 12–15 ential host colonization sites, virulence mechanisms, and the associated with EPEC are the H6 and H2 antigens. A less ensuing clinical symptoms and consequences, and are clas- common EPEC type is H34, and a number of tEPEC strains sified as enteropathogenic E. coli (EPEC), enterohemorrhagic are classified as non-motile (H-) in conventional tests. Typical (Shiga toxin-producing) E. coli (EHEC/STEC), enteroaggregative EPEC strains belonging to non-classical serotypes have also 12,16 E. coli (EAEC), enterotoxigenic E. coli (ETEC), and enteroinvasive been reported. E. coli (EIEC). Based on multilocus enzyme electrophoresis analysis Each of these pathotypes represents a group of clones (MLEE) of allelic differences between housekeeping genes, that share specific virulence factors. Nevertheless, it should tEPEC strains have been subtyped into two major lineages, 13,14 be pointed out that the plasticity of the E. coli genome has previously designated EPEC1 and EPEC2. EPEC1 includes hindered the identification of certain E. coli isolates as a widespread serotypes such as O55:H6 and O119:H6, whereas pathotype, because some isolates combine the main virulence EPEC2 consists of serotypes with more limited occurrence characteristics of different pathotypes and are thus consid- such as O111:H2 and O114:H2. Based on a whole-genome 5 ered potentially more virulent hybrid pathogenic strains. phylogeny and analysis of type III secretion system (T3SS) Another less well-defined pathotype has been described, effectors, tEPEC strains have been demonstrated to cluster that is, the diffusely-adherent E. coli (DAEC) pathotype, which in three main lineages, designated EPEC1, EPEC2, and EPEC4, comprises strains that adhere to epithelial cells in a diffused which probably acquired the locus of enterocyte effacement 6 17 distribution. Despite their classification as a group distinct (LEE) region and pEAF independently. from the other pathotypes, the designation of DAEC as a differ- In turn, aEPEC belong to a large diversity of classical 12,16,18 ent DEC pathotype requires further epidemiological studies, and non-classical serotypes. Over 20% of strains of which have been hampered by the difficulties in its identifi- non-classical EPEC serotypes are O non-typeable and the O- 5 cation and classification. Furthermore, certain E. coli strains typeable strains belong to more than 4200 different serotypes, 12,18 that have been classified as the adherent invasive E. coli (AIEC) with many non-motile and H non-typeable strains. Inter- pathotype, comprise one of the potential agents for Crohn’s estingly, it has been found that 35% of the aEPEC strains also 17 disease (CD). CD is an inflammatory bowel disease (IBD), which belong to the tEPEC lineages. Thus, it has been hypothe- is thought to be caused by a combination of factors (genetics, sized that at least some aEPEC may have originated from tEPEC 17,19,20 the intestinal microbiota, environmental factors, and enteric strains that lost pEAF in the host or in the environment. pathogens).7,8 Diarrheal episodes due to DEC infections are an important Virulence factors, mechanisms and pathogenesis public health issue among children and adults in develop- ing countries, because of their association with morbidity and Typical EPEC strains adhere to HeLa, HEp-2, and other cell lines mortality of children less than five years of age. It was our aim and to organ cultures in vitro in a distinctive pattern of three- with this review to gather information on current definitions, dimensional microcolonies, a so-called localized adherence 6,21 serotypes, lineages, virulence mechanisms, epidemiology, and (LA) pattern. A similar adherence pattern has been seen 22 diagnosis of the major DEC pathotypes with emphasis on the in tissue biopsies of EPEC-infected humans. 23 studies conducted in Brazil. The LA phenotype is mediated by the BFP, which also contributes to antigenicity, autoaggregation, and biofilm 23–27 formation. An operon of 14 genes contained on the pEAF Typical and atypical enteropathogenic E. coli is necessary for BFP expression, with bfpA encoding the major 28 structural subunit (bundlin) and being highly conserved The term enteropathogenic E. coli (EPEC) was first used in among EPEC1 and EPEC2 strains. 9 1995 by Neter et al., to describe a number of E. coli strains The self-transmissible pEAF pMAR2 is found among epidemiologically related to a series of outbreaks of infantile strains of the EPEC1 lineage and contains an intact transfer 10,11 diarrhea in the 1940s and 1950s. Originally identified by region, unlike pB171, which is more common among EPEC2 29,30 23 serotype, EPEC are now defined as those E. coli strains having strains. Besides the bfp gene cluster, encoding BFP, the the ability to cause diarrhea, to produce a histopathology on pEAF carries the per locus, encoding the transcriptional activa- 29 the intestinal epithelium known as the attaching and effac- tor called plasmid-encoded regulator (Per).
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