Enteroaggregative Escherichia coli Virulence Factors Are Found To Be Associated with Infantile Diarrhea in Brazil

Abstract

We have previously shown that enteroaggregative Escherichia coli (EAEC) is an important pathogen among Brazilian infants. Most EAEC strains harbor a plasmid (pAA) from which a DNA fragment has been used as a probe (EAEC probe). To better understand the characteristics of EAEC in Brazil, 109 strains carrying and lacking the EAEC probe sequence were tested for the presence of pAA plasmid-borne and chromosomal factors. Common virulence factors of probe-positive and probe-negative isolates included the presence of the Pet, EAST-1, Shf, Irp2, ShET1/Pic, and Hly virulence markers. The presence of AggR or one other virulence factor (AAF/I, AAF/II, AAF/III, or Aap) was predominantly identified only in probe-positive strains. In EAEC probepositive strains, the virulence marker Aap was found significantly more frequently (P ‫؍‬ 0.023) in isolates from children with diarrhea (22%) than in isolates from controls (3%). EAST-1 and Shf were the markers most frequently detected (61%) in EAEC probe-negative strains and were found to be significantly associated with diarrhea (P ‫؍‬ 0.003 and P ‫؍‬ 0.020, respectively). Furthermore, our data suggest that AggR can be used as an important genetic marker for EAEC probe-positive strains.Enteroaggregative Escherichia coli (EAEC) is increasingly recognized as a cause of diarrhea worldwide (18). EAEC is defined by its characteristic "stacked brick" aggregative adherence (AA) pattern of adherence to HEp-2 cell (17). Most EAEC strains harbor a 60-to 65-MDa virulence plasmid (pAA). A 1-kb fragment of pAA, referred to as the EAEC probe or CVD432 (1), has been widely used for epidemiological studies (7,19,25,29). The pAA plasmid also encodes AA fimbriae (AAF) I, II, and III (2, 4, 15); the transcriptional activator AggR (16); enteroaggregative heat-stable enterotoxin 1 (EAST-1) (23); a 104-kDa cytotoxin designated Pet (8); the cryptic secreted protein Shf (5); and a novel antiaggregation protein (dispersin) encoded by the aap gene (formerly known as aspU) (27). In addition to the pAA plasmid, some EAEC strains express putative virulence factors that are encoded on the chromosome, including a 116-kDa secreted mucinase (Pic) (12), yersiniabactin (26), and the E. coli ␣-hemolysin (30). Shigella enterotoxin 1 (ShET1) is encoded by the antisense strand of the pic gene (10, 21). However, none of these factors is consistently found in all EAEC isolates, as determined by hybridization studies.To find a specific virulence marker for the detection of EAEC in epidemiological and clinical studies, we tested 109 strains, isolated from Brazilian children in a previously described study (25), for their abilities to hybridize to eight pAA plasmid-derived and three chromosomal gene probes. MATERIALS AND METHODSBacterial strains. The strains examined in this work were isolated during a study of the epidemiology of acute diarrhea in children less than 2 years old conducted in different regions of Brazil from 1997 to 1999 (25). The children were admitted to public hospitals in the following cities (states) for t...

Detection of diarrheagenic Escherichia coli from children with and without diarrhea in Salvador, Bahia, Brazil

“…ETEC and EAEC have been frequently detected in children with diarrhea in studies conducted in Brazil and in other countries (Gomes et al 1991, Nataro & Kaper 1998, Scaletsky et al 2002, Zamboni et al 2004, Regua-Mangia et al 2004, which is in agreement with the results reported in this study. EAEC is emerging as an enteric pathogen of great concern, responsible for acute and persistent diarrhea (≥ 14 days) and may cause malnutrition and growth defects in children.…”

Putative Virulence Genes and Biofilm Production Among Typical Enteroaggregative Escherichia coli Isolates from Diarrhoeic Children in Kashmir and Andhra Pradesh

“…Besides, pCVD432 and aggR, the most frequent plasmid-borne genes detected among the EAEC isolates were aap, irp2 and shf. These findings are in agreement with those of a previous study in Kolkata, India [10] and elsewhere [4,23]. The aap gene is under the control of aggR.…”

Molecular Characterization of Diarrheagenic Escherichia coli from Libya

“…Several workers reported relatively similar results. 15,45 Recently, Harrington and others 46 suggested the term "typical EAEC" to refer to strains expressing the aggR regulon. Results of this study show an abundance of typical rather than atypical EAEC among diarrheic Libyan children, as reported elsewhere.…”