*7.2.2 Secretion of cytotoxins*

DAEC secretes a class I SPATE toxin that is called secreted autotransporter toxin (Sat), encoded by *sat* gene. Sat is reported to have enterotoxic activity in an animal model, and mediate the induction of fluid accumulation, loss of microvilli, inflammation, and polymorphonuclear lymphocytes (PMNL) infiltration, like the LT effect of ETEC (**Figure 3**) [184]. Although *sat* gene is reported to be equally expressed in DAEC strains from diarrheal and asymptomatic adults, this gene is significantly associated with DAEC-related diarrhea in children [183]. For example, in two studies, *sat* gene was identified in 44–63% of DAEC strains collected from children with diarrhea while it was found in 0–20% of DAEC strains from asymptomatic children [183–185]. Noteworthy, *sat* gene is not exclusive for DAEC pathotype. In fact, it is prevalent in other *E. coli* pathotypes including EAEC and UPEC [186]. Other virulence factors that have been reported in DAEC include *pet* [187]*, astA* [187], and *senB* [188] genes that encode enterotoxins and *hlyE* gene that encodes alpha-hemolysin [186]. However, the role of these genes in the pathogenesis of DAEC still remains unclear.

### **7.3 Antibiotic resistance in DAEC**

Oral rehydration solution therapy is the only recommended treatment for DAEC-related watery diarrhea. However, there are reports of antibiotic resistance in this pathotype. In a study of 112 DAEC strains isolated from children with watery diarrhea in Brazil [179], all DAEC isolates were susceptible to five antibiotics including gentamicin, ofloxacin, and nalidixic acid while 70% were resistant to three or more antibiotics and 50% showed resistance to either ampicillin, co-trimoxazole, streptomycin, sulfonamide, or tetracycline. Additionally, 20% of the strains were resistant to chloramphenicol [179]. A similar observation was noted in a study from Iran where 75–100% of DAEC strains from pediatric diarrhea were resistant to ampicillin, cefotaxime, and trimethoprim-sulfamethoxazole [182].

#### **7.4 Population structure of DAEC**

DAEC is a heterogeneous group that has also been implicated in extraintestinal infections such as UTI. Despite its implication in diarrhea in children, studies on its population structure are limited. The few studies available on the phylogenetic

*The Biology and the Evolutionary Dynamics of Diarrheagenic* Escherichia coli *Pathotypes DOI: http://dx.doi.org/10.5772/intechopen.101567*

analysis of DAEC strains using MLEE reported that they are distributed among all of the phylogroups [47, 156, 189]. Conversely, a study of 31 DAEC strains from diarrhea and asymptomatic carriers in Peru reported that 87% of the isolates belonged to phylogroup D [190]. A large-scale genomic analysis of DAEC strains would be important to understand the population structure, determine dissemination and transmission dynamics of genetic lineages of this pathotype, as well as identify novel virulence determinants and other genetic factors that contribute to its pathoadaptation in the intestinal epithelium.
