Abstract
To discern if there was a particular genotype associated with clinical enteroaggregative Escherichia coli (EAEC) strains isolated from deployed military personnel (DMP) with travelers' diarrhea (TD), we characterized a collection of EAEC from DMP deployed to Afghanistan, Djibouti, Kenya, or Honduras. Although we did not identify a specific EAEC genotype associated with TD in DMP, we found that EAEC isolated at the first clinic visit were more likely to encode the dispersin gene aap than EAEC collected at follow-up visits. A majority of the EAEC isolates were typical EAEC that adhered to HEp-2 cells, formed biofilms, and harbored genes for aggregative adherence fimbriae (AAF), AggR, and serine protease autotransporters of Enterobacteriaceae (SPATEs). A separate subset of the EAEC had aggR and genes for SPATEs but encoded a gene highly homologous to that for CS22, a fimbriae more commonly found in enterotoxigenic E. coli. None of these CS22-encoding EAEC formed biofilms in vitro or adhered to HEp-2 cells. Whole genome sequence and single nucleotide polymorphism analyses demonstrated that most of the strains were genetically diverse, but that a few were closely related. Isolation of these related strains occurred within days to more than a year apart, a finding that suggests a persistent source and genomic stability. In an ampicillin-treated mouse model we found that an agg4A+ aar- isolate formed a biofilm in the intestine and caused reduced weight gain in mice, whereas a strain that did not form an in vivo biofilm caused no morbidity. Our diverse strain collection from DMP displays the heterogeneity of EAEC strains isolated from human patients, and our mouse model of infection indicated the genotype agg4A+ aar– and/or capacity to form biofilm in vivo may correlate to disease severity.
Highlights
Enteroaggregative Escherichia coli (EAEC) is a causative agent of both acute and persistent diarrhea in adults and children (Okeke and Nataro, 2001)
Isolates that were positive in our laboratory by PCR for aatA and/or aaiC were screened by PCR for aggregative adherence fimbriae (AAF) and serine protease autotransporters of Enterobacteriaceae (SPATEs) genes as well as for aggR and aar and tested for resistance to Amp by overnight growth on Luria Bertani (LB) agar supplemented with 100 μg/ml Amp
We found examples of isolates that were more distantly related isolated from patients on the same day or 1 day apart [E7V1A compared to E8V1A (18,832 SNPs); E37V1A compared to the E13 strains; K40V1 compared to K38V1 and K39V1], findings that indicate that deployed military personnel (DMP) may be exposed to multiple types of enteroaggregative Escherichia coli (EAEC) in the same geographic location
Summary
Enteroaggregative Escherichia coli (EAEC) is a causative agent of both acute and persistent diarrhea in adults and children (Okeke and Nataro, 2001). EAEC is typically the third most identified enteropathogen responsible for TD, whereas EAEC is the second most common bacterial etiologic agent of TD in military travelers (Zboromyrska et al, 2014; Zaidi and Wine, 2015; Porter et al, 2017; Olson et al, 2019) For those deployed military personnel (DMP), TD is a leading cause of lost duty-days (Porter et al, 2017). The genes for the AAF are located on the plasmid of aggregative adherence (pAA), and except for one reported strain (Jonsson et al, 2017), EAEC only encode one of the five AAF types. Two examples of genes commonly found in EAEC that are regulated by AggR include the type 6 secretion system (T6SS) effector of unknown function, aaiC, and aatA, which encodes a component of the dispersin transport system. Other factors that may contribute to adherence by EAEC include heat-resistant hemagglutinin (Bhargava et al, 2009), long polar fimbriae (Ross et al, 2015), E. coli common pilus (Avelino et al, 2010), and Pil (Dudley et al, 2006; Garcia et al, 2019)
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