Characterization of Toxins and Colonization Factors of Enterotoxigenic Escherichia coli Isolates from Children with Acute Diarrhea in Abuja, Nigeria

Abstract

Background: Heat-labile (LT) and heat-stable (ST) toxin variants of enterotoxigenic Escherichia coli (ETEC) are enterotoxins associated with diarrhea among children in Abuja, Nigeria. Enterotoxigenic Escherichia coli is also known as a major etiological agent of diarrheal disease among travelers in developing countries. Continuous identification of commonly expressed bacterial components of ETEC can help extend the protective spectra of future candidate ETEC vaccines in Nigeria. Objectives: This study aimed to provide new insights into the distribution patterns of enterotoxins, colonization factor antigens (CFA phenotypes), and serotypes and to determine the antimicrobial susceptibility patterns of ETEC strains from children with acute diarrhea in Abuja, Nigeria. Methods: Escherichia coli strains, isolated from the stool samples of children aged 0 -60 months, were tested via polymerase chain reaction, ganglioside GM1 ELISA assay, hemagglutination assay, HEp-2 cell adherence assay, dot blot technique, and disc diffusion method for antimicrobial resistance. Results: Rnterotoxigenic Escherichia coli was detected in 16 (4.0%) out of 400 children with acute diarrhea. The toxigenic genotypes expressed by ETEC strains included LT toxin gene 6 (37.5%), ST toxin gene 6 (37.5%), and ST/LT gene 4 (25.0%). The CF phenotypes with major expression included CS2 (25.0%), CS3 (12.5%), and CFA1 (6.3%), with a probability value below 0.05 (P < 0.05). However, no CFA/CS was detected in 56.3% of ETEC strains. Multidrug resistance pattern of nalidixic acid-ciprofloxacin-amoxicillin-augmentincephalexin-cefuroxime was observed in 19% of ETEC strains. The most prevalent ETEC serotype was O8: H9 (n, 5). Based on the findings, ETEC infection peaked to 7.2% in July. Conclusion: Although ST and LT toxins seem to have equal distributions in the analyzed population, continuous identification of CFA phenotypes and toxins is necessary for the evaluation of ETEC vaccines in Nigeria.

Molecular characterization of enterotoxigenic Escherichia coli toxins and colonization factors in children under five years with acute diarrhea attending Kisii Teaching and Referral Hospital, Kenya

“…A similar finding was also reported in a study across four regions of the world and the Global Enteric Multicenter Study where ST was the most frequent toxin [ 25 , 26 ]. However, these findings are not in agreement with reports of a study in Nigeria where ST and LT toxins were detected equally among the ETEC isolates [ 8 ]. Additionally, a study in Bolivia reported that LT was the most common toxin followed by LT/ST and the least was ST. [ 22 ].…”

“…The lack of an identifiable CF could be explained by the following reasons; loss of plasmid harboring the CFs genes due to repeated sub culturing or long-term storage; down regulation of CF genes; a mutation within the genetic locus; expression of a CF not covered by the primers used in the PCR panel and CFs that are unknown and have not been classified [ 7 , 13 , 23 , 28 ]. The lack of CF has been reported to be mainly related to LT strains [ 8 , 13 , 27 , 32 ] which is consistent with our results where 60% of the LT strains lacked a detectable CF. However, some studies have reported that CFs is almost equally associated with LT and ST-positive ETEC strains [ 8 , 28 ].…”

“…We detected CFs genes in 60.9% of the ETEC strains similar to a study in Peru where it was detected at 65% [ 27 ] but lower than 80% reported by Kharat et al [ 25 ]. Our finding is higher than the finding in studies carried out in Nigeria (43.7%), Brazil (50%) and Indonesia (18.2%) [ 7 , 8 , 28 ]. CS6 was the most detected CFs in our study.…”

“…Enterotoxigenic E. coli is identified by its ability to produce plasmid encoded heat-labile (LT) and/or heat-stable (ST) enterotoxins [ 7 , 8 ]. Based on their host species, ST enterotoxins are further divided into heat-stable enterotoxins of porcine origin (STp) and heat-stable enterotoxins of human origin (STh).…”

“…Colonization of the small intestine epithelial cells by ETEC is mediated by means of antigenically diverse thread like appendages (fimbriae) called colonization factors (CF) [ 7 ]. These factors are also referred to as colonization factor antigen 1 (CFA/1) or coli surface (CS) antigen [ 8 ]. To date, more than 25 CFs have been identified and are classified into three families: (i) CFA/I group which include: CFA/I, CS1, CS2, CS4, CS14 and CS17 (ii) CS5 like group which include: CS5, CS7, CS18 and CS20 and (iii) a distinct group which include: CS3, CS6, CS10, CS11 and CS12 [ 12 ].…”