Characterisation of STEC and other diarrheic E. coli isolated on CHROMagar™STEC at a tertiary referral hospital, Cape Town

Abstract

BackgroundShiga toxin producing E. coli (STEC) is an emerging zoonotic pathogen that can cause acute renal failure, especially in children. Clinical microbiology laboratories may fail to detect STEC and other diarrhoeic E. coli unless purposive rigorous screening procedures are followed using appropriate diagnostic technology; CHROMagar™STEC has rarely been used for isolation of African diarrhoeic E. coli hence characteristics of isolates on this medium are not yet fully understood. This study aimed to determine the prevalence and characteristics of STEC and other diarrhoeic E. coli isolated on CHROMagar™STEC from stool samples submitted to the microbiology laboratory of a South African public sector tertiary care hospital.ResultsIn total, 733 stool samples were tested. Of these, 4.5% (33/733) possessed diarrhoeic E. coli. Of the diarrheic E. coli, 5/33 (15.2%) were STEC, 15/33 (45.5%) EAggEC, 6/33 (18.2%) atypical EPEC, 5/33 (15.2%) typical EPEC, and 1/33 (3%) DAEC. None of the STEC isolates had been identified by routine testing (based on using sorbitol media to test for E. coli O157: H7 strains and not the other STEC) in the laboratory. Of the 33 strains, 55% (95% CI = 40.8–72.7) showed resistance to ampicillin.ConclusionsCHROMagar™STEC enabled detection of tellurite - resistant diarrhoeic E. coli that would be missed using routine methods. Further studies are needed to determine the proportion and characteristics of those which might have been missed using this approach.

Evaluation of chromogenic selective agar (CHROMagar STEC) for the direct detection of Shiga toxin-producing Escherichia coli from faecal specimens

“…Previous studies evaluating CHROMagar STEC have focused on the non-O157 serogroups most likely to cause severe symptoms, STEC O26, O103, O111, O121, O145 and O45, referred to in the literature as the ‘top six’; while others have included a wider range of STEC serogroups [8–11, 17, 18]. With the exception of Wylie et al .…”

“…All 106 isolates of STEC that grew on CHROMagar STEC had the ter gene cassette, which in STEC O157:H7 comprises eight genes terZ, terA, terB, terC, terD, terE, terF and terW [19, 20]. Correlation of growth of STEC on CHROMagar STEC with the presence of the ter gene cassette encoding resistance to tellurite is well documented in the literature [8–11, 17, 18]. Successful detection of STEC in a complex background requires an agar medium that suppresses the growth of background micro-organisms with minimal suppression of target STECs.…”

Diversity of the Tellurite Resistance Gene Operon in Escherichia coli

“…Comparative genome analyses indicated that the ter operons and their carrier elements are highly conserved among STEC strains belonging to the major serotypes (Ogura et al, 2009;Lorenz et al, 2017). Some STEC isolates, such as STEC O104:H4 and O178:H19, and non-STEC E. coli isolates also carry ter operons and/or show significant tellurite resistance (Orth et al, 2007;Gouali et al, 2013;Miko et al, 2014;Ferdous et al, 2015;Verhaegen et al, 2015;Kalule et al, 2018;Nguyen et al, 2021). A uropathogenic E. coli isolate was found to carry the ter operon on a large conjugative plasmid (Soltys et al, 2018).…”

Characterization of bacterial communities associated with blood-fed and starved tropical bed bugs, Cimex hemipterus (F.) (Hemiptera): a high throughput metabarcoding analysis

“…With the development of next-generation sequencing (NGS) and bioinformatics, metagenomics study becomes more convenient, efficient, cost-effective and overcome the problem of which most of the microorganism cannot be isolated and maintained in pure culture 12 , 13 . Many metagenomic studies of arthropods including mosquito 14 , tick 15 , assassin bugs 16 , tsetse flies 17 as well as common bed bugs 18 had used the sequencing of 16S rRNA gene to characterize the microbiota. However, the microbiome of tropical bed bugs, C. hemipterus , remains mostly unexplored, and the application of high-throughput sequencing in the characterization of bacteria community in tropical bed bugs is not available.…”