Fecundity of STEC strains in <i>C</i>. <i>elegans</i> compared to that of the <i>E</i>. <i>coli</i> OP50 strain.

<p>Brood sizes of <i>C</i>. <i>elegans</i> were examined at 20°C. n>10 in each case.</p

Correlation between the life span and fertility of <i>C</i>. <i>elegans</i> infected with STEC strains.

<p>The STEC (E15, E18 and E22) strains showed an increase in colonisation, which correlates with a decrease in longevity and fertility of the worm (<i>C</i>. <i>elegans</i>). This is considered evidence of STEC pathogenicity in the <i>C</i>. <i>elegans</i> model.</p

<i>In vivo</i> screening platform for shiga toxin-producing <i>Escherichia coli</i> (STEC) using <i>Caenorhabditis elegans</i> as a model

<div><p>Shiga toxin-producing <i>Escherichia coli</i> (STEC) strains are the main cause of bacillary dysentery, although STEC strains generally induce milder disease symptoms compared to <i>Shigella</i> specie<i>s</i>. This study aimed to determine the virulence of STEC using the nematode <i>Caenorhabditis elegans</i> as a model host. Worm killing, fertility and bacterial colonisation assays were performed to examine the potential difference in the virulence of STEC strains compared to that of the control <i>E</i>. <i>coli</i> OP50 strains on which worms were fed. A statistically significant difference in the survival rates of <i>C</i>. <i>elegans</i> was observed in that the STEC strains caused death in 8–10 days and the <i>E</i>. <i>coli</i> OP50 strains caused death in 15 days. STEC strains severely reduced the fertility of the worms. The intestinal load of bacteria in the adult stage nematodes harbouring the <i>E</i>. <i>coli</i> OP50 strains was found to be 3.5 log CFU mL^-1. In contrast, the STEC strains E15, E18 and E22 harboured 4.1, 4.2 and 4.7 log CFU ml⁻¹ per nematode, respectively. The heat-killed STEC strains significantly increased the longevity of the worms compared to the non-heated STEC strains. In addition, PCR-based genomic profiling of shiga toxin genes, viz., stx1 and stx2, identified in selected STEC strains revealed that these toxins may be associated with the virulence of the STEC strains. This study demonstrated that <i>C</i>. <i>elegans</i> is an effective model to examine and compare the pathogenicity and virulence variation of STEC strains to that of <i>E</i>. <i>coli</i> OP50 strains.</p></div

Conventional PCR and colonisation assay.

<p><b>Conventional PCR</b>: Based on the results of the life span assay, 6 STEC strains (L1—E1; L2—E3; L3—E12; L4—E15; L5—E18; L6—E22; L7 –OP50) out of the 24 strains were selected for further testing for the presence of toxin genes (stx1, stx2 and groEL) using 3 primer pairs (STX1-F/R-O157; STX2-F/R-O157; GroEL-F/R-O157) targeting the genes specific for toxin production(stx1, stx2 and groEL). <b>Colonisation assay</b>: The STEC strains colonised in the intestinal tract of L2 worms (log CFU/worm). p<0.001 was obtained for comparison with the <i>E</i>. <i>coli</i> OP50 control group by the t-test. The total numbers of worms (<i>C</i>. <i>elegans</i>) tested in each group are indicated by n.</p

Bacterial (<i>E</i>. <i>coli)</i> strains used in the study and their respective sources.

<p>Bacterial (<i>E</i>. <i>coli)</i> strains used in the study and their respective sources.</p

Life span assay for <i>C</i>. <i>elegans</i> infected with STEC strains compared to that for <i>C</i>. <i>elegans</i> infected with the control <i>E</i>. <i>coli</i> OP50 strain.

<p><i>C</i>. <i>elegans</i> grown on STEC plates were significantly short-lived compared to those grown on <i>E</i>. <i>coli</i> OP50 plates. The <i>E</i>. <i>coli</i> OP50 strain was compared to 24 different STEC strains (A-L).A) Longevity of <i>C</i>. <i>elegans</i> grown on the <i>E</i>. <i>coli</i> OP50 strain compared to that of <i>C</i>. <i>elegans</i> grown on the E1 and E2 strains. <i>C</i>. <i>elegans</i> grown on both E1 andE2 exhibited a decreased life span at the end of 10 days, but <i>C</i>. <i>elegans</i> grown on <i>E</i>. <i>coli</i> OP50 survived for 15 days. B) Longevity of <i>C</i>. <i>elegans</i> grown on the <i>E</i>. <i>coli</i> OP50 strain compared to that of <i>C</i>. <i>elegans</i> grown on the E3 and E4 strains. <i>C</i>. <i>elegans</i> grown on both E3 and E4 exhibited a decreased life span, but when compared to <i>C</i>. <i>elegans</i> grown on <i>E</i>. <i>coli</i> OP50, <i>C</i>. <i>elegans</i> grown on E3 survived for 8 days, and <i>C</i>. <i>elegans</i> grown on E4 survived for 10 days. C) Longevity of <i>C</i>. <i>elegans</i> grown on the <i>E</i>. <i>coli</i> OP50 strain compared to that of <i>C</i>. <i>elegans</i> grown on the E5 and E6 strains. <i>C</i>. <i>elegans</i> grown on both E5 and E6 exhibited a decreased life span at the end of 10 days, but <i>C</i>. <i>elegans</i> grown on <i>E</i>. <i>coli</i> OP50 survived for 15 days. D) Longevity of <i>C</i>. <i>elegans</i> grown on the <i>E</i>. <i>coli</i> OP50 strain compared to that of <i>C</i>. <i>elegans</i> grown on the E7 and E8 strains. <i>C</i>. <i>elegans</i> grown on both E7 and E8 exhibited a decreased life span at the end of 10 days, but <i>C</i>. <i>elegans</i> grown on <i>E</i>. <i>coli</i> OP50 survived for 15 days. E) Longevity of <i>C</i>. <i>elegans</i> grown on the <i>E</i>. <i>coli</i> OP50 strain compared to that of <i>C</i>. <i>elegans</i> grown on the E9 and E10 strains. <i>C</i>. <i>elegans</i> grown on both E9 and E10exhibited a decreased life span at the end of 10 days, but <i>C</i>. <i>elegans</i> grown on <i>E</i>. <i>coli</i> OP50 survived for 15 days. F) Longevity of <i>C</i>. <i>elegans</i> grown on the <i>E</i>. <i>coli</i> OP50 strain compared to that of <i>C</i>. <i>elegans</i> grown on the E11 and E12 strains. <i>C</i>. <i>elegans</i> grown on both E11 and E12 showed a decreased life span at the end of 10 days, but <i>C</i>. <i>elegans</i> grown on <i>E</i>. <i>coli</i> OP50 survived for 15 days. G) Longevity of <i>C</i>. <i>elegans</i> grown on the <i>E</i>. <i>coli</i> OP50 strain compared that of <i>C</i>. <i>elegans</i> grown on the E13 and E14 strains. <i>C</i>. <i>elegans</i> grown on both E13 and E14 exhibited a decreased life span at the end of 10 days, but <i>C</i>. <i>elegans</i> grown on <i>E</i>. <i>coli</i> OP50 survived for 15 days. H) Longevity of <i>C</i>. <i>elegans</i> grown on the <i>E</i>. <i>coli</i> OP50 strain compared to that of <i>C</i>. <i>elegans</i> grown on the E15 and E16 strains. <i>C</i>. <i>elegans</i> grown on both E15 and E16 exhibited a decreased life span at the end of 9 days, but <i>C</i>. <i>elegans</i> grown on <i>E</i>. <i>coli</i> OP50 survived for 15 days. I) Longevity of <i>C</i>. <i>elegans</i> grown on the <i>E</i>. <i>coli</i> OP50 strain compared to that of <i>C</i>. <i>elegans</i> grown on the E17 and E18 strains. <i>C</i>. <i>elegans</i> grown on E17 exhibited a decreased life span at the end of 10 days, and <i>C</i>. <i>elegans</i> grown on E18 surprisingly survived for 6 days, but <i>C</i>. <i>elegans</i> grown on <i>E</i>. <i>coli</i> OP50 survived for 15 days. J) Longevity of <i>C</i>. <i>elegans</i> grown on the <i>E</i>. <i>coli</i> OP50 strain compared that of <i>C</i>. <i>elegans</i> grown on the E19 and E20 strains. <i>C</i>. <i>elegans</i> grown on both E19 and E20 exhibited a decreased life span at the end of 9 days, but <i>C</i>. <i>elegans</i> grown on <i>E</i>. <i>coli</i>OP50 survived for 15 days. K) Longevity of <i>C</i>. <i>elegans</i> grown on the <i>E</i>. <i>coli</i> OP50 strain compared to that of <i>C</i>. <i>elegans</i> grown on the E21 and E22 strains. <i>C</i>. <i>elegans</i> grown on E21 showed a decreased life span at the end of 10 days, and in contrast, <i>C</i>. <i>elegans</i> grown on E22 survived for 7 days, but <i>C</i>. <i>elegans</i> grown on <i>E</i>. <i>coli</i> OP50 survived for 15 days. L) Longevity of <i>C</i>. <i>elegans</i> grown on the <i>E</i>. <i>coli</i> OP50 strain compared to that of <i>C</i>. <i>elegans</i> grown on the E23 and E24 strains. <i>C</i>. <i>elegans</i> grown on E23 showed a decreased life span at the end of 11 days, and in contrast, <i>C</i>. <i>elegans</i> grown on E24 survived for 9 days, but <i>C</i>. <i>elegans</i> grown on <i>E</i>. <i>coli</i> OP50 survived for 15 days.</p