CHAPITRE 1 - Université de Bourgogne
CHAPITRE 1 - Université de Bourgogne
CHAPITRE 1 - Université de Bourgogne
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acteria and the ability of producing recombinant phage proteins for specific capture of<br />
bacteria must be consi<strong>de</strong>red as a tool with unrivalled properties for bacterial <strong>de</strong>tection<br />
methods.<br />
This novel phage immuno-concentration method was compared to IMS. Nevertheless, with<br />
IMS method, serogroups are immuno-concentrated separately. The IMS reagents are<br />
serogroup specific while with the VIDAS ESPT immuno-concentrates refine serogroups<br />
simultaneously. One must be aware that this test is an automated system.<br />
This study was <strong>de</strong>signed to compare the VIDAS ESPT and IMS method for their ability to<br />
enrich the levels of STEC in samples after enrichment. Sensitivity and specificity studies were<br />
realised on pure cultures and on artificially inoculated meat samples.<br />
For the specificity study, the non-specific strains were tested at high concentrations (10 8<br />
CFU/mL). We could conjectured that the two strains (Citrobacter and “V21”E. coli) were<br />
found positive with the VIDAS ESPT because of such high concentration. In this context,<br />
specificity of the VIDAS ESPT for E. coli O26, O103, O111 and O145 could be enhanced by<br />
the introduction of more selective media. More discriminated media are nee<strong>de</strong>d for the<br />
<strong>de</strong>tection of E. coli O26, O103, O111 and O145. Hiramatsu et al. have shown that many<br />
strains of E. coli O26 do not ferment rhamnose. This finding suggested that MacConkey agar<br />
containing rhamnose may be used to enhance the <strong>de</strong>tection of this serogroup from faecal and<br />
food samples (Hiramatsu et al., 2002). Possé et al. (2008) <strong>de</strong>scribed a new differential and<br />
confirmation media for O26, O103, O111, O145 and O157 isolation from food or faeces.<br />
Our study showed that both the VIDAS ESPT and IMS methods produced comparable results.<br />
However with VIDAS ESPT, less background microflora was presented on the selective<br />
plates. Sensitivity thresholds were around 10 3 CFU/mL in pure culture mixed or not, and<br />
approximatively10 4 CFU/mL in artificially inoculated meat samples.<br />
VIDAS ESPT showed some variability in the sensitivity threshold between serogroups both in<br />
pure culture and in beef matrices tested. Multiple factors might explain the difference in cell-<br />
capture efficiency. For example, interference from components of the ground beef (fat<br />
molecules, background microflora…) might interact with the phage protein or the surface of<br />
the bacteria, which may block the binding. The variability in sensitivity between serogroups<br />
could be explained by different affinity constants between the phage protein and the specific<br />
bacterial binding site.<br />
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