Isolation Procedure
200 μl of prepared sample of a meat rinse solution was
streaked onto MacConkey agar (IVD, UK) plates and
incubated at 37°C for 24 hrs. Following incubation,
lactose-positive (pink) colonies were streaked onto
Sorbitol-MacConkey Agar (IVD, UK) plates and incubated
at 37°C for 24 hrs. The sorbitol negative colorless
colonies were sub-cultured on Rainbow agar.
Rainbow Agar O157 (Hayward, USA) was inoculated
by spreading a suspected colonies of E. coli on its surface.
The plates were then incubated for 20 to 24 hrs, or
longer, at 37°C and observed for the presence of colored
colonies. The distinctive black or gray coloration of E.
coli O157 colonies were easily viewed by laying the Petri
dish against a white background. Upon sub-culturing,
the isolated E. coli O157 colonies showed their typical
black or gray coloration (BiOLOG User Guide 2008).
These colonies were tested further using BiOLOG identification
system to confirm their identity as E. coli and
for any isolate identified as E. coli O157:H7 additional
confirmation by serology may be recommended for the
reasons of serious implications when this pathogen is
determined in a food sample.