Lab M has extended its range of immunomagnetic separation (IMS) products for the isolation of Shiga Toxin-Producing Escherichia coli (STEC) strains.
Captivate O45 comprises magnetic particles coated with specific antibody and is intended for the concentration of E. coli O45 from food, animal feed, beverages, or environmental samples.
It can be used in automated IMS systems and the traditional manual method.
Samples are enriched for 16-24 hours and IMS takes one hour. The magnetic beads are then plated onto appropriate agar medium and incubated for a further 16-24 hours.
Dr Chris Potter, head of R&D, said detection threshold is one cell per test volume since the superparamagnetic beads are coated in purified antibodies specifically targeted at the antigen of interest.
“E.coli O45 is a member of the USDA ‘Big Six’, in that it was shown to be one of the more prevalent STEC serogroups reported in the USA,” he said.
“The demand from this market initially justified the development of the product and it was later shown to be significant in other parts of the world. IMS is an ideal tool for the isolation of STEC E.coli because of the defined outer membrane target for these organisms.
“The R&D team at Lab M closely follows developments throughout the food microbiology field in order to anticipate the most significant challenges for our customers.”
Why use IMS?
IMS is the only specific E. coli O45 isolation process in which a microbiological culture is obtained.
Captivate separates E. coli O45 from background flora in a sample, ensuring that only organisms having O45 antigens are captured.
Particle-organism complexes are then easily inoculated to specific microbiological culture media.
Potter said IMS can be used in a number of different ways.
“Typically it is used after pre-enrichment to specifically isolate target organisms amongst a high non-target background,” he said.
“IMS is also used in cases where a positive result has been generated using a rapid method such as PCR or ELISA.
“Here the enriched sample that gave the positive result is subjected to IMS in order to retrieve the organism of interest for confirmatory testing.”
E.coliO45 is not biochemically unique and on traditional plating media is very difficult, if not currently impossible, to distinguish from other E.coli, said Potter.
“Specific isolation and concentration of O45 using IMS allows a high degree of confidence that the organisms isolated are those possessing the O45 antigenic target.
“Furthermore, IMS yields live organisms. These can be subjected to further testing if necessary.”
The standard PD CEN ISO/TS 13136:2012 is the one in use and the first ISO standard that requires PCR as a core part of the method.
“Previous standards have mostly been designed around traditional microbiology methods, i.e. enrichment and plating,” said Potter.
“However, due to the lack of suitable diagnostic media for the majority of STEC E. Coli, PCR is required for detection.”
Potter said the standard references E. coli O157, O111, O26, O103 and O145 serogroups.
“However if a positive PCR result indicates the presence of a STEC E.coli but fails to confirm it as one of the reference serogroups, it is still reported and further testing is carried out.
“This is to account for the high genomic plasticity of this bacterial species. Such plasticity permits novel arrangements of the organism’s virulence features, which in turn gives rise to novel sero-pathogroups.
“It is therefore critical that all the tools needed to test for such pathogens are immediately ready for laboratories to use.”