While there are relatively few microbial pathogens which are tested for in foods compared to the number of chemicals which might be sought, the holy trinity of cheap, sensitive and rapid methods remains elusive. As the old saying goes ‘pick any two’!
One of the biggest problems in testing for foodborne pathogens is the need to detect their presence at very low concentrations. Standard cultural methods theoretically can detect 1 cell in a 25g sample, equating to 0.04 cell/g. This level of sensitivity cannot be classed as overkill since pathogens can be present in foods associated with outbreaks at very low concentrations. For example Salmonella has been reported at concentrations of around 1 cell in 20g in outbreaks involving flour, paprika flavoured crisps(1), tahini(2), ice cream(3) and herbal tea(4); and as low as 1 cell in 250g in powdered infant formula(5).