Investigate growth conditions for pathogens.
A notion that gained momentum in the past was that populations of C. jejuni under stress gradually lose the ability to grow on agar plates and be detected, but they might grow when consumed and cause illness. This would have serious consequences for the microbiological quality assurance of the food supply. However, no evidence has emerged to support this view.
All the evidence indicates that stressed populations of Campylobacter spp. are always curable when they are capable of colonizing a host, and that the loss of culturability always follows the loss of colonizing ability. In addition, various attempts have been made to define food environments that would uncouple toxin production from growth so that even if the growth of a pathogen occurred accidently in a product, the production of toxins would be minimized.
Researchers also have investigated acid-resistant strains of E. coli O157:H7. All forms of E. coli appear to be sensitive to lactic acid at pH 3. They are especially sensitive to a mixture of lactic acid and 5% ethanol. Peptone has been able to protect E. coli and S. aureus from growth inhibition caused by high concentrations of salt. It stimulates the growth of E. coli under acidic conditions.
Scientists also have developed techniques for studying the effects of new treatments on bacterial membrane activity. The use of pulse electric fields causes the bacterial membrane to leak ultraviolet-absorbing material. But the cells themselves survive either uninjured, or they are killed. There is no injured population.
There may be a reason for this. Susceptibility to pulsed high electric fields may correlate with the fluidity of the membrane. Or a microorganism in an electric field may act as a resistor and make the cell membrane permeable.
Further information. Stephen Pugh; phone: +44 0207-972-5079; fax: +44 0207-972-6555; URL: http://www.doh.gsi.gov.uk.