Food Pathogen Testing: The Pros And Cons Of Culture-Independent Diagnostics
By Isaac Fletcher, contributing writer, Food Online
As CIDTs experience increasing popularity, labs can more-rapidly and -easily reach test results, but some potential issues with the testing method may necessitate the assistance of the CDC.
Culture-independent diagnostic tests (CIDTs) are becoming a more-widely used method for diagnosing Shiga Toxin producing E.coli (STEC) infections and other pathogens in foods. Compared to 2007, the use of antigen-based and DNA-based detection methods for STEC has increased greatly. Nearly every report of STEC infections has been associated with a positive CIDT report, and over 90 percent were confirmed by use of a culture.
CIDTs function by identifying the presence of a particular antigen or sequence of a germ. Unlike some other detection methods, CIDTs do not need isolation or identification of a living organism in order to work effectively, which yields quicker test results when compared to some other traditional, culturing methods. While this is a distinct benefit, CIDTs fall short in the sense that they do not provide the information that is necessary to characterize organisms that are responsible for infections. Since the test does not provide the organism that caused the infection (the isolate), it is impossible for testers to pinpoint the organism’s DNA fingerprint. Although tests can be completed quickly, the delay in outbreak investigation leaves contaminated products on shelves longer.
The Center for Disease Control (CDC) is encouraging labs to conduct reflex culturing, wherein culturing specimens with positive CIDT results for intestinal bacteria are further cultured. Furthermore, the CDC is working alongside companies using CIDTs to ensure specimens are properly collected and the organism is kept alive for culturing. The CDC’s other related endeavors include the development of new CIDTs that can provide information about subtypes, antibiotic resistances, and virulence, as well as the implementation of surveillance systems that overcome challenges faced by public health labs.
As more labs begin to use CIDTs, much of the responsibility for collection and characterization of bacterial isolates will fall upon public health labs. Reliance on this testing method will burden public health laboratories and impact clinical practice, outbreak detection, and the ability to monitor disease trends. For public health surveillance programs to function, they must rely on the ability to distinguish among strains and serotypes of pathogens. In doing so, they can detect foodborne outbreaks and monitor the effectiveness of various interventions.