By Robyn Atkinson, PhD, Unified Utah State Public Health Laboratory Director
As hard as science tries, no microbiological diagnostic laboratory test is 100% perfect. The identification of infectious organisms by culturing patient samples is the gold-standard and is the measure by which all new tests are based. However, even culture has its inherent drawbacks. Not all organisms thrive on synthetic media and the numbers of organisms present in a clinical sample may not be of a sufficient density to yield a recognizable colony.
Manufactures have worked for years to help clinical laboratories overcome these issues while improving upon turn-around-time for results. With the advent of PCR, the drive to default to DNA based tests is appealing since the results should be undeniable and require a minute amount of sample. Either the organism is present and DNA is detected, or the organism is not present and no DNA is detected. In a perfect world, this would be correct, but even PCR assays have a limit of detection and very rarely will these assays detect a single organism’s DNA.
The key hindrance to any type of non-culture based test is that the clinical and public health community lose access to the actual organism. This prevents further study of these organisms for antimicrobial resistance testing to ensure proper patient treatment, prevents the detection of enhanced virulence factors and prevents public health from monitoring the spread of a particular clone of a bacterial species within the population. This tracking of organisms by public health across communities and across states during an outbreak has become the corner stone for foodborne pathogen surveillance. Without access to these organisms, valuable organism characteristics are lost.
A perfect example of a scenario that relied upon the isolation of an organism is the current outbreak and massive recall linked to ground turkey. The organism responsible is a highly antimicrobial resistant strain of Salmonella Heidelberg. This organism was cultured from ground turkey and tested for antimicrobial resistance as a part of the National Antimicrobial Resistance Monitoring System and was subjected to molecular analysis through the PulseNet Program. Once this organism was isolated from a clinical sample, the match was made! Without either of these programs utilizing culture to isolate and describe the characteristics of this organism, we still might not have the connection between the ground turkey and over 100 ill persons.
Maintaining culture is the only way to ensure that we remain prepared for what bacterial pathogens have in-store for us next!