If you ever wondered how Snow White could have been poisoned by eating an apple, you probably did not realize how much this tale of folklore was based on cruel reality. Science has finally caught up with the Brothers Grimm who wrote the fairy tale: a recent outbreak of listeriosis traced to contaminated candied apples [1] gives us good reason to believe that Snow White ate a listeria-laced agricultural product. Thank you, CDC for uncovering a connection which has baffled us already way too long…
(Alright, okay, I admit that the tale of Snow White does not mention specifically that the apple was actually a candied apple. But you have to admit that it could well have been a candied apple. These fairy tales often make no sense at all unless you fill in the gaps with a bit of imagination)
Actually, listeriosis is no laughing matter. Diagnosis is often delayed, and even proper treatment does not guarantee a benign outcome. The organism has found unique ways to avoid immune activation and clearance. Fortunately, resistance is still rare or only slowly increasing [2]; ampicillin, gentamicin, and TMP/SMX remain the drugs of choice. Other useful drugs are imipenem, meropenem, and vancomycin.
Here a few lesser known facts about listeria, a not so uncommon pathogen:
- Truly ubiquitous, Listeria is found in soil, animals, plants, and sewage
- Human intestinal carriage rates as high as 70% in healthy persons have been reported [3]
Prof. Heinz Seeliger, eminent researcher and teacher University of Würzburg, Germany - Serotyping was introduced by Heinz Seeliger following the O and H classification introduced by Fritz Kauffmann (a Danish microbiologist known for his work on Salmonella) and with whom he collaborated. In honor of his contributions, a listeria species was named after him (L. seeligeri). Ironically, apathogenic L. seeligeri cannot be distinguished serologically from pathogenic L. monocytogenes.[4]
- Pasteurization of milk should work for extracellular listeria but may not eliminate all intracellular and more protected microbes [5]
- Listeria can spread from cell to cell via protrusions without any extracellular passage, thus avoiding T-cell activation
- Ampicillin, the drug of choice, is only bacteriostatic against extracellular, but bactericidal against intracellular listeria [6]. The opposite is true for gentamicin which is bactericidal for extracellular organisms but ineffective against intracellular microbes for obvious reasons.
- The organism is able to survive refrigeration, high salt concentrations and low pH conditions. It can grow at 4 degrees Celsius (cold enrichment) and develop acid-tolerance [7].
We are not told whether Snow White was immunocompromised or pregnant at the time when she ate the apple and succumbed to Listeria infection. Needless to say, she may have known already that deli meats, raw milk, unpasteurized cheeses and cantaloupes are big no-no’s. Clearly she could not resist the gift of a candied apple which did her in. Just another example of “what you don’t know may kill you”.
It’s a scary world out there…
References:
[1] http://www.cdc.gov/listeria/outbreaks/caramel-apples-12-14/
[2] B Khen. Zoonoses Public Health. 2014 Feb 10. doi: 10.1111/zph.12106. [Epub ahead of print]
[3] Hernandez-Milian. BioMed Research International; 2014, Article ID 358051, http://dx.doi.org/10.1155/2014/358051
[4] H. Seeliger. Internat J Food Microbiol 8 (1989): 245
[5] http://www.cdc.gov/mmwr/preview/mmwrhtml/00001316.htm
[6] S Carryn. J. Antimicrob. Chemother. 2003, 51: 105
[7] J Smith. Can. J. Microbiol. 59: 141, 2013
