Olive Oil and Fungemia: What’s Cooking?
Abstract & Commentary
Synopsis: The yeast Candida versatilis was isolated from 10 blood cultures from neonates drawn over a period of 10 days. Further investigation revealed that unsterilized olive oil obtained from a local grocery store had been added to promote the in vitro growth of another fungus, Malassezia spp.
Source: Brandt ME, et al. Pseudooutbreak of Candida versatilis fungemia in a microbiology laboratory. Diagn Microbiol Infect Dis. 2003;46:73-75.
During a 10-day period, blood cultures were drawn from 10 infants being nursed in a neonatal intensive care unit. These cultures were intended, among other things, to exclude the lipophilic yeast Malassezia that can be a cause of catheter-related infections when hyperalimentation containing lipids is given. To achieve this, lipid, usually olive oil as in this case, is added directly to broth cultures or overlaid onto agar plates when Isolators samples are used. All 5 broth cultures including those not supplemented with olive oil showed growth within a week, but colonies were seen only on those agar plates overlaid with the oil. The organism proved to be a small budding yeast, and all isolates had the same physiological and biochemical profile. The identity was only confirmed after sending a blood culture isolate and that obtained from the olive oil to a mycology reference laboratory at the CDC in Atlanta. DNA analysis confirmed that the yeast was Candida versatilis, a nonpathogenic yeast used to prepare soy sauce, among other things. The olive oil had been bought 8 months earlier from a local grocery store and had never been sterilized. Brandt and colleagues reminded the reader that "all solutions to be added to blood culture bottles should be sterilized prior to use."
Comment by J. Peter Donnelly, PhD
Quite apart from the dubious practice of adding lipid at all to blood cultures, it seems that there was a breakdown in the system at 2 levels. First, there is nothing against purchasing olive oil or any other exotic ingredient for fastidious micro-organisms for that matter from a local store. However, common sense should prevail to ensure the ingredient is rendered free of microbial inhabitants before being added to culture media that is not going to be further sterilized. This is especially so when investigating clinical material. This clearly did not happen in this case. The second breakdown occurred since no one thought to ensure the olive oil was in fact sterile at the point of use. Although not stated explicitly in the report, it would appear that the original bottle was used presumably replete with its original labels. This alone should have served as an alarm for those technicians whose job it was to add the oil. The fact that it didn’t indicates a worrisome failure that would make me want to thoroughly investigate the entire laboratory service to see what else was amiss. Quite apart from the loss of diagnostic information, the cost of attempting to identify the isolates and of performing DNA analysis was not trivial and would have far outweighed the purchase price of the original oil, making it both an expensive, as well as an avoidable, error. The recommendation that "all solutions to be added to blood culture bottles should be sterilized prior to use" seems rather too mild to me since one of the basic tenets of microbiological analysis is to ensure all cultures are sterile before being inoculated with the sample being investigated so as to be sure that any organism recovered actually originated from the sample. This scenario is one in the eye (in-ocula) for Robert Koch, who went to great lengths to recover bacteria in pure culture from the bull’s eyes he inoculated as a first and necessary step toward diagnosis.
Dr. Donnelly is Clinical Microbiologist University Hospital Nijmegen, The Netherlands Section Editor, Microbiology.
The yeast Candida versatilis was isolated from 10 blood cultures from neonates drawn over a period of 10 days.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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