BACTEC high-blood-volume fungal medium versus Isolator comparison misleading

Abstract

BACTEC High-Blood-Volume Fungal Medium versus Isolator Comparison Misleading Scientific investigation must be evaluated by using actual experimental conditions. Wilson et al. (4) mislead the reader by their global conclusion that BACTEC high-blood-volume fungal medium (HBV-FM) is equivalent and Bactec Plus 26 (BP26) is superior to Isolator. Tenets of microbial nutrition and experimental design were not followed, yet conclusions were drawn from flawed testing. Concerning microbial nutrition, the media and incubation conditions used for Isolator are not entirely those suggested by the manufacturer, and, as such, they create additional variables for simultaneous evaluation of both fungal and bacterial recovery. Regarding temperature, two of the four plates (Isolator) were incubated at 25°C (not optimal for growth of streptococci), whereas all BACTEC media were at 35°C. Regarding media, Why was Sabouraud dextrose agar selected rather than SABHI or BHI (suggested by manufacturer), both of which more closely resemble the formulation of BACTEC FM? Sabouraud (one plate) is neither conducive for bacterial growth nor recommended for recovery of fungi from clinical specimens such as blood (3). Although an option, Sabouraud was devised for dermatophytes (1). The type of Sabouraud (4% dextrose, pH 5.6) or Emmons medium (2% dextrose, pH neutral) used was not indicated. Media selected for recovery of fungi can influence yield (2), and one could postulate quite different results had optimal media been used. Dating back at least to the early 1940s, the literature is replete with examples of interrelationships between temperature, pH, nutritional requirements, and microbial growth. Such blatant omissions and inequalities by design are difficult to understand. Concerning the experimental design, basic principles of investigation, and especially those for blood cultures, dictate Controlled comparison of the BACTEC high-blood-volume fungal medium, BACTEC Plus 26 aerobic blood culture bottle, and 10-milliliter Isolator blood culture system for detection of fungemia and bacteremia. J. Clin. Microbiol. 31:865-871.