Detection of fungemia obscured by concomitant bacteremia: in vitro and in vivo studies

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Abstract
Bacteremia may interfere with the detection of concomitant fungemia when standard blood culture methods are used. To determine the extent to which bacteria may interfere with fungal isolation from blood cultures, an in vitro model simulating blood cultures taken during concomitant fungemia and bacteremia was created. Each of 6 bacteria (Staphylococcus epidermidis, S. aureus, Streptococcus faecalis, Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa) was combined with each of 3 pathogenic yeasts (Candida albicans, C. tropicalis and Torulopsis glabrata) in vented blood cuture bottles containing enriched brain heart infusion broth and fresh normal human blood. Blod culture bottles were analyzed at 1, 2 and 7 days of incubation. Gram strains and subcultures onto chocolate and MacConkey agars failed to detect fungi in 37.0, 66.7 and 100% of samples, respectively. Subcultures onto Sabouraud dextrose agar failed in only 13% of the samples (occurring only with P. aeruginosa). In a rabbit model of concomitant fungemia with C. albicans and bacteremia with P. aeruginosa, no yeasts were recovered from blood cultures despite 100% detection of P. aeruginosa. Therefore, the usual mirobiological techniques may be inadequate to detect fungemia when concomitant bacteremia is present.

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