Utility of the Germ Tube Test for Direct Identification of Candida albicans from Positive Blood Culture Bottles

Abstract

We compared the germ tube test for the direct identification of Candida albicans from positive blood culture bottles, with results obtained from subcultured colonies. The direct germ tube test was 87.1% sensitive and 100% specific for the identification of C. albicans when the results obtained from fungal colonies were compared.Recent evidence has suggested that early institution of appropriate antifungal therapy is a critical factor in improving outcomes during bloodstream infections with Candida species (2, 4, 5). Given that most bloodstream isolates of C. albicans remain susceptible to azoles such as fluconazole (7, 9), the rapid identification of C. albicans is a key step in the diagnostic and treatment algorithm for bloodstream Candida infection to guide targeted and cost-effective antifungal strategy (6).Traditionally, the preliminary identification of C. albicans is made through the use of a germ tube test (GTT) performed on a subcultured colony grown on solid agar. Although the test itself is rapid, growth of sufficient colonies on solid agar requires a delay of a minimum of 24 h and up to 72 h before identification can be performed. In a preliminary report, Terlecka et al. performed the GTT directly from 31 BacTAlert blood culture bottles positive for yeast on Gram stain, thirteen of which were C. albicans (10). Although the numbers were limited, they observed 100% concordance between the direct GTT and a GTT performed with subcultured organisms grown on solid medium. We report here a 2-year prospective study from two sites investigating the possibility that the GTT could be performed directly from blood culture bottles that had been flagged positive. In addition, to extend these results, 67 yeast isolates previously recovered from candidemic patients were tested in blood culture bottles inoculated with human blood.Over a 2-year period, all positive blood cultures in which yeast were visualized by Gram staining were identified at two large teaching hospitals in Montreal, Canada. To maximize strain diversity, only the first positive blood culture was tested for each episode of fungemia. At Maisonneuve-Rosemont Hospital, all blood cultures were inoculated into BacTAlert blood culture bottles (bioMérieux, Inc., Marcy l'Etoile, France), while the Bactec system (BD Diagnostics, Oakville, Ontario, Canada) was used at the Royal Victoria Hospital. All positive cultures were subcultured on Sabouraud dextrose agar, and a direct GTT performed. To perform the direct GTT, 10 to 20 l of the blood culture bottle contents was removed and incubated with 0.5 of rabbit serum for 3 h at 37°C. The presence or absence of germ tubes was recorded. When sufficient growth was obtained on solid agar, a standard GTT was performed by inoculating 0.5 ml of citrated rabbit serum with a loopful of the test strain, followed by incubation at 37°C for 3 h. All isolates were then completely identified using the API20C AUX, the Vitek YBC (bioMérieux), or the Auxacolor 2 (Bio-Rad, Marnes-la Coquette, France) system.To complement these data,...

A Fast Preliminary Identification Test in Fungemia: Evaluation of Germ Tube Test Directly from Positive Blood Culture Bottles

“…Sheppard ve ark. (24) , doğrudan GTT için klinik örneklerde % 87.1 duyarlılık ve % 100 özgüllük bildirmiş ve negatif olan dört C.albicans suşunun ikisinin daha yavaş ürediğini belirtmişlerdir. Aynı çalışmada kan kültürü şişe-lerine insan kanı ve maya izolatları eklenerek yapılan simülatif deneylerde de uyumsuzluk gözlenmemiştir.…”

“…Doğrudan GTT: Mikoloji Laboratuvarı'na ulaştırılan maya pozitif şişelerden alınan 2-3 damla (10-20 µl) materyal, yaklaşık 1 mL insan serumuna eklenmiş ve 3 saate kadar 37°C'de bekletilmiştir. İnkübasyon sonrasında bu materyalden bir damla temiz bir lam üzerine alınmış ve üzerine lamel kapatılarak x400 büyütmede mikroskopta incelenmiştir (21,24,25) . Kan kültürü şişesinden doğrudan yapılan GTT pozitif bulunduğunda C.albicans, negatif bulunduğunda ise "C.albicans dışı maya mantarı" olarak ön tanımlama yapılmıştır.…”

“…Bu nedenle, sonuç için ek bir gün daha gerekmektedir. Ek sürenin ortadan kaldırı-labilmesi ve C.albicans'ın daha erken tanımlana-bilmesi amacıyla, maya pozitif kan kültürü şişelerinden doğrudan GTT uygulanması öne-rilmiş ve araştırmalar yapılmıştır (21,24,25) . Bu çalış-manın amacı, merkezimizde maya pozitif kan kültürü şişesinden doğrudan yapılan GTT uygulamasının etken maya mantarını tanımlamadaki güvenilirliğinin, konvansiyonel tanımlama yön-temleriyle karşılaştırılmasıdır.…”

Evaluation of Different Media for Germ Tube Production of Candida Albicans and Candida Dubliniensis

“…9 Although C. albicans cells reproduce normally by budding, giving rise to the formation of yeast cells, they frequently produce germ tubes under unfavorable conditions. The production of germ tubes results in conversion to filamentous growth or mycelial form.…”

“…Most of the studies on evaluation of media for germ tube production are focused on C. albicans. 8,9,10 Information on efficient media for germ tube testing of C. dubliniensis is limited. The present study was conducted with an aim to evaluate different media like pooled human serum, horse serum, human plasma, egg white, peptone water and trypticase soy broth for germ tube production of C. albicans and C. dubliniensis.…”