Abstract
: , a predominant yeast pathogen can be easily distinguished from other non-albicans species in a diagnostic laboratory based on their property to produce germ tubes using human serum as a routine substrate. As usage of human serum is accompanied with risk of transmission of blood-borne viral infections, several other media were employed by many clinical laboratories. The aim of this study was to evaluate the efficacy of four commonly used non-serum liquid media relative to fresh human serum in germ tube (GT) productivity among various Candida isolates. A total of 146 Candida isolates (96 ; 47 ; 3 ) identified by conventional methods were assessed for germ tube production in five types of media namely peptone water, Mueller Hinton broth, Trypticase soy broth, Brain Heart infusion broth and fresh human serum . Results obtained in different media for germ tube production in all Candida isolates were analysed for sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy.All the Candida isolates showed 100% specificity and PPV in all the five-liquid media. Highest performance in germ tube production (96%) in isolates was found in Trypticase soy broth followed by fresh human serum (95%). Trypticase soy broth was shown to have 96% sensitivity and 97% accuracy for germ tube formation comparable to human serum with 95% sensitivity and 96.5% accuracy. Trypticase soy broth can be suggested as a choice medium for GT production in diagnostic mycology.
Highlights
Candida albicans, a predominant yeast pathogen can be distinguished from other non-albicans species in a diagnostic laboratory based on their property to produce germ tubes using human serum as a routine substrate
The study included a total of 146 Candida strains (96 C. albicans; 47 C. tropicalis; 3 C. dubliniensis;) obtained from diverse clinical samples processed in our microbiology laboratory during the year 2019
Germ tube test (GTT) results were positive in 82 of 96 (85%) strains of Candida albicans in peptone water; 89 0f 96 (93%) in Mueller Hinton broth; 92 of 96 (96%) in Trypticase soy broth, 88 of 96 (92%) in Brain Heart infusion broth and 91 of 96 (95%) in fresh human serum (Table 1)
Summary
A predominant yeast pathogen can be distinguished from other non-albicans species in a diagnostic laboratory based on their property to produce germ tubes using human serum as a routine substrate. The aim of this study was to evaluate the efficacy of four commonly used non-serum liquid media relative to fresh human serum in germ tube (GT) productivity among various Candida isolates. Materials and Methods: A total of 146 Candida isolates (96 C. albicans; 47 C. tropicalis; 3 C. dubliniensis) identified by conventional methods were assessed for germ tube production in five types of media namely peptone water, Mueller Hinton broth, Trypticase soy broth, Brain Heart infusion broth and fresh human serum. Highest performance in germ tube production (96%) in C. albicans isolates was found in Trypticase soy broth followed by fresh human serum (95%). One of the widely employed rapid technique readily available in most clinical laboratories for presumptive identification of Candida albicans from other species is germ tube production test first described by Reynold and Braude in 1956. Due to scant studies available in this area of research from our place the present work was undertaken with an objective to compare the utility of four commonly used non-serum substrates against the pooled human serum to perform the germ tube test
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