Performance of FTIR-Based IR Biotyper for Identification and Strain Discrimination of Cryptococcus Species

The IR Biotyper is a commercialized real-time typing tool based on a Fourier-transform infrared spectroscopy system. To date, it has not been evaluated for use with pathogenic Cryptococcus species complexes. This study aimed to assess the utility of the IR Biotyper for strain typing of pathogenic Cryptococcus species isolated from both environmental and clinical sources. We analyzed 51 isolates of Cryptococcus species, including clinical samples from two university hospitals, environmental isolates, and reference strains. Using a modified protocol optimized for Cryptococcus, we generated a total of 765 spectra that demonstrated high intra-isolate consistency. When the spectrum of Cryptococcus neoformans isolates was analyzed, distinct clusters were formed, clearly separating them from Cryptococcus species other than C. neoformans (Cryptococcus gattii, Cryptococcus deuterogattii, and Cryptococcus deneoformans). However, spectra from C. deuterogattii and C. gattii overlapped, indicating their close relatedness. Spectral discrimination was not clear between environmental and clinical isolates of C. neoformans. A dendrogram analysis grouped the 51 isolates into 10 clusters at a cutoff value of 6.245, which could discriminate four sequence types of C. neoformans. The IR Biotyper is useful for the identification and strain-level discrimination of C. neoformans, but its resolution is insufficient for reliable discrimination within the C. gattii complex. This initial study demonstrates further validation with larger, more diverse training sets is promising.