Efficacy of swabbing versus a conventional technique for isolation of Cryptococcus neoformans from decayed wood in tree trunk hollows.

The efficacy of swabbing versus a conventional sedimentation technique was evaluated for sampling of decayed wood in tree trunk hollows for isolation of Cryptococcus neoformans. Of 52 samples of decayed wood, bark or other plant debris originating from 35 living trees, 42 wood samples yielded C. neoformans. The positive samples included 40 collected from 31 Syzygium cumini trees growing along roadsides in Old Delhi, whereas the remaining two were from inside tree trunk fissures of Ficus religiosa in a New Delhi locality. The number of wood samples found positive by swabbing was 40 (95%) as opposed to 32 (76%) by the conventional technique, and this difference was statistically significant (P < 0.01). Also, the conventional technique showed 24% false-negative results, which was in striking contrast to only 5% by swabbing. Furthermore, swabbing yielded a significantly higher C. neoformans mean colony count than did the conventional technique (P < 0.005), thus highlighting greater efficacy of the former technique. The overall prevalence of C. neoformans in the S. cumini trees investigated was 84% (26/31 trees) which is the highest as yet reported from any tree species in India. Varietal identification and serotyping was done with 33 of the C. neoformans isolates, 31 of which came from 23 tree trunk hollows of S. cumini and two from the tree trunk fissures of F. religiosa. Among the S. cumini isolates, 26 were identified as C. neoformans var. gattii (all serotype B except two untypeable ones) and five as C. neoformans var. neoformans, serotype A (= C. neoformans var. grubii). Both of the F. religiosa isolates belonged to C. n. var. neoformans, serotype A. Being a more efficacious, simple, less time-consuming and less hazardous technique, swabbing is recommended for wider use in order to further elucidate the ecology of C. neoformans.