#45: Phenotypic heterogeneity among isolates of Candida albicans from specific anatomical niches in VLBW premature infants
Authors: Rytlewski Kacie C , Wellington Melanie , Krysan Damian 
Published: June 2021

Background

Disseminated candidiasis is associated with high morbidity and mortality among very low birth weight (VLBW) infants. Research about C. albicans traits which lead to colonization versus invasive disease is lacking. Ability to grow in a filamentous form is a known virulence trait of C. albicans. Nevertheless, significant heterogeneity in filamentous growth in C. albicans clinical isolates has been documented (Hirakawa et. al). However, the clinical isolates investigated were obtained from varied tissue niches from hosts with differing risk factors, which could account for the variation in filamentation. A collection of C. albicans isolates prospectively collected from VLBW infants and their mothers demonstrated vertical transmission of C. albicans from mother to infant (Bliss et. al). We used the infants’ isolates from this collection to investigate filamentation amongst isolates obtained from the same tissue niche and host type.

Methods

The standard C. albicans reference strain in the field, SC5314 was chosen for a positive control as it demonstrates strong filamentation and high virulence. A strain lacking Efg1, a regulatory transcription factor that promotes filamentation, produces hypofilamentous colonies and was used as the negative control. Reference strains and the clinical isolates were grown on two types of stimulation media at 37 C for 7 days after which filamentation was scored.

Results

Filamentation development varied widely among isolates. Of the strains which were acquired through vertical transmission, 5 of 11 strains showed strong filamentation, 5 of 11 had an intermediate phenotype, and 1 did not display any filamentation. Three strains were acquired through horizontal transmission (RO10, RO54, and RO56). Of these, one showed strong filamentation whereas the other two failed to form filaments. None of the neonatal isolates showed colony wrinkling, a prominent phenotype in the reference strain SC5314. Strain RO61, an isolate associated with candidemia showed strong filamentation. In contrast, strain RO39, which was associated with dermatitis, was non-filamentous.

Conclusions

We observed phenotypic heterogeneity with respect to filament development among clinical isolates obtained from the same niche (rectal) in similar hosts (VLBW premature infants). This is consistent with the variation seen in Hirakawa et al and indicates that phenotypic variation is not a function of host risk factors nor clinical niche. Filamentation was not required for vertical transmission. No conclusions can be drawn based on this observation with only 2 strains, but it is interesting to note that the isolate which caused candidemia and death of the patient was highly filamentous whereas the isolate that caused dermatitis was not. Further investigation of these strains, including genomic sequencing and additional phenotypic evaluations, will explore the underlying factors leading to transmission and virulence of C. albicans in VLBW premature infants.