The aim of this study was to investigate oral yeast colonization and oral yeast strain diversity in irradiated (head and neck), dentate, xerostomic individuals. Subjects were recruited from a nasopharyngeal carcinoma clinic and were segregated into group A (age, <60 years [n ‫؍‬ 25; average age ؎ standard deviation {SD}, 48 ؎ 6 years; average postirradiation time ؎ SD, 5 ؎ 5 years]) and group B (age, >60 years [n ‫؍‬ 8; average age ؎ SD, 67 ؎ 4 years; average postirradiation time ؎ SD, 2 ؎ 2 years]) and were compared with age-and sex-matched healthy individuals in group C (age, <60 years [n ‫؍‬ 20; average age ؎ SD, 44 ؎ 12 years] and group D (age, >60 years [n ‫؍‬ 10; average age, 70 ؎ 3 years]). Selective culture of oral rinse samples was carried out to isolate, quantify, and speciate yeast recovery. All test subjects underwent a 3-month comprehensive oral and preventive care regimen plus topical antifungal therapy, if indicated. A total of 12 subjects from group A and 5 subjects from group B were recalled for reassessment of yeast colonization. Sequential (pre-and posttherapy) Candida isolate pairs from patients were phenotypically (all isolate pairs; biotyping and resistotyping profiles) and genotypically (Candida albicans isolate pairs only; electrophoretic karyotyping by pulsed-field gel electrophoresis, restriction fragment length polymorphism [RFLP], and randomly amplified polymorphic DNA [RAPD] assays) evaluated. All isolates were Candida species. Irradiated individuals were found to have a significantly increased yeast carriage compared with the controls. The isolation rate of Candida posttherapy remained unchanged. A total of 9 of the 12 subjects in group A and 3 of the 5 subjects in group B harbored the same C. albicans or Candida tropicalis phenotype at recall. Varying degrees of congruence in the molecular profiles were observed when these sequential isolate pairs of C. albicans were analyzed by RFLP and RAPD assays. Variations in the genotype were complementary to those in the phenotypic characteristics for some isolates. In conclusion, irradiation-induced xerostomia seems to favor intraoral colonization of Candida species, particularly C. albicans, which appeared to undergo temporal modifications in clonal profiles both phenotypically and genotypically following hygienic and preventive oral care which included topical antifungal therapy, if indicated. We postulate that the observed ability of Candida species to undergo genetic and phenotypic adaptation could strategically enhance its survival in the human oral cavity, particularly when salivary defenses are impaired.

The extracellular phospholipases of Candida albicans are considered to play a significant role in the pathogenesis of human infections. Therefore 30 clinical isolates of C. albicans from human immunodeficiency virus (HIV)-infected individuals were screened for phospholipase production in vitro (using an egg-yolk-agar medium). Two groups of six isolates with positive (group A) or deficient (group B) phospholipase activity were then analysed for phospholipase B1 (PLB1) gene expression both in egg-yolk-agar and yeast extract/peptone/dextrose (YPD) broth media. A total of four virulence attributes of these two groups were in turn characterized, namely their germ-tube formation, cell-surface-hydrophobicity (CSH), adhesion to buccal epithelial cells (ABEC) and haemolysin production, and these factors were subsequently correlated with PLB1 expression. In the phospholipase-producing isolates (group A) a positive correlation was demonstrated between phospholipase production and the degree of PLB1 expression in YPD medium (r ¼ 0 . 96, P , 0 . 01). No such association was observed in group A isolates for PLB1 expression in egg-yolk-agar medium. Further, PLB1 expression in egg-yolk agar was less than that in YPD medium, although a positive correlation was seen between the expression levels on regression analysis (r ¼ 0 . 86, P ¼ 0 . 026). Surprisingly, however, no significant associations were observed in either growth media between PLB1 expression and any of the four pathogenic attributes examined (P , 0 . 001). A significant correlation was seen between CSH and ABEC (r ¼ 0 . 74) in group A isolates. The phospholipase-deficient group B, however, demonstrated a significant correlation between the latter parameters (r ¼ þ0 : 50) and also between germ-tube formation and ABEC (r ¼ À0 : 59), and germ-tube formation and haemolysin production (r ¼ þ0 : 31). It appears that in oral C. albicans isolates in HIV infection there may be no significant association between the degree of PLB1 expression and other widely recognized major virulence attributes.

Phospholipases B1, B2, C and D of Candida albicans play a significant role in the host invasive process. Hence we evaluated the in vitro expression of PLB1, PLB2, PLC1 and PLD1 in phospholipase-positive (PL(+)) and -deficient (PL(-)) C. albicans isolates in egg yolk agar (EYA), yeast peptone dextrose broth (YPD), and in a model of oral candidiasis based on reconstituted human oral epithelium (RHOE). The growth of Candida was then determined in YPD and its cellular invasion was investigated using the RHOE model. The PL(+) group demonstrated PLB1, PLB2, PLC1 and PLD1 expression in both EYA and YPD, in contrast to the PL(-) group, which expressed only PLB2 and PLD1. Although PL(+) isolates grew profusely in the RHOE model, they expressed only PLB2, PLC1 and PLD1, and not PLB1. Gene expression investigations could not be carried out with PL(-) isolates due to their inability to grow in the RHOE model. Significant growth differences in YPD medium were also observed within the PL(+) and PL(-) groups. Taken together, these findings indicate that phospholipase gene expression in C. albicans is differentially affected by their growth milieu, and this in turn may modulate the disease outcomes in vivo.