Essential Microbiology for Dentistry

xi. 293 hal.; 30 c

Factors affecting the adherence of Candida albicans to human buccal epithelial cells in human immunodeficiency virus infection

Adherence to host surfaces is an essential prerequisite for colonization and infection. We compared the adherence of 15 oral isolates of Candida albicans harvested from human immunodeficiency virus (HIV)-infected individuals and 12 isolates from HIV-free individuals to buccal epithelial cells (BECs) from HIV-free individuals, and the adherence of a reference strain of C. albicans to BECs from HIV-infected as well as HIV-free individuals. C. albicans from HIV-infected individuals showed adherence values similar to those from HIV-free individuals. The clinical and laboratory parameters of the subjects from whom the Candida were isolated did not correlate with adherence. A reference strain of C. albicans (GDH 1957), however, adhered more readily to BECs from HIV-infected individuals than to cells from an HIV-free cohort. Several variables were found to be associated with the adherence of C. albicans to BECs from HIV-infected individuals: use of zidovudine, antibacterials and antiparasitics was associated with increased adhesion, while haemophilia, heterosexuality, bisexuality, increased age, decreased CD4 + count and use of folate were associated with a decreased candidal adhesion (all P < 0.05). Our data suggest that the quality of BECs including their receptivity to Candida may play an important part in increasing the oral yeast carriage in HIV infection.link_to_subscribed_fulltex

Heterogeneity in antifungal susceptibility of clones of Candida albicans isolated on single and sequential visits from a HIV-infected southern Chinese cohort

The increased frequency and severity of candidal infections in human immunodeficiency virus (HIV)-infected individuals has prompted the wide use of antifungals, such as amphotericin B, ketoconazole, and fluconazole, resulting in the emergence of drug-resistant strains of Candida albicans. To study this phenomenon in an ethnic Chinese cohort, we isolated multiple colonies of Candida from the oral cavities of 16 HIV-infected patients on single and subsequent sequential visits over a period of 12 months. Ten of the 16 patients had sporadic episodes of oropharyngeal candidiasis (Group A), while the remainder were asymptomatic with respect to this condition (Group B). Oral rinses were collected and immediately processed in the laboratory for the isolation of C. albicans in a standard manner. A total of 433 C. albicans isolates were tested for their susceptibility to amphotericin B, ketoconazole and fluconazole by an agar diffusion method using the commercially available E-test. All tested isolates demonstrated variable susceptibility to amphotericin B, ketoconazole and fluconazole. The minimum inhibitory concentration (MIC) of the isolates for amphotericin B, ketoconazole and fluconazole ranged from <0.002-1.5 μg/ml, <0.002-4.0 μg/ml and <0.016-32 μg/ml, respectively. Sequential isolates of a few patients demonstrated variable susceptibility to all the antifungals, and no discernible MIC pattern emerged either in group A or B over time. Interestingly, significant variation in antifungal susceptibility was also noted in isolates obtained from the same patient on a single visit. Sequential yeast isolates in 9 of 16 patients (56%) demonstrated significant differences in MIC within and between visits for both amphotericin B and ketoconazole, while a lower percentage - 44% (7/16) - exhibited this trait for fluconazole. Our study demonstrates the diversity in antifungal susceptibility in either commensal or "infective" oral strains of C. albicans in HIV disease, and shows the need for vigilance for the emergence of resistant strains, and for frequent antifungal susceptibility studies.link_to_subscribed_fulltex

Attitudes to cross-infection measures of UK and Hong Kong patients.

The knowledge and attitudes of dental patients in the UK and Hong Kong towards aspects of cross-infection control have been surveyed. Almost all patients expected dentists to wear protective gloves but only 73% and 40% expected dental staff to wear protective face masks and spectacles respectively. Most patients were aware that such measures were for the benefit of both dental staff and patients. Just over 50% of patients believed that they could contact HIV from an HIV-infected dentist. UK and Cantonese patients had generally similar attitudes to cross-infection protection, but the latter were positively influenced by the routine use of masks and spectacles and were more concerned about HIV transmission than UK patients.link_to_subscribed_fulltex

Deletion of Candida albicans PHO112 reduces phytase activity, hyphal development, and attenuates virulence

Objective: To investigate the functional roles of PHO112 in Candida albicans phytase activity, hyphal development, and virulence. Methods: C. albicans PHO112 null mutants were created by a PCR-based gene targeting method using gene-specific primers. C. albicans PHO112 reintegrants were created by transforming the full length PHO112 gene into the C. albicans PHO112 null mutants. Phytase activity in C. albicans PHO112 null mutants was determined by quantifying the amount of released inorganic phosphate from sodium phytate using ammonium molybdate. The ability to form hyphae was evaluated in YPD medium supplemented with 10% fetal bovine serum at 37oC (hyphal-inducing conditions). Adhesion to buccal epithelial cells (BECs) was evaluated by counting the number of attached fungal cells to Gram’s stained BECs under light microscope. Fungal pathogenicity was determined using reconstituted oral human epithelial (ROHE) tissues, and histological changes of the tissues were observed under light microscope after staining with hematoxylin and eosin. Results: C. albicans PHO112 null mutants were created and verified by PCR and genomic Southern hybridization. C. albicans PHO112 null mutants exhibited the following phenotypic properties (P \u3c 0.05) with respect to the wild type counterparts: (1) a reduction of ~25% of phytase activity; (2) a reduction of ~22% of hyphal growth under hyphal-inducing conditions; (3) a reduction of ~22% of adhesion to BECs; and (4) an inability to infect ROHE tissues. Conclusions: The collective data of the present study suggest that C. albicans PHO112 contributes to phytase activity, hyphal development, and fungal virulence. The ability to inhibit the novel virulence trait may provide another antifungal strategy in the fight against this common human fungal pathogen in clinical settings