Relationship between fluconazole sensitivity of Candida albicans isolates from HIV positive patients and serotype, adherence and CD4+ lymphocyte count

Effect of mouthrinses on Aggregatibacter actinomycetemcomitans biofilms in a hydrodynamic model

The aim of the study was to evaluate the effects of Listerine, Meridol, and Perioaid on the viability and total number of bacteria in established biofilms using an in vitro model under hydrodynamic conditions. Biofilms of Aggregatibacter actinomycetemcomitans were placed in a modified Robbins device and rinsed twice daily during 4 days. Bacteria were quantified by culture and quantitative polymerase chain reaction. Visualization of the samples was performed by scanning electron and confocal laser scanning microscopy, combined with a fluorescent vital staining. All three mouthrinses caused a significant reduction in the number of cultivable A. actinomycetemcomitans in a biofilm. Perioaid was significantly the most powerful in killing the biofilm-protected bacteria and also in counteracting the development of thick dense microbial communities. The total amount of bacteria was not significantly affected by Listerine and Meridol.

Adhesion and cell-surface-hydrophobicity of sequentially isolated genetic isotypes of Candida albicans in an HIV-infected Southern Chinese cohort. Adharenz und Zelloberflachen-Hydrophobizitat von sequentiell isolierten genetischen Isotypen von Candida albicans aus einer HIV-infizierten sudchinesischen Kohorte

Objectives of the study were to investigate the variability in yeast adhesion and cell-surface-hydrophobicity (CSH) during human immunodeficiency virus (HIV) disease progression, using a total of 60 sequential Candida albicans isolated from oral rinse samples of seven HIV-infected individuals with (4) and without (3) clinical symptoms of oropharyngeal candidosis. Significant differences in the adhesion to buccal epithelial cells (BECs) during sequential visits were observed for all genetic isotypes in five of the seven individuals and three isotypes belonging to the sixth individual. A single isotype of patient HK1 and another of HK4 (genotype I) demonstrated significant variations in their CSH during sequential visits whereas no such differences were noted for the remaining genotypes. On Spearman correlation analysis an isotype from HK1 demonstrated a significant increased adherence to BECs and CSH during HIV disease progression whereas no such correlation was noted for the remaining isotypes studied. No significant differences in adherence to BECs or CSH values were observed between the symptomatic oral candidosis and the asymptomatic carrier group. Further, on regression analysis only the single isotype of HK1 demonstrated a significant positive correlation between adherence to BECs and CSH whereas no such correlation was observed when all tested Candida isolates were pooled and evaluated as a single, large group.

HIV-1 and its transmembrane protein gp41 bind to different Candida species modulating adhesion

Oral candidiasis in HIV-1-infected individuals is widely believed to be triggered by the acquired T-lymphocyte immunodeficiency. Recently, binding of the HIV-1 envelope protein gp160 and its subunit gp41, and also of the whole virus itself, to Candida albicans has been shown. The present study shows that, in addition to C. albicans, HIV-1 gp41 also binds to yeast and hyphal forms of Candida dubliniensis, a species which is closely related to C. albicans, and to Candida tropicalis but not to Candida krusei, Candida glabrata or Saccharomyces cerevisiae. The previous finding that gp41 binding to C. albicans augments fungal virulence in vitro is supported by the observation that the yeast showed an enhanced adhesion to HIV-infected H9 cells in comparison to uninfected cells. In line with these results soluble gp41 itself reduced binding of C. albicans to both endothelial and epithelial cell lines, confirming a dominant role of the gp41 binding moiety on the surface of Candida for adhesion. Surface-associated secreted aspartic proteinases (Saps) play an important role in candidial adhesion, but are not likely to be involved in the interaction as gp41 binding to the C. albicans parental wild-type strain was comparable to that of three different isogenic Sap deletion mutants. Furthermore, gp41 binding to the yeast killer toxin-susceptible C. albicans strain 10S was not inhibitable by an anti-YKT receptor antibody. In conclusion, HIV-1 interacts with different clinically important Candida spp., and may thereby affect the outcome of the respective fungal infection.

Susceptibility testing of fungi--current status and open questions

The increase of fungal infections and the improvement of therapeutical options demand reliable antifungal susceptibility testing. In vitro susceptibility testing of fungi--in contrast to bacteria--is not yet established as a routine method. The NCCIS (National Committee for Clinical Laboratory Standards) guidelines for susceptibility testing of yeasts (and proposed for hyphomycetes) are most important for standardization. Meanwhile, essential parts of this test procedure are accepted, but it should still be improved. The concept of using only one test medium for all drugs and test organisms is not realized so far. There are also some test situations that prevent the NCCLS standard from being applied. Based on our experience, this article describes the NCCLS methods and their modifications. It places emphasis on lipophilic drugs showing controversies despite standardization. Furthermore, the prediction of MICs on the clinical outcome is discussed. Since there are some pitfalls in testing antifungals, this should be done in experienced laboratories only. The MIC has to be regarded as only one, but an important, factor in the management of fungal diseases. Host-, drug-, and pathogen-specific data should be considered simultaneously.

Anti-fungal therapy at the HAART of viral therapy

HIV-positive patients receiving combination therapy (highly active anti-retroviral treatment, HAART) suffer significantly fewer oral infections with the opportunistic fungal pathogen Candida albicans than non-HAART-treated patients. One component of HAART is an inhibitor of the HIV proteinase, the enzyme required for correct processing of retroviral precursor proteins. It would appear that HIV proteinase inhibitors also have a direct effect on one of the key virulence factors of C. albicans, the secreted aspartic proteinases (Saps). This suggests that the reduction in C. albicans infections in HIV-positive patients might not be solely the result of improved immunological status but could also be caused by the HAART treatment directly inhibiting Candida proteinases.

Influence of sub-inhibitory concentrations of conventional antifungals on metabolism of Candida albicans and on its adherence to polystyrene and extracellular matrix proteins

Five antifungal agents with different mechanisms of action were compared for their ability to affect mitochondrial dehydrogenase activity and adherence capacity of Candida albicans to polystyrene and extracellular matrix proteins. Only amphotericin B inhibited mitochondrial dehydrogenase activity when the culture medium was supplemented with galactose. 5-Fluorocytosine and terbinafine did not affect this activity, whereas itraconazole and fluconazole improved it. Furthermore, in these experimental conditions, the effect of sub-inhibitory concentrations of antifungals on adherence was dependent on the tested antifungal and the adherence surface: amphotericin B inhibited adherence to polystyrene and fibrinogen, but improved adherence to extracellular matrix. For all surfaces tested, when culture medium was supplemented with galactose, fluorocytosine did not affect adherence, and itraconazole, fluconazole and terbinafine inhibited adherence. Our results also confirmed the influence of the carbohydrates: sub-minimum inhibitory concentrations (MIC) of itraconazole increased or did not modify the mitochondrial metabolism of yeasts when the culture medium was supplemented with galactose, but this antifungal always decreased mitochondrial metabolism when the culture medium was supplemented with glucose. These data indicate that antifungals used below their MIC values can have various effects. It is important to distinguish the effects of antifungals on the metabolism of C. albicans from effects on its adherence capacity. The former effects are linked to the viability of the yeast and the latter depends on the colonization of cellular as opposed to inert surfaces.

Serotype distribution and secretory acid proteinase activity of Candida albicans isolated from the oral mucosa of patients with denture stomatitis

Denture stomatitis is the most common form of oral Candida infection in humans. In the current study, the distribution of Candida albicans serotype A and B as well as the activity of the secreted acid proteinase were determined in clinical isolates from patients with denture stomatitis. It was found that 70% of individuals with clinical signs of denture stomatitis exhibited fungal growth, with C. albicans representing the most frequently isolated species (75%). Of the C. albicans isolates, 75% were serotype A and 25% were serotype B, representing a significant increase of serotype B compared to a control group of non-denture-wearing HIV-seronegative individuals with oral candidiasis, but no significant difference compared with isolates from HIV-seropositive patients, who also exhibited a high percentage of serotype B. The mean secretory acid proteinase activity of C. albicans isolates from denture stomatitis patients (2796 +/- 819 U/l) was statistically not different from the mean secretory acid proteinase activity in non-denture-wearing HIV-seronegative individuals (2324 +/- 1487 U/l). Both values were significantly lower than the mean secretory acid proteinase activity of C. albicans from HIV-seropositive individuals (4256 +/- 2372 U/l). No correlation exists between the C. albicans serotype and the amount of secreted acid proteinase, indicating that serotype and secretory acid proteinase expression are two independent pathogenetic factors in oral candidiasis. These results indicate that there seems to be strain selection for C. albicans serotype B in denture stomatitis. These results further indicate that increased secretion of the acid proteinase seems to be of pathogenetic significance in the candidiasis of HIV-seropositive patients but not in denture stomatitis. Nevertheless, the secretory acid proteinase is likely to be an important pathogenetic factor also in denture stomatitis, where an increased secretion of the acid proteinase may not be required because of decreased salivary flow and a low pH under the denture, which will result in a high enzymatic activity.

The postantifungal effect (PAFE) of antimycotics on oral C. albicans isolates and its impact on candidal adhesion

OBJECTIVE

Postantifungal effect (PAFE) is defined as the suppression of growth that persists following limited exposure of yeasts to antimycotics and subsequent removal of the drug. As there are no data on the PAFE of oral C. albicans isolates the main aim of this investigation was to measure the PAFE of 10 oral isolates of C. albicans following limited exposure (1 h) to five antifungal drugs, including nystatin which has not been previously used in PAFE assays. A secondary aim of the study was to evaluate the biological significance of PAFE, using a nystatin pre-exposed isolate of C. albicans and observing its adherence to denture acrylic surfaces, during the PAFE period.

DESIGN

A total of 10 oral isolates of C. albicans were examined for the presence of the PAFE after 1 h exposure to five antifungal drugs, nystatin, amphotericin B, 5-fluorocytosine, ketoconazole and fluconazole. PAFE was automatically assessed with the help of a Spectramax machine which utilizes the principle of periodic turbidometric assessment of growth rates at a given temperature over a given period. The data thus collected are automatically processed in a graphic format as a computer printout. The PAFE was determined as the difference in time (h) required for growth of the drug-free control and the drug-exposed test cultures to increase to 0.05 absorbance level following removal of the antifungal agent (by repeated washing). The adhesion of the single isolate to denture acrylic following limited exposure to nystatin was assessed by a previously described in vitro adhesion assay.

RESULTS

Significant PAFE were observed for nystatin, amphotericin-B and 5-fluorocytosine. A marginal PAFE was observed for ketoconazole and little or none for fluconazole. The mean duration of the PAFE of nystatin, amphotericin-B, 5-fluorocytosine, ketoconazole and fluconazole were 2.89 (+/- 0.27) h, 2.83 (+/- 0.23) h, 3.18 (+/- 0.31) h, 0.65 (+/- 0.11) h and 0.16 (+/- 0.06) h, respectively. The mean percentage reduction of adhesion of oral C. albicans BU47204 to denture acrylic during the PAFE period following exposure to nystatin for 10, 30, 50, 70 and 90 min was 9.12%, 61.73%, 65.99%, 82.16% and 83.14%, respectively.

CONCLUSIONS

These in vitro findings imply that even a short period of exposure to antifungals may result in modulation of the growth and the virulent attributes of C. albicans, which however is largely dictated by the antimycotic agent in question. Whether such mechanisms operate in vivo needs to be clarified by further studies.

Adhesion of oral C. albicans to human buccal epithelial cells following limited exposure to antifungal agents

The major aetiologic agent of oral candidosis is C. albicans, and adhesion to oral mucosal surfaces is considered a vital prerequisite for successful colonisation and subsequent infection by this agent. Although many antimycotics are available for the treatment of oral candidosis, the diluent effect of saliva and the cleansing action of the oral musculature often tend to reduce the availability of the agents below that of the effective therapeutic concentration. Therefore, the yeasts undergo only a limited exposure to the antifungals during therapy. Hence, the main aim of the present study was to determine the in vitro adhesion of ten isolates of oral C. albicans to buccal epithelial cells (BEC) following a short exposure to sublethal concentrations of four antifungal agents. The yeasts were exposed to sublethal concentrations of nystatin (x6 MIC), 5-fluorocytosine (x8 MIC), ketoconazole (x4 MIC) and fluconazole (x4 MIC) for a period of 1 h. Following subsequent removal of the drug, the adhesion of these isolates to BEC was assessed by a previously described adhesion assay. The mean percentage reductions of candidal adhesion to BEC following exposure to sublethal concentrations of nystatin, 5-fluorocytosine, ketoconazole and fluconazole were 72.88%, 16.52%, 40.16% and 24.36%, respectively. Ultrastructural studies revealed that short exposure to nystatin and the azoles (but not 5-fluorocytosine) resulted in aberrant cellular features. These findings indicate that subtherapeutic levels of antifungals may modulate candidal colonisation of the oral mucosa and thereby suppress the invasive potential of the pathogen.

Increased adherence of Candida albicans to buccal epithelial cells from patients with AIDS

The adherence of six clinical Candida albicans isolates to buccal epithelial cells obtained from AIDS patients, solid organ transplant recipients and healthy individuals was compared. It was shown that Candida albicans bound in significantly greater numbers to epithelial cells obtained from AIDS patients than to those from healthy individuals or transplant patients, and that the adherence capacity varied among the strains tested.

Azole resistance in Candida

Resistance of Candida to azoles is an increasing problem. Susceptibility testing of Candida against fluconazole and ketoconazole is now feasible and desirable. Good correlation of resistance in vitro with clinical failure of fluconazole therapy has now been shown in mucosal candidiasis. The relationship, if any, between resistance and clinical failure in the context of invasive candidiasis is not clear at present and additional correlative work needs to be done. Monitoring of resistance trends in Candida is clearly important now.

Comparative resistance of Candida albicans clinical isolates to fluconazole and itraconazole in vitro and in vivo in a murine model

Relationships between azole susceptibility and in vivo response to antifungal therapy in a murine model of candidiasis were investigated for Candida albicans isolates sampled from human immunodeficiency virus type 1-positive patients with oropharyngeal candidiasis. The susceptibilities of seven clinical isolates and two reference strains to fluconazole (FCZ) and itraconazole (ITZ) were determined in vitro by the broth microdilution method. Four isolates were resistant to FCZ and ITZ, two were susceptible to both azoles, and three were resistant to FCZ and susceptible to ITZ (dissociated resistance). CD1 mice were inoculated with each isolate and treated with either FCZ or ITZ (drug regimen, 5 mg/kg of body weight twice daily for 5 days). Quantitative cultures of kidneys were performed at the end of the treatment. On the other hand, the survival rates of the mice were followed daily. These two parameters were clearly correlated with in vitro susceptibility. Thus, the phenomenon of a dissociation of resistance to FCZ and ITZ may be found in vivo as well as in vitro.

[Laboratory diagnostic peculiarities of mycoses in immunosuppressed patients]

Domestic invasive mycoses are typically present as secondary diseases in patients definitely immunocompromised. This truth should not obscure the fact that a transient overload of the immune system, e.g. in the polytrauma patients, may likewise favour the development of mycoses. The two groups of patients show a comparable course of infection and, to some extent, diagnostic signs: surveillance cultures and monitoring of antibodies are more helpful with trauma patients and less reliable in the typically immunocompromised patients. In the latter, however, antigen tests may yield more reliable results than in the trauma patients. The different functional capacities of the immune system in the two groups of patients may also affect the appearance of fungal elements, particularly of aspergilli, in secretions and biopsies.