Brief exposure to antimycotics reduces the extracellular phospholipase activity of Candida albicans and Candida tropicalis

An Association of an eBURST Group With Triazole Resistance of Candida tropicalis Blood Isolates

Candidemia, a bloodstream infection caused by genus Candida, has a high mortality rate. Candida albicans was previously reported to be the most common causative species among candidemia patients. However, during the past 10 years in Thailand, Candida tropicalis has been recovered from blood more frequently than C. albicans. The cause of this shift in the prevalence of Candida spp. remains unexplored. We conducted in vitro virulence studies and antifungal susceptibility profiles of 48 C. tropicalis blood isolates collected during 2015-2017. To compare to global isolates of C. tropicalis, multilocus sequence typing (MLST), a minimum spanning tree, and an eBURST analysis were also conducted. C. tropicalis and C. albicans were the most (47-48.7%) and second-most (21.5-33.9%) common species to be isolated from candidemia patients, respectively. Of the C. tropicalis blood isolates, 29.2, 0, 100, and 93.8% exhibited proteinase activity, phospholipase activity, hemolytic activity, and biofilm formation, respectively. Moreover, 20.8% (10/48) of the isolates were resistant to voriconazole and fluconazole, and also showed high minimum inhibitory concentrations (MICs) to posaconazole and itraconazole. In contrast, most of the isolates were susceptible to anidulafungin (97.9%), micafungin (97.9%), and caspofungin (97.9%), and showed low MICs to amphotericin B (100%) and 5-flucytosine (100%). The MLST identified 22 diploid sequence types. Based on the eBURST analysis and minimum spanning tree, 9 out of 13 members (69.2%) of an eBURST group 3 were resistant to voriconazole and fluconazole, and also showed high MICs to posaconazole and itraconazole. Association analysis revealed the eBURST group 3 was significantly associated with the four triazole resistance (p < 0.001). In conclusion, the eBURST group 3 was associated with the triazole resistance and resistance to many antifungal drugs might be collectively responsible for the prevalence shift.

The yeast, the antifungal, and the wardrobe: a journey into antifungal resistance mechanisms of Candida tropicalis

Candida tropicalis is a prominent non-Candida albicans Candida species involved in cases of candidemia, mainly causing infections in patients in intensive care units and (or) those presenting neutropenia. In recent years, several studies have reported an increase in the recovery rates of azole-resistant C. tropicalis isolates. Understanding C. tropicalis resistance is of great importance, since resistant strains are implicated in persistent or recurrent and breakthrough infections. In this review, we address the main mechanisms underlying C. tropicalis resistance to the major antifungal classes used to treat candidiasis. The main genetic basis involved in C. tropicalis antifungal resistance is discussed. A better understanding of the epidemiology of resistant strains and the mechanisms involved in C. tropicalis resistance can help improve diagnosis and assessment of the antifungal susceptibility of this Candida species to improve clinical management.

Silymarin, a Popular Dietary Supplement Shows Anti-Candida Activity

Silymarin is a complex of plant-derived compounds obtained from the seed shells of the milk thistle (Silybum marianum). It is used in medicine primarily to protect the liver. The mixture contains mainly flavonolignans, with silybin as a paramount bioactive component of the extract. This article presents the potential health benefits for silymarin as an antifungal drug against five references strains: C. albicans, C. glabrata, C. parapsilosis, C. tropicalis, and C. krusei with MIC (minimum inhibitory concentration) values ranging from 30 to 300 µg/mL. Additionally, this study revealed that the compound suppressed the growth of cells of most of the tested clinical Candida albicans strains with MIC values between 30 and 1200 µg/mL. Based on the fractional inhibitory concentration index (FICI), the combination of silymarin with antifungal drugs caspofungin, fluconazole, and amphotericin B did not significantly change the MIC values for the tested Candida strains. Furthermore, no antagonistic reactions were observed in any combination of drugs. In addition, this substance shows anti-virulence properties including the destabilization of mature biofilm and the inhibition of the secretion of hydrolases. qRT-PCR-based experiments demonstrated that the SAP4 gene involved in virulence was downregulated by silymarin. These results indicate completely new advantages of dietary supplementation with this natural plant extract.

Candida albicans and non-albicans Isolates from Bloodstream Have Different Capacities to Induce Neutrophil Extracellular Traps

Neutrophils activated with pathogens or their products induce formation of extracellular traps (NETs), but if this constitutes a general response against all pathogenic species in a single genus or intrageneric differences exist remains unknown, yet this is of great importance for the establishment of effective treatments. To determine this, we analyzed neutrophil extracellular traps formation after the stimulation with bloodstream isolates from different Candida species (Candida albicans, C. tropicalis, C. parapsilosis, and C. glabrata), and found that each species has a different capacity to induce DNA extrusion, which is independent of their morphology (yeast or hyphae). We observed that phospholipase producer's strains and their secretion products were able to induce NETs, a property not observed with phospholipase deficient strains, with exception of some Candida glabrata sensu stricto isolates, which showed no NETs induction although they did show phospholipase production. To further analyze this, we extended our study to include Candida glabrata cryptic species (C. bracarensis and C. nivariensis) and no extracellular traps formation was observed. Here, we contribute to the understanding of how neutrophils initiate NETs, and we found that certain strains may have a differential capacity to trigger these structures, which may explain the high mortality of some isolates.

Influence of subinhibitory antifungal concentrations on extracellular hydrolases and biofilm production by Candida albicans recovered from Egyptian patients

BACKGROUND

Extracellular hydrolases (phospholipase, aspartyl protease and haemolysin) and biofilm production are considered as major virulence factors of the opportunistic pathogenic fungus Candida albicans. However, the impact of antifungal therapy on such virulence attributes is not well investigated. The common antifungal agents may disturb the production of secreted hydrolases as well as biofilm formation. Accordingly, this study addressed the effect of subinhibitory concentrations (sub-MICs) of selected antifungal agents on some virulence factors of C. albicans clinical isolates.

METHODS

C. albicans isolates (n = 32) were recovered from different clinical samples and their identification was confirmed to the species level. Antifungal susceptibility profiles of isolates were determined against (nystatin, fluconazole and micafungin) and minimum inhibitory concentrations (MICs) were interpreted according to Clinical and Laboratory Standards Institute guidelines. Virulence determinants comprising secreted hydrolases (phospholipase, aspartyl protease and haemolysin) and biofilm formation were investigated in the presence of the sub-MICs of the tested antifungal agents.

RESULTS

Treatment of clinical C. albicans isolates with subinhibitory nystatin, fluconazole and micafungin concentrations significantly decreased production of extracellular hydrolases. Nystatin had the greatest inhibitory effect on phospholipase and aspartyl protease production. However, micafungin showed the highest reducing effect on the hemolytic activity of the treated clinical isolates. Moreover, nystatin and micafungin, but not fluconazole, had a noticeable significant impact on inhibiting biofilm formation of C. albicans clinical isolates.

CONCLUSION

Our findings highlighted the significant influences of commonly prescribed antifungal agents on some virulence factors of C. albicans. Accordingly, antifungal therapy may modulate key virulence attributes of C. albicans.

An Update on Candida tropicalis Based on Basic and Clinical Approaches

Candida tropicalis has emerged as one of the most important Candida species. It has been widely considered the second most virulent Candida species, only preceded by C. albicans. Besides, this species has been recognized as a very strong biofilm producer, surpassing C. albicans in most of the studies. In addition, it produces a wide range of other virulence factors, including: adhesion to buccal epithelial and endothelial cells; the secretion of lytic enzymes, such as proteinases, phospholipases, and hemolysins, bud-to-hyphae transition (also called morphogenesis) and the phenomenon called phenotypic switching. This is a species very closely related to C. albicans and has been easily identified with both phenotypic and molecular methods. In addition, no cryptic sibling species were yet described in the literature, what is contradictory to some other medically important Candida species. C. tropicalis is a clinically relevant species and may be the second or third etiological agent of candidemia, specifically in Latin American countries and Asia. Antifungal resistance to the azoles, polyenes, and echinocandins has already been described. Apart from all these characteristics, C. tropicalis has been considered an osmotolerant microorganism and this ability to survive to high salt concentration may be important for fungal persistence in saline environments. This physiological characteristic makes this species suitable for use in biotechnology processes. Here we describe an update of C. tropicalis, focusing on all these previously mentioned subjects.

Extracellular phospholipase production of oral Candida albicans isolates from smokers, diabetics, asthmatics, denture wearers and healthy individuals following brief exposure to polyene, echinocandin and azole antimycotics

Objective

Candida albicans is the primary causative agent of oral candidosis, and one of its key virulent attributes is considered to be its ability to produce extracellular phospholipases that facilitate cellular invasion. Oral candidosis can be treated with polyenes, and azoles, and the more recently introduced echinocandins. However, once administered, the intraoral concentration of these drugs tend to be sub-therapeutic and rather transient due to factors such as the diluent effect of saliva and cleansing effect of the oral musculature. Hence, intra-orally, the pathogenic yeasts may undergo a brief exposure to antifungal drugs. We, therefore, evaluated the phospholipase production of oral C. albicans isolates following brief exposure to sub-therapeutic concentrations of the foregoing antifungals.

Materials and methods

Fifty C. albicans oral isolates obtained from smokers, diabetics, asthmatics using steroid inhalers, partial denture wearers and healthy individuals were exposed to sub-therapeutic concentrations of nystatin, amphotericin B, caspofungin, ketoconazole and fluconazole for one hour. Thereafter the drugs were removed and the phospholipase production was determined by a plate assay using an egg yolk-agar medium.

Results

The phospholipase production of these isolates was significantly suppressed with a percentage reduction of 10.65, 12.14, 11.45 and 6.40% following exposure to nystatin, amphotericin B, caspofungin and ketoconazole, respectively. This suppression was not significant following exposure to fluconazole.

Conclusions

Despite the sub-therapeutic, intra oral, bioavailability of polyenes, echinocandins and ketoconazole, they are likely to produce a persistent antifungal effect by suppressing phospholipase production, which is a key virulent attribute of this common pathogenic yeast.

Aliphatic fatty acids and esters: inhibition of growth and exoenzyme production of Candida, and their cytotoxicity in vitro: anti-Candida effect and cytotoxicity of fatty acids and esters

The secretion of extracellular phospholipases and proteinases of Candida has been described as a relevant virulence factor in human infections. Aliphatic fatty acids have antimicrobial properties, but the mechanism by which they affect the virulence factors of microorganisms, such as Candida, is still unclear, and there are a few reports about their toxicity. The current study investigated the in vitro antifungal activity, exoenzyme production and cytotoxicity of some aliphatic fatty acids and their ester derivatives against the Candida species. The minimum inhibitory concentration and minimum fungicidal concentrations of aliphatic medium-chain fatty acids, methyl and ethyl esters were performed using the CLSI M27-A3 method and the cytotoxicity assay was performed according to ISO 10993-5. The influence of these compounds in the inhibition of the production of hydrolytic enzymes, phospholipases and proteinases by Candida was also investigated. Data analysis was performed using the one-way ANOVA method (p≤0.05). In relation to the MIC against Candida species, the fatty acid with the best result was Lauric acid, although its ester derivatives showed no activity. The inhibition of phospholipase production was more significant than the inhibition of proteinase production by Candida. Tested fatty acids revealed more than 80% cell viability in their MIC concentrations. Additionally, a cell viability of 100% was reported at concentrations of anti-enzymatic effect. Therefore, the potential use of these fatty acids could be the basis for more antimicrobial tests.

Antifungal susceptibility, exoenzyme production and cytotoxicity of novel oximes against Candida

Novel oximes were synthesized, their in vitro antifungal activity against Candida was evaluated and their cytotoxicity was determined. The procedure used for the synthesis of the oximes is aligned with the current green chemistry trend; water is employed as the solvent in this reaction. The minimum inhibitory and minimum fungicidal concentrations of the oximes were evaluated using the CLSI M27-A3 method. The influence of these compounds on the inhibition of the production of hydrolytic enzymes, phospholipase and proteinase by Candida was also investigated. The compounds showed a good ability to inhibit phospholipase, with a 50 % reduction in most cases. However, the tested compounds did not affect proteinase. The current results showed a substantial reduction in the phospholipase production, which suggests that compounds of this class may interfere with host infection and disease progression. The oximes examined showed lower fungicidal activities than fluconazole but interfered significantly with the expression of phospholipase. Some of the oximes included in this study could be a suitable matrix for the development of novel antifungal compounds.

Candida tropicalis: its prevalence, pathogenicity and increasing resistance to fluconazole

Candida tropicalis has been identified as the most prevalent pathogenic yeast species of the Candida-non-albicans group. Historically, Candida albicans has been the major species responsible for causing candidiasis in immunocompromised and immunocompetent patients. However, infections (candidiasis) due to C. tropicalis have increased dramatically on a global scale thus proclaiming this organism to be an emerging pathogenic yeast. The reasons for this organism's dominance and its resistance to fluconazole have been difficult to elucidate. In addition, the mechanism of this organism's pathogenicity and the consequent immune response remain to be clarified. This paper describes certain predisposing factors potentially responsible for these characteristics and presents a 'root cause analysis' to explain the increasing prevalence of C. tropicalis in developed and undeveloped countries, as well as the organism's acquired drug resistance. Control measures against fluconazole resistance in clinical management have also been discussed.

Phospholipase and proteinase activities of Candida isolates from denture wearers

The aim of the present study was to characterise phospholipase and proteinase activities of oral Candida isolates from 100 denture wearers and to study the relationship of these activities with denture stomatitis. Of 100 patients studied, 44 suffered from denture stomatitis. Specimens were collected by swabbing the denture and underlying mucosa. Isolates were previously identified by conventional mycological and genotypic methods. The phospholipase and proteinase activities were evaluated by agar plate methods. A total of 152 isolates were recovered from denture and underlying mucosa, including 101 Candida albicans, 18 Candida tropicalis, 14 Candida glabrata, 11 Candida guilliermondii, four Candida parapsilosis, two Saccharomyces cerevisiae and one isolate each of Candida dubliniensis and Candida krusei. Most C. albicans (97%) showed phospholipase activity; furthermore, the unique C. dubliniensis isolate showed a moderate phospholipase activity. The isolation of C. albicans (chi-square test, P = 0.0016) and phospholipase production by Candida spp. (chi-square test, P = 0.0213) was found to be significantly associated with denture stomatitis. Proteinase production was observed in <30% of isolates, and it was not related to the presence of denture stomatitis (P = 0.7675). Candida albicans isolates may produce both virulence factors, although the proteinase production was only observed in <30% of the isolates. Phospholipase production was exclusive of C. albicans and C. dubliniensis.

The effect of gentian violet on virulent properties of Candida albicans

The aim of this study was to evaluate the effect of gentian violet (GV) on phospholipase activity, proteinase activity and germ tube formation rate of Candida albicans. Both 12 phospholipase-positive and 12 proteinase-positive C. albicans isolates with Pz values <or=0.89 were obtained. A yeast suspension (1-3 x 10(7) cfu/ml) of each isolate was prepared. After a brief exposure (60 min) to sub-therapeutic concentrations (0.5 or 2 microg/ml) of GV, Pz value of phospholipase, Pz value of proteinase and germ tube formation rate were determined. Phospholipase activity, proteinase activity and germ tube formation rate in two groups exposed to GV were significantly lower than those in the group unexposed (P < 0.05). The results of this study indicated that sub-therapeutic concentrations of GV may lead to reduction in phospholipase activity, proteinase activity and germ tube formation, and then may suppress virulence and pathogenicity of C. albicans.

Distribution and phospholipase activity of Candida species in different denture stomatitis types

The aim of this study was to evaluate the correlation between frequency and phospholipase activity of Candida species and denture stomatitis according to Newton's classification. Seventy-five complete denture wearers were evaluated for the presence of yeasts on the palatal mucosa by culture method. In addition, the number of yeast isolates producing phospholipase and amount of this enzyme were determined using egg yolk agar plate method. According to Newton's classification, 25 denture wearers were with healthy palatal mucosa while 50 were with any types of denture stomatitis. The frequency of yeasts was linked to whether subjects had Type II or Type III, but not Type I denture stomatitis. Candida albicans was the most frequently isolated species in denture wearers with and without clinical signs of denture stomatitis and it was the only species produced phospholipase. Although the amount of phospholipase produced by the C. albicans isolates from denture wearers in control and Type II and III DS groups was not significantly different, there was statistically significant difference in the number of C. albicans isolates producing phospholipase between patients with and without clinical signs of DS.

Phospholipase activity of Candida albicans isolates from patients with denture stomatitis: the influence of chlorhexidine gluconate on phospholipase production

BACKGROUND AND OBJECTIVES

The extracellular phospholipases of Candida albicans are considered to play a significant role in the pathogenesis of human infections. Therefore 23 clinical oral isolates of C. albicans from patients with denture stomatitis and 22 commensal oral isolates obtained from the palatal mucosa of healthy subjects were assayed for phospholipase activity. It is generally accepted that chlorhexidine gluconate is an appropriate adjunct or an alternative to antimycotic therapy in the management of oral candidiasis. However, the intraoral concentrations of this antiseptic fluctuate considerably due to the dynamics of the oral cavity. So the second main objective of this study was to investigate the effect of brief exposure (30 min) to two sub-therapeutic concentrations (0.002% and 0.0012%) of chlorhexidine gluconate on the value of phospholipase production (Pz) of C. albicans.

METHOD

An in vitro phospholipase production was done by plate assay method using an egg yolk-agar medium.

RESULTS

No significant differences were found in the number of C. albicans isolates producing phospholipase between two groups. However, the mean value of Pz produced by the isolates from patients with denture stomatitis was significantly (p<0.05) higher than the commensals. Exposure of the isolates to 0.002% and 0.0012% chlorhexidine led to a significant (p<0.001 and p<0.01, respectively) reduction in the amount of phospholipase.

CONCLUSION

The results of this study imply that sub-therapeutic levels of chlorhexidine may modulate candidal phospholipase activity, thereby suppressing pathogenicity of C. albicans.

Hydrolytic enzymes as virulence factors of Candida albicans

Candida albicans is a facultative pathogenic micro-organism that has developed several virulence traits enabling invasion of host tissues and avoidance of host defence mechanisms. Virulence factors that contribute to this process are the hydrolytic enzymes. Most of them are extracellularly secreted by the fungus. The most discussed hydrolytic enzymes produced by C. albicans are secreted aspartic proteinases (Saps). The role of these Saps for C. albicans infections was carefully evaluated in numerous studies, whereas only little is known about the physiological role of the secreted phospholipases (PL) and almost nothing about the involvement of lipases (Lip) in virulence. They may play an important role in the pathogenicity of candidosis and their hydrolytic activity probably has a number of possible functions in addition to the simple role of digesting molecules for nutrition. Saps as the best-studied member of this group of hydrolytic enzymes contribute to host tissue invasion by digesting or destroying cell membranes and by degrading host surface molecules. There is also some evidence that hydrolytic enzymes are able to attack cells and molecules of the host immune system to avoid or resist antimicrobial activity. High hydrolytic activity with broad substrate specificity has been found in several Candida species, most notably in C. albicans. This activity is attributed to multigene families with at least 10 members for Saps and Lips and several members for PL B. Distinct members of these gene families are differentially regulated in various Candida infections. In future, prevention and control of Candida infections might be achieved by pharmacological or immunological tools specifically modulated to inhibit virulence factors, e.g. the family of Saps.

Exposure to therapeutic concentrations of ritonavir, but not saquinavir, reduces secreted aspartyl proteinase of Candida parapsilosis

The effect of ritonavir and saquinavir, HIV proteinase inhibitors, on the secreted aspartyl proteinase (Sap) activity of Candida parapsilosis was studied. In a proteinase-inducing medium (yeast carbon base-bovine serum albumin), Sap activity in all clinical isolates of C. parapsilosis (n = 20) was observed at 37 degrees C but not at 22 degrees C. The presence of ritonavir at a concentration of 8 microg/ml produced an inhibition close to 50% albumin consumption and also delayed yeast growth; however, saquinavir did not have any effect on growth or on Sap activity. In Sabouraud broth, which does not induce Sap production, no effect was shown on yeast growth by either of the two HIV proteinase inhibitors studied.