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In vitro susceptibilities of Candida bloodstream isolates to the new triazole antifungal agents BMS-207147, Sch 56592, and voriconazole.

BMS-207147, Sch 56592, and voriconazole are three new investigational triazoles with broad-spectrum antifungal activity. The in vitro activities of these three agents were compared with those of itraconazole and fluconazole against 1,300 bloodstream isolates of Candida species obtained from over 50 different medical centers in the United States. The MICs of all of the antifungal drugs were determined by broth microdilution tests performed according to the National Committee for Clinical Laboratory Standards method using RPMI 1640 as a test medium. BMS-207147, Sch 56592, and voriconazole were all quite active against all Candida sp. isolates (MICs for 90% of the isolates tested [MIC90s], 0.5, 1.0, and 0.5 microgram/ml, respectively). Candida albicans was the most susceptible species (MIC90s, 0.03, 0.06, and 0.06 microgram/ml, respectively), and C. glabrata was the least susceptible (MIC90s, 4. 0, 4.0, and 2.0 microgram/ml, respectively). BMS-207147, Sch 56592, and voriconazole were all more active than itraconazole and fluconazole against C. albicans, C. parapsilosis, C. tropicalis, and C. krusei. There existed a clear rank order of in vitro activity of the five azoles examined in this study when they were tested versus C. glabrata: voriconazole > BMS-207147 = Sch 56592 = itraconazole > fluconazole (MIC90s, 2.0, 4.0, 4.0, 4.0, and 64 microgram/ml, respectively). For isolates of Candida spp. with decreased susceptibility to both itraconazole and fluconazole, the MICs of BMS-207147, Sch 56592, and voriconazole were also elevated. These results suggest that BMS-207147, Sch 56592, and voriconazole all possess promising antifungal activity and that further in vitro and in vivo investigations are warranted to establish the clinical value of this improved potency.

Antifungal Agents↗

In vitro and in vivo activities of SCH 56592 (posaconazole), a new triazole antifungal agent, against Aspergillus and Candida.

SCH 56592 (posaconazole), a new triazole antifungal agent, was tested in vitro, and its activity was compared to that of itraconazole against 39 Aspergillus strains and to that of fluconazole against 275 Candida and 9 Cryptococcus strains. The SCH 56592 MICs for Aspergillus ranged from </=0.002 to 0.5 microg/ml, and those of itraconazole ranged from </=0.008 to 1 microg/ml. The SCH 56592 MICs for Candida and Cryptococcus strains ranged from </=0. 004 to 16 microg/ml, and those of fluconazole ranged from </=0.062 to >64 microg/ml. SCH 56592 showed excellent activity against Aspergillus fumigatus and Aspergillus flavus in a pulmonary mouse infection model. When administered therapeutically, the 50% protective doses (PD(50)s) of SCH 56592 ranged from 3.6 to 29.9 mg/kg of body weight, while the PD(50)s of SCH 56592 administered prophylactically ranged from 0.9 to 9.0 mg/kg; itraconazole administered prophylactically was ineffective (PD(50)s, >75 mg/kg). SCH 56592 was also very efficacious against fluconazole-susceptible, -susceptible dose-dependent, or -resistant Candida albicans strains in immunocompetent or immunocompromised mouse models of systemic infection. The PD(50)s of SCH 56592 administered therapeutically ranged from 0.04 to 15.6 mg/kg, while the PD(50)s of SCH 56592 administered prophylactically ranged from 1.5 to 19.4 mg/kg. SCH 56592 has excellent potential for therapy against serious Aspergillus or Candida infections.

Animals↗

Prospective study of Candida species in patients at a comprehensive cancer center.

Since most nosocomial systemic yeast infections arise from the endogenous flora of the patient, we prospectively evaluated the species stratification and antifungal susceptibility profile of Candida spp. associated with heavy colonization and systemic infection in patients at Memorial Sloan-Kettering Cancer Center in New York. A total of 349 Candida isolates were obtained from 223 patients during the later half of 1998. Cancer was the most common underlying disease, occurring in 91% of the patients, including 61.8% with organ and 23.7% with hematological malignancies; 4.4% of the patients had AIDS. Candida albicans was the predominant species (67.3%); among 114 non-albicans Candida spp., C. glabrata (45.6%) was the most frequent, followed by C. tropicalis (18.4%), C. parapsilosis (16.6%), and C. krusei (9.6%). The overall resistance to triazole-based agents among all yeast isolates was 9.4 and 10.8% for fluconazole and itraconazole, respectively. A total of 5% of C. albicans strains were resistant to triazole antifungals, whereas 30.8 and 46.2% of C. glabrata strains were resistant to fluconazole (MIC > or = 64 microg/ml) and itraconazole (MIC > or = 1 microg/ml), respectively. A significant association was observed between prior treatment with triazole and isolation of fluconazole-resistant C. albicans (P = 0.005, OR 36), although this relationship was not seen in C. glabrata isolates (P = 0.4). This study reinforces the importance of periodic, prospective surveillance of clinical fungal isolates to determine appropriate prophylactic, empiric, and preemptive antifungal therapy for the highly susceptible patient population.

Antifungal Agents↗

Fluconazole susceptibility of vaginal isolates obtained from women with complicated Candida vaginitis: clinical implications.

Despite considerable evidence of azole resistance in oral candidiasis due to Candida species, little is known about the azole susceptibilities of the genital tract isolates responsible for vaginitis. The fluconazole susceptibilities of vaginal isolates obtained during a multicenter study of 556 women with complicated Candida vaginitis were determined by evaluating two fluconazole treatment regimens. Of 393 baseline isolates of Candida albicans, 377 (96%) were highly susceptible to fluconazole (MICs, <8 microg/ml) and 14 (3.6%) were resistant (MICs, >or=64 microg/ml). Following fluconazole therapy, one case of in vitro resistance developed during 6 weeks of monitoring. In accordance with the NCCLS definition, in vitro fluconazole resistance correlated poorly with the clinical response, although a trend of a higher mycological failure rate was found (41 versus 19.6% on day 14). By using an alternative breakpoint of 1 micro g/ml, based upon the concentrations of fluconazole achievable in vaginal tissue, no significant differences in the clinical and mycological responses were observed when isolates (n = 250) for which MICs were 1 microg/ml, although a trend toward an improved clinical outcome was noted on day 14 (odds ratio, >2.7; 95% confidence interval, 0.91, 8.30). Although clinical failure was uncommon, symptomatic recurrence or mycological relapse almost invariably occurred with highly sensitive strains (MICs, <1.0 microg/ml). In vitro fluconazole resistance developed in 2 of 18 initially susceptible C. glabrata isolates following fluconazole exposure. Susceptibility testing for women with complicated Candida vaginitis appears to be unjustified.

Candida albicans↗

Fungicidal activity of fluconazole against Candida albicans in a synthetic vagina-simulative medium.

Fluconazole (FLZ) has emerged as a highly successful agent in the management of systemic infections of Candida. Cure rates for symptomatic candidiasis following single 150-mg FLZ dose therapy exceed 90%. In vitro, however, FLZ is fungistatic only in a narrow pH range and is not effective at vaginal pH, 4.2. This study evaluated the effect of FLZ on Candida albicans under in vitro conditions resembling the vaginal microenvironment, using vagina-simulative medium (VS). We found that FLZ was fungicidal for C. albicans in VS, but not in other media at the same pH, 4.2. In VS, FLZ was fungicidal at concentrations of >/=8 micro g/ml and reduced viability by greater than 99.9%. Analysis of the components of VS indicated that 17 mM acetic acid, a concentration achieved in the vagina, was responsible for the synergistic, fungicidal effect. This effect was not seen at neutral pH. Other substrates were not effective substitutes for acetic acid; however, short-chained carboxylic acids, glyoxylate and malonate, were effective. Most strains of C. albicans that were resistant to FLZ under standard conditions were killed by FLZ plus acetate. Other species of Candida were also killed, except C. krusei and C. glabrata. This study shows that FLZ has fungicidal activity for Candida species under in vitro conditions that mimic the vaginal microenvironment. This raises the possibility that FLZ may also have fungicidal effects during treatment of vaginal candidiasis. Elucidating the mechanism by which FLZ and acetate interact may disclose vulnerable pathways that could be exploited in drug development.

Acetic Acid↗

Treatment of Candida glabrata infection in immunosuppressed mice by using a combination of liposomal amphotericin B with caspofungin or micafungin.

While Candida albicans remains the most common Candida isolate, Candida glabrata accounts for approximately 15 to 20% of all Candida infections in the United States. In this study we used immunosuppressed mice infected with C. glabrata to investigate the efficacy of liposomal amphotericin B alone or in combination with the echinocandin caspofungin or micafungin. For monotherapy, mice were given six daily doses of liposomal amphotericin B (3 to 20 mg/kg of body weight), caspofungin (1 to 5 mg/kg), or micafungin (2.5 to 10 mg/kg). With concomitant therapy, mice received liposomal amphotericin B (7.5 mg/kg) in addition to caspofungin (2.5 mg/kg) or micafungin (2.5 mg/kg) for 6 days. For sequential therapy, liposomal amphotericin B was administered on days 1 to 3 and caspofungin or micafungin was given on days 4 to 6; conversely, caspofungin or micafungin was administered on days 1 to 3 and liposomal amphotericin B was given on days 4 to 6. Efficacy was based on the number of CFU per gram of kidney 21 days postchallenge. Monotherapy with liposomal amphotericin B (7.5 to 20 mg/kg) was significantly more effective than no drug treatment (control group) (P < 0.05) and demonstrated a dose-dependent response, with 20 mg/kg lowering the CFU/g from 6.3 to 4.2 (significantly different from the value for the control group [P < 0.001]). Monotherapy with all echinocandin doses lowered the CFU/g from 6.0 to 6.4 to 2.7 to 3.3 (significantly different from the value for the control group [P < 0.001]) with no dose-dependent response. Complete clearance of infection could be achieved only when liposomal amphotericin B was given either concomitantly with caspofungin or micafungin or if liposomal amphotericin B was given sequentially with caspofungin. In conclusion, the combination of liposomal amphotericin B with an echinocandin markedly improved the therapeutic outcome in murine C. glabrata systemic infection.

Amphotericin B↗

Topical caspofungin for treatment of keratitis caused by Candida albicans in a rabbit model.

Candida albicans is the most frequent cause of fungal keratitis in temperate regions. Caspofungin has potent activity against Candida spp. in a variety of clinical settings. Little is known, however, about its activity against fungal keratitis. We compared the efficacy of topical caspofungin with that of topical amphotericin B (AMB) in a rabbit model of experimental keratomycosis. Keratitis was induced with a standardized inoculum of Candida albicans (SC 5314) placed on the debrided cornea. Twenty-four hours after infection, animals were randomly assigned to treatment with 0.15% caspofungin, 0.5% caspofungin, 0.15% AMB, and a saline control (n = 12 rabbits in each group). For the first 12 h, treatment was repeated every 30 min and, after a 12-h pause, was resumed at hourly intervals for another 12 h. The animals were examined and killed 12 h after administration of the last dose. Treatment effects were evaluated by clinical assessment, fungal culture, and histopathology. Drug treatment significantly reduced corneal fungal recovery from 3.78 log10 CFU in saline-treated animals to 2.97, 1.76, and 1.18 log10 CFU in animals treated with 0.15% caspofungin, 0.5% caspofungin, and 0.15% AMB, respectively. By histopathology, the mean hyphal density was significantly lower in the corneas of treated animals than in those of the controls; there was no difference in hyphal densities between the different treatment groups. The depth of corneal invasion was not significantly reduced by the antifungal treatments. By clinical assessment, keratitis progressed in animals treated with saline, whereas disease progression was inhibited by all drug treatment regimens. In our rabbit model, 0.5% caspofungin was as effective as 0.15% AMB for the topical treatment of Candida keratitis. The potential clinical efficacy of caspofungin awaits further investigation.

Administration, Topical↗

Elevated Candida antigen titers are associated with neutrophil dysfunction after injury.

This study was undertaken to determine if impaired neutrophil (polymorphonuclear leukocytes [PMNL]) function is associated with an elevated Candida antigen titer after injury. PMNL from eight severely injured adults with Candida antigen titers of > or = 1:4 (titer positive) were evaluated for the ability to inhibit growth of Candida albicans in vitro by using a [3H]glucose incorporation assay. PMNL from eight severely injured adults with titers of < 1:4 (titer negative) and from eight healthy volunteers were studied for comparison. PMNL from the titer-positive patients had suppressed ability to inhibit C. albicans growth compared with PMNL from titer-negative patients and healthy volunteers. In vitro, PMNL function against C. albicans could be augmented significantly by cytokines. Granulocyte macrophage-colony-stimulating factor was most potent at augmenting function, followed by interleukin-8 and gamma interferon. Injured patients with elevated candida antigen titers have impaired PMNL function against C. albicans, and this function can be restored by cytokines.

Adult↗

Elevated fecal Candida counts in patients with antibiotic-associated diarrhea: role of soluble fecal substances.

To assess the role of soluble fecal substances in the elevation of fecal Candida counts in patients with antibiotic-associated diarrhea (AAD), we investigated the growth of Candida albicans in vitro in serially diluted stool fluids from patients with AAD and healthy subjects. There were significantly higher Candida albicans counts in stool fluids diluted 1:10 from AAD patients than in healthy subjects and the phosphate-buffered saline growth control, which may be due to reduced soluble Candida inhibitors and increased availability of growth factors and nutrients.

Anti-Bacterial Agents↗

Competitive binding inhibition enzyme-linked immunosorbent assay that uses the secreted aspartyl proteinase of Candida albicans as an antigenic marker for diagnosis of disseminated candidiasis.

The secreted aspartyl proteinases (Saps) of Candida albicans have been implicated as virulence factors associated with adherence and tissue invasion. The potential use of proteinases as markers of invasive candidiasis led us to develop a competitive binding inhibition enzyme-linked immunosorbent assay (ELISA) to detect Sap in clinical specimens. Daily serum and urine specimens were collected from rabbits that had been immunosuppressed with cyclophosphamide and cortisone acetate and infected intravenously with 10(7) C. albicans blastoconidia. Disseminated infection was confirmed by organ culture and histopathology. Although ELISA inhibition was observed when serum specimens from these rabbits were used, more significant inhibition, which correlated with disease progression, occurred when urine specimens were used. Urine collected as early as 1 day after infection resulted in significant ELISA inhibition (mean inhibition +/- standard error [SE] compared with preinfection control urine, 15.7% +/- 2.7% [P < 0.01]), and inhibition increased on days 2 through 5 (29.4% +/- 4.8% to 44.5% +/- 3.5% [P < 0.001]). Urine specimens from immunosuppressed rabbits infected intravenously with Candida tropicalis, Candida parapsilosis, Candida krusei, Cryptococcus neoformans, Aspergillus fumigatus, or Staphylococcus aureus were negative in the assay despite culture-proven dissemination. Nonimmunosuppressed rabbits receiving oral tetracycline and gentamicin treatment were given 2 x 10(8) C. albicans blastoconidia orally or intraurethrally to establish colonization of the gastrointestinal tract or bladder, respectively, without systemic dissemination; urine specimens from these rabbits also gave negative ELISA results. Dissemination to the kidney and spleen occurred in one rabbit challenged by intragastric inoculation, and urine from this rabbit demonstrated significant inhibition in the ELISA (mean inhibition +/- SE by day 3 after infection, 32.9% +/- 2.7% [P < 0.001]). The overall test sensitivity was 83%, the specificity was 92%, the positive predictive value was 84%, the negative predictive value was 91%, and the efficiency was 89% (166 urine samples from 33 rabbits tested). The specificity, positive predictive value, and efficiency could be increased to 97, 95, and 92%, respectively, if at least two positive test results were required for a true positive designation. The ELISA was sensitive and specific for the detection of Sap in urine specimens from rabbits with disseminated C. albicans infection, discriminated between colonization and invasive disease, reflected disease progression and severity, and has the potential to be a noninvasive means to diagnose disseminated candidiasis.

Animals↗

Nucleotide oligomerization domain 2 (Nod2) is not involved in the pattern recognition of Candida albicans.

Nucleotide-binding oligomerization domain 2 (Nod2) pathways are known to interact with Toll-like receptor 2 (TLR2) and TLR4, which are pattern recognition receptors for Candida albicans. We observed that the prevalence of Nod2 polymorphisms was not increased in patients with Candida infections. Candida-induced cytokine production in individuals with Nod2 polymorphisms was unaffected. We conclude that Nod2 is unlikely to play an important role in the recognition of Candida albicans.

Adaptor Proteins, Signal Transducing↗

Inactivation of transcription factor gene ACE2 in the fungal pathogen Candida glabrata results in hypervirulence.

During an infection, the coordinated orchestration of many factors by the invading organism is required for disease to be initiated and to progress. The elucidation of the processes involved is critical to the development of a clear understanding of host-pathogen interactions. For Candida species, the inactivation of many fungal attributes has been shown to result in attenuation. Here we demonstrate that the Candida glabrata homolog of the Saccharomyces cerevisiae transcription factor gene ACE2 encodes a function that mediates virulence in a novel way. Inactivation of C. glabrata ACE2 does not result in attenuation but, conversely, in a strain that is hypervirulent in a murine model of invasive candidiasis. C. glabrata ace2 null mutants cause systemic infections characterized by fungal escape from the vasculature, tissue penetration, proliferation in vivo, and considerable overstimulation of the proinflammatory arm of the innate immune response. Compared to the case with wild-type fungi, mortality occurs much earlier in mice infected with C. glabrata ace2 cells, and furthermore, 200-fold lower doses are required to induce uniformly fatal infections. These data demonstrate that C. glabrata ACE2 encodes a function that plays a critical role in mediating the host-Candida interaction. It is the first virulence-moderating gene to be described for a Candida species.

Alleles↗

Effect of L1210 leukemia on the susceptibility of mice to Candida albicans infections.

This study was carried out to determine whether animals bearing L1210 leukemia were more susceptible to candida infection in the absence of immunosuppression and to determine also if the L1210 cells suppressed the inflammatory response of the animal host. Systemic infection was studied by intravenous injection of Candida albicans and checking for the number of candida organisms cultured from the blood and the kidneys. Localized infection was studied by intramuscular injection of C. albicans into the thighs and measuring the changes in the thigh size. Compared with tumor-free controls, the intravenous injection resulted in higher counts of C. albicans from the blood and the kidneys of tumor-bearing animals. No significant difference in the localized swelling was noted between tumor- and nontumor-bearing mice with respect to intramuscular injection of C. albicans. The results thus indicate that L1210 leukemia increases susceptibility of tumor-bearing animals to systemic candida infection. L1210 cells were shown to reduce the accumulation of neutrophils and to suppress the inflammatory reaction elicited by C. albicans.

Animals↗

Production and characterization of three monoclonal antibodies to Candida albicans proteins.

Three monoclonal antibodies, designated A2C7, C2C7, and F19, were produced which recognize proteins from Candida albicans. All are of the immunoglobulin G1 heavy chain and kappa light chain class. A2C7 and C2C7 immunoprecipitated three proteins contained in a partially purified fraction (region A) of a mycelial cytoplasmic extract of C. albicans. The apparent molecular weights of these proteins are 120,000 (120K) to 135K, 44K to 52K, to 38K. Monoclonal antibody F19 was reactive with proteins of 42K, 43K, and 50K in immunoblotting experiments. F19 was also able to form a precipitin band in agarose gel with protein(s) contained in region A. Limited proteolytic digestion of the three proteins immunoprecipitated by A2C7 and C2C7 demonstrated that both monoclonal antibodies recognized the same three Candida proteins and that there exists a significant degree of relatedness in primary structure among the three proteins. Proteins with apparent molecular weights of 120K to 135K, 44K to 52K, and 35K to 38K that were immunoprecipitated by sera from two patients with invasive candidiasis and by the serum from a rabbit immunized against a 48K (44K to 52K) Candida protein were also analyzed by limited proteolysis. Patterns of peptide fragments generated by enzymatic digestion of these proteins showed that the proteins recognized by the monoclonal antibodies are the same proteins recognized by antibodies in the sera of patients during an invasive Candida infection and by antibodies in the serum of the immune rabbit.

Animals↗

Protection by Candida albicans of Staphylococcus aureus in the establishment of dual infection in mice.

Candida albicans has been shown to stimulate infection in mice by a number of bacteria when both organisms are inoculated intraperitoneally (E. Carlson, Infect. Immun. 39:193-197, 1983). When subcutaneous and intraperitoneal inoculations were given with Staphylococcus aureus and C. albicans injected at opposite sites, mixed infection was established at the site of fungal inoculation but not at the site of the bacterial injection. Histopathologic evaluation of tissues for the presence of C. albicans and S. aureus after intraperitoneal inoculation of both showed fungal growth in the mesentery and omentum of the abdominal cavity. Cocci were numerous and always associated with the fungi, located within the fungal growth rather than at its periphery. It was concluded that this growth pattern in some way protected the bacteria and was the basis for the generalized fungal stimulation of the bacterial infections observed. In addition to C. albicans, Candida stellatoidea, Candida tropicalis, Candida parapsilosis, Torulopsis glabrata, and heat-inactivated C. albicans also demonstrated some ability to protect bacteria injected simultaneously, although C. parapsilosis and T. glabrata were less effective than the other yeasts in this respect.

Adhesiveness↗

Characterization of a secretory proteinase of Candida parapsilosis and evidence for the absence of the enzyme during infection in vitro.

The opportunistic yeastlike fungi of the genus Candida comprise three species which are proteolytic in vitro. Among them, C. albicans and C. tropicalis are of foremost medical importance. However, a strict correlation between extracellular proteolytic activity and virulence is opposed by the low virulence of the third proteolytic species, C. parapsilosis. We purified the secretory acid proteinase of C. parapsilosis (clinical isolate 265). The enzyme is a carboxyl proteinase (EC 3.4.23) like all other secretory Candida proteinases handled so far. Proteinase 265 is distinguished by a lower molecular weight (approximately 33,000); it has increased hydrophobicity, which accounts for inhibition of the enzyme by hemin, and required the presence of nonionic detergent in the initial steps of purification. The enzyme already undergoes alkaline denaturation at neutrality. Its activity is thus confined to the acid microenvironment of the fungal cell wall. Within this range, the enzyme may degrade immunoglobulins like immunoglobulin A1 (IgA1), IgA2, and secretory IgA. No indication was found for glycosylation of proteinase 265 and the related enzyme of C. albicans CBS 2730. However, the comparable proteinase of C. tropicalis 293 was identified as a manno protein. Antiserum against proteinase 265 cross-reacted strongly with corresponding enzymes from other Candida species. Antisera against proteinases of C. albicans and C. tropicalis reacted only weakly with proteinase 265. Thus, secretory Candida proteinases are likely to possess common and species-specific antigenic sites. In contrast to C. albicans, infection of phagocytes by C. parapsilosis 265 was not accompanied by secretion of fungal proteinase. This lack of induction of the enzyme under conditions of infection may account for the low virulence of most isolates of C. parapsilosis.

Animals↗

Molecular cloning of the secretory acid proteinase gene from Candida albicans and its use as a species-specific probe.

Candida albicans secretes an acid proteinase when grown with a protein as a sole nitrogen source. The gene encoding this proteinase was isolated from a genomic expression library of C. albicans constructed in lambda gt11 by screening with antiproteinase antibodies. The affinity-purified antibodies used to verify the clones are monspecific; these do not cross-react with any other protein in the culture supernatants or crude extracts of C. albicans but strongly react with fusion proteins encoded by recombinant clones, revealing that these are true proteinase clones. Genomic Southern blot analysis shows that the proteinase gene is present at a unique locus and that there is no other closely related gene in the C. albicans genome. The proteinase gene probe identified two transcripts on Northern blots (RNA blots), which are present at a much higher level in C. albicans cells induced for proteinase secretion than in uninduced cells. The aspartyl proteinase gene reported earlier (T.J. Lott, L.S. Page, P. Boiron, J. Benson, and E. Reiss, Nucleic Acids Res. 17:1779, 1989) is not that of secretory acid proteinase, since the N-terminal amino acid sequence of secretory acid proteinase does not correspond to the deduced amino acid sequence of the aspartyl proteinase gene. The secretory acid proteinase gene was used to probe Southern blots of genomic DNA of several medically important Candida species and Saccharomyces cerevisiae. Under hybridization and wash conditions of low stringency, Candida tropicalis and Candida parapsilosis, in addition to C. albicans strains, gave specific signals, implying that C. tropicalis and C. parapsilosis have homologous secretory acid proteinase genes. However, under under wash conditions of high stringency, signals were obtained only with C. albicans strains, suggesting that this gene can be used as a species-specific probe. A simple yeast colony hybridization technique is sufficient to distinguish C. albicans from other yeasts.

Animals↗

Gene isolation by complementation in Candida albicans and applications to physical and genetic mapping.

We have isolated three genes, ARG57, SER57, and LYS1, on the basis of their function in Candida albicans. A C. albicans transformation vector containing the C. albicans URA3 gene, a Candida ARS sequence, and a portion of the Saccharomyces cerevisiae 2 microns circle containing the replication origin was constructed. Clones from genomic libraries in this vector were isolated by direct complementation of the auxotrophies in strain 1006 (arg57 ser57 lys1 ura3 MPA1). Transformants typically contain two to four plasmids in a mixed tandem multimer. A scheme to resolve mixed multimers into monomers in vivo by transformation of S. cerevisiae with Candida transformant DNA selecting Ura+ transformants was devised. Monomeric plasmids were then isolated by transformation of Escherichia coli with the S. cerevisiae transformant DNA. These were retested by transformation of strain 1006 to identify the specific plasmid that complemented the auxotrophy. The chromosomal locations of the genes were determined by hybridization to C. albicans chromosomes separated on contour-clamped homogenous electric field gels. We used these locations to assess the stability of individual C. albicans chromosomes in parasexual genetic analysis. The Lys(+)-complementing clone was shown to be LYS1 by complementation of S. cerevisiae lys1 mutants. These cloned genes help to align the Candida physical and genetic maps and provide additional markers for the transformation system.

Candida albicans↗