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ABSTRACTAn association between reduced susceptibility to echinocandins and changes in the 1,3-β-d-glucan synthase (GS) subunit Fks1p was investigated. Specific mutations in fks1genes from Saccharomyces cerevisiaeand Candida albicansmutants are described that are necessary and sufficient for reduced susceptibility to the echinocandin drug caspofungin. One group of amino acid changes in ScFks1p, ScFks2p, and CaFks1p defines a conserved region (Phe 641 to Asp 648 of CaFks1p) in the Fks1 family of proteins. The relationship between several of these fks1mutations and the phenotype of reduced caspofungin susceptibility was confirmed using site-directed mutagenesis or integrative transformation. Glucan synthase activity from these mutants was less susceptible to caspofungin inhibition, and heterozygous and homozygous Cafks1 C. albicansmutants could be distinguished based on the shape of inhibition curves. The C. albicansmutants were less susceptible to caspofungin than wild-type strains in a murine model of disseminated candidiasis. Five Candidaisolates with reduced susceptibility to caspofungin were recovered from three patients enrolled in a clinical trial. Four C. albicansstrains showed amino acid changes at Ser 645 of CaFks1p, while a single Candida kruseiisolate had a deduced R1361G substitution. The clinical C. albicansmutants were less susceptible to caspofungin in the disseminated candidiasis model, and GS inhibition profiles and DNA sequence analyses were consistent with a homozygous fks1mutation. Our results indicate that substitutions in the Fks1p subunit of GS are sufficient to confer reduced susceptibility to echinocandins in S. cerevisiaeand the pathogens C. albicansand C. krusei.

ABSTRACTCaspofungin acetate (MK-0991) is an antifungal antibiotic that inhibits the synthesis of 1,3-β-d-glucan, an essential component of the cell wall of several pathogenic fungi. Caspofungin acetate was recently approved for the treatment of invasive aspergillosis in patients who are refractory to or intolerant of other therapies. The activity of 1,3-β-d-glucan synthesis inhibitors against Aspergillus fumigatushas been evaluated in animal models of pulmonary or disseminated disease by using prolongation of survival or reduction in tissue CFU as assay endpoints. Because these methods suffer from limited sensitivity or poor correlation with fungal growth, we have developed a quantitative PCR-based (qPCR) (TaqMan) assay to monitor disease progression and measure drug efficacy. A. fumigatusadded to naı̈ve, uninfected kidneys as either ungerminated conidia or small germlings yielded a linear qPCR response over at least 4 orders of magnitude. In a murine model of disseminated aspergillosis, a burden of A. fumigatuswas detected in each of five different organs at 4 days postinfection by the qPCR assay, and the mean fungal load in these organs was 1.2 to 3.5 log10units greater than mean values determined by CFU measurement. When used to monitor disease progression in infected mice, the qPCR assay detected an increase of nearly 4 log10conidial equivalents/g of kidney between days 1 and 4 following infection, with a peak fungal burden that coincided with the onset of significant mortality. Traditional CFU methodology detected only a marginal increase in fungal load in the same tissues. In contrast, when mice were infected with Candida albicans, which does not form true mycelia in tissues, quantitation of kidney burden by both qPCR and CFU assays was strongly correlated as the infection progressed. Finally, treatment of mice with induced disseminated aspergillosis with either caspofungin or amphotericin B reduced the A. fumigatusburden in infected kidneys to the limit of detection for the qPCR assay. Because of its much larger dynamic range, the qPCR assay is superior to traditional CFU determination for monitoring the progression of disseminated aspergillosis and evaluating the activity of antifungal antibiotics against A. fumigatus.

The JB-6 mouse epidermal cell line has been used as a model system for studying the mechanism of late-stage promoter-dependent preneoplastic progression. The studies reported here are concerned with determining whether there is a requirement for mitogenic stimulation in promotion of anchorage independence and tumorigenicity in JB-6 cells. Such a requirement would predict that variants selected for 12-O-tetradecanoylphorbol 13-acetate (TPA) mitogen resistance would also be promotion resistant. Promotion-responsive cell lines have been selected for resistance to TPA-induced mitogenic stimulation at plateau density by cotreatment with colchicine and removal of mitogen-responsive colchicine-detached cells. The selected TPA-resistant population of cells showed a mitogenic response that was diminished by a factor of four but showed no diminution in the promotion-of-anchorage-independence response to TPA. Mitogen-resistant clonal lines derived from the selected population fell into three phenotypic classes when assayed in soft agar: (i) anchorage-independent transformants; (ii) variants resistant to promotion of anchorage independence by TPA; and (iii) variants sensitive to promotion by TPA. The existence of the latter class (i.e., the mitogen-resistant promotable variants) indicates a lack of obligatory causal relationship between TPa-induced mitogenesis and late-stage promotion and, thereby suggests that the two events can be dissociated.

Rustmicin is a 14-membered macrolide previously identified as an inhibitor of plant pathogenic fungi by a mechanism that was not defined. We discovered that rustmicin inhibits inositol phosphoceramide synthase, resulting in the accumulation of ceramide and the loss of all of the complex sphingolipids. Rustmicin has potent fungicidal activity against clinically important human pathogens that is correlated with its sphingolipid inhibition. It is especially potent against Cryptococcus neoformans, where it inhibits growth and sphingolipid synthesis at concentrations <1 ng/ml and inhibits the enzyme with an IC50 of 70 pM. This inhibition of the membrane-bound enzyme is reversible; moreover, rustmicin is nearly equipotent against the solubilized enzyme. Rustmicin was efficacious in a mouse model for cryptococcosis, but it was less active than predicted from its in vitro potency against this pathogen. Stability and drug efflux were identified as two factors limiting rustmicin's activity. In the presence of serum, rustmicin rapidly epimerizes at the C-2 position and is converted to a gamma-lactone, a product that is devoid of activity. Rustmicin was also found to be a remarkably good substrate for the Saccharomyces cerevisiae multidrug efflux pump encoded by PDR5.

Although many detection methods have been used to determine Helicobacter colonization in small animal models, the sensitivity and specificity of these detection methods are limited. To improve the Helicobacter felis conventional mouse model for accurate evaluation of therapeutic regimens, we developed a PCR for detection of, and a competitive PCR for quantitation of, H. felis in viral antibody-free (VAF) mice. The PCR was based on the H. felis 16S rRNA gene. An internal control DNA was used for competitive quantitation of the PCR. VAF conventional Swiss-Webster mice were infected with an H. felis culture by oral gavage. At various times after H. felis challenge and therapy, stomach mucosa was collected and evaluated by PCR. PCR detected approximately 50 to 100 H. felis cells per mouse stomach and showed no cross-reaction with other bacteria commonly found in mouse stomachs. Colonization of H. felis in the mouse stomach was confirmed by culture isolation from germfree mice and histological examination of VAF mice. Response to therapy in this H. felis model correlated well with results seen in human clinical trials with H. pylori. A model utilizing PCR detection which may be useful for discovering new antibiotics and/or vaccines against Helicobacter ulcer disease has been developed.

Many animal models of Helicobacter infection have been described, including infection in rhesus monkeys, ferrets, gnotobiotic piglets, and mice. These animal models utilize a combination of detection methods, including culture, urease testing, and histopathology, all of which may be unreliable, insensitive, or labor-intensive. Development of new animal models of Helicobacter pylori requires new methods of detection with increased sensitivity and specificity. We have developed sensitive and specific PCR primers based on the 16S ribosomal gene sequence of H. pylori. The primers detected single-copy 16S DNA representing 0.2 cell of pure H. pylori (2 cells in the presence of mouse stomach mucosal DNA) and did not cross-react with closely related bacteria. We were able to detect colonization by H. pylori in conventional, euthymic, outbred mice up to 4 weeks postinoculation with a high percentage of isolates tested. One isolate of H. pylori was detected by PCR in 100% of the mice at 6 months and 60% of the mice 1 year after inoculation. Approximately 10(3) to 10(4) H. pylori cells per stomach were detected by utilizing this PCR methodology semiquantitatively. These primers and PCR methodology have facilitated detection of H. pylori colonization in conventional, euthymic mice, colonization which may not have been detectable by other methods.

The luminol-enhanced chemiluminescence (CL) assay is a measure of the early events of phagocytosis, leukocyte activation, and immune cell interactions. Reduction in the CL response of immune cells may be indicative of an inhibition of the immune response. This study was undertaken to examine the effects of antifungal agents tested at concentrations above and below therapeutically achievable levels on the CL response of mouse spleen cells. The effects of six antifungal agents--amphotericin B, ketoconazole, miconazole, 5-fluorocytosine, Bay-n-7133, and ICI 153,066--were studied. Changes in the CL response were assessed in terms of peak intensity and area under the intensity-time curve compared with appropriate diluent controls for each drug. Only amphotericin B and ketoconazole caused statistically significant lowering of the peak intensity at levels that are therapeutically attainable (mean peak plasma levels of 2 to 4 and 3.5 to 16 micrograms/ml, respectively). Although amphotericin B and ketoconazole caused reduction in the CL response, removal of the unbound drug in the preparation by centrifugation, washing, and suspension of cells in fresh drug-free medium resulted in a return of CL activity equivalent to the activity observed in cells not exposed to these agents. These results suggest that amphotericin B and ketoconazole at therapeutic concentrations may cause a reduction in immune cell antimicrobial activity; the clinical significance of these observations remains to be determined.

Chemiluminescence is the result of the respiratory burst generated by phagocytic cells after stimulation by antigen. The measurement of chemiluminescence represents a sensitive means for detecting antigenic stimulation and immune cell function. Although the kinetics of chemiluminescence reactions have been described, appropriate statistical methods for the evaluation of data from chemiluminescence assays have not been reported. Based on examination of data from several studies in which the chemiluminescence response of spleen cells was investigated after stimulation with the particulate antigen zymosan, recommendations are made for the design and statistical evaluation of such studies. Three parameters were used in assessing the chemiluminescence response; peak intensity of the emitted light, time to peak, and the area under the intensity-time curve. The data indicated that peak intensity alone provides an adequate characterization of the chemiluminescence response. Since percent change in response upon treatment is of interest, analysis on the log scale is appropriate, and the statistical procedure of choice in evaluating data of this type is a trend analysis. The need for a balanced allocation of treatments to avoid potential bias is demonstrated. The methods proposed are illustrated with data from two studies in which the effect of preincubation with low concentrations of ketoconazole, an antifungal agent, on the chemiluminescence response of BALB/cBY spleen cells was examined.

Opportunistic infections caused by Candida tropicalis have been noted with increasing frequency in compromised patients. The pathogenicity of three isolates of C. tropicalis was studied in normal CD-1 mice, streptozotocin-induced diabetic mice, and cyclophosphamide-induced neutropenic mice. Lethal dose 50% endpoints and quantitative distribution of yeast cells in spleen, liver, and kidneys of mice infected intravenously were determined. The virulence of one yeast isolate was greater than that of the other two. The order of susceptibility to mortality and degree of organ colonization was neutropenic greater than diabetic greater than normal. Renal lesions resembling those associated with infection by C. albicans appeared by day 5 postinfection in diabetic and neutropenic mice. Greater numbers of C. tropicalis yeast cells were isolated from homogenates of the affected kidneys, suggesting that the kidney is a target organ for this fungus. This study demonstrates the increased susceptibility of compromised mice to C. tropicalis as compared with normal mice and verifies the ability of these yeasts to cause opportunistic disease.

The isolation and structure elucidation of 1 from the Basidomycete fungus Baeospora myosura is described. This new ene-triyne antibiotic was most potent against Gram-positive bacteria, while it was less active against Gram-negative bacteria and a yeast. MICs against several strains of Staphylococcus aureus were as low as 0.001 μg/mL. Analogues of 1 that did not contain the ene-triyne moiety were inactive against all microorganisms tested. The isolation of this new natural product was complicated by the highly reactive nature of the conjugated terminal polyacetylene.

Lonchocarpol A, a flavanone, demonstrates in vitro inhibitory activity against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium. This activity is antagonized by mouse plasma, which may account for its lack of in vivo activity. This compound demonstrates no differentiation with respect to the inhibition of RNA, DNA, cell wall, and protein synthesis.