Search tips
Search criteria

Results 1-9 (9)

Clipboard (0)

Select a Filter Below

Year of Publication
1.  Molecular Mechanisms of Fluconazole Resistance in Candida parapsilosis Isolates from a U.S. Surveillance System 
Candida parapsilosis is the second or third most common cause of candidemia in many countries. The Infectious Diseases Society of America recommends fluconazole as the primary therapy for C. parapsilosis candidemia. Although the rate of fluconazole resistance among C. parapsilosis isolates is low in most U.S. institutions, the resistance rate can be as high as 7.5%. This study was designed to assess the mechanisms of fluconazole resistance in 706 incident bloodstream isolates from U.S. hospitals. We sequenced the ERG11 and MRR1 genes of 122 C. parapsilosis isolates with resistant (30 isolates; 4.2%), susceptible dose-dependent (37 isolates; 5.2%), and susceptible (55 isolates) fluconazole MIC values and used real-time PCR of RNA from 17 isolates to investigate the regulation of MDR1. By comparing these isolates to fully fluconazole-susceptible isolates, we detected at least two mechanisms of fluconazole resistance: an amino acid substitution in the 14-α-demethylase gene ERG11 and overexpression of the efflux pump MDR1, possibly due to point mutations in the MRR1 transcription factor that regulates MDR1. The ERG11 single nucleotide polymorphism (SNP) was found in 57% of the fluconazole-resistant isolates and in no susceptible isolates. The MRR1 SNPs were more difficult to characterize, as not all resulted in overexpression of MDR1 and not all MDR1 overexpression was associated with an SNP in MRR1. Further work to characterize the MRR1 SNPs and search for overexpression of other efflux pumps is needed.
PMCID: PMC4335858  PMID: 25451046
2.  Role of FKS Mutations in Candida glabrata: MIC Values, Echinocandin Resistance, and Multidrug Resistance 
Candida glabrata is the second leading cause of candidemia in U.S. hospitals. Current guidelines suggest that an echinocandin be used as the primary therapy for the treatment of C. glabrata disease due to the high rate of resistance to fluconazole. Recent case reports indicate that C. glabrata resistance to echinocandins may be increasing. We performed susceptibility testing on 1,380 isolates of C. glabrata collected between 2008 and 2013 from four U.S. cities, Atlanta, Baltimore, Knoxville, and Portland. Our analysis showed that 3.1%, 3.3%, and 3.6% of the isolates were resistant to anidulafungin, caspofungin, and micafungin, respectively. We screened 1,032 of these isolates, including all 77 that had either a resistant or intermediate MIC value with respect to at least one echinocandin, for mutations in the hot spot regions of FKS1 and FKS2, the major mechanism of echinocandin resistance. Fifty-one isolates were identified with hot spot mutations, 16 in FKS1 and 35 in FKS2. All of the isolates with an FKS mutation except one were resistant to at least one echinocandin by susceptibility testing. Of the isolates resistant to at least one echinocandin, 36% were also resistant to fluconazole. Echinocandin resistance among U.S. C. glabrata isolates is a concern, especially in light of the fact that one-third of those isolates may be multidrug resistant. Further monitoring of U.S. C. glabrata isolates for echinocandin resistance is warranted.
PMCID: PMC4136002  PMID: 24890592
3.  Development of a Luminex-Based Multiplex Assay for Detection of Mutations Conferring Resistance to Echinocandins in Candida glabrata 
Journal of Clinical Microbiology  2014;52(3):790-795.
Echinocandins are the recommended treatment for invasive candidiasis due to Candida glabrata. Resistance to echinocandins is known to be caused by nonsynonymous mutations in the hot spot-1 (HS1) regions of the FKS1 and FKS2 genes, which encode a subunit of the β-1,3-glucan synthase, the target of echinocandins. Here, we describe the development of a microsphere-based assay using Luminex MagPix technology to identify mutations in the FKS1 HS1 and FKS2 HS1 domains, which confer in vitro echinocandin resistance in C. glabrata isolates. The assay is rapid and can be performed with high throughput. The assay was validated using 102 isolates that had FKS1 HS1 and FKS2 HS1 domains previously characterized by DNA sequencing. The assay was 100% concordant with DNA sequencing results. The assay was then used for high-throughput screening of 1,032 C. glabrata surveillance isolates. Sixteen new isolates with mutations, including a mutation that was new to our collection (del659F), were identified. This assay provides a rapid and cost-effective way to screen C. glabrata isolates for echinocandin resistance.
PMCID: PMC3957770  PMID: 24353003
4.  Passive Surveillance for Azole-Resistant Aspergillus fumigatus, United States, 2011–2013 
Emerging Infectious Diseases  2014;20(9):1498-1503.
A. fumigatus cyp51A–mediated resistance to azole drugs is rare in the United States.
Emergence of Aspergillus fumigatus strains containing mutations that lead to azole resistance has become a serious public health threat in many countries. Nucleotide polymorphisms leading to amino acid substitutions in the lanosterol demethylase gene (cyp51A) are associated with reduced susceptibility to azole drugs. The most widely recognized mutation is a lysine to histidine substitution at aa 98 (L98H) and a duplication of the untranscribed promoter region, together known as TR34/L98H. This mechanism of resistance has been reported in Europe, Asia, and the Middle East, and is associated with resistance to all azole drugs and subsequent treatment failures. To determine whether isolates with this mutation are spreading into the United States, we conducted a passive surveillance–based study of 1,026 clinical isolates of A. fumigatus from 22 US states during 2011–2013. No isolates harboring the TR34/L98H mutation were detected, and MICs of itraconazole were generally low.
PMCID: PMC4178384  PMID: 25148217
antifungal resistance; azole; azole resistance; fungi; Aspergillus fumigatus; CYP51A; TR34/L98H; susceptibility testing; passive surveillance; United States
5.  Preliminary Laboratory Report of Fungal Infections Associated with Contaminated Methylprednisolone Injections 
Journal of Clinical Microbiology  2013;51(8):2654-2661.
In September 2012, the Centers for Disease Control and Prevention (CDC) initiated an outbreak investigation of fungal infections linked to injection of contaminated methylprednisolone acetate (MPA). Between 2 October 2012 and 14 February 2013, the CDC laboratory received 799 fungal isolates or human specimens, including cerebrospinal fluid (CSF), synovial fluid, and abscess tissue, from 469 case patients in 19 states. A novel broad-range PCR assay and DNA sequencing were used to evaluate these specimens. Although Aspergillus fumigatus was recovered from the index case, Exserohilum rostratum was the primary pathogen in this outbreak and was also confirmed from unopened MPA vials. Exserohilum rostratum was detected or confirmed in 191 specimens or isolates from 150 case patients, primarily from Michigan (n = 67 patients), Tennessee (n = 26), Virginia (n = 20), and Indiana (n = 16). Positive specimens from Michigan were primarily abscess tissues, while positive specimens from Tennessee, Virginia, and Indiana were primarily CSF. E. rostratum antifungal susceptibility MIC50 and MIC90 values were determined for voriconazole (1 and 2 μg/ml, respectively), itraconazole (0.5 and 1 μg/ml), posaconazole (0.5 and 1 μg/ml), isavuconazole (4 and 4 μg/ml), and amphotericin B (0.25 and 0.5 μg/ml). Thirteen other mold species were identified among case patients, and four other fungal genera were isolated from the implicated MPA vials. The clinical significance of these other fungal species remains under investigation. The laboratory response provided significant support to case confirmation, enabled linkage between clinical isolates and injected vials of MPA, and described significant features of the fungal agents involved in this large multistate outbreak.
PMCID: PMC3719655  PMID: 23761142
6.  Detection of Fungal DNA in Human Body Fluids and Tissues during a Multistate Outbreak of Fungal Meningitis and Other Infections 
Eukaryotic Cell  2013;12(5):677-683.
Exserohilum rostratum was the major cause of an outbreak of fungal infections linked to injections of contaminated methylprednisolone acetate. Because almost 14,000 persons were exposed to product that was possibly contaminated with multiple fungal pathogens, there was unprecedented need for a rapid throughput diagnostic test that could detect both E. rostratum and other unusual agents of fungal infection. Here we report development of a novel PCR test that allowed for rapid and specific detection of fungal DNA in cerebrospinal fluid (CSF), other body fluids and tissues of infected individuals. The test relied on direct purification of free-circulating fungal DNA from fluids and subsequent PCR amplification and sequencing. Using this method, we detected Exserohilum rostratum DNA in 123 samples from 114 case-patients (28% of 413 case-patients for whom 627 samples were available), and Cladosporium DNA in one sample from one case-patient. PCR with novel Exserohilum-specific ITS-2 region primers detected 25 case-patients with samples that were negative using broad-range ITS primers. Compared to fungal culture, this molecular test was more sensitive: of 139 case-patients with an identical specimen tested by culture and PCR, E. rostratum was recovered in culture from 19 (14%), but detected by PCR in 41 (29%), showing a diagnostic sensitivity of 29% for PCR compared to 14% for culture in this patient group. The ability to rapidly confirm the etiologic role of E. rostratum in these infections provided an important contribution in the public health response to this outbreak.
PMCID: PMC3647775  PMID: 23457192
7.  Ustilago maydis Rho1 and 14-3-3 Homologues Participate in Pathways Controlling Cell Separation and Cell Polarity▿ †  
Eukaryotic Cell  2009;8(7):977-989.
Proteins of the 14-3-3 and Rho-GTPase families are functionally conserved eukaryotic proteins that participate in many important cellular processes such as signal transduction, cell cycle regulation, malignant transformation, stress response, and apoptosis. However, the exact role(s) of these proteins in these processes is not entirely understood. Using the fungal maize pathogen, Ustilago maydis, we were able to demonstrate a functional connection between Pdc1 and Rho1, the U. maydis homologues of 14-3-3ɛ and Rho1, respectively. Our experiments suggest that Pdc1 regulates viability, cytokinesis, chromosome condensation, and vacuole formation. Similarly, U. maydis Rho1 is also involved in these three essential processes and exerts an additional function during mating and filamentation. Intriguingly, yeast two-hybrid and epistasis experiments suggest that both Pdc1 and Rho1 could be constituents of the same regulatory cascade(s) controlling cell growth and filamentation in U. maydis. Overexpression of rho1 ameliorated the defects of cells depleted for Pdc1. Furthermore, we found that another small G protein, Rac1, was a suppressor of lethality for both Pdc1 and Rho1. In addition, deletion of cla4, encoding a Rac1 effector kinase, could also rescue cells with Pdc1 depleted. Inferring from these data, we propose a model for Rho1 and Pdc1 functions in U. maydis.
PMCID: PMC2708450  PMID: 19411618
8.  Possible additional roles in mating for Ustilago maydis Rho1 and 14-3-3 homologues 
Both the Rho GTPases and 14-3-3 proteins each belong to ubiquitous families of proteins involved in a variety of cellular processes, including cytokinesis, cell polarity, cellular differentiation and apoptosis. In fungi, these components of signaling pathways are involved in cell cycle regulation, cytokinesis and virulence. We study cellular differentiation and pathogenesis for Ustilago maydis, the dimorphic fungal pathogen of maize. We have reported on the interactions of Pdc1, a U. maydis homologue of human 14-3-3ɛ, with Rho1, a small GTP binding protein; these proteins participate in cell polarity and filamentation pathways that include another small G protein, Rac1, and its effector PAK kinase, Cla4. Here we describe additional experiments that explore possible relationships of Pdc1 and Rho1 with another PAK-like kinase pathway and with the a matingtype locus.
PMCID: PMC2881243  PMID: 20539785
MAPK pathway; mating and pheromone response; filamentation; cell cycle; difopein; cytokinesis; cell polarity
9.  A second locus for Aicardi‐Goutières syndrome at chromosome 13q14–21 
Journal of Medical Genetics  2005;43(5):444-450.
Aicardi‐Goutières syndrome (AGS) is an autosomal recessive, early onset encephalopathy characterised by calcification of the basal ganglia, chronic cerebrospinal fluid lymphocytosis, and negative serological investigations for common prenatal infections. AGS may result from a perturbation of interferon α metabolism. The disorder is genetically heterogeneous with approximately 50% of families mapping to the first known locus at 3p21 (AGS1).
A genome‐wide scan was performed in 10 families with a clinical diagnosis of AGS in whom linkage to AGS1 had been excluded. Higher density genotyping in regions of interest was also undertaken using the 10 mapping pedigrees and seven additional AGS families.
Our results demonstrate significant linkage to a second AGS locus (AGS2) at chromosome 13q14–21 with a maximum multipoint heterogeneity logarithm of the odds (LOD) score of 5.75 at D13S768. The AGS2 locus lies within a 4.7 cM region as defined by a 1 LOD‐unit support interval.
We have identified a second AGS disease locus and at least one further locus. As in a number of other conditions, genetic heterogeneity represents a significant obstacle to gene identification in AGS. The localisation of AGS2 represents an important step in this process.
PMCID: PMC2649012  PMID: 15908569
AGS2; Aicardi‐Goutières syndrome; interferon α; intracranial calcification; 13q14–21

Results 1-9 (9)