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Biomedical subjects

D G Ahearn

Publications and source records attributed to D G Ahearn.

At least 91 records · Page 5Linked to original sources
PubMed1979

Regulation of melanin production by Cryptococcus neoformans.

Species of Filobasidiella, the agents of cryptococcosis, produced melanin-like pigments within 4 to 48 h with diphenol, aminophenol, and diaminobenzene compounds as substrates. The rate of phenyloxidase activity was found to be regulated by glucose and nitrogen catabolite repression. Increased glucose concentration reduced pigmentation of all serotypes of Filobasidiella, whereas repression by nitrogen sources varied with the strain. Glutamine repressed the phenyloxidases of all isolates except those of serotype B, and (NH4)2SO4 repressed the phenyloxidase of all isolates except that of serotype A. Tyrosine and glycine appeared to be near optimal for phenyloxidase activity but not necessarily for growth of all strain examined. Representatives of serotype C were unique in that their phenyloxidase system was adpative in contrast to the constitutive system found in the other serotypes. No single medium was found to support pigmentation of all strains of Cryptococcus neoformans within a 72-h incubation period; false-negative reactions can occur.

Catechol Oxidase↗
PubMed1978

Germ-tube formation by atypical strains of Candida albicans.

Atypical isolates of Candida albicans which failed to produce germ tubes in routine diagnostic procedures were examined for their ability to produce germ tubes in various media. Bovine serum was more effective than defined media for induction of germ tubes in the majority of isolates. A few strains formed appreciable germ tubes only in bovine serum with added thioglycollate or cysteine. One strain did not produce germ tubes in any medium. Germ-tube maturation appeared to be dependent upon mitochondrial RNA polymerase activity. The failure by an isolate to produce germ tubes, particularly in tests without strictly controlled conditions, does not preclude the possibility that the organism is C. albicans.

Amphotericin B↗
PubMed1977

Pseudomonas-induced corneal ulcers associated with contaminated eye mascaras.

Seven Pseudomonas-induced corneal ulcers were associated with the use of four brands of mascara contaminated with P. aeruginosa. In laboratory studies, preservative systems of three of the four brands were inadequate in comparison with a control mascara of known antimicrobial activity. If the corneal epithelium is scratched during the application of mascara, particularly if the applicator is old, the cornea should be treated immediately and the mascara cultured to detect Pseudomonas. The high incidence of recurrent corneal ulceration in cases of Pseudomonas-induced keratitis indicates that initial chemotherapy should be intensive and maintained until the lesion stabilizes.

Adult↗
PubMed1977

Isolation of Atypical Candida albicans from the North Sea.

Isolates of Candida albicans with sparse filamentation and weak fermentation were isolated from the surface microlayer of the North Sea, but not from subsurface waters. Such atypical isolates may be misidentified by using normal taxonomic procedures.

Journal Article↗
PubMed1977

Purification and characterization of a neutral protease from Saccharomycopsis lipolytica.

Saccharomycopsis lipolytica 37-1 produced two inducible extracellular proteases, one under neutral or alkaline growth conditions and the second under acid conditions. Secretion of the neutral protease was repressed in the presence of glycerol or glucose, both of which supported rapid growth of the organism. Ammonium ions also repressed the secretion of the enzyme. The neutral protease activity copurified with esterase activity during ammonium sulfate fractionation, chromatography on diethylaminoethyl-cellulose, and gel filtration on Sephadex G-150. The molecular weight of the enzyme was estimated to be 42,000 by sucrose density gradient centrifugation and 38,500 by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The purified enzyme had a pH optimum of 6.8. Phenylmethylsulfonylfluoride inhibited both protease and esterase activities, indicating the presence of a serine residue in the active center. Protease, but not esterase, activity was sensitive to ethylenediaminetetraacetate and was significantly activated by divalent ions. Dithiothreitol inhibited both protease and esterase activities, indicating the presence of a critical disulfide bridge. The enzyme hydrolyzed casein (K(m) = 25.6 muM) and hemoglobin as well as the nitrophenyl esters of tyrosine (K(m) = 2.4 mM), glycine, tryptophan, and phenylalanine.

Ascomycota↗
PubMed1977

Sucrose-negative variants of Candida tropicalis.

Four cultures of a Candida sp. that lacked alpha-glucosidase activity were isolated from clinical specimens. Physiological, morphological, and serological characterizations of the yeasts and deoxyribonucleic acid reassociation studies supported their classification as a variant of C. tropicalis.

Antigens, Fungal↗
PubMed1976

Evaluation of commercial systems for the identification of clinical yeast isolates.

The Analytab Products Inc. (API), Micro-Drop (MD), and Uni-Yeast-Tek (UYT) systems for the presumptive identification of common clinical yeast isolates were compared with the oxidation-fermentation (OF) and a conventional procedure. With 229 coded isolates, the identification accuracies were API 94, MD 83, OF 82, and UYT 99%. The API system required the greatest technical ability. The MD materials were prone to malfunction. OF media, if incubated beyond 14 days, gave an accuracy of 87%, but this offered no advantage over the conventional procedure. The UYT system was the easiest to use.

Carbohydrate Metabolism↗
PubMed1975

Physiological and DNA characterization of Candida maltosa, a hydrocarbon-utilizing yeast.

Selected yeast classified as Candida sake van Uden et Buckley were examined for their physiological, morphological and immunological properties and their DNA relatedness. Candida maltosa Komagata, Nakase et Katsuya is herein recognized as a species separate from C. sake, Candida maltosa was distinguished from C. sake and from C. tropicalis by insignificant DNA reassociation. In addition, C. maltosa was distinguished from C. sake by its higher maximal growth temperature and lower guanine plus cytosine content of its DNA and from C. tropicalis by its failure to utilize soluble starch for growth and its resistance to cycloheximide. The species C. cloacae and C. subtropicalis are placed in synonymy with C. maltosa.

Alkanes↗
PubMed1975

The survival and growth of microorganisms in mascara during use.

Over 150 mascaras representing eight popular brands were examined for their susceptibility to microbial contamination during their use by study group members. Additional mascaras from patients with symptoms and clinical findings of long-term blepharitis also were investigated. Early in the study, two brands without preservatives supported reproducing populations of microorganisms, including potential eye pathogens. These products, as currently manufactured, were recalcitrant to microbial attack. Microbes associated with the facial skin and fingers of the study group users were typically isolated from mascaras after use. Initial microorganisms isolated from mascaras were usually transients. Establishment of reproducing populations within the cosmetics appeared related to the number of uses, personal habits of the user, and the formulation of the product. Four patients with staphylococcal blepharitis and cosmetics heavily laden with Staphylococcus epidermidis showed marked clinical improvement when they stopped using the contaminated cosmetics. The application of used eye area makeup prior to and following ocular surgery should be avoided.

Bacillus↗
PubMed1975

Evaluation of the Uni-Yeast-Tek kit for the identification of medically important yeasts.

The Uni-Yeast-Tek system, a commercially prepared kit and scheme for the rapid identification of medically important yeasts (Corning Medical), was evaluated in comparison with a conventional procedure in the identification of 623 yeasts. The system permitted the presumptive identification of 99.8% of 436 isolates representing 16 common species commonly isolated in the clinical laboratory. Correct biochemical and morphological analyses were obtained with 48 other species, but their specific identification required additional data.

Candida↗
PubMed1970

Effects of alkylbenzene sulfonates on yeasts.

Species of Hansenula and Candida are resistant to high concentrations of anionic alkylbenzene sulfonates and degrade subinhibitory concentrations of these detergents.

Benzene Derivatives↗