Reduction In Number Of Viable Cells Research Articles

4-oxatetradecanoic acid is fungicidal for Cryptococcus neoformans and inhibits replication of human immunodeficiency virus I.

Candida albicans and Cryptococcus neoformans are major causes of systemic fungal infections, particularly in patients with acquired immunodeficiency syndrome. Metabolic labeling studies revealed that these organisms synthesize a small number of N-myristoylproteins, the most prominent being 20-kDa ADP-ribosylation factors (Arfs). C. albicans Arf has approximately 80% identity with the essential Arf1 and Arf2 proteins of Saccharomyces cerevisiae. [3H]Myristic acid analogs with oxygen for -CH2- substitutions at C4, C6, C11, and C13 are incorporated into cellular N-myristoylproteins, phospholipids, and neutral lipids produced by these three yeasts during exponential growth at 30 degrees C in complex media. Analog- and organism-specific differences in the efficiency of labeling of proteins and lipid classes were observed. The effects of oxatetradecanoic acids with oxygen for -CH2- substitutions at C3-C13 on C. neoformans, C. albicans, and S. cerevisiae were assessed during mid-log phase growth at 30 degrees C. A single dose of 3-oxa-, 4-oxa-, 5-oxa- or 6-oxatetradecanoic acid (O3-O6, final concentration = 300 microM) was able to inhibit growth of C. neoformans in the order O4 greater than O5 greater than O3 approximately O6. The other compounds were inactive. 4-Oxatetradecanoic acid was fungicidal, producing a 10,000-fold reduction in viable cell number 1 h after administration and continued suppression of cell growth for 7 h. A clear dose response was observed over a concentration range of 100-300 microM. 4-Oxatridecanoic acid was 100-fold less potent in reducing cell viability than 4-oxatetradecanoic acid but more potent than 5-oxatridecanoic acid. O4 produced approximately 10-100-fold reductions in the viability of C. albicans and S. cerevisiae at 300-500 microM, respectively, whereas O5 and O6 were less active. Since N-myristoylation of the Pr55gag polyprotein precursor produced by human immunodeficiency virus I (HIV-I) is essential for its assembly, we also assessed the antiviral effects of 4-oxatetradecanoic acid. O4 is able to produce a 50% reduction in the replication of HIV-I in acutely infected human T-lymphocyte cell lines at a concentration of 18 microM. Together, these data suggest that (i) the position of the oxygen for methylene substitution is a critical determinant of the fungicidal activity of O4 and (ii) NMT may be an attractive therapeutic target for treating opportunistic fungal infections in patients infected with HIV-I.

Thermal inactivation of Listeria monocytogenes during a process simulating temperatures achieved during microwave heating

Conventional heating was used to expose cells of Listeria monocytogenes, either in broth or in situ on chicken skin, to the mean times and temperatures that are achieved during a 28 min period of microwave cooking of a whole chicken. Heating L. monocytogenes by this method in culture broth resulted in a reduction in viable cell numbers by a factor of greater than 10(6) upon reaching 70 degrees C. Simulated microwave cooking of L. monocytogenes in situ, on chicken skin, resulted in more variability in the numbers of survivors. Heating for the full cook time of 28 min, however, resulted in a mean measured temperature of 85 degrees C and no surviving listerias were detected. This indicated a reduction in viable numbers of greater than 10(6). To reduce temperature variation, cells were heated on skin in a submerged system in which exposure to 70 degrees C for 2 min resulted in a reduction in viable cell numbers of all strains of listerias tested of between 10(6) and 10(8). These results show that when a temperature of 70 degrees C is reached and maintained for at least 2 min throughout a food there is a substantial reduction in the numbers of L. monocytogenes. The survival of this organism during microwave heating when temperatures of over 70 degrees C are reported is probably due to uneven heating by microwave ovens resulting in the presence of cold spots in the product. The heat resistance of L. monocytogenes is comparable with that of many other non-sporing mesophilic bacteria.

Salmonella Inactivation in Liquid Whole Egg by Thermoradiation

ABSTRACT Salmonella enteritidis in liquid whole egg (LWE) was inactivated using heat, radiation and thermoradiation (combined heat and radiation). Rates of Salmonella inactivation were determined as a function of radiation dose, temperature, initial cell number and pH. Thermoradiation caused a greater reduction in viable cell number than either heat or radiation alone. This effect was more pronounced at pH 6.5 than at pH 7.0, and more so at 60°C than at 50°C. The lower the initial cell number, the faster the rate of Salmonella inactivation. Physical denaturation of LWE was not apparent after thermoradiation below 60°C, and endogenous egg white lysozyme was not affected by thermoradiation (19.5 krad, 60°C) treatment.

Survival of Listeria monocytogenes in Low pH Model Broth Systems

Four strains of Listeria monocytogenes were studied for pH tolerance in pH-adjusted tryptic soy broth supplemented with yeast extract. After incubation at 30°C, all strains grew at pH 4.5 and above. Survival of strain F5069(4b) was further investigated in sterile orange serum in which pH was adjusted from 3.6 to 5.0 in 0.2 unit increments. At 4°C, viable cells were reduced from 106 cfu/ml to less than 25 cfu/ml in 25 d at pH 3.6, 43 d at pH 4.0, and 81 d at pH 4.6. Viable cell populations remained at levels about 102 after 90 d in orange serum at pH 4.8 and 5.0. At 30°C, the same reductions were observed at 5 d at pH 3.6 and 4.0 and 8 d at pH 5.0. Growth in orange serum was observed prior to the reduction in viable cell numbers at pH 4.8 and 5.0 for both storage temperatures.

Limb development in mouse embryos. III. Cellular events underlying the determination of altered skeletal patterns following treatment with 5'fluoro-2-deoxyuridine.

A potent inhibitor of thymidylate synthetase, 5-Fluorodeoxyuridine (FUdR), produced dose- and stage-dependent skeletal defects in embryos of mice injected during early development (10th--13th day). The dose of 25 mg/kg was teratogenic producing few resorptions and little reduction in fetal weight. Hindlimbs were much more sensitive to the drug than were the forelimbs and showed dose-dependent long bone reductions. Specific long bone reductions occurred after treatment on the 11th or 11.5 day and were accompanied by preaxial polydactyly; treatment on the 12th or 12.5 day produced high incidence of ectrodactyly but no long bone reductions. Limbs were insensitive on the 13th day of development and beyond. Limb buds in organ culture demonstrated a direct action of FUdR on undifferentiated mesenchymal cells, incurring what has been previously termed "thymineless" cell death. Dose-dependent reduction of viable cell number led to a reduction in chondrogenic expression in vitro--more so in the hindlimb than the forelimb. Similar occurrence of cell death was also noted after in utero exposure, and here, it was followed by a process of recovery. The recovery phase was characterized by the formation of a distal synchronized cell population derived from undamaged subridge cells leaving damaged cells at the proximal extent of the subridge zone. Limb segments maintained their temporal sequence of differentiation, and their regulatory capability was related to the time allotted for repopulation of the subridge zone. We propose that a faster growth during early development of the elements of the hindlimb versus analogous ones of the forelimb allows the former less time for regulation--and hence, higher sensitivity to antiproliferative agents such as FUdR.

Isolating specific auxotrophic mutants of Mycobacterium smegmatis by using vancomycin

After inducing mutagenesis with nitrosoguanidine, we used vancomycin enrichment in isolating auxotrophic mutants of Mycobacterium smegmatis. Compared with cycloserine and penicillin G, which are also cell wall inhibitors, vancomycin, with 24 h of exposure, produced less cell lysis and a greater reduction in viable cell numbers. With vancomycin enrichment, 13 specific auxotrophs were isolated after nitrosoguanidine-induced mutation, whereas only two mutants were isolated without enrichment.

A unique envelope protein in azotobacter vinelandii

Summary An unusual protein has been observed in Azotobacter vinelandii cysts and vegetative cell envelopes. It has a molecular weight of 60,000, constitutes almost 20% of the envelope protein, and is readily dissociated from both isolated membrane fractions and intact cells by washing with distilled water. A 60% reduction in viable cell numbers is found after removal of this protein.

Toxicity of prostaglandins A1 and A2 for cells in culture.

Prostaglandins A1 and A2, in concentrations near 3 x 10(-5) M, produced striking toxicity to muscle, skin and liver cells in culture. Prostaglandins E and F2alpha were much less active in this regard. Toxicity could be measured by reduction in viable cell number, protein and DNA synthesis in the cultures. The sensitivity of cultured cells was related to their age and population density. Dense cultures were sensitive early, in the first 2 days, and resistant after they manifested confluent growth. Sparse cultures remained sensitive later while they continued DNA synthesis and active cell division. It is hypothesized that the prostaglandin A effect is related to active cell division and DNA synthesis.