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Mechanism of Increased Fluconazole Resistance in Candida glabrata during Prophylaxis. John E. Bennett, 2004.Candida glabrata can become resistant to fluconazole, causing persistent colonization and invasive infection during prolonged exposure to the drug . To determine the mechanism of resistance in this setting, weekly oropharyngeal cultures for C . glabrata were obtained over a 2-year period from hematopoietic stem cell transplant recipients who were receiving fluconazole prophylaxis . In 20 patients from whom at least two isolates of the same karyotype were obtained more than two weeks apart, fluconazole MICs doubled every 31 days on average . The mechanism of fluconazole resistance in isolates from the 14 of the 20 patients studied in whom MICs changed at least fourfold was studied . Cellular resistance was accompanied by increased drug efflux as measured by decreased accumulation of fluconazole and rhodamine 6G and increased abundance of transcripts from two drug transporters, CgCDR1 and PDH1. The rapidity and regularity of the rising resistance indicated that C . glabrata is able to upregulate drug efflux without losing the ability to maintain colonization . Stabilization of Oil-Water Emulsions by Hydrophobic Bacteria. Loredana S. Dorobantu, 2004. Corynebacterium glutamicum Utilizes both Transsulfuration and Direct Sulfhydrylation Pathways for Methionine Biosynthesis. Byung-Joon Hwang, 2002.A direct sulfhydrylation pathway for methionine biosynthesis in Corynebacterium glutamicum was found . The pathway was catalyzed by metY encoding O-acetylhomoserine sulfhydrylase . The gene metY, located immediately upstream of metA, was found to encode a protein of 437 amino acids with a deduced molecular mass of 46,751 Da . In accordance with DNA and protein sequence data, the introduction of metY into C . glutamicum resulted in the accumulation of a 47-kDa protein in the cells and a 30-fold increase in O-acetylhomoserine sulfhydrylase activity, showing the efficient expression of the cloned gene . Although disruption of the metB gene, which encodes cystathionine  -synthase catalyzing the transsulfuration pathway of methionine biosynthesis, or the metY gene was not enough to lead to methionine auxotrophy, an additional mutation in the metY or the metB gene resulted in methionine auxotrophy . The growth pattern of the metY mutant strain was identical to that of the metB mutant strain, suggesting that both methionine biosynthetic pathways function equally well . In addition, an Escherichia coli metB mutant could be complemented by transformation of the strain with a DNA fragment carrying corynebacterial metY and metA genes . These data clearly show that C . glutamicum utilizes both transsulfuration and direct sulfhydrylation pathways for methionine biosynthesis . Although metY and metA are in close proximity to one another, separated by 143 bp on the chromosome, deletion analysis suggests that they are expressed independently . As with metA, methionine could also repress the expression of metY . The repression was also observed with metB, but the degree of repression was more severe with metY, which shows almost complete repression at 0.5 mM methionine in minimal medium . The data suggest a physiologically distinctive role of the direct sulfhydrylation pathway in C . glutamicum .
Thermal Inactivation of Nonproteolytic Clostridium botulinum Type E Spores in Model Fish Media and in Vacuum-Packaged Hot-Smoked Fish Products. Miia Lindström, 2003.Thermal inactivation of nonproteolytic Clostridium botulinum type E spores was investigated in rainbow trout and whitefish media at 75 to 93°C . Lysozyme was applied in the recovery of spores, yielding biphasic thermal destruction curves . Approximately 0.1% of the spores were permeable to lysozyme, showing an increased measured heat resistance . Decimal reduction times for the heat-resistant spore fraction in rainbow trout medium were 255, 98, and 4.2 min at 75, 85, and 93°C, respectively, and those in whitefish medium were 55 and 7.1 min at 81 and 90°C, respectively . The z values were 10.4°C in trout medium and 10.1°C in whitefish medium . Commercial hot-smoking processes employed in five Finnish fish-smoking companies provided reduction in the numbers of spores of nonproteolytic C . botulinum of less than 103 . An inoculated-pack study revealed that a time-temperature combination of 42 min at 85°C (fish surface temperature) with >70% relative humidity (RH) prevented growth from 106 spores in vacuum-packaged hot-smoked rainbow trout fillets and whole whitefish stored for 5 weeks at 8°C . In Finland it is recommended that hot-smoked fish be stored at or below 3°C, further extending product safety . However, heating whitefish for 44 min at 85°C with 10% RH resulted in growth and toxicity in 5 weeks at 8°C . Moist heat thus enhanced spore thermal inactivation and is essential to an effective process . The sensory qualities of safely processed and more lightly processed whitefish were similar, while differences between the sensory qualities of safely processed and lightly processes rainbow trout were observed .
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