Acinetobacter sp. CR was grown on a model oil, which consisted of an inert oil matrix of pristane with n-heneicosane dissolved in it as the sole carbon source, in a stirred-tank bioreactor. This bacterium takes up sub...
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Acinetobacter sp. CR was grown on a model oil, which consisted of an inert oil matrix of pristane with n-heneicosane dissolved in it as the sole carbon source, in a stirred-tank bioreactor. This bacterium takes up substrates from the oil phase by direct contact with the oil phase. A previously established mathematical model was applied to reveal the effect of agitation conditions on the growth and n-alkane degradation kinetics of the bacterium. Higher impeller speed resulted in both lower microbial growth and lower n-alkane degradation rate of the bacterium, although it increased the specific surface area of the oil, which was measured by a previously developed device. This result was due to the decreased number of cells adhering to the oil surface, i.e., intense agitation inhibited the adhesion of cells to the oil surface. The addition of a surfactant below a critical micelle concentration (CMC) inhibited the degradation of n-heneicosane dissolved in pristane, although the biodegradability of the substrate recovered gradually with the increase in the dose of surfactant over CMC. The results suggest that efforts to increase the specific surface area of the oil phase have the undesirable result of inhibiting oil degradation when the dominant microbial degraders take up substrates in oil by direct contact with the oil.
Acinetobacter baumannii is becoming increasingly resistant to antibiotics, often requiring combination therapy. Numerous methods exist to detect the presence of in vitro synergy with the time-kill and checkerboard tes...
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Acinetobacter baumannii is becoming increasingly resistant to antibiotics, often requiring combination therapy. Numerous methods exist to detect the presence of in vitro synergy with the time-kill and checkerboard tests being widely used. The Epsilometer test (E test) is a new method that is less labor intensive, but has not been evaluated using a wide range of antimicrobials and organisms. We assessed synergy using the time-kill and checkerboard tests and compared the results to the E test method using 10 clinical isolates of A. baumannii. Antimicrobial combinations evaluated consisted of trovafloxacin or tobramycin in combination with cefepime or piperacillin. Synergy was detected with all combinations by either the checkerboard or time-kill method. Synergy was not detected by the Etest method. The agreement between the time-kill test and Etest method was 72% (range 42-97%);for the time-kill and checkerboard tests, agreement was 51% (range 30-67%). The Etest method appears promising although further testing should be performed with additional antimicrobial agents and organisms. (C) 2000 Elsevier Science Inc. All rights reserved.
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