A spectrophotometric method has been developed for the rapid measurement of the antimicrobial activity of natural products, including crude extracts or pure materials. The assay depends on the measurement of non-specific esterase activity using fluorescein diacetate (FDA) hydrolysis in broth cultures of microbes after they have been treated with test compounds. The assay is accurate, reproducible and economical in both time and materials. The speed and economyof the method make it suitable for the rapid screening of manysamples and the bioassay directed purification of antimicrobial substances. The assay can also be used with a wide variety of micro-organisms since most micro-organisms are FDApositive. Applications are described in the fields of marine natural products chemistry and essential oils research. 1295 The objective of this study was to develop a simple, rapid, inexpensive, accurate and reproducible method for the determination of the minimuminhibitory concentration (MIC) of large numbers of test samples ranging from crude extracts or fractions of natural products to essential oils or pure substances.Methods used for the determination of the MICare varied although they can be grouped into either a single disc diffusion assay (Bauer et ai, 1966) or the dilution plate/broth methods (Haltalin et ai, 1973). The former relates the zone of inhibition produced to the varying concentration of a test compound applied on to a paper disc for the determination of the MIC. There are several problems associated with the disc diffusion method for comparing the relative antimicrobial activity of different compounds. The assay does not always give a sharp demarkation between bacterial growth and inhibition. The time taken for incubation (18~24 hours) may render it unsuitable for volatile or unstable antimicrobial agents. The zones of inhibition may only be compared among antimicrobial agents with similar physical properties such as diffusion rates in agar, volatility or solubilities in aqueous solutions.The dilution plate/broth group of methods measure the bacteriocidal/bacteriostatic effect of a potential antibiotic at a series of concentrations on a given microbial population. While being accurate, these methods are laborious due to the inclusion of viability counts in the assay and are liable to contamination of either the broth or the viable count agar plates or from test samples that often cannot easily be sterilised. Again, the time period involved (1~2 days) can be a major drawback.The method described here is ideal for implementation in a chemistry laboratory by non-microbiologists, can be run under non-aseptic conditions, requires only small amounts of materials and gives results in two hours.Non-specific esterases occur widely amongst microbes (Lundgren, 1981) and have been shown to hydrolyse colourless fluorescein diacetate (FDA) to fluorescein, a yellowish green compound, which absorbs strongly in the visible (/lmax 498 nm; £ l x 105, methanol -potassium hydroxide; Grasselli and Ritchey, 1975). FDAhydr...
Does the emigration of highly-skilled workers deplete local human capital?The answer is not obvious if migration prospects induce human capital formation. We analyze a unique natural quasi-experiment in the Republic of the Fiji Islands, where political shocks have provoked one of the largest recorded exoduses of skilled workers from a developing country. Mass emigration began unexpectedly and has occurred only in a well-defined subset of the population, creating a treatment group that foresaw likely emigration and two different quasi-control groups that did not. We use rich census and administrative microdata to address a range of concerns about experimental validity. This allows plausible causal attribution of post-shock changes in human capital accumulation to changes in emigration patterns. We show that high rates of emigration by tertiary-educated Fiji Islanders not only raised investment in tertiary education in Fiji; they moreover raised the stock of tertiary educated people in Fiji-net of departures.1 To reflect standard practice in Fiji, including in official data sources, we herein frequently use the word "Fijian" to denote indigenous Fiji Islanders of the Fijian ethnicity (usually excluding Rotumans and other indigenous people not strictly Fijian) and the word "Indian" or "Indo-Fijian" to denote Fiji Islanders of South Asian descent (at the time that most of their ancestors arrived in Fiji, "India" included present-day Pakistan and Bangladesh). While a tiny portion of the population claims mixed ethnicity, intermarriage between the groups is extremely rare.
The impact of trade liberalisation on productivity growth is still an empirical issue; the theoretical literature is as yet unclear on the direction of any such association. This paper develops an analytical framework and employs it to empirically test if trade liberalisation in Indian manufacturing has raised total factor productivity (TFP) growth. The answer is in the affirmative. Our results also support a key postulate of the new growth theories that liberalisation of the intermediate good sectors has a larger favourable impact on TFP growth than that of the final good sectors. JEL Classification: F14, D24, O53.
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