We compared the accuracy and repeatability of 2 common methods of estimating percentage covers of sessile organisms: visual estimates and random-point-quadrats (RPQ). Comparisons of estimates were made using both quadrats in the rocky intertidal zone and simulated quadrats drawn on a computer, where estimates could be compared with true, digitized percent cover values. In each case, visual estimates were found to be more repeatable (less within-and among-observer variation) and more accurate (closer to the true value as determined by digitizing) than the RPQ method. RPQs using 100 points were more accurate and less variable than those using 50 points, but were still less accurate (and much slower to carry out) than visual estimates. The RPQ method often missed rare species (<2 % cover) altogether, but when it 'hit' them, values were usually overestunated. Visual estimates also tended to overestimate percent covers of species (although less than the RPQ method), especially uncommon ones. Thus although the probabilistic RPQ method is supposedly more objective and is statistically valid, visual estimates may give a more accurate representation of relahve coverage of sesslle organisms, and can reduce overall s a m p h g error because they make increased sample sizes possible. Use of small subdvisions in quadrats, pre-field observer training, and a conscious effort to avoid bias are necessary to make the visual method valid and accurate.

A human colorectal explant culture was developed to assess the safety and efficacy of topical microbicides proposed for use in humans. Because any product marketed for vaginal application will likely be used for anal intercourse, it is important to evaluate these products in colorectal explant tissue. Microbicides tested included cellulose acetate 1,2-benzenedicarboxylate (CAP), PRO 2000, SPL7013, Vena Gel, and UC781, along with their accompanying placebos. Colorectal tissues were exposed to microbicides overnight and either fixed in formalin to evaluate toxicity by histological analysis or placed in 1-(4,5-dimethylthiazol-2-yl)-3,5-diphenylformazan (MTT) to quantitatively determine tissue viability. Histological analysis showed minimal toxicity for CAP, UC781, and Vena Gel. Shedding of epithelium with intact lamina propria occurred for the PRO 2000 and SPL7013 products, and shedding of epithelium and necrosis of the lamina propria occurred in explants cultured with nonoxynol-9. The MTT assay confirmed these results for PRO 2000 (4% and 0.5%), SPL7013 (and placebo), and nonoxynol-9 but also demonstrated reduced viability for CAP. However, viability of tissues treated with all products was not significantly different from that of the medium control. Efficacy of the microbicides was evaluated by measuring human immunodeficiency virus type 1 (HIV-1) infection of explants in the absence or presence of products. All microbicide formulations tested were highly effective in preventing HIV infection. However, explants treated with some of the placebo formulations also exhibited a lower level of infection. Most of the products developed for vaginal application showed minimal toxicity and were effective in reducing HIV-1 infection in colorectal tissues. These results suggest that this model is useful for evaluating the safety and efficacy of topical microbicides when used rectally.

No abstract

No abstract

No abstract