No abstract

We describe an improved implementation of a segmentation method for retinal blood vessels based on a multi-scale approach and region growing employing modules from the Insight Segmentation and Registration Toolkit (ITK). We present the results of segmentation of retinal blood vessels using this improved method and compare these with results obtained using the original implementation in Matlab, as well as with expert manual segmentations obtained from a public database. We show that the ITK implementation achieves high quality segmentations with markedly improved computational efficiency. The ITK version has greater segmentation accuracy, from 0.94 to 0.96, than the Matlab version due to a decrease in FPR values and it is between 8 and 12 times faster than the original version. Furthermore, the ITK implementation is able to segment high-resolution images in an acceptable timescale.

Do Protozoa Control the Elimination of Vibrio choleraein Brackish Water?key words: Cyclidium glaucoma, ciliate feeding selectivity, toxin producing bacteria AbstractElimination of inoculated Vibrio cholerae (≥10 7 cells ml -1) within a brackish water bacteria assemblage (Mecoacán Lagoon, State of Tabasco, Mexico) was studied in laboratory microcosms with filtrationfractionated water. Feeding of a ciliate, Cyclidium glaucoma was evaluated using fluorescently labelled V. cholerae O1. Even though V. cholerae was not exploited as the major food source, ciliates were able to eliminate it efficiently. An addition of chitin directly supported the growth of bacteria, although not so much of V. cholerae, and indirectly the growth of the protistan assemblage. Generally, the changes in a bacterial assemblage structure were the most important in V. cholerae elimination. IntroductionThe ecological position of human-pathogenic bacteria such as Vibrio cholerae O1 within the aquatic microbial food web has not been studied frequently, however, such studies led to the Viable But Nonculturable Bacteria (VBNC) concept (reviewed in COLWELL, 2000). This theoretical concept is being now changed (compare, BOGOSIAN et al., 2000), but one must accept that it has given us more realistic data on the pathogen distribution in the environment by comparing the use of direct counting methods, e.g. immunofluorescence microscopy, with cultivation methods (XU et al., 1984;BRAYTON et al., 1987;HUQ et al., 1990;TAMPLIN et al., 1990;CORTÉS et al., 2000). It was proven that vibrios could participate directly in the annual plankton -benthic cycle (KANEKO and COLWELL, 1975;TAMPLIN et al., 1990;GUTHRIE and COFIE, 1991;VANOY et al., 1992), entering the microbial loop within a plankton food web (sensu AZAM et al., 1983) along with other bacteria and bacterivorous microorganisms such as protozoa (BERK et al., 1976;MACEK et al., 1997).From the point of view of interactions between bacteria and protozoa, mechanical predation selectivity and/or surface properties of the prey have been suggested as the major mechanism controlling ciliate -bacteria interactions (FENCHEL, 1986;SANDERS, 1988; GON-ZÁLEZ et al, 1990). The ability of ciliates to discriminate between particles is limited to shape, volume and cell wall properties. Frequently, protozoa select larger prey, such as dividing cells, even on the edible size threshold which is of great importance in the control of bacterial assemblages (SHERR et al., 1992;ŠIMEK et al., 1994). Conversely, ingestion of a non-suitable prey affects ciliate growth rate and generally, population development.Internat. Rev. Hydrobiol.

In situ elimination of fluorescently labelled Vibrio cholerae (FLB) was measured in two saline water bodies in Mexico: in a brackish water lagoon, Mecoacán (Gulf of Mexico; State of Tabasco) and an athalassohaline lake, Alchichica (State of Puebla). Disappearance rates of fluorescently labelled V. cholera O1 showed that they were eliminated from the environment at an average rate of 32% and 63%/day, respectively (based on the bacterial standing stocks). The indirect immunofluorescence method confirmed the presence of V. cholerae O1 in the lagoon. However, the elimination of FLB was not directly related either to the presence or absence of the bacterium in the water body or to the phytoplankton concentration.