Dynamic behavior of Salmonella-induced membrane tubules in epithelial cells.

Salmonella Typhimurium is a facultative intracellular pathogen that causes acute gastroenteritis in man. Intracellular Salmonella survive and replicate within a modified phagosome known as the Salmonella-containing vacuole (SCV). The onset of intracellular replication is accompanied by the appearance of membrane tubules, called Salmonella-induced filaments (Sifs), extending from the SCV. Sifs are enriched in late endosomal/lysosomal membrane proteins such as lysosome-associated membrane protein 1, but their formation and ability to interact with endosomal compartments are not characterized. In this study, we use live cell imaging techniques to define the dynamics of Sif formation in infected epithelial cells. At early time-points, Sifs are simple tubules extending from the surface of SCVs. These tubules are highly dynamic and exhibit bidirectional, microtubule-dependent movement. At the distal ends of individual Sif tubules, furthest from the SCV, a distinct 'leader' domain was often observed. At later times, Sifs develop into highly complex tubular networks that extend throughout the cell and appear less dynamic than nascent Sifs; however, individual tubules continue to display bidirectional dynamics. Sifs can acquire endocytic content by fusion, indicating a sustained interaction with the endocytic pathway. Together, these results show that these Salmonella-induced tubules form a highly dynamic network that involves both microtubule-dependent motility and interactions with endosomal compartments.

Screening of antihelminthic effects of Indian plant extracts: a preliminary report.

INTRODUCTION: The purpose of the present study was to evaluate the antihelminthic effect of plants from the Ayurvedic system of medicine traditionally used in India. MATERIALS AND METHODS: Six plant extracts were assayed for their activity against free-living nematodes. Inhibitory effects on free-living nematodes were evaluated in vitro using aqueous or ethanolic extracts. CONCLUSIONS: Of six plants assayed, Momordica charantia yielded the best results, its crude extract producing 96% mortality.

The fadD2 gene is required for efficient Mycobacterium avium invasion of mucosal epithelial cells.

OBJECTIVE: Mycobacterium avium is capable of invading the intestinal epithelial cells, which requires cytoskeleton rearrangement and protein phosphorylation in the host cell. However, little is known about the mechanism. METHODS: A transposon bank was screened for invasion-impaired mutants. RESULTS: Among the genes identified, inactivation of the fadD2 gene resulted in approximately 50% reduction in invasion in vitro and 100-fold reduction in invasion in vivo, compared with the wild-type (wt) strain. Invasion by wt M. avium led to the recruitment of neuronal Wiskott-Aldrich syndrome protein (N-WASp), which was not observed with mutant lacking a functional fadD2 gene. M. avium entry resulted in the phosphorylation of N-WASp and activation of the Arp2/3 complex. Supernatant obtained from wt M. avium incubated with HEp2 epithelial cells rescued the mutant 1B2 ability to enter the cells, which suggests that activation of Cdc42 probably follows the secretion of M. avium proteins. CONCLUSION: fadD2 is a regulator of M. avium invasion, and its effect is through Cdc42.

Paucibacillary tuberculosis--a retrospective study.

Paucibacillary tuberculosis poses difficulty in the treatment and control of tuberculosis. The present study aims at understanding the extent of such cases among the patients, with respiratory symptoms, attending the outpatient department of the VP Chest Institute, Delhi. The analysis is based on the smear and culture examination of the sputum specimens, submitted from such patients during 1992-1998. Present results demonstrate that 34.8% were paucibacillary (direct smear negative; culture positive cases). Sex has no influence on smear examination results. The frequency of smear negative cases varied in the different age groups; the largest number belonged to the > or = 45 years age group (p < 0.05). Culture examination elicited positive result in these cases.

Cryptococcal yeast cells invade the central nervous system via transcellular penetration of the blood-brain barrier.

Cryptococcal meningoencephalitis develops as a result of hematogenous dissemination of inhaled Cryptococcus neoformans from the lung to the brain. The mechanism(s) by which C. neoformans crosses the blood-brain barrier (BBB) is a key unresolved issue in cryptococcosis. We used both an in vivo mouse model and an in vitro model of the human BBB to investigate the cryptococcal association with and traversal of the BBB. Exposure of human brain microvascular endothelial cells (HBMEC) to C. neoformans triggered the formation of microvillus-like membrane protrusions within 15 to 30 min. Yeast cells of C. neoformans adhered to and were internalized by the HBMEC, and they crossed the HBMEC monolayers via a transcellular pathway without affecting the monolayer integrity. The histopathology of mouse brains obtained after intravenous injection of C. neoformans showed that the yeast cells either were associated with endothelial cells or escaped from the brain capillary vessels into the neuropil by 3 h. C. neoformans was found in the brain parenchyma away from the vessels by 22 h. Association of C. neoformans with the choroid plexus, however, was not detected during up to 10 days of observation. Our findings indicate that C. neoformans cells invade the central nervous system by transcellular crossing of the endothelium of the BBB.