Biological Sciences
Trophozoite
A trophozoite is the active, feeding stage of certain parasites and protozoa. It is characterized by its ability to move and ingest nutrients. In medical and biological research, trophozoites are studied to understand the life cycle and pathogenicity of various organisms, particularly those that cause diseases such as malaria and amoebiasis.
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5 Key excerpts on "Trophozoite"
eBook - PDF- N A Khan(Author)
- 2008(Publication Date)
- CRC Press(Publisher)
The feeding and/or growing stage is known as Trophozoite. However, tinder harsh conditions, some protozoa transform into a protective cyst form. Cysts can survive lack of food, extremes in pH or temperature, and resist to toxic chemicals or chemotherapeutic compounds. These properties allow some protozoa to find new hosts, thus help in their transmission. Protozoa reproduce asexually by binary fissions (the parent cell mitotically divides into two daughter cells), multiple fission, also known as schizogony (the parent cell divides into several daughter cells), budding, and spore formation, or sexually by conjugation (two cells join, exchange nuclei and produce the progeny by budding or fission). Some protozoa produce gametes (gametocytes, i.e., haploid sex cells), which fuse to form a diploid zygote. Protozoa are among the five major classes of pathogens including intracellular parasites (viruses), prokaryotes, fungi, protozoa and multicellular pathogens. From more than 20,000 species of protozoa, only a handful cause human diseases. However, these few are a major burden on human health and have a severe economic impact. For example, malaria is the fourth leading cause of death, worldwide. To produce disease, protozoa access their hosts via direct transmission through the oral cavity, the respiratory tract, the genito-urinary tract and the skin, or by indirect transmission through insects, rodents as well as by inanimate objects such as towels, contact lenses and surgical instruments. Once the host tissue is invaded, protozoa multiply to establish themselves in the host, and this may be followed by physical damage to the host tissue or depriving it of 184 nutrients, and/or by the induction of an excessive host immune response resulting in disease. 3. CLASSIFICATION Before the availability of molecular tools, taxonomists divided the protozoa into four groups, based on the organisms' mode of locomotion (Fig. 1) as follows.
eBook - PDF- Mark F Wiser(Author)
- 2010(Publication Date)
- Garland Science(Publisher)
The line between parasitism and commensalism is often blurry and the precise definition between the two terms often varies according to author. For example, according to some definitions, commen-sals, in contrast to parasites, are not physiologically dependent upon the host and can live independently of the host. However, several protozoan species found within the human intestinal tract, that feed upon bacteria and debris and do not cause any human disease, are often referred to as commensals even though they are completely dependent on the host for their survival. In addition, one can also distinguish between obligate sym-bionts, which cannot live apart from their hosts, and facultative symbionts, which can be either free-living or symbiotic. Similarly, many parasitic pro-tozoa are facultative pathogens in that they do not always cause disease. The life cycle of many parasitic protozoa can be completed in a single host. These monoxenous parasites generally have a life cycle stage out-side of the host and transmission almost always involves the ingestion of an infective form. Other parasitic protozoa are heteroxenous in that they require multiple host species to complete their life cycle. Quite often one of the hosts is a blood-feeding arthropod referred to as a vector . Some para-sitic protozoa can only infect a single or limited range of host or vector spe-cies; whereas others are more promiscuous and can infect a wide range of hosts. Human diseases caused by parasites normally found in other animals are called zoonoses and the animal host is the reservoir . Generally zoonotic diseases do not involve a person-to-person transfer. protrusion adhesion traction de-adhesion/ retraction (A) (B) Figure 1.6 Ameboid movement. (A) Schematic of ameboid movement. (B) Light micrograph showing ectoplasm (pseudopodium) and endoplasm (cell body).
eBook - PDF- Wilhelm Tham, Marie Louise Danielsson-Tham, Wilhelm Tham, Marie Louise Danielsson-Tham(Authors)
- 2013(Publication Date)
- CRC Press(Publisher)
Trophozoites are the vegetative stage, residing in the lumen of the large intestine of humans and animals (particularly pigs), where replication occurs by binary fission (during which conjugation may occur). Some Trophozoites may invade the colonic wall and multiply. Encystation of the Trophozoites results in the production of mature infective cysts (spherical, 40–60 μm diameter, with a thick, cyst wall of one or two layers), which are excreted in the faeces and are immediately infectious. Between 0.2 and one percent of the world’s human population has been estimated to be infected with B. coli, with endemic areas in South and Central America, the Philippines, Papua New Guinea and the Middle East (Schuster and Ramirez-Avila 2008). Domestic swine and wild boar are the chief reservoirs for B. coli , with reported prevalence rates in domestic pigs ranging from over 55 percent in USA, over 47 percent in China, and over 33 percent in Venezuela down to under 2 percent in Turkey (Theel and Pritt 2012). The highest reported prevalence rate of porcine B. coli infection is from Denmark, where in one study nearly all of the adult domestic pigs harboured the ciliate; interestingly human infection with B. coli has never Protozoan Parasites: Protozoan Parasites: A A P P lethora of lethora of P P otentially otentially F F oodborne oodborne P P athogens athogens 171 171 Table 1. Protozoan parasites associated with foodborne transmission. Protozoan parasite (Phylum) Transmission Route Documented foodborne transmission Associated matrices Balantidium coli (Ciliophora) Faecal-oral Waterborne transmission documented Water (fresh produce, shellfish) Cryptosporidium spp. (Apicomplexa) Faecal-oral Yes Water, fresh produce, apple juice Cyclospora cayetanensis (Apicomplexa) Faecal-oral Yes Fresh produce (especially raspberries), water Dientamoeba fragilis (Metamonada) Unknown–robust transmission stage yet to be identified.
eBook - PDF- T Pandian(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
In addition, the mean cell v o l u m e of a population m a y vary in response to the same factors. Variability in generation time and mean cell volume present a complication that must be taken into account in energetic investi-gations. Although w e c a n broadly categorize Protozoa into trophic groups, the exact nutritional requirements of the majority of species are poorly re-searched. W e do not know to any real extent w h a t feeding preferences are in the w i l d , or h o w the elements of competition for food on an intra- and interspecific basis affect energy consumption or other aspects of the phys-iology. As Lee (1980) points out, our understanding of energy transforma-tions involving Protozoa requires that t w o fundamental components related to food quality be elucidated, first, information on the molecular constitu-tion of the prey and, second, the ability of Protozoa to recognize and utilize it. Although w e are able to demonstrate h o w food quality and quantity affect growth and reproduction in some species, w e can only place this informa-tion into the context of the natural community to a limited extent. II. INGESTION A. Modes of Feeding and Food Selection The modes of feeding displayed by the various groups of Protozoa are very diverse and differ in relation to the presence or absence of a cytostome, the type of feeding and locomotor organelles present, and the trophic status of the organism. The majority of ciliates feeding on bacteria are filter feeders, producing feeding currents with cilia and ciliary structures to c a p -ture and direct material onto the cell mouth or cytostome. The more primi-tive species, the gymnostomes, are essentially raptorial macrophages taking in algae and other organisms that make contact with the mouth (Fenchel, 1968a).
eBook - PDF- Lynne Shore Garcia(Author)
- 2021(Publication Date)
- ASM Press(Publisher)
Description (Trophozoite) The standard O&P exam is recommended for recovery and identification of G. lamblia in stool specimens. The Trophozoite is usually described as being teardrop shaped from the front, with the posterior end being pointed. From the side, it resembles the curved portion of a spoon. The con- cave portion is the area of the sucking disk, used for attachment to the mucosal lining. There are four pairs of flagella, two nuclei, two linear axo- nemes, and two curved bodies called the median bodies. Trophozoites usually measure 10 to 20 μm long and 5 to 15 μm wide. Although the concentration technique is helpful in demonstrating these organisms, the most important technique for the recovery and identification of protozoan organisms is the permanent stained smear (normally stained with trichrome or iron hematoxylin). As with most intestinal protozoa, the Trophozoite is usually seen in diarrheic or soft stools, while the cyst is seen in the more normal stool or when the patient may be asymptomatic. Trophozoites may remain attached or detach from the mucosal surface. Since the epithelial surface sloughs off the tip of the villus every 72 h, apparently the Trophozoites detach at that time. If mucus from the Entero-Test or fluid from a duodenal aspirate is submitted, the organisms may be trapped in the mucus. Keep the micro- scope light low, particularly when examining wet preparations. Make sure your eye becomes adjusted to each field before moving the stage. Description (Cyst) Cyst formation takes place as the organisms move through the jejunum after exposure to bil- iary secretions. Trophozoites discharge their undigested food and begin to round up prior to precyst and cyst formation. They retract the fla- gella into the axonemes, the cytoplasm becomes condensed, and the cyst wall is secreted. As the cyst matures, the internal structures are doubled, so that when excystation occurs, the cytoplasm divides, producing two Trophozoites.
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