Entamoeba histolytica
Dongyou Liu in Handbook of Foodborne Diseases, 2018
E. histolytica trophozoite is characterized by a large pleomorphism,6 that is elongated in form with protruding pseudopods and cytoplasmic projections and with a posterior uroid; typically, it is uninucleate of 20–40 μm in diameter.2 Active amoebae exhibit directional motility forming cytoplasmic rounded pseudopodial extensions (lobopodia) (Figure 56.1b). The spherical nucleus occupies roughly 20% of the amoeba's volume and serves as a basis for the diagnosis of this species in clinical laboratories; it contains a small karyosome, which is delimited by a clear nuclear membrane lined with small darkly stained round granules of chromatin that are dispersed evenly.7 The cytoplasm is unremarkable by light microscopy, and it may include vacuoles containing phagocytosed red blood cells (RBCs), other host cells, and bacteria. Vacuoles have a circular profile and vary in size (0.5–9.0 μm in diameter). Diverse vacuoles are observed at the ultrastructural level: phagocytic, macropinocytic, micropinocytic, and autophagy vacuoles.1 Ribosomes are often ordered in helical arrays of roughly 300 nm in length and 40 nm in diameter. Currently, research on amoeba cells is focused on identifying an ancestor of classic organelles found in higher eukaryotes (Figure 56.1c).
Some doctors and their defences
John Salinsky, Paul Sackin, Dame Lesley Southgate in What Are You Feeling, Doctor?, 2017
If our sketchy memories of school biology are correct, the amoeba puts out a pseudopodium when attracted by an external object which might be suitable for ingestion. Protoplasm from the main body of the amoeba’s cell flows out into the pseudopodium. The amoeba transfers its substance towards the object, touches it and may then engulf it. If it then experiences a noxious chemical substance, the pseudopodium is quickly withdrawn and the protoplasm flows back towards the centre so that the amoeba resumes a more spherical shape. We likened the doctor’s personal self to the inner protoplasm which flows easily into the professional pseudopodium extended towards the patient – only to be withdrawn again quickly when danger threatens. This image of the amoeba allowed us to see the personal ‘protoplasm’ as an essential substance which is a natural part of the professional process extended towards the patient. A good doctor–patient relationship needs the involvement of the personal self. At the same time we must protect our personal selves if we are to maintain our own good health and survive to be available for the next patient and the one after that.
Connecting up: On making up one’s mind
Derek Steinberg in Consciousness Reconnected, 2018
This argument is of the type I identified early in this book as illustrating the importance of taking nothing for granted in examining the nature of consciousness. Much child psychology has been discussed in terms of the infant being aware of this, doing that, then the parent does that, and so on, but all of this, it seems to me, is already well along the consciousness road. But why should an infant even take the slightest notice of the outside world, still less want to move about in it and do something with it – even merely grasping something – unless it had evolved-in, survival-enabling equipment that made such moves both possible and worth doing? Fortunately, amoeba-like, it comes equipped to move about, reach for, grab, ingest and do other things with what’s outside for the sake of what’s within. Of course, it has also had millions of years of adaptation and development to do such things so much better than an amoeba, or even a primate; for example, gazing at a face as if knowingly, and with a charming smile. But ‘it’ does this without knowing that it does.
Epidemiology of free-living amoebae in the Philippines: a review and update
Published in Pathogens and Global Health, 2022
Giovanni D. Milanez, Frederick R. Masangkay, Gregorio L. Martin I, Ma. Frieda Z Hapan, Edilberto P. Manahan, Jeffrey Castillo, Panagiotis Karanis
Studies on free-living amoebae (FLA) have in recent decades gained traction in the field of protozoology and parasitology. Known for their ubiquity, FLAs have been isolated from various environmental matrices, such as soil, fresh and brackish water, wastewater, hot springs, dust, and others [1–6]. Aside from environmental sources, FLAs were also reported from cooling towers, air conditioning systems, bromeliad plants, dental water supplies, and are known to contaminate contact lens and lens fluids [7]. In addition, FLA can harbor pathogenic microorganisms within its cytoplasm, enabling them to persist and eventually be transmitted to a broad spectrum of biological hosts via multiple transmission routes. Due to this, FLA is dubbed as ‘Trojan horses’ of the microbial community [8,9]. Prokaryotes persisting within FLA have been called amoebae-resistant bacteria (ARB) by some researchers [10], while most recently, the collective term ‘endocytobionts’ has been used to describe the variety of microorganisms that multiply within an FLA host [11]. This term may be more appropriate considering that FLA, in general, can also internalize viruses [12], fungi [13], and protozoa [4,14,15].
The rumen microbiome: a crucial consideration when optimising milk and meat production and nitrogen utilisation efficiency
Published in Gut Microbes, 2019
Chloe Matthews, Fiona Crispie, Eva Lewis, Michael Reid, Paul W. O’Toole, Paul D. Cotter
Amoebae can represent an important reservoir for bacteria in the environment, but their role in the rumen is unclear. In the vegetative cycle (multiplication by binary fission), amoeba, similar to ciliate protozoa, survive by ingesting bacteria through phagocytosis.51 While further research is necessary in order to ascertain the role of amoeba in the rumen, it is known that some bacteria can survive phagocytosis by protozoa and live as endosymbionts.52 For instance, Campylobacter jejuni has been shown to invade Acanthamoeba polyphaga and can replicate in vacuoles.53C. jejuni and C. fetus can have large effects on cow fertility, immunity and overall health.54 Amoeba therefore may be important in rumen and general bovine health.
Curcuma longa ethanol extract and Curcumin inhibit the growth of Acanthamoeba triangularis trophozoites and cysts isolated from water reservoirs at Walailak University, Thailand
Published in Pathogens and Global Health, 2020
Watcharapong Mitsuwan, Chooseel Bunsuwansakul, Theodore Ebenezer Leonard, Sawanya Laohaprapanon, Kruawan Hounkong, Kingkan Bunluepuech, Chalermpon Kaewjai, Tooba Mahboob, Chandramathi Sumudi Raju, Mahaveer Dhobi, Maria de Lourdes Pereira, Muhammad Nawaz, Christophe Wiart, Abolghasem Siyadatpanah, Roghayeh Norouzi, Veeranoot Nissapatorn
Free-living amebae belonging to the genus Acanthamoeba are protozoa ubiquitously in nature such as water and soil. The protozoa are causative agents of several diseases including granulomatous amebic encephalitis [1–3] and amebic keratitis [4]. The occurrence of Acanthamoeba keratitis in contact lens users can cause severe vision loss and complete blindness [5]. In addition, the infection caused by the organism is severe in immunocompromised patients. The parasite has two stages of growth including trophozoite and cyst. Trophozoite is a vegetative amoeba form moving by amoeboid locomotion. Cyst form is dormant stage that survives in harsh environment conditions such as lack of nutrients. Acanthamoeba cysts are classified into three groups including astronyxids, polyphagids, and culbertsonids [6]. The cysts contain two strong layers of cyst wall including ectocyst and endocyst walls. Acanthamoeba cysts have been reported to resist to antimicrobial substances [7,8]. Therefore, the treatment of Acanthamoeba infections is difficult due to its double-walled cyst layers.
Related Knowledge Centers
- Animal
- Eukaryote
- Protoplasm
- Pseudopodia
- Cell
- Lineage
- Microbiologist
- Amoeboid Movement
- Subphylum
- Molecular Phylogenetics