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Principles and practice of Clinical parasitology - Gillespie S.

Gillespie S. Principles and practice of Clinical parasitology - Wiley publishing , 2001. - 675 p.
ISBN 0-471-97729-2
Download (direct link): principlesandpracticeofclin2001.pdf
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Fig. 12-2 Life-cycle of Naegleria fowleri, Acanthamoeba spp. and Balamuthia mandrillaris
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PRINCIPLES AND PRACTICE OF CLINICAL PARASITOLOGY
Fig. 12.3 (A) Trophozoites of Naegleria fowleri. Plastic embedded, toluidine blue, x500. (B) Flagellate form of N. fowleri.
Scanning electron microscopy. Courtesy of Dr D. T. John (John, 1993). (C) Typical cysts of N. fowleri. Scanning electron microscopy. Courtesy of Dr D. T. John (John, 1993). (D) Ultrastructural features of N. fowleri trophozoite, Electron microscopy, x 5000
Acanthamoeba spp.
Acanthamoeba has two stages in its life-cycle, a feeding and reproducing trophozoite stage and a resistant cyst stage (Figure 12.2). The trophozoites feed on bacteria and detritus present in the environment and multiply by binary fission. One of the most characteristic features of Acanthamoeba is the presence of fine, tapering, thorn-like pseudopodia, the acanthopodia, which emanate from the surface of the body (Figure 12.4A). The trophozoites, from culture, measure 15-45 pm. They are uninucleate and the nucleus has a centrally placed, large, densely-staining nucleolus. The cytoplasm is finely granular and contains numerous mitochondria, ribosomes, vacuoles and lysosomes (Figure 12.4B). Cysts are double-walled and measure from 10-25 pm. The outer cyst wall,
the ectocyst, is wrinkled or mamillated and contains protein. The inner cyst wall, the endocyst, is usually stellate, polygonal, oval or spherical and contains cellulose. Pores or osteoles are present at the junction of the ectocyst and the endocyst. The pores are covered by opercula, which pop open at the time of encystation. The cysts are uninucleate and possess a centrally placed dense nucleolus (John, 1993; Ma et al., 1990; Martinez and Visvesvara, 1997; Page, 1967; Visvesvara and Stehr-Green, 1990).
Balamuthia mandrillaris
B. mandrillaris, like Acanthamoeba, has two stages in its life-cycle (Figure 12.2). The trophozoite is pleomorphic and measures 12-60 pm,
PATHOGENIC AND OPPORTUNISTIC FREE-LIVING AMEBAS
273
Fig. 12.4 (A) Trophozoite of Acanthamoeba spp. showing the fine, thorn-like acanthopodia. Scanning electron microscopy.
Courtesy of Dr D. T. John (John, 1993). (B) Ultrastructural features of Balamuthia mandrillaris trophozoite containing numerous mitrochondria. Electron microscopy, x 6000. (C) Trophozoites of B. mandrillaris within infected CNS tissue of a congenitally immunosuppressed mouse. Hematoxylin and eosin, x 300. (D) Cyst of B. mandrillaris from a case of GAE showing a spherical thick wall with endocyst and delicate ectocyst. Electron microscopy, x 5000
with a mean of about 30 pm. It is usually uninucleate but binucleate forms are occasionally seen. The nucleus possesses a large, centrally placed, dense nucleolus. Occasionally, however, trophozoites with two or three nucleolar bodies have been seen, especially in infected tissues (Figure 12.4C). The cysts are also uninucleate, more or less spherical and measure 12-30 pm, with a mean of 15 pm. The cysts, when examined with a light microscope, appear to be doublewalled, the outer wall being wavy and the inner wall round. Ultrastructurally, however, the cysts possess three walls—an outer thin and irregular ectocyst, an inner thick endocyst, and a middle amorphous fibrillar mesocyst (Figure 12.4D)
(Martinez and Visvesvara, 1997; Visvesvara et al., 1990, 1993; Visvesvara and Stehr-Green,
1990).
Culture
Acanthamoeba spp. and N. fowleri, but not
B. mandrillaris, can be easily cultivated on nonnutrient agar plates coated with a suitable Gramnegative bacterium, such as Escherichia coli or Enterobacter aerogenes. The amebas will feed on the bacteria, multiply and completely cover the surface of the plates within a few days. When
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PRINCIPLES AND PRACTICE OF CLINICAL PARASITOLOGY
almost all of the bacteria are gone, the amebas differentiate into cysts. They can be maintained in the laboratory indefinitely by periodically cutting out a small piece of agar containing trophozoites and/or cysts and transplanting it onto a fresh agar plate, coated with bacteria as before. Additionally, both Naegleria fowleri and Acanthamoeba spp. can also be cultured on mammalian cell cultures. Unlike Acanthamoeba and Naegleria, Balamuthia cannot be cultured on agar plates coated with bacteria. B. mandrillaris has not been isolated from the environment so far and the food source of these organisms is not yet known. However, it is well known that when it infects humans and other animals, it feeds on host tissue cells and destroys their normal architecture. Therefore, it is usually isolated by inoculating infected host tissue on to mammalian cell cultures. Balamuthia feeds on the cell culture and multiplies {John, 1993; Martinez and Visvesvara, 1997; Visvesvara et al., 1990, 1993; Visvesvara and Stehr-Green, 1990).
N. fowleri, Acanthamoeba spp. and B. mandrillaris can be cultivated without bacteria in complex chemical media. Although several different formulations are available, Centers for Disease Control and Prevention {CDC) laboratories use a modified version of Nelson’s medium that contains a 0.5% solution of liver digest, 0.1% glucose and a low-osmolarity buffered salt solution supplemented with 3-5% fetal bovine serum. Acanthamoeba spp. can also be easily grown in a medium composed of 2% proteose peptone, 0.5% yeast extract and 0.1% glucose, made up in a low osmotic buffered salt solution with or without serum {John, 1993). B. mandril-laris can also be grown in a highly complex medium {Schuster and Visvesvara, 1996). Serumfree, chemically defined media have also been devised to grow N. fowleri and several species of Acanthamoeba.
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