Entamoeba, Chapter Notes, Class 11, Biology PDF Download

ENTAMOEBA

GENERAL CHARACTERISTICS

Classification

Phylum     -      Protozoa
                        Unicellular or Acellular
                         organism

Class     -         Sarcodina

                        Locomotion by pseudopodia
                        Pseudopodia finger like

Genus   -          Entamoeba
                         Endoparasite

Species -         histolytica

Introduction

(i) Entamoeba histolytica was discovered by Lamble in 1859.
(ii) Pathogenic nature of Entamoeba histolytica was discovered by Losch in 1875.
(iii) Entamoeba histolytica was described in detail by Dobell in his book “Amoebae of Man”.
(iv) Recently Entamoeba has been studied in detail by Fraust, Frye and Neal.

Distribution

(i) Entamoeba is intestinal endoparasite of man.
(ii) Entamoeba is found in mucosa and submucosa of colon of intestine.
Note :Entamoeba histolytica is also found in mammals other than Man.

2. STRUCTURE

Entamoeba histolytica exists in two forms, these two forms are as follows :
Magna form Minuta form

Magna form
(i) Magna form is also called Trophozoite.
(ii) Trophozoite is the adult form of Entamoeba.
(iii) This is highly motile and pathogenic form.
(iv) This is trophic form of Entamoeba.
Note :Trophic form means, feeding form.
(v) This form inhabits in anterior part (colon) of large intestine of man.
(vi) This form have oval body and is about 20 to 30 ? in diameter.
(vii) The body remain covered by thin, elastic and semipermeable plasmalemma.
(viii) Cytoplasm remain divided into outer ectoplasm and inner endoplasm.
(ix) In this form only one broad and blunt pseudopodia get formed.
Note : Pseudopodia of Entamoeba includes only ectoplasm.
(x) In this form locomotion is monopodial.
(xi) In this form single, small spherical nucleus and several food vacuoles are found within endoplasm.
(xii) The nucleus of this form has a central endosome and a symmetrical peripheral crown of chromatin blocks.
(xiii) In this form contractile vacuole remains absent.

Minuta form
(i) Minuta form is also called precystic form.
(ii) This form is round, non motile and non feeding form.
(iii) This form is 10 to 20 ? in diameter.
(iv) Food vacuole remain absent in this form.
(v) This form is non pathogenic form.
(vi) This form is found in lumen of the large intestine.
(vii) This form get encysted.
(viii) This form is non infective form.

3. LIFE CYCLE

(i) Life cycle of Entamoeba is monogenetic.
(ii) It complete its life cycle in single host, in man.
(iii) Life cycle of Entamoeba can be classified into 5 phases, these phases are as follows:

Binary fission

(i) Trophozoite form reproduces asexually by binary fission within wall of the colon, as a result two daughter form get formed.
(ii) Some of the daughter form develops into normal trophozoite, whereas some of the daughter form comes within lumen of large intestine and get changed into minuta form.
(iii) Minuta form stores reserve food in form of glycogen and chromatoid body.
(iv) Chromatoid body is composed of ribonucleoprotein.

(i) Each minuta form get covered by a cyst.
(ii) In beginning encysted minuta possess only one nucleus later on nucleus get divided into 2 daughter nucleus by mitotic division, this cystic minute with 2 nucleus is called Binucleate cyst.

Infective stage

(i) Nucleus of binucleate cyst undergoes to mitotic division as a result 4 nucleus get formed within the cyst. Cyst with 4 nucleus is called tetranucleate cyst.
Note : This tetranucleate cyst is the infective stage of Entamoeba.
(ii) Tetranucleate cyst comes out from the body through stool.
Note : Outside the human body tetranucleate cyst can survive up to 6 to 7 years.

Transmission of Tetranucleate cyst

(i) Food and water get contaminated by tetranucleate cyst.
(ii) When healthy person consume food and water contaminated by tetranucleate cyst he get infected.

Excystment

(i) In small intestine of man cyst of quadri nucleate cyst get dissolved by the action of trypsin, as a result metacystic form or metacystic Amoeba.
Comes out from the quadrinucleate cyst, within lumen of the intestine.
(ii) This metacystic form undergoes to binary fission as a result 8 uninucleate metacystic trophozoite get formed.
(iii) Each uninucleate metacystic trophozoite develops individually into adult form that is trophozoite.

4. PATHOGENESIS

(i) The trophozoite actively secrete proteolytic enzyme which partially dissolve and loosen mucosa and submucosa and blood capillaries of the colon wall.
(ii) The trophozoite invade the colon wall and actively ingest intestinal tissue and red blood corpuscles as a result large number of ulcers get formed on the wall of intestine.
(iii) During pathogenesis trophozoite continuously undergoes binary fission and increases in number.
(iv) Stool of the host becomes loose and contains mucus, and blood, this condition is called “amoebic dysentery”.
(v) The disease may get aggravated by bacterial infections of the ulcer.
(vi) Bacterial infections leads to inflammation and pus formation.
(vii) In severe case colon wall get perforated.
(viii)Through blood stream trophozoite may migrate to vital organs of the host body like, liver, lungs, brain
etc leading to secondary infection.

5. PROPHYLAXIS AND THERAPY

Three types of methods are employed for eradication of Amoebiasis these methods are as follows :
Prevention from infection
Effective therapy
Destruction of infective cysts
Prevention from infection

For prevention from infection of entamoeba following steps should be taken-
(i) Drinking water should be filtered.
(ii) Before meal hands should be properly washed.
(iii) Food should be well covered.

Effective therapy

Effective therapy includes proper use of proper medicine.
(i) The basic medicinal salts used in treatment of amoebic dysentery are metronidazole, Tinadazole, Chloroquine and their derivatives.
(ii) The branded medicines used in treatment of amoebic dysentery are :

Flagyl, Metrogyl, Tini, Amcline, Dependal, Abidogyl, Amoebamagma, Amibactin, Biomebic, Diodoquin,
Entamizole, Enteroquinal.

Note :Chloroquine is given in complicated cases of secondary infections.
Destruction of infective cysts
Destruction of cyst is the most effective method of checking the spread of amoebiasis.

6. SPECIAL POINTS

(i) More than 50% of population of the world is infected with Amoebiasis.
(ii) Entamoeba histolytica is found in whole world in hot places in particular.
(iii) Quadrinucleate cyst get damaged at 50ºC.
(iv) Entamoeba hartmani is found in lumen of the large intestine.
(v) In Entamoeba, number of chromosome is 6.
(vi) Inner layer of cyst of Entamoeba is resistant to HCl.
(viii)Outer layer of cyst of Entamoeba is resistant to intestinal enzyme.

7. ENTAMOEBA GINGIVALIS

(i) Entamoeba gingivalis is also called mouth amoeba.
(ii) It is found in gums, tartar and pus pockets of tonsils.
Note :
(a) Thin yellowish layer generally found on the back of teeth is called tartar
(b) Entamoeba gingivalis is also found in mammals, dogs, cats, horse, monkeys etc.
(iii) It is found in 50-70% of human population.
(iv) Adult form of Entamoeba gingivalis is called trophozoite and has 2-3 pseudopodia.
(v) It feeds on WBC, bacteria and pus cells.
(vi) Its ectoplasm is homogeneous whereas, endoplasm is granular and highly vacuolated.
(vii) It contain several food vacuole and nucleus with central nucleolus.
(viii) Cyst is not formed in E. gingivalis and infection occurs by kissing.

8. ENTAMOEBA COLI

(i) It is found in colon of 50% of human population.
(ii) Its ectoplasm and endoplasm remains undivided.
(iii) It is a commensal parasite and does not produce any disease in human being.
(iv) It has single, small, blunt and granular pseudopodia.
(v) It possess numerous food vacuole.
(vi) It feed upon bacteria and debris present in the lumen of intestine.
(vii) It is monogenetic and infection occurs by direct contact like kissing.
(viii) Its cyst possess 8 nuclei.
Note :It was Walker and Sellards who at first described that E. coli and E. gingivalis is non pathogenic.