GI Micro Lab A- Stool sample is taken and added to Selenite broth to: - 1- Inhibit growth of normal flora bacteria 2- Enhance growth of pathogenic bacteria B- After that the stool sample should be cultured on different types of media S-S Agar (Salmonella Shigella Agar) This agar is Red (pinkish) in colour. 1- Salmonella will cause the agar to become Transparent with the appearance of Black dots due to the production of H2S. 2- Shigella will cause the agar to become Transparent with dots that aren t black.
Hekton Agar This agar is also specific for Salmonella & Shigella. The agar is Green in colour. 1- Salmonella will cause the agar to produce Black dots due to the production of H2S. 2- Shigella will cause the agar to produce colonies that are still Greenish in colour
T.C.B.S Agar (Thiosulfate citrate bile salts sucrose agar) This test is specific for Vibrio Cholera. Grown best at a Ph of 8.5-10 The media is Green in colour, and a positive test for Vibrio cholera will change the colour to Yellow. Biochemical tests Kligler test Here the media is added to a test tube instead of a plate. The media is added in a way that the top part is Slanted, and the bottom part is normal. The media added is Red in colour. The reason for adding it in a slanted manner is that you want the slanted part to be anaerobic for the fermentation of lactose. Salmonella The positive test for this would be turning from Red to Yellow. As we said, the top part (slanted) is for detection of Lactose and the bottom part is for the detection of Glucose. So, the test for this bacterium would produce a Red(top)/Yellow(bottom) result, as Salmonella is a Non- lactose fermenter + Glucose fermenter.
Note: - The black area in the middle is due to the production of H2S. Urease test- Salmonella is Urease Negative. The media usually used here is Yellow in colour, and if positive would change to Pink. Citrate test- Salmonella is Citrate Positive. The media usually used here is Green in colour, and if positive would change to Blue.
SIM test SIM is an abbreviation for H2S, Indole, motility tests. H2S positive would produce a Black area, this test is positive for salmonella. Indole is usually colourless and would change to Pink if the test was positive, for salmonella this test is negative Motility test you tap the bacteria with a needle, if you see the bacteria in the same position then it is a negative test, if the bacteria has moved then the test is positive, and the latter is the case for Salmonella. Basically, this test is positive/negative/positive. Proteus They are Non-lactose fermenters. The main point you should know is that in Blood agar they exhibit what we call Swarming motility as they are Flagellated. You can prevent this swarming pattern by culturing it on CLED (Cystine lactose electrolyte deficient agar) or MacConkey.
Parasites Entamoeba histolytica & Entamoeba coli In general, the Trophozoites are Egg shaped and the Cysts are Circular. They move by Pseudopodia. Entamoeba Histolytica cyst contains 1-4 nuclei and the Karyosme is central Entamoeba Coli cyst contains 1-8 nuclei and the Karyosme is lateral
Giardia Lamblia They are Flagellated. The trophozoites look like a Tree leaf while the cysts are circular. In the trophozoites the Flagella is directed outwards while in the cysts the flagella are directed inwards. The trophozoites nuclei are shaped like a pair of eyes. Balantidium coli They are Ciliated, and their Nucleus is Kidney shaped.
Enterobius Vermicularis Known as the Pinworm. Its eggs are found inside of the mature worm. The egg is D- shaped. Trichuris Trichiura صينية Known as the Whipworm. Its eggs are shaped like a
Echinococcus Granulosus The worm contains a Scolex (head) & Gravid (tail). The lab professor mentioned no details but said memorise how the egg looks. Fasciolopsis Buski The egg here is Operculated which means it has a Cap like structure at its end.
Hymenolepis Nana Again, the professor didn t mention anything at all here except that they contain Suckers. Diphyllobothrium latum The doctor seemed to skip this one, so I ll just add that the egg here looks like its head has been cut off.
Taenia Solium & Taenia Saginata Taenia Solium Transmitted by Pigs. Has 4 suckers + Hooks. Taenia Saginata Transmitted by Beef. Has Suckers but without hooks, this is the differential characteristic between these two. Along with the presence of Hooks in the Taenia Solium as a differential characteristic between these two Taenia s. There are also more Chambers in Taenia Saginata that allows you to differentiate between them.