mikrobiyoloji
Kasım 09, 2018
Eijkman Test
Eijkman Test
Coliform organism is a term used to designate the lactose-fermenting Enterobacteria such as Escherichia coli and Enterobacter. Enterobacteriaceae forms a large group of gram-negative bacteria that inhabit intestinal tract of warmblooded animals. Therefore they constitute the major microbial flora of human faeces. Since coliforms are readily isolated and identified, they are used as indicator organisms to check faecal contamination of food, water and other samples. E.coli is one of the common organisms involved in gram-negative sepsis and endotoxin-induced shock. Eijkman described a method for selective isolation of E.coli from faeces of warm-blooded and cold-blooded animals.
This method had limitations due to the inability to obtain growth after subculturing from positive tubes incubated at 46°C, as acidity and high temperature resulted in death of the culture within 24-48 hours. Perry and Hajna modified Eijkmans original method by decreasing carbohydrate content and adding a phosphate buffer enabling to subculture E.coli after incubation at 46°C for 96 hours or longer where pH was 5.6 unlike 4.5 of Eijkman Medium. Perry modified Eijkman Medium using lactose for isolation of E.coli. This medium can also be used for bacteriological examination in water filtration control work.
Tryptose and lactose in the medium are the energy and the carbon sources respectively. E.coli ferment lactose to form acid and gas. The gas produced gets trapped in the form of gas bubbles in the inverted Durhams tubes. Phosphates buffer the medium whereas sodium chloride helps to maintain the osmotic equilibrium of the medium.
Quality Control
Appearance
Cream to yellow homogeneous free flowing powder
Colour and Clarity of prepared medium
Light yellow coloured, clear solution without any precipitate
Reaction
Reaction of 2.85% w/v aqueous solution at 25°C. pH : 6.8±0.2
pH
6.60-7.00
Cultural Response
Cultural characteristics observed after an incubation at 45.5 to 46ºC for 24 - 48 hours.
Organism Inoculum Growth Gas
(CFU)
Escherichia coli 50-100 luxuriant positive
reaction
Enterobacter aerogenes 50-100 poor negative
reaction
