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Citrobacter freundii

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Research has revealed that C. freundii is responsible for over 29% of all the opportunistic infections (Leboffe & Pierce, 2011). It is therefore important not only to be able to isolate the bacterium but also to sequence its many different strains and plasmids since this will form the basis for antibiotic development. It is the only bacterium in the family Enterobacteriaceae with a plasmid. Through the plasmids, the bacterium produces cephalosporinase enzyme which affects the antibiotic cephamycins and cephalosporin by hydrolyzing them leading to resistance. This bacterium is however beneficial to the environment since it is responsible for reduction of nitrate into nitrite, a crucial nitrogen cycle stage within the environment.

Materials and Methods Samples collection and Preparation Different samples were identified according to Bergey’s manual of Determinative of bacteriology which identifies Citrobacter freundii’s habitats as soil, water and sewage environments. The first sample was collected from backyard soil, the second from fertilizer and the third sample from dog poop. Preparation of the Media MacConkey Agar (MAC) and Eosin Methylene Blue Agar (EMB) were chosen as the best media for selecting Citrobacter freundii after thorough analysis of lab manual.

MacConkey agar is compost of: lactose which serves as energy source, enzymatic digest of animal tissue, gelatin and casein which provides vitamins, nitrogen, minerals and amino acids essential for growth. There are also bile salts which are selective agents inhibiting the growth of gram positive organisms and sodium chloride that supply important electrolytes necessary for transport and osmotic balance. The neutral red is a pH indicator and agar is a solidifying agent. Eosin Methylene blue (EMB) agar is made up of Peptone, Lactose, Sucrose, Eosin Y dyes and Methylene blue.

This is both a selective and a differential media because the methylene blue presence in the media hinders the growth of gram positive bacteria (Berkeley, 2000). Eosin is also a pH sensitive dye changing from colorless to black as the acidity develops. The sugars are important sources of energy and encourage the growth of the bacteria. All these components of the media are important for the differentiation of the bacteria. While sugars provide fermentable substrates and essential for gram negative bacteria, the fermentation process leads to acidification of the media hence the dye produce a dark purple complex (Berkeley, 2000).

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