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Transcript
Study of the biochemical activity of bacteria Omid Tadayoun supervised: berzsu METABOLISM OF LIPIDS, AMINO ACIDS AND OTHER NITROGEN CONTAINING COMPOUNDS METABOLISM OF LIPIDS | Phospholipase y | An enzyme that hydrolyzes phospholipids into fatty acids and other lipophilic substances Lipase An enzyme that catalyzes the hydrolysis of fats into glycerol and fatty acids y Facilitate nutrient absorption from the external medium y In pathogenic microbes, it may promote invasion of a new host y | Lecithinase y Type of phospholipid that acts upon lecithin. METABOLISM OF LIPIDS | Lecithinase y y y y y Can be demonstrated on egg-yolk medium Egg yolk consists of lecithin Lecitinase cleaves lecithin into diglyceride + phosphorylcholine Opalescent part around the colonies Bacillus cereus, Clostridium perfringens (Nagler test) LECITHINASE TEST Lecithin positive B. cereus Lecithin negative B. sphaericus METABOLISM OF AMINO ACIDS AND OTHER NITROGEN CONTAINING COMPOUNDS Urea breakdown | H2S production | Indole production | METABOLISM OF AMINO ACIDS AND OTHER NITROGEN CONTAINING COMPOUNDS | Urea breakdown y y y y y Christensen medium. slant, solid medium containing urea, dextrose, phenol-red indicator Urease +. urease releases ammonia from the urea, ammonia increases the pH, color of the indicator changes into purple Urease -. dextrose utilized, producing acid, decreasing the pH, coloring the medium yellow Originally the color of the medium is dark yellow/orange E.g. Helicobacter pylori; some Proteus sp.; some Klebsiella sp. UREASE TEST Urease - Urease + METABOLISM OF AMINO ACIDS AND OTHER NITROGEN CONTAINING COMPOUNDS | H2S production y y y y y y y y often results from the bacterial breakdown of sulfites in non-organic matter in the absence of oxygen H2S is produces from thiosulfate Indicators: heavy metal salts formed -> black color Lead nitrate in agar traps H2S, forming a black precipitant when lead sulfide is formed Bismuth sulfite medium Iron-high agar Agar turns black when H2S +, no color change when H2S – E.g. Salmonella sp; some Proteus sp. wqc.arizona.edu H2S PRODUCTION Salmonella on Bismuth sulfite agar METABOLISM OF AMINO ACIDS AND OTHER NITROGEN CONTAINING COMPOUNDS | Indole production y y y y y Tryptophanase enzyme activity is seen Free indole ring is generated by deamination from tryptophan, by the enzyme tryptophanase Kovacs´ (Erlich) reagent (containing free aldehyde group) will react with the indole-ring to form a bright red ring at the surface of the tube Final products of the reaction are indole, pyruvic acid, ammonia E.g. Escherichia coli; some Proteus sp. INDOLE TEST Indole + Indole -