Bacterial nutritional requirements. Composition of culture media. Categories of culture media. Solidifying agents. Types of media. Media Quality control. Culturing techniques. Condition of incubation.
1. Carbon Source: ◦ Heterotrphs: from organic compounds such as: a.a., polysaccharides, CHO, proteins and peptides. ◦ Autotrophs: from fixing inorganic carbon dioxide.1. Energy Source: ◦ Phototrophs: from sunlight. ◦ Chemotrophs: from oxidation of chemicals.1. Nitrogen: essential for a.a., nucleotide and vitamins synthesis.
4. Minerals: as cofactors in enzymatic reactions. ◦ E.g., sodium, potassium, calcium, magnesium, iron… etc.4. Growth factors: ◦ Amino acids, a.a.: bacteria possess proteinases. ◦ Purines and pyrimidines: to be converted to nucleotides. ◦ Bacterial vitamins: for co-enzyme production.4. Water: ◦ All metabolic functions of a bacterial cell are performed in aqueous environment. ◦ Distilled water Tap water minerals and their reaction with peptones and meat extracts.
1. Water.2. Peptone: product of protein hydrolysis. ◦ From animal proteins: source of nitrogen. ◦ From soya bean (plant) protein: source of carbohydrates, CHO.1. Meat extracts: as source of a.a. and other essential vitamins and elements.2. Yeast extract: as a stimulant for bacterial growth in the media.3. Mineral salts: for bacterial enzymes activity.4. Carbohydrates: as source of carbon and energy.
Agar: ◦ Is a complex polysaccharide (polymer of galactose) that is extracted from the cell wall of seaweed (red algae). ◦ It has no nutritional value in agar cultures. Gelatin: ◦ A protein which is derived from collagen of skin and bone. ◦ It has no nutritional value in agar cultures.
In broths, bacterial growth is indicated by a change in the appearance from clear to turbid (cloudy). The more turbid, the….
Basal Media: ◦ Simple media that will support the growth of most bacteria that do not require special nutrient. E.g., Nutrient broth. ◦ Nutrient broth+ agar= Nutrient agar Enriched media: ◦ Culture media that are enriched with whole or lysed blood, serum, special extracts or nutrient to support the growth of those bacteria that cannot grow on the basal media. ◦ Nutrient agar+ blood= Blood agar ◦ Blood agar+ heat= chocolate agar Selective media: ◦ Solid media which contain substances that inhibit the growth of some bacteria and letting the others grow.
Enrichment media: ◦ These are liquid media that are similar in function to ... ◦ The only difference is that… Differential media: ◦ Contains indicators that will differentiate one organism from another Transport media: ◦ Contain substances that can prevent overgrowth of commensals and prevent bacteria from dying as a result of change in pH or enzyme action.
Media should be tested for: 1. Sterility. 2. Each medium must be tested with organisms expected to grow or give a positive reaction as well as with organisms expected not to grow.
But when we’ll go over it, it’llThe media looks like this… look like this ;)
Temperature. Hydrogen ion concentration (pH). Gaseous requirements.
Too high temperature will denature bacterial ezymes. While too low temperature…. Types of bacteria according to their growth temperature: 1. Psychrophiles: bacteria that grow between 0-20oC. 2. Mesophiles: those that grow between 21oC and 50oC. 3. Thermophiles: the ones that grow between 50oC and 100oC.
Acidophiles: bacteria that grow in acidic pH. Neutrophiles: those that grow in between 4-9. Alkalophiles: ones that grow in alkaline pH.
Bacteria differ in their need to molecular oxygen for growth: Obligatory (strict)aerobes: require free oxygen for growth. Obligatory (strict) anaerobes: grow only in the absence of free oxygen. Facultative anaerobes: multiply either in the presence or absence of free oxygen. Carboxyphilic (capnophilic): these bacteria require raised level of carbon dioxide (5-10%).