CULTURE MEDIA

1. LECTURE 5: CULTURE MEDIA Microbiology and Virology; 3 Credit hours Atta-ur-Rahman School of Applied Biosciences (ASAB) National University of Sciences and Technology (NUST)

2. CULTURE MEDIA • A culture medium is a solid or liquid preparation used to grow, transport, and store microorganisms. • Much of microbiology depends on the ability to growand maintain microorganisms in the laboratory • Microorganism’s normal habitatreflects its nutritional requirements

3. Types of Culture Media Culture media can be classified on the basis of several parameters

4. Defined medium A medium in which all chemical components are known is a definedor synthetic medium.

5. Complex Media • Media that contain some ingredients of unknown chemical composition are complex media. • Such media are very useful • Nutritional requirements of a particular microorganism are unknown, and thus a defined medium cannot be constructed • Complex media contain undefined components like peptones, meat extract, and yeast extract

6. Components of Complex Media • Peptones are protein hydrolysates prepared by partial proteolytic digestion of meat, casein, soya meal, gelatin, and other protein sources. • They serve as sources of carbon, energy, and nitrogen.

7. Components of Complex Media • Beef extract and yeast extract are aqueous extracts of lean beef and brewer’s yeast, respectively. • Beef extract contains amino acids, peptides, nucleotides, organic acids, vitamins, and minerals. • Yeast extract is an excellent source of B vitamins as well as nitrogen and carbon compounds.

8. Components of Complex Media • Agar is a sulfated polymercomposed mainly of D-galactose, -L-galactose and D-glucuronicacid. • It usually is extracted from red algae. • It melts at about 90°C but once melted does not harden until it reaches about 45°C. • Thus after being melted in boiling water, it can be cooled to a temperature that is tolerated by human hands as well as microbes. • Microbes growing on agar medium can be incubated at a wide range of temperatures. • Most microorganisms cannot degrade it.

9. Components of Complex Media

10. Components of Complex Media

11. Functional Types of Media • Media such as tryptic soy broth and tryptic soy agar are called general purpose media or supportive media because they sustain the growth of many microorganisms • Blood and other special nutrients may be added to general purpose media to encourage the growth of fastidious microbes. • These specially fortified media (blood agar) are called enriched media

12. Functional Types of Media • Selective media favor the growth of particular microorganisms. • Bile salts or dyes like basic fuchsin and crystal violet favor the growth of gram negative bacteria by inhibiting the growth of gram-positive bacteria; the dyes have no effect on gram negative organisms. • Endo agar, eosin methylene blue agar, and MacConkeyagar

13. Functional Types of Media • Differential media are media that distinguish among different groups of microbes and even permit tentative identification of microorganisms based on their biological characteristics. • Blood agar is both a differential medium and an enriched one. • It distinguishes between hemolytic and non-hemolytic bacteria. • Hemolytic bacteria (e.g., many streptococci and staphylococci isolated from throats) produce clear zones around their colonies because of red blood cell destruction

14. Functional Types of Media • It is used to distinguish pathogenic bacteria based on the effect of bacterial enzymes known as hemolysins which lyse red blood cells. • Blood agar is mainly used clinically to detect the presence of Streptococcus pyogenes

15. Functional Types of Media • MacConkey agar is both differential and selective. • Bile salts to support the growth of Gram negative microbesCrystal violet to inhibit the growth of Gram positive microbes • Since it contains lactose and neutral red dye, lactose fermenting colonies appear pink to red in color and are easily distinguished from colonies of non fermenters. Lac+ bacteria such as Escherichia coli, Enterobacter and Klebsiella will produce acid, which lowers the pH of the agar below 6.8 and results in the appearance of red/pink colonies. Non-Lactose fermenting bacteria such as Salmonella, Proteus species, Pseudomonas aeruginosa and Shigella cannot utilize lactose, and will use peptone instead

16. Colony Morphology Characteristics