Medical Microbiology Lec 3 PDF

Medical Microbiology. Microbiological culture media and sterilization Methods of inoculation and isolation of pure culture. Bacterial spores and endospores staining. ‫ فَـرح كاظـم غثيث‬.‫ م‬.‫م‬ ‫ َحـوراء عدنـان‬.‫ ب‬.‫م‬  Microbiological culture media...

Medical Microbiology. Microbiological culture media and sterilization Methods of inoculation and isolation of pure culture. Bacterial spores and endospores staining. ‫ فَـرح كاظـم غثيث‬.‫ م‬.‫م‬ ‫ َحـوراء عدنـان‬.‫ ب‬.‫م‬  Microbiological culture media It is the media containing the required nutrients for bacterial growth and reproduction. Used to growth and Isolation and identification of microorganisms and Performing anti-microbial sensitivity tests.  form of culture media 1. solid culture media : Used to Description of bacterial colonies. in petri dishes. Ex: nutrient agar , blood agar. 2. semisolid culture media : Used as an enrichment media as motility media. 3. Fluid culture media : Used as an enrichment media and as biochemical testing media and as blood culture media. Ex : Nutrient Broth and pepton water , meat infusion broth. 1. Simple: Types of culture media to growth of microorganisms that do not require special nutrients. Ex: Nutrient Broth / Nutrient Agar. 2. Enriched media : with blood, serum , or vitamins to growth of pathogenic bacteria. Ex : Blood Agar / Chocolate Agar. 3. Enrichment media : Ex : Alkaline peptone water. 4. Selective media : Ex: Salmonella- Shigella ( SS) agar.  Sterilization of culture media A medium is sterilized (living organisms removed) before usage in the lab. Methods used to sterilize culture media : A) Autoclaving Autoclaving is used to sterilize most agar and fluid culture media. The principle of sterilization in an autoclave is that steam under pressure is used to produce a temperature of 121ºC / 15 min.. all microorganisms will be destroyed. B) Steaming at 100 OC It is used to sterilize media containing materials that would be inactive at temperature over 100 OC. C) Filtration It is used to sterilize media are heat-sensitive and can not be autoclaved. : Sterility testing test of contamination by incubate the media At 35-37 OC for 24 hours. Turbidity in fluid media and microbial growth in solid media confirm contamination.  Inoculation of culture media producing a bacterial culture by Introduce a tiny sample into a nutrient medium. inoculation of media in petridishes apply the sample to a small area of the plate by using sterile wire loop and then spread and thin out the sample to ensure single colony growth. Inoculation of fluid media To inoculate fluid media, use straight wire or wire loops.  Incubation of cultures The temperature selected for culturing is 35-37 OC.  isolation of pure culture is a separating one species from another and to obtain pure bacterial cultures. the pure colony contains cells just that species. To obtain a pure bacterial culture is the first step to bacterial identification. The Pure culture is essential in the study of the morphology , physiology , biochemical characteristics of a bacterial strain.  Bacterial spores (endospores) -One of the most common coping mechanism for bacteria is forming spores ( a dormant stage ) occurs when bacterial cells develop an outer shell to protect themselves from environmental conditions such as heat , chemicals , and nutrient depletion. When the appropriate conditions for bacterial spore are again , they return to the state in which can multiply. -Among human pathogen bacteria, only the genera Clostridium and Bacillus produce spores.  endospores staining is a technique used to identify the presence of endospores in a bacterial sample. Procedure: 1. Prepare a smear. 2. Cover the smear with malachite green solution and heat over steaming water bath for 3-5 minutes. 3. Wash with water. 4. Cover the smear with safranin for 30 seconds. 5. Wash with water. 6. Dry and examine under the oil immersion objective. Endospores are bright green and vegetative cells are brownish red to pink The location of the spore is an identifying characteristic thank you