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Keith Ireton

PHCY219 – Microbiology Section 1 – Lecture 3 Judith Bateman Lecture 3 – Microbial Nutrition Objectives 1.Describe examples of specialised media Different culture media will be selected for depending on the purpose. - Can use agar purified from red algae as a solidifying agent Defined – All the quantities are known and exact. This is the opposite for complex culture media. What is peptone? Peptones are proteins that are hydrolysed by enzyme or acids. Use this as nutrients for the microbes. 1 | P a g e PHCY219 – Microbiology Section 1 – Lecture 3 Judith Bateman 1.Describe examples of specialised media Specialised media – different environments in the media are created depending on what it’s being used for. There are FIVE examples (remember these)!! Specialised media Use Composition Use this to transport samples from patients Has buffers and salts 1.Temporary Media (temporary storage). Allows organisms to DOES NOT HAVE: carbon, survive, but does not allow division. nitrogen and growth factors Use this when you want to grow a wide Has general nutrient 2.Enriched Media variety or organisms. i.e. – grow as many supplements different types as possible - Serum, or yeast extract Use this when you want to grow a particular organism. Will allow the target organism to become dominant in the culture media so that it can be detected. IMPORTANT FEATURE: will keep normal Specific factors – depends on the 3.Enrichment Broths microflora (very high numbers) static in the organism/s you are targeting. lag phase. Conversely will encourage the target organism (which will be very low in numbers) to grow (logarithmic growth phase). For example: a) Crystal violet will inhibit gram +ve bacteria (allows Use this you want to grow a particular survival of gram –ve). 4.Selective media organism but INHIBIT the growth of others. b) Bile salts discourage the This is a difference between 3 and 4. growth of non-enteric bacteria (enteric organisms can cope with bile salts so they survive) Ultimately this selects for Gram –ve enteric organisms!!!!!! Example: MacConkey agar contains lactose. When the This type of media will allow you to lactose is fermented, it becomes a distinguish between different organisms. red colour. Other colonies that 5. Differential Media Can do this by visual inspection because don’t ferment lactose will have colour compounds are involved white or clear colonies. So just by looking at whether the colonies are red or not you can tell which colonies ferment lactose. Another example of differential media is blood agar (Note: blood agar is also a type of enriched media). Some organisms have haemolysins which lyse animal membranes. By using blood agar plates, we can tell if the bacteria have haemolysins or not (look for zones around the colonies). α-haemolysis = partial lysis of RBC will show as a green-ish zone. β-haemolysis = complete lysis will havezones with NO RBC (refer to slide 9 – black outer region). γ- haemolysis = no RBC lysis has no zone.
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