logging in or signing up Factors Affecting Microbial Growth blamedinnosence Download Post to : URL : Related Presentations : Let's Connect Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Copy embed code: Embed: Flash iPad Dynamic Copy Does not support media & animations Automatically changes to Flash or non-Flash embed WordPress Embed Customize Embed URL: Copy Thumbnail: Copy The presentation is successfully added In Your Favorites. Views: 6190 Category: Science & Tech.. License: All Rights Reserved Like it (4) Dislike it (2) Added: February 22, 2009 This Presentation is Public Favorites: 1 Presentation Description No description available. Comments Posting comment... By: jigssavani (40 month(s) ago) i like it can i get it? Saving..... Post Reply Close Saving..... Edit Comment Close By: bilatu (49 month(s) ago) I like it very much. can i get it? Saving..... Post Reply Close Saving..... Edit Comment Close Premium member Presentation Transcript Factors affecting microbial growth : Factors affecting microbial growth Factors affecting microbial growth : Factors affecting microbial growth pH Moisture Nutrient Content Oxygen Light Temperature pH : pH Most spoilage bacteria grow best near neutral pH Pathogenic bacteria even more narrow in tolerance range of near neutral Yeast and moulds have much greater tolerance to acidic (lower) pH pH : pH The optimum pH range is usually quite narrow so that small changes in the pH can have large effects on the growth rate of the organism pH : pH Effects of acids on organisms energy required to maintain cell's internal pH enzyme activity affected proteins, DNA, other molecules denatured longer lag, less rapid growth Moisture : Moisture Microbes must have a supply of of water available Bacteria most restricted, then yeasts, then moulds Organisms tolerant of low water levels: halophilic bacteria osmophilic yeasts xerophilic molds Moisture : Moisture Effects of low water levels longer lag, slower growth impaired transport loss of membrane fluidity Nutrient content : Nutrient content Required by all organisms: water, carbon, nitrogen, minerals Organic growth factors needed to varying degrees: Gram + > Gram - > yeasts > moulds Nutrient content : Nutrient content How easily are energy sources metabolized? sugar > alcohol > amino acids > complex molecules How easily are nitrogen sources metabolized? amino acids > proteins B vitamins required by many bacteria Oxygen : Oxygen Obligate aerobes, e.g. Mycobacterium, will grow only in presence of free oxygen Oxygen : Oxygen Facultative anaerobes, e.g. Saccharomyces (yeast) will grow in the absence of oxygen, but more slowly than if oxygen were present. Oxygen : Oxygen Obligate anaerobes, e.g. Clostridium will grow only in absence of oxygen which is toxic to them Light : Light Essential for photoautotrophs. As well as its intensity its wavelength may be significant. Temperature : Temperature Psychrophiles: Grow at -10 to 20oC (in aquatic and soil environment) Can contaminate and grow in food and dairy products when refrigerated.e.g. Vibrio marinus Mesophiles : Mesophiles Grow at 30-37oC (most human pathogens are mesophiles). e.g. Corynbacterium dephtherius, Nesseria gonorrhoea Thermophiles : Thermophiles Grow at 45 – 70oC (not pathogenic to human). e.g. Thurmus aquaticus. You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.