Factors Affecting Microbial Growth


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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.

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