PATHOGENIC MICROBIOLOGY

Factors Controlling Growth of Microorganisms

1. NUTRIENT AVAILABILITY: the accessibility of a necessary resource, substance or compound providing nourishment to maintain life, i.e. capable of conversion to energy and structural building blocks

Fastidious: having complex nutritional or cultural requirements that make isolation and culture more difficult

MAJOR ESSENTIAL ELEMENTS:

C, O, H, N, S, P, K, Mg, Ca, Fe, Na, Cl

MINOR ESSENTIAL ELEMENTS:

Zn, Mn, Mo, Se, Co, Cu, Ni, W

2. PHYSICO/ENVIRONMENTAL PARAMETERS:

WATER ACTIVITY/OSMOTIC PRESSURE:

Water activity (aw): represents the available water

Osmotic pressure (p): expressed in atmospheres; reflects the concentration of solute in an aqueous solution

OXYGEN: pathogenic microorganisms may have metabolic oxygen requirements that are OBLIGATE or FACULTATIVE, ANAEROBIC or AEROBIC, or somewhere in between, MICROAEROPHILIC

pH: "power of hydrogen"; a measurement of the amount of hydrogen ion in solution; the logarithm of the reciprocal of the hydrogen ion concentration in an aqueous solution used to express its acidity or alkalinity (0-14)

TEMPERATURE:

Psycrophile(psychrophilic): liking cold temperatures; optimal growth at 15^o to 20^oC

Mesophile (mesophilic): liking moderate temperatures; optimal growth at 20^o to 45^oC

Thermophile (thermophilic): liking elevated temperatures; optimal growth at 50^o to 70^oC

3. COMPETITION: the simultaneous demand by two or more organisms or species for a necessary, common resource or physical space that is in limited or potentially limited supply, resulting in a struggle for survival

Niche: the place of an organism within its community or ecosystem

4. HOST IMMUNE SYSTEM: the cells and tissues involved in recognizing and attacking foreign substances in the body

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