CHAPTER 4 



Microbes Must Eat 



PREREQUISITES FOR A GOOD MICROBIOLOGICAL MEDIUM 



Proper moisture content 



Readily available food materials 



Correct pH 



Sterility 



Desired physical properties 



GELATIN VS. AGAR 



CLASSIFICATION OF MEDIA 



PREPARATION OF STANDARD NUTRIENT AGAR 



It may be difBciilt for you to visualize a living entity the size of a 

 microbe sitting down to an abundant repast, but like every other 

 living thing the microscopic organism must ingest food to provide 

 energy and to allow metabolic processes to take place. Being 

 single cells, bacteria have not been endowed with specialized 

 organs, such as a mouth, a stomach, or intestines. But an in- 

 genious process has been evolved whereby a single-celled organism, 

 whether it be a plant or an animal, can absorb dissolved nutrients 

 directly through the cell wall membrane— holophytic feeding. 

 The outer shell is fastidious in that it selects what shall go into 

 the cell and what shall be secreted or excreted. Such food intake 

 Js called diffusion and the exacting nature of the cell wall depends 



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