Oct. 8, 1921 



Microscopic Study of Bacteria in Cheese 



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present in the cheese, as seen by direct examination, are not present 

 in the same proportions on the plates, because those types which grow 

 abundantly in the presence of lactose have outnumbered all groups 

 which do not grow as readily on such media. 



Table I. — Relation between microscopic and plate counts obtained from cheese 



Results of plate counting may also be lower because of insufficient 

 grinding and emulsifying of the cheese sample previous to plating. This 

 appears to be especially significant in cases where investigators grind the 

 sample with sterile quartz or sugar and suspend the ground mass in 

 sterile water in preparation for plating. If the sample is not well ground, 

 small particles of cheese remain in the emulsion, and the individual bacteria 

 are not separated so as to allow them to grow into separate colonies on 

 the artificial medium. Emulsions examined under the microscope often 

 show comparatively large masses of cheese which have not been affected 

 by the grinding process. 



CONCLUSION 



The microscopic examination of cheese embedded and sectioned by 

 the usual histological method is a valuable and satisfactory method for 

 studying the different stages of cheese ripening. Such a direct method 

 of examination may be used to determine the number of organisms 

 present in the sample. It also serves as an index to the types of organisms 

 present and makes possible a study of the organisms as they actually 

 exist in the cheese mass, allowing observations on the groupings and 

 relationships during cheese ripening. 



The cultural methods do not yield as high a count as the microscopic 

 method, due primarily to the selective action of the medium used and the 

 difficulty of liberating the organisms from the cheese mass previous to 

 plating. 



A combination of microscopic and cultural studies yields a far more 

 complete picture of what takes place in cheese ripening than can be 

 obtained by the use of either method alone. 



