10 An Introduction to Medical Mycology 



transform a single amino acid, such as asparagine, into other amino acids 

 as necessary to synthesize its proteins. Growth is faster when a mixture 

 of amino acids is available. According to Nickerson and Williams, an oxi- 

 dative deamination process results in the production of ammonia from 

 amino acids; this explains the increasing alkalinity of cultures of der- 

 matophytes. 



It is of interest that a highly virulent species of fungus, such as C. 

 immitis, is no more exacting in its nutritional demands than ordinary con- 

 taminants such as species of Aspergillus or Penicillium. As a matter of 

 fact, the growth factor requirements of all types of micro-organisms are 

 very similar. 



6. CARBON REQUIREMENTS 



Goddard added various sugars to a 1 per cent aqueous solution of 

 peptone and later measured the increase in dry weight of the inoculated 

 fungus growth. He found that T. gypseum utilized dextrose, fructose, 

 maltose, mannose and galactose but not lactose, whereas M. lanosum 

 could not assimilate lactose or galactose. 



7. OTHER NUTRITIVE NEEDS 



Requisite for growth or reproduction are traces of many of the minerals, 

 such as ammonium, potassium, calcium, magnesium, zinc, iron, copper, 

 manganese, phosphorus and sulfur. For some fungi, thiamine is a require- 

 ment for growth; biotin occasionally stimulates growth. As shown by 

 Benham, oleic acid is a necessary ingredient of the culture medium when 

 Pityrosporum ovale is cultivated. The hydrogen ion concentration may 

 range between 5 and 7. In our standard dextrose agar, the pH is usually 

 in the region of 5.6. 



8. PIGMENT FORMATION 



In our study on the production of pigment by certain fungi, such as 

 Trichophyton purpureum and Microsporum lanosum, it was concluded 

 that the pigment is a metabolic product. These fungi were found to syn- 

 thesize pigment in the presence of certain monosaccharides with closely 

 related structural formulas, such as dextrose, levulose and mannose. One 

 disaccharide, mannitol, was useful. Pigment was not produced when the 

 only sugars in the culture medium were galactose (a monosaccharide) and 

 other disaccharides, trisaccharides and polysaccharides. According to Fos- 

 ter, the formation of pigment may depend to some degree on the amount 



