Dichloran as an inhibitor of mold spreading in fungal plating media: effects on colony diameter and enumeration.

Problems associated with overgrowth by spreading molds are not addressed by currently recommended fungal enumeration media. Twenty-two fungi, including 12 mold and 3 yeast genera, were evaluated for the effects of dichloran (2,6-dichloro-4-nitroaniline), previously identified as a mold-spreading inhibitor, on colony diameter and enumeration. On malt agar or antibiotic-potato-dextrose agar (APDA), colony diameters were effectively reduced when dichloran was added. Colony diameters decreased as the dichloran concentration increased. Counts obtained with mixed mold spore suspensions were lower on APDA supplemented with 25 mug of dichloran per ml than on APDA and were higher than APDA with the addition of 5 mug of dichloran per ml (APDA-D-5). Overall counts of mixed and individual mold spore and yeast suspensions were higher in APDA-D-5 than in APDA. The additional advantages of APDA-D-5 may be useful in routine enumeration of fungi.

Growth inhibition of Candida albicans by folate pathway inhibitors. Their potential in the selection of auxotrophs.

Growth studies were conducted on C. albicans in a glucose - salts - biotin (GSB) medium in the presence of folate inhibitors. Sulfanilamide inhibited growth which was restored by PABA or tetrahydrofolate (THF). Aminopterin inhibited growth to about the same level as did sulfanilamide, but this inhibition was not reversed with PABA nor THF, singly or in combination. Inhibition by combined sulfanilamide and aminopterin was synergistic, reducing growth by more than 90% for 48 h. The sulfanilamide component of the combined inhibition was reversed by PABA or THF to the level of that of aminopterin alone. Cytochrome synthesis was not affected by the inhibitors, but marked increases occurred in alpha-ketoglutarate, malate, isocitrate, and pyruvate dehydrogenases, especially in the presence of both inhibitors. The pyrimidines in combination with sulfanilamide were as inhibitory as was the combination of aminopterin and sulfanilamide, but they had no effect when added alone or in combination with aminopterin. Unlike the pyrimidines, the purines stimulated about a 50% recovery from inhibition by either of the inhibitors. Growth inhibition by combined sulfanilamide and aminopterin was overcome by about 50% by the addition of the THF-mediated end-produits: deoxythymidylate, adenine, histidine and methionine. The use of GSB medium containing adenine, histidine, methionine and the folate inhibitors but without deoxythymidylate resulted in thymineless death of prototrophic cells providing a method for the selection of auxotrophic mutants.