DEHYDRATED CULTURE MEDIA 241 



Bacto-Littman Oxgall Agar with the addition of streptomycin is a selective 

 medium for the primary isolation of fungi. It is also of especial value for the 

 cultivation of the dermatophytes. 



Littman^ described a selective medium for the primary isolation of fungi. 

 Crystal violet and streptomycin are used as selective bacteriostatic agents, while 

 Bacto-Oxgall is used to restrict the spreading of fungus colonies. The medium is 

 neutral in reaction, which favors the growth of many pathogenic fungi. The 

 studies of Littman have indicated that this medium offers considerable promise as 

 a diagnostic tool for the primary isolation of fungi from specimens possessing 

 a mixed bacterial and fungal flora. 



Littman has shown that his medium is especially valuable for culturing the 

 dermatophytes. Molds and yeasts form non-spreading discrete colonies, easy to 

 isolate in pure culture. He also suggests that the medium may be used for the 

 following purposes: estimation of the normal fungal flora of feces, sputum and 

 other human discharges; evaluation of human disorders of the upper and lower 

 respiratory and gastrointestinal tract caused by fungi; single cell isolation of 

 fungi; plate count of viable saprophytic fungi in foodstuffs and air. In a com- 

 parative study Littman^ compared this medium with Sabouraud Dextrose Agar 

 using a large variety of pathogenic and saprophytic fungi. On the Littman Oxgall 

 Agar the majority of fungi tested produced colonies at the end of the first month 

 of incubation about half the size of the colonies on Sabouraud Dextrose Agar, but 

 equal in size after 56 days of incubation. He reported the isolation of three times 

 as many fungi from feces, sputum, skin scrapings and hair on his medium as 

 were isolated on Sabouraud Dextrose Agar, and four times as many pathogenic 

 dermatophytes on the selective medium as on the Sabouraud medium. The 

 selective oxgall agar of Littman is specified in "Diagnostic Procedures and 

 Reagents"^ of the American Public Health Association for the isolation of 

 pathogenic fungi. 



For inoculation, skin and nail scrapings or infected hairs are placed directly 

 on the surface of the medium. Exudates, sputa, or fecal suspensions are spread 

 over the surface with a sterile swab. The selectivity of the medium permits the 

 use of a heavy inoculum without the danger of overgrowth by bacteria or sapro- 

 phytic fungi. Plates are incubated at room temperature or preferably at 30 °C. 

 for four to eight days. Do not incubate at 37°C. 



To rehydrate the medium, suspend 55 grams of Bacto-Littman Oxgall Agar in 

 1000 ml. of cold distilled water and heat to boiling to dissolve the medium com- 

 pletely. Distribute in flasks and sterilize in the autoclave for 15 minutes at 15 

 pounds pressure (121°C.). Cool to 45-50°C. and add 30 micrograms of strepto- 

 mycin per ml. of medium. Dispense in 27-30 ml. amounts in sterile petri dishes 

 100 mm. in diameter or distribute in sterile tubes. Let stand at room temperature 

 for 6-8 hours before inoculation. Plates or tubes of media may be kept in the 

 refrigerator for 2-3 weeks without deterioration if placed in sealed containers 

 to prevent evaporation. A concentration of 30 micrograms per ml. of medium 

 may be obtained by adding 10 ml. sterile distilled water to a 1 gram (one 

 million micrograms) bottle of streptomycin or dihydrostreptomycin. One (1) 

 ml. of this solution is added to 9 ml. sterile distilled water to give a solution con- 

 taining 10,000 micrograms streptomycin per ml. To each liter of sterile melted 

 medium at 45-50° C. are added 3 ml. of this solution to obtain 30 micrograms 

 per ml. (0.3 ml. for 100 ml. medium). Final reaction of the sterile medium will 

 be pH 7.0. 



One pound of Bacto-Littman Oxgall Agar will make 8.2 liters of medium. 



1 Science, 106:109:1947. ^ pjagnostlc Procedures and Reagents, 3rd Edi- 



2 Tech. Bull., Reg. Med. Tech., 18:409:1948. 1100:452:1950 



