114 DIFGO MANUAL 



289) will yield a somewhat heavier growth on prolonged incubation than will 

 a medium prepared with distilled water. 



Schubert^^ reported that the rapidity and amount of growth of some recently 

 isolated fastidious strains of B. abortus was markedly improved on Bacto- 

 Tryptose Agar in the presence of a specially prepared liver extract demonstrat- 

 ing strong catalase activity. 



Bacto-Tryptose Agar is also recommended as a general solid medium for the 

 cultivation of pathogenic organisms, being an excellent medium, without enrich- 

 ment, for streptococci, pneumococci, meningococci and others. Blood Agar may 

 be prepared by adding 5 per cent sterile defibrinated blood to melted sterile 

 Tryptose Agar at 50° C. Bacto-Tryptose Agar contains 0.1 per cent dextrose, 

 probably slightly more than is present in the average meat infusion medium in 

 the form of muscle sugar. Ruediger,^* Brown^^ and Fuller and Maxted^^ have 

 all demonstrated that the presence of dextrose, or a reducing sugar, inhibits 

 hemolysin production by streptococci, giving rise to false reactions. For that 

 reason hemolytic reactions may be atypical on Bacto-Tryptose Agar and should 

 be confirmed on Blood Agar prepared from Bacto-Tryptose Blood Agar Base, 

 Bacto-Blood Agar Base, Bacto-Heart Infusion Agar or on a medium prepared 

 with 2.0 per cent Bacto-Tryptose, 0.5 per cent sodium chloride and 1.5 per cent 

 Bacto-Agar (Tryptose Agar without dextrose). 



Chapman, Stiles, and Berens^^ in their study of the isolation and "in vitro" 

 testing of pathogenic types of non-exotoxic streptococci, used Bacto-Tryptose 

 Agar as a base for Blood Agar because it gave more luxuriant growth of strep- 

 tococci than other base media. Cultures of Pasteurella multocida were cultivated 

 on Tryptose Agar by Carter.^^ He reported that it was not necessary to freeze 

 dry cultures for storage when grown on Tryptose Agar. By adding 5 per cent 

 saccharose to the medium he was able to identify readily blue, intermediate and 

 fluorescent colonies of the organism. Silverman and Elberg^^ in their study of 

 Brucella antigens used Tryptose Agar for the cultivation of their strains of 

 B. abortus, B. suis and B. melitensis. Boyd and Casman^o reported that Tryptose 

 Agar filtered through absorbent cotton became toxic for a fastidious strain of 

 B. abortus. The toxic factors extracted from the cotton were characterized as 

 fatty acids. This toxicity could be nullified by the simple addition of 0.03-0.1 

 per cent corn starch to the medium, bearing a similarity to the report of Ley 

 and Mueller^i demonstrating the ability of starch to neutralize toxic factors 

 found in samples of some agar using the gonococcus as a test organism. 



Gray, Stafseth, Thorp, Sholl and Riley ^^ described a new technique for the 

 isolation of Listeria monocytogenes from infected brain by grinding the medulla 

 in a mortar with about 10 ml. of Tryptose Broth and then emulsifying with 

 glass beads in a shaking machine for about 20 minutes. About 0.3 ml. of the 

 suspension is then plated on Bacto-Tryptose Agar and incubated at 37 °G. for 

 24 hours. The colonies of Listeria are light green with a finely textured surface 

 when viewed with a dissecting microscope and sufficiently characteristic that 

 they can be identified even in cases of extreme contamination. Storage of the 

 brain suspension in the refrigerator for 24 hours seemed to increase the number 

 of Listeria developing on the medium. Gray, Stafseth and Thorp-^ added po- 

 tassium tellurite in 0.1 to 0.05 per cent concentration to Bacto-Tryptose Agar 

 as a selective medium for the isolation of Listeria. The Listeria colonies were 

 black, as are other organisms developing on the medium but showed the char- 

 acteristic green color at the periphery of the colony when viewed by reflected 

 light with a dissecting microscope. Gray, Stafseth and Thorp^* showed the value 

 of this method for isolation of L. monocytogenes from 36 sheep and 31 cattle 

 over a four year period. 



Schuhardt, Rode, Foster and Oglesby,-^ by special techniques, demonstrated 



