104 DIFGO MANUAL 



BACTO 



PEPTONE COLLOID MEDIUM (B61) 



DEHYDRATED 



Bacto-Tryptose 20 g. 



Sodium Chloride 5 g. 



Bacto-Agar 1 g. 



Bacto-Peptone Colloid Medium, containing 0.1 per cent agar, is a liquid 

 medium recommended for the cultivation of anaerobes, and also for many 

 aerobes generally considered difficult to cultivate. This medium was developed 

 as a basal medium to which carbohydrate and other test materials could be 

 added for studying the physiological properties of anaerobes and other micro- 

 organisms. 



The preparation of the usual peptone-infusion medium employed for patho- 

 genic bacteria, is a costly, laborious, time-consuming task, resulting in media 

 that vary from time to time depending on the age of the meat, condition of 

 infusion and a number of other factors. In Bacto-Peptone Colloid Medium, a 2 

 per cent concentration of Bacto-Tryptose satisfactorily replaces the peptone- 

 infusion portion of infusion media. This medium will support excellent growth 

 of the anaerobes and is also equally well suited for the propagation of men- 

 ingococci, streptococci, pneumococci and other microorganisms that are gener- 

 ally considered difficult to cultivate. For many organisms, especially the an- 

 aerobes, Bacto-Peptone Colloid Medium will be improved by the addition of a 

 small quantity of dextrose as a source of readily available energy. An added 

 0.025 to 0.05 per cent dextrose is sufficient to initiate growth and still not enough 

 to produce gas or to give rise to appreciable acid production. The above men- 

 tioned quantities of dextrose are well within the limits of muscle sugar normally 

 obtained in infusion media. It is not practical to include the indicator in the 

 medium for fermentation studies with anaerobes, since these organisms reduce 

 the indicators to their leuco bases. Solutions of indicator should be added to the 

 culture after incubation to detect changes in hydrogen ion concentration. 



The advantages of a medium with a low agar concentration and its influence 

 on the development of bacteria, particularly the anaerobes, has been described 

 by Kitchens.^ In a broth, to which 0.1 per cent agar has been added, there is a 

 clear upper zone well suited for aerobic growth; below this the flocculent agar 

 develops all degrees of anaerobiosis. This condition makes the medium suitable 

 for the growth of either aerobic or anaerobic bacteria. Falk, Bucca, and Sim- 

 mons^ point out the advantages of the use of small quantities of agar (0.06 to 

 0.25 per cent) in the detection of contaminants in testing the sterility of biologi- 

 cals. They show that the growth of even common forms, such as the hay bacillus 

 and staphylococci, ordinarily considered easy to cultivate, were aided by the 

 addition of a small quantity of agar. They also showed that growth is initiated 

 in a much shorter incubation period in such media. In their routine tests they 

 used 0.1 per cent agar which is the amount present in Bacto-Peptone Colloid 

 Medium. 



To rehydrate the medium, suspend 26 grams of Bacto-Peptone Colloid 

 Medium in 1000 ml. of cold distilled water and heat to boiling to dissolve the 

 medium completely. Distribute in tubes and sterilize in the autoclave for 15 

 minutes at 15 pounds pressure (121°C.). The final reaction of the medium will 

 be pH 7.3. 



For best results Bacto-Peptone Colloid Medium should be freshly prepared. 

 If the medium is not used the same day as sterilized, heat in boiling water or 

 flowing steam for a few minutes to remove absorbed oxygen, cool quickly with- 

 out agitation, just prior to inoculation. 



