DEHYDRATED CULTURE MEDIA 181 



BACTO 



PEPTONE IRON AGAR (B89) 



DEHYDRATED 



Bacto-Peptone 15 g. 



Proteose Peptone, Difco 5 g. 



Ferric Ammonium Citrate 0.5 g. 



Dipotassium Phosphate 1 g. 



Sodium Thiosulfate 0.08 g. 



Bacto-Agar 15 g. 



Bacto-Peptone Iron Agar is a medium designed for use as an indicator of by- 

 drogen sulfide production by microorganisms. 



Levine and co-workers/'^ in their studies on the reactions in the colon group of 

 bacteria, described a medium containing Proteose Peptone, Difco and ferric 

 citrate as being particularly satisfactory for the detection of hydrogen sulfide. 

 They further showed that such a medium served to differentiate the strains which 

 were Voges-Proskauer negative, methyl red positive and citrate positive from 

 other members of the colon-aerogenes group. 



Levine reported that the ferric citrate was a much more sensitive indicator of 

 hydrogen sulfide production than was lead acetate. Their medium gave definite 

 clear-cut reactions within 12 hours. 



Bacto-Peptone Iron Agar is a modification of Levine's original formula, in 

 which Bacto-Peptone has been included with Proteose Peptone and the more 

 soluble ferric ammonium citrate is used in place of ferric citrate. The medium 

 in tubes is inoculated by the stab method. Blackening of the medium indicates 

 the production of hydrogen sulfide. The reaction is intense and takes place quite 

 rapidly. Bacto-Peptone Iron Agar is not toxic and may be used in plates as well 

 as in tubes. Plates are convenient when it is desired to estimate the number of 

 hydrogen sulfide producers. 



Tittsler and Sandholzer^ compared Bacto-Peptone Iron Agar with Lead Ace- 

 tate Agar for the detection of hydrogen sulfide and found that the Bacto-Peptone 

 Iron Agar had the advantage of giving earlier reactions and more clear-cut results. 



Bacto-S I M Medium as discussed on page 173 may be recommended as a 

 more sensitive medium for the detection of hydrogen sulfide. This is a semisolid 

 medium and, in addition to indicating early clear-cut hydrogen sulfide producton, 

 is also recommended for motility determinations and indole production. 



To rehydrate the medium, suspend 36 grams of Bacto-Peptone Iron Agar 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 6.7. 



One pound of Bacto-Peptone Iron Agar will make 12.6 liters of medium. 



^ Proc. Soc. Exp. Biol. Med., 29:1022:1932. 

 2 Am. J. Pub. Health, 24:505:1934. 

 'Am. J. Pub. Health, 27:1240:1937. 



