DEHYDRATED CULTURE MEDIA 169 



BACTO 



LEAD ACETATE AGAR (B88) 



DEHYDRATED 



Bacto-Peptone 15 g. 



Proteose Peptone, Difco 5 g. 



Bacto-Dextrose 1 g. 



Lead Acetate 0.2 g. 



Sodium Thiosulfate 0.08 g. 



Bacto-Agar 15 g. 



Bacto-Lead Acetate Agar, like Russell's medium, is used primarily as a tube 

 medium for the differentiation of the various Gram-negative intestinal bacteria. 



Certain bacteria possess the ability of liberating hydrogen sulfide from pro- 

 teins or their split products. This property has been widely used in culture media 

 for differentiating and identifying members of the Gram-negative intestinal 

 group of bacteria, as well as for the identification of other microorganisms. 

 Orlowski^ noted that Salmonella typhosa could be distinguished from the coli- 

 form organisms by culturing them in a medium containing lead acetate, an indi- 

 cator of hydrogen sulfide production. Jordan and Victorson^ showed further that 

 tS". paratyphi (paratyphoid A) and S. schottmuelleri (paratyphoid B) could be 

 distinguished on the basis of hydrogen sulfide production by growing them in a 

 lead acetate medium. S. paratyphi produced no browning, whereas S, schott- 

 muelleri gave a definite browning of the medium within 1 8-24 hours after inocu- 

 lation. 



Bacto-Lead Acetate Agar was developed after a careful study of the literature 

 on the subject, and after considerable research to obtain a medium which would 

 give an accurate differentiation. The modification finally developed was suggested 

 by R. S. Spray. Unlike many other formulae, this medium shows no inhibition 

 due to the toxicity of lead. The non-toxicity of Bacto-Lead Acetate Agar for cer- 

 tain bacteria is confirmed in "Pure Culture Study of Bacteria."^ See the table 

 on page 161 showing reactions of some of the intestinal bacteria on this and other 

 differential media. 



Bacto-Lead Acetate Agar is sensitive in its cultural reactions, and can be used 

 for plating when it is desired to demonstrate the relative number of strong hydro- 

 gen sulfide producing colonies. Its usual method of use is in tubes. Pure cultures 

 of Gram-negative microorganisms isolated from MacConkey Agar, Bismuth Sul- 

 fite Agar, Eosin Methylene Blue Agar or other plating media should be streaked 

 upon the surface of the slant and stabbed into the butt of the Lead Acetate Agar. 

 With this procedure, surface browning can be observed, as well as browning along 

 the line of puncture. Since the medium contains dextrose it will also indicate gas 

 production from this carbohydrate by the presence of bubbles in the butt of the 

 tube. For the determination of hydrogen sulfide production in a medium free 

 from dextrose, see Bacto-Peptone Iron Agar, as discussed on page 181. 



Morrison and Tanner* used Bacto-Lead Acetate Agar in their study of hydro- 

 gen sulfide production by the thermophilic bacteria from water. They found the 

 medium well adapted to the determination of this characteristic. Spray^ em- 

 ployed it with success in his studies on semisolid media for the cultivation and 

 identification of the sporulating anaerobes. 



To rehydrate the medium, suspend 36 grams of Bacto-Lead Acetate Agar in 

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

 pletely. The solution is dispensed into tubes and sterilized in the autoclave for 

 15 minutes at 15 pounds pressure (121°C.). The tubes are slanted to allow for a 

 generous butt. The final reaction of the medium will be pH 6.6. 



