74 A MANUAL OF THE PENICILLIA 



lected spore is removed under the low power binocular and transferred to a 

 fresh agar plate. The small agar block is then re-examined with the 8 

 mm. objective to insure that the selected spore has been transplanted. 



Spectrum Test Plates: The following procedure has been successfully 

 used to demonstrate the production of antibiotics by species of Penicillium 

 and other molds. Petri dishes are poured with 20 ml. of Wickerham's 

 antibiotics test medium (see p. 69) and the surface of the agar plates al- 

 lowed to dry for one or two days at room temperature. At the end of this 

 period a loopful of a suspension of mold spores or mycelium is streaked 

 across one side of the plate surface, and the culture incubated for four days 

 at 24°C. Following such incubation, suspensions of selected test organ- 

 isms are streaked across the agar at right angles to the mold growth. 

 The reinoculated plates are then incubated at 30°C. for 24 hours, after 

 which the zones of inhibition are read by placing the plate over a millimeter 

 scale. The test organisms, which grow rapidly at 30°C., are used because 

 of their varied physiological characteristics. They include: Bacillus 

 cereus NRRL B-569, Candida albicaus NRRL Y-477, Bacillus subtilis, 

 smooth-form, NRRL B-558, Staphylococcus aureus XRRL B-313, Sal- 

 monella schottmuelleri NRRL B-119, and Proteus mirabilis NRRL B-400. 

 The Salmonella and Proteus strains represent Gram-negative forms, hence 

 are insensitive, or only slightly sensitive, to penicillin. Candida albicans 

 represents a yeast-like form, hence could be expected to differ from the 

 other test species used. The strains of Bacillus subtilis and Staphylococcus 

 aureus are very sensitive to penicillin and in fact represent organisms com- 

 monly used for the assay of this antibiotic. The strain of Bacillus cereus 

 while representing a Gram-positive form, produces a powerful penicillin- 

 ase, hence is generally not inhibited by penicillin. The differential re- 

 sponse of the test organisms to penicillin, citrinin, and claviformin makes 

 possible the identification of these antibiotics. 



When penicillin is produced, the growth of Bacillus subtilis and Staph- 

 ylococcus aureus is markedly inhibited, but that of Bacillus cereus shows 

 little or no inhibition due to the destruction of penicillin by the peni- 

 cillinase (fig. ISO). 



When citrinin is produced, Staphylococcus aureus, Bacillus subtilis, and 

 Bacillus cereus are all markedly inhibited, since the production of peni- 

 cillinase by the latter species does not effect the power of citrinin to in- 

 hibit this Gram -positive strain (fig. 18B). 



When claviformin is produced, growth of all the bacterial species is 

 markedly inhibited since this antibiotic is effective against Gram-negative 

 as well as Gram-positive forms, and the yeast, Candida albicans, is in- 

 hibited to a limited degree also (fig. 18D). 



Since the production and characterization of penicillin, citrinin, and 



