DYE 3 



135 



The difference between the Gram-positive and the Gram-negative organisms 

 is merely one of degree. There is, moreover, a considerable variation in the sus- 

 ceptibility of different species of Gram-positive bacteria. Garrod (1933a) has 

 shown, for example, that staphylococci are much less resistant to the violet dyes — ■ 

 crystal violet, methyl violet, Hofmann violet, gentian violet. Dahlia — than strepto- 

 cocci. The presence of 1/1,000,000 gentian violet in nutrient broth or in 5 per 

 cent, serum broth is sufficient to inhibit the growth of staphylococci, while strepto- 

 cocci can grow in the presence of 1/250,000, and sometimes even stronger con- 

 centrations of this dye. 



Churchman {1923a) stated that, just as gentian violet had a bacteriostatic 

 effect on most Gram-positive organisms, so acid fuchsin had a similar effect on 

 Gram-negative organisms. Garrod (19336) has recently examined this statement, 

 and concluded that it is untrue. He finds that aniline dyes generally, whether 

 of the basic or acid type, destroy Gram-positive more readily than Gram-negative 

 bacteria. On the other hand, Churchman's results gain some support from the 

 work of Stearn and Stearn (1926, 1928). From a study of the reactions of different 

 bacteria to different stains, these workers conclude that Gram-positive bacteria 

 have a lower isoelectric point than Gram-negative bacteria. Hence Gram-positive 

 bacteria combine more actively with basic, and Gram-negative with acid dyes. 

 The subject clearly needs further investigation. 



The aniline dyes have, on account of their marked germicidal effect on bacteria, 

 been used for the treatment of wounds. Browning and his colleagues (1917) 

 recommended flavine — diamino-methyl-acridinium chloride. Though they found 

 that brilliant green sulphate, malachite green, crystal violet, and flavine strongly 

 inhibited the growth of staphylococci and Bad. coli, flavine was the only one that 

 was more active in the presence of serum (Table 13). Churchman (19236) used 

 a mixture of gentian violet and acriflavine. 



TABLE 13 (modified from Browning et al. 1917). 



Showing Concentrations of Different Substances necessary to inhibit the Growth 

 OF Staphylococcus aureus and Bad. coli. 



Substance. 



Chloramine-T 



CI2 water .... 



Phenol 



HgCl, 



Brilliant green sulphate 

 Malachite green 

 Crystal violet 

 Flavine 



Staph, aureus. 



Cone, in 

 P.W. 



1-2,000 



1-2,500 



1-250 



1-1,000,000 



1-10,000,000 



1-10,000,000 



1-4,000,000 



1-20,000 



Cone, in 

 Serum. 



1-250 

 > 1-1, 000* 

 1-250 

 1-10,000 

 1-30,000 

 1-40,000 

 1-400,000 

 1-200,000 



Bact. coli. 



Cone, in 

 P.W. 



1-2,000 



1-2,500 



1-500 



1-1,000,000 



1-130,000 



1-20,000 



1-8,000 



1-1,300 



Cone, in 

 Serum. 



1-250 

 >1-1,000* 

 1-500 

 1-10,000 

 1-3,500 

 1-1,000 

 1-8,000 

 1-100,000 



* These concentrations were insufficient to prevent growth. 



Table 13 is of interest in showing not only that flavine is much stronger in 

 its inhibiting action in ox serum than in peptone water, but that HgClj and the 

 chlorine group of germicides are markedly diminished in activity in the presence 

 of serum, whereas phenol remains unaffected. This diminution of activity in the 

 presence of organic matter will be referred to later. 



