The Selective Bacteriostatic Action of Gentian Violet

Abstract

It was first shown by Churchman (1912) that gentian violet inhibits the growth of almost all Gram-positive bacteria with the exception of streptococci in a concn. permitting the growth of most Gram-negative spp. Garrod has used for 10 yrs. a medium consisting of 1 in 500,000 gentian violet blood agar and has never seen any Gram-positive organism other than a streptococcus grow on it. Francis (1941) isolated hemo-lytic streptococci from 98 (32.7%) out of 300 specimens of wound pus on gentian violet blood agar, whereas on plain blood agar only 68 (22.7%) were isolated. A table shows the maximum concns. of gentian violet in 5% blood agar permitting growth in 4 spp. of Streptococcus, 2 of Staphylococcus and of 4 other organisms. The chief use of the medium is the isolation of streptococci from skin and wound exudates containing so many staphylococci as to obscure streptococci. The media contains 5% horse blood, ox-heart extract peptone agar of pH 7.4. A wide gap in susceptibility separates all streptococci from all staphylococci, other indifferent Gram-positive cocci, diph-theroids and the aerobic spore-bearing bacilli. Cf. Lancet 1941, 1: 271; 2: 159, Brit. Med. Jour. 1: 953, 1941.