The inhibitory activity of some sulfur-containing pyridine derivatives on the growth in vitro of several bacterial species has been recorded during the course of a current investigation concerned with the biological properties of these and related compounds.
The substances reported in this note include S-nitro-2-pyridinethiol and 6-mercaptonicotinonitrile as well as the corresponding disulfides and S-thiuronium chlorides. In addition, observations have been made on .5-imino-1,2,4_dithiazolidin-3-thione and several related compounds.
Each of these compounds had been prepared in this Laboratory in connection with previous studies.
Each compound has been tested on E. coli and A. aerogenes as representative of the Gram negative rod type, and M. pyogenes var. aureus (ATCC No. 10617) and M. pyogenes var. albus (ATCC No. 9491) as representative of the Gram positive coccus type. Various concentrations of each compound were obtained by addition of 0.1 ml. of a 95 per cent ethanol solution of appropriate concentration to 10 ml. of sterile nutrient broth ; the corresponding ethanol controls were included. The highest concentration tested was 50 pg per ml. Inoculations were made with a standard loopful of a 24-hour nutrient broth culture of the respective organism. The minimal concentration of the compound required to cause complete suppression of bacterial growth after 72-hr. incubation at 37" C. served as the arbitrary standard of biological activity.
The results reported are based on duplicate assay. None of the compounds which have been tested effected complete inhibition of growth of E. co,% or A. aerogenes when used at the maximum concentration of 50 j.kg per ml. Some of the compounds, however, manifested activity toward the two variants of M. pyogenes, as shown in Table I. With the exception of compound (VIII), somewhat greater sensitivity is seen to be exhibited by M. pyogenes var. albus as compared to that shown by M. pyogenes var. aureus.
Activity of each of the nitro derivatives (I, II, III) toward both bacterial variants is seen to be, with one exception, slightly greater than that of its corresponding cyano compound (IV, V, VI).
It is evident also that conversion of kitro-2-pyridinethiol (II) or of 6-mercaptonicotinonitrile (V) to its disulfide (I or IV) results in no loss of inhibitory activity.
Inhibitory activity of .5-nitro-2-pyridinethiol (II) toward the growth 5.57