Inhibition of Bacterial Growth by β-Chloro-D-Alanine

The D- and L-isomers of β-chloroalanine inhibit the growth ofDiplococcus pneumoniae, Streptococcus pyogenes, Bacillus subtilis , andEscherichia coli . With pneumococcus the inhibition by β-chloro-D-alanine is completely prevented by either D-alanine or D-alanyl-D-alanine, while L-alanine is not effective in preventing the inhibition. The inhibition of growth by β-chloro-L-alanine is not affected by D-alanine and is only partially prevented by high concentrations of L-alanine. The intracellular free alanine in untreatedE. coli andB. subtilis is about 95% in the D-configuration while the free intracellular alanine in both organisms after treatment with β-chloro-D-alanine is predominantly the L-isomer. These results suggested that the β-chloroamino acid inactivates alanine racemase (EC 5.1.1.1). Indeed, when extracts ofE. coli orB. subtilis were treated with β-chloro-D-alanine, the activities of alanine racemase and of D-glutamate-D-alanine transaminase were found to be 90-95% inhibited. Studies with mice have shown that β-chloro-D-alanine is an effective antibacterial agentin vivo againtD. pneumoniae, S. pyogenes , andE. coli .