Effects of ph, chemicals and antibacterial agents on some strains of Yersinia enterocolitica and Yersinia pseudotuberculosis

Abstract

The effect of pH, some chemicals and antibiotics on the growth of three strains each of Yersinia entercocolitica and Yersinia pseudotuberculosis were studied. Y. enterocolitica was found to be more tolerant to the changes of pH and more resistant to the tested chemicals and antibacterial agents than Y. pseudotuberculosis. The concentrations of oxgall, sodium deoxycholate, cobaltous sulfate, glycine and chloramphenicol that are required for inhibition vary significantly between the two species under study. This variation makes these agents good candidates for any formulation of a selective medium for the selection of Y. enterocolitica from a sample which contains the two species. The concentrations of bile salts, novobiocin and methicillin that are required for inhibition were observed to be very similar for the differ-ent Yersinia strains. However, the concentrations required for inhibition are higher than the concentrations required for the inhibition of most of the Gram-negative bacteria and this may be useful in any formulation of a selective medium for the selection of the two Yersinia species from a sample with a mixed bacterial population.