بررسي اثر PH و غلظت نمك به صورت منفرد و توام به رشد گونه هاي بروسلا با استفاده از روش پليت گراديان

An Investigation on the Effect of pH and NaCl Concentration, Individually and in Combination, on the Growth of Bruce/la spp Using Gradient Plate Technique

Background and Objectives: Brucliae are among the most important pathogenic bacteria for both humans and animals. They often enter the human body through contaminated dairy products. Therefore, the hygiene of such food stuff is of prime importance in controlling human brucellosis. In most parts of Iran a high proportion of cheese production is still based on the traditional methods, in which the raw milk is used, and this could be considered as a major source of contamination. Application of salt (brine) and acid or alkali for preservation of foods including cheese has long been exercised, though, the rate of their effects particularly in combinations on the Brucella has not been studied so far. However, such studies have been carried out on the other bacteria by gradient plate technique which have led to some interesting results. Materials and Methods: The present study was designed to investigate the effect of pH and NaCl concentration, individually and in combination, on the growth of Brocella abortus (544,5.19) mellitensis (16M,Revl) and suis( 1330) (obtained from Razi Institute), using one and two dimensional gradient plates. The bacterial growth rates at any part of the gradient plates were measured by taking cores of samples with a cork borer and measuring their optical density at 550 nm. These data with regard to pH and Nacl variants which were determined by relevant techniques, were analysed by the Core! Chart computer programme in forms of three dimensional graphs. Results: The amount of growth for each strain at any given pH or NaCl concentration was some what different from other strains. The domain and the amount of growth for all tested strains at any given point of the two dimensional pH NaCl gradient plates clearly showed that these factors were suppressing growth in a synergestic manner . The range of decrease in growth was varied from 63% to 95% for B. suis and B. mellitensis respectively. Conclusion: when the two factors ( pH and NaCl) were acting together, their growth suppression effect could be up to twenty times higher than that of any factor alone . Among the tested strains, B. mellitensis (Rev]) and B. suis (1330) were the most and the least affected by the above-mentioned factors respectively.