The effect of pH on bacterial growth and histamine formation by Klebsiella pneumoniae CK02 and Raoultella ornithinolytica TN01

Abstract

Abstract The present work describes the effect of pH on the growth rate and histamine formation by Klebsiella pneumoniae CK02 and Raoultella ornithinolytica TN01. Bacteria were inoculated on Tuna Fish Infusion Broth media with pH 5, 6, 7, 8 at 30°C for 6 hours. Sampling was conducted at 0, 3, and 6 hours to observe the bacteria number and calculate the histamine content formed in the medium. The number of bacteria was calculated using the Total Plate Count method, and the histamine content was analyzed using Thin Layer Chromatography with a combination of ImageJ software. Growth data and incubation time were plotted in the DMFit program to obtain growth rates. The effect of pH on growth rate and histamine formation was analyzed by ANOVA test and Duncan Multiple Range Test. The results revealed that pH affects the growth rate and histamine formation of K. pneumoniae CK02 and R. ornithinolytica TN01. The optimal growth rate of K. pneumoniae CK02 was in the range of 6-8 (0.304-0.380 log CFU/h), with the highest histamine formation ability at pH 7 (824 ppm). R. ornithinolytica TN01 had an optimal growth rate at pH 6-7 (0.480-0.508 log CFU/ml), with optimal ability to produce histamine at pH 6-8 (620-1,077.5 ppm). At pH 5, the growth rate and the ability of histamine formation by K. pneumoniae CK02 and R. ornithinolytica TN01 were inhibited.