The effectiveness of commercial antimicrobial compounds against saccharolytic microorganisms isolated from a beet sugar production line

The antimicrobial activities of five commercial disinfectants containing quaternary ammonium compound-isopropanol (D1), sodium methyl dithiocarbamate (D2), sodium thiocarbamate (D3), sodium dimethyl dithiocarbamate (D4) and formaldehyde (D5) were studied against three main saccharolytic indigenous isolates ( Bacillus cereus, Lactobacillus plantarum and Leuconostoc mesenteroides ) from a beet sugar extraction line. Preliminary studies suggested that although all the disinfectants were effective against those isolates, the high economic cost in combination with large amounts of the disinfectants D2, D3 and D4 weaken their possibility for industrial use. Therefore, the minimum inhibitory concentration (MIC) of the other two examined disinfectants D1 and D5 was determined and survivor curves were obtained, for a period of 7 days. Bacterial counts against time (h) suggested that D1 was more effective than D5 against the microbial population. In particular, D1 was bacteriolytic above 7 mg/l for B. cereus and bactericidal above 80 mg/l for Lc. mesenteroides and above 100 mg/l for L. plantarum . The disinfectant D5 was bacteriolytic above 25 mg/l for B. cereus and bactericidal above 500 mg/l for Lc. mesenteroides and L. plantarum . Taking into consideration both features, i.e. high concentration and very low cost, the use of D5 (formaldehyde) appeared more suitable to the concerned beet sugar processor.