Persistence of Some Lactic Acid Bacteria As Affected By Polycyclic Aromatic Hydrocarbons

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are aromatic hydrocarbons consisting of two or more fused aromatic benzene rings. They are formed during the incomplete combustion of organic substances. They enter the environment and are released to air, soil, water and foods. Some PAHs have been shown to have toxicological, carcinogenic and mutagenic effects on animals and humans. Persistence of some types of lactic acid bacteria (S. thermophilus, L. bulgaricus and B. bifidium) in the presence of different levels (0.01, 0.10 and 0.20µg/ml MRS medium) of PAHs were studied during the incubation periods for (24, 48, 72, 96 and 120 hr) at 37˚C. The growth rate of the studied strains noticeably affected for presence of PAHs according to bacterial species and the PAHs concentrations. After 24hr of incubation period, the relative reduction of S. thermophilus, L. bulgaricus and B. bifidium growth rate in MRS media broth containing 0.01µg PAHs/ml were ranged between (2.33-9.43%) increased to (11.63-32.08%) with 0.10µg PAHs/ml and to (23.26-38.1%) with 0.20µg PAHs/ml. At the end of the incubation period (120hr), the relative increase of growth rate was observed by S. thermophilus and relative reduction with the other two strains. The data proved that the effect of the lowest concentrations of PAHs on the strains not impressive, but PAHs might have an impact if concentrations are higher.