Assessment of lactic acid bacteria sensitivity to terpenoids with the Biolog methodology

Terpenoids are plant metabolites which can be found in traces in the milk of animals fed with fresh forages. To these compounds, many biological properties, including antimicrobial activity, have been recognized. However, no information about the sensitivity of lactic acid bacteria (naturally occurring in milk and dairy products) to terpenoids are currently available. The Biolog methodology, which is traditionally used for the metabolic characterization of microorganisms, has also been found suitable for the evaluation of the activity exerted by plant components against bacterial consortia, allowing to establish the duration of antimicrobial activity (if present) and its resulting effect on microorganisms viability. In the present work, this approach was employed to study the effect of six oxygenated terpenoids (geraniol, linalool, alpha-terpineol, terpinen-4-ol, carvone, and menthone), which can be found in dairy products, towards 27 lactic acid bacterial strains (thermophilic or mesophilic, homo- or hetero-fermenting cocci), previously isolated from raw goat milk. Results showed that microorganisms were variously affected by the selected molecules. In some cases, terpenoids seemed to have a stimulating action; while in others, a transient antimicrobial activity was highlighted, without evident relationship with the metabolic/physiologic groups to which the tested bacterial strains belonged.