Differential Mechanism of Escherichia coli Inactivation by (+)-Limonene as a Function of Cell Physiological State and Drug's Concentration

Chueca, Beatriz ; Pagan, Rafael (Universidad de Zaragoza) ; Garcia-Gonzalo, Diego

Resumen: (+)-limonene is a lipophilic antimicrobial compound, extracted from citrus fruits' essential oils, that is used as a flavouring agent and organic solvent by the food industry. A recent study has proposed a common and controversial mechanism of cell death for bactericidal antibiotics, in which hydroxyl radicals ultimately inactivated cells. Our objective was to determine whether the mechanism of Escherichia coli MG1655 inactivation by (+)-limonene follows that of bactericidal antibiotics. A treatment with 2,000 µL/L (+)-limonene inactivated 4 log10 cycles of exponentially growing E. coli cells in 3 hours. On one hand, an increase of cell survival in the ¿acnB mutant (deficient in a TCA cycle enzyme), or in the presence of 2,2'-dipyridyl (inhibitor of Fenton reaction by iron chelation), thiourea, or cysteamine (hydroxyl radical scavengers) was observed. Moreover, the ¿recA mutant (deficient in an enzyme involved in SOS response to DNA damage) was more sensitive to (+)-limonene. Thus, this indirect evidence indicates that the mechanism of exponentially growing E. coli cells inactivation by 2,000 µL/L (+)-limonene is due to the TCA cycle and Fenton-mediated hydroxyl radical formation that caused oxidative DNA damage, as observed for bactericidal drugs. However, several differences have been observed between the proposed mechanism for bactericidal drugs and for (+)-limonene. In this regard, our results demonstrated that E. coli inactivation was influenced by its physiological state and the drug's concentration: experiments with stationary-phase cells or 4,000 µL/L (+)-limonene uncovered a different mechanism of cell death, likely unrelated to hydroxyl radicals. Our research has also shown that drug's concentration is an important factor influencing the mechanism of bacterial inactivation by antibiotics, such as kanamycin. These results might help in improving and spreading the use of (+)-limonene as an antimicrobial compound, and in clarifying the controversy about the mechanism of inactivation by bactericidal antibiotics.

Idioma: Inglés

DOI: 10.1371/journal.pone.0094072

Año: 2014

Publicado en: PLoS ONE 9, 4 (2014), e94072 [7 pp]
ISSN: 1932-6203

Factor impacto JCR: 3.234 (2014)

Categ. JCR: MULTIDISCIPLINARY SCIENCES rank: 9 / 57 = 0.158 (2014) - Q1 - T1

Financiación: info:eu-repo/grantAgreement/ES/MINECO/AGL2012-32165

Tipo y forma: Article (Published version)

Área (Departamento): Área Tecnología de Alimentos (Dpto. Produc.Animal Cienc.Ali.)