Lactoferrin Inhibits the Acquisition of Dry-Resistance of <i>Salmonella</i> spp.

Abstract

An assay method was established for estimation of dry-resistance of Salmonella. Environmental isolates of Salmonella enterica spp., including S. Enteritidis were grown to the logarithmic phase, washed and re-suspended in saline or Luria-Bertani (LB) medium, followed by drying overnight in an automatic dry-keeper at room temperature. The dried bacteria were recovered by mixing with ice-cold PBS, suspended, and examined for viability by colony-forming activity. A pathogenic clone of S. Enteritidis, SECI#15-1, was not viable in saline alone but maintained its viability in LB medium, suggesting it requires nutrients for the acquisition of dry-resistance. Addition of lactoferrin or apolactoferrin to the bacterial suspension in 20% LB medium prior to the dry-protocol decreased the viability of SECI#15-1 in a dose-dependent manner. However, lactoferrin showed no effect on the growth of SECI#15-1 in liquid culture with LB or M9 medium, suggesting that it exerts bactericidal effects under dry but not under wet conditions. Besides, Salmonella spp. other than S. Emteritidis, such as S. Typhimurium, S. Oranienburg, S. Weltevreden, S. Johannesburg, and S. lnfantis, also showed dry-resistance, which was significantly inhibited by lactoferrin and almost entirely by apolactoferrin. These results suggest that lactoferrin inhibits the acquisition of dry-resistance by Salmonella spp., suggesting that there is a possible use for lactoferrin in the control of Salmonella food-poisoning as an additive in dry food.