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Applied and Environmental Microbiology, November 2009, p. 6973-6980, Vol. 75, No. 22
0099-2240/09/$08.00+0     doi:10.1128/AEM.00608-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Complex Phenotypic and Genotypic Responses of Listeria monocytogenes Strains Exposed to the Class IIa Bacteriocin Sakacin P{triangledown} ,{dagger}

Girum Tadesse Tessema,1,2 Trond Møretrø,1 Achim Kohler,1,3 Lars Axelsson,1 and Kristine Naterstad1*

Nofima Mat AS, Osloveien 1, N-1430 Aas, Norway,1 Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, P.O. Box 5003, N-1432 Aas, Norway,2 CIGENE, Institute of Mathematical Science and Technology, Norwegian University of Life Sciences, P.O. Box 5003, N-1432 Aas, Norway3

Received 13 March 2009/ Accepted 9 September 2009

Sakacin P is a class IIa bacteriocin that is active against the food-borne pathogen Listeria monocytogenes, and use of this compound as a biopreservative in foods has been suggested. In the present study, we characterized 30 spontaneous sakacin P-resistant mutants of L. monocytogenes obtained after single exposure to sakacin P. The frequency of development of sakacin P resistance for all strains was in the range from 10–8 to 10–9. Using the 50% inhibitory concentration (IC50) of sakacin P, the strains could be grouped into strains with high levels of resistance (IC50, ≥104 ng ml–1) and strains with low levels of resistance (IC50, <104 ng ml–1). Resistant strains belonging to the same IC50 group also had similar physiological and genetic characteristics. Generally, the resistant strains showed substantial variations in many parameters, such as differences in the stability of the acquired resistance to sakacin P, growth fitness, food-related stress tolerance, and biofilm-forming ability. Fourier transform infrared spectroscopy revealed differences between wild-type and resistant strains in polysaccharide, fatty acid, and, protein regions. A mannose-specific phosphotransferase (PTS) operon has been described for class IIa bacteriocin resistance, and the sakacin P-resistant strains displayed both up- and downregulation of the expression of the mptA gene encoding the PTS system. This is the first comprehensive study of the diversity of a large number of spontaneous resistant mutants obtained after one exposure to a class IIa bacteriocin, particularly to sakacin P. The great diversity among the resistant strains exposed to the same stress conditions suggests that there are different resistance mechanisms.

* Corresponding author. Mailing address: Osloveien 1, 1430 Ås, Norway. Phone: 4764970214. Fax: 4764970333. E-mail: Kristine.naterstad{at}nofima.no

{triangledown} Published ahead of print on 18 September 2009.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

Applied and Environmental Microbiology, November 2009, p. 6973-6980, Vol. 75, No. 22
0099-2240/09/$08.00+0     doi:10.1128/AEM.00608-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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