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Applied and Environmental Microbiology, September 2009, p. 5846-5852, Vol. 75, No. 18
0099-2240/09/$08.00+0     doi:10.1128/AEM.00816-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Competition of Listeria monocytogenes Serotype 1/2a and 4b Strains in Mixed-Culture Biofilms{triangledown} ,{dagger}

Youwen Pan,1 Frederick Breidt Jr.,2,3* and Sophia Kathariou3

Department of Microbiology, North Carolina State University, Raleigh, North Carolina 27695-7615; USDA Agricultural Research Service,1 Department of Food, Bioprocessing, and Nutrition Sciences, North Carolina State University, Raleigh, North Carolina 27695-7624,2 Department of Food, Bioprocessing, and Nutrition Sciences, North Carolina State University, Raleigh, North Carolina 27695-76243

Received 9 April 2009/ Accepted 22 July 2009

The majority of Listeria monocytogenes isolates recovered from foods and the environment are strains of serogroup 1/2, especially serotypes 1/2a and 1/2b. However, serotype 4b strains cause the majority of human listeriosis outbreaks. Our investigation of L. monocytogenes biofilms used a simulated food-processing system that consisted of repeated cycles of growth, sanitation treatment, and starvation to determine the competitive fitness of strains of serotypes 1/2a and 4b in pure and mixed-culture biofilms. Selective enumeration of strains of a certain serotype in mixed-culture biofilms on stainless steel coupons was accomplished by using serotype-specific quantitative PCR and propidium monoazide treatment to prevent amplification of extracellular DNA or DNA from dead cells. The results showed that the serotype 1/2a strains tested were generally more efficient at forming biofilms and predominated in the mixed-culture biofilms. The growth and survival of strains of one serotype were not inhibited by strains of the other serotype in mixed-culture biofilms. However, we found that a cocktail of serotype 4b strains survived and grew significantly better in mixed-culture biofilms containing a specific strain of serotype 1/2a (strain SK1387), with final cell densities averaging 0.5 log10 CFU/cm2 higher than without the serotype 1/2a strain. The methodology used in this study contributed to our understanding of how environmental stresses and microbial competition influence the survival and growth of L. monocytogenes in pure and mixed-culture biofilms.

* Corresponding author. Mailing address: USDA-ARS, Department of Food, Bioprocessing, and Nutrition Sciences, North Carolina State University, Raleigh, NC 27695-7624. Phone: (919) 513-0186. Fax: (919) 513-0810. E-mail: fred.breidt{at}ars.usda.gov

{triangledown} Published ahead of print on 31 July 2009.

{dagger} Paper FSR09-05 of the journal series of the Department of Food Science, North Carolina State University, Raleigh.

Applied and Environmental Microbiology, September 2009, p. 5846-5852, Vol. 75, No. 18
0099-2240/09/$08.00+0     doi:10.1128/AEM.00816-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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