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Applied and Environmental Microbiology, August 2005, p. 4269-4275, Vol. 71, No. 8
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.8.4269-4275.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Bacteriophages May Bias Outcome of Bacterial Enrichment Cultures

Maite Muniesa, Anicet R. Blanch, Francisco Lucena, and Juan Jofre*

Department of Microbiology, Faculty of Biology, University of Barcelona, Diagonal 645, E-08028 Barcelona, Spain

Received 27 October 2004/ Accepted 7 March 2005

Enrichment cultures are widely used for the isolation of bacteria in clinical, biotechnological, and environmental studies. However, competition, relative growth rates, or inhibitory effects may alter the outcome of enrichment cultures, causing the phenomenon known as enrichment bias. Bacteriophages are a major component in many microbial systems, and it abounds in natural settings. This abundance means that bacteriophages are likely to be present in many laboratory enrichment cultures. Our hypothesis was that bacteriophages present in the sample might bias the enriched subpopulation, since it can infect and lyse the target bacteria during the enrichment step once the bacteria reach a given density. Here we show that the presence of bacteriophages in Salmonella and Shigella enrichment cultures produced a significant reduction (more than 1 log unit) in the number of these bacteria compared with samples in which bacteriophages had been reduced by filtration through 0.45-µm non-protein-binding membranes. Furthermore, our data indicate that the Salmonella biotypes isolated after the enrichment culture change if bacteriophages are present, thus distorting the results of the analysis.

* Corresponding author. Mailing address: Department of Microbiology, Faculty of Biology, University of Barcelona, Diagonal 645, E-08028 Barcelona, Spain. Phone: 34 934 021487. Fax: 34 934 039047. E-mail: jjofre{at}ub.edu.

Applied and Environmental Microbiology, August 2005, p. 4269-4275, Vol. 71, No. 8
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.8.4269-4275.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.





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