Detection and characterization of Streptococcus thermophilus phages based on the antireceptor gene sequence

BINETTI, ANA; H. MAGADÁN, ALFONSO; DEL RÍO, BEATRIZ; MARTÍN, M. CRUZ; REINHEIMER, JORGE; ÁLVAREZ, MIGUEL A.

Key Biscayne, Florida (Estados Unidos)

Conferencia; ASM Conference on the New Phage Biology; 2004

ASM

Bacteriophages found in dairy environments are the main cause of fermentation failures during the manufacture of cheeses and fermented milks. In consequence, the success of commercial lactic starters depends, primary, on the selection of phage-unrelated strains that must be able to withstand viral infections. Despite the technological relevance of Streptococcus thermophilus starter cultures in dairy processes and the marked increase in the number of accidents related to phages in the last decade, phage-host interactions are poorly understood in this specie. Thus, the rotation of strains used in the dairy industry as defense mechanism against phage attacks, is performed without prior knowledge of the phages host range. In fact, all the classifications of S. thermophilus phages indicate very little information about host range and, therefore, have a scarce value for the dairy industry. The aim of this study was to develop a PCR method to amplify a variable region (VR2) belonging to the antireceptor gene (Duplessis and Moineau, 2001). Primers were designed on the basis of orf8 from DT1 and the homologous genes from other S. thermophilus viruses. Nineteen phages from different sources were assayed. A variable size fragment (from 336 to 457 bp) was amplified in all of them. The sequence alignment of the PCR products associated the bacteriophages in 3 groups, showing a correspondence with their host ranges. The classification according to the specific VR2 sequence of the antireceptor reveals a biologically significant advantage in relation to other grouping criteria, since our results have demonstrated a clear correlation between the sequence of the amplified DNA and the host specificity of bacteriophages. Furthermore, it represents a useful tool for phage detection from industrial samples, since specific PCR products were obtained using contaminated milk as template, with a detection limit of 104 pfu ml-1. Our finding represents a step towards understanding the interactions between phages and their hosts and may be one of the routes that lead to the rational design of starter rotational solutions to phage attacks in the dairy industry.