RESUMEN
Two Streptococcus thermophilus phages (ALQ13.2 and phiAbc2) were previously isolated from breakdowns of cheese manufacture in Argentina. Complete nucleotide sequence analysis indicated that both phages contained linear double-stranded DNA: 35,525 bp in length for the pac-type phage ALQ13.2 and 34,882 bp for the cos-type phage phiAbc2. Forty-four and 48 open reading frames (ORF) were identified for ALQ13.2 and phiAbc2, respectively. Comparative genomic analysis showed that these isolates shared many similarities with the eight previously studied cos- and pac-phages infecting different S. thermophilus strains. In particular, part of the phiAbc2 genome was highly similar to a region of phage 7201, which was thought to be unique to this latter phage. Protein analysis of the pac-phage ALQ13.2 using SDS polyacrylamide gel electrophoresis (SDS-PAGE) identified three major proteins and seven minor proteins. Parallel structural proteome analysis of phiAbc2 revealed seven protein bands, two of which were related to major structural proteins, as expected for a cos-type phage. Similarities to other S. thermophilus phages suggest that the streptococcal phage diversity is not extensive in worldwide dairy factories possibly because related high-performing bacterial strains are used in starter cultures.
Asunto(s)
Genoma Viral/genética , Fagos de Streptococcus/genética , Animales , Argentina , Datos de Secuencia Molecular , Proteoma , Origen de Réplica/genética , Fagos de Streptococcus/clasificación , Fagos de Streptococcus/aislamiento & purificación , Streptococcus thermophilus/virología , Factores de Tiempo , Replicación Viral/fisiologíaRESUMEN
Phage infections still represent a serious risk to the dairy industry, in which Streptococcus thermophilus is used in starter cultures for the manufacture of yogurt and cheese. The goal of the present study was to analyze the biodiversity of the virulent S. thermophilus phage population in one Argentinean cheese plant. Ten distinct S. thermophilus phages were isolated from cheese whey samples collected in a 2-mo survey. They were then characterized by their morphology, host range, and restriction patterns. These phages were also classified within the 2 main groups of S. thermophilus phages (cos- and pac-type) using a newly adapted multiplex PCR method. Six phages were classified as cos-type phages, whereas the 4 others belonged to the pac-type group. This study illustrates the phage diversity that can be found in one factory that rotates several cultures of S. thermophilus. Limiting the number of starter cultures is likely to reduce phage biodiversity within a fermentation facility.
Asunto(s)
Queso/microbiología , Queso/virología , Variación Genética , Fagos de Streptococcus/genética , Streptococcus thermophilus/virología , Argentina , Proteínas de la Cápside/genética , Cartilla de ADN/química , Desoxirribonucleasa EcoRI/metabolismo , Desoxirribonucleasas de Localización Especificada Tipo II/metabolismo , Electroforesis en Gel de Campo Pulsado , Industria de Procesamiento de Alimentos/normas , Reacción en Cadena de la Polimerasa/métodos , Alineación de Secuencia , Fagos de Streptococcus/clasificación , Fagos de Streptococcus/aislamiento & purificación , Streptococcus thermophilus/ultraestructuraRESUMEN
Sixty-one natural phages (59 of Streptococcus thermophilus and 2 of Lactobacillus delbrueckii subsp. bulgaricus) were isolated from Argentinian dairy plants from November 1994 to July 2000. Specifically, 17 yogurt samples (18% of all samples) and 26 cheese samples (79%) contained phages lytic to S. thermophilus strains. The number of viral particles found in samples ranged from 10(2) to 10(9) PFU/ml. The phages belonged to Bradley's group B or the Siphoviridae family (morphotype B1). They showed high burst size values and remarkably short latent periods. The results of this study show that phages were found more frequently in cheesemaking processes than in yogurt-making processes. The commercial streptococcus strains appeared to propagate more phages, whereas the natural strains propagated fewer phage strains. These results suggest that the naturally occurring cultures are inherently more phage resistant.